Year

2019

Season

Spring

Paper Type

Master's Thesis

College

College of Arts and Sciences

Degree Name

Master of Science (MS)

Department

Biology

NACO controlled Corporate Body

University of North Florida. Department of Biology

First Advisor

Dr. David Waddell

Second Advisor

Dr. Judith Ochrietor

Third Advisor

Dr. Michael Lentz

Department Chair

Dr. Cliff Ross

College Dean

Dr. George Rainbolt

Abstract

Dusp4 and Ppme1 have been identified as novel genes in skeletal muscle that are upregulated in response to neurogenic atrophy in a mouse model. Overexpression (OE) of Dusp4 wild-type (Dusp4-WT), as well as a Dusp4 Dominant Negative (Dusp4-DN) in C2C12 cells inhibits proper muscle differentiation potentially through its attenuation of ERK-MAPK signaling. Co-immunoprecipitation analysis shows Dusp4-DN associating with ERK1/2 but not p38, suggesting Dusp4 is specific for ERK1/2 but not p38. Quantitative PCR as well as Western blot analysis confirm that Ppme1 is expressed uniformly during muscle cell proliferation and differentiation. Interestingly, Ppme1 mRNA levels appear to decrease as differentiation proceeds whereas the protein levels remain constant throughout proliferation and differentiation. Transcriptional regulation of Ppme1 was observed by cloning proximal promoter fragments of the gene. The Ppme1 promoter is highly active on its own but when myogenic regulatory factors are ectopically expressed they repress promoter activity. Furthermore, mutation of a conserved E-box sequence inhibits full induction of the Ppme1 reporter gene , suggesting this E-box element is necessary for full Ppme1 expression. Additionally, inhibition of Ppme1 using a pharmacologic inhibitor results in delayed muscle cell differentiation and significant attenuation of AP-1 reporter activity. However, Ppme1 inhibition does not result in significant effects on phosphorylation of ERK1/2, c-Jun, or AKT. Additionally, C2C12 cells were treated with ERK1/2 and MEK1/2 inhibitors to compare results to that of Ppme1 inhibition and Dusp4 OE. While all of these conditions exhibit attenuation of AP-1 reporter activity, western blotting showed Dusp4 OE and Ppme1 inhibition do not mimic the results of ERK1/2 and MEK1/2 inhibition. Thus, Dusp4 and Ppme1 likely do not just block phosphorylation but act through more complex protein-protein interactions.

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