Molecular biological analysis of signal transduction system through parathyroid hormone receptor. Evaluation of parathyroid hormone receptor in patients with pseudohypoparathyroidism.

假性甲状旁腺功能低下症（physichypopathyroidism，PHP）是一组以甲状旁腺激素（parathyroidhormone，PTH）抵抗为特征的疾病，PHP 1b被认为是由异常的PTH受体引起的。为探讨PHP 1b的发病机制，采用逆转录-聚合酶链反应（RT-PCR）、北方印迹杂交（Northern blot）和PCR产物直接测序的方法，对PHP 1b患者皮肤成纤维细胞中甲状旁腺素受体（PTH受体）进行了分析。虽然在PHP 1b患者中未发现PTH受体的cDNA突变，但PHP 1b患者皮肤成纤维细胞中PTH受体的表达水平低于正常对照。因此，为了阐明PHP 1b患者PTH受体表达降低的机制，我们接下来克隆了人PTH受体基因的5'端。我们发现人甲状旁腺素受体基因5'端至少有两个启动子和三个非翻译外显子，并且这些启动子和外显子具有组织特异性。然而，在这些启动子区和非翻译外显子的DNA序列从PHP 1b患者与正常对照没有什么不同。因此，有必要分析与人PTH受体启动子区相互作用的核蛋白，以阐明PHP 1b的发病机制。

Pseudohypoparathyroidism (PHP) is a group of diseases characterized by resistance to parathyroid hormone (PTH) and PHP1b has been thought to be caused by abnormal PTH receptor. In order to clarify the pathogenesis of PHP1b, PTH receptor in skin fibroblasts from patients with PHP1b was analyzed by reverse-transcription coupled polymerase chain reaction (RT-PCR), Northern blot analysis and direct sequencing of the PCR products. Although no mutation was found in cDNA for PTH receptor in patients with PHP1b, the expression level of PTH receptor in skin fibroblasts from patients with PHP1b was lower than that from normal control. Therefore, to clarify the mechanism of the reduced expression of PTH receptor in patients with PHP1b, we next cloned the 5' end of human PTH receptor gene. We found that there are at least two promoters and three untranslated exons in the 5' end of human PTH receptor gene, and these promoters and exons are used in a tissue-specific manner. However, the DNA sequences in these promoter regions and untranslated exons from patients with PHP1b are not different from those of normal control. Therefore, it seems necessary to analyze the nuclear proteins that interact with the promoter region of human PTH receptor to elucidate the pathogenesis of PHP1b.