The transcription factor AP-2 causes cell enlargement and insulin resistance in 3T3-L1 adipocytes

Tao Y, Maegawa H, Ugi S, Ikeda K, Nagai Y, Egawa K, Nakamura T, Tsukada S, Nishio Y, Maeda S, Kashiwagi A
Source: Endocrinology
Publication Date: (2006)
Issue: 147(4): 1685-96
Research Area:
Cancer Research/Cell Biology
Nucleofector® I/II/2b
We have reported the association of variations in the AP-2beta transcription factor gene with type 2 diabetes. This gene was preferentially expressed in 3T3-L1 adipocytes in a differentiation-stage-dependent manner and preliminary experiments showed that subjects with disease susceptible allele showed stronger expression in adipose tissue than did those without susceptible allele. Thus, we overexpressed AP-2beta gene in 3T3-L1 adipocytes to clarify whether AP-2beta might play crucial roles in the pathogenesis of type 2 diabetes through dysregulation of adipocyte function. In cells overexpressing AP-2beta, cells increased in size by accumulation of triglycerides accompanied with enhanced glucose uptake. On the contrary, suppression of AP-2beta expression by siRNA inhibited glucose uptake. Enhancement of glucose uptake by AP-2beta overexpression was attenuated by inhibitors of phospholipase C (PLC) and atypical protein kinase C (PKC) zeta/lambda, but not by a phosphatidylinositol 3-kinase (PI3-K) inhibitor. Consistently, we found activation of PLC and atypical PKC, but not PI3-K by AP-2beta expression. Furthermore, overexpression of PLCgamma enhanced glucose uptake and this activation was inhibited by an atypical PKC inhibitor, suggesting that the enhanced glucose uptake may be mediated through PLC and atypical PKCzeta/lambda, but not PI3-K. Moreover, we observed the increased tyrosine phosphorylation of Grb2-associated binder-1 (Gab-1) and its association with PLCgamma, indicating that Gab-1 may be involved in AP-2beta-induced PLCgamma activation. Finally, AP-2beta overexpression was found to relate to the impaired insulin signaling. We propose that AP-2beta is a candidate gene for leading to adipocyte hypertrophy and may relate to the abnormal characteristics of adipocytes observed in obesity.