pRb inactivation in senescent cells leads to an E2F-dependent apoptosis requiring p73.
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.
Alexander
Kamilah
K
Department of Pathology, Harvard Medical School, Boston, MA 02115, USA.
Yang
Hai-Su
HS
Hinds
Philip W
PW
D017209:Apoptosis / Q000235:genetics; D015153:Blotting, Western; D002453:Cell Cycle; D018797:Cell Cycle Proteins / Q000378:metabolism; D016922:Cellular Senescence; D019927:Cyclin E / Q000378:metabolism; D018844:Cyclin-Dependent Kinases / Q000378:metabolism; D004261:DNA Replication / Q000235:genetics; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D050684:E2F Transcription Factors; D005786:Gene Expression Regulation; D016147:Genes, Tumor Suppressor; D006801:Humans; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D016160:Retinoblastoma Protein / Q000235:genetics / Q000378:metabolism*; D016196:S Phase; D013696:Temperature; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic; D014162:Transfection; D014407:Tumor Cells, Cultured; D000072160:Tumor Protein p73; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism; D025521:Tumor Suppressor Proteins
D018797:Cell Cycle Proteins; D019927:Cyclin E; D004268:DNA-Binding Proteins; D050684:E2F Transcription Factors; D009687:Nuclear Proteins; D016160:Retinoblastoma Protein; C000606460:TP73 protein, human; D014157:Transcription Factors; D000072160:Tumor Protein p73; D016159:Tumor Suppressor Protein p53; D025521:Tumor Suppressor Proteins; D018844:Cyclin-Dependent Kinases