Proper regulation of gene expression is required for determining and maintaining cellular identity and for responding to the extracellular environment. In eukaryotes, this entails a multi-step pathway for mRNA from transcription to translation and eventual degradation, and cellular responses to changing conditions often induce highly coordinated changes in many of these steps. The response to adverse stress conditions, such as lack of nutrients or oxidative stress, is often necessary in a wide diversity of organisms in order to ensure cell survival. Given its large energy requirements, changes in protein translation play a particularly critical role in cellular stress responses, resulting in altered translation of thousands of genes. This response also becomes misregulated in the pathologies of a number of diseases. Notably, the ability to circumvent translation regulation during stress is a hallmark of cancer progression that promotes continued cell growth, and alterations to stress responses and the translation machinery also contribute to aging. Despite these disease links, how these massive changes to translation are regulated is not well understood. Ded1 is a conserved RNA helicase that plays critical roles in translation initiation. Alterations in the human homolog of Ded1, DDX3, have been found in a number of cancers, including the pediatric brain cancer medulloblastoma and natural killer/T-cell lymphoma. Mutations of DDX3 are also linked to a cognitive developmental disorder, and DDX3 is involved in replication of several viruses, including HIV. These findings underscore the importance of understanding the normal functioning of Ded1/DDX3 since this can also shed light on its disease-associated functioning. In steady-state conditions, Ded1 stimulates translation initiation; however, recent research has revealed that Ded1 has a major role in the repression of translation during stress conditions, specifically when the TOR pathway, the central nutrient-sensor of the cell, is inactivated. This proposal explores this function of Ded1 and associated factors in controlling the translational response to cellular stress. Specifically, Aim I will characterize the stress function of Ded1 in response to TOR pathway inactivation. The mechanism of this role, which involves remodeling and degradation of the critical translation scaffolding factor eIF4G, will be defined, and the downstream consequences of this mechanism on translation of specific mRNAs will be determined. Upstream regulators and accessory factors for Ded1 and eIF4G during stress will also be identified and characterized.
Aim II will then examine Ded1 involvement in another part of the stress response, the formation of stress granules, cytoplasmic accumulations of mRNA and associated proteins. It will also test whether the stress response is affected in cells containing Ded1/DDX3 mutations associated with medulloblastoma. This work will greatly enhance our understanding of the translational response to cellular stress and will inform future studies of its misregulation in cancer and other diseases.

Public Health Relevance

Cells frequently face adverse conditions such as toxic substances or a lack of nutrients, and they respond by altering protein synthesis and the expression of their genes in order to ensure their survival. The research in this proposal will reveal how this occurs by studying the regulation of the protein synthesis machinery in response to cellular stresses. Misregulation of these cellular processes is common in both cancer and aging, so studying their mechanisms will provide a foundation for designing future treatments as well as broadening our knowledge of the fundamentals of cell biology.

Agency
National Institute of Health (NIH)
Institute
National Institute of General Medical Sciences (NIGMS)
Type
Research Project (R01)
Project #
1R01GM136827-01
Application #
9944734
Study Section
Molecular Genetics B Study Section (MGB)
Program Officer
Brown, Anissa F
Project Start
2020-04-01
Project End
2025-03-31
Budget Start
2020-04-01
Budget End
2021-03-31
Support Year
1
Fiscal Year
2020
Total Cost
Indirect Cost
Name
University of Arizona
Department
Biology
Type
Schools of Arts and Sciences
DUNS #
806345617
City
Tucson
State
AZ
Country
United States
Zip Code
85721