Adiponectin as a protective adipocytokine against leptin signaling in hepatocellu

Emory University, Atlanta GA

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Abstract

DESCRIPTION (provided by applicant): Obesity is an independent risk factor for hepatocellular carcinoma (HCC). Obese patients exhibit a higher risk for larger tumor burden, increased metastasis and poor prognosis. Epidemiological studies have established a link between obesity and HCC. This association might represent the progression of underlying nonalcoholic fatty liver disease (NAFLD) to cirrhosis and hepatocellular carcinoma in obese patients although no study has clearly linked these variables. Obesity affects hepatocellular carcinogenesis by autocrine and paracrine actions mediated by two major adipocytokines, leptin and adiponectin. Our recent studies investigating the oncogenic actions of leptin revealed that - i) leptin induces proliferation via Stat3, Akt and ERK activation, ii) leptin-induced phosphorylation of ERK and Akt was dependent on Stat3 activation, and iii) leptin induces invasion and migration of HCC cells. Displaying opposing effects, adiponectin reduces invasion and migration of HCC cells. Adiponectin activates AMPK in an LKB1-dependent manner, and inhibits S6K activation demonstrating the involvement of LKB1-AMPK-S6K axis. Most importantly, adiponectin treatment blocks leptin-induced i) activation of Stat3, ii) overexpression of cyclin D1, and iii) cell proliferation. These data strongly suggest that adiponectin antagonizes the cancer-promoting effects of leptin on hepatocellular carcinoma cells. The molecular mechanism by which adiponectin inhibits leptin signaling will be analyzed by Electric Cell-substrate Impedance Sensing (ECIS) based invasion and migration assays. The effect of adiponectin on various regulatory steps of leptin signaling will be studied using immunofluorescence, co-IP, western blot analysis and kinase assays. To determine whether suppression of leptin signaling by adiponectin involves LKB1-AMPK axis, we will use specific chemical inhibitors, siRNA and overexpression, dominant negative and/or kinase deficient constructs to target LKB1-AMPK axis, and determine if the antagonistic effects of adiponectin against leptin are mediated through this pathway. To determine whether adiponectin blocks leptin-induced HCC tumor growth and metastasis, HCC tumorigenesis assays in athymic nude mice will be conducted. Tumor growth and metastasis will be monitored by microPET imaging. Key signaling molecules of leptin and adiponectin will be examined in tumor and metastasis samples. We will analyze expression of the key molecules of leptin and adiponectin signaling in different groups of HCC in a comprehensive manner. Relevance to public: Obesity, a major health problem in US is a significant risk factor for hepatocellular carcinoma and its endocrine effects are mediated by adipocytokines. The studies proposed here are designed to establish leptin and adiponectin as novel biomarkers for HCC. Also we will delineate the protective role of adiponectin against leptin signaling in hepatocellular carcinoma which presents role of adiponectin as new preventive and therapeutic option for HCC patients. PUBLIC HEALTH RELEVANCE: Obesity is an independent risk factor for hepatocellular carcinoma (HCC). Obese patients exhibit a higher risk for larger tumor burden, increased metastasis and poor prognosis. Epidemiological studies have established a link between obesity and HCC. We will analyze how adiponectin antagonizes the cancer-promoting effects of leptin on hepatocellular carcinoma cells.