Activated ras and ret oncogenes induce over-expression of c-met (hepatocyte growth factor receptor) in human thyroid epithelial cells
Abstract
Hepatocyte Growth Factor (HGF) receptor, encoded by the protooncogene c-met, is overexpressed in many human tumours, including those of thyroid epithelium. The absence in most cases of any primary structural abnormality of the met gene suggests that overexpression is secondary to mutation of other gene(s). To test this hypothesis we investigated the effect on met expression of two activated oncogenes known to play a major role in thyroid oncogenesis, ras and ret. To minimize the possibility of unknown co-operating events, we introduced these genes directly into normal human thyrocytes in primary culture using amphotropic retroviral vectors and assessed met expression as early as possible in the resulting epithelial colonies. Double immunofluorescence revealed expression of met protein, strictly localized to cells expressing the mutant ras and ret vectors, expression in background normal cells being barely detectable. In contrast, colonies induced to proliferate at a comparable rate by a vector expressing SV40 T showed no increase in met expression. To permit quantitation by Western blotting we also extended these findings to a thyroid cell line (R18) containing a zinc-inducible mutant ras gene. Induction of the oncogene led to ...Continue Reading
Citations
Study of MET protein levels and MET gene copy number in 72 sinonasal intestinal-type adenocarcinomas
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