Hsp70 protects against UVB induced apoptosis by preventing release of cathepsins and cytochrome c in human melanocytes

Abstract

Stress-induced heat shock protein 70 (Hsp70) effectively protects cells against apoptosis, although the anti-apoptotic mechanism is still undefined. Exposure of human melanocytes to heat and subsequent UVB irradiation increased the level of Hsp70 and pre-heating reduced UVB induced apoptosis. Immunofluorescence staining of Hsp70 in combination with staining of lysosomes (Lamp2) or mitochondria (Mitotracker Ò ) in pre-heated UVB exposed cells showed co-localization of Hsp70 with both lysosomes and mitochondria in the surviving cell population. Furthermore, UVB induced apoptosis was accompanied by lysosomal and mitochondrial membrane permeabilization, detected as release of cathepsin D and cytochrome c, respectively, which were prevented by heat pre-treatment. In purified fractions of lysosomes and mitochondria, recombinant Hsp70 attached to both lysosomal and mitochondrial membranes. Moreover, in apoptotic cells Bax was translocated from a diffuse cytosolic location into punctate mitochondrial-like structures, which was inhibited by Hsp70 induction. Such inhibition of Bax translocation was abolished by transfection with Hsp70 siRNA. Furthermore, Hsp70 siRNA eliminated the apoptosis preventive effect observed after pre-heating. These findings show Hsp70 to rescue melanocytes from UVB induced apoptosis by preventing release of cathepsins from lysosomes, Bax translocation and cytochrome c release from mitochondria.

Lysosomal exocytosis and caspase-8 mediated apoptosis in UVA-irradiated keratinocytes

“…The addition of lysosomal protease inhibitors or anti-cathepsin-D reduced caspase-8 activation and nuclear fragmentation, indicating that both cysteine and aspartic cathepsins work upstream of caspase-8 activation in UVA-irradiated keratinocytes. In melanocytes, UVA-induced apoptosis is mediated by lysosomal membrane permeabilization and release of cathepsins to the cytosol (Bivik et al, 2007). It has been suggested that cathepsin D activates caspase-8 in in vitro experiments (Conus et al, 2008;Conus et al, 2012), which further supports our findings.…”

Increased stability of Bcl-2 in HSP70-mediated protection against apoptosis induced by oxidative stress

“…Although it is clear that HSP70 has a general anti-apoptotic function, the mechanism is not known. Some studies have shown that HSP70 affects processes that regulate apoptotic signaling, effecter molecule activation, events downstream of caspase activation, release of cathepsins, cytochrome c, apoptosis-inducing factor (AIF), and even the death-associated permeablization of lysosomes (Feng et al 2006;Lui and Kong 2007;Bivik et al 2007;Matsumori et al 2005;Nylandsted et al 2004). Mitochondria harbor three key modulators of apoptosis: cytochrome c, AIF, and Smac (Kroemer and Reed 2000 Fig.…”

Proteomics of a toxic dinoflagellate Alexandrium catenella DH01: Detection and identification of cell surface proteins using fluorescent labeling

“…Cell surface localization of chaperones has been reported in several studies [49][50][51]. HSP70, previously characterized as a chaperone, regulates apoptosis in response to heat shock and oxidative stress by preventing the release of cathepsins and cytochrome c [52]. This protein prevents lysosome-mediated sudden death by binding to lysosomal cathepsins B, D, L and H and providing structural stability to lysosomal membranes [37,53].…”