Spermidine-dependent proteins are involved in the fusion of mouse alveolar macrophages induced by 1α,25-dihydroxyvitamin D 3 and interleukin 4

Abstract

We have reported that 1α,25-dihydroxyvitamin D 3 [1α,25(OH) 2D 3] directly induces fusion of mouse alveolar macrophages by a mechanism involving protein synthesis (H. Tanaka et al., 1984, FEBS Lett. 174, 61). While examining further the mechanism of the fusion, we found that polyamines, most likely spermidine, are involved as an important intracellular mediator of the 1α,25(OH) 2D 3 action in inducing protein synthesis, which in turn induces fusion of macrophages (T. Hayashi et al., 1986, J. Bone Miner. Res. 1, 235). In this study, spermidine-dependent proteins responsible for inducing fusion were examined by electrophoresis of [ 35S]methionine-labeled proteins. 1 a,25(OH) 2D 3 increased synthesis of 14 proteins at 24 h after the addition, before it initiated fusion at 36 h. When spermidine synthesis was inhibited by adding methylglyoxal bis(guanylhydrazone) (MGBG), the enhanced synthesis in 9 of the 14 proteins induced by 1α,25(OH) 2D 3 was greatly diminished with a concomitant inhibition of fusion. Further addition of spermidine restored the synthesis of these 9 proteins and the fusion as well. The synthesis of 3 of the 9 proteins was similarly induced by interferon-γ, retinoic acid, or lipopolysaccharides, which induced activation but not fusion of macrophages. The apparent molecular weights of the remaining 6 proteins were 142K, 98K, 78K, 60K, 50K, and 42K. Recombinant mouse interleukin 4 (IL-4) also induced fusion of alveolar macrophages by a spermidine-dependent mechanism, and it increased the synthesis of 5 proteins (172K, 98K, 78K, 53K, and 50K). These results suggest that 3 spermidine-dependent proteins (98K, 78K, and 50K) are involved in the fusion of mouse alveolar macrophages induced by 1α,25(OH) 2D 3 and IL-4.