Advisory Committee Chair
Xu Cao
Advisory Committee Members
Jeffrey E Kudlow
Andrew J Paterson
Elias Meezan
Marcas Bamman
Michael Ruppert
Document Type
Dissertation
Date of Award
2007
Abstract
O-glycosylation, a type of posttranslational modification, is abundant and dynamic in the cell, yet its function in cell signaling and destiny regulation is far from known. This study examines the effects of O-glycosylation on muscle differentiation and metabolism, and the potential mechanism behind the effects: proteasome blockade. Proteasome action is required for muscle differentiation. We previously have shown that O-GlcNAc modification of the 19S cap of the proteasome can inhibit the proteolytic function of this organelle. By changing O-GlcNAc modification levels and proteasome function independently in C2C12 skeletal myoblasts, we have found that myoblast differentiation is largely dependent on both. Decreasing O-GlcNAcylation by overexpression of full length Nuclear Cytoplasmic O-GlcNAcase and AcetylTransferase (NCOAT), differentiation was accelerated concomitantly with increased proteasome activity. Conversely, overexpression of GK-NCOAT, a splice variant lacking OGlcNAcase activity, acted as a dominant-negative, increasing cellular protein-O-GlcNAc levels, decreasing proteasome activity and retarding differentiation of myoblasts. Chemical inhibition of O-GlcNAcase also inhibited both proteasome function and C2C12 terminal differentiation. Independently inhibiting proteasome proteases also inhibited muscle differentiation. The mechanism likely results from the inhibition of proteasomes, either directly or with O-GlcNAc, which interferes with the formation of E47-MyoD complexes, which bind to DNA, activate muscle specific gene expression and initiate muscle differentiation. The apoptotic death of pancreatic β-cells caused by STZ, an irreversible NCOAT inhibitor, implies a further hypothesis: irreversible NCOAT inhibition leads to the accumulation of O-GlcNAc on the proteasome and its dysfunction. This loss of function of the proteasome would result in the accumulation of proapoptotic factors and the destiny of apoptotic death for the cell. The current work demonstrates that the increased Oglycosylation levels in muscle inhibit the proteasome function in vivo, and lead to the apoptosis of skeletal muscle and eventually the death of the animal. Dominant negative NCOAT-mediated loss of proteasome function is associated with accumulation of proapoptotic factors and the activation of the apoptotic pathway. This work demonstrates that O-glycosylation inhibits proteasome function and its physiological effects. Furthermore, these studies provide a logical explanation for the association of muscle function with metabolic regulation by O-glycosylation.
Recommended Citation
Huang, Ping, "O -GlcNAc modification in muscle development" (2007). All ETDs from UAB. 6810.
https://digitalcommons.library.uab.edu/etd-collection/6810