Mechanisms of Fusion of Macrophages Induced by 1 ,25(OH)_2D_3

点击翻译按钮获取中文摘要

We have reported that 1<alpha>,25-dihydroxyvitamin D_3 [1<alpha>,25(OH)_2D_3] directly induces fusion of mouse alveolar macrophages at a very high rate (circa 70-80%) by a mechanism involving protein synthesis (Proc. Natl. Acad. Sci. USA 80:5583,1983; FEBS Letters 174:61,1984). While examining further the mechanism of the 1<alpha>,25(OH)_2D_3-induced fusion of macrophages, we found that polyamines are involved in this mechanism. Mouse alveolar macrophages incubated with 12 nM 1<alpha>,25(OH)_2D_3 began to fuse at 36 h and the fusion rate increased linearly up to 60 h. Addition of as much as 0.05 - 5 mM -difluoromethylornithine (<alpha>-DFMO), a specific inhibitor of ornithine decarboxylase, did not inhibit fusion appreciably, but addition of 0.05 - 5<mu>M methylglyoxal bis (guanylhydrazone) (MGBG), an inhibitor of S-adenosylmethionine decarboxylase, strikingly inhibited fusion. When macrophages were treated with both 12 nM 1<alpha>,25(OH)_2D2_3 and 5 <mu>M MGBG for the first 12 h and i … More ncubated further for 60 h in fresh medium containing 1<alpha>,25(OH)_2D_3, fusion was significantly inhibited, suggesting that the 1<alpha>,25(OH)_2D_3-induced synthesis of polyamines precedes fusion. The inhibition by MGBG of the 1<alpha>,25(OH)_2D_3-induced fusion was restored completely by adding 1 <mu>M spermidine or spermine or 100 M putrescine. None of the polyamines alone induced fusion. MGBG suppressed the 1<alpha>,25(OH)_2D_3-induced incorporation of [^3H]-leucine into the trichloroacetic acid-insoluble fraction in macrophages, but its inhibitory effect was restored completely by adding 1<mu> M spermidine. When macrophages were incubated with [^<14>C]-ornithine, the polyamine that accumulated most was [^<14>C]-spermidine. 1<alpha>,25(OH)_2D_3 further enhanced the accumulation of [^<14>C] putrescine and spermine was not appreciably altered by the 1<alpha>,25(OH)_2D_3 treatment. Adding MGBG almost completely suppressed the accumulation of [^<14>C]-spermidine and spermine, but it enhanced the accumulation of [^<14>C]-putrescine considerably. These results indicate that spermidine or spermine is an important intracellular mediator of the 1<alpha>,25(OH)_2D_3 action in inducing protein synthesis, which in turn somehow induces fusion of alvolar macrophages. Less