Cancer stem-like cell marker CD44 promotes bone metastases by enhancing tumorigenicity, cell motility, and hyaluronan production

CD44, an adhesion molecule that binds to the extracellular matrix, primarily to hyaluronan (HA), has been implicated in cancer cell migration, invasion, and metastasis. CD44 has also recently been recognized as a marker for stem cells of several types of cancer. However, the roles of CD44 in the development of bone metastasis are unclear. Here, we addressed this issue by using bone metastatic cancer cell lines, in which CD44 was stably knocked down. Tumor sphere formation and cell migration and invasion were significantly inhibited by CD44 knockdown. Furthermore, the downregulation of CD44 markedly suppressed tumorigenicity and bone metastases in nude mice. Of note, the number of osteoclasts decreased in the bone metastases. Microarray analysis revealed that the expression of HA synthase 2 was downregulated in CD44-knockdown cells. The localization of HA in the bone metastatic tumors was also markedly reduced. We then examined the roles of CD44-HA interaction in bone metastasis using 4-methylumbelliferone (4-MU), an inhibitor of HA synthesis. 4-MU decreased tumor sphere and osteoclast-like cell formation in vitro. Moreover, 4-MU inhibited bone metastases in vivo with reduced number of osteoclasts. These results collectively suggest that CD44 expression in cancer cells promotes bone metastases by enhancing tumorigenicity, cell migration and invasion, and HA production. Our results also suggest the possible involvement of CD44-expressing cancer stem cells in the development of bone metastases through interaction with HA. CD44-HA interaction could be a potential target for therapeutic intervention for bone metastases.

Localization of SUMOylation factors and Osterix in odontoblast lineage cells during dentin formation and regeneration

Small ubiquitin-related modifier (SUMO) conjugation (SUMOylation) is a post-translational modification involved in various cellular processes including the regulation of transcription factors. In this study, to analyze the involvement of SUMOylation in odontoblast differentiation, we examined the immunohistochemical localization of SUMO-1, SUMO-2/3, and Osterix during rat tooth development. At the bud and cap stages, localization of SUMOs and Osterix was hardly detected in the dental mesenchyme. At the bell stage, odontoblasts just beginning dentin matrix secretion and preodontoblasts near these odontoblasts showed intense immunoreactivity for these molecules. However, after the root-formation stage, these immunoreactivities in the odontoblasts decreased in intensity. Next, to examine whether the SUMOylation participates in dentin regeneration, we evaluated the distribution of SUMOs and Osterix in the dental pulp after cavity preparation. In the coronal pulp chamber of an untreated rat molar, odontoblasts and pulp cells showed no immunoreactivity. At 4 days after cavity preparation, positive cells for SUMOs and Osterix appeared on the surface of the dentin beneath the cavity. Odontoblast-like cells forming reparative dentin were immunopositive for SUMOs and Osterix at 1 week, whereas these immunoreactivities disappeared after 8 weeks. Additionally, we further analyzed the capacity of SUMO-1 to bind Osterix by performing an immunoprecipitation assay using C2C12 cells, and showed that Osterix could undergo SUMOylation. These results suggest that SUMOylation might regulate the transcriptional activity of Osterix in odontoblast lineage cells, and thus play important roles in odontoblast differentiation and regeneration.

Bone-derived IGF mediates crosstalk between bone and breast cancer cells in bony metastases

The continuous release of bone-stored growth factors after bone resorption promotes the colonization of circulating cancer cells. However, the precise role of each of the various growth factors remains unclear. In this study, we investigated the role of bone-derived insulin-like growth factor (IGF) in the development of bone metastases in an animal model of breast cancer. We found that local stimulation of calvarial bone resorption before cell inoculation stimulated subsequent bone metastases to that site in vivo, although inhibition of bone resorption inhibited bone metastases. Anchorage-independent growth of cancer cells was stimulated by the culture supernatants from resorbed bones, which contained elevated levels of IGF-I. This stimulation was blocked by IGF type I receptor (IGF-IR) neutralizing antibody, but not antibody targeting other bone-stored growth factors including TGF-β, fibroblast growth factors, and platelet-derived growth factors. Although recombinant human IGF-I caused IGF-IR tyrosine autophosphorylation, followed by activation of Akt and NF-κB in cancer cells, dominant-negative inhibition of IGF-IR, Akt, or NF-κB significantly reduced bone metastases with increased apoptosis and decreased mitosis in metastatic cells. Together, our findings suggest that bone-derived IGF-I bridges the crosstalk between bone and metastasized cancer cells via activation of the IGF-IR/Akt/NF-κB pathway. Disruption of this pathway therefore may represent a promising therapeutic intervention for bone metastasis.

Effects of tiotropium on sympathetic activation during exercise in stable chronic obstructive pulmonary disease patients

BACKGROUND

Tiotropium partially relieves exertional dyspnea and reduces the risk of congestive heart failure in chronic obstructive pulmonary disease (COPD) patients. However, its effect on the sympathetic activation response to exercise is unknown.

AIMS

This study aimed to determine whether tiotropium use results in a sustained reduction in sympathetic activation during exercise.

METHODS

We conducted a 12-week, open-label (treatments: tiotropium 18 μg or oxitropium 0.2 mg × 3 mg), crossover study in 17 COPD patients. Treatment order was randomized across subjects. The subjects underwent a pulmonary function test and two modes of cardiopulmonary exercise (constant work rate and incremental exercise) testing using a cycle ergometer, with measurement of arterial catecholamines after each treatment period.

RESULTS

Forced expiratory volume in 1 second and forced vital capacity were significantly larger in the tiotropium treatment group. In constant exercise testing, exercise endurance time was longer, with improvement in dyspnea during exercise and reduction in dynamic hyperinflation in the tiotropium treatment group. Similarly, in incremental exercise testing, exercise time, carbon dioxide production, and minute ventilation at peak exercise were significantly higher in the tiotropium treatment group. Plasma norepinephrine concentrations and dyspnea intensity were also lower during submaximal isotime exercise and throughout the incremental workload exercise in the tiotropium treatment group.

CONCLUSION

Tiotropium suppressed the increase of sympathetic activation during exercise at the end of the 6-week treatment, as compared with the effect of oxipropium. This effect might be attributed to improvement in lung function and exercise capacity and reduction in exertional dyspnea, which were associated with decreases in respiratory frequency and heart rate and reduced progression of arterial acidosis.

Effects of oxygen on exertional dyspnoea and exercise performance in patients with chronic obstructive pulmonary disease

BACKGROUND AND OBJECTIVE

The results of studies on the oxygen response in patients with COPD should provide important clues to the pathophysiology of exertional dyspnoea. We investigated the exercise responses to hyperoxia in relation to dyspnoea profile, as well as cardiopulmonary, acidotic and sympathetic parameters in 35 patients with stable COPD (mean FEV(1) 46% predicted).

METHODS

This was a single-blind trial, in which patients breathed 24% O(2) or compressed air (CA) in random order during two incremental cycle exercise tests.

RESULTS

PaO(2) and PaCO(2) were higher (P < 0.0001 and P < 0.05, respectively) at each exercise point while patients were breathing 24% O(2) compared with CA. At a standardized time point near peak exercise, use of O(2) resulted in reduced plasma lactate and plasma noradrenaline concentrations (P < 0.01). Peak minute ventilation/indirect maximum voluntary ventilation was similar while breathing 24% O(2) and CA. At peak exercise, the dyspnoea score, pH and plasma noradrenaline concentrations were similar while breathing 24% O(2) and CA. The dyspnoea-ratio (%) of Δoxygen uptake (peak minus resting oxygen uptake) curve reached a break point that occurred at a similar exercise point while breathing 24% O(2) or CA.

CONCLUSIONS

Regardless of whether they breathed CA or 24% O(2) , patients with COPD did not develop ventilatory compensation for exertional acidosis, and the pH values measured were similar. Hyperoxia during a standardized exercise protocol did not alter the pattern of exertional dyspnoea in these patients, compared with breathing CA, although hyperoxia resulted in miscellaneous effects.

1α,25-Dihydroxyvitamin D3 inhibits osteoblastic differentiation of mouse periodontal fibroblasts

OBJECTIVE

Periodontal ligament (PDL) is a non-mineralized tissue connecting cementum and alveolar bone. Recent studies have suggested that periodontal fibroblasts can differentiate into mineralized tissue-forming cells such as osteoblasts and cementoblasts. We elucidated the immunolocalization of vitamin D receptor (VDR) and the effects of vitamin D(3) (VD(3)) on mouse periodontal fibroblasts to clarify the role of VDR and VD(3) in the differentiation of periodontal fibroblasts.

DESIGN

Immunohistochemical analysis using anti-VDR antibody was performed in paraffin sections of mouse mandibles at E13, E14, E17, P10, and P35. The roles of VD(3) in osteoblastic differentiation and mineralization were estimated by alkaline phosphatase (ALP) and alizarin red (AR) staining. In addition, the mRNA expression of osteoblast markers and mineralization inhibitors was examined by real-time PCR.

RESULTS

At the bud, cap and early bell stages, immunoreactivity for VDR was scarcely seen in the cells of dental follicles. Labelling was detected in the nuclei of cemetoblasts, periodontal fibroblasts and osteoblasts during root formation. VD(3) inhibited ALP activity and AR-positive mineralized nodule formation of periodontal fibroblasts in osteogenic culture medium. Real-time PCR revealed that VD(3) down-regulated the levels of osteoblast markers. In contrast, VD(3) significantly up-regulated the level of periodontal ligament associated protein (PLAP)-1, a negative regulator of osteoblastic differentiation.

CONCLUSION

These results suggest that VD(3) negatively regulates the osteoblastic differentiation of mouse periodontal fibroblasts and prevents the periodontal ligament from mineralization via increase of PLAP-1.

Involvement of acidic microenvironment in the pathophysiology of cancer-associated bone pain

Bone pain is one of the most common complications in cancer patients with bone metastases. Although the mechanism of cancer-associated bone pain is poorly understood, clinical observations that inhibitors of osteoclasts such as bisphosphonates (BPs) efficiently reduce bone pain suggest a potential role of osteoclasts, which play a central role in the development and progression of bone metastasis. Osteoclasts dissolve bone minerals by releasing protons through the a3 isoform of the vacuolar-H(+)-ATPase, creating acidic microenvironments. In addition, cancer cells, inflammatory cells and immune cells that reside in bone metastases also produce acidic conditions by releasing protons. It has been well-known that acidic conditions due to proton release cause pain. Our study showed that the sensory nociceptive neurons innervate bone and these neurons express acid-sensing nociceptors such as the acid-sensing ion channels and transient receptor potential channel-vanilloid subfamily members. Acid signals received by these nociceptors subsequently activate intracellular signaling pathways and transcription factors in sensory neurons. The understanding of the nociceptive events following proton release and subsequent creation of acidic microenvironments leads us to design novel molecular-based approaches for reducing bone pain associated with cancer and inflammation.

Side population in MDA-MB-231 human breast cancer cells exhibits cancer stem cell-like properties without higher bone-metastatic potential

An increasing body of evidence suggests that cancers contain a small subset of their own stem-like cells called cancer stem cells (CSCs), which play critical roles in the initiation, maintenance and relapse of tumors. However, the role of CSCs in cancer metastasis, especially in metastasis to bone, has not been extensively studied. Side population (SP) has been shown to enrich CSCs in several types of cancer, including breast cancer. In the present study, we characterized the SP cells isolated from the human breast cancer cell line MDA-MB-231 in comparison to non-SP (NSP). Fluorescence-activated cell sorter analysis demonstrated the existence of SP in MDA-MB-231 cells, which was markedly reduced in the presence of fumitremorgin C, a specific inhibitor of ATP-binding cassette sub-family G member 2 (ABCG2). Quantitative RT-PCR analysis showed that ABCG2 mRNA expression was significantly higher in SP cells than in NSP cells. SP cells formed increased numbers of tumor-spheres in suspension culture. Furthermore, the tumor growth in the orthotopic mammary fat pad in nude mice was significantly accelerated in SP cells. On the other hand, the development of bone metastases determined by intracardiac injection into nude mice showed no difference between SP and NSP cells. SP abundance in the tumor cells isolated from the bone metastases was not increased either compared with that from the mammary tumors. These results suggest that the SP in MDA-MB-231 cells possesses some of the CSC-like properties but does not have higher metastatic potential to bone.

[Susceptibility to rifabutin and novel fluoroquinolones in Mycobacterium avium complex isolates from patients with sputum culture-positive pulmonary disease who are undergoing standard chemotherapy]

We investigated the susceptibility to conventional and newer antimycobacterial agents including rifabutin (RBT) and novel fluoroquinolones (NFQs) among 48 clinical Mycobacterium avium complex (MAC) isolates from patients with sputum culture-positive MAC disease who were undergoing standard chemotherapy. RBT and NFQs were superior to conventional agents because of higher rates of susceptibility and lower minimum inhibitory concentration. NFQs showed cross-resistance among quinolones. In contrast, RBT did not show cross-resistance to RFP. Most clarithromycin-resistant or rifampicin-resistant cases were susceptible to RBT and NFQs. In conclusion, RBT and NFQs possess good in vitro antimicrobial activity among clinical isolates of culture-positive pulmonary MAC disease, which suggests that a combination of such microbiologically active agents may improve clinical effectiveness more than standard chemotherapy regimens.

Acid activation of Trpv1 leads to an up-regulation of calcitonin gene-related peptide expression in dorsal root ganglion neurons via the CaMK-CREB cascade: a potential mechanism of inflammatory pain

Increased CGRP expression in sensory neurons is associated with inflammatory pain. We examined the molecular basis of CGRP expression and found that acid-sensing nociceptor Trpv1 is activated under inflammatory acidic environments and up-regulates the CGRP expression through CaMK-CREB cascade.

Increased production of calcitonin gene-related peptide (CGRP) in sensory neurons is implicated in inflammatory pain. The inflammatory site is acidic due to proton release from infiltrating inflammatory cells. Acid activation of peripheral nociceptors relays pain signals to the CNS. Here, we examined whether acid activated the transient receptor potential vanilloid subtype 1 (Trpv1), a widely recognized acid-sensing nociceptor and subsequently increased CGRP expression. Chemically induced inflammation was associated with thermal hyperalgesia and increased CGRP expression in dorsal root ganglion (DRG) in rats. In organ cultures of DRG, acid (pH 5.5) elevated CGRP expression and the selective Trpv1 antagonist 5′-Iodoresiniferatoxin decreased it. Trpv1-deficient DRG showed reduced CGRP increase by acid. Of note, many of CGRP/Trpv1-positive DRG neurons exhibited the phosphorylation of cAMP response element-binding protein (CREB), a nociceptive transcription factor. Knockdown of CREB by small interfering RNA or a dominant-negative form of CREB diminished acid-elevated CGRP expression. Acid elevated the transcriptional activity of CREB, which in turn stimulated CGRP gene promoter activity. These effects were inhibited by a Ca²⁺/calmodulin-dependent protein kinase (CaMK) inhibitor KN-93. In conclusion, our results suggest that inflammatory acidic environments activate Trpv1, leading to an up-regulation of CGRP expression via CaMK-CREB cascade, a series of events that may be associated with inflammatory pain.

Administration of the bisphosphonate zoledronic acid during tooth development inhibits tooth eruption and formation and induces dental abnormalities in rats

Bisphosphonates (BPs) are potent inhibitors of osteoclastic bone resorption and widely used for the treatment of osteoporosis and metastatic bone diseases. Recently, BPs have also been shown to benefit children with primary and secondary osteoporosis, including osteogenesis imperfecta; however, their long-term safety has not been established yet. Clinical and experimental studies have demonstrated that BPs delay or inhibit tooth eruption. The failure of tooth eruption causes several dental abnormalities. In this study, to determine the effects of BPs on tooth formation, the BP zoledronic acid (ZOL) was injected into 7- and 14-day-old rats, and the development of the mandibular teeth was examined. X-ray analysis demonstrated that ZOL inhibited the eruption of both incisors and molars and their formation, especially in the molar roots. Histological examination showed that, in ZOL-treated animals, alveolar bone remained unresorbed around tooth crowns, which injured ameloblasts and enamel matrix, leading to defects of the enamel. Furthermore, haphazard proliferation of odontogenic epithelium and mesenchyme associated with primitive tooth structures, which resembles human odontomas, was induced at the basal end of incisors but not around the molars. Tooth ankylosis to alveolar bone was occasionally observed in molars. These results suggest that administration of BPs during tooth development has the potential to inhibit tooth eruption and formation and to induce several types of dental abnormalities, which may be attributed to the altered osteoclastic activities.

Exertional dyspnea-related acidotic and sympathetic responses in patients with sequelae of pulmonary tuberculosis

The objective of this study was to investigate whether exertional dyspnea correlates with exercise responses, especially arterial blood pH and plasma norepinephrine (NE) changes, in patients with sequelae of tuberculosis (TBsq). Cardiopulmonary exercise testings were performed in 49 TBsq patients and 9 controls. Each group had a break point in the dyspnea, plasma lactate, and plasma NE changes during exercise, all of which occurred at a similar exercise point. In TBsq patients in both exercise phases before and after the dyspnea break point, the dyspnea-slope (DeltaBorg scale/Deltaminute ventilation) correlated with the pH-slope (DeltapH/Deltaoxygen uptake) (r = -0.616, p < 0.0001; r = -0.629, p < 0.0001, respectively, before and after the break point) and with the NE-slope (DeltaNE/Deltaoxygen uptake) (r = 0.443, p = 0.0012; r = 0.643, p < 0.0001, respectively, before and after the break point). In TBsq patients during exercise, increases in circulating NE levels and exertional acidosis were correlated with exertional dyspnea.

Zoledronic acid delays wound healing of the tooth extraction socket, inhibits oral epithelial cell migration, and promotes proliferation and adhesion to hydroxyapatite of oral bacteria, without causing osteonecrosis of the jaw, in mice

Nitrogen-containing bisphosphonates such as zoledronic acid (ZOL) and pamidronate have been widely and successfully used for the treatment of cancer patients with bone metastases and/or hypercalcemia. Accumulating recent reports have shown that cancer patients who have received these bisphosphonates occasionally manifest bisphosphonate-related osteonecrosis of the jaw (BRONJ) following dental treatments, including tooth extraction. However, little is known about the pathogenesis of BRONJ to date. Here, to understand the underlying pathogenesis of BRONJ, we examined the effects of ZOL on wound healing of the tooth extraction socket using a mouse tooth extraction model. Histomorphometrical analysis revealed that the amount of new bone and the numbers of blood vessels in the socket were significantly decreased in ZOL-treated mice compared to control mice. Consistent with these results, ZOL significantly inhibited angiogenesis induced by vascular endothelial growth factor in vivo and the proliferation of endothelial cells in culture in a dose-dependent manner. In contrast, etidronate, a non-nitrogen-containing bisphosphonate, showed no effects on osteogenesis and angiogenesis in the socket. ZOL also suppressed the migration of oral epithelial cells, which is a crucial step for tooth socket closure. In addition, ZOL promoted the adherence of Streptococcus mutans to hydroxyapatite and the proliferation of oral bacteria obtained from healthy individuals, suggesting that ZOL may increase the bacterial infection. In conclusion, our data suggest that ZOL delays wound healing of the tooth extraction socket by inhibiting osteogenesis and angiogenesis. Our data also suggest that ZOL alters oral bacterial behaviors. These actions of ZOL may be relevant to the pathogenesis of BRONJ.

Localization of Thy-1-positive cells in the perichondrium during endochondral ossification

We elucidated the localization of Thy-1-positive cells in the perichondrium of fetal rat limb bones to clarify the distribution of osteogenic cells in the process of endochondral ossification. We also examined the formation of calcified bone-like matrices by isolated perichondrial cells in vitro. At embryonic day (E) 15.5, when the cartilage primodia were formed, immunoreactivity for Thy-1 was detected in cells of the perichondrium adjacent to the zone of hypertrophic chondrocytes. At E17.5, when the bone collar formation and the vascular invasion were initiated, fibroblast-like cells at the sites of vascular invasion, as well as in the perichondrium, showed Thy-1 labeling. Double immunostaining for Thy-1 and osterix revealed that Thy-1 was not expressed in the osterix-positive osteoblasts. Electron microscopic analysis revealed that Thy-1-positive cells in the zone of hypertrophic chondrocytes came in contact with blood vessels. Perichondrial cells isolated from limb bones showed alkaline phosphatase activity and formed calcified bone-like matrices after 4 weeks in osteogenic medium. RT-PCR demonstrated that Thy-1 expression decreased as calcified nodules formed. Conversely, the expression of osteogenic marker genes Runx2, osterix, and osteocalcin increased. These results indicate that Thy-1 is a good marker for characterizing osteoprogenitor cells.

Acidosis and raised norepinephrine levels are associated with exercise dyspnoea in idiopathic pulmonary fibrosis

BACKGROUND AND OBJECTIVE

Exertional dyspnoea limits patients with IPF in their activities of daily living. The mechanism, however, has not been elucidated. This study tested the hypothesis in IPF that exertional dyspnoea correlates with cardiopulmonary exercise responses, specifically changes in arterial blood pH and plasma norepinephrine (NE).

METHODS

Cardiopulmonary exercise testing with measurements of dyspnoea (Borg scale), plasma NE, plasma lactate and arterial blood gases were performed in 29 patients with IPF and in nine controls.

RESULTS

Both groups showed obvious break points in dyspnoea changes during exercise. In IPF, an abrupt change in the Borg scale, pH, PaCO(2) and plasma NE occurred in the late exercise phase after the 'break point'. Compared with controls, patients with IPF had significantly higher HCO(3)(-) levels and physiologic dead space/tidal volume during exercise. In IPF, during both exercise phases, the dyspnoea slope (DeltaBorg scale/Deltaminute ventilation) correlated with the pH slope (DeltapH/Deltaoxygen uptake) (before the break point: r = -0.537, P = 0.0022; r = -0.886, P < 0.0001, after the break point) and the NE slope (DeltaNE/Deltaoxygen uptake) (before the break point: r = 0.481, P = 0.0075; R = 0.784, P < 0.0001, after the break point).

CONCLUSIONS

In patients with IPF, exercise-induced acidosis and increases in circulating NE levels were associated with intensity of exertional dyspnoea.

Formation of bone-like mineralized matrix by periodontal ligament cells in vivo: a morphological study in rats

Periodontal ligament (PDL) is a unique connective tissue that not only connects cementum and alveolar bone to support teeth, but also plays an important role in reconstructing periodontal tissues. Previous studies have suggested that PDL cells have osteogenic potential; however, they lack precise histological examinations. Here, we studied bone-like matrix formation by PDL cells in rats using morphological techniques. Rat and human PDL cells exhibited substantial alkaline phosphatase activity and induced mineralization in vitro. RT-PCR analyses showed that PDL cells expressed the osteoblast markers, Runx2, osterix, and osteocalcin. These results suggest that PDL cells share similar phenotypes with osteoblasts. To examine the bone-like matrix formation in vivo, PDL cells isolated from green fluorescent protein (GFP)-transgenic rats were inoculated with hydroxyapatite (HA) disks into wild-type rats. Five weeks after the implantation, the pores in HA disks were occupied by GFP-positive cells. Mineralized matrix formation was also found on the surface of HA pores. At 12 weeks, some of the pores were filled with bone-like mineralized matrices (BLMM), which were positive for the bone matrix proteins, osteopontin, bone sialoprotein, and osteocalcin. Immunohistochemical examination revealed that most of the osteoblast- and osteocyte-like cells on or in the BLMM were GFP-positive, suggesting that the BLMM were directly formed by the inoculated PDL cells. On the pore surfaces, Sharpey's fiber-like structures embedded in cementum-like mineralized layers were also observed. These results collectively suggest that PDL cells have the ability to form periodontal tissues and could be a useful source for regenerative therapies of periodontal diseases.

Cadherin-11-mediated interactions with bone marrow stromal/osteoblastic cells support selective colonization of breast cancer cells in bone

Cell adhesion molecules have been implicated in the selective colonization of cancer in distant organs. Breast cancer has a strong predilection for spreading to bone. Cadherin-11, which is one of the classical type-2 cadherin family members and mediates homophilic cell-cell adhesion, is constitutively expressed in stromal and osteoblastic cells in bone marrow. Elevated cadherin-11 expression is also found in aggressive human breast cancers. Here, we investigated the role of the interactions between breast cancer cells and bone marrow stromal/osteoblastic cells via cadherin-11 in the selective spread to bone. The bone-seeking clone of the MDA-MB-231 human breast cancer cells showed greater cadherin-11 expression than the parental and the brain-seeking clone. Cadherin-11 overexpression in MDA-MB-231 cells increased bone metastases with promoted bone resorption, while the natural variant form of cadherin-11 that is unable to establish cell-cell adhesion did not. Of note, introduction of cadherin-11 showed no effects on lung metastases. Fluorescence-activated cell sorter analysis using the fluorescent dye-labeled cancer cells showed that early colonization in bone marrow was increased by cadherin-11. Co-cultures with the MC3T3-E1 osteoblastic cells that constitutively expressed cadherin-11 caused an up-regulation of parathyroid hormone-related protein (PTH-rP) production in MDA-MB-231 cells overexpressing cadherin-11. The conditioned medium of the co-cultures increased osteoclastogenesis, which was blocked by a neutralizing antibody to PTH-rP. In conclusion, our results suggest that cadherin-11 promotes homing and migration to bone and osteoclastogenesis through mediating the homophilic interactions of breast cancer cells with marrow stromal/osteoblastic cells, thereby enhancing bone metastases.

Alveolar bone regeneration of subcutaneously transplanted rat molar

Regeneration of alveolar bone is essential for periodontal treatment. Recently, cell replacement therapy has been focused on periodontal disease, but the source of the cells that regenerate alveolar bone is still uncertain. Therefore, to clarify the source of these bone-regenerating cells, we transplanted GFP-transgenic rat molars into the subcutaneous tissues of wild-type rats. Five days after transplantation, the tooth was surrounded by connective tissue containing many blood vessels. At 10 days, bone-like tissue was formed in the connective tissue between the branches of the bifurcated root. This hard tissue expanded to almost all of this bifurcation area without osseous ankylosis after 20 days. All osteoblast-like cells in the newly formed matrix were immunopositive for GFP. In addition, these cells and the peripheral cells of the matrix showed intense immunoreactivity for BMP4, Runx2, BSP, and OPN. These results demonstrate that periodontal ligament tissue contains osteoprogenitor cells that have the ability to regenerate alveolar bone. Our model suggests that these regeneration processes might be similar to normal alveolar bone formation.

Involvement of cell-cell and cell-matrix interactions in bone destruction induced by metastatic MDA-MB-231 human breast cancer cells in nude mice

To clarify the mechanisms of bone destruction associated with bone metastases, we studied an animal model in which inoculation of MDA-MB-231 human breast cancer cells into the left cardiac ventricle of female nude mice causes osteolytic lesions in bone using morphological techniques. On the bone surfaces facing the metastatic tumor cells, there existed many tartrate-resistant acid phosphatase (TRAP)-positive multinucleated osteoclasts. TRAP-positive mononuclear osteoclast precursor cells were also observed in the tumor nests. Immunohistochemical studies showed that the cancer cells produced parathyroid hormone-related protein (PTHrP) but not receptor activator of NF-kappaB ligand (RANKL). Histochemical and immunohistochemical examinations demonstrated that alkaline phosphatase and RANKL-positive stromal cells were frequently adjacent to TRAP-positive osteoclast-like cells. Immunoelectron microscopic observation revealed that osteoclast-like cells were in contact with RANKL-positive stromal cells. MDA-MB-231 cells and osteoclast-like cells in the tumor nests showed CD44-positive reactivity on their plasma membranes. Hyaluronan (HA) and osteopontin (OPN), the ligands for CD44, were occasionally colocalized with CD44. These results suggest that tumor-producing osteoclastogenic factors, including PTHrP, upregulate RANKL expression in bone marrow stromal cells, which in turn stimulates the differentiation and activation of osteoclasts, leading to the progression of bone destruction in the bone metastases of MDA-MB-231 cells. Because the interactions between CD44 and its ligands, HA and OPN, have been shown to upregulate osteoclast differentiation and function, in addition to the cell-cell interactions mediated by RANK and RANKL, the cell-matrix interactions mediated by these molecules may also contribute to the progression of osteoclastic bone destruction.