Structural implications of the chemical modification of Cys(10) on actin.

Cys(10) is located in subdomain 1 of actin, which has an important role in the interaction of actin with myosin- and actin-binding proteins. Cys(10) was modified with fluorescence probes N-(iodoacetyl)N'-(5-sulfo-1-naphthyl)ethylene diamine (IAEDANS), 7-diethylamino-3-(4'-maleimidylphenyl)-4-methylcoumarin (CPM), or monobromo bimane (MBB) by the method of, J. Biol. Chem. 266:5508-5513). The specificity of Cys(10) modification was verified by showing that the 33-kDa subtilisin fragment of actin (residues 48-375), which contains all of the actin thiols but Cys(10), is not fluorescent. Cys(10) modification exposed a new site on actin to subtilisin cleavage. Edman degradation revealed this site to be between Ala(19) and Gly(20). The modification slightly increased the rate of epsilonATP-ATP exchange and decreased the rates of G-actin ATPase and polymerization. The activation of S1 ATPase by Cys(10)-modified F-actin showed small probe-dependent changes in the values of V(max) and K(M). The sliding speed of actin filaments in the in vitro motility assay remained unchanged upon modification of Cys(10). These results indicate that although the labeling of Cys(10) perturbs the structure of subdomain 1, the modified actin remains fully functional. The binding of S1 to actin filaments decreases the accessibility of Cys(10) probes to acrylamide and nitromethane quenchers. Because Cys(10) does not participate directly in either actin polymerization or S1 binding, our results indicate that actin-actin and actin-myosin interactions induce dynamic, allosteric changes in actin structure

Langerhans cells down-regulate inflammation-driven alveolar bone loss

Excessive bone resorption is frequently associated with chronic infections and inflammatory diseases. Whereas T cells were demonstrated to facilitate osteoclastogenesis in such diseases, the role of dendritic cells, the most potent activators of naive T cells, remains unclear. Using a model involving inflammation-driven alveolar bone loss attributable to infection, we showed that in vivo ablation of Langerhans cells (LCs) resulted in enhanced bone loss. An increased infiltration of B and T lymphocytes into the tissue surrounding the bone was observed in LC-ablated mice, including receptor activator of NF-kappa B ligand (RANKL)-expressing CD4(+) T cells with known capabilities of altering bone homeostasis. In addition, the absence of LCs significantly reduced the numbers of CD4(+)Foxp3(+) T-regulatory cells in the tissue. Further investigation revealed that LCs were not directly involved in presenting antigens to T cells. Nevertheless, despite their low numbers in the tissue, the absence of LCs resulted in an elevated activation of CD4(+) but not CD8(+) T cells. This activation involved elevated production of IFN-gamma but not IL-17 or IL-10 cytokines. Our data, thus, reveal a protective immunoregulatory role for LCs in inflammation-induced alveolar bone resorption, by inhibiting IFN-gamma secretion and excessive activation of RANKL(+)CD4(+) T cells with a capability of promoting osteoclastogenesis

Langerhans cells down-regulate inflammation-driven alveolar bone loss

Excessive bone resorption is frequently associated with chronic infections and inflammatory diseases. Whereas T cells were demonstrated to facilitate osteoclastogenesis in such diseases, the role of dendritic cells, the most potent activators of naive T cells, remains unclear. Using a model involving inflammation-driven alveolar bone loss attributable to infection, we showed that in vivo ablation of Langerhans cells (LCs) resulted in enhanced bone loss. An increased infiltration of B and T lymphocytes into the tissue surrounding the bone was observed in LC-ablated mice, including receptor activator of NF-κB ligand (RANKL)-expressing CD4+ T cells with known capabilities of altering bone homeostasis. In addition, the absence of LCs significantly reduced the numbers of CD4+Foxp3+ T-regulatory cells in the tissue. Further investigation revealed that LCs were not directly involved in presenting antigens to T cells. Nevertheless, despite their low numbers in the tissue, the absence of LCs resulted in an elevated activation of CD4+ but not CD8+ T cells. This activation involved elevated production of IFN-γ but not IL-17 or IL-10 cytokines. Our data, thus, reveal a protective immunoregulatory role for LCs in inflammation-induced alveolar bone resorption, by inhibiting IFN-γ secretion and excessive activation of RANKL+CD4+ T cells with a capability of promoting osteoclastogenesis

Langerhans cells down-regulate inflammation-driven alveolar bone loss

Excessive bone resorption is frequently associated with chronic infections and inflammatory diseases. Whereas T cells were demonstrated to facilitate osteoclastogenesis in such diseases, the role of dendritic cells, the most potent activators of naive T cells, remains unclear. Using a model involving inflammation-driven alveolar bone loss attributable to infection, we showed that in vivo ablation of Langerhans cells (LCs) resulted in enhanced bone loss. An increased infiltration of B and T lymphocytes into the tissue surrounding the bone was observed in LC-ablated mice, including receptor activator of NF-κB ligand (RANKL)-expressing CD4(+) T cells with known capabilities of altering bone homeostasis. In addition, the absence of LCs significantly reduced the numbers of CD4(+)Foxp3(+) T-regulatory cells in the tissue. Further investigation revealed that LCs were not directly involved in presenting antigens to T cells. Nevertheless, despite their low numbers in the tissue, the absence of LCs resulted in an elevated activation of CD4(+) but not CD8(+) T cells. This activation involved elevated production of IFN-γ but not IL-17 or IL-10 cytokines. Our data, thus, reveal a protective immunoregulatory role for LCs in inflammation-induced alveolar bone resorption, by inhibiting IFN-γ secretion and excessive activation of RANKL(+)CD4(+) T cells with a capability of promoting osteoclastogenesis