Phosphorylation of heat shock protein 27 antagonizes TNF-α induced HeLa cell apoptosis via regulating TAK1 ubiquitination and activation of p38 and ERK signaling

Tumor necrosis factor (TNF)-alpha is a potent cytokine that regulates critical cellular processes including apoptosis. TNF-alpha usually triggers both survival and apoptotic signals in various cell types. Heat shock protein 27 (HSP27), an important cellular chaperone, is believed to protect cells from apoptosis. HSP27 can be phosphorylated and changed its cellular function according to different stimuli. However, available reports on the role of HSP27 phosphorylation in apoptosis remain elusive. In this study, we investigated the role of HSP27 phosphorylation in TNF-a induced apoptosis in human cervical carcinoma (HeLa) cells. We found that TNF-alpha induced apoptosis was enhanced if we suppressed the TNF-alpha induced HSP27 phosphotylation by specific inhibitor CMPD1 or MAPKAPK2 (MK2) knockdown or by overexpression of non-phosphorylatable mutant HSP27-3A. Through coimmunoprecipitation and confocal microscopy, we observed that HSP27 associated with transforming growth factor-beta (TGF-beta)-activated kinase 1 (TAK1) in response to TNF-alpha stimulation. By blocking MK2 activity or overexpressing phospho-mimetic mutant Hsp27-3D, we further showed that HSP27 phosphorylation facilitated the TNF-alpha induced ubiquitination and phosphorylation of TAK1 and the activations of p38 MAPK and ERK, the TAK1 downstream pro-survival signaling. In addition, we also found that increased HSP27 phosphorylation inhibited TRADD ubiquitination but did not influence the binding between TRADD and FADD in a pro-apoptotic complex. Taken together, our data indicated that HSP27 phosphotylation was involved in modulating the TNF-alpha induced apoptosis via interacting with TAK1 and regulating TAK1 post-translational modifications in HeLa cells. This study demonstrates that HSP27 phosphorylation serves as a novel regulator in TNF-alpha-induced apoptosis, and provides a new insight into the cytoprotective role of HSP27 phosphotylation. (C) 2014 Elsevier Inc. All tights reserved.