Tumor gene expression in vitro and in vivo

我们最近的大多数生长调控研究都关注ras癌基因及其阳性调节因子，ras特异性鸟嘌呤核苷酸交换因子（ras - gnef）。这些分子在信号转导中起关键作用，ras在许多人类和动物肿瘤中被突变激活。对两种密切相关且广泛表达的ras - gnef sos1和sos2的分析发现，它们编码蛋白的稳定性和信号传导特性的持续时间存在重要差异。Sos2蛋白进行长期信号传导的效率低于Sos1，以至于Sos2的生理水平不能支持酪氨酸激酶等癌蛋白的转化，酪氨酸激酶依赖于依赖于Sos2的Ras激活来实现转化活性。此外，Sos2蛋白是泛素-蛋白酶体系统降解的生理性底物，而Sos1不受这种调节。其他通过Sos信号传导的研究表明，蛋白质的n端和c端的坐标信号是其激活所必需的。我们也在研究GRF1和GRF2，这两种密切相关的脑特异性ras - gnef，它们被钙激活。我们发现GRF的钙依赖性激活通过两个信号刺激Raf，一个是ras依赖性的，另一个是ras非依赖性的。此外，GRF1和GRF2通过其Dbl结构域形成同源和异源二聚体。二聚化可能需要从刺激Raf的GRF传播与ras无关的信号。研究人员计划进一步研究Sos和GRF信号的调控机制。

Most 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. Other studies on signaling through Sos indicate that coordinate signals at the N-terminus and C-terminus of the protein are required for its activation. We are also studying GRF1 and GRF2, two closely related brain-specific Ras-GNEFs, that 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. Further studies are planned to elucidate the mechanisms underlying the regulation of Sos and GRF signaling.