Transforming growth factor stimulates bovine leukemia virus expression in naturally infected cells

Abstract

Fetal calf serum (FCS) and platelet extracts (PE) have been shown to stimulate Bovine Leukemia Virus (BLV) expression in a naturally infected cell line (NBC-10) as well as in primary cultures of bovine peripheral blood mononuclear cells (PBMC). In order to identify the platelet factor responsible for this stimulation we have tested the activity of several recombinant or highly purified platelet factors on the expression of BLV in NBC-10 cells. The 3 mammalian isoforms of transforming growth factor-b (TGF-b) stimulated the synthesis of the major core BLV protein (BLVp24) in a dose dependent manner. Anti TGF-b antibodies neutralized the effect of FCS and PE on the synthesis of BLVp24 in NBC-10 cells. Recombinant TGF-b also stimulated the synthesis of BLVp24 in 24 hr cultures of BLV infected PBMC. It is concluded that TGF-b is the main factor involved in the in vitro activation of BLV expression induced by FCS and PE in NBC-10 cells. The bioassay employing NBC-10 cells as indicator system proved to be useful for the identification of substances regulating the expression of BLV.