Date Thesis Awarded
Honors Thesis -- Access Restricted On-Campus Only
Bachelors of Science (BS)
Shantá D. Hinton
Deborah C. Bebout
Mark H. Forsyth
Pseudoenzymes have recently sparked interest in the world of biology. Ten percent of the human genome codes for pseudoenzymes. These proteins have remained conserved through evolutionary history and perform unique cellular functions despite their loss of catalytic activity. Mitogen activated protein kinase phosphoserine/threonine/tyrosine binding protein (MK-STYX) is a pseudophosphatase; it binds but does not remove phosphate groups from phosphorylated proteins. Lacking phosphatase activity does not translate to lack of function; MK-STYX has important cellular functions such as reducing stress granule formation, inducing neurite formation, and promoting mitochondria-mediated apoptosis. Previous studies found that MK-STYX binds Ras GTPase activating protein binding protein 1 (G3BP-1), key stress granule nucleator, and reduces stress granule formation independent of G3BP-1 phosphorylation. The mechanism of how MK-STYX reduces stress granule formation remains unclear. Autophagy, a cellular degradation pathway, has been shown to clear stress granules in cells. Due to the common outcome of both pathways, the present study explores the autophagy pathway as a possible method behind MK-STYX’s ability to reduce stress granule formation. In particular, the present study investigates whether MK-STYX clears stress granules by modulating the key autophagy protein, microtubule associated protein light chain 3 (LC3). Irreversible post- translational modifications of LC3 result in successful autophagic degradation. Pilot studies show that MK-STYX increases LC3 phosphorylation. Because LC3 involvement in autophagy depends heavily on the phosphorylation site, it is important to understand the effects of MK-STYX on LC3 dynamics.
Using fluorescence microscopy, the degree of MK-STYX colocalization with LC3B (the most common isoform) was tested. Immunoblotting was used to measure the levels of unphosphorylated LC3B and phosphorylated LC3B at Serine 12 (an inhibitory phosphorylation site) in the absence and overexpression of MK-STYX. The data suggests that MK-STYX increases LC3B phosphorylation at Serine 12 in basal cell conditions and decreases LC3B phosphorylation at Serine 12 during serum starvation. This means that MK-STYX may increase autophagy pathway activity and autophagic degradation during stressful conditions such as serum starvation, which are prime conditions for stress granule formation and persistence. These results demonstrate that MK-STYX has a strong potential to modulate autophagy to reduce stress granule formation and serve as the foundation for further analysis.
Prioleau, Tatiana, "Evaluating Autophagy as a Mechanism for MK-STYX-induced Stress Granule Reduction" (2021). Undergraduate Honors Theses. William & Mary. Paper 1639.
Available for download on Wednesday, May 13, 2026
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