title: The myotubularin phosphatase MTMR4 regulates sorting from early endosomes.
abstract: Phosphatidylinositol 3-phosphate [PtdIns(3)P] regulates endocytic trafficking and the sorting of receptors through early endosomes, including the rapid recycling of transferrin (Tfn). However, the phosphoinositide phosphatase that selectively opposes this function is unknown. The myotubularins are a family of eight catalytically active and six inactive enzymes that hydrolyse PtdIns(3)P to form PtdIns. However, the role each myotubularin family member plays in regulating endosomal PtdIns(3)P and thereby endocytic trafficking is not well established. Here, we identify the myotubularin family member MTMR4, which localizes to early endosomes and also to Rab11- and Sec15-positive recycling endosomes. In cells with MTMR4 knockdown, or following expression of the catalytically inactive MTMR4, MTMR4(C407A), the number of PtdIns(3)P-decorated endosomes significantly increased. MTMR4 overexpression delayed the exit of Tfn from early endosomes and its recycling to the plasma membrane. By contrast, expression of MTMR4(C407A), which acts as a dominant-negative construct, significantly accelerated Tfn recycling. However, in MTMR4 knockdown cells Tfn recycling was unchanged, suggesting that other MTMs might also contribute to recycling. MTMR4 regulated the subcellular distribution of Rab11 and, in cells with RNAi-mediated knockdown of MTMR4, Rab11 was directed away from the pericentriolar recycling compartment. The subcellular distribution of VAMP3, a v-SNARE protein that resides in recycling endosomes and endosome-derived transport vesicles, was also regulated by MTMR4. Therefore, MTMR4 localizes at the interface of early and recycling endosomes to regulate trafficking through this pathway.
authors.affiliation: Department of Biochemistry and Molecular Biology, Monash University, Wellington Road, Clayton 3800, Australia.
authors.forename: Monica J
authors.initials: MJ
authors.lastname: Naughtin
authors.forename: David A
authors.initials: DA
authors.lastname: Sheffield
authors.forename: Parvin
authors.initials: P
authors.lastname: Rahman
authors.forename: William E
authors.initials: WE
authors.lastname: Hughes
authors.forename: Rajendra
authors.initials: R
authors.lastname: Gurung
authors.forename: Jennifer L
authors.initials: JL
authors.lastname: Stow
authors.forename: Harshal H
authors.initials: HH
authors.lastname: Nandurkar
authors.forename: Jennifer M
authors.initials: JM
authors.lastname: Dyson
authors.forename: Christina A
authors.initials: CA
authors.lastname: Mitchell
mesh_terms: D000818:Animals; D001692:Biological Transport; D019556:COS Cells; D002460:Cell Line; D002522:Chlorocebus aethiops; D011992:Endosomes / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism; D006801:Humans; D018129:Phosphatidylinositol Phosphates / Q000378:metabolism; D021381:Protein Transport; D054558:Protein Tyrosine Phosphatases, Non-Receptor / Q000235:genetics / Q000378:metabolism*
chemical_list: D018129:Phosphatidylinositol Phosphates; C055525:phosphatidylinositol 3-phosphate; C427064:MTMR4 protein, human; D054558:Protein Tyrosine Phosphatases, Non-Receptor