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Lipocalin-2 (LCN2) is a member of the lipocalin superfamily and plays a critical role in the regulation of various physiological processes, such as inflammation and obesity. In this study, we report that LCN2 negatively modulates the proliferation and differentiation of osteoclast precursors, resulting in impaired osteoclast formation. The overexpression of LCN2 in bone marrow-derived macrophages or the addition of recombinant LCN2 protein inhibits the formation of multinuclear osteoclasts. LCN2 suppresses macrophage colony-stimulating factor (M-CSF)-induced proliferation of osteoclast precursor cells without affecting their apoptotic cell death. Interestingly, LCN2 decreases the expression of the M-CSF receptor, c-Fms, and subsequently blocks its downstream signaling cascades. In addition, LCN2 inhibits RANKL-induced osteoclast differentiation and attenuates the expression of c-Fos and nuclear factor of activated T cells c1 (NFATc1), which are important modulators in osteoclastogenesis. Mechanistically, LCN2 inhibits NF-κB signaling pathways, as demonstrated by the suppression of IκBα phosphorylation, nuclear translocation of p65, and NF-κB transcriptional activity. Thus, LCN2 is an anti-osteoclastogenic molecule that exerts its effects by retarding the proliferation and differentiation of osteoclast lineage cells. [ABSTRACT FROM AUTHOR]

Abstract: Dysregulation of transforming growth factor-β (TGF-β) signaling has been implicated in the pathogenesis of a variety of diseases including cancer; therefore, pharmacological inhibitors that target the TGF-β signaling pathway might be promising drugs for disease therapy. In this study, we investigated the mechanism of inhibition of TGF-β signaling by the Hsp90 inhibitor geldanamycin (GA). Treatment with GA suppressed TGF-β signaling, as evidenced by inhibition of TGF-β-induced phosphorylation and transcriptional activity of Smad3 and decreased induction of target genes. Western blot analysis revealed that GA induced degradation of TGF-β type I and type II receptors through a proteasome-dependent pathway. Notably, induction of Hsp70 by GA correlated with inhibition of TGF-β signaling. Suppression of Hsp70 expression by Hsp70 siRNA or KNK437, an inhibitor of Hsp70 synthesis, blocked the inhibition of TGF-β signaling by GA. Furthermore, Hsp70 interacted directly with TGF-β receptors following GA treatment. Our results suggest that GA-mediated induction of Hsp70 and its subsequent interaction with TGF-β receptors plays a crucial role in inhibition of TGF-β signaling. [Copyright &y& Elsevier]

Abstract: In activated macrophage, large amounts of nitric oxide (NO) are generated by inducible nitric oxide synthase (iNOS), resulting in acute or chronic inflammatory disorders. In Raw 264.7 cells stimulated with lipopolysaccharide (LPS) to mimic inflammation, 8-hydroxyquinoline (8HQ) inhibited the LPS-induced expression of both iNOS protein and mRNA in a parallel dose-dependent manner. 8HQ did not enhance the degradation of iNOS mRNA. To investigate the mechanism by which 8HQ inhibits iNOS gene expression, we examined the activation of MAP kinases in Raw 264.7 cells. We did not observe any significant change in the phosphorylation of MAPKs between LPS alone and LPS plus 8HQ-treated cells. Moreover, 8HQ significantly inhibited the DNA-binding activity of nuclear factor-κB (NF-κB) and CCAAT/enhancer-binding protein β (C/EBPβ), but not activator protein-1 and cAMP response element-binding protein. Taken together, these results suggest that 8HQ acts to inhibit inflammation through inhibition of NO production and iNOS expression through blockade of C/EBPβ DNA-binding activity and NF-κB activation. [Copyright &y& Elsevier]