Mechanistic Study On The Role Of H3K27 Trimethylation Modification On Chemotherapy Resistance Of Colorectal Cancer

Objectives: The incidence and mortality of colorectal cancer ranks third among all cancers in the world.Chemotherapy resistance of colorectal cancer is a key factor affecting the prognosis of patients.It is found that colorectal cancer patients with poorly differentiated have low survival rate and poor chemotherapy effect.And the Histone 3 lysine 27 trimethylation(H3K27me3)plays an important regulatory role in the process of cell differentiation.The main objectives of this study were to determine the role H3K27me3 in oxaliplatin resistance and to evaluate the effects of treatment with H3K27 demethylase inhibitor GSK-J4 on reversing the chemoresistance of CRCs.Methods: Tissue microarrays were used to analyze the relationship between metastasis-free survival and the levels of H3K27me3 in 97 CRC patients.The patient-derived xenograft(PDX)model was used to study the effect of H3K27 demethylase inhibitor on the efficacy of oxaliplatin in vivo.Colorectal cancer cell lines were used in vitro to determine the effect of H3K27 trimethylation modification on chemoresistance of colorectal cancer by Western Blot,Q-PCR,MTT,clone formation and cytometry.Results: We found that H3K27me3 levels positively correlated with the metastasis-free survival of CRC patients,and a low H3K27me3 expression predicted a poor outcome upon chemotherapy.Oxaliplatin treatment significantly induced the expression of the H3K27 demethylases KDM6A/6B,thus decreasing the level of H3K27me3 in CRC cells.Elevation of the H3K27me3 level through KDM6A/6B depletion or GSK-J4 treatment significantly enhanced oxaliplatin-induced apoptosis.In addition,the combination of GSK-J4 and oxaliplatin significantly inhibited tumor growth in anoxaliplatin-resistant PDX model.Importantly,we revealed that oxaliplatin treatment dramatically induced NOTCH2 expression,which was caused by the downregulation of the H3K27me3 level on the NOTCH2 transcription initiation site.Thus,the activated NOTCH signaling promoted the expression of stemness-related genes,which resulted in oxaliplatin resistance.And oxaliplatin-induced NOTCH signaling could be interrupted by GSK-J4 treatment.Conclusion: Low levels of H3K27me3 predict a poor prognosis and enhance oxaliplatin resistance in CRC patients.It can promote the apoptosis induced by oxaliplatin in vitro and in vivo by knocking down KDM6A/KDM6 B or GSK-J4 to increase the level of H3K27me3.Oxaliplatin treatment promoted the expression of KDM6A/KDM6 B,thereby reducing the level of H3K27me3 in the promoter region of NOTCH2 gene and up-regulating NOTCH2,causing chemoresistance.Increase in H3K27me3 by treatment with GSK-J4 sensitizes oxaliplatinresistant CRCs,providing a novel strategy for CRC chemotherapy.