Cell surface alterations of avian sarcoma virus B77- and 3,4-benzo(a)pyrene-transformed rat fibroblasts. I. Cell surface proteins characterized by two-dimensional electrophoresis.

Plasma membrane proteins of avian sarcoma virus B77-, 3,4-benzo(a)pyrene- and spontaneously transformed rat fibroblasts were metabolically- and cell surface radiolabeled and analyzed by electrophoresis under denaturing conditions (SDS-PAGE) or by two-dimensional electrophoresis. Most extensive series of protein alterations on transformed cells was detected by two-dimensional electrophoresis of cell surface proteins radiolabeled by lactoperoxidase catalyzed radioiodination: a fibronectin-like 220k protein with two isoelectric forms (pI 5.9 and 6.2-6.6), a 180k protein of pI 6.2-6.6 and two proteins of 48k and 50k with pI approximately 5.4-all decreased on examined transformed cells. In addition to these proteins, a series of proteins more markedly detectable on transformed cells was found: a 110-120k (pI 5.6) protein found particularly on 3,4-benzo(a)pyrene- and spontaneously transformed cells, a series of proteins in the region of molecular weights 46-54k with pI 5.5-6.0, two proteins of 35k (pI 6.2 and 6.4) and two further, basic proteins of 38k (pI approximately 7.2 and 7.8). Some of these changes were visualized also by further techniques for radiolabeling of proteins, i.e. reductive methylation of cell surface proteins, metaboling radiolabeling by 3H-leucine followed by plasma membrane isolation, as well as by protein staining after two-dimensional electrophoresis of isolated plasma membrane proteins. A 70k and a 120k radioiodinated proteins were immunoprecipitated from all transformed cells and, to a markedly lesser extent from untransformed fibroblasts by the immune serum against rat type-C endogenous virus. A similar 70k protein was immunoprecipitated from avian sarcoma virus B77-transformed cells also by the antiserum against Friend murine leukemia virus envelope glycoprotein gp70.