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Cleveland, OH, United States

Bledzka K.,Joseph cobs Center For Thrombosis And Vascular Biology Nb | Liu J.,Joseph cobs Center For Thrombosis And Vascular Biology Nb | Xu Z.,Blood Research Institute | Dhanuja Perera H.,Joseph cobs Center For Thrombosis And Vascular Biology Nb | And 5 more authors.
Journal of Biological Chemistry | Year: 2012

Both talin head domain and kindlin-2 interact with integrin β cytoplasmic tails, and they function in concert to induce integrin activation. Binding of talin head domain to β cytoplasmic tails has been characterized extensively, but information on the interaction of kindin-2 with this integrin segment is limited. In this study, we systematically examine the interactions of kindlin-2 with integrin β tails. Kindlin-2 interacted well with β1 and β3 tails but poorly with the β2 cytoplasmic tail. This binding selectivity was determined by the non-conserved residues, primarily the three amino acids at the extreme C terminus of the β3tail, and the sequence in β2 was non-permissive. The region at the C termini of integrin β1 and β3 tails recognized by kindlin-2 was a binding core of 12 amino acids. Kindlin-2 and talin head do not interact with one another but can bind simultaneously to the integrin β3 tail without enhancing or inhibiting the interaction of the other binding partner. Kindlin-2 itself failed to directly unclasp integrin α/β tail complex, indicating that kindlin-2 must cooperate with talin to support the integrin activation mechanism. © 2012 by The American Society for Biochemistry and Molecular Biology, Inc.

Tchou G.D.,500 Euclid Ave | Wirka R.C.,Case Western Reserve University | Van Wagoner D.R.,500 Euclid Ave | Barnard J.,Cleveland Clinic | And 2 more authors.
BMC Medical Genetics | Year: 2012

Background: The atrial gap junction protein connexin-40 (Cx40) has been implicated to play an important role in atrial conduction and development of atrial fibrillation (AF). However, the frequency of Cx40 mutations in AF populations and their impact on Cx40 expression remains unclear. In this study, we sought to identify polymorphisms in the Cx40 gene GJA5, investigate the potential functional role of these polymorphisms, and determine their allelic frequencies. The prevalence of nonsynonymous Cx40 mutations in blood and atrial tissue was also compared to mutation frequencies reported in prior studies.Methods: We conducted direct sequencing of the GJA5 coding and 3′ UTR regions in blood samples from 91 lone AF subjects and 67 atrial tissue-derived samples from a lone cohort, a mixed AF cohort, and several transplant donors. Reporter gene transfection and tissue allelic expression imbalance assays were used to assess the effects of a common insertion/deletion polymorphism on Cx40 mRNA stability and expression.Results: We identified one novel synonymous SNP in blood-derived DNA from a lone AF subject. In atrial tissue-derived DNA from lone and mixed AF subjects, we observed one novel nonsynonymous SNP, one rare previously reported synonymous SNP, and one novel 3′ UTR SNP. A previously noted 25 bp insertion/deletion polymorphism in the 3′ UTR was found to be common (minor allele frequency = 0.45) but had no effect on Cx40 mRNA stability and expression. The observed prevalence of nonsynonymous Cx40 mutations in atrial tissues derived from lone AF subjects differed significantly (p = 0.03) from a prior atrial tissue study reporting a high mutation frequency in a group of highly selected young lone AF subjects.Conclusions: Our results suggest that Cx40 coding SNPs are uncommon in AF populations, although rare mutations in this gene may certainly lead to AF pathogenesis. Furthermore, a common insertion/deletion polymorphism in the Cx40 3′ UTR does not appear to play a role in modulating Cx40 mRNA levels. © 2012 Tchou et al.; licensee BioMed Central Ltd.

Wang S.,500 Euclid Ave | Wang S.,Central South University | Gulshan K.,500 Euclid Ave | Brubaker G.,500 Euclid Ave | And 4 more authors.
Arteriosclerosis, Thrombosis, and Vascular Biology | Year: 2013

Objective-To gain insight into the mechanism by which ABCA1 generates nascent high-density lipoprotein. Approach and Results-HEK293 cells were stably transfected with ABCA1 vectors, encoding wild type, and the W590S and C1477R Tangier disease mutation isoforms, along with the K939M ATP-binding domain mutant. Apolipoprotein AI (ApoAI) binding, plasma membrane remodeling, cholesterol efflux, apoAI cell surface unfolding, and apoAI cell surface lipidation were determined, the latter 2 measured using novel fluorescent apoAI indicators. The W590S isoform had decreased plasma membrane remodeling and lipid efflux activities, and the C1477R isoform had decreased apoAI binding, and lipid efflux activities, whereas the K939M isoform did not bind apoAI, remodel the membrane, or efflux cholesterol. However, all ABCA1 isoforms led to apoAI unfolding at the cell surface, which was higher for the isoforms that increased apoAI binding. ApoAI lipidation was not detected on ABCA1-expressing cells, only in the conditioned medium, consistent with rapid release of nascent high-density lipoprotein from ABCA1-expressing cells. Conclusions-We identified a third activity of ABCA1, the ability to unfold the N terminus of apoAI on the cell surface. Our results support a model in which unfolded apoAI on the cell surface is an intermediate in its lipidation and that, once apoAI is lipidated, it forms an unstable structure that is rapidly released from the cells to generate high-density lipoprotein. © 2013 American Heart Association, Inc.

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