論文

NFATc1 is a transcription factor that regulates T-cell development, osteoclastogenesis, and macrophage function. Given that T cells, osteoclasts, and macrophages in the tumor microenvironment are thought to modulate tumor progression, tumor cells may acquire NFATc1 expression through fusion with these NFATc1- expressing normal cells. We here revealed that a small proportion of tumor cells in human carcinoma specimens expressed NFATc1. To investigate the consequences of NFATc1 acquisition by tumor cells, we established A549 and MCF7 cell lines expressing a constitutively active form of NFATc1 (NFATc1CA) in an inducible manner. The expression of NFATc1CA promoted cancer cell invasion in association with changes in cell morphology. Analysis of gene expression andRNAinterference experiments revealed that NFATc1CA suppressed E-cadherin expression by upregulating the transcriptional repressors Snail and Zeb1 in a manner independent of TGF-b signaling. Induced expression of NFATc1CA also downregulated E-cadherin expression and increased invasive activity in tumor xenografts in vivo. Our results thus suggest that the acquisition of NFATc1 expression contributes to tumor progression.

NFATc1 is a transcription factor that regulates T-cell development, osteoclastogenesis, and macrophage function. Given that T cells, osteoclasts, and macrophages in the tumor microenvironment are thought to modulate tumor progression, tumor cells may acquire NFATc1 expression through fusion with these NFATc1- expressing normal cells. We here revealed that a small proportion of tumor cells in human carcinoma specimens expressed NFATc1. To investigate the consequences of NFATc1 acquisition by tumor cells, we established A549 and MCF7 cell lines expressing a constitutively active form of NFATc1 (NFATc1CA) in an inducible manner. The expression of NFATc1CA promoted cancer cell invasion in association with changes in cell morphology. Analysis of gene expression andRNAinterference experiments revealed that NFATc1CA suppressed E-cadherin expression by upregulating the transcriptional repressors Snail and Zeb1 in a manner independent of TGF-b signaling. Induced expression of NFATc1CA also downregulated E-cadherin expression and increased invasive activity in tumor xenografts in vivo. Our results thus suggest that the acquisition of NFATc1 expression contributes to tumor progression.

Previous reports have identified a role for the tyrosine kinase receptor EphB4 and its ligand, ephrinB2, as potential mediators of both bone formation by osteoblasts and bone resorption by osteoclasts. In the present study, we examined the role of EphB4 during bone repair after traumatic injury. We performed femoral fractures with internal fixation in transgenic mice that overexpress EphB4 under the collagen type 1 promoter (Col1-EphB4) and investigated the bone repair process up to 12 weeks postfracture. The data indicated that Col1-EphB4 mice exhibited stiffer and stronger bones after fracture compared with wild-type mice. The fractured bones of Col1-EphB4 transgenic mice displayed significantly greater tissue and bone volume 2 weeks postfracture compared with that of wild-type mice. These findings correlated with increased chondrogenesis and mineral formation within the callus site at 2 weeks postfracture, as demonstrated by increased safranin O and von Kossa staining, respectively. Interestingly, Col1-EphB4 mice were found to possess significantly greater numbers of clonogenic mesenchymal stromal progenitor cells (CFU-F), with an increased capacity to form mineralized nodules in vitro under osteogenic conditions, when compared with those of the wild-type control mice. Furthermore, Col1-EphB4 mice had significantly lower numbers of TRAP-positive multinucleated osteoclasts within the callus site. Taken together, these observations suggest that EphB4 promotes endochondral ossification while inhibiting osteoclast development during callus formation and may represent a novel drug target for the repair of fractured bones.

Osteoclast differentiation depends on receptor activator of nuclear factor-κB (RANK) signaling, which can be divided into triggering, amplifying and targeting phases based on how active the master regulator nuclear factor of activated T-cells cytoplasmic 1 (NFATc1) is. The triggering phase is characterized by immediateearly RANK signaling induced by RANK ligand (RANKL) stimulation mediated by three adaptor proteins, tumor necrosis factor receptor-associated factor 6, Grb- 2-associated binder-2 and phospholipase C (PLC)γ2, leading to activation of IκB kinase, mitogen-activated protein kinases and the transcription factors nuclear factor (NF)-κB and activator protein-1 (AP-1). Mice lacking NF-κB p50/p52 or the AP-1 subunit c-Fos (encoded by Fos) exhibit severe osteopetrosis due to a differentiation block in the osteoclast lineage. The amplification phase occurs about 24 h later in a RANKLinduced osteoclastogenic culture when Ca2+ oscillation starts and the transcription factor NFATc1 is abundantly produced. In addition to Ca2+ oscillation-dependent nuclear translocation and transcriptional auto-induction of NFATc1, a Ca2+ oscillation-independent, osteoblastdependent mechanism stabilizes NFATc1 protein in differentiating osteoclasts. Osteoclast precursors lacking PLCγ2, inositol-1,4,5-trisphosphate receptors, regulator of G-protein signaling 10, or NFATc1 show an impaired transition from the triggering to amplifying phases. The final targeting phase is mediated by activation of numerous NFATc1 target genes responsible for cell-cell fusion and regulation of bone-resorptive function. This review focuses on molecular mechanisms for each of the three phases of RANK signaling during osteoclast differentiation.

Formulating a multi-scan method applied to an X-ray microscope CT with synchrotron radiation, we attempted to analyze the 3D functional structure of osteocyte canaliculi inside the cortical bone of a mouse tibia. We employed a two-method combination to scan the same position of the specimen. To extract the internal bone canalicular structure, we first combined a Talbot interferometer with an X-ray microscope, and applied a differential phase imaging method to measure the absolute value of bone mineral around the canaliculi. Next, we used the X-ray microscope without the Talbot interferometer under a defocus condition, moving the specimen toward the zone plate by 6 mm. This defocus contrast method visualizes the canaliculi by emphasizing the edges of the bone. We performed CT scans by the two configurations and precisely aligned resultant 3D images so that the same position in the specimen is compared. We could extract the osteocyte canaliculi and evaluate the mineral density of their surroundings. The degree of mineralization varied for each osteocyte lacuna and canaliculus. The multi-scan microscopic X-ray CT is a powerful tool for analyzing bone mineralization.

Gefitinib is an anticancer drug developed to inhibit the tyrosine kinase activity of the epidermal growth factor receptor (EGFR). Two structurally-related EGFR tyrosine kinase inhibitors, gefitinib (Iressa) and erlotinib (Tarceva), are used as oral chemotherapy by patients with non-small-cell lung cancer. Immediately after introduction of gefitinib to clinical practice, interstitial lung disease was identified as a life-threatening adverse effect, although this condition can be well managed. It is still unclear whether gefitinib and other EGFR inhibitors induce similar adverse effects in lung. We previously established mouse models of interstitial lung disease in which gefitinib induces expression of Fosl1 (which encodes the AP-1 transcription factor Fra-1) in the presence of exogenous or endogenous Toll-like receptor ligands, leading to abnormal cytokine and chemokine expression. Here, we compared and monitored the effects of EGFR inhibitors gefitinib, erlotinib and AG1517 (PD153035) on the mRNA expression levels of Fosl1, Tnf and Ccl2. Unexpectedly, gefitinib, but not the other tyrosine kinase inhibitors, elicited the Fosl1 expression profile proposed to be predictive of interstitial lung disease, suggesting that gefitinib-induced interstitial lung disease is an off-target effect not elicited by erlotinib.

Eph receptors and ephrin ligands mediate cell-cell communication during development of various tissues including the nervous system, vasculature, and skeletal system. During bone remodeling in adult mice, Eph-ephrin bidirectional signaling regulates differentiation and function of bone cells such as osteoclasts and osteoblasts. When expressed in osteoclasts, ephrinB2 and ephrinA2 act as a coupling stimulator and a coupling inhibitor, respectively, thus enhancing or suppressing osteoblast differentiation. In neurons and endothelial cells, signaling downstream of Eph-ephrin interaction often controls the actin cytoskeleton and dynamic alterations in the topology of lipid bilayers associated with endocytosis, axon guidance and angiogenesis, and mediates the switch from cell attraction to repulsion through activation of multiple effectors such as Rho family small GTPases. Here we review similarities and differences between downstream events of Eph-ephrin signaling in bone cells compared to other cell types.