Infection of the lung by Human Cytomegalovirus (HCMV) leads to inflammatory pneumonitis of great clinical significance. The site and mechanism by which the inflammatory response is regulated remain unclear. During infection of the endothelium, HCMV-induced mechanisms stimulate the expression of the chemokine RANTES. Furthermore, HCMV encodes a G-protein coupled receptor, US28, that binds and signals through CC chemokines and is responsible for depleting extracellular concentrations of the chemokine RANTES during endothelial infection. We propose that HCMV modulates local inflammatory responses in part by encoding a chemokine receptor US28 that regulates the local concentration of RANTES through receptor internalization, and blocks apoptotic mechanisms during RANTES stimulation of infected cells. These hypotheses will be tested with a clinical isolate of HCMV, strain 4010, that has been passaged through endothelial cells from the umbilical vein as a model system of lung endothelium. The HCMV US28 receptor has been isolated from strain 4010, cloned and expressed in human kidney epithelial (293) cells and in 293 cells that express G-alpha-l6 protein to examine US28 receptor/chemokine activation of intracellular signaling pathways. In response to RANTES stimulation, US28 couples to specific G proteins, either G-alpha-l6 or resident G-alpha-i proteins, to activate intracellular calcium flux and mitogen-activated protein (MAP) kinase pathways.
We aim to determine whether signaling pathways leading to inhibition of apoptosis (Raf, ERK activation) are activated or signaling pathways resulting in apoptosis (MEKK, JNK, p38 activation) are inhibited during RANTES stimulation of US28. Further understanding of the role of US28 during infection will provide information on the mechanisms of HCMV-induced modification of local inflammatory responses that lead to persistent infection.
