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Martha K. Cathcart, Ph.D.Staff
Department of Cell Biology |
Area of general research interest:
Human monocyte activation, inflammation, regulation of NADPH oxidase generation of superoxide anion, lipid oxidation, expression of 15-lipoxygenase, signal transduction, regulation of monocyte chemotaxis to MCP1.
Current program:
- Identifying and characterizing the signal transduction pathways regulating superoxide anion production by activated monocytes.
- Exploring the mechanisms involved in IL-13 stimulation of 15-lipoxygenase expression in primary human monocytes.
- Investigating the regulation of monocyte chemotaxis to MCP1.
Investigators:
- Ashish Bhattacharjee, Ph.D., Research Associate
- Rodrigo Cezarino, Technician
- Deena Elsori, Graduate Student
- Linda Hsi, Ph.D., Project Scientist
- Suman Kunda, Senior Technologist
- Anny Mulya, Ph.D., Fellow
- Pravenna Thiagarajan, Graduate Student
- Valentin Yakubenko, Ph.D., Project Scientist
Brief Description:
The focus of the research conducted in our laboratory is to define the mechanisms responsible for regulating the oxidation of lipids during the activation of human monocytes and to study the role of lipids in regulating monocyte chemotaxis into sites of inflammation and the production of oxygen free radicals. These events likely contribute to inordinate lipid accumulation in atherosclerosis and may mediate tissue injury in pathologic settings.
Our work has defined several essential steps in the potentially pathologic process of monocyte-mediated lipid oxidation. Among these, we have demonstrated a critical role for the highly reactive oxygen radical, superoxide anion. Additionally, we have identified an apparent requirement for an enzyme in the lipoxygenase family, enzymes that catalyze highly specific oxidation of lipids.
In the course of these studies, we have identified a requisite role for both calcium influx and calcium release from intracellular stores; yet calcium is not the sole required stimulus for inducing the oxidizing events. We are presently investigating the inter-relationship between the roles of calcium and other signal transduction pathways in regulating monocyte-mediated lipid oxidation; in particular, we are studying the involvement of the various isoforms of protein kinase C (PKC) and phospholipase A2 (PLA2).
In this regard, we found, through the use of pharmacologic inhibitors and antisense oligonucleotides, that PKC activity is essential for activated monocytes to oxidize LDL lipids. We therefore designed studies to identify the particular isoenzymes of PKC that participate in this process. Isoenzymes of the cPKC family (including PKCa, PKCbI and PKCbII) were shown to be required, and recently we have found that PKCa is the isoenzyme that is required for monocyte-mediated LDL lipid oxidation.
Phospholipases A2 comprise a family of enzymes that include an enzyme called cytosolic PLA2, or cPLA2, believed to function in signal transduction. In monocytes, the activity of this enzyme is regulated by calcium. We have also examined the participation of this enzyme in the signal transduction processes required for monocyte oxidation of LDL lipids. Our studies have implicated this enzymatic pathway as an essential one and have further shown that cPLA2 activity is regulated by PKCa activity, thus linking these two pathways. We are pursuing studies to determine the mechanisms for enzymatic regulation of the phosphorylation and translocation of the components of the enzyme complex responsible for producing superoxide anion.
In related studies, we are monitoring lipoxygenase (LO) activity during monocyte activation and investigating the possible involvement of each of the above enzymatic pathways on regulating LO activity and LO expression, particularly 15-LO. We were the first to demonstrate the detection of the products of this enzyme in human atherosclerotic tissue. We are especially interested in understanding the cytokine-mediated induction of expression of this enzyme. To this end, we have recently identified the receptor components and immediate signal transducing kinases involved in the monocyte response to IL-13, a cytokine that is a uniquely potent inducer of 15-LO expression. Our understanding of the regulation of expression of this enzyme may prove important for limiting atherogenesis.
Other studies in the lab are focused on understanding the role of phospholipases and their products in regulating monocyte chemotaxis in response to MCP-1. This chemokine plays a central role in bringing monocytes into the vessel wall in atherosclerosis, and if this process is blocked, atherosclerosis can be markedly inhibited. We have found two lipid products of phospholipases that are required for MCP-1-induced monocyte chemotaxis and are pursuing studies to understand how they control monocyte movement.
In summary, we are studying a variety of regulatory pathways and defining their contributions to modulating the activity of monocytes in inflammatory responses. Our findings will suggest new approaches for inhibiting these processes and limiting the progression of atherosclerosis and inflammation.
Key References
Bey, E. and Cathcart, M.K. Antisense oligonucleotides: A better way to inhibit monocyte superoxide anion production? Methods of Enzymology 353:421-434, 2002.
Zhao, X. and Cathcart, M.K . Cytosolic phospholipase A 2 regulates NADPH oxidase activity by controlling the translocation of p47phox and p67phox. J. Biol Chem. 277: 25385-25392, 2002.
Carnevale, K. and Cathcart, M.K . Protein kinase C b is required for monocyte chemotaxis to MCP1. J. Biol. Chem. 278:25317-22, 2003.
Xu. B., Bhattacharjee, A., Roy, B., Xu. J.-M., Anthony, D., Frank, D., Feldman, G., and Cathcart, M.K. IL-13 induction of 15-lipoxygenase expression requires p38 MapK-mediated serine 727 phosphorylation of Stat1 and Stat3. Mol. Cell Biol. 23:3918-28, 2003.
Zhao, X. and Cathcart, M.K . Human Monocytes Use Rac1, Not Rac2, in the NADPH Oxidase Complex. J. Biol. Chem. 278:40788-92, 2003 .
Bey, E.A., Xu, B., Horton, C., Zhao, X., Li, Q., Subbulakshmi, V., Feldman, G.M., Wientjes, F.B. and Cathcart, M.K . PKC d is required for p47phox phosphorylation and translocation in activated human monocytes. 2004;173:5730-8.
Xu, B., Bhattacharjee, A., Roy, B., Feldman, G.M., and Cathcart, M.K . Role of Protein Kinase C isoforms in the regulation of IL-13 induced 15-lioxygenase gene expression. J. Biol. Chem, in press, 2004.
Cathcart, M.K. Regulation of Superoxide Anion Production by NADPH oxidase in Monocyte/Macrophages: Contributions to Atherosclerosis. Arterio. Thromb. Vasc. Biol. 24:23-28, 2004.
Zhao X, et al. Protein kinase C d regulates p67phox phosphorylation in human monocytes. J Leukoc Biol 2005;77:414-20.
Bhattacharjee A, et al. Monocyte 15-lipoxygenase expression is regulated by a novel cytosolic signaling complex with protein kinase C d and tyrosine-phosphorylated Stat3. J Immunol 2006;177:3771-81.
Li Q, et al. PKCa regulates phosphorylation and enzymatic activity of cPLA2 in vitro and in activated human monocytes. Cell Signal 2007;19:359-66.