Parathyroid Hormone-like Peptide Research Articles

Calcium Mediates the Phosphaturia in Hypercalcemia of Malignancy

Background: Humoral hypercalcemia of malignancy (HHM) is claimed to be caused by circulating parathyroid hormone like peptide (PTHrP) that shares several of the cardinal biochemical and skeletal histological features with hyperparathyroidism (HPT). Both syndromes are characterized by hypercalcemia from increased renal tubular reabsorption of filtered calcium, increased urinary cyclic AMP, renal phosphate wasting and hypophosphatemia, in contrast to low 1,25(OH)2D levels, metabolic alkalosis, and uncoupled bone formation-resorption rate in HHM. The aim of the study was to reassess if phosphaturia of HHM can be attributed to hypercalcemia rather than to humoral effect of PTHrP. Methods: A prospective study was conducted at Mount Sinai Services at Queens Hospital Center, NY. Results: Nine (four females and five males) out of 20 patients with hypercalcemia of malignancy documented having elevated PTHrP, normal renal function, and low PTH levels were finalized for the study. Serum calcium, phosphate, creatinine, albumin, and PTHrP concentration were determined. On the initiation of hydration, 24 h urine for creatinine, calcium and phosphorous were also collected. Blood and urine tests were repeated after serum calcium levels had been decreased by at least 1.5 mg/dL. All patients received vigorous intravenous hydration with normal saline at 200 cc/h. After the first 24 h, small doses of furosemide were given to two out of nine patients for 48 - 72 h. Hydration has shown statistically significant decrease in serum calcium concentration (13.9 ± 2.1 to 10.8 ± 1.48 mg/dL; P < 0.001) and increase in tubular reabsorption of phosphate (TRP) (69.54±8.16% to 77.85±12.24%; P < 0.01). However, PTHrP levels have shown no statistically significant difference on hydration therapy. Conclusion: Improvement of hypercalcemia by hydration reverses phosphaturia without reducing PTHrP levels. It is being proposed that in HHM, PTHrP can lead to hypercalcemia from uncoupled bone formation-resorption rate through a local autocrine or paracrine action produced by bony micrometastases that could not be demonstrated radiologically, rather than from PTHrP’s humoral effect. J Endocrinol Metab. 2017;7(2):55-60 doi: https://doi.org/10.14740/jem402w

Spop promotes skeletal development and homeostasis by positively regulating Ihh signaling

Indian Hedgehog (Ihh) regulates chondrocyte and osteoblast differentiation through the Glioma-associated oncogene homolog (Gli) transcription factors. Previous in vitro studies suggested that Speckle-type POZ protein (Spop), part of the Cullin-3 (Cul3) ubiquitin ligase complex, targets Gli2 and Gli3 for degradation and negatively regulates Hedgehog (Hh) signaling. In this study, we found defects in chondrocyte and osteoblast differentiation in Spop-null mutant mice. Strikingly, both the full-length and repressor forms of Gli3, but not Gli2, were up-regulated in Spop mutants, and Ihh target genes Patched 1 (Ptch1) and parathyroid hormone-like peptide (Pthlh) were down-regulated, indicating compromised Hh signaling. Consistent with this finding, reducing Gli3 dosage greatly rescued the Spop mutant skeletal defects. We further show that Spop directly targets the Gli3 repressor for ubiquitination and degradation. Finally, we demonstrate in a conditional mutant that loss of Spop results in brachydactyly and osteopenia, which can be rescued by reducing the dosage of Gli3. In summary, Spop is an important positive regulator of Ihh signaling and skeletal development.

Impact of growth factors and PTHrP on early and late chondrogenic differentiation of human mesenchymal stem cells

Common in vitro protocols for chondrogenesis of mesenchymal stem cells (MSCs) induce an inadequate, hypertrophic differentiation cascade reminiscent of endochondral bone formation. We aimed to modify chondrogenic protocols in order to identify potent inducers, promotors, and inhibitors to achieve better chondrogenesis. Nine factors suspected to stimulate or inhibit chondrogenesis were used for chondrogenic in vitro induction of MSC. Differentiation was assessed by immunohistochemistry, alcian-blue staining, qRT-PCR, and quantification of alkaline phosphatase (ALP) activity. Pre-differentiated pellets were transplanted subcutaneously into SCID mice to investigate stable cartilage formation. Transforming growth factor (TGF)-beta was always required for chondrogenic differentiation and deposition of a collagen-type-II-positive extracellular matrix, while bone morphogenetic protein (BMP)-2, -4, -6, -7, aFGF, and IGF-I (10 ng/ml) were alone not sufficiently inductive. Each of these factors allowed differentiation in combination with TGF-beta, however, without preventing collagen type X expression. bFGF or parathyroid hormone-like peptide (PTHrP) inhibited the TGF-beta-responsive COL2A1 and COL10A1 expression and ALP induction when added from day 0 or 21. In line with a reversible ALP inhibition, in vivo calcification of pellets was not prevented. Late up-regulation of PTH1R mRNA suggests that early PTHrP effects may be mediated by a receptor-independent pathway. While TGF-beta was a full inducer, bFGF and PTHrP were potent inhibitors for early and late chondrogenesis, seemed to induce a shift from matrix anabolism to catabolism, but did not selectively suppress COL10A1 expression. Within a developmental window of collagen type II(+)/collagen type X(-) cells, bFGF and PTHrP may allow inhibition of further differentiation toward hypertrophy to obtain stable chondrocytes for transplantation purposes.

BMP4 and PTHrP interact to stimulate ductal outgrowth during embryonic mammary development and to inhibit hair follicle induction

The mammary glands develop initially as buds arising from the ventral embryonic epidermis. Recent work has shed light on signaling pathways leading to the patterning and formation of the mammary placodes and buds in mouse embryos. Relatively little is known of the signaling pathways that initiate branching morphogenesis and the formation of the ducts from the embryonic buds. Previous studies have shown that parathyroid hormone-related protein (PTHrP; also known as parathyroid hormone-like peptide, Pthlh) is produced by mammary epithelial cells and acts on surrounding mesenchymal cells to promote their differentiation into a mammary-specific dense mesenchyme. As a result of PTHrP signaling, the mammary mesenchyme supports mammary epithelial cell fate, initiates ductal development and patterns the overlying nipple sheath. In this report, we demonstrate that PTHrP acts, in part, by sensitizing mesenchymal cells to BMP signaling. PTHrP upregulates BMP receptor 1A expression in the mammary mesenchyme, enabling it to respond to BMP4, which is expressed within mesenchymal cells underlying the ventral epidermis during mammary bud formation. We demonstrate that BMP signaling is important for outgrowth of normal mammary buds and that BMP4 can rescue outgrowth of PTHrP(-/-) mammary buds. In addition, the combination of PTHrP and BMP signaling is responsible for upregulating Msx2 gene expression within the mammary mesenchyme, and disruption of the Msx2 gene rescues the induction of hair follicles on the ventral surface of mice overexpressing PTHrP in keratinocytes (K14-PTHrP). Our data suggest that PTHrP signaling sensitizes the mammary mesenchyme to the actions of BMP4, triggering outgrowth of the mammary buds and inducing MSX2 expression, which, in turn, leads to lateral inhibition of hair follicle formation within the developing nipple sheath.

Parathyroid hormone-like peptide and parathyroid hormone are secreted from bovine parathyroid via different pathways

Parathyroid hormone-like peptide is a recently discovered protein which is thought to be responsible for the hypercalcemia of malignancy. Through the use of radioimmunoassay, Northern analysis and Western blot techniques this protein has been demonstrated to occur in a variety of tumor and normal cells. Its role in normal physiology is not established nor is there knowledge regarding its synthesis, secretion, and storage. We have investigated characteristics of the secretion of parathyroid hormone-like peptide in bovine parathyroid gland slices and cells to learn whether or not this protein is secreted in a manner similar to that of parathyroid hormone. We have used radioimmunoassays specific for PTH and PTH-rP to measure the secretion of each protein and have found that, unlike PTH, PTH-rP secretion was not influenced by the medium calcium concentration. Similarly, PTH-rP secretion was not influenced by other known PTH secretagogues such as c-AMP or isoproterenol. An examination of the subcellular distribution of PTH-rP revealed that 75–90% of it occurs in the soluble fraction of cell lysates. Analysis of isolated secretory granules demonstrated the presence of PTH while PTH-rP was undetectable in these organelles. We conclude that PTH-rP is not secreted from parathyroid cells via the regulated pathway utilizing PTH secretory granules.

Parathyroid hormone-like peptide in pancreatic endocrine carcinoma and adenocarcinoma associated with hypercalcemia

Parathyroid hormone-like peptide (PLP) is produced by a number of tumors commonly associated with hypercalcemia as well as by nontumorous tissue, including some endocrine organs. We applied immunohistochemistry using the avidin-biotin-peroxidase technique to localize PLP in formalin-fixed, paraffin-embedded tissues of two human pancreatic carcinomas associated with hypercalcemia and normal blood parathyroid hormone levels. One tumor was endocrine and one was exocrine in differentiation. There was no evidence of bone metastasis in either case. We documented normalization of serum calcium level after removal of the pancreatic endocrine tumor. These observations support the suggestion that PLP production by pancreatic carcinoma may play a role in the development of hypercalcemia. However, the presence of PLP in tumors not associated with hypercalcemia indicates that other factors in addition to PLP are necessary for the manifestation of hypercalcemia. Hypercalcemia associated with exocrine pancreatic tumor has rarely been reported. Our exocrine pancreatic tumor appears to be the first reported case in which immunohistochemistry localized PLP. Since PLP has been localized to cells of exocrine ducts and ductules of normal pancreas, our results provide insight into the cell of origin of this tumor type.

Rapid polymerase chain reaction analysis and characterization of a polymorphism in the human parathyroid hormone-like peptide gene

Rapid polymerase chain reaction analysis and characterization of a polymorphism in the human parathyroid hormone-like peptide gene

Sublocalization of the mouse parathyroid hormone-like peptide gene to distal chromosome 6 by interspecific backcross analysis and [formula omitted] hybridization

Parathyroid hormone 1 (PTH1) receptor antagonists might be of benefit in hypercalcemia of malignancy (HHM) and hyperparathyroidism. We previously identified bovine tuberoinfundibular peptide (7–39) (bTIP(7–39)) as a high-affinity PTH1 receptor antagonist. Mouse TIP(7–39) is an antagonist (rPTH1 KB=44 nM, rPTH2=940 nM) that is more potent than other known PTH1 receptor antagonists: bTIP(7–39) (210 nM), PTH-related protein (PTHrP)(7–34) (640 nM), and bPTH(7–34) (>3000 nM). Plasma proteases slowly (t1/2=81 min) inactivated [125I]mTIP(7–39). Intravenous plasma [125I]mTIP(7–39) was bi-phasically cleared (radioactivity t1/2=2.9 min (70%) and 120 min (30%), binding activity t1/2=3.6 min (92%), and t1/2=21 min (8%)). Loss of unlabeled mTIP(7–39) (250 μg/kg i.v.) receptor binding was similar. mTIP(7–39)’s high-affinity should facilitate animal evaluation of effects of PTH1 receptor antagonism.

Search for human T-cell leukemia virus type I (HTLV-I) proviral sequences by polymerase chain reaction in the central nervous system tissue of HTLV-I-associated myelopathy.

Using the polymerase chain reaction (PCR), proviral DNA sequences of the pol and env regions of human T-cell leukemia virus type I (HTLV-I) were directly amplified in paraffin-embedded and frozen tissue sections of active inflammatory central nervous system (CNS) lesions in three autopsy cases of HTLV-I-associated myelopathy (HAM) with serological confirmation. In parallel, the enumeration of UCHL-1 (monoclonal antibody reactive to T-cells) positive cells in the tissue sections subjected to PCR were carried out. Although the control DNA sequence of parathyroid hormone-like peptide gene was definitely amplified, no signals for HTLV-I proviral sequences were detected in these specimens. The number of UCHL-1 positive cell nuclei was almost on the border line of our PCR sensitivity in formalin-fixed tissue, which was estimated to be 20-200 copies. Therefore, it is unlikely that the central nervous system tissue damage in HAM/TSP is a consequence of productive infection of HTLV-I in the CNS tissue.

Studies on the pathogenesis of osteoblastic metastases by prostate cancer.

Malignancies have long been known to markedly alter skeletal and calcium homeostasis. By far the commonest lesion observed in association with most malignancies is skeletal resorption, occasionally accompanied by elevations in blood calcium (hypercalcemia). Osteolysis and hypercalcemia may occur either when the tumor has metastasized to bone, presumably by a paracrine mechanism, or in the absence of skeletal metastases, by an endocrine mechanism. Considerable effort has been expended over the years to attempt to discern the pathogenetic factors involved in these skeletal responses to cancer. This culminated in the isolation of a parathyroid hormone-like peptide (PLP) from cancers, such as renal cancer, which are commonly associated with osteolysis and hypercalcemia [1]. This material is now believed to be the major factor causing hypercalcemia of malignancy. In the human, 3 isoforms of this peptide may exist and this entity is believed now to be a member of aparathyroid hormone/PLP gene family. Currently it is less clear what pathogenetic moieties may act locally in the vicinity of a skeletal metastasis to cause osteolysis. Although prostaglandins of the E series and transforming growth factor alpha (TGFα) have been implicated in this regard, more evidence supports the role of peptide cytokines such as, interleukin-1 and tumor necrosis factor alpha (TNFα) in the local resorption induced by cancer metastases [2].

Identification and functional characterization of adenylate cyclase- linked receptors for parathyroid hormone-like peptides on immortalized human keratinocytes

We have identified and characterized receptors for the amino-terminal domains of PTH and PTH-like peptide (PLP) on an immortalized human keratinocyte cell line, RHEK-1. Binding of both PLP-(1-34) and PTH-(1-34) to the RHEK-1 cells was consistent with a two-site model; affinities and capacities for each site were similar for the two peptides. Both peptides also stimulated adenylate cyclase activity with an equal ED50 in this cell line. Pertussis toxin pretreatment enhanced this peptide-mediated enzyme activity, suggesting linkage of the receptor to an inhibitory guanyl nucleotide-binding protein (Gi). Adenylate cyclase activity was diminished by both homologous [PLP-(1-34)] and heterologous [epidermal growth factor (EGF)] effectors. Malignant conversion of the immortalized cells with an activated H-ras oncogene to produce the RHEK-ras cell line was associated with a reduction in binding at both PLP/PTH and EGF receptors as well as a postreceptor defect in PLP/PTH-stimulated adenylate cyclase activity. The defect in enzyme activity appeared to be due in part to a decrease in the activity of the stimulatory guanyl nucleotide-binding protein (Gs), but not to an increase in Gi activity. Activation of the keratinocyte amino-terminal PLP/PTH receptor resulted in a small increase in [3H]thymidine incorporation, which was associated with an increase in cell numbers. This mitogenic effect was enhanced in the presence of EGF and was markedly reduced when cells were cultured in a high extracellular calcium environment. These studies demonstrate that the amino-terminal region of PLP and PTH activates adenylate cyclase-linked receptors, which are associated with mitogenesis, in RHEK-1 cells and suggest that this cell line represents a suitable model in which to examine the actions of PLP in keratinocytes.

Identification and functional characterization of adenylate cyclase-linked receptors for parathyroid hormone-like peptides on immortalized human keratinocytes.

We have identified and characterized receptors for the amino-terminal domains of PTH and PTH-like peptide (PLP) on an immortalized human keratinocyte cell line, RHEK-1. Binding of both PLP-(1-34) and PTH-(1-34) to the RHEK-1 cells was consistent with a two-site model; affinities and capacities for each site were similar for the two peptides. Both peptides also stimulated adenylate cyclase activity with an equal ED50 in this cell line. Pertussis toxin pretreatment enhanced this peptide-mediated enzyme activity, suggesting linkage of the receptor to an inhibitory guanyl nucleotide-binding protein (Gi). Adenylate cyclase activity was diminished by both homologous [PLP-(1-34)] and heterologous [epidermal growth factor (EGF)] effectors. Malignant conversion of the immortalized cells with an activated H-ras oncogene to produce the RHEK-ras cell line was associated with a reduction in binding at both PLP/PTH and EGF receptors as well as a postreceptor defect in PLP/PTH-stimulated adenylate cyclase activity. The defect in enzyme activity appeared to be due in part to a decrease in the activity of the stimulatory guanyl nucleotide-binding protein (Gs), but not to an increase in Gi activity. Activation of the keratinocyte amino-terminal PLP/PTH receptor resulted in a small increase in [3H]thymidine incorporation, which was associated with an increase in cell numbers. This mitogenic effect was enhanced in the presence of EGF and was markedly reduced when cells were cultured in a high extracellular calcium environment. These studies demonstrate that the amino-terminal region of PLP and PTH activates adenylate cyclase-linked receptors, which are associated with mitogenesis, in RHEK-1 cells and suggest that this cell line represents a suitable model in which to examine the actions of PLP in keratinocytes.

Localization of mouse parathyroid hormone-like peptide gene (Pthlh) to distal chromosome 6 using interspecific backcross mice and in situ hybridization.

The single copy parathyroid hormone-like peptide gene (Pthlh) was mapped to distal mouse chromosome 6 using genetic linkage analysis with a panel of DNA samples from interspecific backcross mice. In all 114 meiotic events examined, the Pthlh locus cosegregated with the locus for the Kirsten ras-2 gene (Kras-2) which was previously localized to distal mouse chromosome 6. In addition, Pthlh was localized to chromosome 6 band F-G and the mouse parathyroid hormone Pth was localized to chromosome 7 band F, by in situ hybridization. These studies confirm the previous localization of Pthlh to mouse chromosome 6 using somatic cell hybrids and show that the Pthlh/PTHLH locus is a part of a conserved linkage group between distal mouse chromosome 6 and the proximal segment of the short arm of human chromosome 12.

Rapid Induction of Parathyroid Hormone-Like Peptide Gene Expression by Sodium Butyrate in a Rat Islet Cell Line

The PTH-like peptide (PLP) gene is expressed in a diverse number of normal and neoplastic cell types, and induction of PLP gene expression has been observed after the induction of cellular differentiation. The differentiation of islet cells can be studied in vitro, after the exposure of rat islet cell lines to sodium butyrate. The present work found that rat RIN 1056A islet cells express the PLP gene and treatment with sodium butyrate resulted in rapid (detectable by 30 min) induction of PLP gene expression. PLP gene expression was rapidly and transiently induced by serum and cycloheximide, but the butyrate induction of PLP mRNA transcripts was not dependent on serum or new protein synthesis. Dexamethasone inhibited PLP gene expression and blocked the butyrate induction of PLP mRNA transcripts. The rapid induction of PLP gene expression after the exposure of islet cells to sodium butyrate, serum, and cycloheximide suggests that PLP may be a member of a class of early response genes involved in the regulation of cellular growth or differentiation.

Bioactivity of Parathyroid Hormone and Parathyroid Hormone-Like Peptide: Agonist and Antagonist Activities of Amino-Terminal Fragments as Assessed by the Cytochemical Bioassay and in Situ Biochemistry*

Parathyroid hormone-like peptide (PLP) is elaborated from certain tumors and is thought to play a role in the etiology of humoral hypercalcemia of malignancy. The amino-terminal portion of this peptide has a sequence homology with parathyroid hormone PTH. We have compared the agonist potency of the synthetic human amino-terminal 1-34 peptide [human (h)PLP-(1-34)] with that of intact PTH and its amino terminal fragment [hPTH-(1-34)] in the renal and metatarsal cytochemical bioassays (CBA). Furthermore, the antagonist activity of the truncated amino terminal molecule [hPLP-(3-34)] has been compared to that of [Norleu8.18,Tyr34]bovine PTH-(3-34)NH2, and we have also tested their ability to stimulate enzyme activities thought to be associated with bone formation and resorption. In the renal CBA, both PLP-(1-34) and hPTH-(1-34) were equipotent with intact hPTH. In the metatarsal CBA, although the two amino-terminal peptides were equipotent, they elicited an earlier response than the intact PTH molecule. In both assay systems the truncated PLP analog [hPLP-(3-34)] was a more potent antagonist of both PTH and PLP activity than was [Norleu8.18,Tyr34]bovine PTH-(1-34)NH2. In acute studies, hPLP-(1-34) and hPTH-(1-34) stimulated alkaline phosphatase and glucose 6-phosphate dehydrogenase activity in osteoblasts to a similar extent, and both peptides stimulated tartrate-resistant acid phosphatase and succinate dehydrogenase activity in osteoclasts. Longer exposure to the peptides resulted in stimulation of enzyme activity in osteoclasts but not osteoblasts, although there was no difference in potency between the two molecules.

Regulation of parathyroid hormone-like peptide in cultured normal human keratinocytes. Effect of growth factors and 1,25 dihydroxyvitamin D3 on gene expression and secretion.

We have examined the expression and secretion of endogenous parathyroid hormone-like peptide (PLP) in primary cultures of normal human keratinocytes. In response to growth factors and fetal bovine serum, PLP mRNA expression and immunoreactive PLP release into conditioned medium was rapidly increased (within hours) whereas these effects were inhibited by 1,25-dihydroxyvitamin D3 [1,25(OH)2D3]. These early responses were not influenced by raising the medium calcium concentration from 0.15 to 1.0 mM. In contrast, increasing the medium calcium concentration to 1.0 mM, addition of 1,25(OH)2D3, or a combination of both, resulted in a delayed augmentation (after several days) in PLP production which was associated with an increase in cellular differentiation as assessed by production of high molecular weight keratin. To investigate whether these factors were acting at the level of transcription of the PLP gene, a series of vectors were prepared by fusing segments of the 5' flanking region of the rat PLP gene to a growth hormone reporter gene. Transient transfection of these constructs into cultured keratinocytes and measurement of immunoreactive growth hormone in the medium showed that a region stimulated by growth factors is located in a 1.9-kb fragment of the 5' flanking region and that a PLP gene promoter region less than 1.2 kb and greater than 0.3 kb upstream of the cap site contains cis-acting elements which respond positively to serum, and negatively to 1,25(OH)2D3. These combined studies demonstrate that, in normal human keratinocytes, growth factors may acutely stimulate PLP mRNA levels and PLP release, whereas 1,25(OH)2D3 inhibits these responses. At least part of these effects are at the level of gene transcription. Additionally, PLP synthesis and release are enhanced under conditions in which keratinocyte differentiation is induced.

Parathyroid hormone-like peptide.

Parathyroid hormone-like peptide.

Expression of adenylate cyclase-coupled osseous parathyroid hormone and parathyroid hormone-like peptide receptors in Xenopus oocytes.

Functional parathyroid hormone (PTH) and PTH-like peptide receptors were expressed in Xenopus laevis oocytes after injection of poly(A)+ RNA isolated from the rat osteogenic sarcoma cell line, UMR 106. Increases in cAMP were seen in individual oocytes in response to added bovine (b) PTH-(1-34) (10(-6) M), human (h) PLP-(1-34) (hPLP-(1-34), 10(-6) M), isoproterenol (10(-4) M), and forskolin (10(-4) M). Although both intracellular and extracellular cAMP levels were stimulated approximately 1.5-2-fold by these agonists, intracellular concentrations of cAMP were substantially higher than extracellular concentrations. Peak increases with bPTH-(1-34) occurred after a 30-min incubation with the hormone 48 h after oocyte injection. bPTH-(1-34) caused a concentration-dependent augmentation of cAMP in injected oocytes, and the in vitro antagonist hPLP-(3-34) produced dose-dependent inhibition of both bPTH-(1-34)- and hPLP-(1-34)-stimulated cAMP accumulation. Specific binding of PTH to oocyte membranes was also demonstrated 48 h after oocyte injection with UMR 106 cell mRNA. Following size fractionation of isolated UMR 106 poly(A)+ RNA by sucrose density gradients, mRNA directing the expression of both PTH- and PLP-stimulated cAMP in oocytes appeared in the 3.5-4.9-kilobase fraction. These results demonstrate that adenylate cyclase-coupled osseous PTH and PLP receptors can be expressed after injection of naturally occurring mRNA into Xenopus oocytes, that PTH- and PLP-stimulated increases in cAMP concentrations can be detected in individual oocytes injected with bone cell-derived mRNA, that PTH and PLP appear to cross-react at a common receptor after injection of UMR 106 cell mRNA into oocytes, and that size selection of mRNA encoding the PTH and PLP receptors can be achieved by density gradient centrifugation. These studies, therefore, indicate the potential usefulness of the Xenopus oocyte system in expression cloning of PTH and PLP receptor cDNAs and illustrate the feasibility of employing this system to examine the biology of PTH and PLP receptors.

Assignment of the rat parathyroid hormone-like peptide gene (PTHLH) to chromosome 4: evidence for conserved synteny between human chromosome 12, mouse chromosome 6, and rat chromosome 4

The gene coding for rat parathyroid hormone-like peptide (PTHLH) was previously assigned to rat chromosome 2 (Hendy et al., 1988). We reexamined this assignment. According to our results, the gene is on rat chromosome 4. Taking into account the known localizations of the KRAS2 (Kras-2) oncogene and the PTHLH gene, this assignment strongly suggests that a synteny group is conserved on rat chromosome 4, mouse chromosome 6, and human chromosome 12.

Parathyroid hormone-like peptide in normal and neoplastic mesothelial cells

Mesothelioma has not been commonly reported as a cause of hypercalcemia of malignancy. We have studied a patient with malignant mesothelioma and hypercalcemia in association with elevated plasma concentrations of parathyroid hormone-like peptide (PLP). Immunohistochemical analysis of the tumor and seven of eight other mesotheliomas that were not associated with hypercalcemia revealed the presence of PLP cytoplasmic immunopositivity. PLP immunopositivity was also detected in normal and reactive mesothelial cells. The results of these studies suggest that PLP immunoreactivity is common in normal and neoplastic mesothelial cells and raises the possibility that PLP production may play a role in the pathogenesis of hypercalcemia associated with mesothelioma.