Mancini A, El Bounkari O, Norrenbrock A-F, Scherr M, Schaefer D, Eder M, Banham A H, Pulford K, Lyne L, Whetton A D, Tamura T
Institut fuer Biochemie, Medizinische Hochschule Hannover, Hannover, Germany.
Oncogene. 2007 Feb 15;26(7):1020-7. doi: 10.1038/sj.onc.1209853. Epub 2006 Aug 7.
Fms interacting protein (FMIP) is a substrate for Fms tyrosine kinase, and a nuclear/cytoplasm shuttling protein with a leucine zipper. As the phosphorylation of FMIP is observed in insulin-stimulated preadipocytes, we examined the role of FMIP in adipocyte differentiation, using the mesenchymal multipotent stem cells, C2C12 cells, that can differentiate into adipocytes, muscle cells and osteoblasts. Ectopic expression of FMIP in C2C12 impairs the adipocyte differentiation induced by treatment with insulin, dexamethasone and 3-isobutyl-1-methylxanthine. These cells exhibit muscle phenotype with multinuclear morphology. Furthermore, knockdown of endogenous FMIP expression by small interfering RNA improves adipocytic lineage commitment of C2C12 cells, while impairing muscle differentiation. Upon stimulation with insulin, CCAAT/enhancer binding protein (C/EBP)beta, but not C/EBPalpha, is upregulated in cells expressing ectopic FMIP, whereas in FMIP knockdown cells, C/EBPalpha is constitutively expressed. Ectopic expression of C/EBPalpha counteracts the effects of FMIP, whereas C/EBPalpha knockdown partially mimics the effects of FMIP in this system. Northern blot analysis and reverse transcriptase-polymerase chain reaction study reveal that ectopic FMIP-expressing cells do not contain the polyadenylated C/EBPalpha mRNA, but contain the C/EBPalpha pre-mRNA, suggesting that FMIP plays a role in RNA processing and/or export. Indeed, a member of the THO complex that plays a role in mRNA export, THOC1, is co-precipitated with FMIP. The data we have acquired on FMIP suggest that it is a target for tyrosine kinase receptors that potentiate mRNA export.
Fms相互作用蛋白（FMIP）是Fms酪氨酸激酶的底物，是一种具有亮氨酸拉链的核/细胞质穿梭蛋白。由于在胰岛素刺激的前脂肪细胞中观察到FMIP的磷酸化，我们使用能够分化为脂肪细胞、肌肉细胞和成骨细胞的间充质多能干细胞C2C12细胞，研究了FMIP在脂肪细胞分化中的作用。在C2C12细胞中异位表达FMIP会损害胰岛素、地塞米松和3-异丁基-1-甲基黄嘌呤处理诱导的脂肪细胞分化。这些细胞呈现出具有多核形态的肌肉表型。此外，用小干扰RNA敲低内源性FMIP表达可改善C2C12细胞的脂肪细胞谱系定向，同时损害肌肉分化。在用胰岛素刺激后，在表达异位FMIP的细胞中CCAAT/增强子结合蛋白（C/EBP）β上调，而C/EBPα未上调，而在FMIP敲低的细胞中，C/EBPα组成性表达。C/EBPα的异位表达可抵消FMIP的作用，而C/EBPα敲低在该系统中部分模拟了FMIP的作用。Northern印迹分析和逆转录-聚合酶链反应研究表明，表达异位FMIP的细胞不含多聚腺苷酸化的C/EBPα mRNA，但含有C/EBPα前体mRNA，这表明FMIP在RNA加工和/或输出中起作用。实际上，在mRNA输出中起作用的THO复合物成员THOC1与FMIP共沉淀。我们获得的关于FMIP的数据表明，它是增强mRNA输出的酪氨酸激酶受体的靶点。
