MI--SIGNAL RESPONSIVE TRANSCRIPTION IN OSTEOCLASTS

小眼症（Mi）基因编码一种最古老的公认的 破骨细胞发育和功能的关键因素。幂也是 黑素细胞谱系发育所必需的。最近克隆的 Mi基因编码一个HLH-ZIP转录因子，其独特性在于其编码的蛋白质是一种蛋白质。 高度受限的组织分布。我们已经定义了蛋白质和DNA MI的相互作用，并发现它可以结合并潜在地激活 转录关闭含有其识别元件的启动子。我们有 最近研究了一种不寻常的老鼠突变体， 骨质疏松症，解决与老化，并表明这是由于 Mi中的一个大删除。我们还发现了3个二聚体 M1（TFEB、TFEC和TFE 3）的三个家族统称为“MiT”家族。在 这些其他因素中至少有一个存在于MI缺乏者中， 破骨细胞的这种大鼠品系，表明一般的一般作用， 该家族在破骨细胞功能和成熟中的作用。我们的研究在 黑素细胞也显示Mi被MAP强烈激活， 细胞因子刺激后的激酶磷酸化。c-Kit信号 以这种方式通过激活Mi来操作。我们现在还知道， 这种激活的机制是磷酸-Mi选择性募集 转录共激活因子p300/CBP。重要的是，我们目前 结果表明，Mi类似地被磷酸化， 破骨细胞中的细胞因子信号传导，以及这种反应（对诸如 如白细胞介素6和M-CSF）可能关键在于一个主要途径， 破骨细胞的激活。对这些途径的理解显然是 调节破骨细胞功能的未来目标的核心 如骨质疏松症。为了进一步加强我们对这一点的认识， 因子并扩展我们对它在破骨细胞中作用的分析， 格兰特提出：1）系统地研究Mi 'T蛋白的时间 在整个发育和衰老过程中破骨细胞的表达模式，2） 衍生允许内源性MiT上调或下调的病毒载体 破骨细胞中的因子，并检查其对破骨细胞的影响 发展和功能，3）确定机械之间的关系， 和破骨细胞信号通路在骨稳态中的重要性 包括与石骨症有关的其他基因和细胞因子 功能的重要性，和4）确定转录靶基因， Mi在破骨细胞通过测试“合理”的候选人确定通过 已知启动子的序列分析以及高度严格的 差异显示需要野生型Mi上调，下调- 显性负性Mi调节，以及甘氨酸介导的Mi 在放线菌酮的存在下诱导。通过这些研究，我们 希望通过了解破骨细胞生物学， 米的核心角色。

The Microphthalmia (Mi) gene encodes one of the oldest recognized factors critical to osteoclast development and function. Mi is also required for development of the melanocyte lineage. The recently cloned Mi gene encodes a HLH-ZIP transcription factor, and is unique in its highly restricted tissue distribution. We have defined protein and DNA interactions of MI and found it to bind and potentially activate transcription off promoters containing its recognition element. We have recently examined an unusual rat mutant which displays severe osteoporosis which resolves with aging and shown that this results from a large deletion within Mi. We also discovered 3 dimerization partners of Mi (TFEB, TFEC, and TFE3) collectively called the "MiT" family. At least one of these other factors is present in the Mi-deficient osteoclasts of this rat strain, suggesting a general a general role of this family in osteoclast function and maturation. Our studies in melanocytes have also revealed that Mi is strongly activated by MAP kinase phosphorylation following cytokine stimulation. c-Kit signaling operates through activation of Mi in this fashion. We now also know that the mechanism of this activation is phospho-Mi selective recruitment of the transcriptional co-activators p300/CBP. Importantly, our current results suggest that Mi is similarly phosphorylated in response to cytokine signaling in osteoclasts, and this response (to factors such as interleukin 6 and M-CSF) could lie critically within a major pathway of osteoclast activation. The understanding of such pathways is clearly central to future goals of modulating osteoclast function in conditions such as osteoporosis. To further enhance our understanding of this factor and extend our analysis of its actions within osteoclasts, this grant proposes to: 1) systematically examine Mi'T protein temporal expression patterns in osteoclasts throughout development and aging, 2) derive viral vectors permitting up- or down-regulation of endogenous MiT factors in osteoclasts, and examine their consequences on osteoclast development and function, 3) define mechanistic relationships between Mi and osteoclast signaling pathways of importance in bone homeostasis including other genes implicated in osteopetrosis and cytokines of functional importance, and 4) identify transcriptional target genes for Mi in osteoclasts by testing "rational" candidates identified through sequence analysis of known promoters as well as a highly stringent differential display which requires up-regulation by wild type Mi, down- regulation by dominant negative Mi, as well as cytokine-mediated Mi induction in the presence of cycloheximide. Through these studies we hope to gain insight into osteoclast biology through an understanding of Mi's central role.