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Epithelial cells are organized asymmetrically to function as an interface between compartments in multicellulr oganisms. Polar features at the cell surface such as plasma membrane domains and junctional complexes are paralleled intracellularly by the asymmetric arrangement of the cytoskeleton and organelles such as the Golgi complex. Contact of an epithelial cell with the substratum may initiate the polarization process. The long-term objective of this project is to determine if polarization is a hierarchical process stemming from the asymmetric cell contact event. In the proposed studies, a polarized epithelial cell line MDCK will be oncogenically transformed by introduction of the wild-type or temperature sensitive ras oncogene via a retrovirus vector. The effects of transformation on cell polarity will be assessed by examining the localization in the transformants of specific cell surface and cytoskeletal marker proteins using biochemical and immunocytochemical assays. The interaction of the transformants with basal lamina components and the synthesis of collagen type IV, laminin, and fibronectin by the cells will be determined by cell binding assays and radiolabeling/immunoprecipitation experiments respectively. Both polar organization and cell attachment will also be examined in the conditional transformants as they are shifted from the transformed (nonpolar) to untransformed (polar) state. Finally, MDCK cell polarity will be perturbed by creation of somatic cell hybrids with nonpolar cell lines (Specific Aim 5). The polarity of the hybrids will be assessed using the same set of polarity and cell attachment assays used for the transformants. This work will establish an experimental system using the conditinal transformants in which the induction of polarity can be studied in detail. In addition, knowledge gained about the effects of oncogenic transformation and cell hybrid formation on epithelial cell polarity will advance our understanding of carcinogenesis in humans.
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