GADD34 and CReP Regulation in the Unfolded Protein Response, Comparing Molecular Mechanisms in Humans and Zebrafish

Author

Angela Adams, University of the PacificFollow

Date of Award

2025

Document Type

Thesis

Degree Name

Master of Science (M.S.)

Department

Biological Sciences

First Advisor

Lisa Wrischnik

First Committee Member

Douglas Weiser

Second Committee Member

Craig Vierra

Abstract

In eukaryotic cells, many newly synthesized proteins are sent to the endoplasmic reticulum (ER) of a cell to be folded into the proper conformation for functionality. When proteins get misfolded, or cannot be folded fast enough, these proteins accumulate in the ER which causes the cell to become stressed. This leads to a process known as the Unfolded Protein Response (UPR). Once UPR has been initiated, the α subunit of eukaryotic initiation factor 2 (eIF2α) becomes phosphorylated to inhibit global protein synthesis within the cell, while simultaneously activating the expression of several genes to either aid in cell recovery or induce cell death if the cell cannot recover. Two genes involved in cell recovery during UPR are GADD34 (PPP1R15A) and CReP (PPP1R15B). GADD34 and CReP proteins, whose expression is upregulated by UPR, bind as subunits to Protein Phosphatase 1 (PP1) which acts to resume global protein synthesis during UPR. After resolution of UPR, GADD34 and CReP proteins are no longer needed in the cell and can be destroyed, however, the mechanism for selecting these proteins for destruction is unclear. There is some supporting evidence that GADD34 is degraded by a process known as ubiquitination, in which ubiquitin molecules are bound to the protein which tags it to be sent to the proteasome for destruction, but there has not been much evidence to show how CReP is degraded. Additionally, evidence of GADD34 ubiquitination has only been demonstrated in the human version of the gene, which limits our understanding of UPR pathways in other model systems. This project aims to determine if CReP is also degraded by ubiquitination, and to investigate if the zebrafish version of these genes behave in a similar way to the human versions. Additionally, GADD34 contains two uORFs in the 5’ UTR region which are likely involved in translational regulation. These two uORFs will be analyzed to determine if expression levels of zebrafish GADD34 change if they are knocked out, mirroring the uORF regulation in mammals. Zebrafish are a common model organism used for research in molecular biology due to their ease and affordability of care and breeding, while possessing many of the same eukaryotic cell processes observed in human cells. Utilizing zebrafish as a model organism can further our understanding of the genes involved in UPR and lead to experiments and techniques that would not be ethical to perform on human tissues or subjects. The importance of understanding the UPR pathway and involved genes are linked to the connection of UPR being implicated in the onset of human neurodegenerative diseases. If UPR cannot be resolved, the affected cells will die. When neuronal cells undergo UPR, the stakes are incredibly high due to the inability for neuronal cells to regenerate. Neuronal cell death will lead to symptoms of neurodegeneration, observed in conditions such as Alzheimer's disease. Further research of UPR activated genes has the potential to expose preventative measures for neurodegenerative avoidance, as well as future drug treatments for human patients with onset neurodegenerative conditions.

Pages

92

Recommended Citation

Adams, Angela. (2025). GADD34 and CReP Regulation in the Unfolded Protein Response, Comparing Molecular Mechanisms in Humans and Zebrafish. University of the Pacific, Thesis. https://scholarlycommons.pacific.edu/uop_etds/4298