Calcitonin receptors have been characterized for the first time in isolated osteoclasts. These receptors have been demonstrated by autoradiographic and biochemical methods, and the cells have also been shown to respond to calcitonin with a dose-dependent increase in cyclic AMP. The receptors in rat osteoclasts are specific and of high affinity (dissociation constant, Kd, 1 to 6 X 10(-10) M), and are present in greater numbers than in any cell previously studied (greater than 10(6) per cell). Chemical cross-linking of 125I-labeled salmon calcitonin to osteoclasts using disuccinimidyl suberate resulted in identification of a receptor component with a relative molecular weight of 80,000-90,000. By counting grains in autoradiographic experiments, we found that greater than 80% of specifically bound radioactivity was associated with multinucleate osteoclasts and the remainder was associated with mononuclear cells that are not osteoblasts, but that may be osteoclast precursors.

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Abundant calcitonin receptors in isolated rat osteoclasts. Biochemical and autoradiographic characterization.

Two isoforms of the regulatory subunits of cyclic AMP (cAMP)-dependent protein kinase that bind cAMP are inversely expressed during ontogeny and cell differentiation. These cAMP-binding receptor proteins in harmony may regulate the growth of normal cells and their differentiation into nondividing states. Cancer cells can also be made to differentiate and stop growing when the functional balance of these cAMP receptor proteins is restored by treatment with site-selective cAMP analogues or by the use of an antisense oligodeoxynucleotide, suggesting new approaches to cancer treatment.

https://cancerres.aacrjournals.org/content/canres/50/22/7093.full.pdf

Role of cyclic AMP receptor proteins in growth, differentiation, and suppression of malignancy: new approaches to therapy.

The clonal cell line UMR 106, which was originally derived from a rat transplantable osteogenic sarcoma with an osteoblastic phenotype, was subcloned after the emergence of a calcitonin-responsive adenylate cyclase was noted in late passages. Detailed studies on the stimulation of adenylate cyclase and activation profile of the cyclic AMP-dependent protein kinase isoenzymes in response to parathyroid hormone (PTH) and salmon calcitonin (SCT) were conducted on two subclones (UMR 106-01 and UMR 106-06). Both subclones responded in an identical manner to PTH, which stimulated adenylate cyclase and activated both isoenzyme I and isoenzyme II of cyclic AMP-dependent protein kinase. In contrast, only UMR 106-06 cells responded to calcitonin. At 3×10−8M SCT, there was a sevenfold stimulation of adenylate cyclase, 84% activation of isoenzyme I, and 44% activation of isoenzyme II. The activation profiles of the isoenzymes to PTH and SCT in UMR 106-06 were similar. Furthermore, their response to SCT correlates with the presence of specific, saturable binding of125I-labeled SCT. Binding parameters indicate apparent Kd=0.8 nM and 6,000 receptors/cell. These data point to a significant phenotypic change having taken place in this clonal cell line with prolonged maintenance in culture, with the emergence of a calcitonin receptor linked to adenylate cyclase and protein kinase activation.

Characterization of an osteoblast-like clonal cell line which responds to both parathyroid hormone and calcitonin.

Calcitonin (CT), a 32 amino acid peptide hormone produced primarily by the thyroid, and its receptor (CTR) are well known for their ability to regulate osteoclast mediated bone resorption and enhance Ca2+ excretion by the kidney. However, recent studies now suggest that CT and CTRs may play an important role in a variety of processes as wide ranging as embryonic/foetal development and sperm function/physiology. In this review article, CT and CTR gene transcription, signal transduction and function are addressed. The effects of CT on the physiology of a variety of organ systems are discussed and the relationship between polymorphisms in the CTR gene and bone mineral density (BMD)/osteoporosis is examined. Recent studies demonstrating the ability of receptor activity modifying proteins (RAMPs) to post-translationally modify the calcitonin receptor-like receptor (CRLR) are detailed and studies employing transgenic mouse technology to determine the temporal and tissue specific transcriptional activity of the CTR gene in vivo are discussed.

Calcitonin and calcitonin receptors: bone and beyond

Several human breast cancer cell lines express the calcitonin receptor (CTR), but this has not been demonstrated previously in clinical breast cancers. We examined 18 primary breast cancers by reverse transcription-PCR, for expression of CTR and of the bone proteins osteopontin (OPN) and bone sialoprotein (BSP). OPN and CTR were expressed by each of the tumours, and 7 (39%) additionally expressed an alternate form of CTR, whilst BSP was expressed by 13 tumours (72%). In situ hybridisation confirmed that expression of OPN and CTR was confined to the tumour cells. Expression of CTR, BSP and OPN may prove to be a useful marker for breast cancers, and their role in the homing of breast cancer cells to bone remains to be investigated.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/%28SICI%291097-0215%2819971210%2973%3A6%3C812%3A%3AAID-IJC7%3E3.0.CO%3B2-5

Calcitonin receptors, bone sialoprotein and osteopontin are expressed in primary breast cancers

The influence of calcitonin on cell growth was examined in the human breast cancer cell line, T 47D. These cells possess specific high-affinity receptors for calcitonin as well as a sensitive calcitonin-responsive adenylate cyclase. In the T 47D cells, low doses of salmon calcitonin initially stimulated cell growth and the incorporation of [3H]thymidine into acid-insoluble macromolecules. This initial stimulation was followed by an inhibitory effect of calcitonin upon cell proliferation, which occurred during the log phase of growth, was dose dependent, and resulted in prolongation of doubling time from 36 to 90 hr. DNA and protein content correlated well with cell number. By 7 to 9 days of treatment, cell numbers of calcitonin-treated cells reached a mean of 66.5 ± 3.7% of control ( p < 0.001, n = 8) (range, 51.3 to 82.9%). This biphasic effect of calcitonin on T 47D cells was reproduced by human calcitonin and prostaglandin E2 in the order of potency with which they influence adenylate cyclase. Epidermal growth factor (10−9 m) and insulin (10−9 m) stimulated the growth of T 47D cells, but this effect was abolished when either hormone was combined with salmon calcitonin (3 × 10−10 m). Calcitonin specifically activated type II isoenzyme of cyclic adenosine 3′:5′-monophosphate-dependent protein kinase in the T 47D cells. In view of other published data relating activation of this isoenzyme to growth regression in cancer cells, this response to calcitonin may be causally related to the inhibitory effect of the hormone upon cell replication in T 47D cells. The mechanism of the early stimulatory effect of calcitonin upon mitogenesis is not explained, although the possibility of stimulation of activity of type I isoenzyme of cAMP-dependent protein kinase has not been entirely excluded in the present experiments.

https://cancerres.aacrjournals.org/content/canres/43/2/794.full.pdf

Calcitonin Effects on Growth and on Selective Activation of Type II Isoenzyme of Cyclic Adenosine 3′:5′-Monophosphate-dependent Protein Kinase in T 47D Human Breast Cancer Cells

Livesey Sa

Papers

Calcitonin Effects on Growth and on Selective Activation of Type II Isoenzyme of Cyclic Adenosine 3′:5′-Monophosphate-dependent Protein Kinase in T 47D Human Breast Cancer Cells