CAIR-1/BAG-3 Abrogates Heat Shock Protein-70 Chaperone Complex-mediated Protein Degradation

Abstract

BAG family proteins are regulatory co-chaperones for heat shock protein (Hsp) 70. Hsp70 facilitates the removal of injured proteins by ubiquitin-mediated proteasomal degradation. This process can be driven by geldanamycin, an irreversible blocker of Hsp90. We hypothesize that CAIR-1/BAG-3 inhibits Hsp-mediated proteasomal degradation. Human breast cancer cells were engineered to overexpress either full-length CAIR-1 (FL), which binds Hsp70, or a BAG domain-deletion mutant (dBAG) that cannot bind Hsp70. FL overexpression prevented geldanamycin-mediated loss of total and phospho-Akt and other Hsp client proteins. dBAG provided no protection, indicating a requirement for Hsp70 binding. Ubiquitinated Akt accumulated in FL-expressing cells, mimicking the effect of lactacystin proteasomal inhibition, indicating that CAIR-1 inhibits proteasomal degradation distal to protein ubiquitination in a BAG domain-dependent manner. Protein protection in FL cells was generalizable to downstream Akt targets, GSK3␤, P70S6 kinase, CREB, and other Hsp client proteins, including Raf-1, cyclin-dependent kinase 4, and epidermal growth factor receptor. These findings suggest that Hsp70 is a chaperone driving a multiprotein degradation complex and that the inhibitory co-chaperone CAIR-1 functions distal to client ubiquitination. Furthermore, poly-ubiquitination is not sufficient for efficient proteasomal targeting of Hsp client proteins.

Aggravation of diabetic nephropathy in BCL-2 interacting cell death suppressor (BIS)-haploinsufficient mice together with impaired induction of superoxide dismutase (SOD) activity

“…In the case of pro-oxidant or aggregation-prone status, BIS has been suggested to interact with HSP70 to activate macroautophagy, whereas interaction of BAG1 with HSP70 is known to be essential for effective proteasomal degradation [16,22]. The misfolding and aggregation of SOD have been shown to increase with oxidative stress in neuronal cells [39].…”

“…Furthermore, the suppression of BIS expression has been reported to sensitise leukaemic cells to death induced by a glutathionedepriving agent, and the overexpression of BIS attenuates apoptosis induced by the electrophilic 4-hydroxynonenal, suggesting that the induction of BIS could be related to protecting cells exposed to oxidative stress [11,21]. However, the molecular pathway by which BIS modulates cell survival is not well understood, though the binding of BIS to BCL-2 or heat shock 70 kDa protein (HSP70) has provided some insights into this process [10,22]. We recently reported that the downregulation of BIS in C6 glial cells leads to accelerated cell death on oxygen-glucose deprivation (OGD), accompanied by the accumulation of ROS and an impairment in the activation of superoxide dismutase (SOD)1 at the transcriptional level [23].…”

BAG3 controls angiogenesis through regulation of ERK phosphorylation

“…19 It is likely that the Hsp70-mediated delivery of other anti-apoptotic proteins to proteasome could be influenced by BAG3 as well. 23 In addition, BAG3 can also bind to other proteins via its proline-rich (PXXP) or WW domains, 24 possibly resulting in a modulation of their activity. Because of its multifaceted ability to complex with many proteins, BAG3 can regulate factors that are particularly relevant in the context of specific tumour types, such as BAX in glioblastoma cells.…”

BAG3 protein regulates stress-induced apoptosis in normal and neoplastic leukocytes

“…Finally, the BAG3/Hsp70 complex has recently been shown to participate in the proteasome -mediated degradation of intracellular proteins. 21 It is therefore likely that BAG3 protein can influence the activity of more than one factor involved in the apoptotic Effect of BAG3-specific antisense oligodeoxynucleotides on BAG3 protein levels in U937 cells. U937 cells were plated at a density of 5 Â 10 5 /ml and cultured for 15 h without or with DEM (Sigma, St Louis, MO, USA) (1.2 mM) and/or BAG3 antisense or control nonsense phosphorothioate ODN 16 (5 mM).…”