Lowe syndrome protein Ocrl1 is translocated to membrane ruffles upon Rac GTPase activation : a new perspective on Lowe syndrome pathophysiology

Faucherre A, Desbois P, Nagano F, Satre V, Lunardi J, Gacon G and Dorseuil O
Source: Hum Mol Genet
Publication Date: (2005)
Issue: 14(11): 1441-1448
Research Area:
Dermatology/Tissue Engineering
Cells used in publication:
Fibroblast, dermal (NHDF-Neo), human neonatal
Species: human
Tissue Origin: dermal
Fibroblast, dermal(NHDF-Ad), human adult
Species: human
Tissue Origin: dermal
Nucleofector® I/II/2b
Oculocerebrorenal Lowe syndrome is a rare X -linked disorder characterized by bilateral cataract, mental retardation and renal Fanconi syndrome. The Lowe syndrome protein Ocrl1 is a PIP2 5-phosphatase, primarily localized to the trans-Golgi network (TGN), which << loss of function >> mutations result in PIP2 accumulation in patient's cells. Since PIP2 is involved in many cell functions including signalling, vesicle trafficking and actin polymerization, it has been difficult so far to decipher molecular/cellular mechanisms responsible for Lowe syndrome phenotype. We have recently shown that, through its C-terminal Rho GAP domain, Ocrl1 forms a stable complex with Rac GTPase within the cell. In line with this finding, we report here that upon EGF induced Rac activation in COS-7 cells, a fraction of Ocrl1 translocates from TGN to plasma membrane and concentrates in membrane ruffles. In order to investigate the functionality of Ocrl1 in plasma membrane, we have analysed PIP2 distribution in human dermal fibroblasts (HDF) from Lowe patients vs control HDF. As revealed by both immunodetection and GFP-PH binding, PIP2 was found strikingly to accumulate in PDGF induced ruffles in Lowe HDF as compared to control. This suggests that Ocrl1 is active as a PIP2 5-phosphatase in Rac induced membrane ruffles. Cellular properties such as cell migration and establishment of cell-cell contacts which depend on ruffling and lamellipodia formation, should be further investigated to understand the pathophysiology of Lowe syndrome.