Author ORCID Identifier

0000-0003-2312-8536

Date of Graduation

8-2019

Document Type

Thesis (MS)

Program Affiliation

Biomedical Sciences

Degree Name

Masters of Science (MS)

Advisor/Committee Chair

Seung-Hee Yoo

Committee Member

Mark J. Burish

Committee Member

Zheng Chen

Committee Member

Harry Karmouty-Quintana

Committee Member

Darren Boehning

Abstract

Protein turnover is one of the most essential mechanisms controlling circadian rhythms. F-Box and Leucine Rich Repeat Protein21 (FBXL21) is a circadian E3 ligase which shows oscillatory mRNA transcripts and protein levels. It was previously found to perform subcellular compartment-specific E3 ligase activities targeting the core clock proteins CRYPTOCHROME(CRY)1/2. Here we identified a new sarcomeric target substrate, Telethonin(TCAP), which also shows circadian oscillation in its mRNA transcript and protein expression and, importantly, interaction with FBXL21 in an anti-phasic manner. Via computational and pharmacological tests, we identified Glycogen Synthase Kinase-3β(GSK-3β) as a regulator of FBXL21. Biochemical and molecular characterizations demonstrated that GSK-3β interacts with both FBXL21 and TCAP and affects Skp, Cullin1(Cul1), F-box containing (SCF) complex/E3 ligase-Substrate complex formation. Interestingly, GSK-3β knockdown significantly inhibited FBXL21-CUL11 and FBXL21-TCAP complex formation. These results revealed a new circadian regulatory pathway that FBXL21 regulates TCAP via ubiquitin-mediated proteasomal pathway in the cytoplasm coordinatively with GSK-3β.

Keywords

FBXL21, TCAP, Telethonin, GSK-3β, E3 ligase, SCF complex, Circadian, Ubiquitin, Proteasomal pathway

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