Molecular mechanisms of pigment cell differentiation.

小眼相关转录因子（MITF）在色素细胞分化中起重要作用。瞬时转染实验表明，MITF可激活酪氨酸酶和酪氨酸酶相关蛋白1 （TRP-1）基因启动子，但不能激活TRP-2基因启动子。出乎意料的是，缺乏羧基末端125个氨基酸的截断MITF可以反激活TRP-2启动子。因此，使用酵母双杂交系统，我们克隆了几个编码蛋白质的cdna，这些蛋白质可能与MITF的羧基末端部分相互作用。此外，我们已经确定了三种新的MITF亚型，称为A，B和H型，它们的氨基末端和表达模式不同。一个真正的MITF被重新命名为MITF- m，因为它只在黑色素细胞和黑色素瘤中表达。这四种异构体共享整个羧基末端部分，包括基本的螺旋-环-螺旋和亮氨酸拉链结构。我们已经证明，MITF-A和MITF-M一样，可以激活酪氨酸酶和TRP-1基因启动子，但不能激活trp -2。MITF-A mRNA主要表达于视网膜色素上皮。此外，我们还获得了以下结果，总结如下。1.人类酪氨酸酶基因的三个顺式调控元件已经被确定，每个元件都包含一个CATGTG基序的拷贝，并且是色素细胞特异性转录所必需的。2.人类TFEC异构体，称为TFECL，已被确定为转录激活因子。TFECL包含一个激活域，在大鼠TFEC中被删除，最初被确定为大鼠软骨肉瘤的转录抑制因子。3.从大鼠神经纤维蛋白dna的核苷酸序列推导出其氨基酸序列。肾上腺髓质素是一种有效的血管扩张肽，已被证明由培养的脉络膜丛癌细胞产生和分泌，这是一种来自脉络膜丛上皮的罕见肿瘤。

Microphthalmia-associated transcription factor (MITF) plays an important role in pigment cell differentiation. Transient transfection assays have shown that MITF transactivates the tyrosinase and tyrosinase-related protein 1 (TRP-1) gene promoters, but not the TRP-2 gene promoter. Unexpectedly, a truncated MITF lacking the carboxyl-terminal 125 amino acids could transactivate the TRP-2 promoter. Consequently, using a yeast two-hybrid system, we have cloned several cDNAs coding for proteins which may interact with MITF's carboxyl-terminal portion. Moreover, we have identified three novel MITF isoforms, termed A,B,and H types, which differ in their amino-termini and expression patterns. An authentic MITF has been renamed MITF-M,because it is exclusively expressed in melanocytes and melanoma. These four isoforms share the entire carboxyl-terminal portion, including a basic helix-loop-helix and leucine zipper structure. We have shown that MITF-A,like MITF-M,transactivates the tyrosinase and TRP-1 gene promoters, but not-TRP-2. MITF-A mRNA is predominantly expressed in retinal pigment epithelium. In addition, we have obtained the following results as summarized below. 1.The threc cis-regulatory elements of the human tyrosinase gene have been identified, and each of these elements contains one copy of a CATGTG motif and is required for pigment cell-specific transcription. 2.A human TFEC isoform, termed TFECL,has been identified as a transcriptional activator. TFECL contains an activation domain which is deleted in rat TFEC,originally identified as a transcriptional repressor in rat chondrosarcoma. 3.The amino acid sequence of rat neurofibromin has been deduced from the nucleotide sequence of its cDNA.4.Adrenomedullin, a potent vasodilator peptide, has been shown to be produced and secreted by cultured choroid plexus carcinoma cells, a rare neoplasm derived from the epithelium of the choroid plexus.