Regulation of c-Myb activity by tumor suppressor p53.

Heat shock proteins (HSPs) act as chaperones and play important roles during cellular proliferation and apoptosis. Heat shock factors (HSFs) mediate transcriptional induction of HSP genes. Among multiple heat shock transcription factors (HSFs) in vertebrates, HSF3 is specifically activated in unstressed proliferating cells by direct binding to the c-myb proto-oncogene product (c-Myb). Since c-Myb has an important role in cellular proliferation, this regulatory pathway suggests a link between the events of cellular proliferation and the stress response. The c-Myb-induced activation of HSF3 is negatively regulated by the p53 tumor suppressor protein. p53 directly binds to HSF3 and blocks the interaction between c-Myb and HSF3. In addition, p53 stimulates the degradation of c-Myb, which is, at least partly, mediated by induction of Siah in certain types of cells. Thus, c-Myb and p53 regulate the expression of HSPs via HSF3 in opposite ways.