Indomethacin, a cox inhibitor, enhances 15-PGDH and decreases human tumoral C cells proliferation.

High levels of prostaglandins (PGs) are currently found in tumoral cells, due to expression of the inducible PGs synthesis enzyme, the cyclooxygenase 2 (COX 2). Non Steroidal Anti Inflammatory Drugs (NSAIDs) possess an antitumoral effect related, in a large extend, to the inhibition of this enzyme. It was recently suggested that the decreased activity of 15-hydroxyprostaglandin dehydrogenase (15-PGDH), the key enzyme catabolysing PGs, may be responsible too for experimentally induced colon tumor enhancement. We report here, for the first time, that indomethacin, an NSAID, decreased TT cell proliferation, derived from a human Medullary Thyroid Carcinoma (MTC). This effect is time and concentration-dependent. Moreover, indomethacin enhanced expression and activity of 15-PGDH. The 15-PGDH levels were negatively correlated with TT cell proliferation (r = -0.52, p < 0.001). Indomethacin, known to decrease COX levels and activity, could also act in modifying catabolism of PGs. This suggests that 15-PGDH is involved in tumoral development, and could therefore be considered as a target for NSAIDs.

Indomethacin increases 15-PGDH mRNA expression in HL60 cells differentiated by PMA.

We previously reported an induction of 15-hydroxyprostaglandin dehydrogenase type I mRNA (15-PGDH) expression accompanied by a decrease in prostaglandin E2(PGE2) levels during cord blood monocytes differentiation into preosteoclastic cells by 1,25 dihydroxyvitamin D3 (1,25 (OH)2D3). These results suggested a role of prostaglandin (PG) enzymes in adhesion and/or differentiation of monocytes. In the present work, we studied modulation of gene expression of PG metabolism enzymes mRNAs in HL60 cells differentiated by phorbol myristate acetate (PMA) into the monocyte/macrophage lineage. We showed that adhesion of HL60 induced by PMA causes an increase of cyclooxygenase 2 (COX 2) and 15-PGDH mRNAs. When adding indomethacin, a non steroidal antiinflammatory drug known to inhibit COX activity, the cells remained attached and expressed large amounts of 15-PGDH mRNA while COX 2 mRNA expression remained unchanged. Indomethacin, in association with PMA can consequently exert a dual control on key enzymes of PGE2 metabolism without modifying adhesion of the cells.

Biological properties of salmon calcitonin IV.

In this study we characterized the biological activity of the recently identified salmon calcitonin (sCT) IV, in order to evaluate its potential therapeutic value. In the rat bioassay, sCT IV exhibited a 30% higher hypocalcemic activity than sCT I. The capacity of the molecule to inhibit bone resorption was assessed in vitro by the bone resorbing assay and the pit assay. An inhibitory effect, similar to that of sCT I, was observed in both assays. The interaction of sCT IV with the rabbit CT receptor was also studied. The affinity of sCT IV for the receptor was similar to that of sCT I, as was the potency for stimulating cAMP production. The antigenicity of the two molecules was not identical. Thus, this new CT could represent a useful novel therapeutic agent for the treatment of bone disorders.

Influence of laminin substratum on cell proliferation and CALC I gene expression in medullary thyroid carcinoma C cell lines.

Medullary thyroid carcinoma (MTC) originates from C cells, which secrete calcitonin (CT) and CT gene-related peptide (CGRP), the two splice peptide products of the CALC I gene. Normal and hyperplastic C cells are intrafollicular, in contact with the basement membrane (BM) that is maintained around the differentiated tumors. To investigate the relationships between MTC evolution and BM constituents, we examined the modifications induced by laminin-1 and -2 (merosin), two isoforms colocalized in the follicular BM, on three MTC cell lines: murine rMTC 6-23 and CA-77 cells, and human TT cells. Laminin exerted a mitogenic activity on rMTC 6-23 and on TT cells, causing a concurrent decrease in both CT and CGRP mRNA levels and production of the peptides. Conversely, laminin reduced the proliferation rate and enhanced CGRP synthesis and secretion in CA-77 cells. This antiproliferative response, which coincides with an increase in differentiation markers, is comparable to that reported in normal cells and also in the neoplastic Caco-2 cell line. This suggests that laminin could exert opposite effects depending on the stage of tumor evolution.

Calcitonin receptor mRNA expression in TT cells: effect of dexamethasone.

Among the four isoforms of the calcitonin receptor (CTR) described in humans, two differ by the presence of h-CTR1 or absence of h-CTR2 of 16 amino acids in the first intracellular loop. Both receptors are biologically active. The TT cell line derived from a human medullary carcinoma of the thyroid is characterized by the secretion of large amounts of calcitonin. We have recently shown that this cell line expresses h-CTR2. In the present work we have studied the expression of CTR during TT cell proliferation and used dexamethasone to modify calcitonin expression in order to establish if an autocrine regulation involving calcitonin and its receptor was functional in the TT cells. The expression of this receptor and of calcitonin during TT cell proliferation was studied by reverse transcriptase-polymerase chain reaction (RT-PCR). Dexamethasone, a potent inhibitor of TT cell proliferation, levels (day 6 of culture) specifically increased receptor levels from day 8 onwards. CT peptide and CT mRNA levels decreased or were similar during experimental time. CTR regulation by glucocorticoids is suggested in TT cells. Autocrine regulation of CTR is also suggested by relation between CT mRNA levels and CTR mRNA.

Calcitonin receptor mRNA is expressed in human medullary thyroid carcinoma.

We recently reported the presence of a truncated form (h-CTR2) of the human calcitonin receptor (CTR) in TT cells, a cell line derived from medullary thyroid carcinoma (MTC). This form (h-CTR2), characterized by the absence of 16 amino acids in the first intracellular domain, was also detected in two cases of MTC. In the present study we determined the expression of CTR mRNA in a larger sample, representative of the different clinical forms of MTC, and in normal thyroid. h-CTR2 was expressed in all MTC specimens (both sporadic and familial) and in the normal thyroid samples. The expression of the receptor mRNA was higher in MTC compared with normal thyroid. Moreover, CT and CTR mRNA levels were modified significantly during proliferation. This result suggests that CT may be involved in proliferation of MTC via autocrine/paracrine regulation. Calcitonin secretion by MTC may play a role in the development and spread of these tumors.

Cloning and sequencing of a new 15-hydroxyprostaglandin dehydrogenase related mRNA.

NAD+-dependent 15-hydroxyprostaglandin dehydrogenase (type-I 15-PGDH) inactivates prostaglandins. We recently reported an mRNA sequence coding for a predicted isomer (PGDH(rI)) of this enzyme. The TT cell line, derived from medullary thyroid carcinoma (MTC), expresses mRNAs for both isomers. We report here the expression by TT cells and MTC of a third 15-PGDH related mRNA (PGDH(rII)), 241 nt shorter than type-I 15-PGDH. RNase protection assays confirmed that TT cells expressed this mRNA (PGDH(rII)). Thus different splicing patterns could be involved in the post-transcriptional regulation of type-I 15-PGDH gene in MTC.

Chromosomal localization of the type-I 15-PGDH gene to 4q34-q35.

The gene encoding the human NAD(+)-dependent 15-hydroxyprostaglandin dehydrogenase, designated type-I 15-PGDH, was mapped to chromosome 4 by analyzing its segregation in a panel of human-hamster somatic cell hybrids. This gene was further localized to bands 4q34-q35 by in situ hybridization on human chromosomes.

Interleukin-2 and interleukin-4 display potent antitumour activity on rat medullary thyroid carcinoma cells.

Currently, surgical resection is the only treatment used for human medullary thyroid carcinoma (MTC). However, as metastases are commonly observed, we investigated the potential of adjuvant therapy with interleukin-2 (IL-2) and interleukin-4 (IL-4) in a rat model. The interleukins were delivered by means of xenogeneic tumour cells engineered to secrete IL-2 and IL-4. We found that when a mixture of MTC cells and IL-2 or IL-4 secreting cells were implanted in rats, the growth of the resulting tumours was inhibited as a function of the number of interleukin-secreting cells in the inoculum. Moreover, association of the two interleukins exerted a synergistic antitumour effect. These experimental results, showing thyroid C cell tumour rejection, are of major interest, as they show the potential therapeutic application for these two interleukins, which could be used, in particular, as postsurgical adjuvants.

Calcitonin secretion, C cell differentiation and proliferation during the spontaneous development of murine medullary thyroid carcinoma.

Medullary thyroid carcinoma (MTC), a C cell neoplasm, synthesizes large amounts of calcitonin (CT), its biological marker. However, in some cases with a poor prognosis, MTC is associated with low basal CT levels owing to a decrease in the thyroid CT content. Using a murine model of human MTC, we studied the relationships between CT biosynthesis, C cell proliferation, and the circulating CT level during MTC progression. Cell proliferation was revealed by autoradiography of radioactive thymidine incorporation in dividing nuclei, after CT or CT mRNA detection by immunocytochemistry (ICC) or in situ hybridization (ISH). All rat thyroids showed a severe hyperplasia of C cells containing significant amounts of CT and CT mRNA, and a very low mitotic index. Tumours were found in 68% of the thyroids. In the strongly immunoreactive small nodules (ICC+), many labelled nuclei were observed. Subsequently some nodular cells, still containing detectable CT mRNA (ISH+), were not detected by immunocytochemistry (ICC-) owing to a dramatic decrease in secretory granules. Their mitotic index increased, and a rise of the basal CT plasma level was noted. These ISH+, ICC- tumour MTC cells represent a modified aggressive tumour C cell population exhibiting an increased ability to proliferate and were detected by the rise in the basal circulating CT level.

Evaluation of somatostatin biosynthesis, somatostatin receptors and tumor growth in murine medullary thyroid carcinoma.

Spontaneous medullary thyroid carcinomas (MTCs) of old rat thyroids were analyzed for the expression of somatostatin and somatostatin binding sites in tumoral C cells in relation to the stage of tumor development, the mitotic activity of tumoral tissue and calcitonin biosynthesis as a marker of C cell differentiation. High levels of both immunoreactive somatostatin and its mRNA were detected in a subpopulation of tumoral C cells, gathered in areas suggesting a clonal proliferation and located preferentially at the periphery of the tumor. These cells also displayed high levels of calcitonin and its mRNA. However, many calcitonin immunoreactive cells showed no sign of somatostatin synthesis. The proliferative activity of the somatostatin-containing areas was low and slow compared to the areas lacking somatostatin production. However, it increased during the course of tumor growth. Somatostatin binding sites, measured with in vitro receptor autoradiography using 125I-[Tyr3]-octreotide or 125I-[Leu8, dTrp22, Tyr25]SS-28, were not detected in any of the MTCs tested. In rat MTC cells, somatostatin was associated with differentiation and slow proliferation, two parameters inversely correlated with the progression of malignancy. As expected, owing to the highly regulated secretion of the differentiated endocrine cell type, its presence was correlated with low basal calcitonin levels. However, the absence of somatostatin binding sites on any type of MTC cells does not favor a direct autocrine regulation of this peptide in this murine model of human MTC.

CGRP is expressed in primary cultures of human hepatocytes and in normal liver.

We recently reported that human liver and primary cultures of hepatocytes express calcitonin. We therefore studied the expression of calcitonin gene related peptide (CGRP), the alternative splicing product of the calcitonin gene, in hepatocytes and liver. We used polymerase chain reaction amplification with specific primers to detect the presence of CGRP I and II messengers and a specific radioimmunoassay to measure the peptide. We report here that CGRP is synthesized by primary cultures of hepatocytes and in liver. As liver also possesses specific receptors for CGRP in non-parenchymal cells, a paracrine system could be involved in liver metabolism.

Calcitonin gene expression in normal human liver.

Immunoreactive calcitonin (CT) is present in liver. This could represent hormone synthesized by liver cells, degraded or bound to specific receptors reported in this organ. We report here that the calcitonin gene is expressed in liver. We proved this by demonstrating, by PCR amplification using specific primers, the presence of calcitonin messenger in human liver and in primary cultures of human hepatocytes and detected by radioimmunoassay CT in hepatic tissues and cells. The synthesis of hormone by liver that also possesses specific receptors for CT favors the presence of an autocrine or paracrine system involving calcitonin in this organ.

Expression of CGRP mRNAs in the pink salmon, Oncorhynchus gorbuscha.

We report the isolation of calcitonin gene-related peptide (CGRP) mRNAs and expression of these RNAs in different tissues in the pink salmon, Oncorhynchus gorbuscha. Hybridization of poly(A+) RNAs indicated a mature CGRP RNA of 1.1 kb. The CGRP-like immunoreactivity occurring in tissues and plasma had the same relative molecular weight as the synthetic molecule. Variations in CGRP plasma levels were observed during migration, spawning, and postspawning states. These data suggest that CGRP may play an important role during the reproductive cycle of salmon.

An efficient method to detect calcitonin mRNA in normal and neoplastic rat C-cells (medullary thyroid carcinoma) by in situ hybridization using a digoxigenin-labeled synthetic oligodeoxyribonucleotide probe.

We report here an efficient and rapid method for the specific detection of calcitonin in tumor C-cells of medullary thyroid carcinoma (MTC). This occasionally aggressive tumor arises from the endocrine thyroid C-cells. Its principal marker is calcitonin, the predominant C-cell secretion, which is detected in patients and in our animal model by radioimmunoassay of the plasma, as well as by immunohistochemistry of thyroid tissues. Although calcitonin is easily detectable in normal C-cells, its content is greatly reduced in tumor cells owing to the disappearance of the secretory granules that store the mature peptide. This finding suggests cell dedifferentiation correlated with an increasing aggressivity of the tumor. We therefore developed a rapid detection of calcitonin mRNA by in situ hybridization on routine paraffin sections, using a synthetic oligodeoxyribonucleotide probe labeled with digoxigenin-dUTP. The reaction was detected with an anti-digoxigenin antibody conjugated with alkaline phosphatase, and the enzyme catalyzed the appearance of a dark blue color. The signal was exclusively restricted to the normal, hyperplastic, and tumor C-cells. It was specific, as increasing concentrations of the unlabeled oligonucleotide led to progressive disappearance of the reaction. Its sensitivity was slightly diminished as compared with corresponding frozen sections, but the intensity of the signal was quite acceptable. High levels of calcitonin mRNA were found in all normal and hyperplastic C-cells. They were increased in most of the tumor MTC cells, which did not correlate with the amount of intracellular peptide stores but explained the abnormally high basal levels of circulating calcitonin of the tumor-bearing rats. ISH is therefore of greater value than ICC for an early anatomopathological detection of this tumor. Our data show that the tumor cells are not "dedifferentiated." They only lack the granular compartment storing the mature peptide before exocytosis, but CT biosynthesis and the rest of the secretory process seem to be complete. Our results suggest that factors expressed in malignant C-cells affect basic cell mechanisms involved in the storage of the mature calcitonin, rather than the expression of the CALC gene.

Renal calcitonin receptors in the ageing Wistar rat.

Ageing can affect both the secretion of a hormone and the number of its specific receptors. An autoradiographic method was used to quantify renal binding sites for calcitonin (CT) in Wistar rats aged 1, 3, 6, 12 and 18 months. In 1-month-old rats, high densities of calcitonin binding sites were observed in the outer cortex and in the outer medulla. However, an increasing number of rats presenting very low calcitonin binding site density in the outer medulla (that we called 'deficient') appeared during ageing. Ageing also involved a gradual decrease in calcitonin receptor densities in the kidney outer medulla in the non-'deficient' rats. The basal calcitonin concentrations in plasma did not vary with age. The increase in plasma calcitonin in response to a calcium injection increased with age, but this increase was not cor- related with the decrease in binding site density. In 18-month-old rats suffering from C cell hyperplasia or carcinoma, both basal and stimulated levels of calcitonin were increased (basal: x 3; stimulated: x 5), but no major modification in calcitonin binding site densities was observed. Thus in the Wistar rat, receptor density is apparently age-regulated and a relative increase in endogenous CT level is without effect on receptor density.

Increase in calcitonin mRNA levels in rats at high risk of C cell tumours is genetically determined.

C-cells tumours are frequent (50%) in old WAG/Rij rats. In comparison to the original Wistar strain, three month old WAG/Rij rats are characterized by higher calcitonin synthesis and secretion, in addition to a genetically transmitted loss of calcitonin binding sites in the outer renal medulla. In order to determine if the increase of calcitonin gene expression is also of genetic origin, we quantified calcitonin and its specific messenger in the thyroid glands of second generation (Wistar x WAG/Rij) hybrids. These parameters ranged from low Wistar like to higher WAG/Rij like values. The amount of calcitonin messenger in the thyroid was highly correlated to the release of the hormone in plasma elicited by a calcium challenge and inversely correlated with the number of its binding sites in the kidney. Our results suggest that an enhanced expression of the calcitonin gene is genetically transmitted, probably as a consequence of the mutation involved in the loss of renal calcitonin binding sites. It may represent the first event leading to malignancy.

Loss of calcitonin receptors: a genetically transmitted defect in rats with high incidence of C-cell tumors.

C-cell tumors (medullary thyroid carcinoma) occur in humans and several other mammalian species. This tumor develops spontaneously with a high incidence (50%) in old Wag/Rij (Wistar-derived strain) rats. We have recently shown that calcitonin binding sites, which are present in the Wistar rats, are lost from renal medulla of the Wag/Rij rats before they reach the age of 1 month. In the present work, we investigated the distribution of calcitonin binding sites in the kidneys of first and second generation hybrids of Wistar x Wag/Rij rats. The absence of calcitonin binding sites from the renal medullas of 25% of F2 hybrids indicates that the deficiency is inherited in a Mendelian fashion and opens the way to establishing inbred strains lacking renal medullary calcitonin binding sites.

Early calcitonin hypersecretion and C cell hyperplasia in rats with high incidence of C cell tumors (Wag/Rij).

Wag/Rij rats, a Wistar-derived strain, develop on aging a spontaneous medullary thyroid carcinoma which shows many morphological similarities to the human neoplasm. Using biochemical and histological methods, we studied calcitonin secretion and C cell distribution in young and adult Wag/Rij rats, to characterize possible modifications in calcitonin synthesis and secretion as compared to the original Wistar strain. During the period investigated, the mean basal circulating levels of calcitonin of both sexes were not significantly different between the two strains, although the Wag/Rij rats tended to have higher values. After a calcium challenge, the circulating calcitonin levels increased normally in the Wag/Rij strain as compared to Wistar rats of the same ages. Histological observations of their thyroids revealed a significant C cell hyperplasia, along with a weak immunostaining in some of the cells, due to a lack of secretory granules. Thus, in addition to the ability of developing C cell tumours on aging, the Wag/Rij strain is characterized by an early C cell hyperplasia leading to an increase of calcitonin secretion after a provocative secretion test.