TRANSGLUTAMINASE IS INVOLVED IN THE FUSION OF MOUSE ALVEOLAR MACROPHAGES INDUCED BY 1-ALPHA,25-DIHYDROXYVITAMIN-D3

We have reported that 1α,25-dihydroxyvitamin D3 [1α,25(OH)2D3] induces fusion of mouse alveolar macrophages directly by a mechanism involving spermidinedependent protein synthesis (Tanaka, H. et al., 1989, Exp. Cell Res. 180, 72-83). The macrophage fusion induced by 1α,25(OH)2D3 occurred in a calcium-dependent manner (Jin, C. H. et al., 1988, J. Cell. Physiol. 137, 110-116). In the present study, we examined the possibility that transglutaminase, a calcium-dependent enzyme, is involved in the fusion of macrophages induced by 1α,25(OH)2D3. The activity of transglutaminase increased greatly 12 h after 1α,25(OH)2D3 was added and reached a maximum at 48 h. Western blot analysis of the cell lysate using an anti-transglutaminase antibody showed that 1α,25(OH)2D3 induced a 77-kDa protein corresponding to transglutaminase. When spermidine synthesis was inhibited by adding methylglyoxal bis(guanylhydrazone) (MGBG), an inhibitor of S-adenosylmethionine decarboxylase, the increase in the transglutaminase synthesis by 1α,25(OH)2D3 was markedly inhibited with concomitant inhibition of fusion. Adding more spermidine restored both the synthesis of transglutaminase and the fusion. The treatment of macrophages with cystamine, an inhibitor of transglutaminase, inhibited the fusion in parallel with the suppression of transglutaminase activity, both induced by 1α,25(OH)2D3. These results clearly indicate that 1α,25(OH)2D3 induces transglutaminase by a spermidine-dependent mechanism and that this enzyme is involved in a biological reaction(s) essential for inducing macrophage fusion. © 1991.