Camp H S, Tafuri S R
Department of Cell Biology, Parke-Davis Pharmaceutical Research Division, Warner-Lambert Company, Ann Arbor, Michigan 48105, USA.
J Biol Chem. 1997 Apr 18;272(16):10811-6. doi: 10.1074/jbc.272.16.10811.
Adipocyte differentiation is regulated both positively and negatively by external growth factors such as insulin, platelet-derived growth factor (PDGF), and epidermal growth factor (EGF). A key component of the adipocyte differentiation process is PPARgamma, peroxisomal proliferator-activated receptor gamma. To determine the relationship between PPARgamma activation and growth factor stimulation in adipogenesis, we investigated the effects of PDGF and EGF on PPARgamma1 activity. PDGF treatment decreased ligand-activated PPARgamma1 transcriptional activity in a transient reporter assay. In vivo [32P]orthophosphate labeling experiments demonstrated that PPARgamma1 is a phosphoprotein that undergoes EGF-stimulated MEK/mitogen-activated protein (MAP) kinase-dependent phosphorylation. Purified PPARgamma1 protein was phosphorylated in vitro by recombinant activated MAP kinase. Examination of the PPARgamma1 sequence revealed a single MAP kinase consensus recognition site at Ser82. Mutation of Ser82 to Ala inhibited both in vitro and in vivo phosphorylation and growth factor-mediated transcriptional repression. Therefore, phosphorylation of PPARgamma1 by MAP kinase contributes to the reduction of PPARgamma1 transcriptional activity by growth factor treatment.
脂肪细胞分化受到诸如胰岛素、血小板衍生生长因子（PDGF）和表皮生长因子（EGF）等外部生长因子的正向和负向调节。脂肪细胞分化过程的一个关键成分是PPARγ，即过氧化物酶体增殖物激活受体γ。为了确定PPARγ激活与脂肪生成中生长因子刺激之间的关系，我们研究了PDGF和EGF对PPARγ1活性的影响。在瞬时报告基因检测中，PDGF处理降低了配体激活的PPARγ1转录活性。体内[32P]正磷酸盐标记实验表明，PPARγ1是一种磷蛋白，其经历EGF刺激的MEK/丝裂原活化蛋白（MAP）激酶依赖性磷酸化。纯化的PPARγ1蛋白在体外被重组活化的MAP激酶磷酸化。对PPARγ1序列的检查揭示了Ser82处有一个单一的MAP激酶共有识别位点。将Ser82突变为Ala抑制了体外和体内的磷酸化以及生长因子介导的转录抑制。因此，MAP激酶对PPARγ1的磷酸化导致生长因子处理降低PPARγ1转录活性。
