title: 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) 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.
authors.affiliation: Division of Dermatology, Department of Biomedicine and Surgery, Linköping University, Linköping, Sweden. cecbi@ibk.liu.se
authors.forename: Cecilia
authors.initials: C
authors.lastname: Bivik
authors.forename: Inger
authors.initials: I
authors.lastname: Rosdahl
authors.forename: Karin
authors.initials: K
authors.lastname: Ollinger
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000528:radiation effects*; D020169:Caspases / Q000378:metabolism / Q000528:radiation effects; D002403:Cathepsins / Q000378:metabolism* / Q000528:radiation effects; D045304:Cytochromes c / Q000378:metabolism*; D004789:Enzyme Activation; D018840:HSP70 Heat-Shock Proteins / Q000502:physiology*; D006358:Hot Temperature; D006801:Humans; D007425:Intracellular Membranes / Q000502:physiology / Q000528:radiation effects; D008099:Liver / Q000502:physiology; D008247:Lysosomes / Q000502:physiology / Q000528:radiation effects; D008544:Melanocytes / Q000502:physiology* / Q000528:radiation effects; D008928:Mitochondria / Q000528:radiation effects; D008930:Mitochondria, Liver / Q000502:physiology; D051381:Rats; D011994:Recombinant Proteins / Q000378:metabolism; D012867:Skin / Q000528:radiation effects; D014466:Ultraviolet Rays
chemical_list: D018840:HSP70 Heat-Shock Proteins; D011994:Recombinant Proteins; D045304:Cytochromes c; D002403:Cathepsins; D020169:Caspases