Dexamethasone regulation of parathyroid hormone-related protein (PTHrP) expression in a squamous cancer cell line

Parathyroid hormone 1-34 reduces dexamethasone-induced terminal differentiation in human articular chondrocytes

Intra-articular injection of dexamethasone (Dex) is occasionally used to relieve pain and inflammation in osteoarthritis (OA) patients. Dex induces terminal differentiation of chondrogenic mesenchymal stem cells in vitro and causes impaired longitudinal skeletal growth in vivo. Parathyroid hormone 1-34 (PTH 1-34) has been shown to reverse terminal differentiation of osteoarthritic articular chondrocytes. We hypothesized that Dex induces terminal differentiation of articular chondrocytes and that this effect can be mitigated by PTH 1-34 treatment. We tested the effect of Dex on terminal differentiation in human articular chondrocytes and further tested if PTH 1-34 reverses the effects. We found that Dex treatment downregulated chondrogenic-induced expressions of SOX-9, collagen type IIa1 (Col2a1), and aggrecan and reduced synthesis of cartilaginous matrix (Col2a1 and sulfated glycosaminoglycan) synthesis. Dex treatment upregulated chondrocyte hypertrophic markers of collagen type X and alkaline phosphatase at mRNA and protein levels, and it increased the cell size of articular chondrocytes and induced cell death. These results indicated that Dex induces terminal differentiation of articular chondrocytes. To test whether PTH 1-34 treatment reverses Dex-induced terminal differentiation of articular chondrocytes, PTH 1-34 was co-administered with Dex. Results showed that PTH 1-34 treatment reversed both changes of chondrogenic and hypertrophic markers in chondrocytes induced by Dex. PTH 1-34 also decreased Dex-induced cell death. PTH 1-34 treatment reduces Dex-induced terminal differentiation and apoptosis of articular chondrocytes, and PTH 1-34 treatment may protect articular cartilage from further damage when received Dex administration.

Wild-type and specific mutant androgen receptor mediates transcription via 17β-estradiol in sex hormone-sensitive cancer cells

We previously encountered regulatory processes wherein dihydrotestosterone (DHT) exerted its inhibitory effect on parathyroid hormone‐related protein (PTHrP) gene repression through the estrogen receptor (ER)α, but not the androgen receptor (AR), in breast cancer MCF‐7 cells. Here, we investigated whether such aberrant ligand‐nuclear receptor (NR) interaction is present in prostate cancer LNCaP cells. First, we confirmed that LNCaP cells expressed large amounts of AR at negligible levels of ERα/β or progesterone receptor. Both suppression of PTHrP and activation of prostate‐specific antigen genes were observed after independent administration of 17β‐estradiol (E2), DHT, or R5020. Consistent with the notion that the LNCaP AR lost its ligand specificity due to a mutation (Thr‐Ala877), experiments with siRNA targeting the respective NR revealed that the AR monopolized the role of the mediator of shared hormone‐dependent regulation, which was invariably associated with nuclear translocation of this mutant AR. Microarray analysis of gene regulation by DHT, E2, or R5020 disclosed that more than half of the genes downstream of the AR (Thr‐Ala877) overlapped in the LNCaP cells. Of particular interest, we realized that the AR (wild‐type [wt]) and AR (Thr‐Ala877) were equally responsible for the E2‐AR interactions. Fluorescence microscopy experiments demonstrated that both EGFP‐AR (wt) and EGFP‐AR (Thr‐Ala877) were exclusively localized within the nucleus after E2 or DHT treatment. Furthermore, reporter assays revealed that some other cancer cells exhibited aberrant E2‐AR (wt) signaling similar to that in the LNCaP cells. We herein postulate the presence of entangled interactions between wt AR and E2 in certain hormone‐sensitive cancer cells. J. Cell. Physiol. 230: 1594–1606, 2015. © 2014 The Authors. Journal of Cellular Physiology Published by Wiley Periodicals, Inc.

1,25-Dihydroxyvitamin D(3) regulates PTHrP expression via transcriptional, post-transcriptional and post-translational pathways

Parathyroid hormone-related protein (PTHrP) increases the growth and osteolytic potential of prostate cancer cells, making it important to control PTHrP expression. PTHrP expression is suppressed by 1,25-dihydroxyvitamin D(3) (1,25D). The aim of this study was to identify the pathways via which 1,25D exerts these effects. Our main findings are that 1,25D regulates PTHrP levels via multiple pathways in PC-3 and C4-2 (human prostate cancer) cell lines, and regulation is dependent on VDR expression. The human PTHrP gene has three promoters (P); PC-3 cells preferentially utilize P2 and P3, while C4-2 cells preferentially utilize P1. 1,25D regulates PTHrP transcriptional activity from both P1 and P3. The 1,25D-mediated decrease in PTHrP mRNA levels also involves a post-transcriptional pathway since 1,25D decreases PTHrP mRNA stability. 1,25D also suppresses PTHrP expression directly at the protein level by increasing its degradation. Regulation of PTHrP levels is dependent on VDR expression, as using siRNAs to deplete VDR expression negates the 1,25D-mediated downregulation of PTHrP expression. These results indicate the importance of maintaining adequate 1,25D levels and VDR status to control PTHrP levels.

Negative regulation of parathyroid hormone-related protein expression by steroid hormones

Elevated parathyroid hormone-related protein (PTHrP) is responsible for humoral hypercalcemia of malignancy (HHM), which is of clinical significance in treatment of terminal patients with malignancies. Steroid hormones were known to cause suppression of PTHrP expression. However, detailed studies linking multiple steroid hormones to PTHrP expression are lacking. Here we studied PTHrP expression in response to steroid hormones in four cell lines with excessive PTHrP production. Our study established that steroid hormones negatively regulate PTHrP expression. Vitamin D receptor, estrogen receptor α, glucocorticoid receptor, and progesterone receptor, were required for repression of PTHrP expression by the cognate ligands. A notable exception was the androgen receptor, which was dispensable for suppression of PTHrP expression in androgen-treated cells. We propose a pathway(s) involving nuclear receptors to suppress PTHrP expression.

Detection of circulating tumor cells in prostate cancer patients: methodological pitfalls and clinical relevance

Disseminated malignancy is the major cause of prostate cancer-related mortality. Circulating tumor cells (CTCs) are essential for the establishment of metastasis. Various contemporary and molecular methods using prostate-specific biomarkers have been applied to detect extraprostatic disease that is undetectable by conventional imaging techniques, assessing the risk for disease recurrence after therapy of curative intent. However, the clinical relevance of CTC detection is still controversial. We review current literature regarding molecular methods used for the detection of CTCs in the peripheral blood and bone marrow biopsies of patients with prostate cancer, and we discuss the methodological pitfalls that influence the clinical significance of molecular staging.

The parathyroid hormone family of peptides: structure, tissue distribution, regulation, and potential functional roles in calcium and phosphate balance in fish

Parathyroid hormone (PTH) and PTH-related protein (PTHrP) are two factors that share amino acid sequence homology and act via a common receptor. In tetrapods, PTH is the main endocrine factor acting in bone and kidney to regulate calcium and phosphate. PTHrP is an essential paracrine developmental factor present in many tissues and is involved in the regulation of ossification, mammary gland development, muscle relaxation, and other functions. Fish apparently lack an equivalent of the parathyroid gland and were long thought to be devoid of PTH. Only in recent years has the existence of PTH-like peptides and their receptors in fish been firmly established. Two forms of PTH, two of PTHrP, and a protein with intermediate characteristics designated PTH-L are encoded by separate genes in teleost fish. Three receptors encoded by separate genes in fish mediate PTH/PTHrP actions, whereas only two receptors have so far been found in terrestrial vertebrates. PTHrP has been more intensively studied than PTH, from lampreys to advanced teleosts. It is expressed in many tissues and is present in high concentration in fish blood. Administration of this peptide alters calcium metabolism and has marked effects on associated gene expression and enzyme activity in vivo and in vitro. This review provides a comprehensive overview of the physiological roles, distribution, and molecular relationships of the piscine PTH-like peptides.

Cortisol and parathyroid hormone-related peptide are reciprocally modulated by negative feedback

In previous in vitro studies, we have shown that the N-terminal region of parathyroid hormone-related protein (PTHrP) can stimulate cortisol production in sea bream, Sparus auratus, interrenal tissue, possibly through a paracrine action. In the current study, the systemic interaction between cortisol and PTHrP was studied in vivo. Sustained elevated blood cortisol levels, induced either by cortisol injection or confinement stress, suppressed circulating PTHrP 6 and 24-fold, respectively, by comparison to control fish. Dexamethasone treatment reduced cortisol levels, prevented the decrease of plasma PTHrP observed in confined fish and raised plasma PTHrP levels in non-confined fish. In contrast, a single injection of (1-34) PTHrP caused a short-term (within 30 min and up to 2.5 h) decrease in plasma cortisol. The antagonistic effects between PTHrP and cortisol were substantiated by an overall (data pooled from all experiments) highly significant negative correlation (r0=-0.745, p<0.001, n=115) between the plasma levels of the two hormones. Although the underlying mechanism of the interaction still has to be determined, the high levels of PTHrP in circulation and the existence of systemic regulation favour the hypothesis that in fish PTHrP may act as an endocrine factor, although the gland that produces it still remains to be identified.

Medroxyprogesterone acetate decreases secretion of interleukin-6 and parathyroid hormone-related protein in a new anaplastic thyroid cancer cell line, KTC-2

A new thyroid cancer cell line, KTC-2, was established from the malignant pleural effusion of a patient with recurrent thyroid cancer associated with anaplastic transformation from thyroid papillary cancer. Karyotype analysis showed a mode of 109 chromosomes. Subcutaneous cell injections produced small regressing tumors in athymic or severe combined immunodeficiency disorders (SCID) mice. Histologic examination showed anaplastic tumor cells surrounded by prominent mononuclear cells. An expression of thyroglobulin, thyroid transcription factor-1, and PAX-8 but not thyroid peroxidase and thyrotropin (TSH) receptor was detected. Biochemical analysis revealed secretion of interleukin (IL)-6, parathyroid hormone-related protein (PTHrP), and granulocyte-macrophage colony-stimulating factor. All the cytokines are known to induce paraneoplastic syndromes in patients with anaplastic thyroid cancer. Our previous studies revealed that medroxyprogesterone acetate (MPA) reduces secretion of IL-6 and PTHrP from human breast cancer cells. To investigate the regulatory mechanisms of secretion of these cytokines, MPA was administered to the KTC-2 cells. MPA dose-dependently decreased the secretion and mRNA expression of IL-6 and PTHrP. Expression of androgen receptor and glucocorticoid receptor (GR) but not progesterone receptor was detected. Dexamethasone but not dihydrotestosterone and progesterone decreased IL-6 and PTHrP secretion. These findings suggest that MPA decreases IL-6 and PTHrP secretion as a glucocorticoid mediated by GR in the KTC-2 cells. This KTC-2 cell line may be a suitable model for developing new strategies against paraneoplastic syndromes caused by anaplastic thyroid cancer.

Retinoic acid receptors are expressed in human primary astrocytes and their agonists inhibit parathyroid hormone-related peptide expression and secretion

We isolated, by RT-PCR, partial cDNAs encoding retinoic acid receptor (RAR) isoforms, alpha, beta and gamma, in human primary astrocytes and confirmed their expression by western analysis. A naturally occurring RAR agonist, all-trans retinoic acid and a synthetic RAR agonist, [(E)-4-[2-(5,6,7,8-tetrahydro-5,5,8,8-tetramethyl-2-naphthylenyl)-1-propenyl]benzoic acid], each inhibited PTHrP secretion with EC(50) values of approximately 25 and 250 nM, respectively. The two may act at a transcriptional level as assessed by Northern analysis. Thus retinoids, most likely acting via RARs, inhibit parathyroid hormone-related protein expression and secretion in human primary astrocytes, with a synthetic RAR-specific agonist being more potent than a naturally occurring RAR agonist.

Regulation of calcitonin receptor by glucocorticoid in human osteoclast-like cells prepared in vitro using receptor activator of nuclear factor-kappaB ligand and macrophage colony-stimulating factor

Using mouse osteoclast-like cells (OCs), we have shown that treatment with glucocorticoids (GCs) resulted in an increase in calcitonin (CT) binding by enhancing CT receptor (CTR) gene transcription. Additionally, treatment with GCs demonstrated increased sensitivity to CT. There is, however, scant information on the effects of GC or CTR regulation by GCs in human osteoclasts. In this study we examined CTR regulation by GCs and the effects of GCs and CT together in human OCs. OCs were prepared by treatment of peripheral blood mononuclear cells in vitro with soluble receptor activator of nuclear factor-kappaB ligand and macrophage colony-stimulating factor. Treatment of mature OCs with dexamethasone (Dex) resulted in a dose- and time-dependent increase in [(125)I]salmon CT (sCT) binding capacity. Treatment with Dex enhanced CTR messenger RNA (mRNA) expression, suggesting that CTR up-regulation is at least partly due to an increase in de novo CTR synthesis. Triamcinolone and prednisolone reproduced the Dex effect on [(125)I]sCT-specific binding and CTR mRNA expression, but 17beta-estradiol, progesterone, dehydroepiandrosterone, and aldosterone did not. A Scatchard plot analysis showed that Dex enhanced CTR number with a minimal change in the affinity to sCT. Autoradiographic studies using [(125)I]sCT showed that Dex enhanced the CTR density on individual multinuclear OCs. Up-regulation of [(125)I]sCT-specific binding and CTR mRNA expression was seen even in the presence of sCT, but the enhancement diminished subsequently at later times (36-48 h after sCT removal), which was consistent with our previous observation in mouse OCs. This suggests that GCs and CTs act on CTR expression differently, consistent with our previous work using mouse OCs, in which we found that GCs increased transcription of CTR gene expression, whereas CT reduced CTR mRNA stability. The results obtained in this study show that GC increased CTR expression and sensitivity to CT in cells of the human osteoclast lineage and provide the basis for understanding the beneficial effects of combination treatment with GCs and CTs in malignancy-associated hypercalcemia.

Differential regulation of the parathyroid hormone-related protein gene P1 and P3 promoters by cAMP

The role of calcitonin, and other agonists which activate the cAMP pathway, in regulating transcription of the human parathyroid hormone-related protein (PTHrP) gene was investigated in a human lung cancer cell line (BEN). Both calcitonin and forskolin caused a 5-6-fold increase in transcription initiated from both the P1 and P3 promoters, but with no observed effect on the P2 promoter. Maximal 6-fold activation of the P1 promoter occurred at 16 h post-stimulation and effects of calcitonin were observed within the pM range. The PKC agonist, phorbol 12-myristate 13-acetate diester (PMA), did not modulate transcription initiated from the P1 promoter. The ionophore ionomycin had a small effect on transcription of the P1 promoter, and transcriptional control may involve an interaction between the cAMP and intracellular calcium second messenger pathways. Deletion mapping studies indicated that increases in transcription of the human PTHrP gene is being mediated via a CRE element situated at -3313 to -3306 upstream of the P1 promoter. Mutational analysis of this CRE element confirmed a role for this sequence in mediating the increase in transcription effected by cAMP. Consistent with these transfection studies, RT-PCR of PTHrP mRNA also indicated a significant increase in transcripts generated from the P1 promoter. Gel retardation assays utilising a fragment of the P1 promoter region, encompassing the putative CRE, determined that nuclear proteins were binding to this region. Competition binding studies with labelled probe and cold competitors determined that the binding was specific for this sequence. A wild-type CRE consensus oligonucleotide also competed for binding with this sequence.

CpG island methylation and promoter usage in the parathyroid hormone-related protein gene of cultured lung cells

Excessive production of a parathyroid hormone-related protein (PTHrP) by tumours commonly results in the syndrome of humoral hypercalcaemia of malignancy. We have investigated whether epigenetic changes play a role in over-expression of the PTHrP gene, using cultures lung cells as a model system. Study of the methylation status of CpG dinucleotides in the 5' region of the gene showed that in normal cells the CpG island was completely unmethylated. In the lung squamous cell carcinoma cell line, BEN, two-thirds of the CpG island was substantially methylated. RT-PCR analysis showed that this heavy methylation did not prevent expression of any of the three PTHrP gene promoters. This is a surprising finding, since methylation is usually associated with inhibition of gene activity. Methylation of the 5' non-coding region of the PTHrP gene may not play a role in the regulation of adjacent promoters. Alternatively, maintenance of a demethylated state in the 170 bp at the 3' end of the CpG island may be fundamental for the use of PTHrP promoters.

Alteration of secretion of parathyroid hormone-related peptide and expression of its mRNA in a human hepatoma cell line (HEP G2) treated with agents that affect cell growth

Previously, using human hepatoma cells (HepG2), we found that immunoneutralization of secreted PTHrP increased cell growth. Here we asked whether PTHrP production was affected by agents that alter growth of Hep G2 cells. Immunoreactive PTHrP in medium and PTHrP mRNA expression were examined. Treatment of cells with 10 μM hydrocortisone or 1 ng/mL TGF-β1 for 72 h inhibited cell growth by 28±6 and 36±2% and increased PTHrP in medium by 128±10 and 525 ±27%, respectively. The increase in PTHrP produced by both agents was dose-and time-dependent, and the increased PTHrP was accompanied by dose-and time-dependent enhanced expression of PTHrP mRNA. In contrast, 10% fetal bovine serum (FBS) for 72 h increased cell growth by 38±6% (vs serum-free medium) and decreased PTHrP production by 49±4% whereas culture in high glucose (3-4g/L) increased cell growth by 43±1% (vs 1 g/L glucose) and decreased PTHrP by 55±0.4%. Inhibition of PTHrP by both FBS and glucose was dose-dependent; FBS also inhibited PTHrP mRNA. The results show that increased cell growth was associated with decreased PTHrP production, while decreased growth was accompanied by increased PTHrP production. The findings imply that PTHrP may help mediate growth effects of these agents on Hep G2 cells.

Glucocorticoids decrease the production of parathyroid hormone-related protein in vitro but not in vivo in the Walker carcinosarcoma 256 rat model

In 50-90% of cases, humoral hypercalcemia of malignancy (HHM) is due to tumor secretion of parathyroid hormone-related protein (PTHrP). Glucocorticoids are sometimes used as calcium lowering agents and there are in vitro results showing that glucocorticoids diminish PTHrP production. In this study we tested whether the serum-calcium-lowering effect of glucocorticoids is due to decreased PTHrP production by the tumor. As an animal and cell culture model we used the Walker carcinosarcoma (WCS) 256, a rat mammary carcinoma cell line producing PTHrP. In vitro, dexamethasone caused a dose-dependent inhibition of PTHrP production, whereby already 1-5 nmol/L revealed a significant decrease by WCS 256 cells. In contrast to these in vitro results, in WCS 256 tumor-bearing rats, dexamethasone (4 mg/kg body weight on day 4, and 1 mg/kg body weight from day 5 until day 7 after WCS transplantation; circulating dexamethasone levels > 20 nmol/L) did not decrease PTHrP production, PTHrP secretion, serum calcium, or tumor weight in vivo. We conclude that, in this PTHrP-mediated model of humoral hypercalcemia of malignancy, glucocorticoids do not decrease PTHrP production and secretion in vivo and do not show a calcium-lowering effect.

PC8 [corrected], a new member of the convertase family

A novel subtilisin-like protein, PC8, was identified by PCR using degenerate primers to conserved amino acid residues in the catalytic region of members of the prohormone convertase family. PC8 was predicted to be 785 residues long and was structurally related to the mammalian convertases furin, PACE4, PC1 and PC2, sharing more than 50% amino acid identity over the catalytic region with these family members. PC8 possessed the catalytically important Asp, His, Asn and Ser amino acids, the homo B domain of this family of enzymes and a C-terminal hydrophobic sequence indicative of a transmembrane domain. Structurally, PC8 is more related to furin and PACE4 than to PC1 or PC2. Like furin and PACE4, PC8 mRNA was found to be widely expressed; this is in contrast with PC1 and PC2, which have a restricted distribution. Two transcripts, of 4.5 and 3.5 kb, were detected in both human cell lines and rat tissues. Unlike furin and PACE4, both of which map to chromosome 15, PC8 maps to chromosome 11q23-11q24, suggesting that this gene may have resulted from an ancient gene duplication event from either furin or PACE4, or conversely that these genes arose from PC8.

Alternative promoter usage and mRNA splicing pathways for parathyroid hormone-related protein in normal tissues and tumours

The parathyroid hormone-related protein (PTHrP) gene consists of nine exons and allows the production of multiple PTHrP mRNA species via the use of three promoters and 5' and 3' alternative splicing; as a result of 3' alternative splicing one of three protein isoforms may be produced. This organisation has potential for tissue-specific splicing patterns. We examined PTHrP mRNA expression and splicing patterns in a series of tumours and normal tissues, using the sensitive reverse transcription-polymerase chain reaction (RT-PCR) technique. Use of promoter 3 and mRNA specifying the 141 amino acid PTHrP isoform were detected in all samples. Transcripts encoding the 139 amino acid isoform were detected in all but two samples. Use of promoters 1 and 2 was less widespread as was detection of mRNA encoding the 173 amino acid isoform. While different PTHrP splicing patterns were observed between tumours, no tissue- or tumour-specific transcripts were detected. In comparing normal and tumour tissue from the same patient, an increase in the number of promoters utilised was observed in the tumour tissue. Furthermore, mRNA for the PTH/PTHrP receptor was detected in all samples, thus the PTHrP produced by these tumours may potentially act in an autocrine or paracrine fashion.

Steroid regulation of parathyroid hormone-related protein expression and action in the rat uterus

The gene encoding parathyroid hormone-related protein (PTHrP), an autocrine/paracrine inhibitor of vascular and nonvascular smooth muscle contractility, is regulated by hormonal steroids including estrogens (E2), 1,25-dihydroxy vitamin D (Vit D3) and glucocorticoids. While E2 increases PTHrP gene expression, Vit D3 and glucocorticoids inhibit transcriptional activity of this gene. In the uterus of ovariectomized rats, E2-treatment increases both PTHrP mRNA levels and smooth muscle sensitivity to the action of PTHrP(1-34). To examine the action(s) of Vit D3 and glucocorticoids on these parameters, OVX rats were treated with E2, Vit D3 or the synthetic glucocorticoid, dexamethasone (Dex), alone, or with E2 following a 1 h pretreatment with Vit D3 or Dex. PTHrP and PTH/PTHrP receptor mRNA were measured by blot hybridization analysis of RNA prepared from uteri collected 2, 4 and 24 h after treatment. Uterine horns were used to measure the effect of the steroids on the ability of PTHrP(1-34) to inhibit spontaneous myometrial contraction. When E2, Vit D3 and Dex were given alone, only E2 altered PTHrP mRNA levels in the uterus, however, a 1 h pretreatment with Dex but not Vit D3 markedly diminished this effect of E2. The temporal decline in uterine PTH/PTHrP receptor mRNA levels measured 2 and 4 h after E2 treatment inversely correlated to changes in sensitivity of the tissue to PTHrP(1-34) measured at 24 h after E2 administration. In comparison to E2 alone, treatment with Vit D3 and E2 augmented the uterine responsiveness to PTHrP(1-34) while pretreatment with Dex (1 mg/kg) and E2 decreased this response. These data indicate that in the uterus, Dex opposes the positive effect of E2 on PTHrP gene activity and differentially modulates the action of PTHrP on myometrial tone. Moreover, elevations in the circulating levels of cortisol at term may serve to decrease both the uterine expression of PTHrP and the local action of PTHrP on the myometrium prior to parturition, therefore promoting myometrial contraction associated with labor.

Epidermal growth factor-stimulated parathyroid hormone-related protein expression involves increased gene transcription and mRNA stability

Epidermal growth factor (EGF) produced rapid and striking effects on parathyroid hormone-related protein (PTHrP) gene expression in the immortalized human keratinocyte cell line, HaCaT. Steady-state levels of PTHrP mRNA and secreted PTHrP were increased 10-fold by maximally effective concentrations of EGF. EGF increased both PTHrP gene transcription and PTHrP mRNA stability. Nuclear run-on assays demonstrated a 4-fold increase in transcriptional rate in EGF-stimulated cells while transient transfection analysis indicated that the action of EGF on transcription involved both the GC-rich promoter, P2, and the downstream TATA promoter, P3, but apparently not the upstream TATA promoter, P1. In experiments where EGF treatment produced more stable PTHrP transcripts, the half-life of c-fos mRNA was unaltered, suggesting a relatively specific effect of EGF. Moreover, only those species of PTHrP mRNA containing two of the alternative 3' exons (exons VII and VIII) were stable, those containing exon IX were not. Reverse-transcription PCR demonstrated that EGF produced differential increases in the abundance of PTHrP mRNA species initiated by the three PTHrP promoters. The major effect was seen on the abundance of transcripts initiated by P1 and P2, with less marked regulation of P3-initiated transcripts. Thus EGF regulation of PTHrP gene expression in HaCaT cells is multifactorial and the combination of its actions at the 5' and 3' ends of the gene favours the accumulation of subpopulations of PTHrP mRNA containing exons I, VII and VIII.

Evidence for the synthesis of parathyroid hormone-related protein (PTHrP) by nontransformed clonal rat osteoblastic cells in vitro

Parathyroid hormone-related protein (PTHrP) is synthesized by a variety of tumors and is thought to be the main cause of the clinical syndrome of humoral hypercalcemia of malignancy (HHM). In addition to its parathyroid hormone (PTH)-like actions, novel actions of PTHrP on placental calcium transport and inhibition of in vitro osteoclast activity have been demonstrated. The fact that osteoblasts act as mediators of osteoclastic bone resorption prompted us to investigate whether nontranformed, osteoblastlike cells produce PTHrP. PTHrP has been detected in developing human fetal bones and in rat long bones in culture. For this study, osteogenic cells, CRP 5/4 and CRP 10/30, were employed. Both cell types represent clonal bone cell populations established from 1-day-old rats. While CRP 10/30 cells express the osteoblastic phenotype, CRP 5/4 cells resemble cells with preosteoblastic properties. With a radioimmunoassay (RIA), utilizing antiserum directed against the amino-terminal PTHrP(1-40), it was found that both cell types synthesize PTHrP constitutively. CRP 10/30 cells produce about twice as much as CRP 5/4 cells. Transforming growth factor-beta (TGF-beta 1) was shown to increase the synthesis of PTHrP in CRP 5/4 cells by about 2.5-fold, while in CRP 10/30 cells it caused an approximate 50% reduction of PTHrP. Employing the reverse transcriptase polymerase chain reaction (RT-PCR) technique it was found that both bone cell types express mRNA for PTHrP and that the modulation of the PTHrP mRNA levels by TGF-beta 1 in CRP 5/4, and to a lesser degree in CRP 10/30 cells, was reflected in a change in the level of PTHrP protein in the culture medium.(ABSTRACT TRUNCATED AT 250 WORDS)

Parathyroid hormone-related protein

We review the current state of knowledge of the molecular properties and actions of parathyroid hormone-related protein (PTHrP) both in cancer patients and in normal physiology. PTHrP is a common product of squamous cancers and is the major mediator of the syndrome of humoral hypercalcemia of malignancy (HHM) by its actions through parathyroid hormone receptors in bone and kidney. Recently developed radioimmunoassays and tissue localization techniques indicate that PTHrP is produced by many more cancers than was originally indicated by clinical studies and that it contributes significantly to malignancy-related hypercalcemia associated with other etiologies, for example, cancers metastatic to bone and hematological malignancies. The gene encoding PTHrP is complex, with multiple exons coding for up to 12 alternate transcripts and three different length proteins, potentially in a tissue-specific manner, by the use of three promoters. Its expression is regulated by hormones and growth factors, and the untranslated exons display features in common with many cytokine genes. Although potential endocrine actions of PTHrP are evident in fetal development, further evidence suggesting that the normal physiological role of PTHrP is predominantly as a locally produced regulator/cytokine comes from localization studies and investigations of its actions in a variety of tissues. Such studies indicate that in addition to its parathyroid hormone-like actions, PTHrP has multiple activities, including those in fetal development, placental calcium transfer, lactation, smooth muscle relaxation, and on epithelial cell growth. Although PTHrP was discovered because of its production by cancers, evidence for its actions as a local regulator highlights the importance of understanding its roles not only in the etiology of HHM in cancer patients but also in normal tissues.