Nathan Gluck

GCN5 is a required cofactor for a ubiquitin ligase that targets NF-κB/RelA

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.

CCDC22 deficiency in humans blunts activation of proinflammatory NF-kappa B signaling

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 of inhibitory IκB proteins. In addition, the inactivation of DNA-bound NF-κB is essential for its regulation. This step requires a factor known as copper metabolism Murr1 domain-containing 1 (COMMD1), the prototype member of a conserved gene family. While COMMD proteins have been linked to the ubiquitination pathway, little else is known about other family members. Here we demonstrate that all COMMD proteins bind to CCDC22, a factor recently implicated in X-linked intellectual disability (XLID). We showed that an XLID-associated CCDC22 mutation decreased CCDC22 protein expression and impaired its binding to COMMD proteins. Moreover, some affected individuals displayed ectodermal dysplasia, a congenital condition that can result from developmental NF-κB blockade. Indeed, patient-derived cells demonstrated impaired NF-κB activation due to decreased IκB ubiquitination and degradation. In addition, we found that COMMD8 acted in conjunction with CCDC22 to direct the degradation of IκB proteins. Taken together, our results indicate that CCDC22 participates in NF-κB activation and that its deficiency leads to decreased IκB turnover in humans, highlighting an important regulatory component of this pathway.

COMMD1 (Copper Metabolism MURR1 Domain-containing Protein 1) Regulates Cullin RING Ligases by Preventing CAND1 (Cullin-associated Nedd8-dissociated Protein 1) Binding

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.

Bimolecular Affinity Purification (BAP): Tandem Affinity Purification Using Two Protein Baits

The tandem affinity purification (TAP) procedure was pioneered in yeast for the purpose of purifying and characterizing protein complexes. While affinity purification is relatively easy to perform, nonspecific protein interactions can plague the identification of true interacting partners of the given bait utilized in the purification. To alleviate this problem, two sequential affinity purification steps are employed in the TAP procedure. Since its inception in yeast, TAP has gone through many adaptations and has been employed multiple times in diverse organisms, including mammalian systems. In all these approaches, two out of many possible affinity moieties are employed and are usually expressed as a fusion polypeptide in the amino or carboxyl-terminal region of the protein bait. In this protocol, we describe a variation on the TAP procedure in which the affinity moieties are placed on two different proteins of a molecular complex to isolate or detect components present in the complex. This variation, which we refer to as bimolecular affinity purification (BAP), is suited for the identification of specific molecular complexes marked by the presence of two known components.

Predicting Efficacy of Plastic Stents for Posttransplantation Biliary Strictures.

Background: Biliary strictures (BS) are a common complication of liver transplantation. The standard treatment is sequential insertion of increasing numbers of plastic stents by endoscopic retrograde cholangiopancreatography (ERCP). Despite high success rates, some strictures fail to resolve and require surgery as definitive treatment. Goals: To identify predictors of response or failure of standard endoscopic treatment, allowing earlier referral to alternative modalities when needed and avoiding unnecessary procedures. Study: Database of Gastroenterology Department at Tel Aviv Medical Center was retrospectively reviewed, and data regarding patients who underwent liver transplantation and developed BS were analyzed. Results: Thirty-one patients met the study criteria. Twenty-four (77.4%) resolved with plastic stenting and 7 ultimately required surgery. There were no significant differences between stent responders and nonresponders regarding demographics, transplant and postoperative hospitalization data, time from transplantation to presentation with stricture, total number of ERCP sessions, or maximal number of stents. A trend toward difference was noted in the time elapsed between the first and the second ERCP, whereby ERCP nonresponders required a second procedure sooner than responders. Patients presenting to their second procedure as scheduled ultimately had a 95% endoscopic success rate, whereas those presenting urgently with acute cholangitis had a 55% failure rate (P=0.02). Conclusions: Urgent repeat ERCP is a harbinger of ultimate failure of plastic stent treatment for BS after liver transplant. This finding may assist earlier triage of these patients toward alternative treatment such as metal stents or surgery, thus sparing needless procedures and complications.

Retinal detachment after subcranial resection of an anterior skull base tumor

The subcranial approach has emerged as a safe and effective procedure for resection of tumors of the anterior skull base. This approach allows excellent exposure of the nasal cavities, the paranasal sinuses, and the orbit 1 I also enables a wide approach to the anterior cranial fossa, while applying minimal retraction of the frontal lobes. Complications of this procedure are acceptable and comparable to the classical transfacial transcranial approac 2