Identification of a major protein kinase C-binding protein and substrate in rat embryo fibroblasts. Decreased expression in transformed cells.

We have used an interaction cloning strategy to isolate cDNAs for sequences that interact with protein kinase C (Chapline, C., Ramsay, K., Klauck, T., and Jaken, S. (1993) J. Biol. Chem. 268,6858-6861). In this paper, we report a novel sequence, clone 72, isolated according to this method. Clone 72 has a 4.8-kilobase pair open reading frame; antibodies to clone 72 recognize a >200-kDa protein in cell and tissue extracts. Clone 72 message and protein are detected in a variety of tissues. Immunoprecipitation studies demonstrate that clone 72 is the major >200-kDa binding protein described previously in REF52 fibroblasts (Hyatt, S. L., Liao, L., Aderem, A., Nairn, A., and Jaken, S. (1994) Cell Growth & Differ. 5, 495-502). Expression of clone 72 message and protein are decreased in progressively transformed REF52 cells. Since clone 72 is both a protein kinase C (PKC)-binding protein and substrate, decreased levels of clone 72 may influence both the subcellular location of endogenous PKCs as well as signaling events associated with clone 72 phosphorylation. Our results emphasize that the role of PKCs in carcinogenesis may involve several factors, including the quantity and location of the PKCs isozymes and their downstream targets.