Posern G, Weber C K, Rapp U R, Feller S M
Institut für Medizinische Strahlenkunde und Zellforschung (MSZ), Julius-Maximilians-University, D-97078 Würzburg, Germany.
J Biol Chem. 1998 Sep 18;273(38):24297-300. doi: 10.1074/jbc.273.38.24297.
Rap1 and Ras are homologous GTPases that are implicated in cell proliferation and differentiation. At present, little is known about the regulation of Rap1 activity. Using a recently developed assay with activation-specific probes, we found increased activity of endogenous Rap1 in NIH3T3 cells after stimulation with the neuropeptide growth factor bombesin in a concentration- and time-dependent manner. The activity of endogenous Ras was unaffected. Analysis of putative effectors showed no activation of c-Raf-1 or B-Raf after bombesin stimulation. However, MAPK/Erk-phosphorylation and the proliferation rate was increased. In addition, Rap1 was activated during cell adhesion to coated and uncoated tissue culture plates, as well as in response to various mitogens. Surprisingly, the basal Rap1 activity was observed to be cell density-dependent, with low levels when cells were reaching confluency. The results suggest that Rap1 acts as an important mediator of mitogenic signals distinct to Ras activation.
Rap1和Ras是同源GTP酶，与细胞增殖和分化有关。目前，关于Rap1活性的调节知之甚少。使用最近开发的具有激活特异性探针的检测方法，我们发现神经肽生长因子蛙皮素刺激后，NIH3T3细胞内源性Rap1的活性以浓度和时间依赖性方式增加。内源性Ras的活性未受影响。对假定效应器的分析表明，蛙皮素刺激后c-Raf-1或B-Raf未被激活。然而，MAPK/Erk磷酸化和增殖率增加。此外，在细胞粘附于包被和未包被的组织培养板以及对各种有丝分裂原作出反应时，Rap1被激活。令人惊讶的是，观察到基础Rap1活性依赖于细胞密度，当细胞达到汇合时水平较低。结果表明，Rap1作为与Ras激活不同的有丝分裂信号的重要介质发挥作用。
