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Alterations of the transforming growth factor-beta signaling pathway in hepatocellular carcinomas induced
Y Sasaki1, T Tsujiuchi, N Murata
1Department of Oncological Pathology, Cancer Center, Nara Medical University, Kashihara, Nara 634-8521, Japan.
Abstract:
To elucidate involvement of the transforming growth factor-beta (TGF-beta) signaling pathway in endogenous and exogenous liver carcinogenesis, we investigated mutations of TGF-beta receptor type II (TGF-betaRII), Smad2 and Smad4 genes, and expression of TGF-betaRII in hepatocellular carcinomas (HCCs) induced by a choline-deficient L-amino acid-defined (CDAA) diet and by N-nitrosodiethylamine (DEN). Male Fischer 344 rats received a CDAA diet continuously and HCCs were sampled after 75 weeks. Administration of DEN was followed by partial hepatectomy (PH), with colchicine to induce cell cycle disturbance and a selection pressure regimen, HCCs being obtained after 42 weeks. Total RNAs were extracted from individual HCCs and mutations in TGF-betaRII, Smad2 and Smad4 were investigated by reverse transcription (RT)-polymerase chain reaction (PCR)-restriction-single-strand conformation polymorphism (SSCP) analysis followed by sequencing analysis. Mutations of Smad2 were detected in 2 out of 12 HCCs (16.7%) induced by the CDAA diet, a GGT-to-GGC transition (Gly to Gly) at codon 30 and a TCT-to-GCT (Ser to Ala) transversion at codon 118, without any TGF-betaRII or Smad4 alterations. No mutations of TGF-betaRII, Smad2 and Smad4 were encountered in eleven HCCs induced by the exogenous carcinogen. Semi-quantitative RT-PCR revealed reduced expression of TGF-betaRII in 2 HCCs (16.7%) without Smad2 mutations out of 12 HCCs induced by the CDAA diet and none of 11 induced by DEN. These results suggest that the TGF-beta signaling pathway may be disturbed in endogenous liver carcinogenesis in rats.
Insights
The transforming growth factor-beta (TGF-beta) signaling pathway may be disrupted in endogenous liver cancer. Smad2 gene mutations and reduced TGF-beta receptor type II (TGF-betaRII) expression were observed in rats fed a specific diet.
Area of Science:
- Oncology
- Molecular Biology
- Hepatology
Background:
- The transforming growth factor-beta (TGF-beta) signaling pathway plays a critical role in cell growth, differentiation, and apoptosis.
- Dysregulation of TGF-beta signaling is implicated in various cancers, including hepatocellular carcinoma (HCC).
- Understanding the pathway's involvement in both endogenous and exogenous liver carcinogenesis is crucial for developing targeted therapies.
Purpose of the Study:
- To investigate mutations in TGF-beta receptor type II (TGF-betaRII), Smad2, and Smad4 genes.
- To examine the expression of TGF-betaRII in hepatocellular carcinomas (HCCs).
- To elucidate the role of the TGF-beta signaling pathway in endogenous and exogenous liver carcinogenesis models.
Main Methods:
- Hepatocellular carcinomas (HCCs) were induced in male Fischer 344 rats using a choline-deficient L-amino acid-defined (CDAA) diet (endogenous) and N-nitrosodiethylamine (DEN) (exogenous).
- Mutations in TGF-betaRII, Smad2, and Smad4 genes were analyzed using reverse transcription (RT)-polymerase chain reaction (PCR)-restriction-single-strand conformation polymorphism (SSCP) analysis and sequencing.
- Gene expression levels were assessed using semi-quantitative RT-PCR.
Main Results:
- Smad2 gene mutations were detected in 2 out of 12 (16.7%) HCCs induced by the CDAA diet.
- No mutations in TGF-betaRII, Smad2, or Smad4 were found in HCCs induced by DEN.
- Reduced TGF-betaRII expression was observed in 2 out of 12 (16.7%) CDAA diet-induced HCCs, but not in DEN-induced HCCs.
Conclusions:
- The TGF-beta signaling pathway may be disturbed in endogenous liver carcinogenesis.
- Specific mutations in Smad2 and altered TGF-betaRII expression are associated with diet-induced HCC in rats.
- The findings suggest differential mechanisms in endogenous versus exogenous liver carcinogenesis concerning TGF-beta signaling.