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.

Effects of transforming growth factor-beta on parathyroid hormone-related protein production and ribonucleic acid expression by a squamous carcinoma cell line in vitro

The effects of human recombinant transforming growth factor (TGF)-beta 1 were determined on PTH-related protein (PTHrP) production and messenger RNA (mRNA) expression by a canine squamous carcinoma cell line (SCC 2/88) in vitro. TGF-beta increased PTHrP production in a dose- and time-dependent manner (P < 0.05) as measured by RIA, and the effects of TGF-beta treatment persisted up to 72 h after removal. TGF-beta increased PTHrP production by SCC 2/88 cells until cellular confluence, at which time there was no longer a significant increase compared to control. Actinomycin D inhibited the TGF-beta-mediated increase in PTHrP production, suggesting that TGF-beta acted in part by increasing gene transcription. SCC 2/88 cells also produced active TGF-beta as measured by a [3H]thymidine incorporation assay in mink lung epithelial cells. Exposure of SCC 2/88 cells to a neutralizing anti-TGF-beta monoclonal antibody decreased (up to 50%, P < 0.01) basal PTHrP production. TGF-beta increased PTHrP mRNA expression in a dose- and time-dependent manner as evaluated by northern blot analysis. Postconfluent SCC 2/88 cells expressed little mRNA for PTHrP, and there was only a minimal increase in PTHrP mRNA expression in postconfluent TGF-beta-treated cells. These results indicate that TGF-beta increased PTHrP production and mRNA expression in malignant keratinocytes and suggest that TGF-beta may be an important factor in the pathogenesis of humoral hypercalcemia of malignancy.

Transforming growth factor-beta1 regulates steady-state PTH/PTHrP receptor mRNA levels and PTHrP binding in ROS 17/2.8 osteosarcoma cells

The effect of transforming growth factor beta1 (TGF-beta1) on the expression of mRNA for the parathyroid hormone receptor and binding of iodinated parathyroid hormone-related protein in ROS 17/2.8 osteosarcoma cells was evaluated. TGF-beta1 stimulated a 2-7-fold increase in steady state mRNA levels for the parathyroid hormone receptor at a maximal dose of 5 ng/ml, with increased levels of expression at 6 h of TGF-beta1-incubation, and peak levels at 8-24 h. Receptor binding studies revealed a significant increase in PTHrP-specific binding with TGF-beta1 doses as low as 0.5 ng/ml and a 55% increase in numbers of receptors with no alteration in binding affinity with 5.0 ng/ml TGF-beta1. Time course studies indicated that receptor binding was increased at 24 h with peak levels reached at 48 h of treatment. PTH-stimulated cAMP levels were significantly increased in ROS 17/2.8 cells treated with TGF-beta1 (0.5 ng/ml) for 48 h. These data indicate that TGF-beta1 upregulates steady-state mRNA, ligand binding and PTH/PTHrP receptor signaling in rat osteosarcoma cells. The effects of TGF-beta1 on bone may be attributed in part to regulation of the PTH/PTHrP receptor at the molecular level.

Parathyroid hormone-related protein in normal and neoplastic canine tissues: immunohistochemical localization and biochemical extraction

Two polyclonal antibodies, directed against N-terminal amino acids (1-36) or the midregion (amino acids 34-53) of parathyroid hormone-related protein (PTHrP), were used to localize PTHrP in a variety of normal and neoplastic canine tissues. Parathyroid hormone (PTH) immunoreactivity was demonstrated using anti-bovine PTH (amino acids 14-34). The following tissues (among others) stained strongly positive for PTHrP: all layers of epidermal keratinocytes, with the most intense staining of the basal layer; hair follicle keratinocytes; myoepithelial cells of dermal apocrine glands, mammary glands, and apocrine glands of the anal sac; anal sac epithelium; mammary duct epithelium; and thyroid C cells. Adenocarcinomas of the anal sac stained moderately positive (5/22 dogs), weakly positive (11/22 dogs), or did not stain (6/22 dogs). Most parathyroid gland adenomas stained moderately (2/6 dogs) or weakly positive (3/6 dogs) for PTHrP. Squamous cell carcinomas (6/6 dogs) stained strongly positive. Lymphomas stained weakly positive (2/10 dogs) or did not stain (8/10 dogs). There was no consistent relationship between the staining intensity of the tumors and serum calcium concentrations of the dogs. The anti-PTH antibodies stained only parathyroid chief cells strongly positive. Concentrations of PTHrP were measured by radioimmunoassay in protein extracts from an adenocarcinoma derived from the apocrine glands of the anal sac, pancreas, kidney, liver, heart, thyroid, adrenal, and parathyroid glands. PTHrP concentrations varied from undetectable up to 150 pg/mg in normal tissues as compared with 2,000 pg/mg in apocrine adenocarcinoma of the anal sac.(ABSTRACT TRUNCATED AT 250 WORDS)

Parathyroid hormone-related protein production by normal human keratinocytes in vitro

The role of parathyroid hormone-related protein (PTHrP) and its regulation in normal epidermal physiology is not currently known. Recent evidence suggests that PTHrP production may be related to the degree of differentiation of keratinocytes in vitro. This investigation characterized the production of PTHrP by normal human foreskin keratinocytes (NHFK) during both spontaneously occurring and induced differentiation in vitro. PTHrP production in keratinocyte serum-free conditioned medium was determined using an N-terminal radioimmunoassay for human PTHrP (1-36). Agents known to stimulate (calcium, 1,25-dihydroxyvitamin D3) or inhibit (transforming growth factor-beta) keratinocyte differentiation were examined for their ability to alter production of PTHrP. Measurements of cell number and involucrin content of the cultures were made to confirm the effects of these agents on keratinocyte growth and differentiation. The production of PTHrP in control cultures (under low calcium conditions, 0.08 mM) was decreased and involucrin content increased (P < 0.01) after the cells became confluent. The addition of 1 mM calcium to keratinocyte medium increased cell number and involucrin content of the cultures (P < 0.05) but inhibited production of PTHrP (P < 0.01). The 1,25-dihydroxyvitamin D3 (10 nM) had no significant effect on cell number or PTHrP production, but increased involucrin content (P < 0.05). Transforming growth factor-beta (5 ng/ml) decreased both cell number (P < 0.05) and involucrin content (P < 0.01), but significantly stimulated PTHrP production (P < 0.01). These data indicate that the production of PTHrP by NHFK is inhibited with the onset of both spontaneously occurring and calcium-induced differentiation in vitro, while transforming growth factor-beta inhibited differentiation and upregulated PTHrP production in normal human keratinocytes.

Regulation of parathyroid hormone-related protein production by a squamous carcinoma cell line in vitro

BACKGROUND

Humoral hypercalcemia of malignancy is a paraneoplastic syndrome associated with a variety of solid neoplasms including squamous cell carcinomas of various sites. Parathyroid hormone-related protein (PTHrP) is a newly recognized hormone that has been implicated as one of the major causative factors in the pathogenesis of this syndrome. A canine oral squamous carcinoma cell line (SCC 2/88) was used to investigate the regulation of production of PTHrP in response to agents that alter keratinocyte differentiation/proliferation in vitro.

EXPERIMENTAL DESIGN

SCC 2/88 cells grown in serum-free media were exposed to various factors and PTHrP production was measured by radioimmunoassay. This cell line spontaneously produced substantial amounts of PTHrP (up to 7,000 pg/ml) without the need for a fibroblast-feeder layer. Production of PTHrP decreased at cellular confluence, and with increasing passage number.

RESULTS

Epidermal growth factor, cholera toxin, calcium, 1,25-dihydroxyvitamin D, ionomycin, trans-retinoic acid, transforming growth factor-beta 1 and hydrocortisone stimulated production of PTHrP by SCC 2/88 cells to various degrees. Transforming growth factor-beta 1 was the most potent stimulator of PTHrP production, with a maximal stimulation of 25-fold over control. Monensin decreased PTHrP secretion as early as 6 hours post-treatment and by 48 hours, there was no detectable PTHrP in the conditioned cell culture medium. Calcium, cholera toxin, ionomycin, and transforming growth factor-beta 1 decreased keratinocyte proliferation as measured by cell counts at all doses tested.

CONCLUSIONS

The results of this study revealed that SCC 2/88 cells spontaneously produced substantial amounts of PTHrP under baseline conditions and that compounds known to affect keratinocyte differentiation/proliferation up-regulated production of PTHrP. These cells will be valuable to investigate the molecular regulation of PTHrP production by squamous cell carcinomas.

Studies on chicken polyclonal anti-peptide antibodies specific for parathyroid hormone-related protein (1-36)

Chicken polyclonal antibodies were prepared against a synthetic peptide corresponding to the first 36 N-terminal amino acids of parathyroid hormone-related protein (PTHrP) by immunizing laying hens. Significant increases of antibodies to PTHrP were first detected after the second immunization. Production of anti-PTHrP egg yolk antibodies peaked 1-2 weeks after the second through sixth immunizations and declined over a period of 2-4 weeks. Polyclonal IgG (IgY) to PTHrP was purified from the egg yolks with high levels of PTHrP specific binding. The anti-PTHrP IgG was used to develop a radioimmunoassay for PTHrP that was able to detect 100 pg PTHrP ml-1 (23 pM) in conditioned cell culture medium. The anti-PTHrP IgG was bound to a solid phase and utilized to immunopurify iodinated [Tyr36]-PTHrP (1-36). Anti-PTHrP IgG inhibited the in vitro biologic activity of PTHrP as demonstrated by the inhibition of adenylate cyclase stimulation in a rat osteoblast-like cell line (ROS 17/2.8). The anti PTHrP IgG was immunopurified and utilized for immunohistochemical localization of PTHrP in canine skin. Chickens were advantageous in producing large amounts of high affinity, neutralizing antibodies to a highly conserved mammalian protein such as PTHrP. The antibodies will be useful to investigate the function and metabolism of PTHrP in vivo and in vitro.