Mechanism of Parathyroid hormone-Related Protein Production and Paracrine Function on Bovine Mammary Epithelial Cells

具有甲状旁腺激素样功能和结构的甲状旁腺激素相关蛋白（PTHrP）在1987年被确定为恶性肿瘤体液性高钙血症的主要因素。包括泌乳乳腺在内的许多正常组织都产生PTHrP，但PTHrP的作用尚不清楚。在产犊后1周采集泌乳荷斯坦奶牛的乳腺组织。乳腺组织经酶解释放腺泡。细胞镀于24孔胶原包被塑料培养板中。第6天融合后，在培养基中添加不同浓度的莫能菌素、秋水仙碱和细胞松弛素B，观察PTHrP产量的变化。在莫能菌素和细胞松弛素B的刺激下，PTHrP的产生呈剂量依赖性地减少，而在克莱希碱的刺激下，PTHrP的产生略有增加。利用逆转录聚合酶链反应和原位杂交技术检测PTHrP mRNA的表达在莫能菌素处理后呈下降趋势。本研究表明，乳腺上皮细胞分泌PTHrP可能与细胞质中肌动蛋白丝的形成有关，而与微管的形成无关，提示乳腺上皮细胞分泌PTHrP可能通过构成途径而非调控途径。形态学上，莫能菌素处理的乳腺上皮细胞肿胀。这一发现还表明，抑制细胞内囊泡运输可以抑制PT1JrP的产生。

Parathyroid hormone-related protein (PTHrP) that had parathyroid hormone-like function and Structure was identified in 1987 as a major factor of humoral hypercalcemia of malignancy. PTHrP is produced in many normal tissues including the lactating mammary gland, however the role of PTHrP is still unclear. Mammary tissues were collected from lactating Holstein dairy cows at 1 week after calving. The mammary tissues were enzymatically digested to release glandular acini. The cells were plated in 24-well collagen-coated plastic culture plates. After confluent at day 6, various concentrations of monensin, colchicine, and cytochalasin B were supplemented to the medium to investigate the change of PTHrP production. The PTHrP production decreased in the cells supplemented with monensin and cytochalasin B in a dose-dependent manner, whereas its production slightly increased by the stimulation with colehicine. Expression of PTHrP mRNA investigated by using reverse transcription-polymerase chain reaction and in situ hybridization techniques decreased when the cells were treated with monensin. This study indicated that PTHrP production from mammary epithelial cells might associated with the formation of actin filaments in the cytoplasm but not with that of microtubules, suggesting that PTHrP might secrete from mammary epithelial cells by the constitutive pathway but not the regulated pathway. Morphologically, mammary epithelial cells treated with monensin were swollen. This finding also suggested that PT1JrP production was inhibited by the inhibition of intracellular vesicle transport.