Activation of p38 MAPK is required for Bax translocation to mitochondria, cytochrome c release and apoptosis induced by UVB irradiation in human keratinocytes.
This study establishes that activation of p38 MAPK by UVB represents a crucial signal required for the conformational change and translocation of Bax to the mitochondria in human keratinocytes. UVB-induced Bax translocation and mitochondrial cytochrome c release, which precede caspase activation and other endpoints of the apoptotic program such as chromatin fragmentation and loss of mitochondrial transmembrane potential, are blocked by genetic or pharmacological inhibition of the p38alpha MAPK. Inhibition of p38 MAPK strongly reduces the UVB-induced formation of sunburn cells and blocks Bax conformational change both in cultured human keratinocytes and in human skin, providing clear evidence for the physiological role of the p38 MAPK-Bax pathway in the removal of precancerous, UVB-damaged keratinocytes. Furthermore, we show that Bcl-2 overexpression, but not the pan-caspase inhibitor zVAD-fmk, blocks Bax conformational change and its subsequent translocation downstream of p38 MAPK. These data indicate that the activation of p38 MAPK by UVB engages a caspase-independent death signal leading to mitochondrial membrane permeabilization and apoptosis in human keratinocytes and suggest that p38 MAPK might have a preventive role in the process of photocarcinogenesis.
Van Laethem
An
A
Division of Biochemistry, Faculty of Medicine, Catholic University of Leuven, Leuven, Belgium.
Van Kelst
Sofie
S
Lippens
Saskia
S
Declercq
Wim
W
Vandenabeele
Peter
P
Janssens
Stefan
S
Vandenheede
Jackie R
JR
Garmyn
Maria
M
Agostinis
Patrizia
P
D017209:Apoptosis; D020169:Caspases / Q000378:metabolism; D045304:Cytochromes c / Q000378:metabolism; D004789:Enzyme Activation; D004817:Epidermis / Q000201:enzymology / Q000378:metabolism / Q000528:radiation effects; D006801:Humans; D015603:Keratinocytes / Q000201:enzymology / Q000378:metabolism* / Q000528:radiation effects*; D008928:Mitochondria / Q000378:metabolism*; D048290:Mitogen-Activated Protein Kinase 11 / Q000502:physiology; D048308:Mitogen-Activated Protein Kinase 14 / Q000502:physiology; D021381:Protein Transport; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism* / Q000502:physiology; D014466:Ultraviolet Rays; D051028:bcl-2-Associated X Protein; D048051:p38 Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism / Q000502:physiology*
C494826:BAX protein, human; D019253:Proto-Oncogene Proteins c-bcl-2; D051028:bcl-2-Associated X Protein; D045304:Cytochromes c; D048290:Mitogen-Activated Protein Kinase 11; D048308:Mitogen-Activated Protein Kinase 14; D048051:p38 Mitogen-Activated Protein Kinases; D020169:Caspases