title: The pseudophosphatase MK-STYX inhibits stress granule assembly independently of Ser149 phosphorylation of G3BP-1.
abstract: The pseudophosphatase MK-STYX (mitogen-activated protein kinase phosphoserine/threonine/tyrosine-binding protein) has been implicated in the stress response pathway. The expression of MK-STYX inhibits the assembly of stress granules, which are cytoplasmic storage sites for mRNA that form as a protective mechanism against stressors such as heat shock, UV irradiation and hypoxia. Furthermore, MK-STYX interacts with a key component of stress granules: G3BP-1 (Ras-GTPase activating protein SH3 domain binding protein-1). Because G3BP-1 dephosphorylation at Ser149 induces stress granule assembly, we initially hypothesized that the inhibition of stress granules by MK-STYX was G3BP-1 phosphorylation-dependent. However, in the present study, using MK-STYX constructs and G3BP-1 phosphomimetic or nonphosphorylatable mutants, we show that MK-STYX inhibits stress granule formation independently of G3BP-1 phosphorylation at Ser149. The introduction of point mutations at the 'active site' of MK-STYX that convert serine and phenylalanine to histidine and cysteine, respectively, is sufficient to generate an active enzyme. In separate experiments, we show that this active mutant, MK-STYX(active), has opposite effects to wild-type MK-STYK. Not only does MK-STYX(active) induce stress granules, but also it has the capacity to dephosphorylate G3BP-1. Taken together, these results provide evidence that the pseudophosphatase MK-STYX plays a key role in the cellular response to stress.
authors.affiliation: Department of Biology, Integrated Science Center, College of William and Mary, Williamsburg, VA 23185, USA.
authors.forename: Justinn E
authors.initials: JE
authors.lastname: Barr
authors.forename: Michelle R
authors.initials: MR
authors.lastname: Munyikwa
authors.forename: Elizabeth A
authors.initials: EA
authors.lastname: Frazier
authors.forename: Shantá D
authors.initials: SD
authors.lastname: Hinton
mesh_terms: D019943:Amino Acid Substitution; D051017:Apoptosis Regulatory Proteins / Q000235:genetics / Q000378:metabolism*; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D003594:Cytoplasmic Granules / Q000378:metabolism*; D004265:DNA Helicases; D006367:HeLa Cells; D006801:Humans; D010766:Phosphorylation; D000075223:Poly-ADP-Ribose Binding Proteins; D011499:Protein Processing, Post-Translational; D020365:RNA Helicases; D000067776:RNA Recognition Motif Proteins; D012694:Serine / Q000378:metabolism; D015398:Signal Transduction; D013312:Stress, Physiological
chemical_list: D051017:Apoptosis Regulatory Proteins; D002352:Carrier Proteins; D000075223:Poly-ADP-Ribose Binding Proteins; D000067776:RNA Recognition Motif Proteins; C558168:STYXL1 protein, human; D012694:Serine; D004265:DNA Helicases; C116070:G3BP1 protein, human; D020365:RNA Helicases