Control of vesicle fusion by a tyrosine phosphatase

Abstract

The tyrosine phosphatase PTP-MEG2 is targeted by its amino-terminal Sec14p homology domain to the membrane of secretory vesicles. There it regulates vesicle size by promoting homotypic vesicle fusion by a mechanism that requires its catalytic activity. Here, we identify N-ethylmaleimide-sensitive factor (NSF), a key regulator of vesicle fusion, as a substrate for PTP-MEG2. PTP-MEG2 reduced the phosphotyrosine content of NSF and co-localized with NSF and syntaxin 6 in intact cells. Furthermore, endogenous PTP-MEG2 co-immunoprecipitated with endogenous NSF. Phosphorylation of NSF at Tyr 83, as well as an acidic substitution at the same site, increased its ATPase activity and prevented alphaSNAP binding. Conversely, expression of a Y83F mutant of NSF caused spontaneous fusion events. Our results suggest that the molecular mechanism by which PTP-MEG2 promotes secretory vesicle fusion involves the local release of NSF from a tyrosine-phosphorylated, inactive state. This represents a novel mechanism for localized regulation of NSF and the first demonstrated role for a protein tyrosine phosphatase in the regulated secretory pathway.

The Protein Tyrosine Phosphatase SHP-1 Regulates Phagolysosome Biogenesis

“…This finding led the authors of that study to propose that protein phosphatase 1 may be part of a system other than SNARE complexes and NSFa S-nitrosoacetylpenicillamine, which catalyzes bilayer mixing. Similarly, PTP-MEG2 was shown to dephosphorylate NSF, thereby stimulating the homotypic fusion of secretory vesicles (15). PTPs can also negatively regulate phagosome acidification and recruitment of the v-ATPase by acting on the membrane fusion machinery.…”

“…Interestingly, characterization of the nonreceptor PTP MEG2 in neutrophils revealed that it is present on the cytoplasmic face of secretory vesicles, and is recruited to nascent phagosomes (14). A physiological substrate for PTP-MEG2 is the vesicle fusion protein Nethylmaleimide-sensitive factor (NSF), the dephosphorylation of which stimulates the homotypic fusion of secretory vesicles (15). Additional PTP-MEG2-interacting proteins are associated with vesicle traffic, small GTPases, and lipid interaction (16).…”

Circadian proteomics of the mouse retina

“…This mechanism enables transported vesicles to fuse continuously with objective membrane for the release of contained materials, such as receptors and neurotransmitters [30,31]. The function of NSF is known to be inhibited by PTM; Fes/Fer-mediated tyrosine phosphorylation [32], protein kinase C (PKC) -mediated serine phosphorylation [30], Pctaire1-mediated phosphorylation [33], and Snitrosylation [34]. Therefore, it is interesting to speculate that spot 709 and 713 represent differentially modified forms of NSF.…”

Protein-tyrosine Phosphatase 1B Modulates Early Endosome Fusion and Trafficking of Met and Epidermal Growth Factor Receptors

“…The activity of NSF is regulated via its phosphorylation status; the kinases Fes and Ca 2ϩ /calmodulin-dependent protein kinase II (40) and the phosphatases PTP-MEG2 (41) and PTP1B (42) have been shown to control NSF phosphorylation. PTP-MEG2 is located on the cytoplasmic face of secretory vesicles where it regulates vesicle size by promoting homotypic vesicle fusion via tyrosine dephosphorylation of NSF (41). Recently, PTP1B has been identified as a PTP that dephosphorylates NSF in acrosomes (42).…”