Browsing by Author "Teske, Brian F."

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    CHOP induces activating transcription factor 5 (ATF5) to trigger apoptosis in response to perturbations in protein homeostasis
    (American Society for Cell Biology, 2013) Teske, Brian F.; Fusakio, Michael E.; Zhou, Donghui; Shan, Jixiu; McClintick, Jeanette N.; Kilberg, Michael S.; Wek, Ronald C.; Biochemistry and Molecular Biology, School of Medicine
    Environmental stresses that disrupt protein homeostasis induce phosphorylation of eIF2, triggering repression of global protein synthesis coincident with preferential translation of ATF4, a transcriptional activator of the integrated stress response (ISR). Depending on the extent of protein disruption, ATF4 may not be able to restore proteostatic control and instead switches to a terminal outcome that features elevated expression of the transcription factor CHOP (GADD153/DDIT3). The focus of this study is to define the mechanisms by which CHOP directs gene regulatory networks that determine cell fate. We find that in response to proteasome inhibition, CHOP enhances the expression of a collection of genes encoding transcription regulators, including ATF5, which is preferentially translated during eIF2 phosphorylation. Transcriptional expression of ATF5 is directly induced by both CHOP and ATF4. Knockdown of ATF5 increases cell survival in response to proteasome inhibition, supporting the idea that both ATF5 and CHOP have proapoptotic functions. Transcriptome analysis of ATF5-dependent genes reveals targets involved in apoptosis, including NOXA, which is important for inducing cell death during proteasome inhibition. This study suggests that the ISR features a feedforward loop of stress-induced transcriptional regulators, each subject to transcriptional and translational control, which can switch cell fate toward apoptosis.
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    THE EIF2 KINASE PERK AND THE INTEGRATED STRESS RESPONSE FACILITATE ACTIVATION OF ATF6 DURING ENDOPLASMIC RETICULUM STRESS
    (Office of the Vice Chancellor for Research, 2012-04-13) Teske, Brian F.; Wek, Ronald C.; Wek, Sheree A.; Bunpo, Piyawan; Cundiff, Judy K.; McClintick, Jeanette N.; Anthony, Tracy G.; Wek, Ronald C.
    Disruptions of the endoplasmic reticulum (ER) that perturb protein folding cause ER stress and elicit an unfolded protein response (UPR) that involves changes in gene expression aimed at expanding the ER protein processing capacity and alleviating cellular injury. Three ER stress sensors PERK, ATF6, and IRE1 implement the UPR. Mutations of these ER stress sensors have been linked to diabetes, cancer and neurodegenerative diseases. Consequently, understanding the regulation of these three pathways has substantial therapeutic potential for development of biomarkers and pharmaceuticals for management of these conditions. PERK phosphorylation of eIF2 during ER stress represses protein synthesis, which prevents further influx of ER client proteins. PERK phosphorylation of eIF2 (eIF2~P) also induces preferential translation of ATF4, a transcription activator of the UPR. In this study we show that the PERK/eIF2~P/ATF4 pathway is required not only for translational control, but also activation of ATF6 and its target genes. The PERK pathway facilitates both the synthesis of ATF6 and trafficking of ATF6 from the ER to the Golgi for intramembrane proteolysis and activation of ATF6. As a consequence, liver-specific depletion of PERK significantly reduces both the translational and transcriptional phases of the UPR, leading to reduced protein chaperone expression, disruptions of lipid metabolism, and enhanced apoptosis. These findings show that the regulatory networks of the UPR are fully integrated, and helps explain the diverse biological defects associated with loss of PERK.