SHARPIN is a ubiquitin-binding and ubiquitin-like domain-containing protein which, when mutated in mice, results in immune system disorders and multiorgan inflammation1,2. Here we report that SHARPIN functions as a novel component of the Linear Ubiquitin Chain Assembly Complex (LUBAC) and that the absence of SHARPIN causes disregulation of NF-κB and apoptotic signalling pathways, explaining the severe phenotypes displayed by chronic proliferative dermatitis in SHARPIN deficient mice. Upon binding to the LUBAC subunit HOIP, SHARPIN stimulates the formation of linear ubiquitin chains in vitro and in vivo. Co-expression of SHARPIN and HOIP promotes linear ubiquitylation of NEMO, an adaptor of the IκB kinases (IKKs) and subsequent activation of NF-κB signalling, while SHARPIN deficiency in mice causes an impaired activation of the IKK complex and NF-κB in B cells, macrophages, and mouse embryonic fibroblasts (MEFs). This effect is further enhanced upon concurrent downregulation of HOIL-1L, another HOIP-binding component of LUBAC. In addition, SHARPIN deficiency leads to rapid cell death upon TNFα stimulation via FADD- and Caspase-8-dependent pathways. SHARPIN thus activates NF-κB and inhibits apoptosis via distinct pathways in vivo.

Given advanced age, comorbidities, and immune dysfunction, CLL patients may be at particularly high risk of infection and poor outcomes related to coronavirus disease-19 (COVID-19). Robust analysis of outcomes for CLL patients, particularly examining effects of baseline characteristics and CLL-directed therapy, is critical to optimally manage CLL patients through this evolving pandemic. CLL patients diagnosed with symptomatic COVID-19 across 43 international centers (n=198) were included. Hospital admission occurred in 90%. Median age at COVID-19 diagnosis was 70.5 years. Median CIRS score was 8 (range 4-32). Thirty-nine percent were treatment-naïve ("watch and wait") while 61% had received ≥1 CLL-directed therapy (median 2, range 1-8). Ninety patients (45%) were receiving active CLL therapy at COVID-19 diagnosis, most commonly BTK inhibitors (BTKi; n=68/90, 76%). At a median follow-up of 16 days, the overall case fatality rate (CFR) was 33%, though 25% remain admitted. "Watch and wait" and treated cohorts had similar rates of admission (89% vs. 90%), ICU admission (35% vs. 36%), intubation (33% vs. 25%), and mortality (37% vs. 32%). CLL-directed treatment with BTKi at COVID-19 diagnosis did not impact survival (CFR 34% vs. 35%), though BTKi was held during COVID-19 course for most patients. These data suggest that the subgroup of CLL patients admitted with COVID-19, regardless of disease phase or treatment status, are at high risk of death. Future epidemiologic studies are needed to assess SARS-CoV-2 infection risk, these data should be validated independently, and randomized studies of BTKi in COVID-19 are needed to provide definitive evidence of benefit.

The SecY complex associates with the ribosome to form a protein translocation channel in the bacterial plasma membrane. We have used cryo-electron microscopy and quantitative mass spectrometry to show that a nontranslating E. coli ribosome binds to a single SecY complex. The crystal structure of an archaeal SecY complex was then docked into the electron density maps. In the resulting model, two cytoplasmic loops of SecY extend into the exit tunnel near proteins L23, L29, and L24. The loop between transmembrane helices 8 and 9 interacts with helices H59 and H50 in the large subunit RNA, while the 6/7 loop interacts with H7. We also show that point mutations of basic residues within either loop abolish ribosome binding. We suggest that SecY binds to this primary site on the ribosome and subsequently captures and translocates the nascent chain.

The spatial organization of transmembrane receptors is a critical step in signal transduction and receptor trafficking in cells. Transmembrane receptors engage in lateral homotypic and heterotypic cis-interactions as well as intercellular trans-interactions that result in the formation of signalling foci for the initiation of different signalling networks. Several aspects of ligand-induced receptor clustering and association with signalling proteins are also influenced by the lipid composition of membranes. Thus, lipid microdomains have a function in tuning the activity of many transmembrane receptors by positively or negatively affecting receptor clustering and signal transduction. We review the current knowledge about the functions of clustering of transmembrane receptors and lipid-protein interactions important for the spatial organization of signalling at the membrane.

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