Myddosome clustering in IL-1 receptor signaling regulates the formation of an NF-kB activating signalosome.

IL-1 receptor (IL-1R) signaling can activate thresholded invariant outputs and proportional outputs that scale with the amount of stimulation. Both responses require the Myddosome, a multiprotein complex. The Myddosome is required for polyubiquitin chain formation and NF-kB signaling. However, how these signals are spatially and temporally regulated to drive switch-like and proportional outcomes is not understood. During IL-1R signaling, Myddosomes dynamically reorganize into multi-Myddosome clusters at the cell membrane. Blockade of clustering using nanoscale extracellular barriers reduces NF-kB activation. Myddosomes function as scaffolds that assemble an NF-kB signalosome consisting of E3-ubiquitin ligases TRAF6 and LUBAC, K63/M1-linked polyubiquitin chains, phospho-IKK, and phospho-p65. This signalosome preferentially assembles at regions of high Myddosome density, which enhances the recruitment of TRAF6 and LUBAC. Extracellular barriers that restrict Myddosome clustering perturbed the recruitment of both ligases. We find that LUBAC was especially sensitive to clustering with 10-fold lower recruitment to single Myddosomes than clustered Myddosomes. These data reveal that the clustering behavior of Myddosomes provides a basis for digital and analog IL-1R signaling.

MyD88 oligomer size functions as a physical threshold to trigger IL1R Myddosome signaling.

A recurring feature of innate immune receptor signaling is the self-assembly of signaling proteins into oligomeric complexes. The Myddosome is an oligomeric complex that is required to transmit inflammatory signals from TLR/IL1Rs and consists of MyD88 and IRAK family kinases. However, the molecular basis for how Myddosome proteins self-assemble and regulate intracellular signaling remains poorly understood. Here, we developed a novel assay to analyze the spatiotemporal dynamics of IL1R and Myddosome signaling in live cells. We found that MyD88 oligomerization is inducible and initially reversible. Moreover, the formation of larger, stable oligomers consisting of more than four MyD88s triggers the sequential recruitment of IRAK4 and IRAK1. Notably, genetic knockout of IRAK4 enhanced MyD88 oligomerization, indicating that IRAK4 controls MyD88 oligomer size and growth. MyD88 oligomer size thus functions as a physical threshold to trigger downstream signaling. These results provide a mechanistic basis for how protein oligomerization might function in cell signaling pathways.

Thymoma Causing Bilateral Upper Extremity Deep Vein Thrombosis.

A 38-year-old African American male presented with progressive pain, swelling, numbness, and warmth of the left upper extremity ten days before admission. A chest computerized tomography scan showed a large 8.3 cm × 6.1 cm x 9.9 cm anterior mediastinal mass with compression of the left brachiocephalic vein and superior vena cava. A venous doppler showed multiple occlusive venous thrombi in bilateral upper extremities, including the bilateral internal jugular and subclavian veins, as well as the left subclavian, axillary, cephalic, brachial and median cubital veins. Further laboratory workup came positive for acetylcholine receptor binding antibody suggesting myasthenia gravis, but the patient was asymptomatic for myasthenia gravis. A percutaneous core CT guided biopsy pathology resulted in a predominant T-cell population CD5 positive with few B cells; the immunophenotypic features suggested Type B2 thymoma. To the best of our knowledge, this case is the only reported thymoma presenting with bilateral deep vein thrombosis of the upper extremities. The deep vein thrombosis therapy was enoxaparin 1mg/kg subcutaneously every 12 hours and dexamethasone 4mg intravenously every 4 hours as an anti-inflammatory drug for thymoma related compression of the mediastinum. The patient was referred to a tertiary oncological medical center for a total thymectomy, chemotherapy, and adjuvant radiotherapy.

Rickettsia typhi infection presenting as severe ARDS.

Murine typhus, also known as endemic typhus, is a disease resulting from an infection caused by the gram-negative bacillus Rickettsia typhi. Murine typhus is identified worldwide, predominantly in tropical and subtropical geographic locations. Transmission occurs through direct inoculation by an arthropod vector, most commonly the rat flea, Xenopsylla cheopis. rickettsial infections are notorious for disseminated infections throughout the endothelial cells. The increase in permeability is an immediate consequence and has the potential of leading to non-cardiogenic pulmonary edema, otherwise known as acute respiratory distress syndrome (ARDS). Clinical manifestations are non-specific and initially mimic typical viral etiologies, obscuring early diagnosis. As a result, clinicians often do not include rickettsial infections in their differential diagnoses. Definitive diagnosis is based on clinical recognition, epidemiologic awareness, and serological testing. Here we present a confirmed case of murine typhus in a young non-immunocompromised patient who developed ARDS one week from the initial onset of symptoms.

Cryptococcus laurentii meningitis in a non-HIV patient.

Cryptococcus species (other than Cryptococcus neoformans) have been labeled as saprophytic and nonpathogenic in immunocompetent individuals in the past. In recent years, infections caused by non-neoformans Cryptococcus species have been recognized. Cryptococcus laurentii is known to be a rare human pathogen. In this case report, we present a 59-year-old man who did not have HIV infection with meningoencephalitis caused by Cryptococcus laurentii. No significant underlying immunosuppressive disorder was found. The only identifiable risk factors were that the patient was a farmer with previous exposure to pigeon droppings. Here, we describe what we believe to be the fifth reported case of meningitis caused by Cryptococcus laurentii.

Nontyphoidal Salmonella purulent pericarditis presenting with pericardial tamponade in a patient on infliximab therapy.

Infection with nontyphoidal Salmonella is traditionally characterized by intestinal manifestations. However, extra-intestinal infections are known to occur, with purulent pericarditis associated with cardiac tamponade being rare. This case report is of a 57-year-old male with Crohn's disease initiated on infliximab therapy two months prior to presentation. He presented with recurrent chest pain and a single occurrence of fever. A Computed Tomography (CT) scan of the chest revealed a pericardial effusion. An echocardiogram confirmed the presence of the fluid with tamponade physiology, requiring immediate surgical decompression. The pericardial fluid culture grew Salmonella enterica, despite the patient having only a single episode of fever, disproportionate to the severity of the infection. Conceivably, the lack of systemic symptoms may be attributed to recent infliximab therapy. Upon conducting a literature review, immunosuppressive factors seem to play a significant role in nontyphoid Salmonella enterica pericardial effusion presenting with cardiac tamponade.

Copper tolerance of Saccharomyces cerevisiae nonsense-mediated mRNA decay mutants.

The eukaryotic nonsense-mediated mRNA (NMD) is a specialized pathway that leads to the recognition and rapid degradation of mRNAs with premature termination codons, and importantly some natural mRNAs as well. Natural mRNAs with atypically long 3'-untranslated regions (UTRs) are degraded by NMD in Saccharomyces cerevisiae. A number of S. cerevisiae mRNAs undergo alternative 3'-end processing producing mRNA isoforms that differ in their 3'-UTR lengths. Some of these alternatively 3'-end processed mRNA isoforms have atypically long 3'-UTRs and would be likely targets for NMD-mediated degradation. Here, we investigated the role NMD plays in the regulation of expression of CTR2, which encodes a vacuolar membrane copper transporter. CTR2 pre-mRNA undergoes alternative 3'-end processing to produce two mRNA isoforms with 300-nt and 2-kb 3'-UTRs. We show that both CTR2 mRNA isoforms are differentially regulated by NMD. The regulation of CTR2 mRNA by NMD has physiological consequences, since nmd mutants are more tolerant to toxic levels of copper relative to wild-type yeast cells and the copper tolerance of nmd mutants is dependent on the presence of CTR2.