Parathyroid hormone-related peptide stimulates proliferation of highly tumorigenic human SV40-immortalized breast epithelial cells

Intermittent parathyroid hormone enhances the healing of medication-related osteonecrosis of the jaw lesions in rice rats

Medication-related osteonecrosis of the jaw (MRONJ) is a potentially severe adverse event in patients treated with antiresorptives. Management of MRONJ is challenging, and no non-antibiotic, established medical treatment exists. Intermittent parathyroid hormone (iPTH) has been used off-label to treat MRONJ with favorable results. However, its medical efficacy has rarely been substantiated in clinical or preclinical experiments. Using a validated rice rat, infection-based model of MRONJ, we evaluated the effects of iPTH on established MRONJ. We hypothesize that iPTH contributes to MRONJ resolution by enhancing alveolar bone turnover and healing oral soft tissues. Eighty-four rice rats began a standard rodent chow diet at age 4 weeks to induce localized periodontitis. Rats were simultaneously randomized to receive saline (vehicle, VEH) or zoledronic acid (ZOL, 80 μg/kg IV) every 4 weeks. Oral exams were conducted bi-weekly to assign a gross quadrant grade (GQG, 0-4) to evaluate any lesion at the lingual aspect of the interdental space between maxillary molar (M2) and M3. 14 of 20 VEH-treated rice rats (70%) developed maxillary localized periodontitis with GQG 2-3 after 30 ± 10 weeks of saline. Additionally, 40 of 64 ZOL-treated rice rats with periodontitis developed MRONJ-like lesions after 30 ± 10 weeks of ZOL treatment. Rice rats with localized periodontitis or MRONJ-like lesions were treated with saline or iPTH (40 μg/kg) subcutaneously (SC) 3 times/week For 6 weeks until euthanasia. We found that iPTH -treated ZOL rats had a lower prevalence of MRONJ (p < 0.001), with lower severity extent of oral lesions (p = 0.003) and percentage of empty osteocyte lacunae (p < 0.001). ZOL rats treated with iPTH displayed a higher osteoblast surface (p < 0.001), more osteoblasts (p < 0.001), higher osteoclast surface (p < 0.001) and more osteoclasts (p = 0.002) at alveolar bone surfaces than ZOL/VEH rats. Greater gingival epithelial thickness and epithelial cell proliferation rate was found in the oral mucosa and gingiva of ZOL/PTH rats than in ZOL/VEH rats (p < 0.001). Our data suggest that iPTH is an efficacious non-operative medicinal therapy that accelerates oral healing and enhances the resolution of MRONJ lesions in ZOL-treated rice rats.

Roles of Parathyroid Hormone-Related Protein (PTHrP) and Its Receptor (PTHR1) in Normal and Tumor Tissues: Focus on Their Roles in Osteosarcoma

Osteosarcoma (OS) is the most common primary bone tumor and originates from bone forming mesenchymal cells and primarily affects children and adolescents. The 5-year survival rate for OS is 60 to 65%, with little improvement in prognosis during the last four decades. Studies have demonstrated the evolving roles of parathyroid hormone-related protein (PTHrP) and its receptor (PTHR1) in bone formation, bone remodeling, regulation of calcium transport from blood to milk, regulation of maternal calcium transport to the fetus and reabsorption of calcium in kidneys. These two molecules also play critical roles in the development, progression and metastasis of several tumors such as breast cancer, lung carcinoma, chondrosarcoma, squamous cell carcinoma, melanoma and OS. The protein expression of both PTHrP and PTHR1 have been demonstrated in OS, and their functions and proposed signaling pathways have been investigated yet their roles in OS have not been fully elucidated. This review aims to discuss the latest research with PTHrP and PTHR1 in OS tumorigenesis and possible mechanistic pathways.

This review is dedicated to Professor Michael Day who died in May 2020 and was a very generous collaborator.

Conditional reprogramming: next generation cell culture

Long-term primary culture of mammalian cells has been always difficult due to unavoidable senescence. Conventional methods for generating immortalized cell lines usually require manipulation of genome which leads to change of important biological and genetic characteristics. Recently, conditional reprogramming (CR) emerges as a novel next generation tool for long-term culture of primary epithelium cells derived from almost all origins without alteration of genetic background of primary cells. CR co-cultures primary cells with inactivated mouse 3T3-J2 fibroblasts in the presence of RHO-related protein kinase (ROCK) inhibitor Y-27632, enabling primary cells to acquire stem-like characteristics while retain their ability to fully differentiate. With only a few years' development, CR shows broad prospects in applications in varied areas including disease modeling, regenerative medicine, drug evaluation, drug discovery as well as precision medicine. This review is thus to comprehensively summarize and assess current progress in understanding mechanism of CR and its wide applications, highlighting the value of CR in both basic and translational researches and discussing the challenges faced with CR.

Serum levels of vitamin D, parathyroid hormone and calcium in relation to survival following breast cancer

Purpose

Vitamin D, parathyroid hormone (PTH) and calcium in blood are correlated with each other. Previous studies have suggested vitamin D to have anti-proliferative effects on tumor cells, whereas PTH may have carcinogenic effects. A cancer disease may influence calcium levels in blood, but less is known about calcium and its potential effect on cancer risk and survival. The aim of this study was to examine pre-diagnostic levels of vitamin D (25OHD), PTH and calcium in relation to survival after breast cancer.

Methods

The Malmö Diet and Cancer Study enrolled 17,035 women between 1991 and 1996. 672 patients developed incident invasive breast cancer up until 31 December 2006. Serum samples collected at baseline were analyzed for 25OHD, PTH and calcium. All patients were followed until 31 December 2010 using the Swedish Cause of Death Registry. The analytes were divided into tertiles and the risk of death from breast cancer was analyzed using an adjusted Cox proportional hazards analysis, yielding hazard ratios with 95 % confidence intervals.

Results

Levels of 25OHD and breast cancer mortality were associated in a u-shaped manner with the highest mortality among patients in the first (2.46: 1.38–4.37) and third tertiles (1.99: 1.14–3.49), as compared to the second. An inverse relation was found between calcium levels and breast cancer mortality, with the lowest mortality in the third tertile, (0.53: 0.30–0.92) as compared to the first. There was no clear association between PTH and breast cancer mortality.

Conclusions

This study shows that pre-diagnostic 25OHD and calcium may affect survival following breast cancer.

Pthlh, a promising cancer modifier gene in rat tongue carcinogenesis

Susceptibly to the induction of rat tongue cancer (TC) by oral 4-nitroquinoline 1-oxide (4NQO) exposure is a polygenic trait. Among several quantitative trait loci identified by crosses between TC-susceptible Dark Agouti (DA) rats and TC-resistant Wistar-Furth (WF) rats, we focused on tongue cancer susceptibility locus (Tcas3) of chromosome 4. We examined tongue carcinogenesis in the reciprocal congenic strains DA.WF-Tcas3 and WF.DA-Tcas3 and in their parental strains. The Tcas3DA allele, and not the Tcas3WF allele, significantly favored tumor latency, incidence and TC number/size. In genomic DNA of TCs induced in (DA x WF) F1 rats, the resistant Tcas3WF allele was frequently and selectively lost, particularly in larger tumors. Thus, we searched the possible candidate genes in the Tcas3 region using microarray analysis of TCs in F1 rats and revealed significant upregulation of 2 cancer-related genes, parathyroid hormone-like hormone (Pthlh) and Kras2. The relevance of the WF allele of Pthlh as a cancer modifier was indicated by 3 single nucleotide polymorphisms specific to this strain. In contrast, no consistent strain-specific variations were found in Kras2. Moreover, the plasma Ca2+ level was consistently higher in DA rats when compared to the level in WF rats bearing TCs; moreover, the Pthlh-mRNA expression level was >30-fold higher in TCs when compared to this level in the normal tongue mucosa. Immunostaining experiments showed strong PTHrP protein expression in TCs of DA rats, and the signal was intensified in larger TCs. Kras2 was also upregulated in TCs, but to a lesser degree than PTHrP. Thus, Pthlh is a promising candidate modifier gene in the development and progression of rat TCs.

Autocrine-derived epidermal growth factor receptor ligands contribute to recruitment of tumor-associated macrophage and growth of basal breast cancer cells in vivo

Epidermal growth factor receptor (EGFR) expression has been linked to progression of basal breast cancers. Many breast cancer cells harbor the EGFR and produce its family of ligands, suggesting they may participate in autocrine and paracrine signaling with cells of the tumor microenvironment. EGFR ligand expression was profiled in the basal breast cancer cell line MDA-231 where AREG, TGF-alpha, and HBEGF were the three ligands most highly expressed. Autocrine signaling was modulated through silencing or overexpression of these three ligands using lentiviral constructs and the impact measured using motility, proliferation, and cytokine expression assays. Changes in receptor phosphorylation and receptor turnover were examined. Knockdown of AREG or TGF-alpha in vitro resulted in decreased motility (p < 0.05) and decreased expression of macrophage chemoattractants. Overexpression of TGF-alpha increased motility and chemoattractant expression, whereas AREG did not. HBEGF modulation had no effect on any cellular behaviors. All the cells with altered ligand production were inoculated into female athymic nude mice to form mammary fat pad tumors, followed by immunohistochemical analysis for necrosis, angiogenesis, and macrophage recruitment. In vivo, knockdown of AREG or TGF-alpha increased survival (p < 0.001) while decreasing angiogenesis (p < 0.001), tumor growth (p < 0.001), and macrophage attraction (p < 0.001). Overexpression of AREG appeared to elicit a greater effect than TGF-alpha on mammary fat pad tumor growth by increasing angiogenesis (p < 0.001) and macrophage attraction to the tumor (p < 0.01). We propose these changes in mammary tumor growth were the result of increased recruitment of macrophages to the tumor by cells with altered autocrine EGFR signaling. We conclude that AREG and TGF-alpha were somewhat interchangeable in their effects on EGFR signaling; however, TGF-alpha had a greater effect in vitro and AREG had a greater effect in vivo.

Parathyroid hormone-related protein protects against mammary tumor emergence and is associated with monocyte infiltration in ductal carcinoma in situ

Parathyroid hormone-related protein (PTHrP) is required for mammary gland development and promotes the growth of breast cancer metastases within bone. However, there are conflicting reports of the prognostic significance of its expression in primary breast cancers. To study the role of PTHrP in early breast cancer, the effect of conditional deletion of PTHrP was examined in the context of neu-induced mammary tumorigenesis. Loss of PTHrP resulted in a higher tumor incidence. Transcriptional profiling of the tumors revealed that PTHrP influenced genes relevant to heterotypic cell signaling, including regulators of monocyte recruitment. Immunohistochemical analysis of human breast cancers revealed that PTHrP expression was associated with both HER-2/neu expression and macrophage infiltration in preinvasive ductal carcinoma in situ. The gene expression signature associated with loss of PTHrP expression in vivo correlated with poorer outcome in human breast cancer. Together, these data indicate that loss of PTHrP accelerates mammary tumorigenesis possibly by a non-cell-autonomous tumor suppressor pathway.

Tumor expressed PTHrP facilitates prostate cancer-induced osteoblastic lesions

Expression of parathyroid hormone-related protein (PTHrP) correlates with prostate cancer skeletal progression; however, the impact of prostate cancer-derived PTHrP on the microenvironment and osteoblastic lesions in skeletal metastasis has not been completely elucidated. In this study, PTHrP overexpressing prostate cancer clones were stably established by transfection of full length rat PTHrP cDNA. Expression and secretion of PTHrP were verified by western blotting and IRMA assay. PTHrP overexpressing prostate cancer cells had higher growth rates in vitro, and generated larger tumors when inoculated subcutaneously into athymic mice. The impact of tumor-derived PTHrP on bone was investigated using a vossicle co-implant model. Histology revealed increased bone mass adjacent to PTHrP overexpressing tumor foci, with increased osteoblastogenesis, osteoclastogenesis and angiogenesis. In vitro analysis demonstrated pro-osteoclastic and pro-osteoblastic effects of PTHrP. PTHrP enhanced proliferation of bone marrow stromal cells and early osteoblast differentiation. PTHrP exerted a pro-angiogenic effect indirectly, as it increased angiogenesis but only in the presence of bone marrow stromal cells. These data suggest PTHrP plays a role in tumorigenesis in prostate cancer, and that PTHrP is a key mediator for communication and interactions between prostate cancer and the bone microenvironment. Prostate cancer-derived PTHrP is actively involved in osteoblastic skeletal progression.

Over-expression of parathyroid hormone Type 1 receptor confers an aggressive phenotype in osteosarcoma

Osteosarcoma is the most common primary bone malignancy in children and is associated with rapid bone growth. Parathyroid hormone-related peptide (PTHrP) signaling via parathyroid hormone Type 1 receptor (PTHR1) is important for skeletal development and is involved in bone metastases in other tumors. The aim of this study was to investigate the status of PTHrP/PTHR1 and its possible role in osteosarcoma. In a preliminary screening, a higher level of PTHR1 mRNA, but not PTHrP, was found in 4 osteosarcoma xenografts as compared with 4 standard cell lines, or 5 patient derived cell lines (p < 0.05) using quantitative RT-PCR. It was therefore extended to 55 patient specimens, in which a significantly higher level of PTHR1 mRNA was detected in metastatic or relapsed samples than those from primary sites (p < 0.01). Cell behavior caused by PTHR1 overexpression was further studied in vitro using PTHR1 transfected HOS cell line as a model. Over-expression of PHTR1 resulted in increased proliferation, motility and Matrigel invasion without addition of exogenous PTHrP suggesting an autocrine effect. Importantly, the aggressiveness in PTHR1-expressing cells was completely reversed by RNAi mediated gene knockdown. In addition, PTHR1 over-expression led to delayed osteoblastic differentiation and upregulation of genes involved in extracellular matrix production, such as TGF-beta1 and connective tissue growth factor. When cocultured with bone marrow derived monocytes, PTHR1 transfected HOS cells induced a greater number of osteoclasts. This study suggests that PTHR1 over-expression may promote osteosarcoma progression by conferring a more aggressive phenotype, and forming a more favorable microenvironment.

Amphiregulin-EGFR signaling regulates PTHrP gene expression in breast cancer cells

Parathyroid hormone-related protein (PTHrP) is an autocrine/paracrine factor produced by breast cancer cells that is speculated to play a major role in permitting breast cancer cells to grow into the bone microenvironment by stimulating the bone resorption axis. It has been previously shown that EGFR signaling induces the production of PTHrP in several primary and transformed epithelial cell types. Therefore, we investigated the relationship between EGFR and PTHrP gene expression in human breast cancer cells. Of a panel of 7 breast epithelial and cancer cell lines, the osteolytic, EGFR- positive lines (MDA-MB-231 and NS2T2A1) exhibited higher levels of PTHrP transcript expression. Amphiregulin mRNA levels in all lines were approximately 2 orders of magnitude higher than those of TGFalpha or HB-EGF. In the EGFR bearing lines, the receptor was phosphorylated at tyrosine 992 under basal conditions, and the addition of 100 nM amphiregulin did not lead to the phosphorylation of other tyrosine residues typically phosphorylated by the prototypical ligand EGF. Treatment of the EGFR positive lines with the EGFR inhibitor PD153035 and amphiregulin-neutralizing antibodies reduced PTHrP mRNA levels by 50-70%. Stable EGFR expression in the MCF7 line failed to increase basal PTHrP mRNA levels; however, treatment of this cell line with exogenous EGF or amphiregulin increased PTHrP transcription 3-fold. Transient transfection analysis suggests that the MAPK pathway and ETS transcription factors mediate EGFR coupling to PTHrP gene expression. Taken together, it appears that autocrine stimulation of EGFR signaling by amphiregulin is coupled to PTHrP gene expression via EGFR Tyr992 and MAPK, and that this pathway may contribute to PTHrP expression by breast tumor cells.

PTHrP, calcitonin and calcitriol in a case of severe, protracted and refractory hypercalcemia due to a pancreatic neuroendocrine tumor

A patient with a primary neuroendocrine tumor of the pancreas, presented with severe hypercalcemia. This hypercalcemia of malignancy (HCM) failed to respond to intensive bisphosphonate treatment and needed continuous enhanced diuresis. Only after successful antitumor therapy did the hypercalcemia subside. Hypercalcemia was associated with increased concentrations of plasma PTHrP, calcitonin and 1,25-(OH)(2)D(3). Bone mineral density was markedly increased. We demonstrated the presence of both PTHrP and calcitonin in the tumor at the mRNA and protein level, using RT-PCR, immunohistochemistry and Western blotting. The high levels of plasma PTHrP and the demonstrated predominant renal mechanism in this case of HCM are suspected to be the cause for its refractoriness to bone resorption inhibitors. Our findings furthermore suggest that the tumoral production of calcitonin and PTHrP might have contributed to the increased bone mineral storage of calcium and thus probably attenuated the development of frank hypercalcemia.

PTHrP P3 promoter activity in breast cancer cell lines: role of Ets1 and CBP (CREB binding protein)

Parathyroid hormone-related protein (PTHrP) is produced by many tumors including breast cancer. We have reported that Ets1 factor activates P3 PTHrP promoter in our model of tumorigenic breast cancer cell and not in pre- or non-tumorigenic cell lines, thus contributing to an increased PTHrP production. In this study, gel retardation assays revealed that Etsl and its promoter binding site (EBS) specifically formed complexes whose abundance correlates with Ets1 levels in the three cell lines. Coexpression of Etsl and CBP induced a synergistic activation of the P3 promoter only in the tumorigenic cell line. This synergism required the integrity of the EBS and was abrogated by E1A. All breast cancer cell lines showed high basal concentrations of phosphorylated CREB. Moreover a CRE-like sequence was also required for Ets1/CBP synergy and, finally, CREB expression was found to enhance the PTHrP P3 promoter activity. Thus a multipartite complex of transcription factors and coactivators seems to regulate PTHrP transcription and contribute to the alterations that promote tumorigenic behavior in breast epithelial cells.

Skeletal metastasis: Established and emerging roles of parathyroid hormone related protein (PTHrP)

Parathyroid hormone related protein (PTHrP) is a well characterized tumor derived product that also has integral functions in normal development and homeostasis. PTHrP is produced by virtually all tumor types that metastasize to bone and numerous studies have demonstrated a correlation between PTHrP expression and skeletal localization of tumors. PTHrP has prominent effects in bone via its interaction with the PTH-1 receptor on osteoblastic cells. Through indirect means, PTHrP supports osteoclastogenesis by upregulating the receptor activator of NFkappaB ligand (RANKL) in osteoblasts. PTHrP also regulates osteoblast proliferation and differentiation in manners that are temporal and dose dependent. Bone turnover has been implicated in the localization of tumors to bone and PTHrP increases bone turnover. Bone turnover results in the release of growth factors such as TGFbeta and minerals such as calcium, both of which impact tumor cell growth and contribute to continued PTHrP production. PTHrP also has anabolic properties and could be in part responsible for osteoblastic type reactions in prostate cancer. Finally, emerging roles of PTH and PTHrP in the support of hematopoietic stem cell development in the bone marrow microenvironment suggest that an interaction between hematopoietic cells and tumor cells warrants further investigation.

Parathyroid Hormone-related Protein Regulates Tumor-relevant Genes in Breast Cancer Cells

The effect of endogenous parathyroid hormone-related protein (PTHrP) on gene expression in breast cancer cells was studied. We suppressed PTHrP expression in MDA-MB-231 cells by RNA interference and analyzed changes in gene expression by microarray analysis. More than 200 genes showed altered expression in response to a PTHrP-specific small interfering (si) RNA (siPTHrP). Cell cycle-regulating gene CDC2 and genes (CDC25B and Tome-1) that control CDC2 activity showed increased expression in the presence of siPTHrP. CDC2 activity was also found to be higher in siPTHrP-treated cells. Studies with PTHrP peptides 1-34 and 67-86, forskolin, and a PTH1 receptor (PTH1R)-specific siRNA showed that PTHrP regulates CDC2 and CDC25B, at least in part, via PTH1R in a cAMP-independent manner. Other siPTHrP-responsive genes included integrin alpha6 (ITGA6), KISS-1, and PAI-1. When combined, siRNAs against ITGA6, PAI-1, and KISS-1 could mimic the negative effect of siPTHrP on migration, whereas siKISS-1 and siPTHrP similarly reduced the proliferative activity of the cells. Comparative expression analyses with 50 primary breast carcinomas revealed that the RNA level of ITGA6 correlates with that of PTHrP, and higher CDC2 and CDC25B values are found at low PTHrP expression. Our data suggest that PTHrP has a profound effect on gene expression in breast cancer cells and, as a consequence, contributes to the regulation of important cellular activities, such as migration and proliferation.

A moderately low phosphate intake may provide health benefits analogous to those conferred by UV light - a further advantage of vegan diets

Although exposure to ultraviolet light is often viewed as pathogenic owing to its role in the genesis of skin cancer and skin aging, there is growing epidemiological evidence that such exposure may decrease risk for a number of more serious cancers, may have a favorable impact on blood pressure and vascular health, and may help to prevent certain autoimmune disorders - in addition to its well-known influence on bone density. Most likely, these health benefits are reflective of improved vitamin D status. Increased synthesis or intake of vitamin D can be expected to down-regulate parathyroid hormone (PTH), and to increase autocrine synthesis of its active metabolite calcitriol in certain tissues; these effects, in turn, may impact cancer risk, vascular health, immune regulation, and bone density through a variety of mechanisms. Presumably, a truly adequate supplemental intake of vitamin D - manyfold higher than the grossly inadequate current RDA - could replicate the benefits of optimal UV exposure, without however damaging the skin. Diets moderately low in bioavailable phosphate - like many vegan diets - might be expected to have a complementary impact on disease risks, inasmuch as serum phosphate suppresses renal calcitriol synthesis while up-regulating that of PTH. A proviso is that the impact of dietary phosphorus on bone health is more equivocal than that of vitamin D. Increased intakes of calcium, on the other hand, down-regulate the production of both PTH and calcitriol - the latter effect may explain why the impact of dietary calcium on cancer risk (excepting colon cancer), hypertension, and autoimmunity is not clearly positive. An overview suggests that a vegan diet supplemented with high-dose vitamin D should increase both systemic and autocrine calcitriol production while suppressing PTH secretion, and thus should represent a highly effective way to achieve the wide-ranging health protection conferred by optimal UV exposure.

Ets-1 activates parathyroid hormone-related protein gene expression in tumorigenic breast epithelial cells

Parathyroid hormone-related protein (PTHrP) is produced by many tumors not associated with humoral hypercalcemia, including breast cancers. In this study, we used three human immortalized mammary epithelial cell lines that differ in tumorigenicity and PTHrP expression. Using RT-PCR we investigated 5' and 3' alternative splicing of PTHrP transcripts and promoter usage in the lines. Increased levels of P3-derived transcripts and the 1-139 mRNA isoform were observed in the most tumorigenic cell line. Transient transfection experiments identified elements close to P3 promoter that appeared to account for a portion of differential PTHrP expression among the three cell lines. Using site-directed mutagenesis, a previously described Ets-1/Sp1 binding site upstream of P3 was determined to be crucial for full activity of this promoter. RT-PCR and western blot evaluation of Ets family member expression found that Ese-1 was present in all three lines, but that appreciable levels of Ets-1 protein were present exclusively in the most tumorigenic line. Cotransfection of Ets-1 expression vectors activated PTHrP reporter constructs in the most tumorigenic line but not in the other cell lines. These findings suggest a potential mechanism by which PTHrP transcription may be regulated as a consequence of events that promote tumorigenic behavior in breast epithelial cells.

PTHrP [67-86] regulates the expression of stress proteins in breast cancer cells inducing modifications in urokinase-plasminogen activator and MMP-1 expression

It was previously reported that a midregion domain of parathyroid hormone-related protein (PTHrP), that is, [67-86]-amide, is able to restrain growth and promote matrigel penetration by the 8701-BC cell line, derived from a biopsy fragment of a primary ductal infiltrating carcinoma of the human breast, and that cell invasion in vitro is drastically impaired by inactivation of urokinase-plasminogen activator (uPa). In this study we started a more detailed investigation of the possible effects on gene expression arising from the interaction between PTHrP [67-86]-amide and 8701-BC breast cancer cells by a combination of conventional-, differential display-and semi-quantitative multiplex-polymerase chain reaction (PCR) assays. We present here the first evidence that the upregulation of some stress-related genes, most noticeably heat shock factor binding protein-1 (hsbp1) and heat shock protein 90 (hsp-90), is involved in the acquisition of an in vitro more invasive phenotype by cells treated with midregion PTHrP. This is conceivably accomplished by sequestering and inactivating heat shock factor-1 (hsf1) which is able to recognize Ets transcription-factor-binding sites present in some gene promoters, such as those of uPa and matrix metalloprotease-1 (MMP-1). In fact, our data show that incubation of PTHrP [67-86]-amide-treated cells with either antisense hsbp1-oligonucleotide or geldanamycin, an hsp90-inactivating antibiotic, results in downregulation of uPa and upregulation of MMP-1, and in a prominent inhibition of cell invasion in matrigel-containing Transwell chambers. Alternatively, incubation of untreated 8701-BC cells with quercetin, a flavonoid known to decrease the amount of free hsf1, is found to induce upregulation of uPa and downregulation of MMP-1, and an increase of matrigel invasion by cells, thus providing further supporting data of the involvement of hsf unavailability on the modulation of uPa and MMP-1 expression and on cell invasive behaviour. These studies confirm a previous postulate that over-secretion of uPa, rather than of other extracellular proteases, is a primary condition for the increase of invasive activity triggered by PTHrP [67-86]-amide in vitro, and support a role for midregion forms of PTHrP in potentially affecting pathological mammary growth and differentiation. They also identify two new key protagonists in the complex scenario of breast tumor cell invasiveness in vitro, that is, hsbp1 and hsp90, which deserve further and more extensive studies as potential and attractive molecular targets for anti-breast cancer treatments.

Functional type I PTH/PTHrP receptor in freshly isolated newborn rat keratinocytes: identification by RT-PCR and immunohistochemistry

The presence of identical or distinct type I parathyroid hormone (PTH)/parathyroid hormone-related peptide (PTHrP) receptors in keratinocytes is still a matter of debate. We studied the expression and functionality of PTHrP receptors in freshly isolated keratinocytes from newborn rat skin. Four overlapping primers, amplifying different regions in the rat PTH receptor, were used for reverse transcriptase-polymerase chain reaction (RT-PCR). The first region corresponded to the N-terminal extracellular region and the first transmembrane domain (S/M1), the second region amplified the connecting intracellular and extracellular loops transmembrane domain (E2/M5), the third spanned the range from the transmembrane to the intracellular domain (M4/T), and the fourth region amplified the C-terminal tail (M6/7/T). The PCR products from the keratinocyte RNA were identical to those from kidney RNA of the same rats. The cloned four transcripts showed 100% of homologies with the cDNA sequence from bone ROS cells. Keratinocytes, freshly isolated or present in situ in the epidermis, recognized an anti-PTH receptor antibody (PTH-II) directed against the receptor extracellular domain. Western blotting showed the same protein patterns in keratinocytes, kidney, and ROS cell extracts. Low doses of PTHrP(1-34) (10(-12)-10(-9) M) increased the cell number studied by [3H]thymidine incorporation and DNA content. Treatment with the PTH/PTHrP receptor antagonist [Asn10, Leu11, D Trp12] PTHrP(7-34) or two different PTH receptor antibodies inhibited the increase in cell proliferation induced by PTHrP(1-34). All these findings indicate that newborn rat epidermis and keratinocytes express functional PTHrP receptors, which are identical to type I PTH/PTHrP receptor and are recognized by PTHrP(1-34).

The parathyroid hormone-related protein receptor is expressed in breast cancer bone metastases and promotes autocrine proliferation in breast carcinoma cells

Overproduction of parathyroid hormone-related protein (PTHRP) occurs in a high proportion of primary breast cancers (PBC) and is strongly implicated in their metastatic spread to bone. Although the PTHRP-receptor (PTHRP-R) is often coexpressed with PTHRP in PBC, its role in regulating breast cancer cell proliferation and metastases to bone remains unclear. The aims of this study were to determine the expression of the PTHRP-R in breast cancer bone metastases (BM) and to investigate the effects of PTHRP-R overexpression on breast cancer cell proliferation. PTHRP-R expression occurred in 85% (11 out of 13) of BM compared with 58% (39 out of 67) of PBC. Median expression was higher (P<0.05) in BM compared with PBC. PTHRP increased cAMP accumulation and DNA synthesis in MCF-7 cells stably overexpressing the PTHRP-R (MCF-7(WTR)) but not in MCF-7(VEC) control cells. The increase in DNA synthesis was mimicked by the cAMP pathway activator forskolin. The receptor antagonist PTHRP(7-34) reduced DNA synthesis in MCF-7(WTR) cells, but not MCF-7(VEC) cells, indicating that receptor overexpression promotes autocrine PTHRP activity. MCF-7(WTR) cells showed increased mitogenic responsiveness to fetal calf serum and reduced doubling times. PTHRP induced weak activation of ERK1 and ERK2 and potentiated their activation by serum growth factors. Collectively these results show that the PTHRP-R is frequently expressed in breast cancer BM and indicate that receptor overexpression drives proliferation via autocrine signals that are mediated via cAMP and ERK pathways.

Overexpression of parathyroid hormone-related protein causes hypercalcemia but not bone metastases in a murine model of mammary tumorigenesis

Several lines of evidence suggest that production of parathyroid hormone-related protein (PTHrP) by breast cancer cells contributes to the formation of bone metastases. However, it is not clear if PTHrP promotes access of cancer cells to the skeleton or if it simply promotes bone resorption around cells already within bone. To study the effects of PTHrP on the development of bone metastases, we treated mice overexpressing PTHrP in their mammary glands (K14-PTHrP transgenic mice) with 9,10-dimethyl-1,2-benz-anthracene (DMBA), a known mammary carcinogen. After DMBA treatment, K14-PTHrP mice showed a higher incidence of tumor formation and a shorter latency to tumor formation than wild-type littermates. Transgenic tumors expressed the K14-PTHrP transgene and secreted excess amounts of PTHrP. In response, tumor-bearing transgenic mice became hypercalcemic and had elevated circulating levels of PTHrP. Despite the development of visceral metastases, neither transgenic mice nor wild-type controls developed bone metastases. This was true even if tumor cells were introduced into the arterial circulation of immunodeficient mice. Our results are consistent with the emerging notion that the ability of breast cancer cells to produce PTHrP in response to cues from the bone microenvironment may be more important to the development of skeletal metastases than the production of PTHrP by cells within the primary breast cancer.

Specificity and stability of a new PTH1 receptor antagonist, mouse TIP(7-39)

Parathyroid hormone 1 (PTH1) receptor antagonists might be of benefit in hypercalcemia of malignancy (HHM) and hyperparathyroidism. We previously identified bovine tuberoinfundibular peptide (7-39) (bTIP(7-39)) as a high-affinity PTH1 receptor antagonist. Mouse TIP(7-39) is an antagonist (rPTH1 K(B)=44 nM, rPTH2=940 nM) that is more potent than other known PTH1 receptor antagonists: bTIP(7-39) (210 nM), PTH-related protein (PTHrP)(7-34) (640 nM), and bPTH(7-34) (>3000 nM). Plasma proteases slowly (t(1/2)=81 min) inactivated [125I] mTIP(7-39). Intravenous plasma [125I]mTIP(7-39) was bi-phasically cleared (radioactivity t(1/2)=2.9 min (70%) and 120 min (30%), binding activity t(1/2)=3.6 min (92%), and t(1/2)=21 min (8%)). Loss of unlabeled mTIP(7-39) (250 microg/kg i.v.) receptor binding was similar. mTIP(7-39)'s high-affinity should facilitate animal evaluation of effects of PTH1 receptor antagonism.