细胞质内微环境直接影响FGFR1酪氨酸激酶介导的SNT1细胞特异性磷酸化

成纤维细胞生长因子受体(FGFR)介导的SNT1(亦称为FRS2)底物磷酸化具有宿主细胞以及受体特异性。为探明这种宿主细胞特异性的决定因素,我们构建了1个FGFR2Ⅲb/R1嵌合受体。该嵌合受体具有1个FGFR2Ⅲb的胞外片段及1个FGFR1蛋白质酪氨酸激酶片断。当表达在3T3细胞(内源性受体为FGFR1并能强烈响应FGFR1的信号)以及DTE-R1/100细胞时,该嵌合受体能即刻诱导SNT1磷酸化。DTE-R1/100细胞为经长期培养的带有外源性FGFR1的非恶性前列腺肿瘤上皮细胞(DTE)并已获得未转化DTE细胞所不具备的FGFR1信号响应性。与此相反,当表达在非转化DTE细胞或未经长期培养的FGFR1转化细胞(DTE-R1)时,FGFR2Ⅲb/R1嵌合受体则无法诱导SNT1磷酸化。我们曾报导DTE细胞对FGFR1介导的SNT1磷酸化活力及其刺激细胞生长信号的响应性是一种获得性的性质,这种性质的获得与细胞恶化是紧密联系在一起的。在此我们进一步证明FGFR介导的SNT1磷酸化具有宿主细胞特异性。这些结果表明细胞内围绕着激酶的微环境而不是细胞外环境决定了SNT1是否可为FGFR1所磷酸化。而且,长期受外源性FGFR1刺激诱发DTE细胞内微环境的变化,从而使表达在DTE细胞里的FGFR1激酶可强烈地磷酸化SNT1。

THE INTRACELLULAR MICROENVIRONMENT IN HOST CELL-SPECIFIC PHOSPHORYLATION OF SNT1 BY THE FGFR1 TYROSINE KINASE

The phosphorylation of the fibroblast growth factor receptor (FGFR) kinase substrate SNT1 (also called FGFR substrate 2, FRS2) by FGFR tyrosine kinases is both host cell- and receptor isotype-specific. To study the determinants of the host cell-specific phosphorylation of SNT1 by FGFR1 tyrosine kinase, we constructed a chimeric receptor FGFR2IIIb/R1 that consisted of an FGFR2IIIb ligand-binding ectodomain and an FGFR1 tyrosine kinase domain. The chimeric FGFR2IIIb/R1 kinase mediated robust phosphorylation of SNT1 immediately after transfection in mouse 3T3 cells where the FGFR1 kinase was residential, and in pro-liferative aged prostate tumor epithelial cells (DTE-R1/100) that ectopically expressed FGFR1 kinase. This is in contrast to the fact that the robust phosphorylation of SNT1 by ectopic FGFR1 kinase is an acquisition property in DTE premalignani prostate epithelial cells, which normally do not express FGFR1. The data suggest that the microenvironment of intracellular, rather than components in the extracellular compartment, of host cells is im- portant in permitting FGFR1 kinase to strongly phosphorylate SNT1. Together with our previous data that the acquisition of SNT1 phosphorylation activity is concurrent with the acquisition of mitogenic activity of FGFR1 in prostate epithelial cells, the results here further demonstrate that the phosphorylation of SNT1 is host cell specific and that alterations induced by chronic exposure to ectopic FGFR1 kinase are involved in acquisition of SNT1 phosphorylation activity to the ectopic FGFR1 in prostate epithelial cells.