A Quantitative Proteomics Approach in the Study of MicroRNA 181a in HepG2 Cells

Yi      Lin Jane Tan; Nagy      A. Habib; Wei      Ning Chen

Abstract

Hepatocellular carcinoma (HCC) is currently of great concern due to its poor patient outcome despite the various therapies available. The cause of HCC usually stems from liver cirrhosis, which mainly results from Hepatitis B virus (HBV) or Hepatitis C virus (HCV) infection or environmental and genetic risk factors like alcoholism. Despite the preventive measures available now, the incidence and mortality rates are still high due to chronic infection, making it the third leading cause of cancer –related deaths in the world today and claiming approximately 600,000 lives annually. Patients are usually also diagnosed with HCC later in the stages, leading to a very poor prognosis. It is therefore imperative that a more effective treatment method is developed such that patient survival rates may be improved from current statistics of less than 50%. The role of microRNAs (miRNAs) in the regulation of gene expression and cellular development makes it an important player in cancer initiation and progression. Mir-181a has been shown to be an important miRNA involved in HCC. In this study, we propose to investigate the potential effects of miR-181a in HepG2 cells and also to explore the mechanisms in which it works in controlling cell fate. As chemotherapy is widely used in liver cancer treatment, we also study the use of miR-181a along with chemotherapy (i.e. Cisplatin). Using iTRAQ-coupled 2D LC-MS/MS analysis, we report here the study of protein profile of HepG2 cells transfected with miR-181a mimic and inhibitor separately. Three main types of cellular proteins including metabolic enzymes, protein binding and stress proteins displayed changes. The changes in the level of proteins involved in important cancer processes like cell growth were further supported by a western blot analysis. MiR-181a was subsequently found to increase HepG2 cell viability while the inhibitor displayed the opposite effect. The inhibitor also sensitized HepG2 cells to cisplatin. Cell cycle analysis showed that the inhibitor retards cell cycle progression by decreasing the proportion of cells in S and G2/M phases. Our findings therefore provide molecular evidence on the mechanism of action of miR-181a inhibitor, including its beneficial effects in inhibiting the development of HCC.

Keywords: Cell cycle, cellular protein profile, cisplatin, heat shock protein 90β, hepatocellular carcinoma, HepG2, high performance liquid chromatography, LC-MS/MS analysis, MicroRNA 181a, nucleophosmin