Date of Award

2019

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Graduate Group

Cell & Molecular Biology

First Advisor

Doris A. Stoffers

Abstract

In type 2 diabetes, oxidative stress contributes to the dysfunction and loss of pancreatic β cells. A highly conserved feature of the cellular response to stress is the regulation of mRNA translation, however, the mechanisms underlying this process in β cells are not fully understood. Here we use TRAP-seq to examine changes in the ribosome occupancy of mRNAs during conditions associated with β cell dysfunction, leading us to identify a cohort of translationally regulated genes with 3’UTR enrichment of a cytosine-rich motif. Of particular interest was the gene encoding JUND, a transcription factor with anti-oxidant functions in other cell types but whose role in cells is unknown. Interestingly, JUND is translationally upregulated in islets exposed to high glucose and free fatty acid levels, and depletion of JUND in β cells reduces oxidative stress and apoptosis caused by these conditions. Transcriptome assessment demonstrates that JUND regulates a cohort of genes that are commonly dysregulated during β cell dysfunction, including pro-oxidant and pro-inflammatory genes, consistent with this factor enhancing, rather than reducing, oxidative stress levels in cells. Further, hnRNPK, an RNA binding protein with specificity for cytosine-rich stretches, binds to the mRNA encoding JUND and is required for its post-transcriptional upregulation during metabolic stress. Although the absolute levels of hnRNPK do not change, there is a significant increase in hnRNPK phosphorylation during glucolipotoxicity. Importantly, this hnRNPK/JUND axis is activated in islets from diabetic db/db mice and in human islets exposed to metabolic stress. Finally, a series of mechanistic studies indicate that hnRNPK post-transcriptionally regulates JUND in a MEK/ERK- and DDX3X-dependent manner. Thus, a translation-centric approach uncovered hnRNPK and JUND as stress-responsive factors in β cells that contribute to redox imbalance and apoptosis during pathophysiologically relevant stress.

Files over 3MB may be slow to open. For best results, right-click and select "save as..."

Share

COinS