WOX1 is essential for UVB irradiation-induced apoptosis and down-regulated via translational blockade in UVB-induced cutaneous squamous cell carcinoma in vivo.
OBJECTIVE
We investigated the role of candidate tumor suppressor and proapoptotic WOX1 (also named WWOX, FOR, or WWOXv1) in UVB-induced apoptosis and formation of cutaneous squamous cell carcinomas (SCC).


METHODS
Expression of WOX1 and family proteins (WWOX) in human primary cutaneous SCCs was examined by immunohistochemistry, in situ hybridization, and reverse transcription-PCR. UVB irradiation-induced WOX1 activation (Tyr33 phosphorylation and nuclear translocation), apoptosis, and cutaneous SCC formation were examined both in vitro and in vivo.


RESULTS
Up-regulation of human WOX1, isoform WOX2, and Tyr33 phosphorylation occurred during normal keratinocyte differentiation before cornification and death. Interestingly, significant reduction of these proteins and Tyr33 phosphorylation was observed in nonmetastatic and metastatic cutaneous SCCs (P < 0.001), but without down-regulation of WWOX mRNA (P > 0.05 versus normal controls), indicating a translational blockade of WWOX mRNA to protein. During acute exposure of hairless mice to UVB, WOX1 was up-regulated and activated in epidermal cells in 24 hours. In parallel with the clinical findings in humans, chronic UVB-treated mice developed cutaneous SCCs in 3 months, with significant reduction of WOX1 and Tyr33 phosphorylation and, again, without down-regulation of WWOX mRNA. Human SCC-25 and HaCaT cells were transfected with small interfering RNA-targeting WOX1 and shown to resist UVB-induced WOX1 expression, activation, and apoptosis.


CONCLUSIONS
WOX1 is essential for UVB-induced apoptosis and likely to be involved in the terminal differentiation of normal keratinocytes. During UVB-induced cutaneous SCC, epidermal cells have apparently prevented the apoptotic pressure from overexpressed WOX1 by shutting down the translation machinery for WWOX mRNA.
Lai
Feng-Jie
FJ
Department of Dermatology, National Cheng Kung University, Tainan, Taiwan. laifj@mail.ncku.edu.tw
Cheng
Ching-Li
CL
Chen
Shur-Tzu
ST
Wu
Chin-Han
CH
Hsu
Li-Jin
LJ
Lee
J Yu-Yun
JY
Chao
Sheau-Chiou
SC
Sheen
Maw-Chang
MC
Shen
Ching-Liang
CL
Chang
Nan-Shan
NS
Sheu
Hamm-Ming
HM
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000818:Animals; D017209:Apoptosis / Q000528:radiation effects*; D002294:Carcinoma, Squamous Cell / Q000209:etiology / Q000235:genetics* / Q000378:metabolism; D002454:Cell Differentiation / Q000235:genetics; D045744:Cell Line, Tumor; D015536:Down-Regulation / Q000235:genetics; D005260:Female; D015972:Gene Expression Regulation, Neoplastic / Q000528:radiation effects; D006801:Humans; D007150:Immunohistochemistry; D017403:In Situ Hybridization; D015603:Keratinocytes / Q000166:cytology / Q000378:metabolism; D008297:Male; D051379:Mice; D008875:Middle Aged; D010088:Oxidoreductases / Q000235:genetics* / Q000378:metabolism; D010766:Phosphorylation / Q000528:radiation effects; D014176:Protein Biosynthesis / Q000235:genetics*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D034741:RNA, Small Interfering / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012878:Skin Neoplasms / Q000209:etiology / Q000235:genetics* / Q000378:metabolism; D013997:Time Factors; D014162:Transfection; D025521:Tumor Suppressor Proteins; D014443:Tyrosine / Q000378:metabolism; D014466:Ultraviolet Rays; D000074584:WW Domain-Containing Oxidoreductase
D012333:RNA, Messenger; D034741:RNA, Small Interfering; D025521:Tumor Suppressor Proteins; D014443:Tyrosine; D010088:Oxidoreductases; D000074584:WW Domain-Containing Oxidoreductase; C486071:WWOX protein, human