ErbB2 Degradation Mediated by the Co-chaperone Protein CHIP

Abstract

ErbB2 overexpression contributes to the evolution of a substantial group of human cancers and signifies a poor clinical prognosis. Thus, down-regulation of ErbB2 signaling has emerged as a new anti-cancer strategy. Ubiquitinylation, mediated by the Cbl family of ubiquitin ligases, has emerged as a physiological mechanism of ErbB receptor down-regulation, and this mechanism appears to contribute to ErbB2 down-regulation induced by therapeutic anti-ErbB2 antibodies. Hsp90 inhibitory ansamycin antibiotics such as geldanamycin (GA) induce rapid ubiquitinylation and down-regulation of ErbB2. However, the ubiquitin ligase(s) involved has not been identified. Here, we show that ErbB2 serves as an in vitro substrate for the Hsp70/Hsp90-associated U-box ubiquitin ligase CHIP. Overexpression of wild type CHIP, but not its U-box mutant H260Q, induced ubiquitinylation and reduction in both cell surface and total levels of ectopically expressed or endogenous ErbB2 in vivo, and this effect was additive with that of 17-allylamino-geldanamycin (17-AAG). The CHIP U-box mutant H260Q reduced 17-AAG-induced ErbB2 ubiquitinylation. Wild type ErbB2 and a mutant incapable of association with Cbl (ErbB2 Y1112F) were equally sensitive to CHIP and 17-AAG, implying that Cbl does not play a major role in geldanamycin-induced ErbB2 down-regulation. Both endogenous and ectopically expressed CHIP and ErbB2 coimmunoprecipitated with each other, and this association was enhanced by 17-AAG. Notably, CHIP H260Q induced a dramatic elevation of ErbB2 association with Hsp70 and prevented the 17-AAG-induced dissociation of Hsp90. Our results demonstrate that ErbB2 is a target of CHIP ubiquitin ligase activity and suggest a role for CHIP E3 activity in controlling both the association of Hsp70/Hsp90 chaperones with ErbB2 and the down-regulation of ErbB2 induced by inhibitors of Hsp90.

miR-764-5p promotes osteoblast differentiation through inhibition of CHIP/STUB1 expression

“…(3) Several groups have reported that Runx2 protein stability is controlled through a ubiquitinproteasome-mediated protein degradation mechanism by Smurf1, (4) Schnurr-3 (Shn3)/WWP1, (5) and CHIP. (6) CHIP/STUB1 is a cochaperone protein identified through its interaction with Hsc/Hsp70, (7) and promotes the ubiquitination and degradation of chaperone-bound proteins, including receptor tyrosine kinase ErbB2, glucocorticoid receptor, (8) SCR-3, (9) Smads, and the mis-folded cystic fibrosis transmembrane conductance regulator protein. (10) Previously, we found that CHIP negatively regulates osteoblast differentiation by mediating degradation of Runx2.…”

Akt shows variable sensitivity to an Hsp90 inhibitor depending on cell context

“…In each case, treatment with GA or 17-AAG results in loss of chaperone function that leads to ubiquitination and degradation by the proteasome [5]. The ubiquitin ligase called Chip is thought to play a role in this process since it stimulates degradation of Hsp90 client proteins in the presence of GA [6][7][8][9]. However, GA can still promote degradation of a client kinase, ErbB2, even in Chip −/− fibroblasts, albeit with reduced kinetics [6].…”

Endocytic Down-Regulation of ErbB2 Is Stimulated by Cleavage of Its C-Terminus

“…One possibility is that free ubiquitin becomes sequestered when the proteasome is inhibited with lactacystin. However, inhibition of proteasomal activity leads to an accumulation of ubiquitinylated ErbB2 (Zhou et al, 2003;our unpublished data), and more importantly ErbB2 was found still to become ubiquitinylated in cells treated with lactacystin and GA (Mimnaugh et al, 1996; our unpublished data).…”