ENDOSOMAL FRACTIONS FROM VIRAL K-RAS-TRANSFORMED MDCK CELLS REVEAL TRANSFORMATION SPECIFIC CHANGES ON 2-DIMENSIONAL GEL MAPS

We have investigated the effects of viral Kirsten ras oncogene express ion in Madin-Darby canine kidney (MDCK) II epithelial cell on the diff erential protein expression of organelle proteins. MDCK cells, stably transformed via infection with a helper-independent retroviral vector construct, were grown on permeable filter supports. Whereas normal cel ls form highly polarized monolayers, ras-transformed cells display an unpolarized phenotype, detaching from the substratum and developing mu ltilayers (Schoenenberger, C.-A. et al., J. Cell Biol. 1991, 112, 873- 889). We postulate that this breakdown of epithelial polarity reflects disturbed intracellular protein transport and sorting, namely, protei ns will no longer be sorted correctly in intracellular organelles and will therefore not reach their appropriate target membrane. Here we em phasize the role of endosomes as sorting platform in epithelial cells. We found significant differences in the molecular composition of endo somes from normal vs. oncogenic transformed epithelial cells, strength ening previous evidence indicating that oncogenic transformation resul ts in abnormal expression of normal genes (Cells, J. E., Olsen, E., El ectrophoresis 1994, Ii, 309-344) as well as the expression of new ones (Huber, L. A. et al., Electrophoresis 1994, IS, 468-473).