Heat shock protein 90α (HSP90α), a substrate and chaperone of DNA-PK necessary for the apoptotic response

Abstract

The “apoptotic ring” is characterized by the phosphorylation of histone H2AX at serine 139 (γ-H2AX) by DNA-dependent protein kinase (DNA-PK). The γ-H2AX apoptotic ring differs from the nuclear foci patterns observed in response to DNA-damaging agents. It contains phosphorylated DNA damage response proteins including activated Chk2, activated ATM, and activated DNA-PK itself but lacks MDC1 and 53BP1, which are required to initiate DNA repair. Because DNA-PK can phosphorylate heat shock protein 90α (HSP90α) in biochemical assays, we investigated whether HSP90α is involved in the apoptotic ring. Here we show that HSP90α is phosphorylated by DNA-PK on threonines 5 and 7 early during apoptosis and that both phosphorylated HSP90α and DNA-PK colocalize in the apoptotic ring. We also show that DNA-PK is a client of HSP90α and that HSP90α is required for full DNA-PK activation, γ-H2AX formation, DNA fragmentation, and apoptotic body formation. In contrast, HSP90 inhibition by geldanamycin markedly enhances TRAIL-induced DNA-PK and H2AX activation. Together, our results reveal that HSP90α is a substrate and chaperone of DNA-PK in the apoptotic response. The response of phosphorylated HSP90α to TRAIL and its localization to the γ-H2AX ring represent epigenetic features of apoptosis that offer insights for studying and monitoring nuclear apoptosis.

Collaboration of geldanamycin-activated P70S6K and Hsp70 against beta-amyloid-induced hippocampal apoptosis: an approach to long-term memory and learning

“…In support of this conclusion, it was reported that Hsp70 protects against oxidative-induced cellular injury through improving cell endogenous antioxidant stability (Afolayan et al 2014). As another contributing factor, Solier et al (2012) provided evidence for proapoptotic phosphorylation and activation of Hsp90 in an in vitro context. Moreover, altered kinase activity has been subjected to pathologic events in Aβ toxicity, which is tightly regulated by Hsp90 (Luo et al 2008 GA-inhibited Hsp90 protective pathways in Aβ-induced neuronal toxicity and long-term memory impairment.…”

“…In this manner, Hsp70 protein plays a role in suppressing apoptotic cascades by directly mediating the conformation of molecules involved in signal transduction, beyond chaperone activity in protein folding and stabilization (Lu et al 2002;Sabirzhanov et al 2012;Gallo 2006). Conversely, Hsp90 has been suggested to contribute to upregulation of proapoptotic factors (Solier et al 2012). Also, Hsp70 acts as a sensor of cellular redox changes and is involved in occupying the pocket of the chaperone protein (Miyata et al 2012).…”

Hsp90α forms a stable complex at cilia neck for signal molecules interaction in cilia-mediated IGF-1 receptor signaling

“…S3). It could be the case that geldanamycin induced an apoptotic response, because rapid Hsp90a phosphorylation at Thr5 and Thr7 is induced in apoptotic cells (Solier et al, 2012). In our immunofluorescence analysis, this subset of cells was excluded.…”

Safety control for apoptotic irreversibility

“…Essentially, cells surviving a transient and reversible apoptotic response acquire permanent genetic changes and undergo oncogenic transformation (14). The dual activity of HSP90α described by Solier et al (2), associating its phosphorylation by DNA-PK at the H2AX apoptotic ring and the stabilization of the kinase during this process, could be crucial in ensuring complete HSP90α phosphorylation and consequent inhibition of its cytoprotective activity, given that the apoptotic ring is present (Fig. 1).…”

“…Therefore, there is a need for direct sensors to ensure the correct completion of the apoptotic process. The work of Solier et al (2) contributes to our understanding of such complex control mechanisms by demonstrating an interplay between the heat shock protein chaperone (HSP90α) chaperone and the DNA-dependent protein kinase (DNA-PK) during apoptosis.…”