Miao Dengshun, Su Hanyi, He Bin, Gao Jianjun, Xia Qingwen, Zhu Min, Gu Zhen, Goltzman David, Karaplis Andrew C
Department of Anatomy, Histology and Embryology, The Research Center for Bone and Stem Cells, Nanjing Medical University, Nanjing, Jiangsu, People's Republic of China.
Proc Natl Acad Sci U S A. 2008 Dec 23;105(51):20309-14. doi: 10.1073/pnas.0805690105. Epub 2008 Dec 17.
Parathyroid hormone (PTH) plays a central role in the regulation of serum calcium and phosphorus homeostasis, while parathyroid hormone-related protein (PTHrP) has important developmental roles. Both peptides signal through the same G protein-coupled receptor, the PTH/PTHrP or PTH type 1 receptor (PTH1R). PTHrP, normally a secreted protein, also contains a nuclear localization signal (NLS) that in vitro imparts functionality to the protein at the level of the nucleus. We investigated this functionality in vivo by introducing a premature termination codon in Pthrp in ES cells and generating mice that express PTHrP (1-84), a truncated form of the protein that is missing the NLS and the C-terminal region of the protein but can still signal through its cell surface receptor. Mice homozygous for the knock-in mutation (Pthrp KI) displayed retarded growth, early senescence, and malnutrition leading postnatally to their rapid demise. Decreased cellular proliferative capacity and increased apoptosis in multiple tissues including bone and bone marrow cells were associated with altered expression and subcellular distribution of the senescence-associated tumor suppressor proteins p16(INK4a) and p21 and the oncogenes Cyclin D, pRb, and Bmi-1. These findings provide in vivo experimental proof that substantiates the biologic relevance of the NLS and C-terminal portion of PTHrP, a polypeptide ligand that signals mainly via a cell surface G protein-coupled receptor.
甲状旁腺激素（PTH）在调节血清钙和磷稳态中起核心作用，而甲状旁腺激素相关蛋白（PTHrP）具有重要的发育作用。这两种肽都通过同一G蛋白偶联受体——甲状旁腺激素/甲状旁腺激素相关蛋白受体或1型甲状旁腺激素受体（PTH1R）进行信号传导。PTHrP通常是一种分泌蛋白，也含有一个核定位信号（NLS），在体外该信号可使该蛋白在细胞核水平上具有功能。我们通过在胚胎干细胞（ES细胞）的Pthrp中引入一个提前终止密码子，并生成表达PTHrP（1-84）的小鼠来研究这种体内功能，PTHrP（1-84）是该蛋白的一种截短形式，缺失了NLS和蛋白的C末端区域，但仍可通过其细胞表面受体进行信号传导。敲入突变（Pthrp KI）的纯合小鼠生长迟缓、早衰且营养不良，导致出生后迅速死亡。包括骨骼和骨髓细胞在内的多个组织中细胞增殖能力下降和细胞凋亡增加，这与衰老相关的肿瘤抑制蛋白p16（INK4a）和p21以及癌基因细胞周期蛋白D、视网膜母细胞瘤蛋白（pRb）和Bmi-1的表达改变和亚细胞分布改变有关。这些发现提供了体内实验证据，证实了PTHrP的NLS和C末端部分的生物学相关性，PTHrP是一种主要通过细胞表面G蛋白偶联受体进行信号传导的多肽配体。
