V-RAS AND V-RAF BLOCK DIFFERENTIATION OF TRANSFORMABLE C3H10T1 2-DERIVED PREADIPOCYTES AT LOWER LEVELS THAN REQUIRED FOR NEOPLASTIC TRANSFORMATION/

To investigate the functional relationship between the transforming ab ility of Ras and its role as an integral component of the differentiat ive insulin signaling pathway, we introduced a leu61-activated ms gene into a Ras-transformable, C3H1OT1/2-derived preadipocytic cell line. The results demonstrate that ras(leu61) expression in this Line blocks differentiation and that this block. appears at lower levels than req uired for full. neoplastic transformation, In addition, to examine whe ther the inability of Ras(leu61) to induce differentiation by replacin g the insulin signal could be attributed to its transforming effect in this system, we examined the effect of Ras(leu61) at levels below the baseline, by expressing ras(leu61) in a series of preadipocytes which were rendered deficient in endogenous c-Ras activity, The results sho w that even very low Ras(leu61) levels, insufficient to restore the gr owth rate of these cells to normal, blocked rather than enhanced diffe rentiation, indicating that ras(leu61) expression alone is not suffici ent to promote adipocytic differentiation in this system, even in the absence of neoplastic transformation. Consistent with its established role as a downstream effector of Ras, v-Raf expression mirrored the v- Ras effects upon adipocytic differentiation and transformation. (C) 19 97 Academic Press.