Background/Aims: Hepatocellular carcinomas (HCC) often show resistance to the effects of transforming growth factor-β(TGF-β). This study focuses on molecular mechanisms of this resistance to explore ways to overcome...Background/Aims: Hepatocellular carcinomas (HCC) often show resistance to the effects of transforming growth factor-β(TGF-β). This study focuses on molecular mechanisms of this resistance to explore ways to overcome it. Methods: Transcription and protein expression of TGF-βtype I and type II receptors (TGF-βRI/RII) were analyzed in clinical HCCs and the human hepatoma cell lines HuH-7 and HepG2. HuH-7 cells were transiently and stably transfected with a constitutively active TGF-βRI mutant (CATGF-βRI). Resulting growth kinetics, integrin expression, invasiveness, TGF-β-mediated activation of human plasminogen activator inhibitor type-1 (PAI-1) promoter and Smad expression were determined. Results: In clinical HCCs, there was less TGF-βRII (6/10 cases) and more TGF-βRI (8/10 cases) protein expression detectable in tumor compared to adjacent liver tissue. In HuH-7 cells, TGF-βRII expression was likewise decreased. Cells transiently transfected with CA TGF-βRI exhibited strong TGF-β-related PAI-1 promoter activation. Stably transfected cells showed an attenuated response of the PAI-1 promoter, but increased Smad7 expression. Proliferation of stable clones was decreased. There was no change in integrin expression or invasiveness. Conclusions: Decreased TGF-βRII protein expression might cause TGF-βresistance in a subset of clinical HCCs. Stable transfection with CA TGF-βRI reverses this in HuH-7 cells without increasing invasiveness.展开更多
. Transforming growth factor β (TGF- β ) is a multifunctional cytokine that strongly inhibits epithelial cell growth. Disabling of TGF- β signaling is thought to be involved in development of a variety of tumors in.... Transforming growth factor β (TGF- β ) is a multifunctional cytokine that strongly inhibits epithelial cell growth. Disabling of TGF- β signaling is thought to be involved in development of a variety of tumors in which abnormal expression or function of TGF- β receptor plays critical roles. In the present study, we examined aberrant expression and mutation of the gene TGF- β receptor type II (Tβ RII) in endometrial cancers of endometrioid subtype. Methods and results. Real-time PCR analysis using surgical tissue specimens of 27 endometrial cancers and 24 normal endometria revealed that endometrial cancers had significantly decreased levels of Tβ RII mRNA expression (mean level 2.44 ± 2.65), compared to normal endometria (mean level 7.23 ± 6.07) (P < 0.001). Methylation status of Tβ RII promoter containing 30 CpGs was examined by bisulfite sequencing analysis, and 98% (51/52) of the patients were found to have unmethylated Tβ RII promoter, indicating that promoter hypermethylation is not the major cause of decreased expression of Tβ RII in endometrial cancers. Mutational analysis revealed that 15.1% (8/53) of endometrial cancers had frameshift mutations at polyadenine repeats in exon 3 of the Tβ RII gene. Notably, these mutations were preferentially accumulated in patients with MSI- H phenotype (7/19:37% ) (P < 0.001) or with those with methylated MLH1 promoters (6/16:38% ) (P < 0.01). Thus, it appears that the Tβ RII gene is a target of mismatch repair deficiency. Conclusion. Taken together, we found that the decreased expression of Tβ RII as well as frameshift mutation of Tβ RII via mismatch repair deficiency frequently occurs in this tumor type, possibly causing loss of receptor function and unresponsiveness of TGF- β signaling that may lead to endometrial carcinogenesis.展开更多
文摘Background/Aims: Hepatocellular carcinomas (HCC) often show resistance to the effects of transforming growth factor-β(TGF-β). This study focuses on molecular mechanisms of this resistance to explore ways to overcome it. Methods: Transcription and protein expression of TGF-βtype I and type II receptors (TGF-βRI/RII) were analyzed in clinical HCCs and the human hepatoma cell lines HuH-7 and HepG2. HuH-7 cells were transiently and stably transfected with a constitutively active TGF-βRI mutant (CATGF-βRI). Resulting growth kinetics, integrin expression, invasiveness, TGF-β-mediated activation of human plasminogen activator inhibitor type-1 (PAI-1) promoter and Smad expression were determined. Results: In clinical HCCs, there was less TGF-βRII (6/10 cases) and more TGF-βRI (8/10 cases) protein expression detectable in tumor compared to adjacent liver tissue. In HuH-7 cells, TGF-βRII expression was likewise decreased. Cells transiently transfected with CA TGF-βRI exhibited strong TGF-β-related PAI-1 promoter activation. Stably transfected cells showed an attenuated response of the PAI-1 promoter, but increased Smad7 expression. Proliferation of stable clones was decreased. There was no change in integrin expression or invasiveness. Conclusions: Decreased TGF-βRII protein expression might cause TGF-βresistance in a subset of clinical HCCs. Stable transfection with CA TGF-βRI reverses this in HuH-7 cells without increasing invasiveness.
文摘. Transforming growth factor β (TGF- β ) is a multifunctional cytokine that strongly inhibits epithelial cell growth. Disabling of TGF- β signaling is thought to be involved in development of a variety of tumors in which abnormal expression or function of TGF- β receptor plays critical roles. In the present study, we examined aberrant expression and mutation of the gene TGF- β receptor type II (Tβ RII) in endometrial cancers of endometrioid subtype. Methods and results. Real-time PCR analysis using surgical tissue specimens of 27 endometrial cancers and 24 normal endometria revealed that endometrial cancers had significantly decreased levels of Tβ RII mRNA expression (mean level 2.44 ± 2.65), compared to normal endometria (mean level 7.23 ± 6.07) (P < 0.001). Methylation status of Tβ RII promoter containing 30 CpGs was examined by bisulfite sequencing analysis, and 98% (51/52) of the patients were found to have unmethylated Tβ RII promoter, indicating that promoter hypermethylation is not the major cause of decreased expression of Tβ RII in endometrial cancers. Mutational analysis revealed that 15.1% (8/53) of endometrial cancers had frameshift mutations at polyadenine repeats in exon 3 of the Tβ RII gene. Notably, these mutations were preferentially accumulated in patients with MSI- H phenotype (7/19:37% ) (P < 0.001) or with those with methylated MLH1 promoters (6/16:38% ) (P < 0.01). Thus, it appears that the Tβ RII gene is a target of mismatch repair deficiency. Conclusion. Taken together, we found that the decreased expression of Tβ RII as well as frameshift mutation of Tβ RII via mismatch repair deficiency frequently occurs in this tumor type, possibly causing loss of receptor function and unresponsiveness of TGF- β signaling that may lead to endometrial carcinogenesis.
