TRANSFORMATION OF OB17 CELLS PROMOTES PROLIFERATION AND DIFFERENTIATION OF OB17 PREADIPOCYTES VIA DISTINCT EXTRACELLULAR INTERMEDIATES

Conditioned serum-free medium of Ob17 cells transformed by the middle-T-only gene of polyoma virus (Ob17MT cells) is able to support growth and adipose conversion of the parental Ob17 cells. Conditioned media from 3T3-F442A cells (untransformed preadipocyte clonal line) and MTT4 cells (middle-T-transformed non-preadipocyte clonal line) are inactive. The serum-free conditioned medium of Ob17MT cells is also active on growth and adipose conversion of 3T3-F442A cells. The morphological differentiation of Ob17 cells is accompanied by the expression of early (lipoprotein lipase, LPL) and late (glycerol-3-phosphate dehydrogenase, GPDH) biochemical markers of adipose conversion. Bio-Gel P-60 chromatography and SDS-PAGE have allowed characterization of a mitogenic fraction of apparent MW .simeq. 28 Kd distinct from an adipogenic fraction of apparent MW < 10 Kd. This adipogenic fraction is only required for the acquisition of the GPDH activity and is therefore active on terminal differentiation.