Oncogenic Smad3 signaling induced by chronic inflammation is an early event in ulcerative colitis-associated carcinogenesis.
BACKGROUND
Both chronic inflammation and somatic mutations likely contribute to the pathogenesis of ulcerative colitis (UC)-associated dysplasia and cancer. On the other hand, both tumor suppression and oncogenesis can result from transforming growth factor (TGF)-β signaling. TGF-β type I receptor (TβRI) and Ras-associated kinases differentially phosphorylate a mediator, Smad3, to become C-terminally phosphorylated Smad3 (pSmad3C), linker phosphorylated Smad3 (pSmad3L), and both C-terminally and linker phosphorylated Smad3 (pSmad3L/C). The pSmad3C/p21(WAF1) pathway transmits a cytostatic TGF-β signal, while pSmad3L and pSmad3L/C promote cell proliferation by upregulating c-Myc oncoprotein. The purpose of this study was to clarify the alteration of Smad3 signaling during UC-associated carcinogenesis.


METHODS
By immunostaining and immunofluorescence, we compared pSmad3C-, pSmad3L-, and pSmad3L/C-mediated signaling in colorectal specimens representing colitis, dysplasia, or cancer from eight UC patients with signaling in normal colonic crypts. We also investigated p53 expression and mutations of p53 and K-ras genes. We further sought functional meaning of the phosphorylated Smad3-mediated signaling in vitro.


RESULTS
As enterocytes in normal crypts migrated upward toward the lumen, cytostatic pSmad3C/p21(WAF1) tended to increase, while pSmad3L/c-Myc shown by progenitor cells gradually decreased. Colitis specimens showed prominence of pSmad3L/C/c-Myc, mediated by TGF-β and tumor necrosis factor (TNF)-α, in all enterocyte nuclei throughout entire crypts. In proportion with increases in frequency of p53 and K-ras mutations during progression from dysplasia to cancer, the oncogenic pSmad3L/c-Myc pathway came to be dominant with suppression of the pSmad3C/p21(WAF1) pathway.


CONCLUSIONS
Oncogenic Smad3 signaling, altered by chronic inflammation and eventually somatic mutations, promotes UC-associated neoplastic progression by upregulating growth-related protein.
Kawamata
Seiji
S
Department of Gastroenterology and Hepatology, Kansai Medical University, Osaka, Japan.
Matsuzaki
Koichi
K
Murata
Miki
M
Seki
Toshihito
T
Matsuoka
Katsuyoshi
K
Iwao
Yasushi
Y
Hibi
Toshifumi
T
Okazaki
Kazuichi
K
D000230:Adenocarcinoma / Q000378:metabolism* / Q000473:pathology; D000328:Adult; D015153:Blotting, Western; D002471:Cell Transformation, Neoplastic / Q000378:metabolism / Q000473:pathology*; D002908:Chronic Disease; D003093:Colitis, Ulcerative / Q000378:metabolism* / Q000473:pathology; D015179:Colorectal Neoplasms / Q000378:metabolism* / Q000473:pathology; D018450:Disease Progression; D005260:Female; D005455:Fluorescent Antibody Technique; D006801:Humans; D007124:Immunoenzyme Techniques; D047468:Immunoprecipitation; D008297:Male; D008875:Middle Aged; D010766:Phosphorylation; D016133:Polymerase Chain Reaction; D012150:Polymorphism, Restriction Fragment Length; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism; D000077293:Receptor, Transforming Growth Factor-beta Type I; D018125:Receptors, Transforming Growth Factor beta / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction; D051900:Smad3 Protein / Q000235:genetics / Q000378:metabolism*; D016212:Transforming Growth Factor beta / Q000235:genetics / Q000378:metabolism
D018125:Receptors, Transforming Growth Factor beta; D051900:Smad3 Protein; D016212:Transforming Growth Factor beta; D017346:Protein Serine-Threonine Kinases; D000077293:Receptor, Transforming Growth Factor-beta Type I