Transgenic models of metabolic bone disease: impact of estrogen receptor deficiency on skeletal metabolism

Estrogen has protective effects on the skeleton via its inhibition of bone resorption. Mechanisms for these effects and the selectivity to the estrogen receptor alpha (ER alpha) or ER beta are unclear. The purpose of our study was to determine the impact of the ER alpha on skeletal metabolism using murine models with targeted disruption of the ER alpha and beta. Mice generated by homologous recombination and Cre/loxP technology yielding a deletion of the ER alpha exon 3 were evaluated and also crossed with mice with a disruption of the exon 3 of the ER beta to result in double ER alpha and ER beta knockout mice. Skeletal analysis of long bone length and width, radiographs, dual X-ray absorptiometry, bone histomorphometry, micro computerized tomography, biomechanical analysis, serum biochemistry, and osteoblast differentiation were evaluated. Male ER alpha knockout mice had the most dramatic phenotype consisting of reduced bone mineral density (BMD), and bone mineral content (BMC) of femurs at 10 and 16 weeks and 8-9 months of age. Female ER alpha knockout mice also had reduced density of long bones but to a lesser degree than male mice. The reduction of trabecular and cortical bone in male ER alpha knockout mice was statistically significant. Male double ER alpha and ER beta knockouts had similar reductions in bone density versus the single ER alpha knockout mice suggesting that the ER alpha is more protective than the ER beta in bone. In vitro analysis revealed no differences in osteoblast differentiation or mineralized nodule formation among cells from ER alpha genotypes. These data suggest that estrogens are important in skeletal metabolism in males; the ER alpha plays an important role in estrogen protective effects; osteoblast differentiation is not altered with loss of the ER alpha; and compensatory mechanisms are present in the absence of the ER alpha and/or another receptor for estrogen exists that mediates further effects of estrogen on the skeleton.

Animal models of bone metastasis

Animal models will continue to be indispensable to investigate the pathogenesis of bone metastasis in vivo, conduct preclinical chemotherapeutic, chemoprevention and genetic therapy studies, test gene delivery mechanisms, and identify metastasis suppressor and inducer genes. It is likely that the bone marrow microenvironment, such as the endothelial cells, stromal cells, hematopoietic cells, bone cells, and the intercellular matrix play important roles in the localization and clonal growth of cancer cells in bone. Given the complexity of bone metastasis, many genes are expected to be involved in the pathogenesis and few are likely indispensable. The use of genomic and proteomic approaches to study these animal models will identify key targets for therapeutic intervention. As we further refine these models and use imaging for real-time evaluation of cells, and eventually target genes, these models will more closely mirror human disease and will hopefully become more predictive of the human response to therapy.

Parathyroid hormone (PTH) secretion, PTH mRNA and calcium-sensing receptor mRNA expression in equine parathyroid cells, and effects of interleukin (IL)-1, IL-6, and tumor necrosis factor-alpha on equine parathyroid cell function

Parathyroid hormone (PTH) is secreted by the chief cells of the parathyroid gland in response to changes in ionized calcium (Ca(2+)) concentrations. In this study, we measured PTH secretion, and PTH mRNA and calcium-sensing receptor (CaR) mRNA expression by equine parathyroid chief cells in vitro. We also evaluated the effects of interleukin (IL)-1beta, IL-6, and tumor necrosis factor (TNF)-alpha on PTH secretion, and PTH and CaR mRNA expression. The relationship between PTH and Ca(2+) was inversely related. PTH secretion decreased from 100% (day 0) to 13% (day 30). PTH mRNA expression declined from 100% (day 0) to 25% (day 30). CaR mRNA decreased from 100% (day 0) to 16% (day 30). Chief cells exposed to high (2.0 mM) Ca(2+) concentrations had a lower PTH mRNA expression compared with low Ca(2+) concentrations. Ca(2+) concentrations had no effect on CaR mRNA expression. The inhibitory effect of high Ca(2+) concentrations on PTH secretion also declined over time. After day 10, there was no significant difference in PTH secretion between low and high Ca(2+ )concentrations. IL-1beta decreased both PTH secretion (75%) and PTH mRNA expression (73%), and resulted in a significant overexpression of CaR mRNA (up to 142%). The effects of IL-1beta were blocked by an IL-1 receptor antagonist. IL-1beta decreased the Ca(2+) set-point from 1.4 mM to 1.2 mM. IL-6 decreased PTH secretion (74%), but had no effect on PTH and CaR mRNA expression. TNF-alpha had no effect on PTH secretion, and PTH and CaR mRNA expression. In summary, the decreased responsiveness of parathyroid cells to Ca(2+) from 0 to 30 days can be explained, in part, by the reduced CaR expression. IL-1beta and IL-6 but not TNF-alpha affected parathyroid function in vitro and may be important in influencing PTH secretion in the septic horse.

In vivo visualization of metastatic prostate cancer and quantitation of disease progression in immunocompromised mice

While survival periods for patients with localized prostate cancer have increased, there is still no curative therapy for metastatic disease. Using non-invasive bioluminescent imaging, we designed a comprehensive murine model to monitor tumor location and expansion. We detected micrometastases after one week that correlated by gross necropsy, autoradiography, and histopathology with organ and skeletal lesions seen clinically. We calculated in vivo kinetics for tumor growth based on biophoton emissions and observed significantly faster growth of bone lesions and of overall tumor burden in young mice compared to old mice. This model provides a controllable biological system for further investigation into the pathogenesis of metastatic prostate cancer and evaluation of new therapies.

Rb function in extraembryonic lineages suppresses apoptosis in the CNS of Rb-deficient mice

Retinoblastoma (Rb)-deficient embryos show severe defects in neurogenesis, erythropoiesis, and lens development and die at embryonic day 14.5. Our recent results demonstrated a drastic disorganization of the labyrinth layer in the placenta of Rb-deficient embryos, accompanied by reduced placental transport function. When these Rb-/- embryos were supplied with a wild-type placenta by using either tetraploid aggregation or genetic approaches, animals survived until birth. Here we analyze the role of extraembryonic Rb in regulating proliferation, apoptosis, and differentiation in the rescued animals at different developmental stages. Many of the neurological and erythroid abnormalities thought to be responsible for the embryonic lethality of Rb-/- animals, including the ectopic apoptosis in the CNS, were virtually absent in rescued Rb-/- pups. However, rescued animals died at birth with severe skeletal muscle defects. Like in Rb knockout embryos, rescued animals showed a marked increase in DNA replication and cell division in the CNS. In sharp contrast, the typical widespread neuronal apoptosis was absent in Rb-deficient embryos reconstituted with a normal placenta. In lens fiber cells, however, the inappropriate proliferation and apoptosis that is normally observed in Rb-/- embryos continued unabated in rescued animals. These results demonstrate that Rb function in extraembryonic lineages plays an important role in the survival of neuronal cells and in the differentiation of the erythroid lineage, providing mechanistic insight into the cell autonomous and nonautonomous functions of Rb during development.

Estrogen receptors in skeletal metabolism: lessons from genetically modified models of receptor function

Estrogens have long been known to be important for skeletal homeostasis, but their precise mechanisms of action in bone are still unclear. Mice with targeted deletions of the estrogen receptors alpha (ERalpha) and beta (ERbeta) have been generated by two research groups and several studies performed characterizing the phenotype of ERalpha knockout (ERKOalpha), ERbeta knockout (ERKObeta), or double deletion of ERalpha and ERbeta (DERKO) mice. Initial studies reported a reduction in bone mineral density in male ERKOalpha mice. More extensive analyses have been puzzling, likely because of compensatory mechanisms in ERKO mice. Furthermore, the existence of a third ER continues to be a potential explanation for some actions of estrogen in bone. Other rodent models, including the testicular feminized mouse and rat, the aromatase knockout mouse, and a rat with a dominant negative ER mutation, have added information regarding estrogen's actions in bone. This review summarizes many reports characterizing available rodent models with genetic alterations relevant to estrogen action. The sum of these reports suggests that the ERbeta is not highly protective in bone because loss of its function results in minimal alterations in the skeleton. Furthermore, loss of both the ERalpha and the ERbeta does not account for loss of estrogen action in bone, because the impact of DERKO is seemingly not as great as the impact of gonadectomy on the skeleton. Finally, through studies of ERKO mice and other rodent models of altered sex steroid action, it appears that estrogen may be more protective in the skeleton than androgens.

Pathophysiology of calcium metabolism

Calcium (Ca) is a mineral that plays a central role in maintaining the homeostasis of vertebrate animals, including muscle contraction, blood coagulation, enzyme activity, neural excitability, hormone secretion, and cell adhesion.(1) It is also involved in the pathogenesis of metabolic diseases which disrupt the normal regulation of Ca balance and may result in hypercalcemia or hypocalcemia.(2) The purpose of this manuscript is to review current concepts of the function of Ca, its regulation, and the role of Ca in specific disease processes.

Extra-embryonic function of Rb is essential for embryonic development and viability

The retinoblastoma (Rb) gene was the first tumour suppressor identified. Inactivation of Rb in mice results in unscheduled cell proliferation, apoptosis and widespread developmental defects, leading to embryonic death by day 14.5 (refs 2-4). However, the actual cause of the embryonic lethality has not been fully investigated. Here we show that loss of Rb leads to excessive proliferation of trophoblast cells and a severe disruption of the normal labyrinth architecture in the placenta. This is accompanied by a decrease in vascularization and a reduction in placental transport function. We used two complementary techniques-tetraploid aggregation and conditional knockout strategies-to demonstrate that Rb-deficient embryos supplied with a wild-type placenta can be carried to term, but die soon after birth. Most of the neurological and erythroid abnormalities thought to be responsible for the embryonic lethality of Rb-null animals were virtually absent in rescued Rb-null pups. These findings identify and define a key function of Rb in extra-embryonic cell lineages that is required for embryonic development and viability, and provide a mechanism for the cell autonomous versus non-cell autonomous roles of Rb in development.

Hysteresis and calcium set-point for the calcium parathyroid hormone relationship in healthy horses

Abnormalities in calcium (Ca(2+)) homeostasis are reported in horses with several pathological conditions; however, there is little information on Ca(2+) regulation in horses. The objectives of the present study were to determine the Ca(2+) set-point in healthy horses, to determine whether the Ca(2+)/parathyroid hormone (PTH) response curves were characterized by hysteresis, and to determine if the order of experimentally induced hypocalcemia or hypercalcemia had an effect on PTH secretion. The Ca(2+) set-point and hysteresis were determined in 12 healthy horses by infusing Na(2)EDTA and calcium gluconate. The Ca(2+) set-point was 1.37 +/- 0.05 mmol/L, which is higher than values reported for humans and dogs (1.0-1.2 mmol/L). Hysteresis was present during hypocalcemia and hypercalcemia. Horses in which hypocalcemia was followed by hypercalcemia secreted more PTH (7440 +/- 740 pmol min/L) than horses in which hypercalcemia was followed by hypocalcemia (5990 +/- 570 pmol min/L). This study has demonstrated that the Ca(2+) set-point in the horse is higher than in other domestic animals and man. We have shown that the Ca(2+)/PTH relationship in horses is sigmoidal and displays hysteresis during both hypocalcemia and hypercalcemia, and that extracellular Ca(2+) concentrations may affect the response of the parathyroid gland to hypocalcemia.

Animal models of bone metastasis

BACKGROUND

Animal models are important tools to investigate the pathogenesis and develop treatment strategies for bone metastases in humans. However, there are few spontaneous models of bone metastasis despite the fact that rodents (rats and mice) and other animals (dogs and cats) often spontaneously develop cancer. Therefore, most experimental models of bone metastasis in rodents require injection or implantation of neoplastic cells into orthotopic locations, bones, or the left ventricle of the heart.

METHODS

The current study reviews the natural incidence and clinical manifestation of bone metastases of mammary and prostate carcinoma in animals, as well as the experimental models developed in mice using animal and human-derived neoplasms.

RESULTS

Rats, mice, dogs, and cats often develop spontaneous mammary carcinoma, but bone metastases are rare. Intact and neutered dogs develop prostate carcinoma that is usually androgen independent and may be associated with regional bone invasion or distant bone metastasis. Normal dog prostate tissue induces new bone formation in vivo and can serve as a model of osteoblastic metastasis without concurrent bone destruction. Experimental models of osteolytic, osteoblastic, and mixed osteolytic/osteoblastic bone metastases include syngeneic rodent neoplasms or human xenografts implanted at orthotopic sites (e.g., breast or prostate glands) in immunodeficient mice, injection of cancer cells into the left ventricle of the heart, or direct injection into bones. New transgenic mouse models of cancer have a low incidence of spontaneous bone metastasis, but cell lines derived from these tumors can be selected in vivo for increased incidence of bone metastasis. It is essential to validate and correctly interpret the lesions in models of bone metastasis to accurately correlate the data from animal models to human disease. Animal models have provided support for the "seed and soil" hypothesis of bone metastasis. However, the roles of vascular patterns in the metaphyses of long bones and rapid bone turnover in young animals in the pathogenesis of metastasis in experimental models are uncertain. Improvements in the imaging of experimental animals in vivo using fluorescent markers or light emitted from luciferase have led to increased sensitivity of detection and more accurate quantification of bone metastases. For example, imaging of human prostate carcinoma PC-3M cells transfected with luciferase, following injection into the left ventricle, has demonstrated that there is rapid localization of tumor cells to bones and other organs, such as the kidneys and lungs.

CONCLUSIONS

Animal models of metastasis have supported drug development and have been useful for identification of metastasis suppressor and promoter genes as novel targets for the development of novel therapies. Further refinement of these models will involve spatiotemporal analysis of the metastatic process by imaging and use of image data to stage disease and guide tissue sampling for gene expression profiling via gene array technology. In the future, integrated analyses of these models will be needed to understand the complexities of this important disease process.

Molecular cloning and expression of equine calcitonin, calcitonin gene-related peptide-I, and calcitonin gene-related peptide-II

In this study, we describe the cloning and tissue expression of equine calcitonin (CT), calcitonin-gene related peptide (CGRP)-I, and CGRP-II cDNA. We also describe a novel divergent form of CGRP (CGRP-I). Equine CT has greatest homology (>85%) to human, rat and mouse subgroups of calcitonins. Equine CGRP-I has low homology (<59%) to CGRPs of other species. The signal and N-terminal peptides for equine CT and CGRP-I were identical, indicating that these peptides are encoded by a gene equivalent to the human CALC-I gene. Equine CGRP-II has >80% homology to chicken, human, rat, ovine, swine, and bovine CGRPs. The homology between equine CGRP-I and CGRP-II is low (56%). The high homology of equine CGRP-II and the low homology of equine CGRP-I to CGRP in other species were unexpected findings. Northern blot analysis revealed that CT mRNA expression was restricted to the thyroid gland; however, RT-PCR revealed that CT mRNA expression was also present in the pituitary gland and in the liver. CGRP-I and CGRP-II mRNA expression was present in several regions of the nervous system and other tissues of neuroectodermal origin. An unexpected finding was CGRP-I expression in the kidney by both Northern analysis and by RT-PCR. Based on these results, CT gene expression in the horse was not restricted to the thyroid gland, and CT may be important in regulating pituitary cell function. CGRPs are widely expressed in tissues of the central and peripheral nervous system. Information from this study will be valuable to study the role of CT, CGRP-I, and CGRP-II in equine health and disease.

New bone formation in nude mouse calvaria induced by canine prostate tissue

Osteoblastic metastases are common in patients with advanced prostate cancer. The pathophysiology of the new bone formation at metastatic sites is not currently known, but it is hypothesized that growth factors secreted by the prostate may be involved. Unfortunately, most rodent models of prostate cancer with metastasis to bone are osteolytic and not osteoblastic. Significant osteolysis by tumor cells at metastatic sites also may lead to fractures or bone instability. Misinterpretation of new periosteal bone due to bone instability as tumor-cell osteo-induction is another disadvantage of the osteolytic models. To circumvent these problems, we have developed a model system of new bone formation in the calvaria of nude mice stimulated by normal canine prostate tissue. Collagenase-digested normal prostate tissue was implanted adjacent to the calvaria of nude mice. Calvaria were examined at 2 weeks post-implantation for changes in the bone microenvironment by histology, calcein uptake at sites of bone mineralization, and tartrate-resistant acid phosphatase staining for osteoclasts. The prostate tissue remained viable and induced abundant new woven bone formation on the adjacent periosteal surface. In some cases new bone formation also was induced on the distant or concave calvarial periosteum. The new bone stained intensely with calcein, which demonstrated mineralization of the bone matrix. The new bone formation on prostate-implanted calvaria significantly increased (1.7-fold) the thickness of the calvaria compared with control calvaria. New bone formation was not induced in calvaria of mice implanted with normal canine kidney, urinary bladder, spleen, or skeletal muscle tissue, or mice with surgically-induced disruption of the periosteum. Osteoclast numbers in the medullary spaces and periosteum of calvaria were mildly increased (61%) in mice with implanted prostate tissue. In conclusion, this animal model will be useful for investigating the roles of prostate-derived growth factors on new bone formation in vivo.

Detection of parathyroid hormone-related protein in cats with humoral hypercalcemia of malignancy

BACKGROUND

Increased serum parathyroid hormone-related peptide (PTHrP) concentration is used to diagnose humoral hypercalcemia of malignancy (HHM) in humans and animals. A commercially available assay for human PTHrP has diagnostic utility in the dog, but has not been assessed in cats.

OBJECTIVE

The goals of this study were to determine serum or plasma levels of PTHrP in a population of hypercalcemic cats and to determine whether increased PTHrP concentration was associated with malignancy. In addition, we validated immunoradiometric assays (IRMAs) for intact parathormone (iPTH) and PTHrP for use with feline samples.

METHODS

A retrospective analysis of iPTH and PTHrP results from 322 hypercalcemic cats (ionized calcium concentration > 1.4 mmol/L) was performed. Immunoassays for human iPTH and PTHrP (residues 1-84) were validated using standard methods, and reference intervals were calculated using values from 31 healthy adult cats. Hypercalcemic cats were classified as parathyroid-independent (iPTH < 2.3 pmol/L), equivocal (iPTH 2.3-4.6 pmol/L), or parathyroid-dependent (iPTH > 4.6 pmol/L). Seven cats with detectable or increased PTHrP concentrations were evaluated further for underlying disease. Formalin-fixed neoplastic tissues were immunohistochemically stained using rabbit antibody to human midregion PTHrP.

RESULTS

Assays for iPTH and PTHrP showed acceptable precision for feline samples. The reference interval for iPTH was 0.8-4.6 pmol/L and for PTHrP was < 1.5 pmol/L. The majority of hypercalcemic cats (263/322, 81.7%) were parathyroid-independent, with fewer cats in the equivocal (32/322, 9.9%) and parathyroid-dependent (27/322, 8.4%) groups. In 31 (9.6%) cats, PTHrP concentration was > 1.5 pmol/L (range 1.5-26.6 pmol/L). All 7 cats for which follow-up information was available had HHM; 6 had carcinomas (4 lung carcinomas, 1 undifferentiated carcinoma, 1 thyroid carcinoma) and 1 had lymphoma. All tumors had mild to moderate positive staining for PTHrP; however, lung carcinomas from normocalcemic cats also stained positive.

CONCLUSIONS

Human IRMA for PTHrP (1-84) can be used to measure PTHrP in cats. Malignancies, particularly carcinomas, appear to secrete PTHrP and induce HHM in this species. Immunohistochemistry alone cannot predict the occurrence of HHM in cats.

Effects of chlorpromazine, pentoxifylline and dexamethasone on mRNA expression of lipopolysaccharide-induced inflammatory cytokines in bovine peripheral blood mononuclear cells

The effects of chlorpromazine (CPZ), pentoxifylline (PTX) and dexamethasone (DEX) on mRNA expression of lipopolysaccharide (LPS)-induced proinflammatory cytokines were examined in bovine peripheral blood mononuclear cells (PBMCs) in vitro. The expression of inflammatory cytokine mRNAs was analyzed by RT-PCR and Southern blot hybridization in bovine PBMCs. CPZ and DEX decreased the expression of cytokine mRNA (such as interleukin-1 beta and tumor necrosis factor-alpha) after stimulation with LPS in a dose-dependent manner. However, pretreatment with PTX had no inhibitory effect on the mRNA expression of proinflammatory cytokines. These results indicated that pretreatment with CPZ and DEX might be effective to reduce the production of LPS-induced inflammatory cytokines in bovine PBMCs in vitro.

Hypercalcemia and high parathyroid hormone-related protein concentration associated with malignant melanoma in a dog

A 12-year-old Cocker Spaniel with an oral malignant melanoma was evaluated for progressive lethargy and anorexia. No metastases were identified during antemortem evaluation, but severe hypercalcemia was evident. Antemortem diagnostic testing failed to identify a cause for the hypercalcemia. No neoplasms other than the melanoma were identified on postmortem examination. Serum parathyroid hormone-related protein concentration was markedly high, and the melanoma had moderate to marked immunostaining for this protein. Paraneoplastic syndromes are rare in dogs with malignant melanoma.

Engraftment and tumorigenesis of HTLV-1 transformed T cell lines in SCID/bg and NOD/SCID mice

Human T cell leukemia/lymphoma virus type-1 (HTLV-1) is recognized as the etiological agent of adult T cell leukemia (ATL). Although HTLV-1 can immortalize human lymphocytes in culture, identification of molecular events leading to tumorigenesis after HTLV-1 infection remain elusive. SCID/bg and NOD/SCID mice have reduced natural killer (NK) cell activity and were inoculated intraperitoneally with HTLV-1 transformed cells to refine and characterize the SCID mouse as a small animal model for investigation of HTLV-1 tumorigenesis. HTLV-1 transformed cell lines originally derived by cocultivation of uninfected peripheral blood mononuclear cells (PBMC) with lethally irradiated leukemic cells from patient samples (SLB-1, MT-2 and HT-1-RV) were lymphomagenic when inoculated into NOD/SCID mice. In contrast, immortalized cell lines generated by transfection PBMC with an infectious molecular clone of HTLV-1 (ACH or ACH.p12) were not tumorigenic. The differing behaviors of HTLV-1 infected cell lines in NOD/SCID mice indicates that viral infection and immortalization of human PBMC for growth in culture is not sufficient for induction of a tumorigenic phenotype. The higher level of engraftment of HTLV-1 transformed cell lines in NOD/SCID mice suggests that this is an effective animal model to investigate molecular determinants of HTLV-1 lymphomagenesis.

Specificity of E2F1, E2F2, and E2F3 in mediating phenotypes induced by loss of Rb

The Rb/E2F pathway plays a critical role in the control ofcellular proliferation. Here, we report that E2F1, E2F2, and E2F3 make major individual contributions toward the in vivo phenotypic consequences of Rb deficiency. In the developing lens of Rb(-/-) embryos, loss of E2F1, E2F2, or E2F3 reduces the unscheduled proliferation of fiber cells, with the loss of E2F3 having the most pronounced effect. In Rb-deficient retinas, all three E2Fs contribute equally to the ectopic proliferation of postmitotic neuronal cells. In contrast, E2F1 is unique in mediating apoptosis in both Rb(-/-) lenses and retinas. In the central nervous system, loss of E2F1 or E2F3 can almost completely eliminate the ectopic DNA replication and apoptosis observed in Rb(-/-) embryos, and loss of E2F2 partially reduces the unscheduled DNA replication and has no effect on apoptosis. These results provide clear evidence for functional specificity among E2Fs in the control of Rb-dependent proliferation and apoptosis in a tissue-specific manner.

Cloning and sequencing of the 3'-region of the canine parathyroid hormone-related protein gene and analysis of alternate mRNA splicing in two canine carcinomas

A canine genomic library in Lambda FIX II vector was screened with a 281-base pair canine PTHrP cDNA to the prepro- and coding regions. Two genomic clones were isolated and mapped to the 3'-end of the PTHrP gene by polymerase chain reaction (PCR) amplification of exons in this region. One clone (3.5 kb) was amplified by PCR, partially sequenced, and compared to the human PTHrP gene. Regions were identified with a high degree of homology to exons 6, 7, and 8 of the human PTHrP gene. A polyadenylation site was present 3' to the exon 8-like region. Reverse transcriptase-polymerase chain reaction (RT-PCR) demonstrated that exon 7 of the PTHrP gene was transcribed in two canine carcinomas (SCC 2/88 cells and CAC-8 tumor line) which produce PTHrP. This confirmed that the 3'-region of the canine PTHrP gene is alternately spliced with splicing of exon 6 to exons 7 or 9. Transcription of exon 8 was not demonstrated by RT-PCR and suggests that the exon 8-like region of the dog PTHrP gene is not utilized. The exon 8-like region contained an early stop codon that was not present in exon 8 of the human PTHrP gene.

Messenger RNA stability of parathyroid hormone-related protein regulated by transforming growth factor-beta1

Humoral hypercalcemia of malignancy (HHM), a paraneoplastic syndrome associated with epithelial cancers, including squamous cell carcinoma (SCC), is due to expression and secretion of parathyroid hormone-related protein (PTHrP). Transforming growth factor-beta1 (TGFbeta1), expressed by many tumors, has been demonstrated in vitro to increase the half-life of PTHrP mRNA. In this study, oral squamous carcinoma cells (SCC2/88) had a two-fold increase in PTHrP mRNA stability (from 45 to 90 min) in response to treatment with TGFbeta1. In order to examine the mechanism of TGFbeta1-mediated PTHrP mRNA stability, a cell-free assay of mRNA degradation was utilized in which the degradation of in vitro-transcribed mRNA incubated with cytoplasmic protein extracts from SCC2/88 treated with vehicle or TGFbeta1 was measured. In this assay, full-length PTHrP mRNA was not significantly stabilized in TGFbeta1-treated samples when compared to vehicle treated samples. However, there was a striking (>5-fold) increase in PTHrP mRNA half-life in TGFbeta1-treated samples when PTHrP mRNA lacked the 3'-untranslated region (3'-UTR). In contrast, the degradation of 3'-UTR-truncated PTHrP mRNA using the cell-free assay was not altered in vehicle-treated samples. UV cross-linking of PTHrP mRNA and cytoplasmic proteins from cells treated with either vehicle or TGFbeta1 revealed numerous mRNA-binding proteins. TGFbeta1 treatment resulting in decreased binding of 33, 31, 27, 20 and 18 kDa binding proteins to the terminal coding region. These studies revealed that TGFbeta1-induced PTHrP mRNA stability might be, in part, the result of cis-acting sequences within the coding region of the PTHrP mRNA.

Canine prostate induces new bone formation in mouse calvaria: A model of osteoinduction by prostate tissue

BACKGROUND

Osteoblastic metastases are common in patients with advanced prostate cancer. The pathophysiology of the new bone formation at metastatic sites is not currently known, but it is hypothesized that growth factors secreted by the prostate may be involved. Unfortunately, most rodent models of prostate cancer with metastasis to bone are osteolytic and not osteoblastic. Significant osteolysis by tumor cells at metastatic sites may also lead to fractures or bone instability. Misinterpretation of new periosteal bone due to bone instability as tumor-cell osteoinduction is another disadvantage of the osteolytic models. To circumvent these problems, we have developed a model system of new bone formation in the calvaria of nude mice stimulated by normal canine prostate tissue.

METHODS

Collagenase-digested normal prostate tissue was implanted adjacent to the calvaria of nude mice. Calvaria were examined at 2 weeks post-implantation for changes in the bone microenvironment by histology, calcein uptake at sites of bone mineralization, and tartrate-resistant acid phosphatase staining for osteoclasts.

RESULTS

The prostate tissue remained viable and induced abundant new woven bone formation on the adjacent periosteal surface. In some cases new bone formation also was induced on the distant or concave calvarial periosteum. The new bone stained intensely with calcein, which demonstrated mineralization of the bone matrix. The new bone formation on prostate-implanted calvaria significantly increased (1.7-fold) the thickness of the calvaria compared with control calvaria. New bone formation was not induced in calvaria of mice implanted with normal canine kidney, urinary bladder, spleen, or skeletal muscle tissue, or mice with surgically-induced disruption of the periosteum. Osteoclast numbers in the medullary spaces and periosteum of calvaria were mildly increased (61%) in mice with implanted prostate tissue.

CONCLUSIONS

This animal model will be useful for investigating the roles of prostate-derived growth factors on new bone formation in vivo.

Cloning and sequence analysis of the complementary DNA for feline preproparathyroid hormone

OBJECTIVES

To clone and sequence the cDNA for feline preproparathyroid hormone (preproPTH) and to compare that sequence with other known parathyroid hormone (PTH) sequences.

SAMPLE POPULATION

Parathyroid glands from 1 healthy cat.

PROCEDURES

A cDNA library was constructed in lambda phage from feline parathyroid gland mRNA and screened with a radiolabeled canine PTH probe. Positive clones were sequenced, and nucleic acid and deduced amino acid sequences were analyzed and compared with known preproPTH and PTH sequences.

RESULTS

Screening of approximately 2 X 10(5) recombinant plaques revealed 3 that hybridized with the canine PTH probe; 2 clones comprised the complete sequence for feline preproPTH. Feline preproPTH cDNA consisted of a 63-base pair (bp) 5'-untranslated region (UTR), a 348-bp coding region, and a 326-bp 3'-UTR. The coding region encoded a 115-amino acid peptide. Mature feline PTH consisted of 84 amino acids. Amino acid sequence analysis revealed that feline PTH was > 83% identical to canine, bovine, swine, equine, human, and macaque PTH and 69, 71, and 44% identical to mouse, rat, and chicken PTH, respectively. Within the region responsible for hormonal activity (amino acids 1 to 34), feline PTH was > 79% identical to other mammalian PTH sequences and 64% identical to the chicken sequence.

CONCLUSIONS AND CLINICAL RELEVANCE

The amino acid sequence of PTH is conserved among mammalian species. Knowledge of the cDNA sequence for feline PTH may be useful to investigate disturbances of calcium metabolism and alterations in PTH expression in cats.

Feline head and neck squamous cell carcinoma cell line: characterization, production of parathyroid hormone-related protein, and regulation by transforming growth factor-beta

A natural animal model for human head and neck squamous cell carcinoma (H/N SCC) has not been described. The domestic cat has a high spontaneous occurrence of oropharyngeal SCC, which is similar to the human disease in aggressiveness and incurability. We have developed a cell line (SCCF1) from a laryngeal SCC of a cat. Keratinocytes were maintained in culture for greater than 50 passages. SCCF1 had strong cytokeratin immunohistochemical staining, weak vimentin staining, and no p53 staining. Ultrastructual features included cytokeratin filaments and desmosomes, as well as features of anaplasia (irregular cytoplasmic and nuclear margins, surface filopodia, and abnormal intermediate filament production). Karyotype analysis revealed aneuploidy, with a stemline chromosomal number of 34. The cells grew logarithmically for 6 d until confluency. SCCF1 expressed parathyroid hormone-related protein (PTHrP) messenger ribonucleic acid (mRNA) and protein, and secreted the protein into the medium. Treatment of SCCF1 with transforming growth factor-beta increased PTHrP production but did not affect PTHrP mRNA stability. Reverse transcriptase-polymerase chain reaction was used to amplify a 282-base pair region of feline PTHrP mRNA, encoding portions of the pre-pro and coding regions. The complementary deoxyribonucleic acid (cDNA) was cloned and sequenced. The cDNA and the predicted amino acid sequences had a high degree of homology to human and canine PTHrP. RT-PCR was used to confirm alternate splicing of PTHrP mRNA for translation of PTHrP 1-139 and PTHrP 1-141. The SCCF1 cell line will permit mechanistic experiments on genetic dysregulation in neoplastic keratinocytes of the feline oropharynx, and development of an in vitro model for H/N cancer.

Genetic and physical interactions between Microphthalmia transcription factor and PU.1 are necessary for osteoclast gene expression and differentiation

The microphthalmia transcription factor (MITF), a basic-helix-loop-helix zipper factor, regulates distinct target genes in several cell types. We hypothesized that interaction with the Ets family factor PU.1, whose expression is limited to hematopoietic cells, might be necessary for activation of target genes like tartrate-resistant acid phosphatase (TRAP) in osteoclasts. Several lines of evidence were consistent with this model. The combination of MITF and PU.1 synergistically activated the TRAP promoter in transient assays. This activation was dependent on intact binding sites for both factors in the TRAP promoter. MITF and PU.1 physically interacted when coexpressed in COS cells or in vitro when purified recombinant proteins were studied. The minimal regions of MITF and PU.1 required for the interaction were the basic-helix-loop-helix zipper domain and the Ets DNA binding domain, respectively. Significantly, mice heterozygous for both the mutant mi allele and a PU.1 null allele developed osteopetrosis early in life which resolved with age. The size and number of osteoclasts were not altered in the double heterozygous mutant mice, indicating that the defect lies in mature osteoclast function. Taken in total, the results afford an example of how lineage-specific gene regulation can be achieved by the combinatorial action of two broadly expressed transcription factors.

Effects of 1,25(OH)2D3, EB1089, and analog V on PTHrP production, PTHrP mRNA expression and cell growth in SCC 2/88

BACKGROUND

We investigated the effects of 1,25(OH)2D3 and selected analogs on canine squamous carcinoma cells (SCC 2/88) and tested whether these compounds could effectively decrease proliferation, induce differentiation, and inhibit PTHrP production and PTHrP mRNA expression.

MATERIALS AND METHODS

SCC 2/88 cells were cultured and treated with three substrates. The media were collected for PTHrP immunoradiometric assay. The cells were analyzed for DNA concentration and PTHrP mRNA expression by Northern blot analysis, involucrin by Western blot analysis and 1,25(OH)2D3-receptor (VDR) and PTHrP by immunohistochemistry.

RESULTS

The SCC 2/88 cells were stained positively for VDR and PTHrP by immunohistochemistry. 1,25(OH)2D3 and its analogs inhibited cell growth and stimulated differentiation in a dose-dependent manner. All three substrate-treated groups had significantly increased PTHrP secretion at 10(-7) M. Cells treated with 1,25(OH)2D3 at 10(-7) M had 2- to 4-fold increased PTHrP mRNA expression at 12 and 24 hours compared to the vehicle-treated controL PTHrP mRNA in cells treated with TGF-beta (1.5 ng/ml) was increased 7- to 17-fold at 6, 12 and 24 hours compared to the vehicle-treated controL PTHrP mRNA expression was reduced by 0.5- to 2-fold in cells treated with 1,25(OH)2D3 at 10(-7) M and TGF-beta (1.5 ng/ml) together compared to cells treated with TGF-beta alone.

CONCLUSION

1,25(OH)2D3, EB1089, and analog V inhibited SCC 2/88 growth and induced differentiation in a dose-dependent manner, but did not inhibit PTHrP production. 1,25(OH)2D3 treatment led to increased PTHrP mRNA expression and reduced the stimulatory effect of TGF-beta on PTHrP mRNA expression in SCC 2/88 cells.

Humoral hypercalcemia of malignancy: severe combined immunodeficient/beige mouse model of adult T-cell lymphoma independent of human T-cell lymphotropic virus type-1 tax expression

The majority of patients with adult T-cell leukemia/lymphoma (ATL) resulting from human T-cell lymphotropic virus type-1 (HTLV-1) infection develop humoral hypercalcemia of malignancy (HHM). We used an animal model using severe combined immunodeficient (SCID)/beige mice to study the pathogenesis of HHM. SCID/beige mice were inoculated intraperitoneally with a human ATL line (RV-ATL) and were euthanized 20 to 32 days after inoculation. SCID/beige mice with engrafted RV-ATL cells developed lymphoma in the mesentery, liver, thymus, lungs, and spleen. The lymphomas stained positively for human CD45RO surface receptor and normal mouse lymphocytes stained negatively confirming the human origin of the tumors. The ATL cells were immunohistochemically positive for parathyroid hormone-related protein (PTHrP). In addition, PTHrP mRNA was highly expressed in lymphomas when compared to MT-2 cells (HTLV-1-positive cell line). Mice with lymphoma developed severe hypercalcemia. Plasma PTHrP concentrations were markedly increased in mice with hypercalcemia, and correlated with the increase in plasma calcium concentrations. Bone densitometry and histomorphometry in lymphoma-bearing mice revealed significant bone loss because of a marked increase in osteoclastic bone resorption. RV-ATL cells contained 1.5 HTLV-1 proviral copies of the tax gene as determined by quantitative real-time polymerase chain reaction (PCR). However, tax expression was not detected by Western blot or reverse transcriptase (RT)-PCR in RV-ATL cells, which suggests that factors other than Tax are modulators of PTHrP gene expression. The SCID/beige mouse model mimics HHM as it occurs in ATL patients, and will be useful to investigate the regulation of PTHrP expression by ATL cells in vivo.

Comparison of serum parathyroid hormone and ionized calcium and magnesium concentrations and fractional urinary clearance of calcium and phosphorus in healthy horses and horses with enterocolitis

OBJECTIVE

To evaluate calcium balance and parathyroid gland function in healthy horses and horses with enterocolitis and compare results of an immunochemiluminometric assay (ICMA) with those of an immunoradiometric assay (IRMA) for determination of serum intact parathyroid hormone (PTH) concentrations in horses.

ANIMALS

64 horses with enterocolitis and 62 healthy horses.

PROCEDURES

Blood and urine samples were collected for determination of serum total calcium, ionized calcium (Ca2+) and magnesium (Mg2+), phosphorus, BUN, total protein, creatinine, albumin, and PTH concentrations, venous blood gases, and fractional urinary clearance of calcium (FCa) and phosphorus (FP). Serum concentrations of PTH were measured in 40 horses by use of both the IRMA and ICMA.

RESULTS

Most (48/64; 75%) horses with enterocolitis had decreased serum total calcium, Ca2+, and Mg2+ concentrations and increased phosphorus concentrations, compared with healthy horses. Serum PTH concentration was increased in most (36/51; 70.6%) horses with hypocalcemia. In addition, FCa was significantly decreased and FP significantly increased in horses with enterocolitis, compared with healthy horses. Results of ICMA were in agreement with results of IRMA.

CONCLUSIONS AND CLINICAL RELEVANCE

Enterocolitis in horses is often associated with hypocalcemia; 79.7% of affected horses had ionized hypocalcemia. Because FCa was low, it is unlikely that renal calcium loss was the cause of hypocalcemia. Serum PTH concentrations varied in horses with enterocolitis and concomitant hypocalcemia. However, we believe low PTH concentration in some hypocalcemic horses may be the result of impaired parathyroid gland function.

Adrenal gland: structure, function, and mechanisms of toxicity

The adrenal gland is one of the most common endocrine organs affected by chemically induced lesions. In the adrenal cortex, lesions are more frequent in the zona fasciculata and reticularis than in the zona glomerulosa. The adrenal cortex produces steroid hormones with a 17-carbon nucleus following a series of hydroxylation reactions that occur in the mitochondria and endoplasmic reticulum. Toxic agents for the adrenal cortex include short-chain aliphatic compounds, lipidosis inducers, amphiphilic compounds, natural and synthetic steroids, and chemicals that affect hydroxylation. Morphologic evaluation of cortical lesions provides insight into the sites of inhibition of steroidogenesis. The adrenal cortex response to injury is varied. Degeneration (vacuolar and granular), necrosis, and hemorrhage are common findings of acute injury. In contrast, chronic reparative processes are typically atrophy, fibrosis, and nodular hyperplasia. Chemically induced proliferative lesions are uncommon in the adrenal cortex. The adrenal medulla contains chromaffin cells (that produce epinephrine, norepinephrine, chromogranin, and neuropeptides) and ganglion cells. Proliferative lesions of the medulla are common in the rat and include diffuse or nodular hyperplasia and benign and malignant pheochromocytoma. Mechanisms of chromaffin cell proliferation in rats include excess growth hormone or prolactin, stimulation of cholinergic nerves, and diet-induced hypercalcemia. There often are species specificity and age dependence in the development of chemically induced adrenal lesions that should be considered when interpreting toxicity data.

Head and neck squamous cell carcinoma: measurement of plasma parathyroid hormone-related protein and serum and urine calcium concentrations

OBJECTIVES

Parathyroid hormone-related protein (PTHrP) is expressed by squamous cell carcinomas. Our first objective was to examine the stability of PTHrP in normal human plasma. Our second objective was to determine whether plasma PTHrP could be used in patients with head and neck squamous cell carcinoma (HNSCC) as an indicator of tumor burden or relapse.

STUDY DESIGN AND SETTING

Blood and urine samples from 55 HNSCC patients undergoing tumor resection at The Ohio State University were measured for plasma PTHrP (1-86) concentration, serum ionized calcium concentration, and urine calcium/creatinine ratio.

RESULTS

Two of 55 HNSCC patients had detectable levels of plasma PTHrP. Serum ionized calcium concentrations and urinary calcium/creatinine ratios were within normal limits in all patients.

CONCLUSIONS

Plasma PTHrP was not a valuable indicator of tumor presence or recurrence in our patient population.

SIGNIFICANCE

Plasma PTHrP is not a useful marker of tumor presence or recurrence in patients with stage II to IV or recurrent HNSCC.

Parathyroid hormone-related protein as a growth regulator of prostate carcinoma

Parathyroid hormone-related protein (PTHrP) is produced by prostate carcinoma cells and tumors, but little is known of its role in prostate carcinogenesis. The goal of this study was to evaluate PTHrP expression in the regulation of prostate carcinoma growth using human and animal models. PTHrP expression was assessed in prostate cancer cell lines in vitro. Seven of nine cell lines produced PTHrP, and increased expression was seen during cell proliferation. The MatLyLu rat prostate carcinoma model was used to determine the effects of PTHrP overexpression on prostate tumor growth. PTHrP overexpression did not alter proliferation of the cells in vitro. However, when PTHrP-overexpressing cells were injected into rat hind limbs, primary tumor growth and tumor size were significantly enhanced as compared with control cells. To evaluate PTHrP in human prostate carcinoma patients, immunohistochemistry was performed on metastatic bone lesions. Immunolocalization of PTHrP protein was found in the cytoplasm and nucleus of cancer cells in the bone microenvironment. Because nuclear localization of PTHrP has been associated with an inhibition of apoptosis, the ability of full-length PTHrP to protect prostate cancer cells from apoptotic stimuli was examined. Cells transfected with full-length PTHrP showed significantly increased cell survival after exposure to apoptotic agents as compared with cells producing no PTHrP (plasmid control) or cells transfected with PTHrP lacking its nuclear localization signal. To determine the mechanism of action of PTHrP in prostate cancer cells, the parathyroid hormone/PTHrP receptor status of the cells was determined. These cell lines did not demonstrate parathyroid hormone/PTHrP receptor-mediated binding of iodinated PTHrP or steady-state receptor message by Northern blot analysis, but they did have a detectable receptor message by reverse transcription-PCR analysis. In summary, PTHrP is expressed in many prostate cancer cell lines in vitro and in metastatic bone lesions in vivo. PTHrP expression positively influences primary tumor size in vivo and protects cells from apoptotic stimuli. These data suggest that PTHrP plays an important role in the promotion of prostate tumor establishment and/or progression.

3',5'-Cyclic adenosine monophosphate activation in osteoblastic cells: effects on parathyroid hormone-1 receptors and osteoblastic differentiation in vitro

PTH has anabolic and catabolic effects in bone through activation of the PTH-1 (PTH/PTHrP) receptor and the cAMP/protein kinase A pathway. The effects of agents that regulate cAMP in nontransformed osteoblasts in relation to cell differentiation have not been described. The purpose of this study was to determine the effects of PTH fragments with differing cAMP-stimulating activity, and nonPTH cAMP regulators on PTH-1 receptor expression and activity, and osteoblast differentiation in vitro using MC3T3-E1 and primary rat calvarial cells. PTH (1-34), but not PTH (53-84), (7-34), or PTHrP (107-139) treatment (24 h) resulted in down-regulation of steady-state messenger RNA for the PTH-1 receptor. Forskolin (a stimulator of cAMP accumulation) also down regulated the PTH-1 receptor, whereas 9-(tetrahydro-2-furyl) adenine (THFA) (an inhibitor of adenylyl cyclase) had no effect. Similarly, PTH (1-34) treatment for 48 h abolished PTHrP binding to cell surface receptors; however, neither the PTH analogs nor the cAMP regulating agents altered PTH binding or numbers of binding sites on osteoblastic cells. Basal levels of cAMP were reduced in cultured cells treated for 6 days with PTH (7-34) or THFA compared with controls. In contrast, PTH-stimulated cAMP levels were significantly increased in cultures treated with PTH (7-34) and THFA for 6 days during osteoblast differentiation and were decreased in cultures treated with PTH (1-34) and forskolin compared with controls. To evaluate effects of the cAMP pathway on osteoblast differentiation, cultures were treated continuously with PTH analogs and cAMP regulators during an 18-day differentiation regime, total RNA was isolated at multiple time points, and Northern blot analysis for osteocalcin (OCN) was performed. THFA and PTH (7-34)-treated cultures had increased OCN expression; whereas, PTH (1-34) and forskolin reduced OCN expression. Interestingly, PTH (7-34) and THFA-treated cultures had increased mineralized nodule formation, in contrast to PTH (1-34) and forskolin treatment, which reduced nodule formation. Similarly, calcium accumulation in cultures was significantly increased in the PTH (7-34) and THFA-treated cultures and reduced in the PTH (1-34) and forskolin-treated cultures. These data demonstrate that agents that increase cAMP down regulate PTH-1 receptor messenger RNA and inhibit osteoblast differentiation in vitro. Agents that reduce or block adenylyl cyclase or cAMP activity do not alter PTH-1 receptor expression or binding, but have striking effects on promoting osteoblast differentiation. We conclude that many effects of PTH on osteoblasts may be mimicked or antagonized by agents that alter cAMP activity and bypass the PTH-1 receptor.

Parathyroid hormone-related protein is a positive regulator of keratinocyte growth factor expression by normal dermal fibroblasts

Parathyroid hormone-related protein (PTHrP), an important factor in the pathogenesis of humoral hypercalcemia of malignancy, is produced by many normal tissues, including the skin, where it regulates keratinocyte growth and differentiation and dermal fibroblast function. Keratinocyte growth factor (KGF), a member of the fibroblast growth factor (FGF) family, is a secretory product of stromal cells and functions as a mediator of epithelial cell growth and differentiation. Phenotypes of the skin in several transgenic mouse models, in which the KGF and PTHrP genes have been overexpressed or disrupted, suggest that these two factors interact in vivo to regulate homeostasis of the skin. In this study, we investigated the effects of KGF on PTHrP secretion and expression by normal human foreskin keratinocytes (NHFK) and the effects of PTHrP on KGF secretion and expression by normal human dermal fibroblasts (NHDF) in vitro. N-terminal PTHrP(1-36) increased KGF secretion, protein expression and mRNA expression by NHDF in a dose-dependent manner, however, KGF did not regulate PTHrP expression and secretion by NHFK. By flow cytometry, PTHrP also increased the percentage of NHDF producing KGF. Our results indicate that PTHrP produced by keratinocytes is a potential paracrine regulator of KGF expression by dermal fibroblasts in vivo. This paracrine regulation may explain, in part, the epidermal atrophy seen in the PTHrP null mice and epidermal hyperplasia seen in transgenic mice overexpressing PTHrP in their basal keratinocytes. Our results also suggest that PTHrP is an important mediator for the healing of skin wounds and growth of neoplasms of squamous origin.

Skeletal metastasis of prostate adenocarcinoma in rats: morphometric analysis and role of parathyroid hormone-related protein

BACKGROUND

Prostate cancer frequently metastasizes to bone, where it induces osteoblastic lesions. Parathyroid hormone-related protein (PTHrP), a product of normal and neoplastic prostate cells, may promote growth and bone metastasis of certain types of cancer. In this study, we investigated the: 1) pathogenesis and morphology of bone metastases in the MATLyLu rat prostate adenocarcinoma model, and 2) effect of PTHrP overexpression on tumor growth and incidence of bone metastasis.

METHODS

MATLyLu cells were stably transfected with a PTHrP expression vector or control plasmid. PTHrP expression was determined in vitro by immunoradiometric assay and Northern blot analysis. MATLyLu cells were injected into the left ventricle of Copenhagen rats to induce bone metastases. Histology and radiography were used to quantify the size and number of bone metastases. Serum alkaline phosphatase isoenzyme concentrations and histomorphometric analysis were used to evaluate bone formation and resorption.

RESULTS

All rats developed osteolytic metastases in long bones and vertebrae. There was no evidence of increased intramedullary bone formation. PTHrP overexpression by MATLyLu cells was not associated with any difference in the incidence of bone metastasis, size of metastatic foci or tumor-cell proliferation.

CONCLUSIONS

The MATLyLu intracardiac injection model of prostate carcinoma is an aggressive tumor model with a high incidence of osteolytic skeletal metastases, and is not altered by increased PTHrP production by neoplastic prostate epithelial cells.

Effects of isoprothiolane on cell growth of cultured bovine mammary epithelial cells

This study was performed to investigate the effects of isoprothiolane on cell growth and the production of interleukin (IL)-1 and IL-6 by bovine mammary epithelial cells in vitro. Isoprothiolane increased proliferation of mammary epithelial cells in a dose-dependent manner at the concentration of 0.05 to 5 microM when cultured either with or without serum-supplemented medium. In contrast, isoprothiolane (0.0005-5 microM) significantly inhibited the production of IL-1 and IL-6 by mammary epithelial cells. Moreover, the cytokines, IL-1alpha, IL-1beta, IL-6, and tumor necrosis factor (TNF)-alpha tended to inhibit the proliferation of mammary epithelial cells in a dose-dependent manner. These results indicated that isoprothiolane regulated mammary epithelial cell growth in vitro possibly by modulating the production of cytokines.

Spatial and temporal expression of parathyroid hormone-related protein during wound healing

Parathyroid hormone-related protein is produced by many normal tissues including the skin, where it regulates growth and differentiation of keratinocytes. To define better the role of parathyroid hormone-related protein in the skin, we investigated the spatial and temporal expression of parathyroid hormone-related protein and mRNA by immunohistochemistry and in situ hybridization during the healing of skin wounds, and the effects of topical administration of a parathyroid hormone-related protein agonist [parathyroid hormone-related protein (1-36)] and a parathyroid hormone-related protein antagonist [parathyroid hormone (7-34)] on the healing rate and morphology of the wounds. Wounds were produced on the back of guinea pigs with a 4 mm punch, and wound sites were collected at different time points during the healing process. Parathyroid hormone-related protein was expressed in normal skin by all viable keratinocyte layers, hair follicles, and adnexae. Following injury, migratory keratinocytes at wound margins and the newly restored epidermis expressed increased levels of parathyroid hormone-related protein. The remodeling phase was associated with progressive restoration of the pattern of parathyroid hormone-related protein expression in normal epidermis. Granulation tissue myofibroblasts and infiltrating macrophages also expressed parathyroid hormone-related protein. In vitro studies using THP-1 cells (a promonocytic cell line) confirmed that macrophages expressed parathyroid hormone-related protein, especially after activation. Topical application of parathyroid hormone related protein (1-36) or parathyroid hormone (7-34) did not result in significant changes in the healing rate and morphology of the wounds. These findings demonstrated that, in addition to keratinocytes, myofibroblasts and macrophages also represent sources of parathyroid hormone-related protein during the healing of skin wounds. Although the data suggest a role for parathyroid hormone-related protein in the healing of skin and in the restoration of epidermal homeostasis, parathyroid hormone-related protein does not appear to be required for proper re-epithelialization in response to injury, potentially because of redundancy in epidermal growth and wound healing, as has been shown for other paracrine and autocrine growth factors of the epidermis.

Expression of PTHrP and the PTH/PTHrP receptor in purified alveolar epithelial cells, myoepithelial cells, and stromal fibroblasts derived from the lactating rat mammary gland

Parathyroid hormone-related protein (PTHrP) is produced by the lactating mammary gland and secreted into the milk; however, the function of PTHrP during lactation is unknown. Since messenger RNA for both PTHrP and the PTH/PTHrP receptor have been demonstrated within mammary tissue, a paracrine or autocrine function for PTHrP has been proposed. To investigate this hypothesis in lactating tissue, the expression of PTHrP and the PTH/PTHrP receptor was examined in purified subpopulations of cells derived from lactating rat mammary glands. Subpopulations of stromal, myoepithelial, and alveolar epithelial cells were isolated from mammary tissue using enzymatic digestion and immunomagnetic purification. Isolated cells were phenotypically characterized by immunohistochemistry and ultrastructural morphology. The purity of the separated alveolar and myoepithelial cells was assessed ultrastructurally and ranged from 91 to 96%. Messenger RNA and protein expression of PTHrP and the PTH/PTHrP receptor were examined using reverse transcription polymerase chain reaction, immunohistochemistry, and Western blot analysis, respectively. PTHrP mRNA and protein were expressed in alveolar epithelial cells and stromal fibroblasts, whereas PTH/PTHrP receptor mRNA and protein were expressed in all three cell types. The expression patterns for PTHrP and the PTH/PTHrP receptor support an autocrine or paracrine function for PTHrP in alveolar epithelial cells and stromal fibroblasts and a paracrine function for PTHrP in myoepithelial cells in the rat mammary gland during lactation.

Effects of lipopolysaccharide on production of interleukin-1 and interleukin-6 by bovine mammary epithelial cells in vitro

This investigation was performed to determine the effect of lipopolysaccharide (LPS) on production of interleukin (IL)-1 and IL-6 by bovine mammary epithelial cells in vitro. After confluence, the cells were stimulated with LPS (0.1, 1.0 or 10 micrograms/ml) for 4, 8, 24, and 48 hr. LPS increased production of both IL-1 and IL-6 production from mammary cells in a dose dependent manner. The expression of mRNA for IL-1 receptor antagonist (IL-1ra) was demonstrated by reverse transcription-polymerase chain reaction in bovine mammary epithelial cells.

Regulation of parathyroid hormone-related protein expression in a canine squamous carcinoma cell line by colchicine

The regulation of parathyroid hormone-related protein expression by colchicine, vinblastine, nocodazole, taxol, transforming growth factor-beta1 (TGFbeta1), and epidermal growth factor (EGF) was investigated in a canine squamous carcinoma cell line (SCC 2/88 cells). SCC 2/88 cells were stably transfected with a human P2/P3 PTHrP promoter-luciferase reporter gene construct and gene expression was measured after chemical treatments. The greatest increase in reporter gene expression was observed after colchicine treatment and small increases occurred after treatment with vinblastine, taxol, TGFbeta1, or EGF. Nocodazole had no significant effect on reporter gene expression. Colchicine also increased PTHrP steady state mRNA expression and PTHrP secretion by SCC 2/88 cells. These results demonstrated that PTHrP production was increased in SCC 2/88 cells by colchicine and suggested that factors or events during mitosis are capable of stimulating PTHrP production. An increase in PTHrP production during mitosis of malignant epithelial cells may be important in the pathogenesis of humoral hypercalcemia of malignancy.

Dependence of humoral hypercalcemia of malignancy on parathyroid hormone-related protein expression in the canine anal sac apocrine gland adenocarcinoma (CAC-8) nude mouse model

Circulating parathyroid hormone-related protein (PTHrP) is the primary humoral factor in dogs with spontaneous humoral hypercalcemia of malignancy (HHM) and adenocarcinomas derived from apocrine glands of the anal sac. A canine apocrine adenocarcinoma model of HHM in nude mice (CAC-8) was developed and characterized. After 32 passages in vivo, a spontaneous variant of the tumor (CAC-8 Lo Ca) that has altered cellular morphology and that fails to induce HHM in tumor-bearing nude mice has been discovered. The hypercalcemic and nonhypercalcemic tumor lines were compared by tumor weight, effect on body weight, serum calcium concentration, plasma PTHrP concentration, histopathology, expression of PTHrP protein by radioimmunoassay and immunohistochemistry, and expression of PTHrP mRNA by in situ hybridization and northern blot analysis. Messenger RNA expression for other factors and cytokines known to alter PTHrP secretion or bone resorption in vivo, including tumor necrosis factor alpha (TNF alpha), interleukin (IL)-1, IL-6, and transforming growth factor beta (TGF beta), were also measured in the adenocarcinomas. There was no significant difference in weight of individual tumors. Nude mice bearing the CAC-8 (Lo Ca) tumor maintained normal body weight as compared with non-tumor-bearing control mice. In contrast, mice with the CAC-8 (Hi Ca) tumor had markedly decreased body weights. The CAC-8 (Hi Ca) tumor-bearing mice had severe hypercalcemia (mean = 13.4 mg/dl) and increased plasma concentrations of PTHrP (30.4 pM), whereas the CAC-8 (Lo Ca) tumor-bearing mice had a mean serum calcium concentration of 10.1 mg/dl and mildly increased PTHrP concentrations (5.7 pM) as compared with control mice (9.0 mg/dl and 1.0 pM, respectively). The original tumor (CAC-8 [Hi Ca]) is a well-differentiated adenocarcinoma, whereas the variant tumor (CAC-8 [Lo Ca]) is a solid carcinoma with both polygonal and spindle-shaped cells. The CAC-8 (Lo Ca) tumor had decreased PTHrP mRNA expression and protein synthesis. Messenger RNA expression of TGF beta, TNF alpha, IL-1, and IL-6 was similar in both tumors and was consistent with the central role of PTHrP in the induction of hypercalcemia in this animal model.

Immunohistochemical localization of chromogranin A in endocrine tissues and endocrine tumors of dogs

Chromogranin A is present in the secretory granules of endocrine cells and functions in hormone packaging, secretory granule stabilization, and regulation of hormone secretion. Immunohistochemical identification of chromogranin A can facilitate diagnosis of endocrine neoplasia. Normal and neoplastic canine tissues were stained immunohistochemically for chromogranin A. Staining of normal endocrine tissues demonstrated chromogranin A in chromaffin cells of the adrenal medulla, C cells of the thyroid gland, and pancreatic islets. The parathyroid chief cells and anterior pituitary stained lightly positive for chromogranin A. Pheochromocytomas (7/7), chemodectomas (5/7), islet cell carcinomas (2/6), pituitary adenomas (4/6), parathyroid adenomas (3/7), and a C-cell carcinoma (1/1) stained positive for chromogranin A. The data indicate that chromogranin A is widely distributed in canine endocrine tissues, and immunohistochemical staining of chromogranin A can be used to confirm the presence of secretory granules in endocrine tumors.

Stromal and epithelial cells of the canine prostate express parathyroid hormone-related protein, but not the PTH/PTHrP receptor

BACKGROUND

Parathyroid hormone-related protein (PTHrP), a principal factor in the pathogenesis of humoral hypercalcemia of malignancy, is also widely expressed in many normal tissues, including human prostatic epithelial cells. The role of PTHrP in the prostate is not known, but may include regulation of cell growth and differentiation or calcium secretion into prostatic fluid. The dog is a valuable animal model for human prostatic diseases. The objective was to investigate the expression of PTHrP and the PTH/PTHrP (type 1) receptor in primary cultures of canine stromal and epithelial prostatic cells.

METHODS

Expression and secretion of PTHrP and the PTH/PTHrP receptor was measured in homogeneous primary cultures of canine prostatic stromal and epithelial cells using immunohistochemistry, Northern blots, radioimmunoassay, RT-PCR, and receptor stimulation assays.

RESULTS

Epithelial and stromal cells expressed and secreted abundant PTHrP, but PTH/PTHrP receptor expression was not detected in either cell type.

CONCLUSIONS

PTHrP expression by stromal and epithelial prostatic cells and the absence of the PTH/PTHrP (type I) receptor suggest that some functions previously proposed for PTHrP in the prostate are unlikely. The separation procedure presented is a valuable tool for studying the role and regulation of PTHrP in the prostate.

Effect of transforming growth factor-beta1 on parathyroid hormone-related protein secretion and mRNA expression by normal human keratinocytes in vitro

Parathyroid hormone-related protein (PTHrP) is produced by a wide range of neoplastic and normal cells, including keratinocytes where it may regulate growth and differentiation. Transforming growth factor-beta (TGF-beta) is a growth factor produced by many cells, including keratinocytes where it regulates epidermal homeostasis. TGF-beta has been reported to be cosecreted with PTHrP in some neoplasms and to stimulate PTHrP production by neoplastic keratinocytes. However, the effects of TGF-beta on PTHrP production by normal keratinocytes are not well characterized. In this study, we investigated the effects of endogenous and exogenous TGF-beta on PTHrP production by normal human foreskin keratinocytes. PTHrP secretion, mRNA expression, and mRNA transcription in vitro were determined by N-terminal radioimmunoassay, ribonuclease protection assay, and transient transfections. PTHrP production and secretion of latent TGF-beta activity were greatest in proliferating keratinocytes prior to and at confluence of monolayer cultures. TGF-beta1 increased PTHrP mRNA expression by normal keratinocytes in a dose-dependent manner with maximal stimulation at 6-1 2 h after treatment. In addition, keratinocytes treated with a monoclonal anti-TGF-beta antibody expressed decreased levels of PTHrP mRNA. The increased levels of PTHrP mRNA following TGF-beta1 treatment were owing, at least partly, to an increase in PTHrP mRNA stability. TGF-beta1 failed to activate transcription of the luciferase reporter gene driven by either the human or mouse PTHrP promoters. In conclusion, TGF-beta1 functions as a paracrine or autocrine regulator of PTHrP production in normal human keratinocytes, and this may play a role in the regulation of keratinocyte proliferation or differentiation.

Parathyroid hormone-related protein expression and secretion in a skin organotypic culture system

Parathyroid hormone-related protein (PTHrP), an important factor in the pathogenesis of humoral hypercalcemia of malignancy, is produced by many normal tissues, including the epidermis, where it is thought to play a role in the regulation of keratinocyte growth and differentiation. Most in vitro studies of normal keratinocytes use monolayer cell cultures, which have limitations, including the inability to reproduce the stratified structure of the epidermis. The objective of this study was to investigate PTHrP production and secretion, and mRNA expression in skin organotypic cultures. The cultures consisted of an artificial dermis with differentiating keratinocytes grown at the air-liquid interface. Immunohistochemical assessment of cytokeratins 14 and 10/13, involucrin, and proliferative cell nuclear antigen (PCNA) demonstrated that keratinocytes differentiated in a manner similar to keratinocytes in normal epidermis. PTHrP expression was demonstrated in all viable layers of the epidermis, as well as in some fibroblasts of the collagen lattice by immunohistochemistry and in situ hybridization. Since most fibroblasts expressed alpha-smooth muscle actin, these cells were interpreted to be consistent with myofibroblasts. PTHrP expression by myofibroblasts suggests a possible role for PTHrP in the regulation of contractibility of these cells. PTHrP was also detected in conditioned media for 50 days. In conclusion, because of its superior tissue morphology and ability to induce organized keratinocyte differentiation, this culture system will be an excellent model to study the role of PTHrP in pathologic and physiologic processes involving the epidermis in vitro.

Cloning of bovine parathyroid hormone-related protein (PTHrP) cDNA and expression of PTHrP mRNA in the bovine mammary gland

Parathyroid hormone-related protein (PTHrP) produced by the mammary gland has been postulated to have multiple functions in both the mother and neonate. In humans, alternative 3'-mRNA splicing and endoproteolytic processing result in multiple bioactive PTHrP peptides. Multiple PTHrP peptides also have been reported in bovine milk. To investigate the source of molecular heterogeneity of PTHrP in bovine milk, bovine PTHrP was cloned from a bovine brain cDNA library, sequenced and used to characterize the mammary PTHrP transcript. A 1065 bp clone (bP1) for bovine PTHrP was isolated from a brain cDNA library. The bP1 clone contained the entire coding sequence of PTHrP and 61 and 473 nucleotides of the 5'- and 3'-untranslated regions (UTRs) respectively. The predicted amino acid sequence of bovine PTHrP was 72-92% homologous to the sequences of chicken, rat, mouse, human, and canine PTHrP with the highest sequence divergence present in the C-terminal region of the peptide. The 5'- and 3'-UTRs of bovine brain PTHrP have a high degree of homology to exons 4 and 9 of human PTHrP respectively. PTHrP was expressed as a single 1200 nucleotide mRNA transcript in lactating bovine mammary tissue. RT-PCR using region-specific oligonucleotide primers derived from bP1 demonstrated that PTHrP mRNA transcripts in bovine brain and lactating mammary gland utilize the same 5'- and 3'-UTRs. Expression of PTHrP mRNA was localized to secretory and ductular epithelial cells within the lactating mammary gland, as detected using in situ hybridization. Expression of PTHrP mRNA was demonstrated in the mammary gland during late pregnancy and throughout lactation in cows.

Influence of extracellular matrix macromolecules on normal human keratinocyte phenotype and parathyroid hormone-related protein secretion and expression in vitro

Parathyroid hormone-related protein (PTHrP) is produced by a wide range of neoplastic and normal cells, including keratinocytes where it may be involved in the regulation of cellular growth and differentiation. There is evidence that the nature of the extracellular matrix (ECM) influences gene expression and cell phenotype. The objective of this study was to investigate the phenotype of normal human keratinocytes grown on different types of ECM (basement membrane components or collagen type I), as well as the expression and secretion of PTHrP. Normal keratinocytes grown on basement membrane extract (Matrigel) actively reorganized the matrix and formed networks of cells with traction of the matrix. This was associated with linear arrays of intracellular microtubules and formation of prominent actin stress fibers and was suppressed by treatment with colchicine or cytochalasin B, confirming the role of the cytoskeleton in this process. In addition, growth on Matrigel was associated with increased PTHrP nuclear translocation, secretion, and mRNA expression compared to growth on collagen where keratinocytes exhibited decreased proliferation and increased differentiation. PTHrP, as a paracrine keratinocyte factor, did not appear to mediate the morphologic changes, since they were not altered by treatment with neutralizing anti-PTHrP antibodies. It was concluded that different types of ECM influenced the morphologic, functional, and proliferative characteristics of keratinocytes, as well as the level of PTHrP expression and secretion in vitro.

Proto-oncogene c-fos is transcriptionally regulated by parathyroid hormone (PTH) and PTH-related protein in a cyclic adenosine monophosphate-dependent manner in osteoblastic cells

PTH and PTH-related protein (PTHrP) bind to the PTH-1 (PTH/PTHrP) receptor and produce anabolic and catabolic effects in bone. To investigate postreceptor mechanisms of action, MC3T3-E1 cells were induced to differentiate to optimize PTH-1 receptor expression, and differentiated MC3T3-E1 cells were treated with varying doses of PTH (1-34) for 1 h. Northern blot analysis revealed a dose-dependent stimulation of steady state c-fos messenger RNA (mRNA), with measurable expression at doses as low as 1 pM PTH. The time course of c-fos mRNA induction was rapid, with peak levels detected at 30-45 min. Increased steady state c-fos mRNA was due to increased transcription of the c-fos gene as demonstrated by nuclear run-on assays and was dependent on the temporal differentiation state of the MC3T3-E1 cells. Stimulation of c-fos mRNA was induced exclusively by N-terminal PTH and PTHrP (which is also responsible for cAMP activation), and did not occur with PTH (7-34), (53-84), or PTHrP (107-139). The effects of PTH (1-34) on c-fos stimulation were dependent on intracellular cAMP. Forskolin [a guanine-nucleotide-binding protein (G(alpha)) agonist] stimulated c-fos mRNA, whereas 9-(tetrahydro-2-furyl) adenine (THFA) (a cAMP antagonist), 1,9 dideoxyforskolin (a cAMP independent analog of forskolin), and phorbol 12-myristate 13-acetate (a protein kinase C activator) did not. Furthermore, THFA inhibited the ability of PTH (1-34) to stimulate c-fos mRNA in a time-dependent manner. These findings indicate that c-fos is transcriptionally regulated by PTH (1-34) in osteoblastic cells, and that cAMP is a mediator of PTH-stimulated c-fos induction. Several known bone-associated proteins contain DNA binding sites in their promoter regions that recognize c-fos in conjunction with c-jun (AP-1 sites). Consequently, the induction of c-fos by PTH (1-34) in osteoblastic cells may be a sensitive indicator of PTH effects in vitro and in vivo, and provide valuable information regarding mechanisms of PTH action in bone.

Immunohistochemical localization of parathyroid hormone-related protein in canine mammary tumors

Parathyroid hormone-related protein (PTHrP) was localized immunohistochemically in 58 canine mammary tumors (31 malignant, 27 benign) and adjacent normal or hyperplastic mammary tissue. PTHrP immunoreactivity was significantly enhanced by pretreatment with microwave heating in normal and neoplastic tissues. Epithelial cells of hyperplastic and neoplastic mammary tissues, myoepithelial cells, and metaplastic osteoblasts in mammary tumors stained moderately to strongly positive for PTHrP No significant difference between staining intensity for PTHrP and histologic pattern of mammary tumors was found. The presence of PTHrP in normal and neoplastic canine mammary tissues supports a pathophysiological role for PTHrP as a paracrine or autocrine hormone in the mammary gland.

Detection of interleukin-1 and interleukin-6 on cryopreserved bovine mammary epithelial cells in vitro

This investigation was performed to determine whether primary cultures of mammary cells from lactating cows would sustain production of interleukin (IL)-1, IL-6, and tumor necrosis factor (TNF), and express mRNA for cytokines interleukin (IL)-1alpha, IL-1beta, IL-2, IL-4, IL-6, IL-10, interferon (INF)-tau, TNF-alpha, and granulocyte-macrophage colony-stimulating factor (GM-CSF) by the reverse transcription-polymerase chain reaction (RT-PCR) in vitro. Cryopreserved mammary epithelial cells collected from cows at 1 week post calving were plated in collagen-coated 24-well culture plates (250,000 cells/well). IL-1 and IL-6 productions were measured using a A375 cell growth inhibition assay and a 7TD1 hybridoma proliferation assay, respectively. Production of IL-1 was demonstrated in mammary epithelial cells cultured with unsupplemented medium, but was not produced by cells cultured in medium supplemented with fetal bovine serum. IL-6 production in the conditioned medium was continued at steady level until day 14, whereas IL-6-like bioactivity was not detected in medium alone. TNF-like activity was not detectable in any experiments. This study also demonstrated the expression of mRNA for multiple cytokines including IL-1alpha, IL-1beta, IL-6, IL-10, TNF-alpha, and GM-CSF by RT-PCR in mammary cell cultures. The results indicate that bovine mammary epithelial cells of lactating cows produce IL-1 and IL-6 and have gene expression for multiple cytokines. This in vitro model will be useful to investigate the function and regulation of IL-1 and IL-6 in the lactating mammary gland.