Inhibitory Role Of Chromodomain Helicase DNA Binding Protein5(CHD5) In The Growth And Invasion Of Breast Cancer Cells

Introduction: Breast cancer is becoming more and more common, and breastcancer morbidity is steadily increasing in recent years. In addition, more and moreyounger women suffer from breast cancer. In some large cities in China, breast cancerhas become the most common cancer among women. Understanding the molecularbasis of breast cancer is an important step for improving the diagnosis and treatmentof breast cancer.One important area of cancer research is gene discovery. Many oncogenes andtumor suppressor genes have been discovered in breast cancer, but more such genesremain to be identified and much more remain to be characterized. Thechromodomain helicase DNA binding protein5(CHD5) has recently been identifiedas a tumor suppressor in a mouse model. The CHD5locus at1p36is deleted, and itsmutation has been detected in breast cancer. We therefore evaluated whether CHD5plays a role in human breast cancer.Methods: We screened55breast cancers for CHD5mutations by PCR andsequencing, determined promoter methylation in39tumors by bisulfite treatment andsequencing of clones of each PCR products, measured RNA expression in90tumorsand CHD5copy number changes in44tumors by real-time PCR, analyzed proteinexpression in289tumors by immunohistochemical staining, and correlatedexpression changes to clinicopathological characteristics of breast cancer. Functionaleffects of CHD5on cell proliferation, invasion and tumorigenesis were tested, and themechanisms of function were explored.Results: Although only one mutation was detected in MDA-MB-231breastcancer cell line, CHD5mRNA expression was significantly reduced in breast cancer,accompanied by frequent genomic deletion and promoter methylation. The extent ofmethylation was significantly associated with reduced mRNA expression, anddemethylating treatment restored CHD5expression. Lower CHD5mRNA levelscorrelated with lymph node metastasis (P=0.026). CHD5protein expression was also reduced in breast cancer, and lack of CHD5expression significantly correlatedwith higher histological grade, ER/PR-negativity, HER2positivity, distant metastasis,and worse patient survival (P≤0.01). Functionally, ectopic expression of CHD5inMDA-MB-231and Hs578T breast cancer cells inhibited cell proliferation andinvasion in vitro and tumorigenesis of MDA-MB-231cells in nude mice. Consistentwith the inhibition of cell invasion, CHD5decreased the expression of mesenchymalmarkers (Vimentin, ZEB1and N-cadherin), and upregulated the expression ofmiR-192.Conclusion: Downregulation of CHD5expression in breast cancer cell linesand tumors, mediated mainly by promoter methylation and partially by hemizygousdeletion, contributes to the development and progression of human breast cancer.