Faucherre Adèle, Desbois Pierrette, Satre Véronique, Lunardi Joël, Dorseuil Olivier, Gacon Gérard
Institut Cochin, Département de Génétiques, Développement et Pathologie Moléculaire, INSERM U567/CNRS UMR8104/Université Paris V, France.
Hum Mol Genet. 2003 Oct 1;12(19):2449-56. doi: 10.1093/hmg/ddg250. Epub 2003 Jul 29.
The oculocerebrorenal syndrome of Lowe (OCRL) is a rare X-linked disorder characterized by severe mental retardation, congenital cataracts and renal Fanconi syndrome. OCRL1 protein is a phosphatidylinositol 4,5-bisphosphate 5-phosphatase with a C-terminal RhoGAP domain. Considering the pleiotropic cellular functions of Rho GTPases (Rho, Rac and Cdc42) and their dysregulation in several forms of mental retardation, we have investigated the so far unexplored function of the RhoGAP domain of OCRL1. Activated Rac GTPase was found to stably associate with the OCRL1 RhoGAP domain in vitro and to co-immunoprecipitate with endogenous OCRL1. Contrasting with other GAPs, OCRL1 RhoGAP exhibited a significant interaction with GDP bound Rac in vitro. As compared to Rac, other Rho GTPases tested showed reduced (Cdc42) or no binding (RhoA, RhoG) to OCRL1 RhoGAP. Immunofluorescence studies in HEK and COS7 cells and Golgi perturbation assays with Brefeldin A demonstrated that a fraction of endogenous Rac co-localizes with OCRL1 and gamma-adaptin in the trans-Golgi network. The OCRL1 RhoGAP domain showed low Rac GAP activity in vitro, and when expressed in Swiss 3T3 cells induced specific inhibition of RacGTP dependent ruffles, consistent with OCRL1 being an active RacGAP. OCRL1 appears to be a bifunctional protein which, in addition to its PIP2 5-phosphatase activity, binds to Rac GTPase. This novel property may play a role in localizing OCRL1 to the trans-Golgi network. Moreover, loss of OCRL1 RhoGAP and the resulting alteration in Rho pathways may contribute to mental retardation in Lowe syndrome, as illustrated in other forms of X-linked mental retardation.
洛氏眼脑肾综合征（OCRL）是一种罕见的X连锁疾病，其特征为严重智力发育迟缓、先天性白内障和肾范科尼综合征。OCRL1蛋白是一种具有C末端RhoGAP结构域的磷脂酰肌醇4,5 - 二磷酸5 - 磷酸酶。鉴于Rho GTP酶（Rho、Rac和Cdc42）具有多效性细胞功能且它们在多种形式的智力发育迟缓中失调，我们研究了OCRL1的RhoGAP结构域迄今未被探索的功能。发现活化的Rac GTP酶在体外与OCRL1 RhoGAP结构域稳定结合，并与内源性OCRL1进行共免疫沉淀。与其他GAP不同，OCRL1 RhoGAP在体外与结合GDP的Rac表现出显著相互作用。与Rac相比，所测试的其他Rho GTP酶与OCRL1 RhoGAP的结合减少（Cdc42）或无结合（RhoA、RhoG）。在HEK和COS7细胞中进行的免疫荧光研究以及用布雷菲德菌素A进行的高尔基体扰动试验表明，一部分内源性Rac与OCRL1和γ - 衔接蛋白在反式高尔基体网络中共定位。OCRL1 RhoGAP结构域在体外显示出低Rac GAP活性，并且当在瑞士3T3细胞中表达时可诱导对RacGTP依赖性褶皱的特异性抑制，这与OCRL1作为一种活性RacGAP一致。OCRL1似乎是一种双功能蛋白，除了其PIP2 5 - 磷酸酶活性外，还与Rac GTP酶结合。这种新特性可能在将OCRL1定位到反式高尔基体网络中起作用。此外，OCRL1 RhoGAP的缺失以及由此导致的Rho途径改变可能导致洛氏综合征中的智力发育迟缓，正如在其他形式的X连锁智力发育迟缓中所显示的那样。
