Engelman J A, Berg A H, Lewis R Y, Lin A, Lisanti M P, Scherer P E
Department of Cell Biology, Albert Einstein College of Medicine, Bronx, New York 10461, USA.
J Biol Chem. 1999 Dec 10;274(50):35630-8. doi: 10.1074/jbc.274.50.35630.
Although much has been learned regarding the importance of p38 mitogen-activated protein kinase in inflammatory and stress responses, relatively little is known concerning its role in differentiation processes. Recently, we demonstrated that p38 mitogen-activated protein kinase activity is necessary for the differentiation of 3T3-L1 fibroblasts into adipocytes (Engelman, J. A., Lisanti, M. P., and Scherer, P. E. (1998) J. Biol. Chem. 273, 32111-32120). p38 activity is high during the initial stages of differentiation but decreases drastically as the fibroblasts undergo terminal differentiation into adipocytes. However, it remains unknown whether activation of p38 is sufficient to stimulate adipogenesis and whether the down-regulation of p38 activity in mature adipocytes is critical for maintaining adipocyte homeostasis. In this report, we have directly addressed these questions by analyzing 3T3-L1 cell lines harboring a specific upstream activator of p38 (a constitutively active mitogen-activated protein kinase kinase 6 (MKK6) mutant, MKK6(Glu)) under the control of an inducible promoter. Induction of MKK6(Glu) in 3T3-L1 fibroblasts spurs adipocyte conversion in the absence of the hormonal mixture normally required for efficient differentiation of wild-type cells. However, activation of p38 in adipocytes leads to cell death. Furthermore, treatment of 3T3-L1 fibroblasts with salicylate, a potent stimulator of p38, produces adipocyte-specific changes consistent with those observed with induction of MKK6(Glu). Expression of MKK6(Glu) in NIH-3T3 fibroblasts (cells that do not differentiate into adipocytes under normal conditions) is capable of converting these fibroblasts into lipid-laden fat cells following hormonal stimulation. Thus, p38 activation has pro-adipogenic effects in multiple fibroblast cell lines.
尽管关于p38丝裂原活化蛋白激酶在炎症和应激反应中的重要性已了解很多，但对于其在分化过程中的作用却知之甚少。最近，我们证明p38丝裂原活化蛋白激酶活性对于3T3-L1成纤维细胞分化为脂肪细胞是必需的（恩格尔曼，J.A.，利桑蒂，M.P.，和谢勒，P.E.（1998年）《生物化学杂志》273，32111 - 32120）。在分化的初始阶段p38活性很高，但随着成纤维细胞向脂肪细胞进行终末分化，其活性急剧下降。然而，p38的激活是否足以刺激脂肪生成以及成熟脂肪细胞中p38活性的下调对于维持脂肪细胞内稳态是否至关重要仍不清楚。在本报告中，我们通过分析在可诱导启动子控制下携带p38特异性上游激活剂（一种组成型活性丝裂原活化蛋白激酶激酶6（MKK6）突变体，MKK6（Glu））的3T3-L1细胞系，直接解决了这些问题。在3T3-L1成纤维细胞中诱导MKK6（Glu）可在缺乏野生型细胞高效分化通常所需激素混合物的情况下促使脂肪细胞转化。然而，脂肪细胞中p38的激活会导致细胞死亡。此外，用p38的强效刺激剂水杨酸盐处理3T3-L1成纤维细胞会产生与诱导MKK6（Glu）时观察到的一致的脂肪细胞特异性变化。在NIH-3T3成纤维细胞（在正常条件下不会分化为脂肪细胞的细胞）中表达MKK6（Glu）能够在激素刺激后将这些成纤维细胞转化为充满脂质 的脂肪细胞。因此，p38激活在多种成纤维细胞系中具有促脂肪生成作用。
