MK‐STYX alters localization dynamics of autophagosomes and phenotypic dynamics of lysosomes
Authors: Mattei Andrew M. , Christian Patrick , Hinton Shantá D. 
Published: June 2021

MK‐STYX[MAPK (mitogen‐activated protein kinase)phosphoserine/threonine/tyrosine‐binding protein] is a pseudophosphatase, a member of the dual‐specificity family subfamily of MAPK phosphatases (MKPs)that lack the essential nucleophilic cysteine in its signature motif required for catalytic activity. MK‐STYX maintains its three dimensional fold and ability to bind proteins; it is involved in cellular pathways such as those for stress response, apoptosis, and neuronal differentiation. Previously, were ported that MK‐STYX interacts with G3BP‐1 [Ras‐GAP (GTPAse‐activating protein) SH3 (Src homology 3) domain binding protein‐1], and inhibits stress granule formation. Stress granules, cytoplasmic storage sites for mRNA, form as a protective mechanism against stress caused by UV irradiation, hypoxia, and heat shock. Stress induces stress granules, and involves many cellular mechanisms such as post‐translational modifications, protein‐protein interactions, and microtubule networks. Furthermore, stress granules are targeted and cleared by autophagy, an initiated response to cellular stress. They are responsible for the degradation of cellular components. Therefore, autophagy is essential for cellular degradation. Since autophagy and MK‐STYX each negatively affect stress granule assembly, we sought to determine whether MK‐STYX has a role in autophagy. Pursuing the role of MK‐STYX in regulating autophagy will enhance our understanding of MK‐STYX's mechanism in the stress response pathway. Our studies show that MK‐STYX causes cytosolic TFEB (Transcription factor E‐Box; the autophagy “master switch”) to form perinuclear aggregates independent of nutrient status. Whereas, MK‐STYXactive (active mutant in which catalytic activity has been “restored”), only increased TFEB cytosolic aggregates in serum starved cells, suggesting that the catalytic signature motif of MK‐STYX may play a role in stress responses. TFEB is also found to localize to the lysosomal surface, acting as negative regulator of lysosomal and autophagosomal biogenesis. MK‐STYX alters lysosomal and autophagosomal dynamics; oversized lysosomes are observed in the presence of MK‐STYX. Furthermore, autophagosomes localize to the distal ends of HEK/293 cellular extensions in the presence of MK‐STYX. Autophagy plays a major role in major cellular processes ranging from initial developmental stages to the onset of progressive human pathologies such as neurodegenerative diseases and cancer. These studies suggest that MK‐STYX may have an important role in autophagy.

Support or Funding Information

This work was supported by the National Science Foundation Grant MCB1113167 to S.D.H.; Coco Award to S.D.H.; Howard Hughes Medical Research Institute grant through the Undergraduate Science Education Program to the College of William and Mary (HHMI Summer Fellowships to P.C. and A.M.).

This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.