Altered expression and function of regulator of G-protein signaling-17 (RGS17) in hepatocellular carcinoma

Guanine nucleotide regulatory proteins (G-proteins) are central to normal hepatocyte function and are implicated in hepatic disease initiation and progression. Regulators of G-protein signaling (RGS) are critical to defining G-protein-dependent signal fidelity, yet the role of RGS proteins in the liver is poorly defined. The aims of this study were to determine RGS17 expression in normal and transformed hepatic tissue and cells, and address the function of RGS17 in hepatic tumorgenicity. RGS17 expression was determined in human and rat HCC tissue and cell lines. Molecular approaches were used to alter RGS17 expression in HCC cells, effects on cell function measured, and RGS17 association with specific Gα-subunits determined. Using these approaches RGS17 mRNA, but not protein, was detectable in human and rat HCC tissue and cells. Conversely, RGS17 mRNA was not detected in normal tissue, isolated hepatocytes, or non-tumorigenic hepatic cells. Subsequent studies using transfected cells demonstrated that RGS17 proteins were not post-translationally modified in HCC cells, and RGS17 expression is governed by protein degradation and not via miRNAs. Notwithstanding inherently low RGS17 protein levels, altering RGS17 expression profoundly affected HCC cell mitogenesis and migration. Analysis of RGS17-G-protein interaction demonstrated RGS17 associates with both Giα- and Gqα-subunits in HCC cells of human and rat origin. In conclusion, these data demonstrate that, despite difficulties in measuring endogenous RGS protein expression, RGS17 is differentially expressed in HCC and plays a central role in regulating transformed hepatocyte tumorgenicity.