B-Myc is preferentially expressed in hormonally-controlled tissues and inhibits cellular proliferation

The myc family of genes plays an important role in several cellular process es including proliferation, apoptosis, differentiation, and transformation. B-myc, a relatively new and largely unstudied member of the myc family, en codes a protein that is highly homologous to the N-terminal transcriptional regulatory domain of c-Myc, Here, we show that high level B-myc expression is restricted to specific mouse tissues, primarily hormonally-controlled t issues, with the highest level of expression in the epididymis, We also rep ort the identification of the endogenous B-Myc protein from mouse tissues. Like other Myc family proteins, B-Myc is a short-lived nuclear protein whic h is phosphorylated on residues Ser-60 and Ser-68, Rapid proteolysis of B-M yc occurs via the ubiquitin-proteasome pathway. Finally, we found that over expression of B-Myc significantly slows the growth of Rat la fibroblasts an d COS cells suggesting B-Myc functions as an inhibitor of cellular prolifer ation.