Doctor of Philosophy, Case Western Reserve University, 2024, Pathology

The Unfolded Protein Response In T Cell Thymic Development And Peripheral Differentiation Abstract by BRENDAN M. BARTON Effector T cell differentiation involves coordination of transcription factor networks reinforced by signals integrated from their microenvironment. Herein, I demonstrate that the tripartite unfolded protein response (UPR) integrated signals in vitro downstream of T cell receptor signaling and co-stimulation and in vivo in response to viral infection. While mice with T cell specific deficiency of individual UPR enzymes mounted normal anti-viral responses, mice containing T cells devoid of all three UPR enzymes markedly failed to generate anti-viral T cell responses and exhibited early exhaustion. Transcriptome and epigenetic analysis revealed UPR-deficient CD4+ and CD8+ antiviral T cells failed to upregulate the Ets1-Id2 transcription factor network to promote chromatin accessibility at multiple effector gene loci. Re-expression of the transcription factor XBP1s downstream of UPR sensor IRE1α was sufficient to rescue these defects. Thus, I demonstrate the underlying compensation of UPR enzymes and an interdependent role of UPR sensors in T cell effector differentiation.

Committee: Brian Cobb (Committee Chair); Derek Abbott (Committee Member); Stanley Adoro (Advisor); Clive Hamlin (Committee Member); John Tilton (Committee Member) Subjects: Immunology

Doctor of Philosophy, Case Western Reserve University, 2023, Biochemistry

Endoplasmic Reticulum (ER) stress, caused by the accumulation of misfolded proteins in the ER, elicits a homeostatic mechanism known as the Unfolded Protein Response (UPR). The UPR reprograms gene expression to promote adaptation to chronic ER stress. The UPR comprises an acute phase involving inhibition of bulk protein synthesis and a chronic phase of transcriptional induction coupled with the partial recovery of protein synthesis. However, the role of transcriptional regulation during the acute phase of the UPR is not well understood. In this study (Alzahrani et al., 2022), I analyzed the fate of newly synthesized mRNA encoding the protective and homeostatic transcription factor X-box binding protein 1 (XBP1) during this acute phase of UPR. Global translational repression induced during the acute UPR was documented and characterized by decreased translation and increased stability of XBP1 mRNA. My data suggest this stabilization of XBP1 mRNA is independent of new transcription. In contrast, newly synthesized XBP1 mRNA is shown to accumulate with long poly(A) tails and escapes translational repression during the acute phase of UPR. Inhibition of nascent RNA polyadenylation during the acute phase decreased cell survival with no effect in unstressed cells. During the chronic phase of the UPR, XBP1 mRNA abundance and long poly(A) tails decreased in a manner consistent with co-translational deadenylation. Finally, additional pro-survival, transcriptionally-induced genes show similar regulation, supporting the broad significance of the pre-steady state UPR in translational control during ER stress. I conclude that the biphasic regulation of poly(A) tail length during the UPR represents a previously unrecognized pro-survival mechanism of mammalian gene regulation.

Committee: Maria Hatzoglou (Advisor) Subjects: Molecular Biology