UFD2a mediates the proteasomal turnover of p73 without promoting p73 ubiquitination

Abstract

p73 protein level is kept extremely low in mammalian cultured cells and its stability may be regulated by not only the ubiquitin/proteasome-dependent proteolysis but also through other unidentified mechanisms. Here, we found for the first time that p73 is physically as well as functionally associated with the U-box-type E3/E4 ubiquitin ligase UFD2a. The immunoprecipitation experiments demonstrated that this interaction is mediated by the COOH-terminal region of p73alpha containing SAM domain. During the cisplatin-induced apoptosis in SH-SY5Y neuroblastoma cells, p73alpha accumulated at a protein level, whereas the endogenous UFD2a was significantly reduced in response to cisplatin. Ectopic expression of UFD2a decreased the half-life of p73alpha in association with a significant inhibition of the p73alpha-mediated transactivation as well as proapoptotic activity. Downregulation of endogenous UFD2a by antisense strategy resulted in a remarkable accumulation of p73alpha. Unexpectedly, UFD2a-mediated degradation of p73alpha was sensitive to the proteasomal inhibitor, however, UFD2a did not affect the ubiquitination levels of p73alpha. Taken together, our present findings imply that UFD2a might promote the proteasomal turnover of p73 in a ubiquitination-independent manner, and also suggest that UFD2a might play an important role in the regulation of cisplatin-induced apoptosis mediated by p73.

DFF45/ICAD restores cisplatin-induced nuclear fragmentation but not DNA cleavage in DFF45-deficient neuroblastoma cells

“…We found that NBL cell lines, NB-1 and NB-C201, carry a homozygous deletion at 1p36.2, and identified six genes within this region including DFF45/ICAD, PGD, CORT, UFD2a, KIF1B-b and PEX14 (Ohira et al, 2000). Among them, we have demonstrated that UFD2a promotes the proteasome-dependent degradation of p73 (Hosoda et al, 2005).…”

TAp73 Protein Stability Is Controlled by Histone Deacetylase 1 via Regulation of Hsp90 Chaperone Function

“…Furthermore, p73 proteins are sub-jected to post-translational modifications such as acetylation by acetyltransferase CBP/p300 (27) and phosphorylation by kinases including c-Abl (28 -30), JNK (31), p38 (32), and PKC␦ (33). Finally, p73 proteins can be targeted for ubiquitin-dependent and -independent proteasomal degradation by several E3 ligases, including the NEDD4-like ubiquitin ligase Itch (34), the F-box protein FBXO45 (35), the Ring finger domain ubiquitin ligases PIR2 and Pirh2 (36,37), and the U-box type E3/E4 ubiquitin ligase UFD2a (38). These results suggest that p73 expression is regulated by complex molecular signaling pathways.…”

STAT1 regulates p73‐mediated Bax gene expression

“…Data published previously have demonstrated that the Bax promoter can be activated upon TA-p73 overexpression [30,39,40]. Moreover, overexpression of p73 has been reported in various tumour types when compared with normal tissues [41][42][43][44][45] and has been reported to confer resistance to p53-mediated apoptosis induced by certain chemotherapeutic agents [46].…”

“…Positive stabilizers of TA-p73 protein and activity include MDM2 [50] -as in the case of p53 [51][52][53], YAP [54], and phosphorylation by PKC-d [55]. Conversely, TA-p73 activity can be negatively regulated by cyclin G [56], SUMO-1 [57], PIAS-1 [19] calpain I [58], UFD2a [39], PKA-Cb [30] and Itch [59]. Other identified binding partners to TA-p73 include HMGB1 and HMGB2, which stimulate or abrogate the binding of TA-p73 to p53 responsive elements (within the Bax promoter) in a cell specific manner [40].…”