Browsing by Subject "Protein phosphorylation"

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    Characterization of a novel IRE1 substrate pact and interacting miRNAS
    (2022-06) Doğan, Aslı Ekin
    The double-stranded RNA-dependent protein kinase activator A (PACT) anchors the RNAinduced silencing complex (RISC) to the endoplasmic reticulum (ER)’s membranous platform where RISC nucleation occurs and thus, PACT plays a key role in microRNA (miR)-mediated translational repression. Previous studies have shown that ER stress leads to PACT phosphorylation while simultaneously inducing changes in the expression of many miRs. Here, we demonstrate that PACT is phosphorylated by the ER-resident Inositol-requiring enzyme-1 (IRE1), a bifunctional kinase/endoribonuclease (RNase), both under ER stress and no stress conditions. While the role of IRE1 as a stress-induced RNase driving the unfolded protein response (UPR) is well understood, the function or the target(s) of its kinase activity have remained unexplored. Findings of this thesis show that IRE1- mediated phosphorylation of PACT regulates mature miR-181c levels, which suppresses the expression of key regulators of mitochondrial biogenesis (mitobiogenesis). Phosphorylation by IRE1 causes PACT-mediated suppression of mitobiogenesis and respiration. Partial PACT-deficiency in mice leads to enhanced mitobiogenesis during brown fat activation in cells and mice. Furthermore, cardiopulmonary bypass-induced ischemia/reperfusion injury downregulates PACT protein expression in human hearts while simultaneously inducing mitobiogenesis. Collectively, these findings demonstrate PACTmiR- 181c signaling axis is a key regulator of mitochondrial biogenesis and energetics.
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    The prosurvival IKK-related kinase IKKϵ integrates LPS and IL17A signaling cascades to promote Wnt-dependent tumor development in the intestine
    (American Association for Cancer Research, 2016-05) Göktuna, S. I.; Shostak, K.; Chau, T.-L.; Heukamp, L.C.; Hennuy, B.; Duong, H.-Q.; Ladang, A.; Close, P.; Klevernic, I.; Olivier, F.; Florin, A.; Ehx, G.; Baron, F.; Vandereyken, M.; Rahmouni, S.; Vereecke, L.; Loo, G. V.; Büttner, R.; Greten, F. R.; Chariot, A.
    Constitutive Wnt signaling promotes intestinal cell proliferation, but signals from the tumor microenvironment are also required to support cancer development. The role that signaling proteins play to establish a tumor microenvironment has not been extensively studied. Therefore, we assessed the role of the proinflammatory Ikk-related kinase Ikkϵ in Wnt-driven tumor development. We found that Ikkϵ was activated in intestinal tumors forming upon loss of the tumor suppressor Apc. Genetic ablation of Ikkϵ in b-catenin-driven models of intestinal cancer reduced tumor incidence and consequently extended survival. Mechanistically, we attributed the tumor-promoting effects of Ikkϵ to limited TNF-dependent apoptosis in transformed intestinal epithelial cells. In addition, Ikkϵ was also required for lipopolysaccharide (LPS) and IL17A-induced activation of Akt, Mek1/2, Erk1/2, and Msk1. Accordingly, genes encoding proinflammatory cytokines, chemokines, and anti-microbial peptides were downregulated in Ikkϵ-deficient tissues, subsequently affecting the recruitment of tumor-associated macrophages and IL17A synthesis. Further studies revealed that IL17A synergized with commensal bacteria to trigger Ikkϵ phosphorylation in transformed intestinal epithelial cells, establishing a positive feedback loop to support tumor development. Therefore, TNF, LPS, and IL17A-dependent signaling pathways converge on Ikkϵ to promote cell survival and to establish an inflammatory tumor microenvironment in the intestine upon constitutive Wnt activation.