Phosphorylation of PPARγ at Ser84 promotes glycolysis and cell proliferation in hepatocellular carcinoma by targeting PFKFB4

Abstract

// Yuxin Shu 1, * , Yan Lu 1, * , Xiaojuan Pang 1 , Wei Zheng 1 , Yahong Huang 1 , Jiahong Li 1 , Jianguo Ji 3, 4 , Can Zhang 2 , Pingping Shen 1 1 State Key Laboratory of Pharmaceutical Biotechnology and Model Animal Research Center (MARC), Nanjing University, Nanjing 210023, China 2 Center of Drug Discovery, State Key Laboratory of Natural Medicines, China Pharmaceutical University, Nanjing 210009, PR China 3 The State Key Laboratory of Protein and Plant Gene Research, College of Life Sciences, Peking University, Beijing 100871, China 4 Institute of System Biomedicine, School of Basic Medical Sciences, Peking University, Beijing 100191, China * These authors contributed equally to this work Correspondence to: Pingping Shen, email: ppshen@nju.edu.cn Can Zhang, email: zhangcan@cpu.edu.cn Keywords: phosphorylation, PPARγ, PFKFB4, hepatocellular carcinoma, glycolysis Received: June 01, 2016      Accepted: October 14, 2016      Published: October 19, 2016 ABSTRACT Peroxisome proliferator-activating receptor γ (PPARγ), a transcription factor, is involved in many important biological processes, including cell terminal differentiation, survival and apoptosis. However, the role of PPARγ, which regulates tumour promoter and oncogene expression, is not well understood in hepatocellular carcinoma (HCC). In the present study, based on evidence from clinical samples that phosphorylation of PPARγ at Ser84 is up-regulated in human liver tumours, we confirmed that phosphorylation of PPARγ was also significantly increased in an HCC mouse model and was increased by Mitogen-activated protein kinase (MEK)/ Extracellular-signal-regulated kinases (ERK) kinase. Next, we performed an RNA microarray analysis, and our data indicated that dephosphorylation of PPARγ at Ser84 affects the expression of glycolysis-related genes and pro-proliferation genes, which supposedly promote proliferation of HCC cells. Using a chromatin immunoprecipitation (ChIP) assay, we demonstrated that the observed PPARγ-mediated induction of 6-phosphofructo-2-kinase/fructose-2,6-biphosphatase 4 (PFKFB4) expression was directly modulated by the transcriptional activity of its promoter. Furthermore, using knockdown of PFKFB4, we elucidated that the stimulation of PPARγ phosphorylation on glycolysis and proliferation in HCC is dependent on PFKFB4. Together, these findings extend our understanding of how liver tumour cells reprogram their glycolytic pathways by post-translational modification of specific transcription factors and lay a foundation for the screening of new targets for the treatment of HCC.