Environmental Health Science Laboratory, Sumitomo Chemical Co., Ltd., Konohana-ku, Osaka 554-8558, Japan.
Biochem Biophys Res Commun. 2011 Dec 16;416(3-4):385-90. doi: 10.1016/j.bbrc.2011.11.049. Epub 2011 Nov 19.
XLGα(olf) is an extra large transcriptional variant of the heterotrimeric G protein, Gα(olf), which we previously reported to be localized in the Golgi apparatus and interacted with Rab3A and Rab8A through its N-terminal region. However, many physiological functions of XLGα(olf) remain to be elucidated. In this study, performance of yeast two-hybrid screening with XLGα(olf) allowed isolation of COP9 signalosome subunit 5 (CSN5), known to regulate the p27(Kip1) protein level through a proteasome dependent pathway. Co-immunoprecipitation experiments followed by Western blotting also showed association of CSN5 with XLGα(olf) linked to down-regulation of p27(Kip1). Gene silencing of endogenous CSN5 by siRNA attenuated the XLGα(olf)-mediated down-regulation, which was also demonstrated to require CDK2. Both knock down of CDK2 and the treatment with a CDK2 inhibitor reversed the reduction of p27(Kip1) due to XLGα(olf). Our findings provide important clues to understanding physiological functions of XLGα(olf).
XLGα(olf) 是三聚体 G 蛋白 Gα(olf) 的一个特大转录变体，我们之前曾报道其定位于高尔基体，通过其 N 端区域与 Rab3A 和 Rab8A 相互作用。然而，XLGα(olf) 的许多生理功能仍有待阐明。在这项研究中，我们利用 XLGα(olf) 进行酵母双杂交筛选，分离到了 COP9 信号小体亚基 5（CSN5），已知其通过蛋白酶体依赖的途径调节 p27(Kip1) 蛋白水平。随后的免疫共沉淀实验和 Western blot 也表明 CSN5 与 XLGα(olf) 相关联，导致 p27(Kip1)下调。通过 siRNA 对内源性 CSN5 的基因沉默减弱了 XLGα(olf)介导的下调，这也表明需要 CDK2。敲低 CDK2 和用 CDK2 抑制剂处理均可逆转由于 XLGα(olf)导致的 p27(Kip1)减少。我们的研究结果为理解 XLGα(olf) 的生理功能提供了重要线索。
