PNPLA3 I148M mediates the regulatory effect of NF-kB on inflammation in PA-treated HepG2 cells

Both PNPLA3 I148M and hepatic inflammation are associated with nonalcoholic fatty liver disease (NAFLD) progression. This study aimed to elucidate whether PNPLA3 I148M is involved in NF-kB-related inflammation regulation in NAFLD. HepG2 cells homozygous for the PNPLA3 I148M mutation were used. The human PNPLA3 promoter sequence was screened for NF-kB binding sites using the MATCH and PATCH tools. NF-kB-mediated transcriptional regulation of the PNPLA3 gene was assessed by luciferase reporter assay, EMSA and ChIP-qPCR. Wild-type (I148I) and mutant (M148M) PNPLA3 were overexpressed using stable lentivirus-mediated transfection. The pCMV vector and siRNA were transiently transfected into cells to direct NF-kB overexpression and PNPLA3 silencing, respectively. A putative NF-kB binding site in the human PNPLA3 promoter was shown to be necessary for basal and NF-kB-driven transcriptional activation of PNPLA3 and protein/DNA complex formation. Supershift analysis demonstrated a protein/DNA complex specifically containing the NF-kB p65 and p50 subunits. ChIP-qPCR confirmed the endogenous binding of NF-kB to the human PNPLA3 promoter in response to NF-kB overexpression and palmitic acid (PA) challenge. The silencing of PNPLA3 blocked the overexpression of NF-kB or PA-induced TNF-alpha up-regulation. Moreover, mutant PNPLA3 overexpression prevented NF-kB inhibitor-induced down-regulation of TNF-alpha expression in PA-treated HepG2 cells. Finally, the overexpression of mutant but not wild-type PNPLA3 increased TNF-alpha expression and activated the ER stress-mediated and NF-kB-independent inflammatory IRE-1 alpha/JNK/c-Jun pathway. Human PNPLA3 was shown to be a target of NF-kB, and PNPLA3 I148M mediated the regulatory effect of NF-kB on inflammation in PA-treated HepG2 cells, most likely via the IRE-1 alpha/JNK/c-Jun ER stress pathway.