Expression of a down-regulated target, SSeCKS, reverses v-Jun-induced transformation of 10T1/2 murine fibroblasts

Line 10T1/2 mouse fibroblast overexpressing the v-Jun oncoprotein mere morp hologically altered, grew into multilayered foci in culture and formed colo nies when suspended in agar, The growth rate of the v-Jun-transformed 10T1/ 2 cells was not changed significantly from that of the untransformed parent al cells, but the saturation density of the transformed cultures exceeded t hat of normal controls by a factor of 2, mRNA extracted from v-Jun-transfor med 10T1/2 cells was analysed for differential gene expression with DNA mic ro-array technology. One of the targets downregulated by v-Jun was identifi ed as SSeCKS (Src-suppressed C kinase substrate). Re-expression of SSeCKS i n v-Jun-transformed fibroblasts reversed the transformed phenotype of the c ells. Their ability to form foci was reduced to background levels, the numb er and size of agar colonies was lowered by a factor of 10 and the saturati on density was significantly diminished. However, expression of SSeCKS had little effect on the morphology of v-Jun-transformed 10T1/2 cells. These da ta suggest that the SSeCKS protein has growth-attenuating properties. Down- regulation of SSeCKS may be essential for Jun-induced transformation.