A p38(MAPK)/HIF-1 pathway initiated by UVB irradiation is required to induce Noxa and apoptosis of human keratinocytes.
The signal transduction pathways leading to apoptosis of human keratinocytes responding to UVB irradiation are complex and not completely understood. Previously, we reported that in UVB-irradiated keratinocytes, p38(MAPK) instigates Bcl-2-associated X protein (Bax) activation and mitochondrial apoptosis. However, the molecular mechanism underlying the pro-apoptotic function of p38(MAPK) remained unclear. Here, we show that in UVB-treated human primary keratinocytes the activation of p38(MAPK) is necessary to upregulate Noxa, a BH3-only pro-apoptotic dominantly induced by UVB and required for apoptosis. Whereas p53-silencing was marginally cytoprotective and poorly affected Noxa expression, p38(MAPK) inhibition in p53-silenced keratinocytes or in p53(-/-) cells could still efficiently prevent Noxa induction and intrinsic apoptosis after UVB, indicating that p38(MAPK) signals mainly through p53-independent mechanisms. Furthermore, p38(MAPK) was required for the induction and activation of hypoxia-inducible factor 1 (HIF-1) in response to UVB, and HIF-1 knockdown reduced Noxa expression and apoptosis. In UVB-irradiated keratinocytes, Noxa targeted the anti-apoptotic myeloid cell leukemia sequence 1 (Mcl-1) for degradation, and small-interfering RNA (siRNA)-mediated knockdown of Noxa or p38(MAPK) inhibition restored levels of Mcl-1 and abolished apoptosis. Thus, the pro-apoptotic mechanisms orchestrated by p38(MAPK) in human keratinocytes in response to UVB involve an HIF-1/Noxa axis, which prompts the downregulation of anti-apoptotic Mcl-1, thereby favoring Bax-mediated mitochondrial apoptosis of UVB-damaged keratinocytes.
Nys
Kris
K
Cell Death Research and Therapy Laboratory, Department of Molecular Cell Biology, Catholic University of Leuven, Leuven, Belgium.
Van Laethem
An
A
Michiels
Carine
C
Rubio
Noemi
N
Piette
Jacques G
JG
Garmyn
Maria
M
Agostinis
Patrizia
P
D017209:Apoptosis / Q000502:physiology / Q000528:radiation effects; D001549:Benzamides; D002294:Carcinoma, Squamous Cell / Q000473:pathology; D045744:Cell Line, Tumor; D006801:Humans; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000378:metabolism*; D015603:Keratinocytes / Q000166:cytology / Q000201:enzymology / Q000528:radiation effects; D020935:MAP Kinase Signaling System / Q000502:physiology / Q000528:radiation effects*; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000235:genetics* / Q000378:metabolism; D012878:Skin Neoplasms / Q000473:pathology; D016159:Tumor Suppressor Protein p53 / Q000235:genetics / Q000378:metabolism; D014466:Ultraviolet Rays / Q000009:adverse effects*; D015854:Up-Regulation / Q000502:physiology; D051028:bcl-2-Associated X Protein / Q000378:metabolism; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism*
C494826:BAX protein, human; D001549:Benzamides; C497442:HIF1A protein, human; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; C579095:MCL1 protein, human; D064549:Myeloid Cell Leukemia Sequence 1 Protein; C498702:PMAIP1 protein, human; D019253:Proto-Oncogene Proteins c-bcl-2; C495901:TP53 protein, human; D016159:Tumor Suppressor Protein p53; D051028:bcl-2-Associated X Protein; C023957:triflumuron; D048051:p38 Mitogen-Activated Protein Kinases