Identification and characterization of parathyroid hormone receptors on dog kidney, human kidney, chick bone and human dermal fibroblast. A comparative study of functional and structural properties

Abstract

To evaluate the functional and structural characteristics of the parathyroid hormone (PTH) receptors on different tissues and the possible heterogeneity in structure and function, PTH receptors on dog kidney membrane, human kidney membrane, chick bone cell membrane and human dermal fibroblast membrane were evaluated. The results showed that human kidney plasma membrane, canine kidney plasma membrane and chick bone cell membrane possess one single class of PTH receptor with a Kd (dissociation constant) of 1-5 nM and an IC50 also of 1-5 nM. The number of binding sites was 800 fmol per mg of protein for chick bone cell particulate membrane, 1-5 pmol per mg of protein for human kidney plasma membrane and 2.2 pmol per mg of protein for dog kidney plasma membrane. Photoaffinity labelling identified a major binding component with a molecular mass of 70 kDa in all three types of membrane. The plasma membrane fraction from human dermal fibroblast contained two different binding sites for PTH with high (Kd = 2 nM) and low (Kd = 580 nM) affinities respectively. The IC50 for the adenylate cyclase is about 2 nM, which is similar to the Kd of the high-affinity site. Photoaffinity labelling also demonstrated a major binding component with a molecular weight of 70 kDa. We conclude that structural and functional similarity exists among the PTH receptors present on chick bone cell membrane, dog kidney membrane and human kidney membrane. The human dermal fibroblast possesses two different binding sites, one of which is coupled to adenylate cyclase.

Stimulation of Protein Kinase C Activity in Cells Expressing Human Parathyroid Hormone Receptors by C- and N-Terminally Truncated Fragments of Parathyroid Hormone 1–34

“…They could arise from intrinsic differences between hPTHR1s and opossum and rat PTHR1s, from differences in cellular PTHR1 expression or effector coupling or in the case of N-truncated fragments from PLC-independent PKC-activating mechanisms. To address these questions, we have measured the activation of membrane PKC activity by hPTH fragments in LLC-PK1 cells expressing hPTHR1s, for which adenylyl cyclase and PLC responses are known in detail and in a homologous human foreskin fibroblast system (fibroblasts have PTH/PTHrP receptors (17)(18)(19)(20)(21)(22) ). We will show that PLC-stimulating (14 -16) C-terminally truncated fragments such as hPTH(1-31)NH 2 and hPTH(1-28)NH 2 stimulate PKC activity as efficiently as hPTH(1-34)NH 2 in LLC-PK1 cells, whereas N-terminally truncated fragments that do not detectably stimulate IP 3 production in LLC-PK1 cells (14 -16) stimulate PKC activity in human fibroblasts.…”

Haematological manifestations in primary hyperparathyroidism

“…The elevated PTH levels are likely to be related to bone marrow fibrosis 10 11 12 13 . The induction of certain cytokines, such as interleukin-6 and tumour necrosis factor is also thought to be the alternate mechanism due to the elevated PTH levels 5 14 15 . Some studies have demonstrated that intact PTH has inhibitory effects on the growth of erythroid progenitor cells and erythropoietin synthesis 16 17 .…”

Stk11 (Lkb1) deletion in the osteoblast lineage leads to high bone turnover, increased trabecular bone density and cortical porosity

“…Previous studies have demonstrated that PTH is a potent stimulator of fibroblast proliferation [27]. It is speculated that osteoblasts respond to PTH to release paracrine factors such Igfs and Pdgfs that modulate adjacent fibroblastic cell types [28] considered to be preosteoblastic cells based on their location and expression of osteoblast marker proteins [29] and [30].…”