New Role Discovered for Calmodulin: Modulating Inflammatory Response
Calmodulin (CaM) is a calcium regulatory protein that regulates signal transduction through reversible association with a large number of target proteins. It plays a central role in mediating activation of macrophages—cells that engulf cellular debris and foreign material, such as pathogens—and bacteria killing, but the mechanisms associated with these roles remain poorly understood.
Researchers at Pacific Northwest National Laboratory (PNNL) investigated the functional relationships among CaM, the lipopolysaccharide (LPS) complex associated with the outer membrane of Gram-negative pathogens, and key inflammatory mediators tumor necrosis factor alpha (TNFα) and inducible nitric oxide synthase (iNOS) in RAW 264.7 macrophage-like cells.
Using cells transfected with a gene encoding CaM to increase cellular CaM abundance, and cells transfected with small interfering RNA (siRNA) to silence TNFα expression, the researchers found that CaM abundance in RAW cells is associated with modulation of the inflammatory response. These results indicate a previously unrecognized central role for CaM in inflammation. The scientists suggest the cytokine-dependent signaling pathways regulated by CaM provide the necessary stability to initiate macrophage activation rapidly and correctly in response to pathogen exposure. Understanding this new role of CaM has potential application to detection of environmental threats and the development of anti-inflammatory therapeutics.
This research was initiated by PNNL's Biomolecular Systems Initiative. Results were published in the American Journal of Physiology Cellular Physiology in January 2006. The publication is co-authored by Thomas Weber, Heather Smallwood, Loel Kathmann, Meng Markillie, Thomas Squier, and Brian Thrall.
Increased cellular CaM abundance protects macrophages from apoptosis. Images are of Vector Control and RAW cells that were transfected with CaM either untreated (control) or treated with endotoxin (LPS). Apoptotic nuclei (indicated by arrows) were detected by epifluorescence using DAPI as the nuclear stain.
Reference Weber TJ, HS Smallwood, LE Kathmann, LM Markillie, TC Squier, and BD Thrall. 2006. "Functional link between TNF biosynthesis and CaM-dependent activation of inducible nitric oxide synthase in RAW 264.7 macrophages." Am. J. Physiol. Cell Physiol. 290:C1512-C1520.