Down-regulation of vascular endothelial growth factor in a human colon carcinoma cell line transfected with an antisense expression vector specific for c-src.
Ellis LM. Staley CA. Liu W. Fleming RY. Parikh NU. Bucana CD. Gallick GE.
Department of Surgical Oncology, University of Texas M. D. Anderson Cancer Center, Houston, Texas 77030, USA.
Vascular endothelial growth factor (VEGF) is implicated in the angiogenesis of human colon cancer. Recent evidence suggests that factors that regulate VEGF expression may partially depend on c-src-mediated signal transduction pathways. The tyrosine kinase activity of Src is activated in most colon tumors and cell lines. We established stable subclones of the human colon adenocarcinoma cell line HT29 in which Src expression and activity are decreased specifically as a result of a transfected antisense expression vector. This study determined whether VEGF expression is decreased in these cell lines and whether the smaller size and reduced growth rate of antisense vector-transfected cell lines in vivo might result, in part, from reduced vascularization of tumors. Northern blot analysis of these cell lines revealed that VEGF mRNA expression was decreased in proportion to the decrease in Src kinase activity. Under hypoxic conditions, cells with decreased Src activity had a 50-fold increase. VEGF protein in the supernatants of cells was also reduced in antisense transfectants compared with that from parental cells. In nude mice, subcutaneous tumors from antisense transfectants showed a significant reduction in vascularity. These results suggest that Src activity regulates the expression of VEGF in colon tumor cells.
Heparan sulfate undergoes specific structural changes during the progression from human colon adenoma to carcinoma in vitro.
Jayson GC. Lyon M. Paraskeva C. Turnbull JE. Deakin JA. Gallagher JT.
Cancer Research Campaign Department, Medical Oncology, University of Manchester and Christie Hospital National Health Service Trust, Withington, Manchester M20 4BX, United Kingdom.
We report a detailed analysis of heparan sulfate (HS) structure using a model of human colon carcinogenesis. Metabolically radiolabeled HS was isolated from adenoma and carcinoma cells. The chain length of HS was the same in both cell populations (Mr 20,000; 45-50 disaccharides), and the chains contained on average of two sulfated domains (S domains), identified by heparinase I scission. This enzyme produced fragments of approximate size 7 kDa, suggesting that the S domains were evenly spaced in the intact HS chain. The degree of polymer sulfation and the patterns of sulfation were strikingly different between the two HS species. When compared with adenoma HS, the iduronic acid 2-O-sulfate content of the carcinoma-derived material was reduced by 33%, and the overall level of N-sulfation was reduced by 20%. However, the level of 6-O-sulfation was increased by 24%, and this was almost entirely attributable to an enhanced level of N-sulfated glucosamine 6-O-sulfate, a species whose data implied was mainly located in the mixed sequences of alternating N-sulfated and N-acetylated disaccharides. The results indicate that in the transition to malignancy in human colon adenoma cells, the overall molecular organization of HS is preserved, but there are distinct modifications in both the S domains and their flanking mixed domains that may contribute to the aberrant behavior of the cancer cell.
Radicicol leads to selective depletion of Raf kinase and disrupts K-Ras-activated aberrant signaling pathway.
Soga S. Kozawa T. Narumi H. Akinaga S. Irie K. Matsumoto K. Sharma SV. Nakano H. Mizukami T. Hara M.
Tokyo Research Laboratories, Kyowa Hakko Kogyo Co. Ltd., Asahi-machi 3-6-6, Machida-shi, Tokyo 194, Japan.
Activation of Ras leads to the constitutive activation of a downstream phosphorylation cascade comprised of Raf-1, mitogen-activated protein kinase (MAPK) kinase, and MAPK. We have developed a yeast-based assay in which the Saccharomyces cerevisiae mating pheromone-induced MAPK pathway relied on co-expression of K-Ras and Raf-1. Radicicol, an antifungal antibiotic, was found to inhibit the K-ras signaling pathway reconstituted in yeast. In K-ras-transformed, rat epithelial, and K-ras-activated, human pancreatic carcinoma cell lines, radicicol inhibited K-Ras-induced hyperphosphorylation of Erk2. In addition, the level of Raf kinase was significantly decreased in radicicol-treated cells, whereas the levels of K-Ras and MAPK remained unchanged. These results suggest that radicicol disrupts the K-Ras-activated signaling pathway by selectively depleting Raf kinase and raises the possibility that pharmacological destabilization of Raf kinase could be a new and powerful approach for the treatment of K-ras-activated human cancers.
A novel nk-2-related transcription factor associated with human fetal liver and hepatocellular carcinoma.
Apergis GA. Crawford N. Ghosh D. Steppan CM. Vorachek WR. Wen P. Locker J.
Department of Pathology, School of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania 15261, USA.
A novel cDNA was partially isolated from a HepG2 cell expression library by screening with the promoter-linked coupling element (PCE), a site from the alpha-fetoprotein (AFP) gene promoter. The remainder of the cDNA was cloned from fetal liver RNA using random amplification of cDNA ends. The cDNA encodes a 239-amino acid peptide with domains closely related to the Drosophila factor nk-2. The new factor is the eighth vertebrate factor related to nk-2, hence nkx-2.8. Northern blot and reverse transcriptase polymerase chain reaction analysis demonstrated mRNA in HepG2, two other AFP-expressing human cell lines, and human fetal liver. Transcripts were not detected in adult liver. Cell-free translation produced DNA binding activity that gel shifted a PCE oligonucleotide. Cotransfection of nkx-2.8 expression and PCE reporter plasmids into HeLa cells demonstrated transcriptional activation; NH2-terminal deletion eliminated this activity. Cotransfection into AFP-producing hepatocytic cells repressed AFP reporter expression, suggesting that endogenous activity was already present in these cells. In contrast, cotransfection into an AFP-negative hepatocytic line produced moderate activation of the AFP gene. The cardiac developmental factor nkx-2.5 could substitute for nkx-2.8 in all transfection assays, whereas another related factor, thyroid transcription factor 1, showed a more limited range of substitution. Although the studies have yet to establish definitively that nkx-2.8 is the AFP gene regulator PCF, the two factors share a common DNA binding site, gel shift behavior, migration on SDS-acrylamide gels, and cellular distribution. Moreover, the nk-2-related genes are developmental regulators, and nkx-2.8 is the first such factor associated with liver development.
Evidence for the absolute conformational specificity of the intestinal H+/peptide symporter, PEPT1.
Brandsch M. Thunecke F. Kullertz G. Schutkowski M. Fischer G. Neubert K.
Biozentrum,Martin-Luther-University Halle-Wittenberg, D-06120 Halle, Germany.
This study was initiated to determine whether the intestinal H+/peptide symporter PEPT1 differentiates between the peptide bond conformers of substrates. We synthesized a modified dipeptide where the peptide bond is replaced by the isosteric thioxo peptide bond. The Ala-Pro derivative Ala-psi[CS-N]-Pro exists as a mixture of cis and trans conformation in aqueous solution and is characterized by a low cis/trans isomerization rate. The compound was recognized by PEPT1 with high affinity. The Ki value of Ala-psi[CS-N]-Pro for the inhibition of the uptake of radiolabeled glycylsarcosine in Caco-2 cells was 0.30 +/- 0.02 mM, determined in solution with 96% trans conformation. In contrast, the Ki value was 0.51 +/- 0.02 mM when uptake media with 62% trans conformer were used. We conclude that only the trans conformer interacts with the transport system. From our data, a significant affinity of the cis conformer at PEPT1 cannot be derived. In a second approach, conformer-specific uptake of Ala-psi[CS-N]-Pro was studied by analyzing the intracellular content of Caco-2 cells following transport as well as the composition of the extracellular medium using capillary electrophoresis. The percentage of trans conformer that was 62% in the uptake medium increased to 92% inside the cells. This is the first direct evidence that an H+/peptide cotransport system selectively binds and transports the trans conformer of a peptide derivative.
Signal transduction pathways activated by RET oncoproteins in PC12 pheochromocytoma cells.
Xing S. Furminger TL. Tong Q. Jhiang SM.
Department of Physiology, The Ohio State University, Columbus, Ohio 43210, USA.
Gene alterations in the ret proto-oncogene, which encodes a receptor tyrosine kinase, have been found to associate with several human diseases. In this study, we showed that induction of the vgf promoter activity is a good molecular indicator for RET activation in PC12 cells, a rat pheochromocytoma cell line. We demonstrated that all forms of RET oncoprotein, including RET chimeric oncoproteins found in human papillary thyroid carcinomas (RET/PTC) as well as RET oncoproteins found in patients with multiple endocrine neoplasia type 2A and 2B (2A/RET and 2B/RET) can induce vgf promoter activity in PC12 cells. In contrast, a RET mutant found in a patient with Hirschsprung's disease, as well as a RET/PTC1 mutant with deletion of the dimerization domain, failed to induce vgf promoter activity in PC12 cells. We further determined that the signaling events mediated by phosphorylated Tyr294 and phosphorylated Tyr451 binding sites are essential for RET/PTC1 to induce vgf promoter activity in PC12 cells. We also showed that RET/PTC1, 2A/RET, and 2B/RET induce ELK-, cAMP-responsive element binding protein (CREB), or JUN-mediated gene expression in PC12 cells, and these three signaling events are mediated by phosphorylated Tyr294 and phosphorylated Tyr451 binding sites in RET/PTC1.
Lithostathine, the presumed pancreatic stone inhibitor, does not interact specifically with calcium carbonate crystals.
De Reggi M. Gharib B. Patard L. Stoven V.
INSERM U399, 27 Boulevard Jean-Moulin, 13385 Marseille cedex 5, France.
Lithostathine (pancreatic stone protein, Reg protein) is, in addition to albumin, the major nonenzymatic protein of the pancreatic juice. It has been assumed to inhibit calcium carbonate precipitation and therefore to prevent stone formation in the pancreatic ducts. This function is, however, debatable. The assumption is based on the inhibition of in vitro crystal nucleation and growth by lithostathine. Considering that these phenomena occur only under certain critical conditions, we re-examined the question using a protein preparation where the purity and folding have been tested by mass spectroscopy and NMR in the absence of nonprotein contaminants. Under these conditions, we showed conclusively that lithostathine does not inhibit calcium carbonate nucleation and crystal growth. We demonstrated that previous findings on the alleged inhibition can be attributed to the uncontrolled presence of salts in the protein preparation used. Moreover, the affinity of lithostathine to calcite crystals, expressed as the half-life of bound iodinated protein in the presence of unlabeled competitor, was significantly lower than that of bovine serum albumin (8.8 and 11.2 h, respectively). Using glass microspheres instead of crystals did not significantly change the half-life of bound lithostathine (8.0 h). These findings are incompatible with the hypothesis of a specific interaction of lithostathine with calcium carbonate crystals. In conclusion, considering that components of pancreatic juice such as NaCl and phosphate ions are powerful inhibitors of calcium carbonate crystal growth, the mechanism of stone formation in pancreatic ducts must be reconsidered. The presence in normal pancreatic juice of small amounts of the 133-residue isoform of lithostathine (PSP-S1), which precipitates at physiological pH, should be noted, and the possibility should be considered that they form micro-precipitates that aggregate and are progressively calcified.
Small GTP-binding protein Rho stimulates the actomyosin system, leading to invasion of tumor cells.
Yoshioka K. Matsumura F. Akedo H. Itoh K.
Department of Molecular Biology and Biochemistry, Rutgers University, Piscataway, New Jersey 08854-1059, USA.
We have shown previously that Rho plays a pivotal role in 1-oleoyl-lysophosphatidic acid (LPA)-dependent invasion of rat hepatoma cells (MM1). Herein we made stable transfectants of MM1 expressing active and Botulinum exoenzyme C3 (C3)-sensitive (Val14), or active and C3-insensitive (Val14/Ile41) forms of human RhoA. Both transfectants showed greatly promoted invasive ability in vitro in the absence of LPA as well as in vivo, adherence to the dish with scattered shape, and enhanced phosphorylation level of 20-kDa myosin light chain (MLC20). A specific MLC kinase inhibitor (KT5926) could inhibit their invasion and the phosphorylation level of MLC20. Stable active RhoA transfectants of W1 cells (low invasive counterpart of MM1) also demonstrated promoted invasive ability in vitro and in vivo, and enhanced phosphorylation level of MLC20. C3 treatment inhibited the invasiveness of the Val14 RhoA transfectant but not that of the Val14/Ile41 RhoA transfectant. LPA enhanced the invasiveness of both transfectants, and this enhancement was abolished by the C3 treatment. These results suggested that 1) the Rho signaling pathway and actomyosin system were linked in the transmigration of tumor cells, and 2) expressed active RhoA enhanced LPA-induced tumor cell invasion via the activation of endogenous RhoA pathway, indicating a positive feedback mechanism in the activation of RhoA.
The HepG2 extracellular matrix contains separate heparinase- and lipid-releasable pools of ApoE. Implications for hepatic lipoprotein metabolism.
Burgess JW. Gould DR. Marcel YL.
Lipoprotein and Atherosclerosis Group, University of Ottawa Heart Institute, Department of Biochemistry, University of Ottawa, Ottawa, Ontario K1Y 4E9, Canada.
We have examined the association of apoE with the extracellular matrix (ECM) of HepG2 cells. Comparison of ECM prepared by previously published methods demonstrated that cytochalasin B-prepared material yielded the highest endogenous apoE, representing 23.6% of that in cell monolayers. ECM prepared with EDTA or Triton X-100 exhibited decreased levels of apoE, 3 and 6%, respectively. ECM bound very low density lipoprotein poorly (5-6% of the monolayer capacity); however, these incubations dramatically increased the apoE content of the ECM. Heparinase or suramin decreased apoE of the ECM by 19.6 and 37.3%, respectively, suggesting association with heparin sulfate proteoglycans. EDTA or EGTA also displaced 35% of the apoE, suggesting a Ca2+-dependent association. Incubation with phosphatidylcholine vesicles (PCV) displaced 30% of the apoE, suggesting that lipid content affects association of apoE with the ECM. Data derived from sequential incubations with combinations of suramin, EGTA, and PCV were consistent with the presence of two distinct pools of apoE on the HepG2 ECM, one releasable with suramin and EGTA and the other releasable with lipids. Exogenously applied lipid-free apoE readily bound to the ECM; however, increasing the lipid content decreased its association. Lipid-free apoE could be equally displaced from the ECM with PCV or suramin. When lipid-free apoE adsorbed to microtiter wells was incubated with a triglyceride emulsion or palmitoyloleyl phosphatidylcholine micelles, the immunoreactivity of 3H1 (but not other antibodies), a monoclonal antibody against an epitope in the C-terminal domain of apoE, increased about 4-fold. In a similar manner, incubation of ECM with lipid dramatically increased the immunoreactivity of 3H1, indicating that apoE of the ECM exists in a lipid-poor form. Scatchard analysis demonstrated that the increased immunoreactivity was due to an increase in the number of antibody binding sites. In conclusion, the ECM contains two pools of lipid-poor apoE. One pool associates with the ECM through heparin sulfate proteoglycans- and Ca2+-dependent interactions. A second pool of apoE dissociates from the ECM upon lipidation. The lipid-sensitive pool of apoE may participate in secretion or efflux of lipids or in the capture of lipoproteins by providing the apoE needed for receptor-mediated uptake.
Direct activation of cystic fibrosis transmembrane conductance regulator channels by 8-cyclopentyl-1,3-dipropylxanthine (CPX) and 1,3-diallyl-8-cyclohexylxanthine (DAX).
Arispe N. Ma J. Jacobson KA. Pollard HB.
Institute for Molecular Medicine and Department of Anatomy and Cell Biology, Uniformed Services University School of Medicine (USUHS), Bethesda, Maryland 20814, USA.
8-Cyclopentyl-1,3-dipropylxanthine (CPX) and 1,3-diallyl-8-cyclohexylxanthine (DAX) are xanthine adenosine antagonists which activate chloride efflux from cells expressing either wild-type or mutant (DeltaF508) cystic fibrosis transmembrane conductance regulator (CFTR). These drugs are active in extremely low concentrations, suggesting their possible therapeutic uses in treating cystic fibrosis. However, knowledge of the mechanism of action of these compounds is lacking. We report here that the same low concentrations of both CPX and DAX which activate chloride currents from cells also generate a profound activation of CFTR channels incorporated into planar lipid bilayers. The process of activation involves a pronounced increase in the total conductive time of the incorporated CFTR channels. The mechanism involves an increase in the frequency and duration of channel opening events. Thus, activation by these drugs of chloride efflux in cells very likely involves direct interaction of the drugs with the CFTR protein. We anticipate that this new information will contribute fundamentally to the rational development of these and related compounds for cystic fibrosis therapy.
Cloning and expression of mouse liver phosphatidylserine synthase-1 cDNA. Overexpression in rat hepatoma cells inhibits the CDP-ethanolamine pathway for phosphatidylethanolamine biosynthesis.
Stone SJ. Cui Z. Vance JE.
Lipid and Lipoprotein Research Group, University of Alberta, Edmonton, AB T6G 2S2, Canada.
In eukaryotic cells, phosphatidylserine (PtdSer) is synthesized by two distinct synthases on the endoplasmic reticulum by a base-exchange reaction in which the polar head-group of an existing phospholipid is replaced with serine. We report the cloning and expression of a cDNA for mouse liver PtdSer synthase-1. The deduced protein sequence is >90% identical to that of PtdSer synthase-1 from Chinese hamster ovary cells and a sequence from a human myeloblast cell line. PtdSer synthase-1 cDNA was stably expressed in M.9.1.1 cells which are mutant Chinese hamster ovary cells defective in PtdSer synthase-1 activity, are ethanolamine auxotrophs, and have a reduced content of PtdSer and phosphatidylethanolamine (PtdEtn). The growth defect of M.9.1.1 cells was eliminated, and a normal phospholipid composition was restored in the absence of exogenous ethanolamine, implying that the cloned cDNA encoded PtdSer synthase. Mouse liver PtdSer synthase-1 was also expressed in McArdle 7777 rat hepatoma cells. In addition to a 3-fold higher in vitro serine-exchange activity, these cells also exhibited enhanced choline- and ethanolamine-exchange activities and incorporated more [3H]serine into PtdSer than did control cells. However, the levels of PtdSer and PtdEtn in cells overexpressing PtdSer synthase-1 activity were not increased. Excess PtdSer produced by the transfected cells was rapidly decarboxylated to PtdEtn and the degradation of PtdSer, and/or PtdEtn derived from PtdSer, was increased. Moreover, the CDP-ethanolamine pathway for PtdEtn biosynthesis was inhibited. These data suggest that (i) cellular levels of PtdSer and PtdEtn are tightly controlled, and (ii) the metabolism of PtdSer and PtdEtn is coordinately regulated to maintain phospholipid homeostasis.
Up-regulation of transforming growth factor (TGF)-beta receptors by TGF-beta1 in COLO-357 cells.
Kleeff J. Korc M.
Department of Medicine, University of California, Irvine, California 92697, USA.
In the present study we investigated the actions of transforming growth factor (TGF)-beta1 on gene induction and cyclin-dependent kinase inhibitors in relation to TGF-beta receptor modulation in COLO-357 pancreatic cancer cells. TGF-beta1 inhibited the growth of COLO-357 cells in a time- and dose-dependent manner and caused a rapid but transient increase in plasminogen activator inhibitor-I and insulin-like growth factor binding protein-3 mRNA levels. TGF-beta1 caused a delayed but sustained increase in the protein levels of the cyclin-dependent kinase inhibitors p15(Ink4B), p21(Cip1), and p27(Kip1) and a sustained increase in type I and II TGF-beta receptors (TbetaRI and TbetaRII) mRNA and protein levels. The protein synthesis inhibitor cycloheximide (10 microg/ml) completely blocked the TGF-beta1-mediated increase in TbetaRI and TbetaRII expression. Furthermore, a nuclear runoff transcription assay revealed that the increase in receptor mRNA levels was due to newly transcribed RNA. There was a significant increase in TbetaRI and TbetaRII mRNA levels in confluent cells in comparison to subconfluent (
Aberrant regulation of transforming growth factor-alpha during the establishment of growth arrest and quiescence of growth factor independent cells.
Howell GM. Humphrey LE. Awwad RA. Wang D. Koterba A. Periyasamy B. Yang J. Li W. Willson JK. Ziober BL. Coleman K. Carboni J. Lynch M. Brattain MG.
Department of Biochemistry and Molecular Biology, Medical College of Ohio, Toledo, Ohio 43699-0008, USA. email@example.com
Autocrine transforming growth factor alpha (TGFalpha) is an important positive growth effector in malignant cells and plays a significant role in generating the growth factor-independent phenotype associated with malignant progression. However, the molecular mechanisms by which TGFalpha confers a growth advantage in progression is poorly understood. The highly tumorigenic cell line HCT116 up-regulates TGFalpha mRNA expression during growth arrest, whereas the poorly tumorigenic growth factor-dependent FET cell line down-regulates TGFalpha mRNA expression as it becomes quiescent. We have identified a 25-bp sequence at -201 to -225 within the TGFalpha promoter which mediates the differential regulation of TGFalpha expression during quiescence establishment in these two cell lines. This same sequence confers TGFalpha promoter responsiveness to exogenous growth factor or autocrine TGFalpha. The abberant upregulation of TGFalpha mRNA in quiescent HCT116 cells may allow them to return to the dividing state under more stringent conditions (nutrient replenishment alone) then quiescent FET cells (requires nutrients and growth factors). Antisense TGFalpha approaches showed that the dysregulated TGFalpha expression in quiescent HCT116 cells is a function of the strong TGFalpha autocrine loop (not inhibited by blocking antibodies) in these cells.
Estrogen regulation of the apolipoprotein AI gene promoter through transcription cofactor sharing.
Harnish DC. Evans MJ. Scicchitano MS. Bhat RA. Karathanasis SK.
Department of Nuclear Receptors, Wyeth-Ayerst Research, Radnor, Pennsylvania 19087, USA.
Estrogen replacement therapy increases plasma concentrations of high density lipoprotein and its major protein constituent, apolipoprotein AI (apoAI). Studies with animal model systems, however, suggest opposite effects. In HepG2 cells stably expressing estrogen receptor alpha (ERalpha), 17beta-estradiol (E2) potently inhibited apoAI mRNA steady state levels. ApoAI promoter deletion mapping experiments indicated that ERalpha plus E2 inhibited apoAI activity through the liver-specific enhancer. Although the ERalpha DNA binding domain was essential but not sufficient for apoAI enhancer inhibition, ERalpha binding to the apoAI enhancer could not be detected by electrophoretic mobility shift assays. Western blotting and cotransfection assays showed that ERalpha plus E2 did not influence the abundance or the activity of the hepatocyte-enriched factors HNF-3beta and HNF-4, two transcription factors essential for apoAI enhancer function. Expression of the ERalpha coactivator RIP140 dramatically repressed apoAI enhancer function in cotransfection experiments, suggesting that RIP140 may also function as a coactivator on the apoAI enhancer. Moreover, estrogen regulation of apoAI enhancer activity was dependent upon the balance between ERalpha and RIP140 levels. At low ratios of RIP140 to ERalpha, E2 repressed apoAI enhancer activity, whereas at high ratios this repression was reversed. Regulation of the apoAI gene by estrogen may thus vary in direction and magnitude depending not only on the presence of ERalpha and E2 but also upon the intracellular balance of ERalpha and coactivators utilized by ERalpha and the apoAI enhancer.
Cell growth inhibition by a novel vitamin K is associated with induction of protein tyrosine phosphorylation.
Ni R. Nishikawa Y. Carr BI.
Thomas E. Starzl Transplantation Institute, University of Pittsburgh, Pittsburgh, Pennsylvania 15213, USA.
We have shown that a synthetic vitamin K analog, 2-(2-mercaptoethanol)-3-methyl-1,4-naphthoquinone or compound 5 (Cpd 5), potently inhibits cell growth and suggested that the analog exerts its effects mainly via sulfhydryl arylation rather than redox cycling. Since protein-tyrosine phosphatases (PTPases), which have pivotal roles in many cellular functions, have a critical cysteine in their active site, we have proposed PTPases as likely targets for Cpd 5. To test this hypothesis, we examined the effects of Cpd 5 on protein tyrosine phosphorylation of cellular proteins and on the activity of PTPases. We found that Cpd 5 rapidly induced protein tyrosine phosphorylation in a human hepatocellular carcinoma cell line (Hep3B) at growth inhibitory doses, and the effect was blocked by thiols but not by non-thiol antioxidants or tyrosine kinase inhibitors. Cpd 5 inhibited PTPase activity, which was also significantly antagonized by reduced glutathione. Furthermore, the well studied PTPase inhibitor orthovanadate also induced protein tyrosine phosphorylation and growth inhibition in Hep3B cells. These results suggest that inhibition of cellular PTPases by sulfhydryl arylation and subsequent perturbation of protein tyrosine phosphorylation may be involved in the mechanisms of Cpd 5-induced cell growth inhibition.
Novel mutations of the endothelin B receptor gene in patients with Hirschsprungs disease and their characterization.
Tanaka H. Moroi K. Iwai J. Takahashi H. Ohnuma N. Hori S. Takimoto M. Nishiyama M. Masaki T. Yanagisawa M. Sekiya S. Kimura S.
Department of Obstetrics and Gynecology, Chiba University School of Medicine, Chiba, Japan.
Hirschsprung's disease (HSCR) is a congenital intestinal disease, characterized by the absence of ganglion cells in the distal portion of the intestinal tract. Recently, three susceptibility genes have been identified in HSCR, namely the RET protooncogene, the endothelin B (ETB) receptor gene (EDNRB), and the endothelin-3 (ET-3) gene (EDN3). To investigate whether mutations in EDNRB could be related with HSCR in non-inbred populations in Japan, we examined alterations of the gene in 31 isolated patients. Three novel mutations were detected as follows: two transversions, A to T and C to A at nucleotides 311 (N104I) and 1170 (S390R), respectively, and a transition, T to C at nucleotide 325 (C109R). To analyze functions of these mutant receptors, they were expressed in Chinese hamster ovary cells. S390R mutation did not change the binding affinities but caused the decreases in the ligand-induced increment of intracellular calcium and in the inhibition of adenylyl cyclase activity, showing the impairment of the intracellular signaling. C109R receptors were proved to be localized near the nuclei as an unusual 44-kDa protein with the extremely low affinity to endothelin-1 (ET-1) and not to be translocated into the plasma membrane. On the other hand, N104I receptors showed almost the same binding affinities and functional properties as those of the wild type. Therefore, we conclude that S390R and C109R mutations could cause HSCR but that N104I mutation might be polymorphous.
Identification and characterization of a novel human aldose reductase-like gene.
Cao D. Fan ST. Chung SS.
Institute of Molecular Biology, University of Hong Kong, Pokfulam, Hong Kong.
We have identified a novel human protein that is highly homologous to aldose reductase (AR). This protein, which we called ARL-1, consists of 316 amino acids, the same size as AR, and its amino acid sequence is 71% identical to that of AR. It is more closely related to the AR-like proteins such as mouse vas deferens protein, fibroblast growth factor-regulated protein, and Chinese hamster ovary reductase, with 81, 82, and 83%, respectively, of its amino acid sequence identical to the amino acid sequence of these proteins. The cDNA of ARL-1 was expressed in Escherichia coli to obtain recombinant protein for characterization of its enzymatic activities. For comparison, the cDNA of human AR was also expressed in E. coli and analyzed in parallel. These two enzymes differ in their pH optima and salt requirement, but they act on a similar spectrum of substrates. Similar to AR, ARL-1 can efficiently reduce aliphatic and aromatic aldehydes, and it is less active on hexoses. While AR mRNA is found in most tissues studied, ARL-1 is primarily expressed in the small intestines and in the colon, with a low level of its mRNA in the liver. The ability of ARL-1 to reduce various aldehydes and the locations of expression of this gene suggest that it may be responsible for detoxification of reactive aldehydes in the digested food before the nutrients are passed on to other organs. Interestingly, ARL-1 and AR are overexpressed in some liver cancers, but it is not clear if they contribute to the pathogenesis of this disease.
Expression of the Cdx1 and Cdx2 homeotic genes leads to reduced malignancy in colon cancer-derived cells.
Mallo GV. Soubeyran P. Lissitzky JC. Andre F. Farnarier C. Marvaldi J. Dagorn JC. Iovanna JL.
U.315 INSERM, F 13009 Marseille, France.
We have previously described an inverse relationship between Cdx1 and Cdx2 mRNA levels and the extent of dysplasia and severity of clinical outcome in colorectal carcinoma, suggesting that altered expression of these genes was associated with colorectal carcinogenesis or tumor progression. To investigate further their involvement in the physiopathology of colorectal cancer, HT29 colon carcinoma cells that show very low Cdx expression were transfected with Cdx1 and/or Cdx2 cDNA to elicit their overexpression. Growth rate, tumorigenicity, resistance to apoptosis, and migration potential of the corresponding cells were analyzed. Growth rate of cells overexpressing Cdx2 decreased by half, whereas overexpression of Cdx1 had no effect. However, cells overexpressing both Cdxs had a growth rate reduced to 20% of control. In cells overexpressing Cdx1 or Cdx2, tumorigenicity and resistance to apoptosis induced by serum starvation, ceramide, or staurosporine were not changed compared with control cells; yet phorbol ester-stimulated cell migration was decreased by 50%. In cells overexpressing both Cdx1 and Cdx2, tumorigenicity was decreased by 50%, resistance to apoptosis was significantly lowered, and stimulated cell migration was further decreased to 15% of control compared with cells expressing Cdx1 or Cdx2. Finally, cells overexpressing both Cdxs showed strongly decreased Bcl-2 expression, which could account for their increased sensitivity to apoptosis. These findings show that, in HT29 cells, both Cdx1 and Cdx2 genes must be expressed to reduce tumorigenic potential, to increase sensitivity to apoptosis, and to reduce cell migration, suggesting that the two genes control the normal phenotype by independent pathways. This may explain why loss of Cdx1 or Cdx2 expression is associated with tumor development and invasiveness in colorectal tumors.
Inhibition by platelet-activating factor of Src- and hepatocyte growth factor-dependent invasiveness of intestinal and kidney epithelial cells. Phosphatidylinositol 3-kinase is a critical mediator of tumor invasion.
Kotelevets L. Noe V. Bruyneel E. Myssiakine E. Chastre E. Mareel M. Gespach C.
INSERM U482 and IFR 65, Hopital Saint-Antoine, 75571 Paris Cedex 12, France.
This study was designed to characterize platelet-activating factor receptor (PAF-R) expression and function in normal and cancerous human colonic epithelial cells. PAF-R gene transcripts were analyzed by reverse transcription-polymerase chain reaction and Southern blot, using three sets of primers corresponding either to the coding region of the human PAF-R sequence (polymerase chain reaction product: 682 base pairs (bp)) or to the leukocyte- and tissue-type transcripts of 166 and 252 bp, respectively. An elongated splice variant was identified in the 5'-untranslated region of the tissue-type PAF-R transcript (334 bp) in colonic epithelial crypts and tumors. In human colonic PCmsrc cells transformed by c-src oncogene, the hepatocyte growth factor (HGF)-dependent invasiveness of collagen gels was abolished by 0.1 microM PAF and restored by the PAF-R antagonists WEB2086 and SR27417. PAF blocked HGF-induced tyrosine phosphorylation of p125 focal adhesion kinase. The phosphatidylinositol 3'-kinase (PI3'-K) inhibitors wortmannin and LY294002 totally blocked the HGF-induced invasion. Similar effects were observed in ts-srcMDCK kidney epithelial cells transformed by a v-Src temperature-sensitive mutant: (i) PAF and wortmannin exerted additive inhibitory effects on Src-induced invasion and (ii) activated and dominant negative forms of p110alpha PI3'-K, respectively, amplified and abrogated the Src- and HGF-dependent invasiveness of parental and ts-srcMDCK cells. We also provided the first evidence for the contribution of rapamycin-insensitive, pertussis toxin-dependent G-protein pathways to the integration of the signals emerging from activated Met and PAF receptors. These results indicate that PI3'-K is a critical transducer of invasiveness and strongly suggest that PAF exerts a negative control on invasion by inhibiting this signaling pathway. A possible beneficial role of PAF analogs on tumor invasion is therefore proposed.
An electrophile responsive element (EpRE) regulates beta-naphthoflavone induction of the human gamma-glutamylcysteine synthetase regulatory subunit gene. Constitutive expression is mediated by an adjacent AP-1 site.
Moinova HR. Mulcahy RT.
Department of Human Oncology, University of Wisconsin Medical School, Madison, Wisconsin 53792, USA.
Exposure of HepG2 cells to beta-naphthoflavone (beta-NF) results in time- and dose-dependent increase in the steady-state mRNA levels for both the catalytic (GCSh) and regulatory (GCS1) subunits of gamma-glutamylcysteine synthetase (GCS) which catalyzes the rate-limiting step in the de novo synthesis of the cellular antioxidant glutathione (GSH) (Mulcahy, R. T., Wartman, M. A., Bailey, H. B., and Gipp, J. J. (1997) J. Biol. Chem. 272, 7445-7454). Cloning and sequencing of the GCS1 promoter region is reported. Regulatory sequences mediating basal and beta-NF induced expression of the GCSl gene were identified using a series of promoter/reporter fusion genes transfected into HepG2 cells. Sequences directing basal and beta-NF induced expression were localized between nucleotides -344 and -242 (numbered relative to the translation start site). Mutational analyses indicate that basal expression of the GCSl gene is directed by a consensus AP-1-binding site located 33 base pairs upstream of a consensus electrophile responsive element (EpRE) sequence; both cis-elements are capable of supporting beta-NF inducibility. Elimination of the inducible response requires simultaneous mutation of both sequences, however, in the presence of an intact EpRE the upstream AP-1 site is irrelevant to induction. Regulation of expression of both human GCS subunit genes in response to beta-NF is therefore mediated by cis-elements satisfying the consensus core EpRE motif.
Enhanced cytotoxicity of nucleoside analogs by overexpression of mitochondrial deoxyguanosine kinase in cancer cell lines.
Zhu C. Johansson M. Permert J. Karlsson A.
Division of Clinical Virology, Karolinska Institute, Huddinge University Hospital, S-14186 Stockholm, Sweden.
The cytotoxic anti-cancer purine nucleoside analogs 2-chloro-2'-deoxyadenosine (CdA), 9-beta-D-arabinofuranosylguanine (araG), and 2',2'-difluorodeoxyguanosine (dFdG) are phosphorylated by human mitochondrial deoxyguanosine kinase (dGK) in vitro. We overexpressed dGK as a fusion protein to the green fluorescent protein in the human pancreatic cancer cell lines PanC-1 and MIA PaCa-2 to determine the importance of dGK-mediated nucleoside analog phosphorylation. The transfected cells showed mitochondrial fluorescence patterns, and the mitochondrial locations of endogenous and overexpressed dGK were verified by Western blot analysis of cell extracts with polyclonal anti-dGK antibodies. The increase of dGK activity in the overexpressing cells was approximately 4-fold. These cell lines exhibited increased sensitivity to CdA, araG, and dFdG as compared with the untransfected parent cell lines. This is, to our knowledge, the first demonstration of a correlation between the activity of a mitochondrial deoxyribonucleoside kinase and the cytotoxicity of nucleoside analogs. Our data imply that the dGK activity is rate-limiting for the efficacy of nucleoside analogs in the cell lines investigated.
Potato carboxypeptidase inhibitor, a T-knot protein, is an epidermal growth factor antagonist that inhibits tumor cell growth.
Blanco-Aparicio C. Molina MA. Fernandez-Salas E. Frazier ML. Mas JM. Querol E. Aviles FX. de Llorens R.
Unitat de Bioquimica, Departament de Biologia, Facultat de Ciencies, Universitat de Girona 17071, Spain.
Epidermal growth factor (EGF) and its receptor (EGFR) are involved in many aspects of the development of carcinomas, including tumor cell growth, vascularization, invasiveness, and metastasis. Because EGFR has been found to be overexpressed in many tumors of epithelial origin, it is a potential target for antitumor therapy. Here we report that potato carboxypeptidase inhibitor (PCI), a 39-amino acid protease inhibitor with three disulfide bridges, is an antagonist of human EGF. It competed with EGF for binding to EGFR and inhibited EGFR activation and cell proliferation induced by this growth factor. PCI suppressed the growth of several human pancreatic adenocarcinoma cell lines, both in vitro and in nude mice. PCI has a special disulfide scaffold called a T-knot that is also present in several growth factors including EGF and transforming growth factor alpha. PCI shows structural similarities with these factors, a fact that can explain the antagonistic effect of the former. This is the first reported example of an antagonistic analogue of human EGF.