Mitotic Phosphorylation of TREX1 C Terminus Disrupts TREX1 Regulation of the Oligosaccharyltransferase Complex

Martin Kucej,Charles S Fermaintt,Kun Yang,Ricardo A Irizarry-Caro,Nan Yan

doi:10.1016/j.celrep.2017.02.051

Martin Kucej, Charles S Fermaintt + Show 3 more

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https://doi.org/10.1016/j.celrep.2017.02.051

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SUMMARYTREX1 mutations are associated with several auto-immune and inflammatory diseases. The N-terminal DNase domain of TREX1 is important for preventing self-DNA from activating the interferon response. The C terminus of TREX1 is required for ER localization and regulation of oligosacchariyltransferase (OST) activity. Here, we show that during mitosis TREX1 is predominately phosphorylated at the C-terminal Serine-261 by Cyclin B/CDK1. TREX1 is dephosphorylated quickly at mitotic exit, likely by PP1/PP2-type serine/threonine phosphatase. Mitotic phosphorylation does not affect TREX1 DNase activity. Phosphomimetic mutations of mitotic phosphorylation sites in TREX1 disrupted the interaction with the OST subunit RPN1. RNA-seq analysis of Trex1−/− mouse embryonic fibroblasts expressing TREX1 wild-type or phosphor-mutants revealed a glycol-gene signature that is elevated when TREX1 mitotic phosphorylation sites are disrupted. Thus, the cell-cycle-dependent post-translation modification of TREX1 regulates its interaction with OST, which may have important implications for immune disease associated with the DNase-independent function of TREX1.

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TREX1, known as DNase III, is a 30 / 50 DNA exonuclease tail-anchored at the endoplasmic reticulum (ER)
Cyclin B/CDK1 Phosphorylates TREX1 in Mitosis To determine whether endogenous TREX1 protein is phosphorylated, we analyzed TREX1 protein migration in SDS-PAGE
We found that TREX1 was completely phosphorylated in cells that were arrested in mitosis (Figure 1A)

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Introduction

TREX1, known as DNase III, is a 30 / 50 DNA exonuclease tail-anchored at the endoplasmic reticulum (ER). Missense mutations that disrupt TREX1 DNase activity cause self-DNA to accumulate in the cytosol, which triggers the cGAS-STING innate immune sensing and type I interferon (IFN). We recently showed that frameshift mutations that truncate the TREX1 C-terminal ER localization domain, without affecting DNase activity, cause dysregulation of the ER oligosaccharyltransferase (OST), leading to the release of free glycans and potentially glycosylation defects (Hasan et al, 2015). These two distinct functions of TREX1 are spatially separated into the N and C terminus of the protein.

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