Control of ASPP2/53BP2L Protein Levels by Proteasomal Degradation Modulates p53 Apoptotic Function

• DOI: 10.1074/jbc.m503736200
• Publication Date: 2005-08-10T02:32:39Z
• Authors: Zhiyi Zhu; Jason Ramos; Kerstin Kampa; Shanthi Adimoolam; Mint Sirisawad; Zhiyong Yu; Dexi Chen; Louie Naumovski; Charles D. Lopez
• Keywords: 0301 basic medicine; Proteasome Endopeptidase Complex; Dose-Response Relationship, Drug; Blotting, Western; Apoptosis; Blotting, Northern; Boronic Acids; Cell Line; E2F Transcription Factors; Bortezomib; Gene Expression Regulation, Neoplastic; 03 medical and health sciences; Cell Line, Tumor; Pyrazines; Humans; RNA; Anthracyclines; RNA Interference; RNA Processing, Post-Transcriptional; RNA, Small Interfering; Apoptosis Regulatory Proteins; Carrier Proteins

The p53 pathway is a central mediator of the apoptotic response. ASPP2/(53BP2L) (apoptosis-stimulating protein 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.