Identification of the major phosphoprotein secreted by many rodent cell lines as 2ar/osteopontin: enhanced expression in H-ras-transformed 3T3 cells

Abstract

/ar, a tumor promoter-inducible protein secreted by mouse JB6 epidermal cells, is the murine homolog of rat osteopontin, or 44 kD bone phosphoprotein. We report here that 2ar is also related to pp69, a major phosphoprotein secreted by normal rat kidney cells. Antisera raised against pp69 and against beta-galactosidase-2ar fusion proteins are able to immunoprecipitate the same major phosphoproteins, of apparent Mr 55-69 kD, secreted by several rat and mouse cell lines. The levels of secreted protein and cytoplasmic mRNA are dramatically elevated in NIH 3T3 cells transformed with the human bladder cancer T24 (H-ras) oncogene. These results and the work of Senger and colleagues (Cancer Res., 45, 5818-5823, 1985) imply that enhanced secretion of 2ar/pp69/osteopontin by transformation of a wide variety of mammalian fibroblasts and epithelial cells is often correlated with tumorigenicity.