The Critical Role of the Ubiquitin Ligase System in Pancreatic Beta Cells Alexis Oguh

Format:

Book

Thesis/Dissertation

Author/Creator:

Oguh, Alexis, author.

Contributor:

University of Pennsylvania. Cell and Molecular Biology., degree granting institution.

Language:

English

Subjects (All):

Genetics.

Molecular biology.

Cellular biology.

0369.

0307.

0379.

Local Subjects:

Genetics.

Molecular biology.

Cellular biology.

0369.

0307.

0379.

Physical Description:

1 electronic resource (167 pages)

Contained In:

Dissertations Abstracts International 86-12B

Place of Publication:

Ann Arbor : ProQuest Dissertations and Theses, 2025

Language Note:

English

Summary:

Post-translational modifications control protein function by modulating a multitude of factors including protein stability. Given that there is dysregulated expression of key pancreatic β cell proteins in all forms of diabetes, understanding mechanisms that control protein turnover is important to developing therapies to treat the disease. Here, I explore the potential roles of regulators of protein stability in maintaining β cell function. Stability of the key β cell transcription factor PDX1 has been shown to be regulated by several mechanisms. The Cullin-3 E3 ligase adaptor protein, SPOP, targets PDX1 for ubiquitination and proteasomal degradation. Additionally, phosphorylation in the PDX1 C terminus by the kinase GSK3β in response to low glucose and glucolipotoxicity destabilizes PDX1. This suggests a functional role for SPOP and raises the question of other undiscovered regulatory phosphorylation sites in β cells. In this study I generate a β cell specific Spop deletion mouse strain (SpopβKO) and find that Spop is necessary to prevent aberrant basal insulin secretion and for maintaining glucose- stimulated insulin secretion. Transcription factor-regulatory gene network and biochemical analyses finds that Spop prevents hyper-activation of the IRE1α-XBP1 axis of unfolded protein response signaling and that SPOP is ER-stress regulated. Next, I determine how acute low and high glucose exposure shape the β cell phosphoproteome. In a preliminary experiment I used mass spectrometry with Glu-C enzyme digestion to identify novel glucose-dependent phosphorylation sites in primary mouse β cells. Phosphorylation sites are found on key β cell proteins. Additionally, I identify sites on 26S proteasome subunits, E3 ubiquitin ligases, and proteins whose expression levels are glucose regulated. Further, I discover how potential crosstalk between phosphorylation sites and diabetes mutation in the PDX1 C terminus may impact PDX1 stability. These data both establish SPOP, a player in the ubiquitin proteasomal pathway, as necessary for proper insulin secretion and present new potential roles of phosphorylation in regulating protein degradation in β cells during glucose response

Notes:

Source: Dissertations Abstracts International, Volume: 86-12, Section: B.

Advisors: Stoffers, Doris Committee members: Kaestner, Klaus; Epstein, Douglas; Gadue, Paul; Busino, Luca

Ph.D. University of Pennsylvania 2025

Local Notes:

School code: 0175

ISBN:

9798280760813

Access Restriction:

Restricted for use by site license