All-trans retinoic acid suppresses Stat3 signaling during skin carcinogenesis.
Squamous cell carcinoma (SCC) of the skin is the most clinically aggressive form of nonmelanoma skin cancer. We have determined the effects of all-trans retinoic acid (ATRA), a naturally occurring chemopreventive retinoid, on signal transducer and activator of transcription 3 (Stat3) signaling during the development of skin SCC. Stat3 is a transcription factor that plays a critical role in cell proliferation and survival, and it is constitutively active in several malignant cell types. We have previously shown that Stat3 is required for the initiation, promotion, and progression of skin SCC. ATRA is a highly efficient suppressor of tumor formation in the two-stage mouse skin carcinogenesis model and we have shown that this effect correlates with the suppression of the B-Raf/Mek/Erk signaling pathway. In this study, we have determined the pattern of Stat3 phosphorylation throughout the course of the two-stage protocol, both in the presence and absence of ATRA. We have used both SENCAR mice and K5.Stat3C transgenic mice, which express the Stat3C protein, a constitutively active form of Stat3, in the skin. Using Western blotting and immunohistochemical staining with phosphospecific antibodies, we show that coadministration of ATRA suppressed the 12-O-tetradecanoylphorbol-13-acetate-induced phosphorylation of Stat3 in both models, but was only able to suppress tumor formation in the SENCAR mice. Surprisingly, ATRA actually enhanced tumor formation in 12-O-tetradecanoylphorbol-13-acetate-treated K5.Stat3C mice. We hypothesize that ATRA blocks tumor formation, at least in part, by targeting events upstream of Stat3, such as the B-Raf/Mek/Erk pathway, and that in the K5.Stat3C mice, in which Stat3 activity is constitutive, it cannot suppress tumor formation.
Syed
Zanobia
Z
Department of Biochemistry and Molecular Biology, Louisiana State University Health Sciences Center and the Feist-Weiller Cancer Center, 1501 Kings Highway, Shreveport, LA 71130, USA.
Cheepala
Satish B
SB
Gill
Jennifer N
JN
Stein
Jennica
J
Nathan
Cherie Ann
C
Digiovanni
John
J
Batra
Vinita
V
Adegboyega
Patrick
P
Kleiner
Heather E
HE
Clifford
John L
JL
D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology*; D015153:Blotting, Western; D002273:Carcinogens / Q000633:toxicity*; D002294:Carcinoma, Squamous Cell / Q000139:chemically induced / Q000378:metabolism*; D002471:Cell Transformation, Neoplastic / Q000187:drug effects / Q000378:metabolism; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D005260:Female; D007150:Immunohistochemistry; D020930:MAP Kinase Kinase Kinases / Q000378:metabolism; D051379:Mice; D018632:Mice, Inbred SENCAR; D008822:Mice, Transgenic; D050796:STAT3 Transcription Factor / Q000187:drug effects*; D015398:Signal Transduction / Q000187:drug effects*; D012878:Skin Neoplasms / Q000139:chemically induced / Q000378:metabolism*; D013755:Tetradecanoylphorbol Acetate / Q000633:toxicity*; D014212:Tretinoin / Q000494:pharmacology*; D048490:raf Kinases / Q000378:metabolism
D000970:Antineoplastic Agents; D002273:Carcinogens; D050796:STAT3 Transcription Factor; D014212:Tretinoin; D048490:raf Kinases; D048049:Extracellular Signal-Regulated MAP Kinases; D020930:MAP Kinase Kinase Kinases; D013755:Tetradecanoylphorbol Acetate