Tumor Necrosis Factor Alpha-Induced Apoptosis Requires p73 and c-ABL Activation Downstream of RB Degradation

Abstract

The retinoblastoma protein (RB) suppresses cell proliferation and apoptosis. We have previously shown that RB degradation is required for tumor necrosis factor alpha (TNF-α) to induce apoptosis. We show here the identification of two apoptotic effectors, i.e., c-ABL tyrosine kinase and p73, which are activated by TNF-α following RB degradation. In cells expressing a degradation-resistant RB protein (RB-MI), TNF-α does not activate c-ABL. RB-MI also inhibits TNF-α-mediated activation of p73. Genetic deletion and pharmacological inhibition of c-ABL or p73 diminish the apoptotic response to TNF-α in human cell lines and mouse fibroblasts. Thymocytes isolated from Rb^MI/MI, Abl^−/−, or p73^−/− mice are resistant to TNF-α-induced apoptosis compared to their wild-type counterparts. This is in contrast to p53^−/− thymocytes, which exhibit a wild-type level of apoptosis in response to TNF-α. Thus, c-ABL and p73 contribute to apoptosis induced by TNF-α, in addition to their role in promoting DNA damage-associated cell death.

We thank members of the Wang lab for their critical comments throughout the course of this work. We are particularly indebted to Sewon Ki for reconstituting HA-p73α expression in p73^−/− fibroblasts and to Irina Hunton for generating Rb^−/−Abl^−/− and Rb^−/−p53^−/− fibroblasts.

B.N.C. is a Robert Black Fellow of the Damon Runyon Cancer Research Foundation (DRG-1725-02). This work was supported by NIH grant CA58320 to J.Y.J.W. and American Cancer Society grant RSG LIB-101051 to J.D.