Disruption of Smad-dependent signaling for growth of GST-P-positive lesions from the early stage in a rat two-stage hepatocarcinogenesis model.

Abstract

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.

• Authors: Ryohei Ichimura, Sayaka Mizukami, Miwa Takahashi, Eriko Taniai, Sayaka Kemmochi, Kunitoshi Mitsumori, Makoto Shibutani
• Journal: Toxicology and applied pharmacology (Toxicol Appl Pharmacol) Vol. 246 Issue 3 Pg. 128-40 (Aug 01 2010) ISSN: 1096-0333 [Electronic] United States
• PMID: 20423715 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)
• Copyright: Copyright © 2010 Elsevier Inc. All rights reserved.

Chemical References

• Activating Transcription Factor 2
• Activating Transcription Factor 3
• Atf2 protein, rat
• Atf3 protein, rat
• Carcinogens
• Extracellular Matrix Proteins
• Receptors, Transforming Growth Factor beta
• Smad Proteins
• Transforming Growth Factor beta
• betaIG-H3 protein
• Glutathione S-Transferase pi
• Gstp1 protein, rat
• Protein Serine-Threonine Kinases
• p38 Mitogen-Activated Protein Kinases
• Receptor, Transforming Growth Factor-beta Type I
• Tgfbr1 protein, rat

Topics

• Activating Transcription Factor 2 (genetics, metabolism)
• Activating Transcription Factor 3 (genetics, metabolism)
• Animals
• Carcinogenesis (genetics, metabolism, pathology)
• Carcinogens (toxicity)
• Disease Models, Animal
• Extracellular Matrix Proteins (genetics, metabolism)
• Genes, myc
• Glutathione S-Transferase pi (genetics, metabolism)
• Liver Neoplasms, Experimental (chemically induced, genetics, metabolism, pathology)
• Male
• Protein Serine-Threonine Kinases (genetics, metabolism)
• Rats
• Rats, Inbred F344
• Receptor, Transforming Growth Factor-beta Type I
• Receptors, Transforming Growth Factor beta (genetics, metabolism)
• Signal Transduction
• Smad Proteins (genetics, metabolism)
• Transforming Growth Factor beta (genetics, metabolism)
• p38 Mitogen-Activated Protein Kinases (genetics, metabolism)