Koh C G, Manser E, Zhao Z S, Ng C P, Lim L
Glaxo-IMCB Group, Institute of Molecular and Cell Biology, 30 Medical Drive, Singapore 117609.
J Cell Sci. 2001 Dec;114(Pt 23):4239-51. doi: 10.1242/jcs.114.23.4239.
PIX is a Rho-family guanine nucleotide exchange factor that binds PAK. We previously described two isoforms of PIX that differ in their N termini. Here, we report the identification of a new splice variant of betaPIX, designated beta2PIX, that is the dominant species in brain and that lacks the region of approximately 120 residues with predicted coiled-coil structure at the C terminus of beta1PIX. Instead, beta2PIX contains a serine-rich C terminus. To determine whether these splice variants differ in their cellular function, we studied the effect of expressing these proteins in HeLa cells. We found that the coiled-coil region plays a key role in the localization of beta1PIX to the cell periphery and is also responsible for PIX dimerization. Overexpression of beta1, but not beta2PIX, drives formation of membrane ruffles and microvillus-like structures (via activation of Rac1 and Cdc42, respectively), indicating that its function requires localized activation of these GTPases. Thus, beta1PIX, like other RhoGEFs, exerts specific morphological functions that are dependent on its intracellular location and are mediated by its C-terminal dimerization domain.
PIX是一种与PAK结合的Rho家族鸟嘌呤核苷酸交换因子。我们之前描述过两种N端不同的PIX同工型。在此，我们报告了一种新的βPIX剪接变体的鉴定，命名为β2PIX，它是大脑中的主要类型，并且在β1PIX的C端缺少一个约120个残基的具有预测卷曲螺旋结构的区域。相反，β2PIX含有一个富含丝氨酸的C端。为了确定这些剪接变体在细胞功能上是否存在差异，我们研究了在HeLa细胞中表达这些蛋白质的效果。我们发现卷曲螺旋区域在β1PIX定位于细胞周边过程中起关键作用，并且还负责PIX的二聚化。β1PIX而非β2PIX的过表达驱动膜皱褶和微绒毛样结构的形成（分别通过激活Rac1和Cdc42），表明其功能需要这些GTP酶的局部激活。因此，β1PIX与其他RhoGEF一样，发挥特定的形态学功能，这些功能取决于其细胞内位置，并由其C端二聚化结构域介导。
