Control of ASPP2/53BP2L protein levels by proteasomal degradation modulates p53 apoptotic function

Abstract

The p53 pathway is a central mediator of the apoptotic response. ASPP2/53BP2L (apoptosis-stimulating grotein of p53 2, also known as 53BP2L) enhances apoptosis through selective stimulation of p53 transactivation of proapoptotic target genes. Although the Rb/E2F pathway regulates ASPP2/ 53BP2L transcription, the complex mechanisms controlling ASPP2/ 53BP2L levels and function remain unknown. We now report that proteasomal degradation modulates ASPP2/53BP2L protein levels and apoptotic function. Treatment of cells with proteasomal inhibitors, including the clinically utilized proteasomal inhibitor bortezomib, increases ASPP2/ 53BP2L protein but not RNA levels. Likewise, anthracycline-based chemotherapy, which has multiple mechanisms of action, including proteasomal inhibition, increases ASPP2/53BP2L protein but not RNA levels. Proteasomal inhibition or anthracycline treatment increases ASPP2/ 53BP2L protein stability and half-life. Furthermore, the central region of the ASPP2/53BP2L protein is ubiquitinated as would be expected for a proteasomal substrate. More importantly, small interfering RNA knockdown of ASPP2/53BP2L levels attenuated bortezomib-induced apoptosis, and this effect was greater in wild-type p53 cells. Because elevated levels of ASPP2/53BP2L are proapoptotic, these results described an important new molecular mechanism that modulates the p53-ASPP2/53BP2L apoptotic pathway. © 2005 by The American Society for Biochemistry and Molecular Biology, Inc.