Three distinct anti-allergic drugs, amlexanox, cromolyn and tranilast, bind to S100A12 and S100A13 of the S100 protein family

To investigate the roles of calcium-binding proteins in degranulation, we u sed three anti-allergic drugs, amlexanox, cromolyn and tranilast, which inh ibit IgE-mediated degranulation of mast cells, as molecular probes in affin ity chromatography. All of these drugs, which have different structures but similar function, scarcely bound to calmodulin in bovine lung extract, but bound to the same kinds of calcium-binding proteins, such as the 10-kDa pr oteins isolated in this study, calcyphosine and annexins I-V. The 10-kDa pr oteins obtained on three drug-coupled resins and on phenyl-Sepharose were a nalysed by reversed-phase HPLC. It was found that two characteristic 10-kDa proteins, one polar and one less polar, were bound with all three drugs, a lthough S100A2 (S100L), of the S100 family, was bound with phenyl-Sepharose . The cDNA and deduced amino acid sequence proved our major polar protein t o be identical with the calcium-binding protein in bovine amniotic fluid (C AAF1, S100A12). The cDNA and deduced amino acid sequence of the less-polar protein shared 95% homology with human and mouse S100A13. In addition, it w as demonstrated that the native S100A12 and recombinant S100A12 and S100A13 bind to immobilized amlexanox. On the basis of these findings, we speculat e that the three anti-allergic drugs might inhibit degranulation by binding with S100A12 and S100A13.