MOUSE JUND NEGATIVELY REGULATES FIBROBLAST GROWTH AND ANTAGONIZES TRANSFORMATION BY RAS

As NIH 3T3 fibroblasts become quiescent, the level of c-Jun protein de creases while JunD accumulates. When resting cells are stimulated with fresh serum, nuclear-localized JunD is rapidly degraded, followed by resynthesis of both c-Jun and JunD later in G1. Overexpression of JunD results in slower growth and an increase in the percentage of cells i n G0/G1 while c-Jun overexpression produces larger S/G2 and M phase po pulations. In addition, JunD partially suppresses transformation by an activated ras gene whereas c-Jun cooperates with ras to transform cel ls. These data indicate that two closely related transcription factors can function in an opposing manner.