Analysis of mast cell-specific transcription by mutant mice

MITF是一种碱性-螺旋-环-螺旋亮氨酸拉链（bHLH-Zip）转录因子，对肥大细胞的发育具有重要意义。编码MITF的mi位点具有多种突变等位基因。这对研究MITF在体内的结构-功能关系是有用的。mi/mi基因型肥大细胞表达正常数量的异常MITF (mi-MITF)，而tg/tg基因型肥大细胞不表达任何异常MITF。mi/mi小鼠的肥大细胞异常比tg/tg小鼠更为严重，说明mi- mitf具有抑制作用。由mi^<ce>突变等位基因编码的MITF （ce-MITF）缺少Zip结构域。我们使用mi^<ce>/mi^<ce>小鼠检验了Zip域的重要性。mi^<ce>/mi^<ce>小鼠肥大细胞中c-kit、颗粒酶B （Gr B）和色氨酸羟化酶（TPH） mrna的数量下降至与tg/tg小鼠相当的水平，数量介于+/+小鼠和mi/mi小鼠之间。grb介导肥大细胞的细胞毒性活性，TPH是合成血清素的限速酶。mi^<ce>/mi^<ce>肥大细胞的细胞毒活性和血清素含量与tg/tg肥大细胞相当，且显著高于mi/mi肥大细胞。mi^<ce>/mi^<ce>肥大细胞的表型与tg/tg肥大细胞相似，而与mi/mi肥大细胞的表型相似，提示ce- mitf无功能。MITF的Zip结构域似乎对肥大细胞的发育很重要。我们还发现，MITF在小鼠肥大细胞蛋白酶(mMCP)-6、-7、α -黑色素细胞刺激激素受体、n -去乙酰化酶n -硫转移酶2基因的转录中发挥重要作用。MITF通过与PEBP2/CBF、c-Jun和GABP等其他转录因子的相互作用调控它们的转录。MITF似乎在肥大细胞特异性基因的转录调控中起着至关重要的作用。

MITF is a basic-helix-loop-helix leucine zipper (bHLH-Zip) transcription factor, which is important for the development of mast cells. The mi locus encoding MITF possesses various mutant alleles. These are useful for examining the structure-function relationship of MITF in vivo. Mast cells of mi/mi genotype express normal amount of abnormal MITF (mi-MITF), whereas mast cells of tg/tg genotype do not express any MITFs. Mast cells of mi/mi mice show more severe abnormalities than those of tg/tg mice, indicating that the mi-MITF possesses the inhibitory function. The MITF encoded by the mi^<ce> mutant allele (ce-MITF) lacks the Zip domain. We examined the importance of the Zip domain using mi^<ce>/mi^<ce> mice. The amounts of c-kit, granzyme B (Gr B), and tryptophan hydroxylase (TPH) mRNAs decreased in mast cells of mi^<ce>/mi^<ce> mice to levels comparable to those of tg/tg mice, and the amounts were intermediate between those of +/+ mice and those of mi/mi mice. Gr B mediates the cytotoxic activity of mast cells, and TPH is a rate-limiting enzyme for the synthesis of serotonin. The cytotoxic activity and serotonin content of mi^<ce>/mi^<ce> mast cells were comparable to those of tg/tg mast cells, and were significantly higher than those of mi/mi mast cells. The phenotype of mi^<ce>/mi^<ce> mast cells was similar to that of tg/tg mast cells rather than to that of mi/mi mast cells, suggesting that the ce-MITF had no functions. The Zip domain of MITF appeared to be important for the development of mast cells. We also revealed that MITF played an important role in the transcription of mouse mast cell protease (mMCP)-6, -7, alpha-melanocyte stimulating hormone receptor, N-deacetylase N-sulfotransferase 2 genes. MITF regulated their transcription through the interaction of other transcription factors, such as PEBP2/CBF, c-Jun and GABP.MITF appeared to play a crucial role in the transcriptional regulation of mast cell specific genes.