Tumor gene expression in vitro and in vivo

我们最近的大部分生长调节研究一直关注ras癌基因及其正调控因子，Ras特异性鸟嘌呤核苷酸交换因子（Ras-GNEFs）。这些分子在信号转导中起关键作用，并且ras在许多人类和动物肿瘤中被突变激活。对两个密切相关的、广泛表达的Ras-GNEFs sos 1和sos 2的分析已经确定了它们编码的蛋白质的稳定性和它们的信号传导特性的持续时间的重要差异。 Sos 2蛋白进行长期信号传导的效率低于Sos 1，其程度使得生理水平的Sos 2不能支持癌蛋白如酪氨酸激酶的转化，其转化活性依赖于Ras的Sos依赖性激活。此外，Sos 2蛋白是泛素-蛋白酶体系统降解的生理底物，而Sos 1不受这种调节。对通过Sos信号传导的其他研究表明，蛋白质的N-末端和C-末端的协调信号是其激活所必需的。我们还在研究GRF 1和GRF 2，这两种密切相关的脑特异性Ras-GNEFs，它们被钙激活。我们已经发现，钙依赖性激活的GRF刺激Raf通过两个信号，一个是Ras依赖的，另一个是Ras独立的。此外，GRF 1和GRF 2通过其Db 1结构域形成同源和异源二聚体。可能需要二聚化来传播来自刺激Raf的GRF的Ras独立信号。进一步的研究计划阐明潜在的机制的调节Sos和GRF信号。

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.