GROWTH IN SERUM-FREE MEDIUM OF NIH3T3 CELLS TRANSFORMED BY THE EJ-H-RAS ONCOGENE - EVIDENCE FOR MULTIPLE AUTOCRINE GROWTH-FACTORS

Rodent fibroblastic cells transformed by ras oncogenes can grow in serum-free (S-) medium. We have studied clonal lines of mouse NIH3T3 fibroblasts transfected with the EJ-H-ras oncogene, and observed that practically all become independent of exogenous growth and attachment factors shortly after transfection. Moreover, all the clones tested soon form anchorage-independent (Al) colonies in S- medium, and most give rise to spheroids able to grow in suspension. The cell-conditioned S-medium of the transformed (TR) cells stimulates autocrinally the Al and anchored growth of these cells, in the absence of serum, and it contains growth factors related to TGF-alpha (or EGF), PDGF and bFGF, and other uncharacterized factors. Some of these factors are not found, or are found only in very small amounts, in the S- medium of non-transformed NIH3T3 cells, which also stimulates the growth of the TR cells, in the absence of serum. In addition, the TR cells contain 4-6 times more cell-associated bFGF than the non-transformed cells and release more latent TGF-beta-activatable by acid treatments. However, no active TGF-beta is secreted by either cell type. Activated TGF-beta and pure TGF-beta-I stimulate the growth of the anchored TR and NIH3T3 cells, but inhibit the Al growth of the TR cells. Another inhibitor of this growth is also found in the concentrated medium of the NIH3T3 cells.