Publication Date

Fall 2016

Degree Type

Thesis

Degree Name

Master of Science (MS)

Department

Biological Sciences

Advisor

J. Brandon White

Keywords

Mastermind, Myocyte Enhancer Factor 2 C, myogenesis, Notch signaling, transcription regulation, ubiquitin proteasome pathway

Subject Areas

Molecular biology

Abstract

Mastermind-like 1 (MAML1) is well characterized for its involvement in the Notch signaling pathway where it functions as a transcriptional co-activator and facilitates the degradation of the Notch intracellular domain (NICD). MAML1 has recently been implicated as a multifunctional protein that interacts with a variety of other signaling pathways, including Wnt-β-catenin, NF-B, and MEF2C (myocyte enhancer factor 2C). MEF2C is a member of the family of transcription factors involved in muscle cell differentiation and proliferation. MAML1 has previously been shown to activate MEF2C transcription. Given that MAML1 is responsible for degradation of the NICD, we wanted to know if MAML1 could also induce degradation of MEF2C. Here we show that full length MAML1 induces degradation of MEF2C. MEF2C is not degraded when co-expressed with MAML1 deletion constructs, MAML1 1-301 and MAML1 Δ75-300, suggesting the entire c-terminus is needed for degradation. In addition, treatment with the proteasome inhibitor MG132 stabilized MEF2C expression both in the absence and presence of MAML1 when compared to dimethyl sulfoxide (DMSO) controls. Immuno-preciptations of MEF2C in the presence of MAML1 with MG132 treatment showed an increase in the amount of ubiquitin detected. Serine 98 and 110 in MEF2C appear to be essential for ubiquitination. In order to determine if S98 and S110 are required for MAML1 degradation of MEF2C, we cloned the double serine mutant MEF2C S98A S110A. However, co-expression of the mutant with MAML1 still resulted in decreased protein levels. Our results showed MAML1-induced degradation of MEF2C occurs through the proteasomal pathway and that S98 and S110 are not required for degradation.

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