Regulation of myotubularin-related (MTMR)2 phosphatidylinositol phosphatase by MTMR5, a catalytically inactive phosphatase

Abstract

The myotubularin (MTM) family constitutes one of the most highly conserved protein-tyrosine phosphatase subfamilies in eukaryotes. MTM1, the archetypal member of this family, is mutated in X-linked myotubular myopathy, whereas mutations in the MTMrelated (MTMR)2 gene cause the type 4B1 Charcot-Marie-Tooth disease, a severe hereditary motor and sensory neuropathy. In this study, we identified a protein that specifically interacts with MTMR2 but not MTM1. The interacting protein was shown by mass spectrometry to be MTMR5, a catalytically inactive member of the MTM family. We also demonstrate that MTMR2 interacts with MTMR5 via its coiled-coil domain and that mutations in the coiledcoil domain of either MTMR2 or MTMR5 abrogate this interaction. Through this interaction, MTMR5 increases the enzymatic activity of MTMR2 and dictates its subcellular localization. This article demonstrates an active MTM member being regulated by an inactive family member.T he myotubularin (MTM) family constitutes one of the largest and most highly conserved protein-tyrosine phosphatase (PTP) subfamilies in eukaryotes (1-3). The human MTM family of phosphatases includes MTM1͞MTM-related (MTMR)1͞ MTMR2, MTMR3͞MTMR4, and MTMR6͞MTMR7͞MTMR8 subgroups (1, 3). The consensus CX 5 R active site motif is found in the MTM family and the sequence "CSDGWDR" is invariant within all of the enzymatically active members of this family. Most PTPs use phosphoproteins as substrates and specifically dephosphorylate substrates containing only phosphotyrosine sites. Other phosphatases, collectively known as dual-specificity phosphatases, are capable of removing phosphoserines͞ threonines and phosphotyrosines from protein substrates.Initially, MTM1 was reported to be a dual-specificity phosphatase (4-6). However, we and others have demonstrated that MTM1 utilizes the lipid second messenger, phosphatidylinositol 3-phosphate [PI(3)P], as a physiological substrate (7,8). Recent findings demonstrate that other MTMR phosphatases MTMR1, MTMR2, MTMR3, MTMR4, and MTMR6 also dephosphorylate PI(3)P, suggesting that activity toward this substrate is common to all active MTM family members (9-12). MTMR2 and MTMR3 have also been shown to dephosphorylate phosphatidylinositol 3,5-bisphosphate (9, 13). PI(3)P plays a key role in membrane trafficking͞vesicular transport processes and serves as a targeting mechanism for proteins containing specific PI(3)P-binding modules such as Fab1͞YOTB͞Vac1p͞EEA1 (FYVE), pleckstrin homology (PH), and Phox homology domains (14-17).To date, two MTMR proteins have been associated with human diseases. The MTM1 gene on chromosome Xq28 is mutated in X-linked myotubular myopathy, a severe congenital muscular disorder characterized by hypotonia and generalized muscle weakness in newborn males (18,19 MTM1 and MTMR2 are highly similar proteins (64% identity, 76% similarity), use the same physiologic substrate, and have a ubiquitous expression pattern (6, 9-12). However, mutations in MTM1 and MTMR2 cause different diseases with different target tissues...

Differential phosphorylation of the phosphoinositide 3-phosphatase MTMR2 regulates its association with early endosomal subtypes

“…This would be evident by the occurrence of a MTMR2 shift from the typical diffuse cytoplasmic pattern when phosphorylated (Berger et al, 2003;Franklin et al, 2011;Kim et al, 2003;Laporte et al, 2002), to an endosomal punctate pattern exhibited by unphosphorylated MTMR2 (Franklin et al, 2011). Consistent with the in vitro kinase assays, inhibitors to JNK and p38 did not alter the localization pattern of MTMR2 (Fig.…”

Membrane association of myotubularin-related protein 2 is mediated by a pleckstrin homology-GRAM domain and a coiled-coil dimerization module

“…In resting cells, Mtmr2 is localized mainly in the cytosol, with a stronger staining in the perinuclear region (Fig. 1B) (30,31). Studies with markers for the endoplasmic reticulum and the Golgi revealed partial colocalization, suggesting that some Mtmr2 may be associated with membranes of those organelles (data not shown).…”

Myotubularin-related protein (MTMR) 9 determines the enzymatic activity, substrate specificity, and role in autophagy of MTMR8

“…For example, the association of myotubularin (MTM1) with MTMR12 results in a threefold increase in the 3-phosphatase activity of MTM1, alters the subcellular localization of MTM1 from the plasma membrane to the cytosol, and attenuates the filopodia formation seen with MTM1 overexpression (21,22). MTMR2 binds to MTMR5 via the coiled-coil domains resulting in a three-to fourfold increase in 3-phosphatase activity and altered subcellular localization of MTMR2 (19). MTMR2 also binds to MTMR13, resulting in a dramatic increase in the catalytic activity of MTMR2 toward both PtdIns(3)P and PtdIns(3,5)P 2 (23).…”

“…The myotubularin family consists of 16 different proteins, 9 members of which possess catalytic activity (10,11) (16)(17)(18)(19)(20)(21). One mechanism that regulates the myotubularins is the formation of heterodimers between catalytically active and inactive proteins.…”