CORK--A NOVEL, PUTATIVE ALPHA-2 INTEGRIN KINASE

α2gbeta1整合素是一种胶原受体，参与了血小板活化、平滑肌细胞和T淋巴细胞迁移、内皮附着等血管系统活动。我们先前证明，胶原诱导的血小板聚集依赖于这种整合素的占有率(以及一种未知的辅助受体，可能是糖蛋白VI)。我们还发现，胶原蛋白以α2beta1依赖的方式激活非受体酪氨酸激酶Syk，随后激活磷脂酶CGamma2，这些事件似乎是胶原诱导聚集所必需的。目前尚不清楚α2beta1整合素如何激活血小板或诱导这些信号转导事件。整合素领域的大量证据表明，整合素的短胞浆域在向细胞内传递信号方面发挥着关键作用，可能是由于与这些域结合的调控分子。为了确定潜在的胞质结构域调控蛋白，我们在酵母双杂交系统中筛选了一个文库，以Lapha2整合素胞质结构域为诱饵。我们已经确定了一个部分cdna序列，它编码了一种似乎非常有趣的蛋白质。该蛋白的mRNA大小(9.5kb)，分布广泛，在血小板、平滑肌细胞和其他血管和非血管细胞中均有表达。此外，核苷酸序列分析表明，该蛋白的一个区域与许多丝氨酸/苏氨酸和双特异性激酶高度同源，表明该蛋白是一种激酶。另一个较小的区域与Ras GTP酶激活蛋白RasGAP同源，确实该蛋白在酵母双杂交系统中与RAS结合，但不与其他控制蛋白结合，这表明他的蛋白可能也在调节RAS或RAS相关蛋白中发挥作用。我们建议首先完成编码该蛋白的cDNA的测序，然后进一步确定该蛋白的结构、细胞和组织分布以及功能。对这一新蛋白的研究有助于我们更好地理解α2beta1在血小板和其他血管细胞中的调节作用。

The alpha2gbeta1 integrin is a collagen receptor involved in platelet activation, smooth muscle cell and T lymphocyte migration, endothelial attachment and other events in the vasculature. We previously demonstrated that collagen-induced platelet aggregation depends upon occupancy of this integrin (along with an unknown co-receptor, possible glycoprotein VI). We also found that collagen activates, in an alpha2beta1-dependent manner, the non-receptor tyrosine kinase Syk, followed by phospholipase Cgamma2, events that appear necessary for collagen-induced aggregation. How the alpha2beta1 integrin activates platelets or induces these signal transduction events is unknown. Much evidence in the integrin field suggests that the short cytoplasmic domains of integrins play critical roles in transmitting signals into cells, potentially due to regulatory molecular that bind to these domains. To identify potential cytoplasmic domain regulatory proteins, we screened a library in the yeast two-hybrid system, using the lapha2 integrin cytoplasmic domain as bait. We have identified a partial cDNA sequence that encodes what appears to be an extremely interesting protein. The mRNA for this protein is large (9.5kb), widely distributed, and appears to be expressed in platelets, smooth muscle cells and other vascular and non-vascular cells. Moreover, nucleotide sequence analysis indicates a region of this protein that is highly homologous to numerous serine/threonine and dual specificity kinases, suggesting that the protein is a kinase. A separate smaller region is homologous to RasGAP, a Ras GTPase activating protein, and indeed this protein binds to Ras in the yeast two- hybrid system, but not to other control proteins, suggesting that his protein might also play a role in regulating Ras or Ras-related proteins. We propose to first complete the sequencing of the cDNA encoding this protein, and second to further characterize the protein with regard to its structure, cell and tissue distribution, and function. Characterizing of this novel protein may help us to better understand alpha2beta1-mediated in platelets and other vascular cells.