Li R, Liu Y, Ladisch S
Glycobiology Program, Center for Cancer and Transplantation Biology, Children's Research Institute, Washington, DC 20010, USA.
J Biol Chem. 2001 Nov 16;276(46):42782-92. doi: 10.1074/jbc.M101481200. Epub 2001 Sep 4.
In a recent study, inhibition of cellular ganglioside synthesis blocked growth factor-induced fibroblast proliferation. Conversely, enrichment of cell membrane gangliosides by ganglioside preincubation enhanced growth factor-elicited cell proliferation. In the absence of serum and growth factors, NeuNAcalpha2-3Galbeta1-3GalNAcbeta1-4(NeuNAcalpha2-3)Galbeta1-4Glcbeta1-1Cer (G(D1a)) acted like a growth factor when cells were pretreated with the ganglioside, stimulating proliferation of normal human dermal fibroblasts and Swiss 3T3 fibroblasts. In contrast, growth inhibition was observed when high concentrations of gangliosides were continuously present in the culture medium during incubation of fibroblasts with growth factors (Li, R., Manela, J., Kong, Y., and Ladisch, S. (2000) J. Biol. Chem. 275, 34213-34223). Here, we investigated the mechanisms whereby gangliosides elicit proliferation-coupled signaling in normal human dermal fibroblasts. Incubation of the fibroblasts with G(D1a) enhanced epidermal growth factor (EGF) receptor autophosphorylation and Ras and MAPK activation in a dose-dependent manner. Exposure of the cells to G(D1a) also enhanced the phosphorylation of Elk-1 by the activated MAPK. Brief pretreatment of the cells with PD98059 blocked the enhancing effect of gangliosides on EGF-induced MAPK activation. In the absence of serum and growth factors, G(D1a) incubation induced phosphorylation of Src kinase, Ras activation, and phosphorylation of MAPK and Elk-1 in a dose-dependent manner. The activation of Src kinase was confirmed by enhanced Src kinase activity. Brief treatment of the cells with PP1 blocked the activation of Src kinase and MAPK. Again, PD98059 treatment inhibited ganglioside-elicited MAPK phosphorylation. Among the gangliosides tested, G(D1a), was the most active molecule, whereas lactosylceramide was the least active one, indicating relative structural specificity of the ganglioside action. In conclusion, gangliosides promote fibroblast proliferation through enhancement of growth factor signaling and activation of Src kinase.
在最近的一项研究中，细胞神经节苷脂合成的抑制作用阻断了生长因子诱导的成纤维细胞增殖。相反，通过神经节苷脂预孵育使细胞膜神经节苷脂富集可增强生长因子引发的细胞增殖。在无血清和生长因子的情况下，当用神经节苷脂预处理细胞时，NeuNAcalpha2-3Galbeta1-3GalNAcbeta1-4(NeuNAcalpha2-3)Galbeta1-4Glcbeta1-1Cer (G(D1a)) 的作用类似于生长因子，可刺激正常人皮肤成纤维细胞和瑞士3T3成纤维细胞的增殖。相比之下，当成纤维细胞与生长因子一起孵育时，如果培养基中持续存在高浓度的神经节苷脂，则会观察到生长抑制现象（Li, R., Manela, J., Kong, Y., and Ladisch, S. (2000) J. Biol. Chem. 275, 34213 - 34223）。在此，我们研究了神经节苷脂在正常人皮肤成纤维细胞中引发增殖偶联信号的机制。用G(D1a)孵育成纤维细胞可增强表皮生长因子（EGF）受体的自磷酸化以及Ras和MAPK的激活，且呈剂量依赖性。将细胞暴露于G(D1a)也可增强活化的MAPK对Elk-1的磷酸化作用。用PD98059对细胞进行短暂预处理可阻断神经节苷脂对EGF诱导的MAPK激活的增强作用。在无血清和生长因子的情况下，G(D1a)孵育以剂量依赖性方式诱导Src激酶的磷酸化、Ras激活以及MAPK和Elk-1的磷酸化。Src激酶活性增强证实了其激活。用PP1对细胞进行短暂处理可阻断Src激酶和MAPK的激活。同样，PD98059处理可抑制神经节苷脂引发的MAPK磷酸化。在所测试的神经节苷脂中，G(D1a)是最具活性的分子，而乳糖基神经酰胺是活性最低的分子，这表明神经节苷脂作用具有相对的结构特异性。总之，神经节苷脂通过增强生长因子信号传导和激活Src激酶来促进成纤维细胞增殖。
