The discovery of a 3-phosphomonoesterase that hydrolyzes phosphatidylinositol 3-phosphate in NIH 3T3 cells.
Phosphatidylinositol 3-phosphate (PtdIns(3)P), a recently described phospholipid, has been linked to polyoma virus-induced cellular transformation and platelet-derived growth factor-mediated mitogenesis. PtdIns(3)P, in contrast to phosphatidylinositol, phosphatidylinositol 4-phosphate (PtdIns(4)P), and phosphatidylinositol 4,5-bisphosphate (PtdIns(4,5)P2), is resistant to hydrolysis by bovine brain phospholipase C gamma. We present here the identification of a phosphomonoesterase activity from the soluble fraction of NIH 3T3 cells which removes the phosphate from the D-3 position of PtdIns(3)P. This enzyme is specific as it has little or no activity on the monoester phosphates of PtdIns(4)P, PtdIns(4,5)P2, or inositol 1,3-bisphosphate and is tentatively designated phosphatidylinositol 3-phosphatase (PtdIns 3-phosphatase). The enzyme does not require added metal ions for activity and is maximally active in the presence of EDTA. It is inhibited by Ca2+, Mg2+, Zn2+, and the phosphatase inhibitor VO4(3-). In addition, there is no phospholipase C activity toward PtdIns(3)P in the soluble fraction of NIH 3T3 cells. In view of the absence of a phospholipase C activity that hydrolyzes PtdIns(3)P, we propose that PtdIns(3)P is not a precursor for a soluble inositol phosphate messenger but that it instead may act directly to control certain cellular processes or as a precursor for other phosphatidylinositols. PtdIns 3-phosphatase may thus terminate a metabolic signal or regulate precursor levels for other phosphatidylinositols that are phosphorylated in the D-3 position.
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Department of Internal Medicine, Washington University School of Medicine, St. Louis, Missouri 63110.
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D000818:Animals; D002478:Cells, Cultured; D002851:Chromatography, High Pressure Liquid; D002852:Chromatography, Ion Exchange; D006868:Hydrolysis; D007295:Inositol Phosphates / Q000302:isolation & purification; D007700:Kinetics; D051379:Mice; D008815:Mice, Inbred Strains; D018129:Phosphatidylinositol Phosphates; D010716:Phosphatidylinositols / Q000378:metabolism*; D010744:Phosphoric Monoester Hydrolases / Q000302:isolation & purification / Q000378:metabolism*
D007295:Inositol Phosphates; D018129:Phosphatidylinositol Phosphates; D010716:Phosphatidylinositols; C055525:phosphatidylinositol 3-phosphate; D010744:Phosphoric Monoester Hydrolases; C061816:phosphatidylinositol-3-phosphatase