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The alpha2beta1 integrin inhibitor rhodocetin binds to the A-domain of the integrin alpha2 subunit proximal to the collagen-binding site.

ABSTRACT: Rhodocetin is a snake venom protein that binds to alpha2beta1 integrin, inhibiting its interaction with its endogenous ligand collagen. We have determined the mechanism by which rhodocetin inhibits the function of alpha2beta1. The interaction of alpha2beta1 with collagen and rhodocetin differed: Ca(2+) ions and slightly acidic pH values increased the binding of alpha2beta1 integrin to rhodocetin in contrast with their attenuating effect on collagen binding, suggesting that rhodocetin preferentially binds to a less active conformation of alpha2beta1 integrin. The alpha2A-domain [von Willebrand factor domain A homology domain (A-domain) of the integrin alpha2 subunit] is the major site for collagen binding to alpha2beta1. Recombinant alpha2A-domain bound rhodocetin, demonstrating that the A-domain is also the rhodocetin-binding domain. Although the interaction of alpha2beta1 with rhodocetin is affected by altering divalent cations, the interaction of the A-domain was divalent-cation-independent. The rhodocetin-binding site on the alpha2A-domain was mapped first by identifying an anti-alpha2 antibody that blocked rhodocetin binding and then mapping the epitope of the antibody using human-mouse alpha2A-domain chimaeras; and secondly, by binding studies with alpha2A-domain, which bear point mutations in the vicinity of the mapped epitope. In this way, the rhodocetin-binding site was identified as the alpha3-alpha4 loop plus adjacent alpha-helices. This region is known to form part of the collagen-binding site, thus attaining a mainly competitive mode of inhibition by rhodocetin.

SUBMITTER: Eble JA

PROVIDER: S-EPMC1223739 | biostudies-other | 2003 Nov

REPOSITORIES: biostudies-other

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Project description:Previous reports demonstrate that the Î±2-integrin (Î±2) mediates pancreatic ductal adenocarcinoma (PDAC) cell interaction with collagens. We found that untransformed pancreatic ductal epithelial cells and well-differentiated PDAC cells use Î±2 exclusively to adhere and migrate on collagenI. In contrast, poorly-differentiated PT45P1 and MIAPaCa2 cells demonstrate reduced reliance on, or complete loss of Î±2, respectively. Further, well-differentiated PDAC lines exhibit reduced in vitro invasion compared to poorly-differentiated lines, and Î±2-blockade suppressed invasion of well-differentiated lines exclusively. Based on these data and the demonstrated role of Î±2 in maintaining tissue architecture in other organs, we hypothesized that Î±2 may actually suppress the malignant phenotype in PDAC. Accordingly, stable ectopic expression of Î±2 in MIAPaCa2 cells (MP2-Î±2) retarded in vitro invasion. MP2-Î±2 cells maintained on collagenI were more invasion-retarded than MP2-Î±2 cells maintained in standard tissue culture, and demonstrated higher Î±2Î²1 expression that was reflected in faster and more complete adhesion/migration on collagenI. Affymetrix gene expression profiling of Î±2-expressing and mock-transfected cells revealed that kallikrein-related peptidases (KLK)-5, 6 and 7 were specifically upregulated by Î±2. Accordingly, well-differentiated PDAC lines express KLK-5, 6 and 7 and KLK blockade increased invasion as well as collagenI-migration in KLK-positive lines. Importantly, an Î±2 cytoplasmic deletion mutant promoted KLK expression and retarded invasion, while an Î±9Î±2 chimera retarded invasion less efficiently, and did not impact KLK expression. These data demonstrate for the first time that the Î±2-ectodomain and KLKâ??s coordinately regulate a less invasive phenotype in PDAC cells. Experiment Overall Design: Affymetrix global gene arrays were used to analyse differences in gene expression patterns in MIAPaCa2 cells stably reexpressing the alpha2 integrin, a cytoplasmic deletion of the alpha2 integrin (dCYTO) or an alpha9 ectodomain and transmembrane domain/alpha2 cytoplasmic domain chimera, versus vector-only mock controls. RNA was harvested from cells passaged identically and maitained under standard tissue culture conditions or on collagenI- or tenascin FNIII-coated plates.. Experiment Overall Design: Genetic manipulation (stable transgene expression)

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The alpha2beta1 integrin inhibitor rhodocetin binds to the A-domain of the integrin alpha2 subunit proximal to the collagen-binding site.

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