This cell line stably expresses low levels of Tubby-GFP, a specific biosensor of PtdIns(4,5)P2 (Quinn et al., 2008). human Lowe syndrome cells and rescues OCRL phenotypes in a zebrafish Lowe syndrome model. Our findings identify a novel PTEN/dPLCXD pathway AN3199 that controls PtdIns(4,5)P2 levels on endosomes. They also point to a potential new strategy for the treatment of Lowe syndrome. Introduction Phosphoinositides (PtdIns) are lipids composed by a membrane-associated diacylglycerol backbone linked to a cytoplasmic inositol ring. PtdIns regulate a number of cellular AN3199 processes including cell growth, survival, intracellular trafficking, and cell morphogenesis (Balla, 2013; Cauvin and Echard, 2015). You will find seven different PtdIns obtained by phosphorylation of the third and/or fourth and/or fifth position of the inositol ring (Fig. 1 A). More than 100 kinases, phosphatases, and phospholipases control the levels of PtdIns directly on membranes (Ilmonen et al., 2005; Balla, 2013). However, how these enzymes collaborate to control homeostasis of the different pools of PtdIns is usually poorly understood. Open in a separate window Physique 1. PTEN overexpression prevents cytokinesis and PtdIns(4,5)P2 homeostasis defects in dOCRL-depleted cells. (A) A schematic depicting the PtdIns pathway. (B) S2 cells were treated or not with dOCRL dsRNA, transfected after 4 d, and labeled for F-actin (reddish) and DNA (blue) after 2 d of expression of the indicated constructs. Asterisks show multinucleated cells. (C) Percentage of multinucleated S2 cells following the different indicated treatments; blue dots show individual independent experiments with 300 cells/experiment (bars represent mean and SD). P values were calculated using one-way ANOVA, Tukeys multiple comparisons test with a single pooled variance. (D) Tubby-GFP S2 cells were treated or not with dOCRL dsRNA. After 4 d of dsRNA treatment, cells were transfected with PTENC132S-mCherry (reddish). After two more days, cells were labeled for DNA (blue) and Tubby-GFP (anti-GFP antibody, green). (E) The ratio of Tubby-GFP fluorescence associated with endomembranes to that associated with the plasma membrane. P values were calculated using KruskalCWallis test and Dunns multiple comparisons test. = 1, total number of cells >40. Dots symbolize the ratio for a single cell; bars represent imply and SD. Bars, 10 m. **, P < 0.01; ****, P < 0.0001. ns, not significant. Dysregulation of PtdIns large quantity or distribution prospects to numerous pathologies including malignancy and genetic diseases (Viaud et al., 2016). For instance, mutation of the inositol polyphosphate-5-phosphatase OCRL1 causes the oculocerebrorenal Lowe syndrome and Dent-2 disease, two rare multisystemic orphan diseases (Pirruccello and AN3199 De Camilli, 2012; Mehta et al., 2014; De Matteis et al., 2017). Patients suffering from these diseases present with neurological defects, congenital cataracts, poor muscle firmness, and life-threatening kidney abnormalities and have a reduced life expectancy. There is no remedy for these diseases, and the therapeutic treatments only alleviate some symptoms. We AN3199 as well as others have previously reported that depletion of OCRL1 or depletion of dOCRL, its orthologue, causes several characteristic phenotypes: abnormal accumulation of KRT17 PtdIns(4,5)P2 on endosomes, disorganization of the endocytic compartments, and cytokinetic defects (Ungewickell et al., 2004; Choudhury et al., 2005; Erdmann et al., 2007; Ben El Kadhi et al., 2011, 2012; Dambournet et al., 2011; Vicinanza et al., 2011; Nndez et al., 2014; Cauvin et al., 2016; De Leo et al., 2016; Del Signore et al., 2017; Carim et al., 2019). In control dividing cells, PtdIns(4,5)P2 concentrates at the cortical equator (Emoto et al., 2005; Field et al., 2005; Roubinet et al., 2011) and recruits the cytokinetic machinery that allows subsequent cytokinesis (Ben El Kadhi et al., 2011; Liu et al., 2012; Cauvin and Echard, 2015). We found that by dephosphorylating PtdIns(4,5)P2 into PtdIns(4)P, both OCRL1 and dOCRL.