The inositol polyphosphate 5-phosphatase Ocrl associates with endosomes that are partially coated with clathrin

Abstract

The subcellular localization of Ocrl, the inositol polyphosphate 5-phosphatase that is mutated in Lowe syndrome, was investigated by fluorescence microscopy. Ocrl was localized to endosomes and Golgi membranes along with clathrin, giantin, the mannose 6-phosphate receptor, transferrin, and the early endosomal antigen 1 endosomal marker in fixed cells. The endosomal localization of Ocrl was confirmed by live-cell time-lapse microscopy in which we monitored the dynamics of Ocrl on endosomes. GST binding assays show that Ocrl interacts with the clathrin terminal domain and the clathrin adaptor protein AP-2. Our findings suggest a role for Ocrl in endosomal receptor trafficking and sorting.

Clathrin-dependent Association of CVAK104 with Endosomes and theTrans-Golgi Network

“…Furthermore, in COS-7 cells that expressed the FLAGtagged phosphatidyl inositol 5-phosphatase OCRL and GFP-CVAK104, we noted extensive colocalization of the two proteins in the perinuclear area ( Figure 4C). Previous work had shown that OCRL localizes to endosomes and the TGN (Ungewickell et al, 2004;Lowe, 2005). CVAK104 overlapped also significantly with the adaptor protein complex AP3, which is involved in the sorting of lysosomal membrane proteins (Le Borgne et al, 1998;Rous et al, 2002) (Figure 4C).…”

All known patient mutations in the ASH-RhoGAP domains of OCRL affect targeting and APPL1 binding

“…OCRL was initially localized to the Golgi complex [9,10]. Recently, OCRL was also found to have a prominent localization on endosomes and to be important at early stations of the endocytic pathway, including clathrincoated pits [11], consistent with its ability to bind clathrin, the endocytic clathrin adaptor AP-2, the endosomal protein Rab5, and the plasma membrane associated Rho family GTPases Rac and Cdc42 [12][13][14][15]. In addition, OCRL was also found to bind to, and colocalize on endosomes with, APPL1, an endosomal adaptor protein and another Rab5 interactor [11].…”

Targeting of the type II inositol polyphosphate 5-phosphatase INPP5B to the early secretory pathway

“…This pathway probably links growth factor signalling with membrane dynamics in the endocytic pathway. Like INPP5B, OCRL1 is found in lamellipodia and endosomes, but it is also abundant at the Golgi apparatus Faucherre et al, 2005;Olivos-Glander et al, 1995;Ungewickell et al, 2004). It can interact with RAC1, components of the clathrin coat and both secretory and endosomal RAB proteins Faucherre et al, 2003;Hyvola et al, 2006;Ungewickell et al, 2004).…”