Decreased hepatocyte membrane potential differences and GABAa-β3 expression in human hepatocellular carcinoma

Abstract

To determine whether hepatocyte membrane potential differences (PDs) are depolarized in human HCC and whether depolarization is associated with changes in GABA_A receptor expression, hepatocyte PDs and γ‐aminobutyric acid (GABA)_A receptor messenger RNA (mRNA) and protein expression were documented in HCC tissues via microelectrode impalement, real‐time reverse‐transcriptase polymerase chain reaction, and Western blot analysis, respectively. HCC tissues were significantly depolarized (−19.8 ± 1.3 versus −25.9 ± 3.2 mV, respectively [P < 0.05]), and GABA_A‐β3 expression was down‐regulated (GABA_A‐β3 mRNA and protein expression in HCC; 5,693 ± 1,385 and 0.29 ± 0.11 versus 11,046 ± 4,979 copies/100 mg RNA and 0.62 ± 0.16 optical density in adjacent tumor tissues, respectively [P = 0.002 and P < 0.0001, respectively]) when compared with adjacent nontumor tissues. To determine the physiological relevance of the down‐regulation, human malignant hepatocytes deficient in GABA_A‐β3 receptor expression (Huh‐7 cells) were transfected with GABA_A‐β3 complementary DNA (cDNA) or vector alone and injected into nu/nu nude mice (n = 16‐17 group). Tumors developed after a mean (± SD) of 51 ± 6 days (range: 41‐60 days) in 7/16 (44%) mice injected with vector‐transfected cells and 70 ± 12 days (range: 59‐86 days) in 4/17 (24%) mice injected with GABA_A‐β3 cDNA‐transfected cells (P < 0.005). Conclusion: The results of this study indicate that (1) human HCC tissues are depolarized compared with adjacent nontumor tissues, (2) hepatic GABA_A‐β3 receptor expression is down‐regulated in human HCC, and (3) restoration of GABA_A‐β3 receptor expression results in attenuated in vivo tumor growth in nude mice. (HEPATOLOGY 2007;45:735–745.)