G alpha(12) gep oncogene deregulation of p53-responsive microRNAs promotes epithelial-mesenchymal transition of hepatocellular carcinoma

Abstract

Hepatocellular carcinoma (HCC) has a poor prognosis owing to aggressive phenotype. Gα₁₂ gep oncogene product couples to G-protein-coupled receptors, whose ligand levels are frequently increased in tumor microenvironments. Here, we report Gα₁₂ overexpression in human HCC and the resultant induction of zinc-finger E-box-binding homeobox 1 (ZEB1) as mediated by microRNA deregulation. Gα₁₂ expression was higher in HCC than surrounding non-tumorous tissue. Transfection of Huh7 cell with an activated mutant of Gα₁₂ (Gα₁₂QL) deregulated microRNA (miRNA or miR)-200b/a/429, -194-2/192 and -194-1/215 clusters in the miRNome. cDNA microarray analyses disclosed the targets affected by Gα₁₂ gene knockout. An integrative network of miRNAs and mRNA changes enabled us to predict ZEB1 as a key molecule governed by Gα₁₂. Decreases of miR-200a/b, -192 and -215 by Gα₁₂ caused ZEB1 induction. The ability of Gα₁₂ to decrease p53 levels, as a result of activating protein-1 (AP-1)/c-Jun-mediated mouse double minute 2 homolog induction, contributed to transcriptional deregulation of the miRNAs. Gα₁₂QL induced ZEB1 and other epithelial–mesenchymal transition markers with fibroblastoid phenotype change. Consistently, transfection with miR-200b, -192 or -215 mimic prevented the ability of Gα₁₂QL to increase tumor cell migration/invasion. In xenograft studies, sustained knockdown of Gα₁₂ decreased the overall growth rate and average volume of tumors derived from SK-Hep1 cell (mesenchymal-typed). In HCC patients, miR-192, -215 and/or -200a were deregulated with microvascular invasion or growth advantage. In the HCC samples with higher Gα₁₂ level, a correlation existed in the comparison of relative changes of Gα₁₂ and ZEB1. In conclusion, Gα₁₂ overexpressed in HCC causes ZEB1 induction by deregulating p53-responsive miRNAs, which may facilitate epithelial–mesenchymal transition and growth of liver tumor. These findings highlight the significance of Gα₁₂ upregulation in liver tumor progression, implicating Gα₁₂ as an attractive therapeutic target.