TFAP2B and obesity due to melanocortin 4 receptor deficiency: Further studies revealed the overexpression of AP-2β in 3T3-L1 adipocytes, where AP-2β subsequently bound specifically to the IRS1 promoter region, impairing the promoter activity of IRS1 and subsequently decreasing the expression of downstream mRNAs and proteins, which could increase susceptibility to obesity and T2DM (77).