Transforming growth factor-beta1 (TGF-beta1) causes growth inhibition in many cell types. Since its role in the outgrowth of human hepatocellular carcinoma (HCC) is not clearly understood, we investigated the growth inhibitory effects of TGF-beta1, the genetic and molecular integrity of TGF-beta receptors, and the expression levels of cell cycle regulating proteins in 11 human HCC cell lines. Of 11 cell lines, 3 (27%) showed growth inhibition to TGF-beta1, whereas the other 8 cell lines did not. We performed Southern and Northern analysis of TGF-beta type I and II receptors and examined poly-adenine track mutation of the TGF-beta type II receptor, but failed to find any genetic mutation. The transcriptional induction of plasminogen activator inhibitor-1 and p21(WAF1/CIP1) by TGF-beta were detected in all HCC cell lines, implying that the molecular integrity of the TGF-beta receptors might be intact. The amplification and overexpression of cyclin D1 gene was detected in 4 (50%) of 8 HCC cells that showed resistance to TGF-beta1. The suppression of cyclin D1 expression with antisense cyclin D1 facilitated the TGF-beta1-triggered growth inhibition in a TGF-beta1 resistant HCC cell line containing amplified cyclin D1 gene. In conclusion, the overexpression of cyclin D1 may be responsible for the attenuation of TGF-beta1 induced growth inhibition in some HCC cells. (C) 2002 Elsevier Science (USA).