Hsp27 Inhibits Bax Activation and Apoptosis via a Phosphatidylinositol 3-Kinase-dependent Mechanism

Abstract

Hsp27 inhibits mitochondrial injury and apoptosis in both normal and cancer cells by an unknown mechanism. To test the hypothesis that Hsp27 decreases apoptosis by inhibiting Bax, Hsp27 expression was manipulated in renal epithelial cells before transient metabolic stress, an insult that activates Bax, induces mitochondrial injury, and causes apoptosis. Compared with control, enhanced Hsp27 expression inhibited conformational Bax activation, oligomerization, and translocation to mitochondria, reduced the leakage of both cytochrome c and apoptosis-inducing factor, and significantly improved cell survival by >50% after stress. In contrast, Hsp27 down-regulation using RNA-mediated interference promoted Bax activation, increased Bax translocation, and reduced cell survival after stress. Immunoprecipitation did not detect Hsp27-Bax interaction before, during, or after stress, suggesting that Hsp27 indirectly inhibits Bax. During stress, Hsp27 expression prevented the inactivation of Akt, a pro-survival kinase, and increased the interaction between Akt and Bax, an Akt substrate. In contrast, Hsp27 RNA-mediated interference promoted Akt inactivation during stress. Hsp27 up-or down-regulation markedly altered the activity of phosphatidylinositol 3-kinase (PI3-kinase), a major regulator of Akt. Furthermore, distinct PI3-kinase inhibitors completely abrogated the protective effect of Hsp27 expression on Akt activation, Bax inactivation, and cell survival. These data show that Hsp27 antagonizes Bax-mediated mitochondrial injury and apoptosis by promoting Akt activation via a PI3-kinase-dependent mechanism.

HSP27/HSPB1 as an adaptive podocyte antiapoptotic protein activated by high glucose and angiotensin II

“…58 In renal tubular cells, HSPB1 overexpression inhibited apoptosis and HSPB1 knockdown promoted apoptosis in response to culture in glucose-free medium containing sodium cyanide and 2-deoxy-D-glucose. 51 However, this kind of metabolic stress is of dubious clinical significance in the particular setting of DN. We now show that glomerular HSPB1 is upregulated in humans and in rats with short-(6 weeks) and long-standing (7 months) DN and that podocytes are the key sources of glomerular HSPB1 in both clinical and experimental DN.…”

“…However, HSPB1 target molecules differ for different lethal stimuli and cell types. 50,51 In certain cells HSPB1 binds to cytochrome c released from the mitochondria and HSPB1 overerexpression prevents cytochrome-cmediated interaction of Apaf-1 with procaspase-9 and procaspase-9 activation. 28,30 In this regard, in human podocytes we observed that HSPB1 targeting promoted caspase-9 and HSP27 and podocytes MD Sanchez-Niñ o et al caspase-3 activity in the presence of Ang II.…”

The BH3-mimetic ABT-737 targets the apoptotic machinery in cholangiocarcinoma cell lines resulting in synergistic interactions with zoledronic acid

“…Although ABT-737 was able to cause in EGI-1 cells a marked increase of sensitivity to apoptosis mediated by ZOL, this increment, in TFK1 cells, was less pronounced. In short, ZOL treatment could behave as "priming" agent [37] which induces S-phase arrest, an insufficient pro-apoptotic signal, while ABT-737 by blocking BCL-2 and BCL-XL action lowers the threshold at which apoptosis may occur. The ZOL or ABT-737-induced apoptosis resistance, observed in cholangiocarcinoma cells when used as single agent prompted us to speculate the plausible involvement of HSP72-dependent PARP-1 inactivation and/or an HSP27-mediated BAX inactivation that may contribute to explain the increased cell survival.…”

“…A potential additional mechanism that may contribute to increase the apoptosis resistance in TFK-1 cells is represented by the constitutive expression of pro-survival HSP27 [21,39,40]. This protein antagonizes BAX-mediated mitochondrial injury by inhibiting conformational activation of BAX thus reducing cytochrome c and AIF leakage and increasing significantly cell survival [37,41]. The resistance of EGI-1 and TFK-1 cholangiocarcinoma cell lines exposed to ABT-737 is multifactorial and could be ascribed to the presence of high levels of MCL-1 prosurvival protein (TFK-1), low level of BCL-2 (TFK-1), overexpression of HSP72 (TFK-1, EGI-1) or HSP27 (TFK-1).…”

Impact of hyperthermic intraperitoneal chemotherapy on Hsp27 protein expression in serum of patients with peritoneal carcinomatosis

“…By regulating the metabolism of glutathione (a major intracellular antioxidant) through the activation of glucose-6-phosphate dehydrogenase, Hsp27 protects cells from oxidative stress. Hsp27 can inhibit apoptosis through direct interaction with cytochrome c and inhibition of caspase activation and is also involved in the regulation of the Akt serine/threonine protein kinase pathway involved in cell survival (Aloy et al 2008;Havasi et al 2008). Because the overexpression of Hsp27 is frequently associated with thermotolerance and chemoresistance (Takhashi et al 2008;Li et al 1995), it appears to be a good candidate for explaining resistance to HIPEC.…”