Production of phosphatidylinositol 5-phosphate by the phosphoinositide 3-phosphatase myotubularin in mammalian cells.
MTM1, the gene encoding myotubularin (MTM1), is mutated in the X-linked myotubular myopathy (XLMTM), a severe genetic muscular disorder. MTM1 is a phosphoinositide phosphatase hydrolyzing phosphatidylinositol 3-phosphate (PtdIns(3)P) in yeast and in vitro. Because this lipid is implicated in the regulation of vesicular trafficking, we used established cell lines from XLMTM patients to evaluate whether the lack of endogenous MTM1 expression could affect PtdIns(3)P labeling patterns. Our results showed that the vesicular trafficking related to early endosomes was not significantly affected in the XLMTM cell lines compared with control cells. However, in addition to PtdIns(3)P, we found that MTM1 can hydrolyze phosphatidylinositol 3,5-bisphosphate both in vitro and in mammalian cells. Using a mass assay, we demonstrated that the product generated is phosphatidylinositol 5-phosphate (PtdIns(5)P), a recently discovered phosphoinositide, the function of which is still unknown. In L6 myotubes overexpressing MTM1, hyperosmotic shock induced an increase in the mass level of PtdIns(5)P that was reduced by 50% upon overexpression of the MTM1 inactive mutant D278A. These data demonstrate for the first time a role for MTM1 in the production of PtdIns(5)P in mammalian cells, suggesting that the lack of transformation of phosphatidylinositol 3,5-bisphosphate into PtdIns(5)P might be an important component in the etiology of myotubular myopathy.
Tronchère
Hélène
H
INSERM U563, Département d'Oncogenèse et Signalisation dans les Cellules Hématopoïétiques, CPTP, IFR 30, Hôpital Purpan, 31059 Toulouse Cedex, France. helenetro@toulouse.inserm.fr
Laporte
Jocelyn
J
Pendaries
Caroline
C
Chaussade
Claire
C
Liaubet
Laurence
L
Pirola
Luciano
L
Mandel
Jean-Louis
JL
Payrastre
Bernard
B
D000818:Animals; D001692:Biological Transport; D019556:COS Cells; D002460:Cell Line; D002478:Cells, Cultured; D003001:Cloning, Molecular; D004305:Dose-Response Relationship, Drug; D011992:Endosomes / Q000378:metabolism; D005347:Fibroblasts / Q000378:metabolism; D008040:Genetic Linkage; D049452:Green Fluorescent Proteins; D006801:Humans; D006868:Hydrolysis; D019169:Jurkat Cells; D008164:Luminescent Proteins / Q000378:metabolism; D008856:Microscopy, Fluorescence; D009154:Mutation; D020914:Myopathies, Structural, Congenital / Q000378:metabolism; D018129:Phosphatidylinositol Phosphates / Q000096:biosynthesis* / Q000737:chemistry; D010744:Phosphoric Monoester Hydrolases / Q000737:chemistry*; D017027:Protein Tyrosine Phosphatases / Q000096:biosynthesis / Q000737:chemistry* / Q000502:physiology*; D054558:Protein Tyrosine Phosphatases, Non-Receptor; D051381:Rats; D011994:Recombinant Proteins / Q000737:chemistry; D013379:Substrate Specificity; D013997:Time Factors; D014960:X Chromosome / Q000235:genetics; D000099182:Phosphoinositide 5-Phosphatases
D049452:Green Fluorescent Proteins; D008164:Luminescent Proteins; D018129:Phosphatidylinositol Phosphates; D010744:Phosphoric Monoester Hydrolases; D017027:Protein Tyrosine Phosphatases; D054558:Protein Tyrosine Phosphatases, Non-Receptor; D011994:Recombinant Proteins; D000099182:Phosphoinositide 5-Phosphatases; C113567:phosphatidylinositol 5-phosphate; C099588:myotubularin