HDAC1-Smad3-mSin3A complex is required for Smad3-induced transcriptional inhibition of hepatocyte growth factor receptor in human lung cancers.

c-Met hyperactivity has been observed in numerous neoplasms. Several researchers have shown that the abnormal activation of c-Met is mainly caused by transcriptional activation. However, the molecular mechanism behind this transcriptional regulation is poorly understood. Here, we suggest that Smad3 negatively regulates the expression and activation of c-Met via a transcriptional mechanism. We explore the molecular mechanisms that underlie Smad3-induced c-Met transcription inhibition. We found in contrast to the high expression of c-Met, Smad3 showed low protein and mRNA levels. Smad3 and c-Met expressions were inconsistent between lung cancer tissues and cell lines. We also found that Smad3 overexpression suppresses whereas Smad3 knockdown significantly promotes Epithelial-Mesenchymal Transition and production of the angiogenic factors VEGF, CTGF and COX-2 through the ERK1/2 pathway. In addition, Smad3 overexpression decreases whereas Smad3 knockdown significantly increases protein and mRNA levels of invasion-related ß-catenin and FAK through the PI3K/Akt pathway. Furthermore, using the chromatin immunoprecipitation analysis method, we demonstrate that a transcriptional regulatory complex consisting of HDAC1, Smad3 and mSin3A binds to the promoter of the c-Met gene. By either silencing endogenous mSin3A expression with siRNA or by pretreating cells with a specific HDAC1 inhibitor (MS-275), Smad3-induced transcriptional suppression of c-Met could be effectively attenuated. These results demonstrate that Smad3-induced inhibition of c-Met transcription depends on of a functional transcriptional regulatory complex that includes Smad3, mSin3A and HDAC1 at the c-Met promoter. Collectively, our findings reveal a new regulatory mechanism of c-Met signaling, and suggest a potential molecular target for the development of anticancer drugs.