p53 affects epigenetic signature on SOCS1 promoter in response to TLR4 inhibition.

Suppressor of cytokine signaling (SOCS1) functions as a negative regulator of toll-like receptor (TLR) induced inflammatory signaling. As silencing of SOCS1 is concomitant with elevated TLR4 levels in glioblastoma, we investigated the effect of TLR4 inhibition on SOCS1 expression. Pharmacological inhibition of TLR4 signaling by TAK242 or its siRNA-mediated knockdown in p53 mutant or wild-type glioma cells resulted in either increased or decreased SOCS1 expression and promoter activity, respectively. Genetic manipulation of p53 indicated that SOCS1 expression upon TLR4 inhibition is dependent on p53 mutational status. Increased SOCS1 level was concomitant with diminished nucleosomal occupancy around p53-binding site on SOCS1 promoter. This altered nucleosomal landscape was accompanied by (i) diminished nuclear H3K9me3 and (ii) increased JMJD2A and Brg1 levels. JMJD2A inhibition or ectopic expression of ATPase-deficient BRG1 prevented TAK242 mediated increase in SOCS1 expression. Recruitment of Brg1-p53-JMJD2A complex on p53 binding sites of SOCS1 promoter upon TLR4 inhibition was concomitant with increased SOCS1 expression in p53-mutant cells. The Cancer Genome Atlas (TCGA) dataset indicated an inverse correlation between TLR4 and SOCS1 levels in p53 mutant but not in p53WT GBM. Taken together, p53 mutational status regulates transcriptional plasticity of SOCS1 promoter through differential recruitment of chromatin remodelers and epigenetic regulators in response to TLR4 inhibition.