The R251Q Mutation Of LSD1 Promotes Invasion And Migration Of Luminal A Breast Cancer Cells

Breast cancer is the most commonly diagnosed cancer and the leading cause of cancer-associated deaths among women worldwide,which also has a rising incidence rates.Breast cancer is a highly heterogeneous disease,which could be categorized into six subtypes,including Luminal A,Luminal B,HER2/ERBB2+,Basal-like,Normal-like and Claudin-low subtypes.The causes of breast cancer include genetic changes and epigenetic regulatory abnormalities.Various studies have demonstrated that a variety of epigenetic regulatory factors dynamically and reversibly regulate key genes and signaling pathways involved in breast cancer,and the abnormalities of these epigenetic regulatory facilitates the initiation and progression of breast cancer.Therefore,it is crucial to clarify the molecular mechanism underlying the altered epigenetic regulatory network that promotes breast cancer.Epigenetics modification plays a key role in regulating the organ development,cellular differentiation,and cancer-associated gene expression,and those modifications is reversible.Therefore,enzymes that catalyze essential epigenetic modifications become key targets in disease treatment.LSD1(Lysine specific demethylase 1),an important histone demethylase,plays a key role in the chromosomal remodeling and transcription regulation by demethylasing H3K4me2 and H3K9me2.LSD1 participates in multiple processes of cell differentiation and cancer progression by forming a variety of protein complexes.Since the influence of LSD1 in normal and disease conditions is largely dependent on cell types and protein complexes that involve LSD1,the exact roles and also the underlying mechanisms of LSD1 in different subtypes of breast cancer remain elusive.Therefore,the molecular mechanism underlying LSD1-mediated breast cancer progression requires further investigation.In this study,we found that the breast cancer patients with LSD1 mutation show significantly worse prognosis compared to those without LSD1 mutation.The patient with the worst outcomes has a R251 Q mutation of LSD1 and a Luminal A breastcancer.Luminal A breast cancer is the most common type of invasive breast cancer.Although it is sensitive to the hormone therapy and has a relatively good prognosis,Luminal A breast cancer still demonstrates substantial metastasis and recurrence.Metastasis is the major cause of breast cancer-associated mortality,and Epithelial-Mesenchymal Transition(EMT)plays a key role in cancer metastasis.Therefore,it is crucial to clarify the mechanisms underlying EMT of breast cancer and identify the key regulators.Our previous study shows that LSD1 plays a tumor suppressive role in Luminal breast cancer.The current study has investigated the role of R251 Q mutation of LSD1 in the progression of Luminal A breast cancer and the molecular mechanisms under which the R251 Q mutation affects the expression of key oncogenes and EMT-related genes.To investigate the effects of the LSD1 R251 Q mutation in Luminal A breast cancer cells,the cells that express the R251 Q mutated LSD1 were generated by restoring R251 Q mutated LSD1 into the LSD1 knockdown MCF7 cells.The Luminal A breast cancer cells that express the R251 Q mutated LSD1 showed characteristic morphology of mesenchymal cells both in the two-dimensional and three-dimensional analysis.In addition,the R251 Q mutation of LSD1 increased the invasion and migration of Luminal A breast cancer cells in transwell and wound-healing assays.Furthermore,the R251 Q mutation of LSD1 affected the expression of key markers of EMT.It decreased the expression of epithelial markers associated with cell adhesion(e.g.,E-cadherin,Vinculin,α-catenin),increased the expression of Vimentin that promotes mesenchymal cell morphology and motility.Collectively,these results demonstrated that the R251 Q mutation of LSD1 influences the invasion and migration of Luminal A breast cancer cells by promoting the process of EMT.More importantly,the R251 Q mutation abolished the inhibition of LSD1 on the transcription of its target gene TRIM37,which was an oncogene and suppressed the expression of a variety of tumor suppressor genes and epithelial marker gene CDH1.Ch IP analysis showed that the R251 Q mutation caused the reduced recruitment of LSD1 and the enhanced level of H3K4me2 on the TRIM37 gene locus simultaneously,which confirmed that the R251 Q mutation released the inhibitory effects of LSD1 onTRIM37 expression by increasing the H3K4me2 at TRIM37 gene locus.Further investigation demonstrated that the R251 Q mutation of LSD1 did not affect the demethylation of H3K4me2 on free histone proteins but reduced the demethylation of H3K4me2 on nucleosomal histone proteins.The LSD1-mediated demethylation of H3K4me2 on nucleosomal histone proteins requires the formation of the LSD1/Co REST complex,and the immunoprecipitation and GST-pull down results showed that the R251 Q mutation greatly reduced the interaction between LSD1 and Co REST.To summarize,our research shows that the R251 Q mutation of LSD1 abolishes the inhibition of TRIM37 expression by reducing the formation of LSD1/Co REST complex and promotes the invasion and migration of Luminal A breast cancer cells subsequently.Together,our research demonstrates that LSD1 and the mutation of LSD1 play important roles in the Luminal breast cancer,and enhances our understanding of the molecular mechanism of epigenetic modification on the progression of breast cancer.Meanwhile,our results reveal some new ideas for the development of novel breast cancer treatments.