Dietary fat/cholesterol-sensitive PKCβ-RB signaling: Potential role in NASH/HCC axis
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Wei Huang1, Devina Mehta2, Said Sif1, Lindsey N. Kent3, Samson T. Jacob3, Kalpana Ghoshal3 and Kamal D. Mehta1
1Department of Biological Chemistry and Pharmacology, Dorothy M. Davis Heart and Lung Research Institute, The Ohio State University College of Medicine, Columbus, Ohio, USA
2Department of Medicine, University of Cincinnati College of Medicine, Cincinnati, Ohio, USA
3Department of Cancer Genetics, OSU Comprehensive Cancer Center, The Ohio State University College of Medicine, Columbus, Ohio, USA
Kamal D. Mehta, email: [email protected]
Keywords: dietary fat, protein kinase Cβ, retinoblastoma phosphorylation, tumor suppressor
Received: November 02, 2016 Accepted: March 30, 2017 Published: May 15, 2017
Hepatocellular carcinoma (HCC) is a frequent form of cancer with a poor prognosis, and environmental factors significantly contribute to the risk. Despite knowledge that a Western-style diet is a risk factor in the development of nonalcoholic steatohepatitis (NASH) and subsequent progression to HCC, diet-induced signaling changes are not well understood. Understanding molecular mechanisms altered by diet is crucial for developing preventive and therapeutic strategies. We have previously shown that diets enriched with high-fat and high-cholesterol, shown to produce NASH and HCC, induce hepatic protein kinase C beta (PKCβ) expression in mice, and a systemic loss of PKCβ promotes hepatic cholesterol accumulation in response to this diet. Here, we sought to determine how PKCβ and diet functionally interact during the pathogenesis of NASH and how it may promote hepatic carcinogenesis. We found that diet-induced hepatic PKCβ expression is accompanied by an increase in phosphorylation of Ser780 of retinoblastoma (RB) protein. Intriguingly, PKCβ-/- livers exhibited reduced RB protein levels despite increased transcription of the RB gene. It is also accompanied by reduced RBL-1 with no significant effect on RBL-2 protein levels. We also found reduced expression of the PKCβ in HCC compared to non-tumorous liver in human patients. These results raise an interesting possibility that diet-induced PKCβ activation represents an important mediator in the functional wiring of cholesterol metabolism and tumorigenesis through modulating stability of cell cycle-associated proteins. The potential role of PKCβ in the suppression of tumorigenesis is discussed.
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