Transient exposure to PTHrP (107-139) exerts anabolic effects through vascular endothelial growth factor receptor 2 in human osteoblastic cells in vitro

Osteostatin, a peptide for the future treatment of musculoskeletal diseases

Nowadays, the treatment of musculoskeletal diseases represents a major challenge in the developed world. Diseases such as osteoporosis, osteoarthritis and arthritis have a high incidence and prevalence as a consequence of population aging, and they are also associated with a socioeconomic burden. Many efforts have been made to find a treatment for these diseases with various levels of success, but new approaches are still needed to deal with these pathologies. In this context, one peptide derived for the C-terminal extreme of the Parathormone related Peptide (PTHrP) called Osteostatin can be useful to treat musculoskeletal diseases. This pentapeptide (TRSAW) has demonstrated both in different in vitro and in vivo models, its role as a molecule with anti-resorptive, anabolic, anti-inflammatory, and anti-antioxidant properties. Our aim with this work is to review the Osteostatin main features, the knowledge of its mechanisms of action as well as its possible use for the treatment of osteoporosis, bone regeneration and fractures and against arthritis given its anti-inflammatory properties.

Osteogenic Potential of a Biomaterial Enriched with Osteostatin and Mesenchymal Stem Cells in Osteoporotic Rabbits

Mesoporous bioactive glasses (MBGs) of the SiO2-CaO-P2O5 system are biocompatible materials with a quick and effective in vitro and in vivo bioactive response. MBGs can be enhanced by including therapeutically active ions in their composition, by hosting osteogenic molecules within their mesopores, or by decorating their surfaces with mesenchymal stem cells (MSCs). In previous studies, our group showed that MBGs, ZnO-enriched and loaded with the osteogenic peptide osteostatin (OST), and MSCs exhibited osteogenic features under in vitro conditions. The aim of the present study was to evaluate bone repair capability after large bone defect treatment in distal femur osteoporotic rabbits using MBGs (76%SiO2-15%CaO-5%P2O5-4%ZnO (mol-%)) before and after loading with OST and MSCs from a donor rabbit. MSCs presence and/or OST in scaffolds significantly improved bone repair capacity at 6 and 12 weeks, as confirmed by variations observed in trabecular and cortical bone parameters obtained by micro-CT as well as histological analysis results. A greater effect was observed when OST and MSCs were combined. These findings may indicate the great potential for treating critical bone defects by combining MBGs with MSCs and osteogenic peptides such as OST, with good prospects for translation to clinical practice.

Re-Evaluating the Role of PTHrP in Breast Cancer

Parathyroid-hormone-related protein (PTHrP) is a protein with a long history of association with bone metastatic cancers. The paracrine signaling of PTHrP through the parathyroid hormone receptor (PTHR1) facilitates tumor-induced bone destruction, and PTHrP is known as the primary driver of humoral hypercalcemia of malignancy. In addition to paracrine signaling, PTHrP is capable of intracrine signaling independent of PTHR1 binding, which is essential for cytokine-like functions in normal physiological conditions in a variety of tissue types. Pre-clinical and clinical studies evaluating the role of PTHrP in breast cancer have yielded contradictory conclusions, in some cases indicating the protein is tumor suppressive, and in other studies, pro-growth. This review discusses the possible molecular basis for the disharmonious prognostic indications of these studies and highlights the implications of the paracrine, intracrine, and nuclear functions of the protein. This review also examines the current understanding of the functional domains of PTHrP and re-evaluates their role in the unique context of the breast cancer environment. This review will expand on the current understanding of PTHrP by attempting to reconcile the functional domains of the protein with its intracrine signaling in cancer.

Activation of PGRN/MAPK axis stimulated by the hypoxia-conditioned mesenchymal stem cell-derived HIF-1α facilitates osteosarcoma progression

BACKGROUND

Progranulin (PGRN) is an important survival factor in the progression of multiple cancers.

PURPOSE

To explore the effects and mechanisms of PGRN on malignant biological behavior of osteosarcoma (OS) cells and the effects of mesenchymal stem cells (MSCs) and the hypoxic microenvironment on PGRN alteration.

MATERIAL AND METHODS

The expression pattern of PGRN in OS were evaluated in OS tissues and cell lines. Next, a loss-of-function assay investigated the function of PGRN on the proliferation, migration and cell death of OS cells. The activation of MAPK signaling in the process was examined by western blot and functional experiments accompanied by skatole. Additionally, we internally silenced hypoxia-inducible factor-1α (HIF-1α) in MSCs along with exogenously added HIF-1α (exo-HIF-1α) to explore how MSCs affect PGRN alteration and the malignant behavior of OS cells.

RESULTS

An aberrantly high expression of PGRN was observed in OS and associated with the poor prognosis of OS patients. PGRN knockdown repressed the proliferation, migration and induced cell death of OS cells, and activating MAPK pathway reversed these effects. Further evidence showed that MSCs regulated PGRN to mediate the malignant biological behavior of OS cells. Hypoxia enhanced HIF-1α expression in MSCs. HIF-1α silencing in MSCs under hypoxia suppressed the oncogenic effects of MSCs and reduced PGRN expression in OS cells, while the treatment of exo-HIF-1α reversed the depressive effects of HIF1α silencing on OS progression.

CONCLUSION

Overall, we concluded that PGRN, which was activated by the increase of hypoxic-MSCs-derived HIF-1α, promoted OS progression through the activation of MAPK signaling.

Physiological and Pharmacological Roles of PTH and PTHrP in Bone Using Their Shared Receptor, PTH1R

Parathyroid hormone (PTH) and the paracrine factor, PTH-related protein (PTHrP), have preserved in evolution sufficient identities in their amino-terminal domains to share equivalent actions upon a common G protein-coupled receptor, PTH1R, that predominantly uses the cyclic adenosine monophosphate-protein kinase A signaling pathway. Such a relationship between a hormone and local factor poses questions about how their common receptor mediates pharmacological and physiological actions of the two. Mouse genetic studies show that PTHrP is essential for endochondral bone lengthening in the fetus and is essential for bone remodeling. In contrast, the main postnatal function of PTH is hormonal control of calcium homeostasis, with no evidence that PTHrP contributes. Pharmacologically, amino-terminal PTH and PTHrP peptides (teriparatide and abaloparatide) promote bone formation when administered by intermittent (daily) injection. This anabolic effect is remodeling-based with a lesser contribution from modeling. The apparent lesser potency of PTHrP than PTH peptides as skeletal anabolic agents could be explained by lesser bioavailability to PTH1R. By contrast, prolongation of PTH1R stimulation by excessive dosing or infusion, converts the response to a predominantly resorptive one by stimulating osteoclast formation. Physiologically, locally generated PTHrP is better equipped than the circulating hormone to regulate bone remodeling, which occurs asynchronously at widely distributed sites throughout the skeleton where it is needed to replace old or damaged bone. While it remains possible that PTH, circulating within a narrow concentration range, could contribute in some way to remodeling and modeling, its main physiological role is in regulating calcium homeostasis.

ZnO-mesoporous glass scaffolds loaded with osteostatin and mesenchymal cells improve bone healing in a rabbit bone defect

The use of 3D scaffolds based on mesoporous bioactive glasses (MBG) enhanced with therapeutic ions, biomolecules and cells is emerging as a strategy to improve bone healing. In this paper, the osteogenic capability of ZnO-enriched MBG scaffolds loaded or not with osteostatin (OST) and human mesenchymal stem cells (MSC) was evaluated after implantation in New Zealand rabbits. Cylindrical meso-macroporous scaffolds with composition (mol %) 82.2SiO₂-10.3CaO-3.3P₂O₅-4.2ZnO (4ZN) were obtained by rapid prototyping and then, coated with gelatin for easy handling and potentiating the release of inorganic ions and OST. Bone defects (7.5 mm diameter, 12 mm depth) were drilled in the distal femoral epiphysis and filled with 4ZN, 4ZN + MSC, 4ZN + OST or 4ZN + MSC + OST materials to evaluate and compare their osteogenic features. Rabbits were sacrificed at 3 months extracting the distal third of bone specimens for necropsy, histological, and microtomography (µCT) evaluations. Systems investigated exhibited bone regeneration capability. Thus, trabecular bone volume density (BV/TV) values obtained from µCT showed that the good bone healing capability of 4ZN was significantly improved by the scaffolds coated with OST and MSC. Our findings in vivo suggest the interest of these MBG complete systems to improve bone repair in the clinical practice.

A Potential Role of RUNX2- RUNT Domain in Modulating the Expression of Genes Involved in Bone Metastases: An In Vitro Study with Melanoma Cells

Ectopic expression of RUNX2 has been reported in several tumors. In melanoma cells, the RUNT domain of RUNX2 increases cell proliferation and migration. Due to the strong link between RUNX2 and skeletal development, we hypothesized that the RUNT domain may be involved in the modulation of mechanisms associated with melanoma bone metastasis. Therefore, we evaluated the expression of metastatic targets in wild type (WT) and RUNT KO melanoma cells by array and real-time PCR analyses. Western blot, ELISA, immunofluorescence, migration and invasion ability assays were also performed. Our findings showed that the expression levels of bone sialoprotein (BSP) and osteopontin (SPP1) genes, which are involved in malignancy-induced hypercalcemia, were reduced in RUNT KO cells. In addition, released PTHrP levels were lower in RUNT KO cells than in WT cells. The RUNT domain also contributes to increased osteotropism and bone invasion in melanoma cells. Importantly, we found that the ERK/p-ERK and AKT/p-AKT pathways are involved in RUNT-promoted bone metastases. On the basis of our findings, we concluded that the RUNX2 RUNT domain is involved in the mechanisms promoting bone metastasis of melanoma cells via complex interactions between multiple players involved in bone remodeling.

Osteostatin Inhibits Collagen-Induced Arthritis by Regulation of Immune Activation, Pro-Inflammatory Cytokines, and Osteoclastogenesis

In chronic inflammatory joint diseases, such as rheumatoid arthritis, there is an important bone loss. Parathyroid hormone-related protein (PTHrP) and related peptides have shown osteoinductive properties in bone regeneration models, but there are no data on inflammatory joint destruction. We have investigated whether the PTHrP (107-111) C-terminal peptide (osteostatin) could control the development of collagen-induced arthritis in mice. Administration of osteostatin (80 or 120 μg/kg s.c.) after the onset of disease decreased the severity of arthritis as well as cartilage and bone degradation. This peptide reduced serum IgG2a levels as well as T cell activation, with the downregulation of RORγt+CD4+ T cells and upregulation of FoxP3+CD8+ T cells in lymph nodes. The levels of key cytokines, such as interleukin(IL)-1β, IL-2, IL-6, IL-17, and tumor necrosis factor-α in mice paws were decreased by osteostatin treatment, whereas IL-10 was enhanced. Bone protection was related to reductions in receptor activator of nuclear factor-κB ligand, Dickkopf-related protein 1, and joint osteoclast area. Osteostatin improves arthritis and controls bone loss by inhibiting immune activation, pro-inflammatory cytokines, and osteoclastogenesis. Our results support the interest of osteostatin for the treatment of inflammatory joint conditions.

PTHrP treatment of colon cancer cells promotes tumor associated-angiogenesis by the effect of VEGF

We showed that Parathyroid Hormone-related Peptide (PTHrP) induces proliferation, migration, survival and chemoresistance via MAPKs and PI3K/AKT pathways in colorectal cancer (CRC) cells. The objective of this study was to investigate if PTHrP is also involved in tumor angiogenesis. PTHrP increased VEGF expression and the number of structures with characteristics of neoformed vessels in xenografts tumor. Also, PTHrP increased mRNA levels of VEGF, HIF-1α and MMP-9 via ERK1/2 and PI3K/Akt pathways in Caco-2 and HCT116 cells. Tumor conditioned media (TCMs) from both cell lines treated with PTHrP increases the number of cells, the migration and the tube formation in the endothelial HMEC-1 cells, whereas the neutralizing antibody against VEGF diminished this response. In contrast, PTHrP by direct treatment only increased ERK1/2 phosphorylation and the HMEC-1 cells number. These results provide the first evidence related to the mode of action of PTHrP that leads to its proangiogenic effects in the CRC.

PTH1R signalling regulates the mechanotransduction process of cementoblasts under cyclic tensile stress

Objective

To investigate the regulatory role of type I parathyroid hormone receptor (PTH1R) signalling in the mechanotransduction process of cementoblasts under cyclic tensile stress (CTS).

Materials and methods

Immortalized cementoblast cell line OCCM-30 were employed and subjected to cyclic tensile strain applied by a four-point bending system. The expression of PTHrP and PTH1R, as well as cementoblastic transcription factor Runx-2, Osterix, and extracellular matrix protein COL-1 and OPN were assessed by quantitative real-time polymerase chain reaction and western blot analysis. PTH1R expression was knocked down by siPTH1R transfection, and the alteration of cementoblastic biomarkers expression was examined to evaluate the function of PTH1R. Furthermore, to investigate possible downstream molecules, expression of signal molecule ERK1/2 with or without siPTH1R transfection, and the effect of ERK inhibitor PD98059 on the expression of cementoblastic biomarkers was also examined.

Results

Cyclic tensile strain elevated the expression of PTHrP and PTH1R, as well as cementoblastic biomarkers Runx-2, Osterix, COL-1, and OPN in a time-dependent manner, which was inhibited by siPTH1R transfection. The expression of phosphorylated ERK1/2 was upregulated time-dependently under cyclic stretch, which was also inhibited by siPTH1R transfection, and pretreatment of p-ERK1/2 inhibitor PD98059 undermined the increase of Runx-2, Osterix, COL-1, and OPN prominently.

Conclusion

The findings of the present study indicate that PTH1R signalling plays a regulatory role in the CTS induced cementoblastic differentiation in mature cementoblasts, and ERK1/2 is essentially involved as a downstream intracellular signal molecule in this mechanotransduction process.

Microvesicles derived from human bone marrow mesenchymal stem cells promote U2OS cell growth under hypoxia: the role of PI3K/AKT and HIF-1α

Studies have demonstrated that mesenchymal stem cells (MSCs) can promote tumor growth, and MSC microvesicles (MVs) are very important in the tumor microenvironment and information transfer between cells during tumorigenesis and development. However, the potential effects and mechanisms of MSC-MVs on tumor growth are still controversial. Here in this study, we investigated the roles and effects of human bone marrow MSC-MVs (hBMSC-MVs) on human osteosarcoma (U2OS) cell growth under hypoxia in vitro and in vivo. BMSC-MVs were harvested and purified by ultracentrifugation. U2OS cells were treated with different concentrations of hBMSC-MVs under hypoxia. Cell viability and migration was measured by MTT test, transwell invasion assay and scratch migration assay. The expression of the signaling molecules of AKT, VEGF, GLUT1 and Bax, cleaved-caspase3 in U2OS cells cultured with MVs under hypoxia was determined by western blot. U2OS/siHIF-1α or U2OS/NC cells mixed with/without MVs were subcutaneously injected into nude mice; the tumor size and weight were detected. We found that hBMSC-MVs promoted U2OS cell proliferation and migration under hypoxia in vitro, and that was partially associated with the PI3K/AKT and HIF-1α pathways. MVs co-injected with U2OS cells promoted tumor growth in a mouse xenograft model. siHIF-1α transfection reversed these changes to some extent. The function of hBMSC-MVs on U2OS cell progression and tumor growth was associated with PI3K/AKT and HIF-1α pathway under hypoxia. These findings support a new mechanism suggesting the contribution of MSC-MVs to tumor growth.

Osteogenic Effect of ZnO-Mesoporous Glasses Loaded with Osteostatin

Mesoporous Bioactive Glasses (MBGs) are a family of bioceramics widely investigated for their putative clinical use as scaffolds for bone regeneration. Their outstanding textural properties allow for high bioactivity when compared with other bioactive materials. Moreover, their great pore volumes allow these glasses to be loaded with a wide range of biomolecules to stimulate new bone formation. In this study, an MBG with a composition, in mol%, of 80% SiO₂⁻15% CaO⁻5% P₂O₅ (Blank, BL) was compared with two analogous glasses containing 4% and 5% of ZnO (4ZN and 5ZN) before and after impregnation with osteostatin, a C-terminal peptide from a parathyroid hormone-related protein (PTHrP107-111). Zn2+ ions were included in the glass for their bone growth stimulator properties, whereas osteostatin was added for its osteogenic properties. Glasses were characterized, and their cytocompatibility investigated, in pre-osteoblastic MC3T3-E1 cell cultures. The simultaneous additions of osteostatin and Zn2+ ions provoked enhanced MC3T3-E1 cell viability and a higher differentiation capacity, compared with either raw BL or MBGs supplemented only with osteostatin or Zn2+. These in vitro results show that osteostatin enhances the osteogenic effect of Zn2+-enriched glasses, suggesting the potential of this combined approach in bone tissue engineering applications.

Parathyroid hormone-related protein exhibits antioxidant features in osteoblastic cells through its N-terminal and osteostatin domains

Objectives

Oxidative stress plays a major role in the onset and progression of involutional osteoporosis. However, classical antioxidants fail to restore osteoblast function. Interestingly, the bone anabolism of parathyroid hormone (PTH) has been shown to be associated with its ability to counteract oxidative stress in osteoblasts. The PTH counterpart in bone, which is the PTH-related protein (PTHrP), displays osteogenic actions through both its N-terminal PTH-like region and the C-terminal domain.

Methods

We examined and compared the antioxidant capacity of PTHrP (1-37) with the C-terminal PTHrP domain comprising the 107-111 epitope (osteostatin) in both murine osteoblastic MC3T3-E1 cells and primary human osteoblastic cells.

Results

We showed that both N- and C-terminal PTHrP peptides at 100 nM decreased reactive oxygen species production and forkhead box protein O activation following hydrogen peroxide (H₂O₂)-induced oxidation, which was related to decreased lipid oxidative damage and caspase-3 activation in these cells. This was associated with their ability to restore the deleterious effects of H₂O₂ on cell growth and alkaline phosphatase activity, as well as on the expression of various osteoblast differentiation genes. The addition of Rp-cyclic 3′,5′-hydrogen phosphorothioate adenosine triethylammonium salt (a cyclic 3',5'-adenosine monophosphate antagonist) and calphostin C (a protein kinase C inhibitor), or a PTH type 1 receptor antagonist, abrogated the effects of N-terminal PTHrP, whereas protein phosphatase 1 (an Src kinase activity inhibitor), SU1498 (a vascular endothelial growth factor receptor 2 inhibitor), or an anti osteostatin antiserum, inhibited the effects of C-terminal PTHrP.

Conclusion

These findings indicate that the antioxidant properties of PTHrP act through its N- and C-terminal domains and provide novel insights into the osteogenic action of PTHrP.

Cite this article: S. Portal-Núñez, J. A. Ardura, D. Lozano, I. Martínez de Toda, M. De la Fuente, G. Herrero-Beaumont, R. Largo, P. Esbrit. Parathyroid hormone-related protein exhibits antioxidant features in osteoblastic cells through its N-terminal and osteostatin domains. Bone Joint Res 2018;7:58–68. DOI: 10.1302/2046-3758.71.BJR-2016-0242.R2.

Anti-senescence and Anti-inflammatory Effects of the C-terminal Moiety of PTHrP Peptides in OA Osteoblasts

Osteoarthritis (OA) is characterized by degenerative changes in the whole joint leading to physical disability in the elderly population. This condition is associated with altered bone metabolism in subchondral areas suggesting that therapeutic strategies aimed at modifying bone cell metabolism may be of interest. We have investigated the effects of several parathyroid hormone-related protein (PTHrP)-derived peptides (1-37): (N-terminal), (107-111) and (107-139) (C-terminal) on senescence features induced by inflammatory stress in human OA osteoblasts. Incubation of these primary cells with interleukin(IL)-1β led to an increased expression of senescence markers senescence-associated-β-galactosidase activity, γH2AX foci, p16, p21, p53, and caveolin-1. PTHrP (107-111) and PTHrP (107-139) significantly reduced all these parameters. Both peptides decreased the production of IL-6 and prostaglandin E2 which was the consequence of cyclo-oxygenase-2 downregulation. PTHrP (107-139) also reduced tumor necrosis factor-α release. These anti-inflammatory effects would be related to the reduction of nuclear factor-κB activation by both peptides and activator protein-1 by PTHrP (107-139). The three PTHrP peptides favored osteoblastic function although the C-terminal domain of PTHrP was more efficient than its N-terminal domain. Our data support an anti-senescence and anti-inflammatory role for the C-terminal moiety of PTHrP with potential applications in chronic inflammatory conditions such as OA.

The Role of Parathyroid Hormone-Related Protein (PTHrP) in Osteoblast Response to Microgravity: Mechanistic Implications for Osteoporosis Development

Prolonged skeletal unloading through bedrest results in bone loss similar to that observed in elderly osteoporotic patients, but with an accelerated timeframe. This rapid effect on weight-bearing bones is also observed in astronauts who can lose up to 2% of their bone mass per month spent in Space. Despite the important implications for Spaceflight travelers and bedridden patients, the exact mechanisms involved in disuse osteoporosis have not been elucidated. Parathyroid hormone-related protein (PTHrP) regulates many physiological processes including skeletal development, and has been proposed as a mechanosensor. To investigate the role of PTHrP in microgravity-induced bone loss, trabecular and calvarial osteoblasts (TOs and COs) from Pthrp^+/+ and ^-/- mice were subjected to actual Spaceflight for 6 days (Foton M3 satellite). Pthrp^+/+, ^+/- and ^-/- osteoblasts were also exposed to simulated microgravity for periods varying from 6 days to 6 weeks. While COs displayed little change in viability in 0g, viability of all TOs rapidly decreased in inverse proportion to PTHrP expression levels. Furthermore, Pthrp^+/+ TOs displayed a sharp viability decline after 2 weeks at 0g. Microarray analysis of Pthrp^+/+ TOs after 6 days in simulated 0g revealed expression changes in genes encoding prolactins, apoptosis/survival molecules, bone metabolism and extra-cellular matrix composition proteins, chemokines, insulin-like growth factor family members and Wnt-related signalling molecules. 88% of 0g-induced expression changes in Pthrp^+/+ cells overlapped those caused by Pthrp ablation in normal gravity, and pulsatile treatment with PTHrP_1-36 not only reversed a large proportion of 0g-induced effects in Pthrp^+/+ TOs but maintained viability over 6-week exposure to microgravity. Our results confirm PTHrP efficacy as an anabolic agent to prevent microgravity-induced cell death in TOs.

Parathyroid Hormone-Related Protein, Its Regulation of Cartilage and Bone Development, and Role in Treating Bone Diseases

Although parathyroid hormone-related protein (PTHrP) was discovered as a cancer-derived hormone, it has been revealed as an important paracrine/autocrine regulator in many tissues, where its effects are context dependent. Thus its location and action in the vasculature explained decades-long observations that injection of PTH into animals rapidly lowered blood pressure by producing vasodilatation. Its roles have been specified in development and maturity in cartilage and bone as a crucial regulator of endochondral bone formation and bone remodeling, respectively. Although it shares actions with parathyroid hormone (PTH) through the use of their common receptor, PTHR1, PTHrP has other actions mediated by regions within the molecule beyond the amino-terminal sequence that resembles PTH, including the ability to promote placental transfer of calcium from mother to fetus. A striking feature of the physiology of PTHrP is that it possesses structural features that equip it to be transported in and out of the nucleus, and makes use of a specific nuclear import mechanism to do so. Evidence from mouse genetic experiments shows that PTHrP generated locally in bone is essential for normal bone remodeling. Whereas the main physiological function of PTH is the hormonal regulation of calcium metabolism, locally generated PTHrP is the important physiological mediator of bone remodeling postnatally. Thus the use of intermittent injection of PTH as an anabolic therapy for bone appears to be a pharmacological application of the physiological function of PTHrP. There is much current interest in the possibility of developing PTHrP analogs that might enhance the therapeutic anabolic effects.

Parathyroid Hormone-Related Protein Analogs as Osteoporosis Therapies

The only bone anabolic agent currently available for osteoporosis treatment is parathyroid hormone (PTH)-either its N-terminal 1-34 fragment or the whole molecule of 1-84 aminoacids-whose intermittent administration stimulates new bone formation by targeting osteoblastogenesis and osteoblast survival. PTH-related protein (PTHrP) is an abundant factor in bone which shows N-terminal homology with PTH and thus exhibits high affinity for the same PTH type 1 receptor in osteoblasts. Therefore, it is not surprising that intermittently administered N-terminal PTHrP peptides induce bone anabolism in animals and humans. Furthermore, the C-terminal region of PTHrP also elicits osteogenic features in vitro in osteoblastic cells and in various animal models of osteoporosis. In this review, we discuss the current concepts about the cellular and molecular mechanisms whereby PTHrP may induce anabolic actions in bone. Pre-clinical studies and clinical data using N-terminal PTHrP analogs are also summarized, pointing to PTHrP as a promising alternative to current bone anabolic therapies.

Investigational parathyroid hormone receptor analogs for the treatment of osteoporosis

INTRODUCTION

Intermittent parathyroid hormone (PTH) administration, acting through multiple signaling pathways, exerts an osteoanabolic effect on the skeleton that surpasses the effect of other antiosteoporotic agents. However, its efficacy is limited by the coupling effect and relatively common adverse events. Thus, the development of more sophisticated PTH receptor analogs seems imperative.

AREAS COVERED

In this review, the authors summarize the role of PTH signaling pathway in bone remodeling. The authors also summarize investigational analogs targeting this pathway, which may be potential treatments for osteoporosis.

EXPERT OPINION

β-arrestins are multifunctional cytoplasmic molecules that are decisive for regulating intracellular PTH signaling. Recently, in preclinical studies, arrestin analogs have achieved the anabolic bone effect of PTH without an accompanying increase in bone resorption. However, it is not yet known whether these analogs have adverse effects and there are no clinical data for their efficacy to date. On the other hand, several molecules derived either from PTH and PTH-related protein (PTHrP) molecules have been developed. Alternative routes of PTH 1 - 34 delivery (oral, transdermal), the PTH analog ostabolin and the N-terminal PTHrP analogs PTHrP 1 - 36 and abaloparatide, have recently been or are currently being tested in clinical trials and are more likely to become available for use in the near future.

Parathyroid hormone-related protein (107-111) improves the bone regeneration potential of gelatin-glutaraldehyde biopolymer-coated hydroxyapatite

Biopolymer-coated nanocrystalline hydroxyapatite (HA) made as macroporous foams which are degradable and flexible are promising candidates as orthopaedic implants. The C-terminal (107-111) epitope of parathyroid hormone-related protein (PTHrP) exhibits osteogenic properties. The main aim of this study was to evaluate whether PTHrP (107-111) loading into gelatin-glutaraldehyde biopolymer-coated HA (HAGlu) scaffolds would produce an optimal biomaterial for tissue engineering applications. HAGlu scaffolds with and without PTHrP (107-111) were implanted into a cavitary defect performed in both distal tibial metaphysis of adult rats. Animals were sacrificed after 4 weeks for histological, microcomputerized tomography and gene expression analysis of the callus. At this time, bone healing occurred only in the presence of PTHrP (107-111)-containing HAGlu implant, related to an increase in bone volume/tissue volume and trabecular thickness, cortical thickness and gene expression of osteocalcin and vascular cell adhesion molecule 1, but a decreased gene expression of Wnt inhibitors, SOST and dickkopf homolog 1. The autonomous osteogenic effect of the PTHrP (107-111)-loaded HAGlu scaffolds was confirmed in mouse and human osteoblastic cell cultures. Our findings demonstrate the advantage of loading PTHrP (107-111) into degradable HAGlu scaffolds for achieving an optimal biomaterial that is promising for low load bearing clinical applications.

Functional characterization of the parathyroid hormone 1 receptor in human periodontal ligament cells

OBJECTIVES

Intermittent parathyroid hormone (PTH) exerts anabolic effects on bone and has been approved for osteoporosis therapy. The dual actions of PTH are mediated primarily through the parathyroid hormone 1 receptor (PTH1R). Upon ligand binding, PTH1R activates diverse signaling pathways, including cAMP/protein kinase A (PKA)- and phospholipase C/protein kinase C (PLC/PKC)-dependent pathways. PTH1R has been abundantly studied in bone cells. Knowledge on PTH1R characteristics and physiology in periodontal ligament (PDL) cells is still in its infancy.

MATERIALS AND METHODS

We characterized PTH1R in PDL cells in terms of its cellular localization, binding affinity, and signal transduction and compared these characteristics to those of MG63 osteoblast-like cells.

RESULTS

PTH1R mRNA/protein was identified in PDL and MG63 cells. PTH1R was mainly localized on the plasma membrane, in vesicular structures inside the cell, and, to some extent, in the nucleus of both cell types. Binding characteristics of PTH1R were cell type specific, with PDL cells demonstrating a lower binding affinity. The response of cAMP and active PKC production in MG63 cells was dose dependent with increasing PTH(1-34) concentration, whereas in PDL cells, it was regulated biphasically. However, we observed a cross talk between the cAMP/PKA and PLC/PKC signaling pathways, which were regulated diametrically opposed at a given concentration of PTH(1-34).

CONCLUSION

These data indicate that, albeit the similarity in its subcellular distribution, PTH1R in PDL cells exhibits characteristics different from those in MG63 cells, pointing to the cell type specificity of this receptor.

CLINICAL RELEVANCE

The findings further elucidate the characteristics of PTH action in dental tissues and widen the theoretical basis for the development of anabolic treatment strategies.

Current perspectives on parathyroid hormone (PTH) and PTH-related protein (PTHrP) as bone anabolic therapies

Osteoporosis is characterized by low bone mineral density and/or poor bone microarchitecture leading to an increased risk of fractures. The skeletal alterations in osteoporosis are a consequence of a relative deficit of bone formation compared to bone resorption. Osteoporosis therapies have mostly relied on antiresorptive drugs. An alternative therapeutic approach for osteoporosis is currently available, based on the intermittent administration of parathyroid hormone (PTH). Bone anabolism caused by PTH therapy is mainly accounted for by the ability of PTH to increase osteoblastogenesis and osteoblast survival. PTH and PTH-related protein (PTHrP)-an abundant local factor in bone- interact with the common PTH type 1 receptor with similar affinities in osteoblasts. Studies mainly in osteoporosis rodent models and limited data in postmenopausal women suggest that N-terminal PTHrP peptides might be considered a promising bone anabolic therapy. In addition, putative osteogenic actions of PTHrP might be ascribed not only to its N-terminal domain but also to its PTH-unrelated C-terminal region. In this review, we discuss the underlying cellular and molecular mechanisms of the anabolic actions of PTH and the similar potential of PTH-related protein (PTHrP) to increase bone mass and improve bone regeneration.

Osteostatin improves the osteogenic activity of fibroblast growth factor-2 immobilized in Si-doped hydroxyapatite in osteoblastic cells

Si-doped hydroxyapatite (Si-HA) is a suitable ceramic for the controlled release of agents to improve bone repair. We recently showed that parathyroid hormone-related protein (PTHrP) (107-111) (osteostatin) has remarkable osteogenic features in various in vitro and in vivo systems. Fibroblast growth factor (FGF)-2 modulates osteoblastic function and induces angiogenesis, and can promote osteoblast adhesion and proliferation after immobilization on Si-HA. In the present study we examined whether osteostatin might improve the biological efficacy of FGF-2-coated Si-HA in osteoblastic MC3T3-E1 cells in vitro. We found that Si-HA/FGF-2 in the presence or absence of osteostatin (100 nM) similarly increased cell growth (by about 50%). However, addition of the latter peptide to Si-HA/FGF-2 significantly enhanced gene expression of Runx2, osteocalcin, vascular endothelial growth factor (VEGF) and the VEGF receptors 1 and 2, without significantly affecting that of FGF receptors in these cells. Moreover, secreted VEGF in the MC3T3-E1 cell conditioned medium, which induced the proliferation of pig endothelial-like cells, was also enhanced by these combined factors. The synergistic action of osteostatin and Si-HA/FGF-2 on the VEGF system was abrogated by a mitogen-activated protein kinase inhibitor (U0126) and by the calcium antagonist verapamil. This action was related to an enhancement of alkaline phosphatase activity and matrix mineralization in MC3T3-E1 cells, and also in primary human osteoblastic cells. These in vitro data show that osteostatin increases the osteogenic efficacy of a Si-HA/FGF-2 biomaterial by a mechanism involving mitogen-activated protein kinases and intracellular Ca(2+). These findings provide an attractive strategy for bone tissue engineering.

Osteostatin-loaded onto mesoporous ceramics improves the early phase of bone regeneration in a rabbit osteopenia model

Parathyroid hormone-related protein (PTHrP) is an important modulator of bone formation. Recently, we reported that PTHrP (107-111) (osteostatin) coating onto mesoporous ceramics confers osteogenic activity to these materials. Bone repair is dramatically compromised in osteopenia/osteoporosis. Thus, we examined the efficacy of unmodified and organically modified SBA15 ceramics loaded with osteostatin in promoting bone repair in an osteoporotic rabbit model. Osteoporosis was induced in New Zealand rabbits by methylprednisolone administration, and healthy rabbits were used as controls. Tested materials were implanted into a femoral cavitary defect, and animals were sacrificed at 2 weeks post-implantation. At this time, implants were encapsulated by a variable layer of fibrotic tissue with no evidence of inflammation. Similarly to observations in normal rabbits, both types of osteostatin-loaded bioceramics induced tissue regeneration associated with increased staining for PCNA, Runx2, osteopontin, and/or vascular endothelial growth factor in osteoporotic rabbits. Our present findings demonstrate that these osteostatin-bearing bioceramics increase the early repair response not only in normal bone but also in osteoporotic bone after a local injury.

PTHrP isoforms have differing effect on chondrogenic differentiation and hypertrophy of mesenchymal stem cells

While several isoforms of parathyroid hormone-related peptide (PTHrP) have been commercially available, the difference in their effect has not been widely studied. The purpose of this study was to determine which isoform most effectively promoted chondrogenesis and suppressed hypertrophy from mesenchymal stem cells (MSCs). MSCs isolated from fresh bone marrow were cultured in pellet in chondrogenic medium containing 5 ng/ml of transforming growth factor (TGF)-β(3). From day 14 of culture, subsets of pellets were additionally treated with one of the four PTHrP isoforms (1-34, 1-86, 7-34, and 107-139) at 100 nM. After a further 2 weeks of in vitro culture, pellets were harvested for analysis. PTHrPs 1-34 and 1-86 significantly decreased the DNA level (p<0.05) while PTHrPs 7-34 and 107-139 significantly increased DNA level (p<0.05) compared with the control treated with TGF-β(3) only. Glycosaminoglycan per DNA significantly increased when treated with PTHrPs 1-34 and 1-86 (p<0.05) while it significantly decreased with PTHrPs 7-34 and 107-139 (p<0.05). PTHrP 1-34 significantly increased the gene and protein expression of the chondrogenic marker COL2A1, and decreased those of hypertrophic markers COL10A1 and alkaline phosphatase while other isoforms showed inconsistent effects. All of PTHrP isoforms significantly suppressed the gene and protein expression of indian hedgehog (p<0.05) while all isoforms except PTHrP 107-139 significantly reduced the gene and protein expression of patched 1 (p<0.05). In conclusion, of several PTHrP isoforms, PTHrP 1-34 most significantly enhanced chondrogenesis and suppressed hypertrophy in MSCs, supporting its use for cartilage tissue engineering.

The C-terminal fragment of parathyroid hormone-related peptide promotes bone formation in diabetic mice with low-turnover osteopaenia

BACKGROUND AND PURPOSE

Current data suggest that parathyroid hormone (PTH)-related peptide (PTHrP) domains other than the N-terminal PTH-like domain contribute to its role as an endogenous bone anabolic factor. PTHrP-107-139 inhibits bone resorption, a fact which has precluded an unequivocal demonstration of its possible anabolic action in vivo. We thus sought to characterize the osteogenic effects of this peptide using a mouse model of diabetic low-turnover osteopaenia.

EXPERIMENTAL APPROACH

PTHrP-107-139 was administered to streptozotocin-induced diabetic mice, with or without bone marrow ablation, for 13 days. Osteopaenia was confirmed by dual-energy X-ray absorptiometry and microcomputed tomography analysis. Histological analysis was performed on paraffin-embedded bone tissue sections by haematoxylin/eosin and Masson's staining, and tartrate-resistent acid phosphatase immunohistochemistry. Mouse bone marrow stromal cells and osteoblastic MC3T3-E1 cells were cultured in normal and/or high glucose (HG) medium. Osteogenic and adipogenic markers were assessed by real-time PCR, and PTHrP and the PTH(1) receptor protein expression by Western blot analysis.

KEY RESULTS

PTHrP-107-139 reversed the alterations in bone structure and osteoblast function, and also promoted bone healing after marrow ablation without affecting the number of osteoclast-like cells in diabetic mice. This peptide also reversed the high-glucose-induced changes in osteogenic differentiation in both bone marrow stromal cells and the more differentiated MC3T3-E1 cells.

CONCLUSIONS AND IMPLICATIONS

These findings demonstrate that PTHrP-107-139 promotes bone formation in diabetic mice. This mouse model and in vitro cell cultures allowed us to identify various anabolic effects of this peptide in this scenario.

The N- and C-terminal domains of parathyroid hormone-related protein affect differently the osteogenic and adipogenic potential of human mesenchymal stem cells

Parathyroid hormone-related protein (PTHrP) is synthesized by diverse tissues, and its processing produces several fragments, each with apparently distinct autocrine and paracrine bioactivities. In bone, PTHrP appears to modulate bone formation in part through promoting osteoblast differentiation. The putative effect of PTH-like and PTH-unrelated fragments of PTHrP on human mesenchymal stem cell (MSCs) is not well known. Human MSCs were treated with PTHrP (1-36) or PTHrP (107-139) or both (each at 10 nM) in osteogenic or adipogenic medium, from the start or after 6 days of exposure to the corresponding medium, and the expression of several osteoblastogenic and adipogenic markers was analyzed. PTHrP (1-36) inhibited adipogenesis in MSCs and favoured the expression of osteogenic early markers. The opposite was observed with treatment of MSCs with PTHrP (107-139). Moreover, inhibition of the adipogenic differentiation by PTHrP (1-36) prevailed in the presence of PTHrP (107-139). The PTH/PTHrP type 1 receptor (PTH1R) gene expression was maximum in the earlier and later stages of osteogenesis and adipogenesis, respectively. While PTHrP (107-139) did not modify the PTH1R overexpression during adipogenesis, PTHrP (1-36) did inhibit it; an effect which was partially affected by PTHrP (7-34), a PTH1R antagonist, at 1 microM. These findings demonstrate that both PTHrP domains can exert varying effects on human MSCs differentiation. PTHrP (107-139) showed a tendency to favor adipogenesis, while PTHrP (1-36) induced a mild osteogenic effect in these cells, and inhibited their adipocytic commitment. This further supports the potential anabolic action of the latter peptide in humans.

Alterations of the Wnt/beta-catenin pathway and its target genes for the N- and C-terminal domains of parathyroid hormone-related protein in bone from diabetic mice

Type 1 diabetes mellitus (T1D) is associated with bone loss. Given that the Wnt/beta-catenin pathway is a major regulator of bone accrual, we assessed this pathway in mice with streptozotozin-induced T1D. In diabetic mouse long bones, we found alterations favouring the suppression of this pathway by using PCR arrays and beta-catenin immunostaining. Downregulation of sclerostin, an inhibitor of this pathway, also occurred, and related to increased osteocyte apoptosis. Our data show that both N- and C-terminal parathyroid hormone-related peptide fragments might exert osteogenic effects in this setting by targeting several genes of this pathway and increasing beta-catenin in osteoblastic cells.

PTHrP 1-141 and 1-86 increase in vitro bone formation

BACKGROUND

Parathyroid hormone-related protein (PTHrP) has anabolic effects in bone, which has led to the clinical use of N-terminal fragments of PTHrP and PTH. Since 10% to 20% of fractures demonstrate healing complications and osteoporosis continues to be a debilitating disease, the development of bone-forming agents is of utmost importance. Due to evidence that regions of PTHrP other than the N-terminus may have bone-forming effects, this study was designed to compare the effects of full-length PTHrP 1-141 to N-terminal PTHrP 1-86 on in vitro bone formation.

MATERIALS AND METHODS

MC3T3-E1 pre-osteoblasts were treated once every 6 d for 36 d with 5, 25, and 50 pM of PTHrP 1-141 or 1-86 for 1 or 24 h. Cells were also treated after blocking the N-terminus, the nuclear localization sequence (NLS), and the C-terminus of PTHrP, individually and in combination. Area of mineralization, alkaline phosphatase (ALP), and osteocalcin (OCN) were measured.

RESULTS

PTHrP 1-141 and 1-86 increased mineralization after 24-h treatments, but not 1-h. PTHrP 1-141 was more potent than 1-86. Treatment with PTHrP 1-141 for 24-h, but not 1-86, resulted in a concentration-dependent increase in ALP, with no effect after 1-h. Exposure to both peptides for 1- or 24-h induced a concentration-dependent increase in OCN, with 24-h exceeding 1-h. Antibody blocking revealed that the NLS and C-terminus are anabolic.

CONCLUSIONS

Both PTHrP 1-141 and 1-86 increased in vitro bone formation; however, PTHrP 1-141 was more effective. The NLS and C-terminus have anabolic effects distinct from the N-terminus. This demonstrates the advantage of PTHrP 1-141 as a skeletal anabolic agent.

Osteostatin-loaded bioceramics stimulate osteoblastic growth and differentiation

Parathyroid hormone-related protein (PTHrP) is an important regulator of bone remodeling. Recent studies show that this protein can induce osteogenic features through its N- and C-terminal domains. Silica-based ordered mesoporous bioceramics with an SBA-15 structure - known to be bioactive and biocompatible - have recently been evaluated for their capacity to uptake and deliver L-tryptophan. This amino acid corresponds to the end position of the 107-111 domain (called osteostatin) of the native C-terminal PTHrP (107-139) fragment, whose true action in bone metabolism is still ill-defined. In the present study, we assessed some effects of the aforementioned biomaterials pressed into disks, loaded or not with osteostatin, in osteoblastic cell cultures. Our data demonstrate that both unmodified and organically modified SBA-15 loaded with this peptide increase cell growth and the expression of several osteoblastic products (alkaline phosphatase, osteocalcin, collagen, osteoprotegerin, receptor activator of nuclear factor-kappaB ligand and vascular endothelial growth factor) in osteoblastic cells. These findings support the notion that osteostatin coating confers osteogenic features to silica-based ordered mesoporous materials, which make them suitable biomaterials for bone repair.

The midregion, nuclear localization sequence, and C terminus of PTHrP regulate skeletal development, hematopoiesis, and survival in mice

The functions of parathyroid hormone-related protein (PTHrP) on morphogenesis, cell proliferation, apoptosis, and calcium homeostasis have been attributed to its N terminus. Evidence suggests that many of these effects are not mediated by the N terminus but by the midregion, a nuclear localization sequence (NLS), and C terminus of the protein. A knock-in mouse lacking the midregion, NLS, and C terminus of PTHrP (Pthrp(Delta/Delta)) was developed. Pthrp(Delta/Delta) mice had craniofacial dysplasia, chondrodysplasia, and kyphosis, with most mice dying by d 5 of age. In bone, there were fewer chondrocytes and osteoblasts per area, bone mass was decreased, and the marrow was less cellular, with erythroid hypoplasia. Cellular proliferation was impaired, and apoptosis was increased. Runx2, Ocn, Sox9, Crtl1, beta-catenin, Runx1, ephrin B2, cyclin D1, and Gata1 were underexpressed while P16/Ink4a, P21, GSK-3beta, Il-6, Ffg3, and Ihh were overexpressed. Mammary gland development was aberrant, and energy metabolism was deregulated. These results establish that the midregion, NLS, and C terminus of PTHrP are crucial for the commitment of osteogenic and hematopoietic precursors to their lineages, and for survival, and many of the effects of PTHrP on development are not mediated by its N terminus. The down-regulation of Runx1, Runx2, and Sox9 indicates that PTHrP is a modulator of transcriptional activation during stem cell commitment.

RUNX2 mutations in Chinese patients with cleidocranial dysplasia

Cleidocranial dysplasia (CCD) is an autosomal dominant bone disease in humans caused by haploinsufficiency of the RUNX2 gene. The RUNX2 has two major isoforms derived from P1 and P2 promoters. Over 90 mutations of RUNX2 have been reported associated with CCD. In our study, DNA samples of nine individuals from three unrelated CCD families were collected and screened for all exons of RUNX2 and 2 kb of P1 and P2 promoters. We identified two point mutations in the RUNX2 gene in Case 1, including a nonsense mutation (c.577C>T) that has been reported previously and a silent substitution (c.240G>A). In vitro studies demonstrated that c.577C>T mutation led to truncated RUNX2 protein production and diminished stimulating effects on mouse osteocalcin promoter activity when compared with full-length Runx2-II and Runx2-I isoforms. These results confirm that loss of function RUNX2 mutation (c.577C>T) in Case 1 family is responsible for its CCD phenotype.

Role of parathyroid hormone-related protein in the decreased osteoblast function in diabetes-related osteopenia

A deficit in bone formation is a major factor in diabetes-related osteopenia. We examined here whether diabetes-associated changes in osteoblast phenotype might in part result from a decrease in PTH-related protein (PTHrP). We used a bone marrow ablation model in diabetic mice by multiple streptozotocin injections. PTHrP (1-36) (100 microg/kg, every other day) or vehicle was administered to mice for 13 d starting 1 wk before marrow ablation. Diabetic mice showed bone loss in both the intact femur and the regenerating tibia on d 6 after ablation; in the latter, this was related to decreased bone-forming cells, osteoid surface, and blood vessels, and increased marrow adiposity. Moreover, a decrease in matrix mineralization occurred in ex vivo bone marrow cultures from the unablated tibia from diabetic mice. These skeletal alterations were associated with decreased gene expression (by real-time PCR) of Runx2, osterix, osteocalcin, PTHrP, the PTH type 1 receptor, vascular endothelial growth factor and its receptors, and osteoprotegerin to receptor activator of nuclear factor-kappaB ligand mRNA ratio, and increased peroxisome proliferator-activated receptor-gamma2 mRNA levels. Similar changes were induced by hyperosmotic (high glucose or mannitol) medium in osteoblastic MC3T3-E1 cells, which were mimicked by adding a neutralizing anti-PTHrP antibody or PTH type 1 receptor antagonists to these cells in normal glucose medium. PTHrP (1-36) administration reversed these changes in both intact and regenerating bones from diabetic mice in vivo, and in MC3T3-E1 cells exposed to high glucose. These findings strongly suggest that PTHrP has an important role in the altered osteoblastic function related to diabetes.

Parathyroid hormone-related protein interacts with vascular endothelial growth factor to promote fibrogenesis in the obstructed mouse kidney

Parathyroid hormone-related protein (PTHrP) interacts with vascular endothelial growth factor (VEGF) in osteoblasts. Since both PTHrP and VEGF have both proinflammatory and profibrogenic features, we assessed here whether these factors might act in concert to promote fibrogenesis in the obstructed kidney. VEGF receptor (VEGFR)-1 was upregulated, while VEGFR-2 was downregulated (at both mRNA and protein levels) in the mouse kidney within 2-6 days after ureteral obstruction. VEGF protein levels also increased in the obstructed kidney at the latter time. Moreover, this VEGF and VEGFR-1 upregulation was higher in mice overexpressing PTHrP in the proximal tubule than in control littermates. These changes were associated with higher fibronectin mRNA expression and alpha-smooth muscle actin (alpha-SMA) and integrin-linked kinase (ILK) immunostaining and lower apoptotic tubulointerstitial cells in the mouse obstructed kidney than in control littermates. Pretreatment with a neutralizing anti-VEGF antibody reversed these responses in the obstructed kidney of both types of mice. In vitro, PTHrP-(1-36) increased (maximal 2-fold vs. basal, at 100 nM) alpha-SMA and ILK protein expression and decreased E-cadherin protein levels in renal tubuloepithelial mouse cortical tubule and normal rat kidney (NRK) 52E cells. PTHrP-(1-36) also decreased cyclosporine A- and/or osmotic stress-induced apoptosis in these cells and in renal fibroblastic NRK 49F cells. These effects elicited by PTHrP-(1-36) were associated with both VEGF and VEGFR-1 upregulation, and abolished by the anti-VEGF antibody. Collectively, these findings strongly suggest that VEGF acts as an important mediator of PTHrP to promote fibrogenesis in the obstructed kidney.

Beta-arrestins and heterotrimeric G-proteins: collaborators and competitors in signal transduction

G-protein-coupled receptors (GPCRs), also known as seven transmembrane receptors (7-TMRs), are the largest protein receptor superfamily in the body. These receptors and their ligands direct a diverse array of physiological responses, and hence have broad relevance to numerous diseases. As a result, they have generated considerable interest in the pharmaceutical industry as drug targets. Recently, GPCRs have been demonstrated to elicit signals through interaction with the scaffolding proteins, beta-arrestins-1 and 2, independent of heterotrimeric G-protein coupling. This review discusses several known G-protein-independent, beta-arrestin-dependent pathways and their potential physiological and pharmacological significance. The emergence of G-protein-independent signalling changes the way in which GPCR signalling is evaluated, from a cell biological to a pharmaceutical perspective and raises the possibility for the development of pathway specific therapeutics.

Midregion PTHrP regulates Rip1 and caspase expression in MDA-MB231 breast cancer cells

It was previously reported that the midregion PTHrP domain (38-94)-amide restrains growth and invasion "in vitro", causes striking toxicity and accelerates death of some breast cancer cell lines, the most responsive being MDA-MB231 whose tumorigenesis was also attenuated "in vivo". In addition, we have demonstrated that midregion PTHrP is imported in the nucleoplasm of cultured MDA-MB231 cells, and that "in vitro" it can bind chromatin of metaphase spread preparations and also an isolated 20-mer oligonucleotide, thereby appearing endowed with a putative transcription factor-like DNA-binding ability. Here, we examined whether PTHrP (38-94)-amide was able to modulate the expression of genes encoding for apoptosis factors and caspases. Employing a combination of conventional and semi-quantitative multiplex PCR techniques, antisense oligonucleotide (asODN) transfections, proliferation/invasion assays and protein analyses, here we report that PTHrP treatment induces the up-regulation of Bcl-xS, Bad and Rip1 and switches-on the expression of caspase-2, -5, -6, -7 and -8 in MDA-MB231 cells. Moreover, we demonstrate for the first time that asODN-induced under-expression of Rip1 can lead to a more pronounced up-regulation of some caspases due, at least in part, to JNK inactivation, thus providing a new example of factor involved in the transcriptional regulation of the apoptotic enzymes.