CC1020 Sigma-AldrichHuman Integrin αVβ3, Octyl-β-D-glucopyranoside Formulation

Kaposi's sarcoma-associated herpesvirus (KSHV) envelope-associated glycoprotein B (gB) is involved in the initial steps of binding to host cells during KSHV infection. gB contains an RGD motif reported to bind the integrin alpha(3)beta(1) during virus entry. Although the ligand specificity of alpha(3)beta(1) has been controversial, current literature indicates that alpha(3)beta(1) ligand recognition is independent of RGD. We compared alpha(3)beta(1) to the RGD-binding integrin, alpha(V)beta(3), for binding to envelope-associated gB and a gB(RGD) peptide. Adhesion assays demonstrated that beta(3)-CHO cells overexpressing alpha(V)beta(3) specifically bound gB(RGD), whereas alpha(3)-CHO cells overexpressing alpha(3)beta(1) did not. Function-blocking antibodies to alpha(V)beta(3) inhibited the adhesion of HT1080 fibrosarcoma cells to gB(RGD), while antibodies to alpha(3)beta(1) did not. Using affinity-purified integrins and confocal microscopy, alpha(V)beta(3) bound to gB(RGD) and KSHV virions, demonstrating direct receptor-ligand interactions. Specific alpha(V)beta(3) antagonists, including cyclic and dicyclic RGD peptides and alpha(V)beta(3) function-blocking antibodies, inhibited KSHV infection by 70 to 80%. Keratinocytes from alpha(3)-null mice lacking alpha(3)beta(1) were fully competent for infection by KSHV, and reconstitution of alpha(3)beta(1) function by transfection with alpha(3) cDNA reduced KSHV infectivity from 74% to 55%. Additional inhibitory effects of alpha(3)beta(1) on the cell surface expression of alpha(V)beta(3) and on alpha(V)beta(3)-mediated adhesion of alpha(3)-CHO cells overexpressing alpha(3)beta(1) were detected, consistent with previous reports of transdominant inhibition of alpha(V)beta(3) function by alpha(3)beta(1). These observations may explain previous reports of an inhibition of KSHV infection by soluble alpha(3)beta(1). Our studies demonstrate that alpha(V)beta(3) is a cellular receptor mediating both the cell adhesion and entry of KSHV into target cells through binding the virion-associated gB(RGD).

Integrins of the beta 1 family were isolated from human smooth muscle. SDS-PAGE analysis and subsequent immunoblotting demonstrated that integrin samples contain a protein immunologically related to beta 1 integrin subunit with the previously undescribed apparent molecular mass 205 kD. One-dimensional peptide mapping showed that the 205 kD protein is not a novel beta 1 related integrin subunit, but a beta 1 integrin subunit dimer. After reduction the major part of the beta 1 immunoreactive material migrated from the 205 kD to 130 kD region, indicating that beta 1 integrin subunit dimers were formed via disulfide bonds. When electrophoretically pure beta 1 monomer and dimer forms were analized it was found that during SDS-PAGE about 30% of beta 1 integrin subunit monomers were organized into dimers while approximately 70% of the beta 1 dimer form was partly disrupted into monomers. It was suggested that this steady-state process is a result of a reversible reaction between intra- and intermolecular disulfide bonds. Possible in vivo dimerization of integrins via disulfide bonds is discussed.