Search

NF-κB is a master regulator of inflammation and has been implicated in the pathogenesis of immune disorders and cancer. Its regulation involves a variety of steps, including the controlled degradation [...]

Background Although the risk of exposure to Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) is higher for frontline healthcare workers, not all personnel have similar risks. Determining infection rate is difficult due to the limits on testing and the high rate of asymptomatic individuals. Detection of antibodies against SARS-CoV-2 may be useful for determining prior exposure to the virus and assessing mitigation strategies, such as isolation, masks, and other protective equipment. Methods An online assessment that included demographic, clinical, and exposure information and a blood sample was collected from 20 614 participants out of ~43 000 total employees at Beaumont Health, which includes 8 hospitals distributed across the Detroit metropolitan area in southeast Michigan. The presence of anti-SARS-CoV-2 IgG was determined using the EUROIMMUN assay. Results A total of 1818 (8.8%) participants were seropositive between April 13 and May 28, 2020. Among the seropositive individuals, 44% reported that they were asymptomatic during the month prior to blood collection. Healthcare roles such as phlebotomy, respiratory therapy, and nursing/nursing support exhibited significantly higher seropositivity. Among participants reporting direct exposure to a Coronavirus Disease 2019 (COVID-19) positive individual, those wearing an N95/PAPR mask had a significantly lower seropositivity rate (10.2%) compared to surgical/other masks (13.1%) or no mask (17.5%). Conclusions Direct contact with COVID-19 patients increased the likelihood of seropositivity among employees but study participants who wore a mask during COVID-19 exposures were less likely to be seropositive. Additionally, a large proportion of seropositive employees self-reported as asymptomatic. (Funded by Beaumont Health and by major donors through the Beaumont Health Foundation) ClinicalTrials.gov number NCT04349202 [ABSTRACT FROM AUTHOR]

Cullin RING ligases (CRLs), the most prolific class of ubiquitin ligase enzymes, are multimeric complexes that regulate a wide range of cellular processes. CRL activity is regulated by CAND1 (Cullin-associated Nedd8-dissociated protein 1), an inhibitor that promotes the dissociation of substrate receptor components from the CRL. We demonstrate here that COMMD1 (copper metabolism MURR1 domain-containing 1), a factor previously found to promote ubiquitination of various substrates, regulates CRL activation by antagonizing CAND1 binding. We show that COMMD1 interacts with multiple Cullins, that the COMMD1-Cul2 complex cannot bind CAND1, and that, conversely, COMMD1 can actively displace CAND1 from CRLs. These findings highlight a novel mechanism of CRL activation and suggest that CRL regulation may underlie the pleiotropic activities of COMMD1. [ABSTRACT FROM AUTHOR]

The transcription factor NF-κB is a critical regulator of inflammatory and cell survival signals. Proteasomal degradation of NF-κB subunits plays an important role in the termination of NF-κB activity, and at least one of the identified ubiquitin ligases is a multimeric complex containing Copper Metabolism Murr1 Domain 1 (COMMD1) and Cul2. We report here that GCN5, a histone acetyltransferase, associates with COMMD1 and other components of the ligase, promotes RelA ubiquitination, and represses κB-dependent transcription. In this role, the acetyltransferase activity of GCN5 is not required. Interestingly, GCN5 binds more avidly to RelA after phosphorylation on Ser 468, an event that is dependent on IKK activity. Consistent with this, we find that both GCN5 and the IκB Kinase (IKK) complex promote RelA degradation. Collectively, the data indicate that GCN5 participates in the ubiquitination process as an accessory factor for a ubiquitin ligase, where it provides a novel link between phosphorylation and ubiquitination. [ABSTRACT FROM AUTHOR]

Copper metabolism MURR1 domain1 (COMMD1) is a novel inhibitor of the transcription factors NF-kappaB and HIF-1, which play important roles in inflammation and tumor growth, respectively. In this study, we identified two highly conserved nuclear export signals (NESs) in COMMD1 and revealed that these NESs were essential and sufficient to induce maximal nuclear export of COMMD1. Inhibition of CRM1-mediated nuclear export by Leptomycin B resulted in nuclear accumulation of COMMD1. In addition, low oxygen concentrations induced the active export of COMMD1 from the nucleus in a CRM1-dependent manner. Disruption of the NESs in COMMD1 increased the repression of COMMD1 in transcriptional activity of NF-kappaB and HIF-1. In conclusion, these data indicate that COMMD1 undergoes constitutive nucleocytoplasmic transport as a novel mechanism to regulate NF-kappaB and HIF-1 signaling.

The transcription factor NF-kappaB is a critical regulator of inflammatory and cell survival signals. Proteasomal degradation of NF-kappaB subunits plays an important role in the termination of NF-kappaB activity, and at least one of the identified ubiquitin ligases is a multimeric complex containing Copper Metabolism Murr1 Domain 1 (COMMD1) and Cul2. We report here that GCN5, a histone acetyltransferase, associates with COMMD1 and other components of the ligase, promotes RelA ubiquitination, and represses kappaB-dependent transcription. In this role, the acetyltransferase activity of GCN5 is not required. Interestingly, GCN5 binds more avidly to RelA after phosphorylation on Ser 468, an event that is dependent on IKK activity. Consistent with this, we find that both GCN5 and the IkappaB Kinase (IKK) complex promote RelA degradation. Collectively, the data indicate that GCN5 participates in the ubiquitination process as an accessory factor for a ubiquitin ligase, where it provides a novel link between phosphorylation and ubiquitination.

COMMD {COMM [copper metabolism Murr1 (mouse U2af1-rs1 region 1)] domain-containing} proteins participate in several cellular processes, ranging from NF-kappaB (nuclear factor kappaB) regulation, copper homoeostasis, sodium transport and adaptation to hypoxia. The best-studied member of this family is COMMD1, but relatively little is known about its regulation, except that XIAP [X-linked IAP (inhibitor of apoptosis)] functions as its ubiquitin ligase. In the present study, we identified that the COMM domain of COMMD1 is required for its interaction with XIAP, and other COMMD proteins can similarly interact with IAPs. Two conserved leucine repeats within the COMM domain were found to be critically required for XIAP binding. A COMMD1 mutant which was unable to bind to XIAP demonstrated a complete loss of basal ubiquitination and great stabilization of the protein. Underscoring the importance of IAP-mediated ubiquitination, we found that long-term expression of wild-type COMMD1 results in nearly physiological protein levels as a result of increased ubiquitination, but this regulatory event is circumvented when a mutant form that cannot bind XIAP is expressed. In summary, our findings indicate that COMMD1 expression is controlled primarily by protein ubiquitination, and its interaction with IAP proteins plays an essential role.

The COMM domain containing (COMMD) family of proteins represents a recently discovered set of evolutionarily conserved factors characterized by the presence of a defining carboxy-terminal motif. In vertebrates, there are ten members of the family, and among their emerging functions the control of the transcription factor NFkappaB has been most extensively studied. NFkappaB plays a critical role in a number of homeostatic processes in multicellular organisms, including the regulation of immunity and cell survival. COMMD proteins inhibit NFkappaB mediated gene expression, and recent mechanistic studies have revealed that COMMD1 controls the ubiquitination of NFkappaB subunits, an event linked to transcriptional termination. COMMD1 binds to a multimeric ubiquitin ligase containing Elongins B/C, Cul2 and SOCS1 (ECS( SOCS1)). In this complex, COMMD1 facilitates the binding of NFkappaB subunits to the ligase, thereby promoting their ubiquitination and degradation. Additional insights gained from these studies indicate that COMMD proteins likely play a broader role in cellular homeostasis through their participation in the ubiquitination pathway.