RB BINDS C-JUN AND ACTIVATES TRANSCRIPTION

The retinoblastoma protein (Rb) acts as a critical cell-cycle regulato r and loss of Rb function is associated with a variety of human cancer types. Here we report that Rb binds to members of the AP-1 family of transcription factors, including c-Jun, and stimulates c-Jun transcrip tional activity from an AP-1 consensus sequence. The interaction invol ves the leucine zipper region of c-Jun and the B pocket of Rb as well as a C-terminal domain. We also present evidence that the complexes ar e found in terminally differentiating, keratinocytes and cells enterin g the G(1) phase of the cell cycle after release from serum starvation . The human papillomavirus type 16 E7 protein, which binds to both c-J un and Rb, inhibits the ability of Rb to activate c-Jun. The results p rovide evidence of a role for Rb as a transcriptional activates in ear ly G(1) and as a potential modulator of c-Jun expression during kerati nocyte differentiation.