Disruption of Smad-dependent signaling for growth of GST-P-positive lesions from the early stage in a rat two-stage hepatocarcinogenesis model.
To clarify the involvement of signaling of transforming growth factor (TGF)-β during the hepatocarcinogenesis, the immunohistochemical distribution of related molecules was analyzed in relation with liver cell lesions expressing glutathione S-transferase placental form (GST-P) during liver tumor promotion by fenbendazole, phenobarbital, piperonyl butoxide, or thioacetamide, using rats. Our study focused on early-stage promotion (6weeks after starting promotion) and late-stage promotion (57weeks after starting promotion). With regard to Smad-dependent signaling, cytoplasmic accumulation of phosphorylated Smad (phospho-Smad)-2/3 - identified as Smad3 by later immunoblot analysis - increased in the subpopulation of GST-P(+) foci, while Smad4, a nuclear transporter of Smad2/3, decreased during early-stage promotion. By late-stage promotion, GST-P(+) lesions lacking phospho-Smad2/3 had increased in accordance with lesion development from foci to carcinomas, while Smad4 largely disappeared in most proliferative lesions. With regard to Smad-independent mitogen-activated protein kinases, GST-P(+) foci that co-expressed phospho-p38 mitogen-activated protein kinase increased during early-stage promotion; however, p38-downstream phospho-activating transcriptional factor (ATF)-2, ATF3, and phospho-c-Myc, were inversely downregulated without relation to promotion. By late-stage promotion, proliferative lesions downregulated phospho-ATF2 and phospho-c-Myc along with lesion development, as with downregulation of phospho-p38 in all lesions. These results suggest that from the early stages, carcinogenic processes were facilitated by disruption of tumor suppressor functions of Smad-dependent signaling, while Smad-independent activation of p38 was an early-stage phenomenon. GST-P(-) foci induced by promotion with agonists of peroxisome proliferator-activated receptor-α did not change Smad expression, suggesting an aberration in the Smad-dependent signaling prerequisites for induction of GST-P(+) proliferative lesions.
Ichimura
Ryohei
R
Laboratory of Veterinary Pathology, Tokyo University of Agriculture and Technology, 3-5-8 Saiwai-cho, Fuchu-shi, Tokyo 183-8509, Japan.
Mizukami
Sayaka
S
Laboratory of Veterinary Pathology, Tokyo University of Agriculture and Technology, 3-5-8 Saiwai-cho, Fuchu-shi, Tokyo 183-8509, Japan.
Takahashi
Miwa
M
Division of Pathology, National Institute of Health Sciences, 1-18-1 Kamiyoga, Setagaya-ku, Tokyo 158-8501, Japan.
Taniai
Eriko
E
Laboratory of Veterinary Pathology, Tokyo University of Agriculture and Technology, 3-5-8 Saiwai-cho, Fuchu-shi, Tokyo 183-8509, Japan.
Kemmochi
Sayaka
S
Laboratory of Veterinary Pathology, Tokyo University of Agriculture and Technology, 3-5-8 Saiwai-cho, Fuchu-shi, Tokyo 183-8509, Japan; Pathogenetic Veterinary Science, United Graduate School of Veterinary Sciences, Gifu University, 1-1 Yanagido, Gifu-shi, Gifu 501-1193, Japan.
Mitsumori
Kunitoshi
K
Laboratory of Veterinary Pathology, Tokyo University of Agriculture and Technology, 3-5-8 Saiwai-cho, Fuchu-shi, Tokyo 183-8509, Japan.
Shibutani
Makoto
M
Laboratory of Veterinary Pathology, Tokyo University of Agriculture and Technology, 3-5-8 Saiwai-cho, Fuchu-shi, Tokyo 183-8509, Japan.
D051698:Activating Transcription Factor 2 / Q000235:genetics / Q000378:metabolism; D051700:Activating Transcription Factor 3 / Q000235:genetics / Q000378:metabolism; D000818:Animals; D063646:Carcinogenesis / Q000235:genetics / Q000378:metabolism / Q000473:pathology*; D002273:Carcinogens / Q000633:toxicity; D004195:Disease Models, Animal; D016326:Extracellular Matrix Proteins / Q000235:genetics / Q000378:metabolism; D016259:Genes, myc; D051549:Glutathione S-Transferase pi / Q000235:genetics / Q000378:metabolism*; D008114:Liver Neoplasms, Experimental / Q000139:chemically induced / Q000235:genetics / Q000378:metabolism / Q000473:pathology*; D008297:Male; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism; D051381:Rats; D011916:Rats, Inbred F344; D000077293:Receptor, Transforming Growth Factor-beta Type I; D018125:Receptors, Transforming Growth Factor beta / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction; D051785:Smad Proteins / Q000235:genetics / Q000378:metabolism*; D016212:Transforming Growth Factor beta / Q000235:genetics / Q000378:metabolism; D048051:p38 Mitogen-Activated Protein Kinases / Q000235:genetics / Q000378:metabolism; D000099222:betaIG-H3 Protein
D051698:Activating Transcription Factor 2; D051700:Activating Transcription Factor 3; D002273:Carcinogens; D016326:Extracellular Matrix Proteins; D051549:Glutathione S-Transferase pi; D017346:Protein Serine-Threonine Kinases; D000077293:Receptor, Transforming Growth Factor-beta Type I; D018125:Receptors, Transforming Growth Factor beta; D051785:Smad Proteins; D016212:Transforming Growth Factor beta; D048051:p38 Mitogen-Activated Protein Kinases; D000099222:betaIG-H3 Protein; C497107:Atf2 protein, rat; C497108:Atf3 protein, rat; C496558:Gstp1 protein, rat; C000625843:Tgfbr1 protein, rat