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Title: Increases in Calmodulin Abundance and Stabilization of Activated iNOS Mediate Bacterial Killing in RAW 264.7 Macrophages

Abstract

The rapid activation of macrophages in response to bacterial antigens is central to the innate immune system that permits the recognition and killing of pathogens to limit infection. To understand regulatory mechanisms underlying macrophage activation, we have investigated changes in the abundance of calmodulin (CaM) and iNOS in response to the bacterial cell wall component lipopolysaccharide (LPS) using RAW 264.7 macrophages. Critical to these measurements was the ability to differentiate free iNOS from the CaM-bound (active) form of iNOS associated with nitric oxide generation. We observe a rapid two-fold increase in CaM abundance during the first 30 minutes that is blocked by inhibition of NF?B nuclear translocation or protein synthesis. A similar two-fold increase in the abundance of the complex between CaM and iNOS is observed with the same time dependence. In contrast, there are no detectable increases in the CaM-free (i.e., inactive) form of iNOS within the first hour; it remains at a very low abundance during the initial phase of macrophage activation. Increasing cellular CaM levels in stably transfected cells results in a corresponding increase in the abundance of the CaM/iNOS complex that promotes effective bacterial killing following challenge by Salmonella typhimurium. Thus, LPS-dependent increases in CaM abundancemore » function in the stabilization and activation of iNOS on the rapid time-scale associated with macrophage activation and bacterial killing. These results explain how CaM and iNOS coordinately function to form a stable complex that is part of a rapid host-response that functions within the first 30 minutes following bacterial infection to up-regulate the innate immune system involving macrophage activation.« less

Authors:
; ;
Publication Date:
Research Org.:
Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
891139
Report Number(s):
PNWD-SA-7421
TRN: US200621%%583
DOE Contract Number:
AC05-76RL01830
Resource Type:
Journal Article
Resource Relation:
Journal Name: Biochemistry, 45(32):9717-9726
Country of Publication:
United States
Language:
English
Subject:
59 BASIC BIOLOGICAL SCIENCES; 60 APPLIED LIFE SCIENCES; ABUNDANCE; ANTIGENS; CALMODULIN; CELL WALL; LIPOPOLYSACCHARIDES; MACROPHAGES; NITRIC OXIDE; PATHOGENS; PROTEINS; SALMONELLA TYPHIMURIUM; STABILIZATION; SYNTHESIS; TIME DEPENDENCE; TRANSLOCATION; signal transduction; macrophage; pathogen; sensors

Citation Formats

Smallwood, Heather S., Shi, Liang, and Squier, Thomas C. Increases in Calmodulin Abundance and Stabilization of Activated iNOS Mediate Bacterial Killing in RAW 264.7 Macrophages. United States: N. p., 2006. Web. doi:10.1021/bi060485p.
Smallwood, Heather S., Shi, Liang, & Squier, Thomas C. Increases in Calmodulin Abundance and Stabilization of Activated iNOS Mediate Bacterial Killing in RAW 264.7 Macrophages. United States. doi:10.1021/bi060485p.
Smallwood, Heather S., Shi, Liang, and Squier, Thomas C. Tue . "Increases in Calmodulin Abundance and Stabilization of Activated iNOS Mediate Bacterial Killing in RAW 264.7 Macrophages". United States. doi:10.1021/bi060485p.
@article{osti_891139,
title = {Increases in Calmodulin Abundance and Stabilization of Activated iNOS Mediate Bacterial Killing in RAW 264.7 Macrophages},
author = {Smallwood, Heather S. and Shi, Liang and Squier, Thomas C.},
abstractNote = {The rapid activation of macrophages in response to bacterial antigens is central to the innate immune system that permits the recognition and killing of pathogens to limit infection. To understand regulatory mechanisms underlying macrophage activation, we have investigated changes in the abundance of calmodulin (CaM) and iNOS in response to the bacterial cell wall component lipopolysaccharide (LPS) using RAW 264.7 macrophages. Critical to these measurements was the ability to differentiate free iNOS from the CaM-bound (active) form of iNOS associated with nitric oxide generation. We observe a rapid two-fold increase in CaM abundance during the first 30 minutes that is blocked by inhibition of NF?B nuclear translocation or protein synthesis. A similar two-fold increase in the abundance of the complex between CaM and iNOS is observed with the same time dependence. In contrast, there are no detectable increases in the CaM-free (i.e., inactive) form of iNOS within the first hour; it remains at a very low abundance during the initial phase of macrophage activation. Increasing cellular CaM levels in stably transfected cells results in a corresponding increase in the abundance of the CaM/iNOS complex that promotes effective bacterial killing following challenge by Salmonella typhimurium. Thus, LPS-dependent increases in CaM abundance function in the stabilization and activation of iNOS on the rapid time-scale associated with macrophage activation and bacterial killing. These results explain how CaM and iNOS coordinately function to form a stable complex that is part of a rapid host-response that functions within the first 30 minutes following bacterial infection to up-regulate the innate immune system involving macrophage activation.},
doi = {10.1021/bi060485p},
journal = {Biochemistry, 45(32):9717-9726},
number = ,
volume = ,
place = {United States},
year = {Tue Aug 01 00:00:00 EDT 2006},
month = {Tue Aug 01 00:00:00 EDT 2006}
}
  • Understanding the molecular mechanisms that modulate macrophage radioresistance is necessary for the development of effective radiation therapies, as tumor-associated macrophages promote both angiogenesis and matrix remodeling that, in turn, enhance metastasis. In this respect, we have identified a dose-dependent increase in the abundance of the calcium regulatory protein calmodulin (CaM) in RAW 264.7 macrophages upon irradiation. CaM overexpression results in increased macrophage survival following radiation exposure, acting to diminish the sensitivity to low-dose exposures. Increases in CaM abundance also result in an increase in the number of phosphorylated histone H2AX protein complexes associated with DNA repair following macrophage irradiation, withmore » no change in the extent of double-stranded DNA damage. In comparison, when NFκB-dependent pathways are inhibited, through the expression of a dominant-negative IκB construct, there is no significant increase in phosphorylated H2AX upon irradiation. These results indicate that the molecular basis for the up-regulation of histone H2AX mediated DNA-repair pathways is not the result of nonspecific NFκB-dependent pathways or a specific threshold of DNA damage. Rather, increases in CaM abundance act to minimize the low-dose hypersensitivity to radiation to enhance macrophage radioresistance through processes that include the upregulation of DNA repair pathways involving histone protein H2AX phosphorylation.« less
  • ABSTRACT: To evade host resistance mechanisms, Salmonella enterica serovar Typhimurium (STM), a facultative intracellular pathogen, must alter its proteome following macrophage infection. To identify new colonization and virulence factors that mediate STM pathogenesis, we have isolated STM cells from RAW 264.7 macrophages at various time-points following infection and used a liquid chromatography-mass spectrometry (LC-MS)-based proteomic approach to detect the changes in STM protein abundances. Because host resistance to STM infection is strongly modulated by the expression of a functional host resistant regulator, i.e., natural resistance associated macrophage protein 1 (Nramp1, also called Slc11a1), we have also examined the effects ofmore » Nramp1 activity on the changes of STM protein abundances. A total of 315 STM proteins have been identified from isolated STM cells, which are largely house-keeping proteins whose abundances remain relatively constant during the time-course of infection. However, 39 STM proteins are strongly induced after infection, suggesting their involvement in modulating colonization and infection. Of the 39 induced proteins, 6 proteins are specifically modulated by Nramp1 activity, including STM3117, as well as STM3118-3119 whose time-dependent abundance changes were confirmed using Western blot analysis. Deletion of the gene encoding STM3117 resulted in a dramatic reduction in the ability of STM to colonize wild-type RAW 264.7 macrophages, demonstrating a critical involvement of STM3117 in promoting the replication of STM inside macrophages. The predicted function common for STM3117-3119 is biosynthesis and modification of the peptidoglycan layer of STM cell wall, emphasizing their important roles in the colonization of macrophages by Salmonella.« less
  • Inflammatory responses stimulated by bacterial endotoxin (lipopolysaccharide, LPS) involve calcium-mediated signaling, yet the cellular sensors that determine cell fate in response to LPS remain poorly understood. We report that exposure of RAW 264.7 macrophage-like cells to LPS induces a rapid increase in calmodulin (CaM) abundance, which is associated with the modulation of the inflammatory response. Increases in CaM abundance precedes nuclear localization of key transcription factors (i.e., NFκB p65 subunit, phospho-c-Jun, and Sp1) and subsequent increases in the pro-inflammatory cytokine tumor necrosis factor α (TNF) and inducible nitric oxide synthase (iNOS). Cellular apoptosis following LPS challenge is blocked following inhibitionmore » of iNOS activity, whether accomplished using the pharmacological inhibitor 1400W, through gene silencing of TNFα, or by increasing the level of cellular CaM by stable transfection. Increasing CaM expression also results in reductions in the cellular release of TNFα and iNOS, and activation of their transcriptional regulators, indicating the level of available CaM plays a key role in determining the expression of the pro-inflammatory and pro-apoptotic cascade during cellular activation by LPS. These results indicate a previously unrecognized central role for CaM in maintaining cellular homeostasis in response to LPS, such that under resting conditions cellular concentrations of CaM are sufficient to inhibit the biosynthesis of proinflammatory mediators associated with macrophage activation. Although CaM and iNOS protein levels are coordinately increased as part of the oxidative burst, limiting cellular concentrations of CaM due to association with iNOS (and other high-affinity binders) commit the cell to an unchecked inflammatory cascade leading to apoptosis.« less
  • Macrophages plan important roles in controlling Salmonella-mediated systemic infection. To investigate the responses of macrophages to Salmonella infection, we infected RAW 264.7 macrophages with Salmonella enterica serovar Typhimurium (STM) and then performed a comparative liquid chromatography-tandem mass spectrometry [LC-MS(/MS)]-based proteomics analysis of the infected macrophages. A total of 1006 macrophage and 115 STM proteins were indentified from this study. Most of STM proteins were found at late stage of the time course of infection, consistent with the fact that STM proliferates inside RAW 264.7 macrophages. Majority of the identified macrophage proteins were house keeping-related, including cytoplasmic superoxide dismutase 1 (SOD1),more » whose peptide abundances were relatively constant during the time course of infection. Compared to those in no infection control, the peptide abundances of 244 macrophage proteins (or 24% of total indentified macrophage proteins) changed considerably after STM infection. The functions of these STM infection-affected macrophage proteins were diverse and ranged from production of antibacterial nitric oxide (i.e., inducible nitric oxide synthase or iNOS) or production of prostaglandin H2 (i.e., prostaglandin-endoperoxide synthase 2, also know as cyclooxygenase-2 or COX-2) to regulation of intracellular traffic (e.g., sorting nexin or SNX 5, 6 and 9), demonstrating a global impact of STM infection on macrophage proteome. Western-blot analysis not only confirmed the LC-MS(/MS) results of SOD1, COX-2 and iNOS, but also revealed that the protein abundances of mitochondrial SOD2 increased after STM infection, indicating an infection-induced oxidative stress in mitochondria.« less
  • Crotafuran B, a natural pterocarpanoid isolated from Crotalaria pallida, inhibited the lipopolysaccharide (LPS)-stimulated nitric oxide (NO) production (IC{sub 5} 16.4 {+-} 0.7 {mu}M) and inducible nitric oxide synthase (iNOS) protein and mRNA expression (IC{sub 5} 11.5 {+-} 0.6 {mu}M and 11.8 {+-} 2.2 {mu}M, respectively), but not via its cytotoxicity or the inhibition of iNOS enzyme activity, in RAW 264.7 macrophages. Crotafuran B also reduced the iNOS promoter activity (IC{sub 5} 13.4 {+-} 0.1 {mu}M) in piNOS-LUC-transfected cells. Crotafuran B treatment inhibited the p65 nuclear translocation and the nuclear factor-{kappa}B (NF-{kappa}B) DNA binding activity in LPS-activated macrophages. Crotafuran B alsomore » reduced the NF-{kappa}B transcriptional activity in pNF-{kappa}B-LUC-transfected cells. Crotafuran B had no effect on the LPS-induced phosphorylation of inhibitory {kappa}B{alpha} (I{kappa}B{alpha}), but enhanced the cellular level of I{kappa}B{alpha} that rebounded to the basal levels and increased the I{kappa}B{alpha} mRNA expression. These results indicate that the crotafuran B inhibition of NO production involves a decrease in the iNOS gene expression via the inhibition of NF-{kappa}B activation through the increase in I{kappa}B{alpha} synthesis.« less