The Effect And Mechanism Of Inflammatory Cytokine IL6 In Promoting PD-L1 Expression In Colorectal Cancer Cells

PD-L1 is an important immune checkpoint protein,and its high expression in tumors often affects the effect of immunotherapy and promotes the malignant progression of tumors.Current research shows that PD-L1 expression is regulated by a variety of factors.IL6 is an important inflammatory cytokine present in the tumor microenvironment(TME).In previous studies,we found that IL6 can not only promote the stemness of colorectal cancer cells,but also regulate the expression of PD-L1 in colorectal cancer cells.Therefore,it is of great clinical significance to study the regulation effect and mechanism of IL6 on PD-L1 for colorectal cancer immunotherapy.By real-time quantitative reverse transcription polymerase chain reaction(q RT-PCR),protein immunoblotting(Western Blot),flow cytometry(FCM),and cellular immunofluorescence(IF)experiments,we found that the inflammatory cytokine IL6 can upregulate the expression of PD-L1 in colorectal cancer cells.More important,we separated and cultured CSCs marked by CD44+/CD133+ and found that the effect was more pronounced in CSCs.Further,by combining Western Blot and Luciferase reporter gene assay with specific small-molecule inhibitors,small interfering RNA and overexpression assay,we found that IL6 could activate the JAK/STAT3 signaling pathway,enhance the promoter activity of PD-L1 and upregulate the expression of PD-L1 at the transcriptional level.In addition,we also found that IL6 could improve the stability of PD-L1 protein,delay its half-life and increase its expression by cycloheximide(CHX)inhibiting protein synthesis assay.Our results indicate that IL6 can promote the high expression of PD-L1 in colorectal cancer cells in both transcriptional level and post-translational modification of proteins.By separating CSCs,we find that CSCs can have a better respond to the phenomenon that IL6 upregulate PD-L1 expression.The results of our study provide new evidence for the correlation among tumor microenvironment,CRC and tumor immune escape,and also provide new ideas for tumor immunotherapy.