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Carcinogenesis Advance Access originally published online on August 31, 2006
Carcinogenesis 2007 28(3):537-544; doi:10.1093/carcin/bgl152
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© The Author 2006. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oxfordjournals.org

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

Cecilia Bivik1,*, Inger Rosdahl1 and Karin Öllinger2

1 Division of Dermatology, Department of Biomedicine and Surgery SE-581 85 Linköping, Sweden
2 Division of Experimental Pathology, Department of Neuroscience and Locomotion; Faculty of Health Sciences, Linköping University SE-581 85 Linköping, Sweden

*To whom correspondence should be addressed. Tel: +46 13228739; Fax: +46 13127465; Email: cecbi{at}ibk.liu.se

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.

Abbreviations: AIF, apoptosis-inducing factor; Hsp, heat shock protein; NAG, ß-N-acetylglucosaminidase; tBid, truncated Bid; UV, ultraviolet

Received March 28, 2006; revised August 14, 2006; accepted August 18, 2006.


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