tumor cell migration and invasion are enhanced by depletion of Rap1 GTPase summary paper

tumor cell migration and invasion are enhanced by depletion of Rap1 GTPase summary paper

Human Molecular Genetics, 2009, Vol. 18, No. 23 4478-4491 doi: 10. 1093/hmg/ddp407 Advance Access published on August 21, 2009
Lowe syndrome patient fibroblasts display ‘Dull-specific cell migration defects that cannot be rescued by the homologous Inpp5b phosphatase
Brian G. Coon1,2, Debarati Mukherjee1,2, Claudia B. Hanna1,2, David J. Riese 112, Martin Lowe3 and R. Claudio Aguilar1,2,*
‘Department of Biological Sciences and 2Purdue Center for Cancer Research, Purdue University, West Lafayette, IN 47907, USA and 3Faculty of Life Sciences, University of Manchester, Manchester M13 9PT, UK
Received May 20, 2009; Revised July 24, 2009; Accepted August 20, 2009
The Lowe syndrome (LS) is a life-threatening, developmental disease characterized by mental retardation, cataracts and renal failure. Although this human illness has been linked to defective function of the phospha-tidylinositol 5-phosphatase, OcrI1 (Oculo-Cerebro-Renal syndrome of Lowe protein 1), the mechanism by which this enzyme deficiency triggers the disease is not clear. OcrI1 is known to localize mainly to the Golgi apparatus and endosomes, however it translocates to plasma membrane ruffles upon cell stimulation with growth factors. The functional implications of this inducible translocation to the plasma membrane are presently unknown. Here we show that OcrI1 is required for proper cell migration, spreading and fluid-phase uptake in both established cell lines and human dermal fibroblasts. We found that primary fibroblasts from two patients diagnosed with LS displayed defects in these cellular processes. Importantly, these abnormal-ities were suppressed by expressing wild-type OcrI1 but not by a phosphatase-deficient mutant. Interestingly, the homologous human PI-5-phosphatase, Inpp5b, was unable to complement the OcrI1-dependent cell migration defect. Further, OcrI1 variants that cannot bind the endocytic adaptor AP2 or clathrin, like Inpp5b, were less apt to rescue the migration phenotype. However, no defect in membrane recruitment of AP2/clathrin or in transferrin endocytosis by patient cells was detected. Collectively, our results suggest that Ocr11, but not Inpp5b, is involved in ruffle-mediated membrane remodeling. Our results provide new elements for understanding how OcrI1 deficiency leads to the abnormalities associated with the LS.
INTRODUCTION
The Oculo-Cerebro-Renal syndrome of Lowe (OCRL) is a recessive, X-linked genetic disease characterized by the pres-ence of congenital cataracts, mental retardation and renal dys-function (1-3). This disorder is associated with abnormal function of the Inositol 5-phosphatase (EC 3.1.3.36) Ocrll, responsible for the hydrolysis of Phosphatidyl Inositol (Ptdlns) 5-phosphates including Ptdlns (4,5) bi-phosphate (PIP2) (4-7), a plasma membrane-enriched phospholipid. Most OCRL1 gene mutations found in Lowe syndrome (LS) patients either lead to absence of the gene product or to deficient phosphatase activity (4,8). Indeed, cells of LS
patients frequently possess higher intracellular levels of PIP2 than do normal cells (6,9). However, it is still uncertain how this lipid imbalance, or the lack of Ocrll, causes the develop-mental abnormalities that characterize the disease. Although Ocrll primarily localizes to the Golgi apparatus (1,10,11) and early endosomes (12-15), the pioneering work of Faucherre et al. (9) demonstrates that this protein also trans-locates to membrane ruffles upon stimulation of growth factor receptors. Therefore, we and others (9) have speculated that this protein might be relevant to processes that require plasma membrane remodeling, such as cell migration. Here we report a novel cellular phenotype associated with LS. Relative to fibroblasts from normal individuals, LS
*To whom correspondence should be addressed. +1 7654963547; Fax: +1 7654961496; Email: [email protected]
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