Submitted on April 9, 2007
Accepted on September 17, 2007
Functional genomics of silencing TREM-1 on TLR4 signaling in macrophages
Magdalena Ornatowska1, Anser Chaudhry Azim1, Xuerong Wang1, John W. Christman2, Lei Xiao3, Myungsoo Joo4, and Ruxana T Sadikot5*
1 Pulmonary/Critical Care Medicine, University of Illinois at Chicago, Chicago, Illinois, United States
2 Professor of Medicne and Pharmacology, Chief, Section of Pulmonary, Critical Care, and Sleep Medicine, University of Illinois, Chicago, Illinois, United States; Pulmonary/Critical Care Medicine, University of Illinois at Chicago, Chicago, Illinois, United States
3 Medicine, UIC, Chiago, Illinois, United States
4 Allergy, pulmonary and Critical Care Medicine, Vanderbilt University, Nashville, Tennessee, United States
5 Pulmonary Critical Care and Sleep Medicine, University of Illinois, Chicago, Illinois, United States
* To whom correspondence should be addressed. E-mail: sadikot{at}uic.edu.
Triggering receptor expressed on myeloid cells 1 (TREM-1) is a recently discovered molecule that is expressed on the cell surface of monocytes and neutrophils. Engagement of TREM-1 triggers synthesis of pro-inflammatory cytokines in response to microbes, but the extent and mechanism by which TREM-1 modulates the inflammatory response is poorly defined. In the present study, we investigated the functional effects of blocking TREM-1 on the TLR4 mediated signaling pathway in macrophages. By transfecting cells with a small hairpin interfering RNA molecules to TREM-1 (ShRNA), we confirmed that TREM-1 mRNA and protein expression was greatly attenuated in RAW cells in response to treatment with LPS. PCR array for genes related to or activated by the Toll like receptor pathway revealed that although the expression of TLR4, itself, was not significantly altered by silencing of TREM-1; expression of several genes, including MyD88, CD14, I
B
, IL-1
, MCP-1, IL-10 was significantly attenuated in the TREM-1 knockdown cells in response to treatment with LPS. These data indicate that activation of TREM-1 modulates the TLR signaling in macrophages by altering the expression of both adaptor and effector proteins that are critical to the endotoxin response.
