Molecular mechanisms of triggering,amplifying and targeting RANK signaling in osteoclasts

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 dif-ferentiating 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.

Changes in secretory pathway Ca^(2+)-ATPase 2 following focal cerebral ischemia/reperfusion injury

This study aimed to investigate changes in secretory pathway Ca2＋-ATPase 2 expression following cerebral ischemia/reperfusion injury, and to define the role of Ca2＋-ATPases in oxidative stress. A rat model of cerebral ischemia/reperfusion injury was established using the unilateral middle cerebral artery occlusion method. Immunohistochemistry and reverse transcription-PCR assay results showed that compared with the control group, the expression of secretory pathway Ca2＋-ATPase 2 protein and mRNA in the cerebral cortex and hippocampus of male rats did not significantly change during the ischemic period. However, secretory pathway Ca2＋-ATPase 2 protein and mRNA expression reduced gradually at 1, 3, and 24 hours during the reperfusion period. Our experimental findings indicate that levels of secretory pathway Ca2＋-ATPase 2 protein and mRNA expression in brain tissue change in response to cerebral ischemia/reperfusion injury.

Effects of Aconitine on [Ca^(2+)] Oscillation in Cultured Myocytes of Neonatal Rats

In order to investigate the effects of aconitine on [Ca2＋] oscillation patterns in cultured myocytes of neonatal rats, fluorescent Ca2＋ indicator Fluo-4 NW and laser scanning confocal micro- scope （LSCM） were used to detect the real-time changes of [Ca2＋] oscillation patterns in the cultured myocytes before and after aconitine （1.0 μmol/L） incubation or antiarrhythmic peptide （AAP） and aconitine co-incubation. The results showed under control conditions, [Ca2＋] oscillations were irregu- lar but relatively stable, occasionally accompanied by small calcium sparks. After incubation of the cultures with aconitine, high frequency [Ca2＋] oscillations emerged in both nuclear and cytoplasmic regions, whereas typical calcium sparks disappeared and the average [Ca2＋] in the cytoplasm of the cardiomyocyte did not change significantly. In AAP-treated cultures, intracellular [Ca2＋] oscillation also changed, with periodic frequency, increased amplitudes and prolonged duration of calcium sparks. These patterns were not altered significantly by subsequent aconitine incubation. The basal value of [Ca2＋] in nuclear region was higher than that in the cytoplasmic region. In the presence or absence of drugs, the [Ca2＋] oscillated synchronously in both the nuclear and cytoplasmic regions of the same cardiomyocyte. It was concluded that although oscillating strenuously at high frequency, the average [Ca2＋] in the cytoplasm of cardiomyocyte did not change significantly after aconitine incuba- tion, compared to the controls. The observations indicate that aconitine induces the changes in [Ca2＋] oscillation frequency other than the Ca2＋ overload.

Open Sesame: treasure in store-operated calcium entry pathway for cancer therapy

Store-operated Ca2+ entry(SOCE) controls intracellular Ca2+ homeostasis and regulates a wide range of cellular events including proliferation,migration and invasion.The discovery of STIM proteins as Ca2+ sensors and Orai proteins as Ca2+ channel pore forming units provided molecular tools to understand the physiological function of SOCE.Many studies have revealed the pathophysiological roles of Orai and STIM in tumor cells.This review focuses on recent advances in SOCE and its contribution to tumorigenesis.Altered Orai and/or STIM functions may serve as biomarkers for cancer prognosis,and targeting the SOCE pathway may provide a novel means for cancer treatment.