Receptors for the carboxyl-terminal region of PTH(1-84) are highly expressed in osteocytic cells
Receptors for the carboxyl-terminal region of PTH(1-84) are highly expressed in osteocytic cells
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DOI：
10.1210/en.142.2.916
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发表时间：
2001-02-01
期刊：
影响因子：
4.8
通讯作者：
Bringhurst, FR
中科院分区：
文献类型：
--
作者：
Divieti, P;Inomata, N;Bringhurst, FR
甲状旁腺激素是骨中细胞分化和功能的强有力的系统调节因子。它通过G蛋白偶联的1型甲状旁腺激素/甲状旁腺素相关多肽受体(PTH1R)作用于成骨细胞系的细胞。完整的甲状旁腺激素(1-84)的羧基片段(C-PTH片段)由甲状旁腺以钙依赖的方式与之共分泌，也通过外周组织中激素的蛋白分解产生。识别C-甲状旁腺素片段的受体(CPTHR)已在成骨细胞和软骨细胞中被描述。为了直接研究骨细胞中的CPTHR，我们从小鼠胚胎头盖骨中分离出克隆的、条件转化的细胞系，这些细胞系是靶向切割PTH1R基因的纯合子，并且转基因表达温度敏感的突变SV40T抗原。具有最高特异性结合CPTHR放射性配体I-125-[Tyr(34)]hPTH(19-84)的细胞显示出提示骨细胞表型的星状、树突状外观，并且表达的CPTHR位点/细胞比先前从相同骨骼分离的成骨细胞多6-10倍。在这些骨细胞(OC)中，CD44、连接蛋白43和骨钙素的mRNAs表达较高，而碱性磷酸酶和CBFA-1/OSF-2的mRNAs表达较少。HPTH(1-84)、hPTH(19-84)和hPTH(24-84)(IC(50)S=20-50 nm)和kPTH(39-84)(IC_(50)=500 nm)完全取代CPTHR放射性配基，但被10,000 nM hPTH(1-34)置换最少(24%)。HPTH(1-84)剂量依赖性地下调CPTHR的结合，这种作用可被离子霉素和活性佛波酯所模拟。人PTH(1-84)和hPTH(39-84)改变了OC细胞连接蛋白43的表达，促进了OC细胞的凋亡。半胱氨酸天冬氨酸氨基转移酶抑制剂DEVD可阻断甲状旁腺素(1-84)诱导的细胞凋亡，提示骨细胞可能是CPTHR介导的完整甲状旁腺素(1-84)和循环甲状旁腺素C片段独特作用的主要靶细胞。
PTH is a potent systemic regulator of cellular differentiation and function in bone. It acts upon cells of the osteoblastic Lineage via the G protein-coupled type-1 PTH/PTH-related peptide receptor (PTH1R). Carboxyl fragments of intact PTH(1-84) (C-PTH fragments) are cosecreted with it by the parathyroid glands in a calcium-dependent manner and also are generated via proteolysis of the hormone in peripheral tissues. Receptors that recognize C-PTH fragments (CPTHRs) have been described previously in osteoblastic and chondrocytic cells. To directly study CPTHRs in bone cells, we isolated clonal, conditionally transformed cell lines from fetal calvarial bone of mice that are homozygous for targeted ablation of the PTH1R gene and transgenically express a temperature-sensitive mutant SV40 T antigen. Cells with the highest specific binding of the CPTHR radio-ligand I-125-[Tyr(34)]hPTH(19-84) exhibited a stellate, dendritic appearance suggestive of an osteocytic phenotype and expressed 6- to 10-fold more CPTHR sites/cell than did osteoblastic cells previously isolated from the same bones. In these osteocytic (OC) cells, expression of mRNAs for CD44, connexin 43, and osteocalcin was high, whereas that for alkaline phosphatase and cbfa-1/osf-2 was negligible. The CPTHR radioligand was displaced completely by hPTH(1-84), hPTH(19-84) and hPTH(24-84) (IC(50)s = 20-50 nM) and by kPTH(39-84) (IC50 = 500 nM) but only minimally (24%) by 10,000 nM hPTH(1-34). CPTHR binding was down-regulated dose dependently by hPTH(1-84), an effect mimicked by ionomycin and active phorbol ester. Human PTH(1-84) and hPTH(39-84) altered connexin 43 expression and increased apoptosis in OC cells. Apoptosis induced by PTH(1-84) was blocked by the caspase inhibitor DEVD, We conclude that osteocytes, the most abundant cells in bone, may be principal target cells for unique actions of intact PTH(1-84) and circulating PTH C-fragments that are mediated by CPTHRs.