Tumor gene expression in vitro and in vivo

我们最近的大部分生长调节研究都与ras癌基因及其正向调节因子，即RAS特异性鸟嘌呤核苷酸交换因子(RAS-GNEFs)有关。这些分子在信号转导中起关键作用，在许多人类和动物肿瘤中，ras被突变激活。对两个密切相关的、广泛表达的RAS-GNEF，sos1和sos2的分析发现，它们在编码蛋白的稳定性和信号特性持续时间方面存在重要差异。Sos2蛋白执行长期信号的效率低于Sos1，以至于生理水平的Sos2不能支持酪氨酸激酶等癌蛋白的转化，这些蛋白依赖于SOS依赖的RAS的激活来实现其转化活性。此外，Sos2蛋白是泛素-蛋白酶体系统降解的生理底物，而Sos1不受这种调节。我们目前正在研究Sos1 VX基因差异的遗传基础。SOS2信号转导，以及SOS1功能的调节。我们发现E-钙粘附素可能通过抑制上游分子来干扰SOS的信号功能。E-钙粘附素抑制转化的意义正在研究中。我们还在研究GRF1和GRF2，这两个密切相关的RAS-GNEF的表达比钙激活的SOS更受限制。我们已经发现GRF的钙依赖激活通过两个信号来刺激Raf，一个是RAS依赖的，另一个是RAS不依赖的。此外，GRF1和GRF2通过它们的DBL结构域形成同二聚体和异二聚体。可能需要二聚化来传播来自刺激Raf的GRF的RAS非依赖性信号。出乎意料的是，我们还发现RAS-GRF可能通过GRF的RAS催化区刺激RAS相关蛋白Rap1a。

Much of our recent growth regulation research has been concerned with the ras oncogene and its positive regulators, the Ras-specific guanine nucleotide exchange factors (Ras-GNEFs). These molecules play a key role in signal transduction, and ras is mutationally activated in many human and animal tumors. The analysis of two closely related, widely expressed Ras-GNEFs, sos1 and sos2, has identified important differences in the stability of their encoded proteins and in the duration of their signaling properties. The Sos2 protein carries out long-term signaling less efficiently than Sos1 to a degree that physiologic levels of Sos2 cannot support transformation by oncoproteins such as tyrosine kinases, which rely on Sos-dependent activation of Ras for their transforming activity. In addition, the Sos2 protein is a physiologic substrate for degradation by the ubiquitin-proteasome system, while Sos1 is not subject to such regulation. We are currently examining the genetic basis for the difference in Sos1 vx. Sos2 signaling, as well as the regulation of Sos1 function. We have found that E-cadherin can interfere with the signaling function of Sos, probably via inhibition of upstream molecules. The implications for inhibition of transformation by E-cadherin are under investigation. We are also studying GRF1 and GRF2, two closely related Ras-GNEFs with more restricted expression than Sos which are activated by calcium. We have found that the calcium-dependent activation of GRF stimulates Raf via two signals, one that is Ras-dependent and another that is Ras-independent. Also, GRF1 and GRF2 form homo- and hetero-dimers through their Dbl domains. Dimerization may be required for propagating the Ras-independent signal from GRF that stimulates Raf. Unexpectedly, we also find that Ras-GRF stimulates the Ras-related protein Rap1a, probably via the Ras catalytic region of GRF.