Downregulation of HMGB1 by miR-34a is sufficient to suppress proliferation, migration and invasion of human cervical and colorectal cancer cells
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High mobility group box 1 (HMGB1) is a ubiquitous nuclear protein known to be highly expressed in human cervical (CaCx) and colorectal (CRC) cancers, and sustained high levels of HMGB1 contribute to tumourigenesis and metastasis. HMGB1-targeted cancer therapy is of recent interest, and there are not many studies on miRNA-mediated HMGB1 regulation in these cancers. Since miRNA-based therapeutics for cancer is gaining importance in recent years, it was of interest to predict miRNAs targeting HMGB1. Based on the identification of a potential miR-34a response element in HMGB1–3′ untranslated region (3′UTR) and an inverse correlation between HMGB1 and miR-34a expression levels in CaCx and CRC tissues, from a subset of the local population as well as a large sampling from TCGA database, experiments were performed to validate HMGB1 as a direct target of miR-34a in CaCx and CRC cells. Ectopic expression of miR-34a decreased the wild-type HMGB1–3′UTR luciferase activity but not that of its mutant in 3′UTR luciferase assays. While forced expression of miR-34a in CaCx and CRC cells inhibited HMGB1 mRNA and protein levels, proliferation, migration and invasion, inhibition of endogenous miR-34a enhanced these tumourigenic properties. siRNA-mediated HMGB1 suppression imitated miR-34a expression in reducing proliferation and metastasis-related events. Combined with the disparity in expression of miR-34a and HMGB1 in clinical specimens, the current findings would help in not only understanding the complexity of miRNA-target regulatory mechanisms but also in designing novel therapeutic interventions in CaCx and CRC.
KeywordsmicroRNA-34a HMGB1 Human cervical cancer Human colorectal cancer Tumourigenicity
This work was supported by an exploratory research grant (to D.K.) and a project associateship (to K.S.C.) from the Centre for Industrial Consultancy and Sponsored Research, Indian Institute of Technology Madras and a senior research fellowship (to A.S.) from the Council of Scientific and Industrial Research, Government of India. The authors would like to thank Dr. Prabhavathy Devan, Indian Institute of Technology Madras, Dr. Radha Bai Prabhu, Institute of Obstetrics and Gynaecology and Government Hospital for Women and Children, Government of India and Dr. Shankar Srinivasan, Consultant Medical Oncologist, Apollo Specialty Hospitals, Chennai, India, for their help in procurement of clinical specimens and Dr. Rao Srinivasa Rao, Nuffield Department of Surgical Sciences, University of Oxford, Oxford, for his help in analysing data from TCGA. TCGA Research Network (http://cancergenome.nih.gov/) is acknowledged for providing access to their data. The following were kind gifts: C33A, SiHa, SW480 and SW620 cells from Dr. Ygal Haupt, Peter MacCallum Cancer Centre, Victoria, Australia; HCT116WT cells from Dr. Bert Vogelstein, Sidney Kimmel Comprehensive Cancer Center, Baltimore, USA and CaSki cells from Dr. Sudhir Krishna, National Centre for Biological Sciences, Bangalore, India.
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Conflicts of interest
Informed consent was obtained from all individuals included in this study.
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