Enhanced invasion and liver colonization by lung carcinoma cells overexpressing the type 1 insulin-like growth factor receptor.
Long L. Rubin R. Brodt P.
Department of Surgery, McGill University, Montreal, Quebec, Canada.
The receptor for the type 1 insulin-like growth factor (IGF-1R) and its ligands IGF-1 and IGF-2 play important roles in the maintenance of the malignant phenotype. In previous studies with two sublines of the Lewis lung carcinoma (H-59 and M-27, expressing high and low levels of IGF-1R, respectively) we have shown that receptor levels in these tumor cells correlated with metastasis to the liver. In the present study we asked whether the metastatic properties can be modulated by increasing receptor levels. M-27 carcinoma cells were transfected with a plasmid vector expressing a full-length human IGF-1R cDNA. Expression of the human receptor in the stable transfectants was confirmed by RT-PCR and immunoprecipitation analysis. These cells had an enhanced proliferative response to IGF-1 and hepatocyte-conditioned medium and an increased clonogenic potential in semisolid medium. Moreover, they acquired an invasive potential as measured in the reconstituted basement membrane (Matrigel) invasion assay. When inoculated via the splenic/portal route in vivo, these cells but not mock-transfected cells gave rise to multiple tumor nodules. The results suggest that IGF-1R can modulate several cellular functions which impact on the metastatic phenotype including invasion and liver colonization.
Retinoic acid differentially regulates retinoic acid receptor-mediated pathways in the Hep3B cell line.
Wan YJ. Cai Y. Magee TR.
Department of Pathology, Harbor-UCLA Medical Center, Torrance 90509, USA. email@example.com
Retinoic acid (RA) up-regulates retinoic acid receptor beta (RAR beta) gene expression in a variety of cell lines. Whether up-regulation of the RAR beta gene reflects increased activity in a RAR beta-mediated biological process is unclear since RAR beta tends to heterodimerize with retinoid x receptor (RXR). In F9 teratocarcinoma cell line, RA-induced differentiation is accompanied by increased expression of the RAR beta, RXR alpha, and alpha-fetoprotein (AFP) genes. Previously, we have shown that the RA-mediated regulation of the AFP gene is through RXR alpha homodimers. In contrast to F9 cells, Hep3B is unique in that the AFP gene is down-regulated by RA in a manner reminiscent of down-regulation of AFP in postfetal liver. In this paper, we have examined the RA-mediated regulation of the RAR, RXR, peroxisome proliferator-activated receptor (PPAR), and AFP genes in Hep3B cells. RA induced the expression of RAR alpha, beta, and gamma mRNA in Hep3B cells. However, the expression of RXR alpha mRNA was down-regulated, and the levels of RXR beta and RXR gamma mRNA remained unchanged after RA treatment. In addition, the expression of the PPAR alpha, beta, and gamma genes was also unchanged. Gel retardation assays demonstrated that RA decreased the overall binding of nuclear receptors to the RA and PPAR response elements. By super-shift assays using specific anti-RAR and -RXR antibodies, RA treatment decreased the amount of RXR alpha while increasing the amount RAR beta bound to retinoic acid response element-DR1 (direct repeat with spacer of one nucleotide), indicating the levels of RAR/RXR heterodimer, RXR/RXR homodimer, or RAR/RAR homodimers were altered upon RA treatment of Hep3B cells. In addition, the RA-mediated reduction of RXR alpha in part results in down-regulation of the AFP gene. Our data indicates that RA exerts its effects by differentially regulating its own receptor gene expression.
Production of trypsin by cells of the exocrine pancreas is paralleled by the expression of the KH protein vigilin.
Kruse C. Emmrich J. Rumpel E. Klinger MH. Grunweller A. Rohwedel J. Krammer HJ. Kuhnel W. Muller PK.
Department of Medical Molecular Biology, Medical University of Lubeck, Germany.
Vigilin, a protein with a continuous series of 14 KH motifs, forms part of a multiprotein complex containing tRNA. Several lines of evidence have suggested that vigilin expression is enhanced in those cells which were actively engaged in protein synthesis. Accordingly, we show here by immunoelectronmicroscopy a close association of vigilin with the rough endoplasmic reticulum in rat pancreatic cells. Histological examination of these cells furthermore demonstrates the highest intensity of vigilin staining in the perinuclear, intranuclear, and basolateral regions where the endoplasmic reticulum is mainly amassed. In vivo challenge of starving rats fed prior to sacrifice raised in parallel the protein levels of both trypsin and vigilin when compared to unchallenged animals and was associated with enhanced expression of the vigilin gene. In contrast, in human and rat cell lines of pancreatic tumors with a constitutively high expression of vigilin no further stimulation by cholecystokinin treatment could be achieved. Our data provide circumstantial evidence that vigilin may play a crucial role in the ability of an organ, e.g., pancreas, to cope with the physiological demand to upregulate protein synthesis.