Protein C Mutation (A267T) Results in ER Retention and Unfolded Protein Response Activation

BACKGROUND: Protein C (PC) deficiency is associated with a high risk of venous thrombosis. Recently, we identified the PC-A267T mutation in a patient with PC deficiency and revealed by in vitro studies decreased intracellular and secreted levels of the mutant. The aim of the present study was to characterize the underlying mechanism(s). METHODOLOGY/PRINCIPAL FINDINGS: CHO-K1 cells stably expressing the wild-type (PC-wt) or the PC mutant were generated. In order to examine whether the PC mutant was subjected to increased intracellular degradation, the cells were treated with several inhibitors of various degradation pathways and pulse-chase experiments were performed. Protein-chaperone complexes were analyzed by treating the cells with a cross-linker followed by Western blotting (WB). Expression levels of the immunoglobulin-binding protein (BiP) and the phosphorylated eukaryotic initiation factor 2α (P-eIF2α), both common ER stress markers, were determined by WB to examine if the mutation induced ER stress and unfolded protein response (UPR) activation. We found no major differences in the intracellular degradation between the PC variants. The PC mutant was retained in the endoplasmic reticulum (ER) and had increased association with the Grp-94 and calreticulin chaperones. Retention of the PC-A267T in ER resulted in UPR activation demonstrated by increased expression levels of the ER stress markers BiP and P-eIF2α and caused also increased apoptotic activity in CHO-K1 cells as evidenced by elevated levels of DNA fragmentation. CONCLUSIONS/SIGNIFICANCE: The reduced intracellular level and impaired secretion of the PC mutant were due to retention in ER. In contrast to other PC mutations, retention of the PC-A267T in ER resulted in minor increased proteasomal degradation, rather it induced ER stress, UPR activation and apoptosis

Quality control for unfolded proteins at the plasma membrane

A temperature-sensitive chimeric transmembrane protein reveals a mechanism for disposing misfolded proteins that make it to the plasma membrane

Alternatively spliced form of human thyroperoxidase, TPOzanelli: activity, intracellular trafficking, and role in hormonogenesis.

International audienceThyroperoxidase (TPO), a type I transmembrane heme containing glycoprotein, catalyzes iodide organification and thyroid hormone synthesis. One of the two main alternatively spliced forms of this enzyme, TPOzanelli, which is present in Graves's disease thyroid tissue, has a cytoplasmic domain completely modified. In the first stage of this study, the results of RT-PCR experiments showed that the TPOzanelli mRNA is present in normal thyroid tissue. We then generated CHO cell lines expressing the wild-type TPO (TPO1) and the alternatively spliced form TPOzanelli. Upon investigating a panel of 12 mAbs directed against the extracellular domain of TPO1 and sera from patients with a high titer of TPO autoantibodies, we observed that (i) the three-dimensional structure of this domain is similar in both isoforms; (ii) the autoantibodies recognize TPOzanelli as well as TPO1. The results of pulse chase and cell surface biotinylation experiments showed that the TPOzanelli has a shorter half-life (7 versus 11 h) and is expressed at the cell surface in lesser amounts than TPO1 (7 versus 15%). The total enzymatic activity and cell surface activity were determined in CHO cells expressing TPO1 and TPOzanelli, and TPO1 and TPOzanelli were found to have similar levels of activity. It was established that approximately 20% of the TPO purified from a Graves' disease thyroid gland was precipitated by polyclonal antibodies directed against a specific part of the cytoplasmic tail of TPOzanelli. This confirmed that the protein corresponding to the mRNA is present in the thyroid tissue. All in all, these results indicate that TPOzanelli can be expected to play a role in thyroid hormone synthesis and in thyroid autoimmunity

Preclinical characterization and clinical translation of pharmacodynamic markers for MK-5890: a human CD27 activating antibody for cancer immunotherapy

Background Immune checkpoint inhibitors (ICI) have radically changed cancer therapy, but most patients with cancer are unresponsive or relapse after treatment. MK-5890 is a CD27 agonist antibody intended to complement ICI therapy. CD27 is a member of the tumor necrosis factor receptor superfamily that plays a critical role in promoting responses of T cells, B cells and NK cells. Methods Anti-CD27 antibodies were generated and selected for agonist activity using NF-kB luciferase reporter assays. Antibodies were humanized and characterized for agonism using in vitro T-cell proliferation assays. The epitope recognized on CD27 by MK-5890 was established by X-ray crystallography. Anti-tumor activity was evaluated in a human CD27 knock-in mouse. Preclinical safety was tested in rhesus monkeys. Pharmacodynamic properties were examined in mouse, rhesus monkeys and a phase 1 dose escalation clinical study in patients with cancer. Results Humanized anti-CD27 antibody MK-5890 (hIgG1) was shown to bind human CD27 on the cell surface with sub-nanomolar potency and to partially block binding to its ligand, CD70. Crystallization studies revealed that MK-5890 binds to a unique epitope in the cysteine-rich domain 1 (CRD1). MK-5890 activated CD27 expressed on 293T NF-kappa B luciferase reporter cells and, conditional on CD3 stimulation, in purified CD8+ T cells without the requirement of crosslinking. Functional Fc-receptor interaction was required to activate CD8+ T cells in an ex vivo tumor explant system and to induce antitumor efficacy in syngeneic murine subcutaneous tumor models. MK-5890 had monotherapy efficacy in these models and enhanced efficacy of PD-1 blockade. MK-5890 reduced in an isotype-dependent and dose-dependent manner circulating, but not tumor-infiltrating T-cell numbers in these mouse models. In rhesus monkey and human patients, reduction in circulating T cells was transient and less pronounced than in mouse. MK-5890 induced transient elevation of chemokines MCP-1, MIP-1 alpha, and MIP-1 beta in the serum of mice, rhesus monkeys and patients with cancer. MK-5890 was well tolerated in rhesus monkeys and systemic exposure to MK-5890 was associated with CD27 occupancy at all doses. Conclusions MK-5890 is a novel CD27 agonistic antibody with the potential to complement the activity of PD-1 checkpoint inhibition in cancer immunotherapy and is currently undergoing clinical evaluation.Tumorimmunolog

Caenorhabditis elegans and Human Dual Oxidase 1 (DUOX1) “Peroxidase” Domains: INSIGHTS INTO HEME BINDING AND CATALYTIC ACTIVITY*

The seven members of the NOX/DUOX family are responsible for generation of the superoxide and H2O2 required for a variety of host defense and cell signaling functions in nonphagocytic cells. Two members, the dual oxidase isozymes DUOX1 and DUOX2, share a structurally unique feature: an N-terminal peroxidase-like domain. Despite sequence similarity to the mammalian peroxidases, the absence of key active site residues makes their binding of heme and their catalytic function uncertain. To explore this domain we have expressed in a baculovirus system and purified the Caenorhabditis elegans (CeDUOX11–589) and human (hDUOX11–593) DUOX1 “peroxidase” domains. Evaluation of these proteins demonstrated that the isolated hDUOX11–593 does not bind heme and has no intrinsic peroxidase activity. In contrast, CeDUOX11–589 binds heme covalently, exhibits a modest peroxidase activity, but does not oxidize bromide ion. Surprisingly, the heme appears to have two covalent links to the protein despite the absence of a second conserved carboxyl group in the active site. Although the N-terminal dual oxidase motif has been proposed to directly convert superoxide to H2O2, neither DUOX1 domain demonstrated significant superoxide dismutase activity. These results strengthen the in vivo conclusion that the CeDUOX1 protein supports controlled peroxidative polymerization of tyrosine residues and indicate that the hDUOX1 protein either has a unique function or must interact with other protein factors to express its catalytic activity