Expanding Roles of the E2F-RB-p53 Pathway in Tumor Suppression.

Simple Summary: The RB and p53 pathways are two major tumor suppressive pathways. Hence, in almost all cancers, both pathways are disabled. E2F transcription factor is under the control of the RB pathway and fulfills pivotal roles in tumor suppression by triggering the p53 pathway upon loss of RB function. Although this notion has been well established, emerging evidence indicates that each player of the E2F-RB-p53 pathway possesses novel functions and regulatory mechanisms. This review aims to introduce the expanding roles of the E2F-RB-p53 pathway in tumor suppression. The transcription factor E2F links the RB pathway to the p53 pathway upon loss of function of pRB, thereby playing a pivotal role in the suppression of tumorigenesis. E2F fulfills a major role in cell proliferation by controlling a variety of growth-associated genes. The activity of E2F is controlled by the tumor suppressor pRB, which binds to E2F and actively suppresses target gene expression, thereby restraining cell proliferation. Signaling pathways originating from growth stimulative and growth suppressive signals converge on pRB (the RB pathway) to regulate E2F activity. In most cancers, the function of pRB is compromised by oncogenic mutations, and E2F activity is enhanced, thereby facilitating cell proliferation to promote tumorigenesis. Upon such events, E2F activates the Arf tumor suppressor gene, leading to activation of the tumor suppressor p53 to protect cells from tumorigenesis. ARF inactivates MDM2, which facilitates degradation of p53 through proteasome by ubiquitination (the p53 pathway). P53 suppresses tumorigenesis by inducing cellular senescence or apoptosis. Hence, in almost all cancers, the p53 pathway is also disabled. Here we will introduce the canonical functions of the RB-E2F-p53 pathway first and then the non-classical functions of each component, which may be relevant to cancer biology. [ABSTRACT FROM AUTHOR]