[Methyl CpG-binding protein 2 (MeCP2) inhibits the activity of methylated IL-6 promoter of HEK293 cells and its molecular mechanism].

Objective To investigate the underlying molecular mechanism of methyl-CpG-binding protein 2 (MeCP2) inhibiting interleukin 6 (IL-6) transcriptional activity by observing the sequence of methylated IL-6 promoter, overexpression of MeCP2, and transcription factor P300 in HEK293 cells. Methods The binding site of P300 in the IL-6 promoter region was confirmed by electrophoretic mobility shift assay (EMSA); the IL-6 promoter sequence was ligated into luciferase reporter plasmid and transfected into HEK293 cells. The methylation of the promoter was mediated by clustered regularly interspaced short palindromic repeats-deactivated Cas9 (CRISPR-dCas9)-mediated DNA methyltransferase 3A (DNMT3A) transfection, and then MeCP2 and P300 overexpression plasmids were transfected. The bisulfate sequencing PCR(BSP)was used to analyze the cytosine methylation in the IL-6 promoter region of each group. The contents of intracellular MeCP2 and P300 were detected by the Western blot. A chemiluminescence detector was used to determine the luciferase activity of HEK293 cells. The binding level of P300 and MeCP2 in the IL-6 promoter region was analyzed by chromatin immunoprecipitation followed by sequencing(ChIP-seq). Results EMSA confirmed the presence of P300 binding sites in the IL-6 promoter of mice. CRISPR-dCas9-DNMT3A transfection into HEK293 cells successfully methylated the IL-6 promoter. MeCP2 and P300 overexpression plasmid steadfastly synthesized the target protein and was not affected by other transfection. Compared with the unmodified promoter, methylation could reduce the transcriptional activity of the promoter. When P300 was overexpressed, MeCP2 could further inhibit the transcriptional activity of the promoter, when compared with methylation alone. Also, overexpression of P300 could not promote the transcriptional activity of IL-6 promoter after the methylation modified promoter combined with MeCP2, while the overexpression of P300 enhanced the transcriptional activity when the promoter was not methylated or MeCP2 was not overexpressed. ChIP-seq analysis revealed that the methylated IL-6 promoter showed no difference in binding to P300; however, when combined with MeCP2, the binding capacity would be repressed. Conclusion The combination of MeCP2 with methylated IL-6 promoter can inhibit the binding of the transcription factor to the promoter, thereby impeding the transcriptional activity of the promoter.