NMR analysis of the alphaIIb beta3 cytoplasmic interaction suggests a mechanism for integrin regulation

The integrin αIIbβ3 is a transmembrane (TM) heterodimeric adhesion receptor that exists in equilibrium between resting and active ligand binding conformations. In resting αIIbβ3, the TM and cytoplasmic domains of αIIb and β3 form a heterodimer that constrains αIIbβ3 in its resting conformation. To study the structure and dynamics of the cytoplasmic domain heterodimer, we prepared a disulfide-stabilized complex consisting of portions of the TM domains and the full cytoplasmic domains. NMR and hydrogen-deuterium exchange of this complex in micelles showed that the αIIb cytoplasmic domain is largely disordered, but it interacts with and influences the conformation of the β3 cytoplasmic domain. The β3 cytoplasmic domain consists of a stable proximal helix contiguous with the TM helix and two distal amphiphilic helices. To confirm the NMR structure in a membrane-like environment, we studied the β3 cytoplasmic domain tethered to phospholipid bilayers. Hydrogen-deuterium exchange mass spectrometry, as well as circular dichroism spectroscopy, demonstrated that the β3 cytoplasmic domain becomes more ordered and helical under these conditions, consistent with our NMR results. Further, these experiments suggest that the two distal helices associate with lipid bilayers but undergo fluctuations that would allow rapid binding of cytoplasmic proteins regulating integrin activation, such as talin and kindlin-3. Thus, these results provide a framework for understanding the kinetics and thermodynamics of protein interactions involving integrin cytoplasmic domains and suggest that such interactions act in a concerted fashion to influence integrin stalk separation and exposure of extracellular ligand binding sites.     

DSMM XI study: dose definition for intravenous cyclophosphamide in combination with bortezomib/dexamethasone for remission induction in patients with newly diagnosed myeloma

A clinical trial was initiated to evaluate the recommended dose of cyclophosphamide in combination with bortezomib and dexamethasone as induction treatment before stem cell transplantation for younger patients with newly diagnosed multiple myeloma (MM). Thirty patients were treated with three 21-day cycles of bortezomib 1.3 mg/m² on days 1, 4, 8, and 11 plus dexamethasone 40 mg on the day of bortezomib injection and the day after plus cyclophosphamide at 900, 1,200, or 1,500 mg/m² on day 1. The maximum tolerated dose of cyclophosphamide was defined as 900 mg/m². At this dose level, 92% of patients achieved at least a partial response. The overall response rate [complete response (CR) plus partial response (PR)] across all dose levels was 77%, with a 10% CR rate. No patient experienced progressive disease. The most frequent adverse events were hematological and gastrointestinal toxicities as well as neuropathy. The results suggest that bortezomib in combination with cyclophosphamide at 900 mg/m² and dexamethasone is an effective induction treatment for patients with newly diagnosed MM that warrants further investigation.     

Felty's syndrome without rheumatoid arthritis?

Felty's syndrome (FS) is characterized by neutropenia and splenomegaly in patients with seropositive (RF+, anti-CCP+) rheumatoid arthritis (RA). As a result of neutropenia, affected persons are increasingly susceptible to infections. In the majority of patients, FS appears in the course of long-standing and well-established RA. Manifestations of FS without clinical but only with laboratory features of RA are extremely rare. We present a case of severe neutropenia and mild splenomegaly in a patient with high titers of RF and anti-CCP. For 4 years, patient's neutropenia remained asymptomatic. The neutropenia reduction to agranulocytosis was followed by successful methotrexate–corticosteroid therapy. Efficacy of the standard anti-RA therapy confirmed autoimmune mechanism of the Felty's neutropenia. The most important lesion from our case is to recognize this condition in the range of autoimmune rheumatic diseases without delay. We reviewed literature with non-articular FS.