Delmas E, Jah N, Pirou C, Bouleau S, Le Floch N, Vayssière J-L, Mignotte B, Renaud F
Laboratoire de Génétique et Biologie Cellulaire, EA4589 Université de Versailles St Quentin en Yvelines (UVSQ), Ecole Pratique des Hautes Etudes (EPHE), UFR des Sciences de la Santé Simone Veil, Montigny-Le-Bretonneux 78180, France.
Cell Death Dis. 2016 Feb 4;7(2):e2079. doi: 10.1038/cddis.2016.2.
Fibroblast growth factor 1 (FGF1) is a prototypic member of the FGFs family overexpressed in various tumors. Contrarily to most FGFs, FGF1 lacks a secretion peptide signal and acts mainly in an intracellular and nuclear manner. Intracellular FGF1 induces cell proliferation, differentiation and survival. We previously showed that intracellular FGF1 induces neuronal differentiation and inhibits both p53- and serum-free-medium-induced apoptosis in PC12 cells. FGF1 nuclear localization is required for these intracellular activities, suggesting that FGF1 regulates p53-dependent apoptosis and neuronal differentiation by new nuclear pathways. To better characterize intracellular FGF1 pathways, we studied the effect of three mutations localized in the C-terminal domain of FGF1 (i.e., FGF1(K132E), FGF1(S130A) and FGF1(S130D)) on FGF1 neurotrophic and anti-apoptotic activities in PC12 cells. The change of the serine 130 to alanine precludes FGF1 phosphorylation, while its mutation to aspartic acid mimics phosphorylation. These FGF1 mutants kept both a nuclear and cytosolic localization in PC12 cells. Our study highlights for the first time the role of FGF1 phosphorylation and the implication of FGF1 C-terminal domain on its intracellular activities. Indeed, we show that the K132E mutation inhibits both the neurotrophic and anti-apoptotic activities of FGF1, suggesting a regulatory activity for FGF1 C terminus. Furthermore, we observed that both FGF1(S130A) and FGF1(S130D) mutant forms induced PC12 cells neuronal differentiation. Therefore, FGF1 phosphorylation does not regulate FGF1-induced differentiation of PC12 cells. Then, we showed that only FGF1(S130A) protects PC12 cells against p53-dependent apoptosis, thus phosphorylation appears to inhibit FGF1 anti-apoptotic activity in PC12 cells. Altogether, our results show that phosphorylation does not regulate FGF1 neurotrophic activity but inhibits its anti-apoptotic activity after p53-dependent apoptosis induction, giving new insight into the poorly described FGF1 intracrine/nuclear pathway. The study of nuclear pathways could be crucial to identify key regulators involved in neuronal differentiation, tumor progression and resistances to radio- and chemo-therapy.
成纤维细胞生长因子1（FGF1）是FGFs家族的一个原型成员，在多种肿瘤中过表达。与大多数FGFs不同，FGF1缺乏分泌肽信号，主要以细胞内和细胞核方式发挥作用。细胞内的FGF1可诱导细胞增殖、分化和存活。我们之前表明，细胞内的FGF1可诱导PC12细胞的神经元分化，并抑制p53和无血清培养基诱导的细胞凋亡。FGF1的核定位是这些细胞内活性所必需的，这表明FGF1通过新的核途径调节p53依赖性细胞凋亡和神经元分化。为了更好地表征细胞内FGF1途径，我们研究了位于FGF1 C末端结构域的三个突变（即FGF1(K132E)、FGF1(S130A)和FGF1(S130D)）对PC12细胞中FGF1神经营养和抗凋亡活性的影响。丝氨酸130突变为丙氨酸可阻止FGF1磷酸化，而突变为天冬氨酸则模拟磷酸化。这些FGF1突变体在PC12细胞中同时保持核定位和胞质定位。我们的研究首次突出了FGF1磷酸化的作用以及FGF1 C末端结构域对其细胞内活性的影响。事实上，我们表明K132E突变抑制了FGF1的神经营养和抗凋亡活性，提示FGF1 C末端具有调节活性。此外，我们观察到FGF1(S130A)和FGF1(S130D)突变体形式均可诱导PC12细胞的神经元分化。因此，FGF1磷酸化并不调节FGF1诱导的PC12细胞分化。然后，我们表明只有FGF1(S130A)可保护PC12细胞免受p53依赖性细胞凋亡，因此磷酸化似乎抑制了PC12细胞中FGF1的抗凋亡活性。总之，我们的结果表明，磷酸化不调节FGF1的神经营养活性，但在p53依赖性细胞凋亡诱导后抑制其抗凋亡活性，这为对描述较少的FGF1内分泌/核途径提供了新的见解。对核途径的研究对于识别参与神经元分化、肿瘤进展以及对放疗和化疗耐药的关键调节因子可能至关重要。
