pRb inactivation in senescent cells leads to an E2F-dependent apoptosis requiring p73

• Published in: Molecular cancer research Vol. 1; no. 10; pp. 716 - 728
• Main Authors: ALEXANDER, Kamilah, YANG, Hai-Su, HINDS, Philip W
• Format: Journal Article
• Language: English
• Published: Philadelphia, PA American Association for Cancer Research 01.08.2003
• Subjects: Ageing, cell death; Apoptosis - genetics; Biological and medical sciences; Blotting, Western; Cell Cycle; Cell Cycle Proteins - metabolism; Cell physiology; Cellular Senescence; Cyclin E - metabolism; Cyclin-Dependent Kinases - metabolism; DNA Replication - genetics; DNA-Binding Proteins - genetics; DNA-Binding Proteins - metabolism; E2F Transcription Factors; Fundamental and applied biological sciences. Psychology; Gene Expression Regulation; Genes, Tumor Suppressor; Humans; Molecular and cellular biology; Nuclear Proteins - genetics; Nuclear Proteins - metabolism; Retinoblastoma Protein - genetics; Retinoblastoma Protein - metabolism; S Phase; Temperature; Transcription Factors - genetics; Transcription Factors - metabolism; Transcription, Genetic; Transfection; Tumor Cells, Cultured; Tumor Protein p73; Tumor Suppressor Protein p53 - metabolism; Tumor Suppressor Proteins
• ISSN: 1541-7786; 1557-3125

Senescent cells in which pRb is inactivated undergo apoptosis on attempted reinitiation of DNA synthesis. To further explore the cell death resulting from loss of pRb function in senescent cells, we employed a temperature-sensitive pRb mutant protein (tspRb). We found that tspRb inactivation results in rapid E2F reactivation and subsequent S-phase reentry associated with the up-regulation of E2F target gene expression and cyclin E-dependent kinase activity. Total inhibition of cyclin-dependent kinase 2 activity results in a cell cycle arrest on pRb loss and a nearly complete suppression of apoptosis. Furthermore, blocking of E2F activity with a dominant-negative DP1 inhibits S-phase reentry and cell death following tspRb inactivation. Finally, inhibition of p73 activity abolishes apoptosis but not S-phase entry on pRb inactivation, suggesting that activation of E2F in senescent cells can result in the use of p73 as a cell death effector. Interestingly, senescent cells rescued from apoptosis maintain their altered shape and express senescence-associated beta-galactosidase despite loss of pRb function. Thus, maintenance of the terminal cell cycle arrest of senescent cells requires continuous pRb-mediated inactivation of E2F activity, the reappearance of which in these irrevocably altered cells triggers a cell death program instead of an inappropriate resumption of cell cycling.