Studies have shown that treatment of intact cells with tumor promoters (TPA), as well as with certain growth factors and hormones, causes a rapid redistribution or stabilizaton (activation) of protein kinase C to the particulate fraction. Results indicate that part of the PK-C stabilized to the membrane fraction with exposure to tumor promoters may be recovered associated with nuclear-cytoskeletal components. Following treatment of NIH 3T3 cells with TPA for 20 min, PK-C activity is found tightly associated with the highly purified nuclear fraction. Immunohistochemical localization studies further support the observation that TPA treatment mediates association of PK-C to the nucleus and cytoskeleton of NIH 3T3 cells. This TPA-induced redistribution of PK-C to the nuclear fraction is not observed with HL-60 cells. The different subcellular ditributions of PK-C induced by TPA with different cell types may help to explain, in part, the different responses noted with various cell types with exposure to TPA. The same type of TPA-induced association of PK-C with membranes can be obtained in a reconstitution system with purified PK-C and isolated plasma membranes in the presence of TPA, Ca2+, and phosphatidylserine. This TPA mediated binding is dependent upon Ca2+, is time and temperature dependent, and reaches saturation at about 245 ng PK-C/mg PYS cell membrane protein. NIH 3T3 cells transformed with Kirsten (Ki) murine sarcoma virus have elevated membrane-associated PK-C activity and increased phosphatidylinositol (PI) metabolism relative to control 3T3 cells. In vitro studies with membranes isolated from NIH 3T3 and Ki-3T3 cells indicate PIP2-phosphodiesterase activity is increased with Ki-SV transformation of NIH 3T3 cells. The PIP2-PDE enzyme from Ki-3T3 cells also is more responsive to activation by GPT analogues. These results further support the suggestion for the involvement of PK-C activation (membrane association) in regulating cell proliferation, and in tumor promotion and malignant transformation, and also suggest possible modulation of this membrane signal transmission system by ras p21 protein.
