| Co-Investigator(Kenkyū-buntansha) |
TANAKA Hirofumi School of Dentistry, Showa University, 歯学部, 助手 (30146899)
MIYAURA Chisato School of Dentistry, Showa University, 歯学部, 助手 (20138382)
TAKAHASHI Naoyuki School of Dentistry, Showa University, 歯学部, 講師 (90119222)
SHINKI Toshimasa School of Dentistry, Showa University, 歯学部, 講師 (90138420)
ABE Etsuko School of Dentistry, Showa University, 歯学部, 助教授 (70119147)
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| Research Abstract |
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
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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
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