Submitted August 1, 2007
Accepted January 8, 2008
Phosphatidylcholine-specific phospholipase C activation is required for CCR5-dependent, NF-kB-driven CCL2 secretion elicited in response to HIV-1 gp120 in human primary macrophages
Laura Fantuzzi, Francesca Spadaro, Cristina Purificato, Serena Cecchetti, Franca Podo, Filippo Belardelli, Sandra Gessani*, and Carlo Ramoni
Department of Cell Biology and Neurosciences, Istituto Superiore di Sanita, Rome, Italy
* Corresponding author; email: gessani{at}iss.it.
CCL2 (MCP-1) has been shown to enhance HIV-1 replication. The expression of this chemokine by macrophages is up-modulated as a consequence of viral infection or gp120 exposure. In this study, we show for the first time that the phosphatidylcholine-specific phospholipase C (PC-PLC) is required for the production of CCL2 triggered by gp120 in human monocyte-derived macrophages (MDM). Using a combination of pharmacologic inhibition, confocal laser-scanner microscopy and enzymatic activity assay, we demonstrate that R5 gp120 interaction with CCR5 activates PC-PLC, as assessed by a time-dependent modification of its sub-cellular distribution and a concentration-dependent increase of its enzymatic activity. Furthermore, PC-PLC is required for NF-kB-mediated CCL2 production triggered by R5 gp120. Notably, PC-PLC activation through CCR5 is specifically induced by gp120, since triggering CCR5 through its natural ligand CCL4 (MIP-1
) does not affect PC-PLC cellular distribution and enzymatic activity, as well as CCL2 secretion, thus suggesting that different signaling pathways can be activated through CCR5 interaction with HIV-1 or chemokine ligands. The identification of PC-PLC as a critical mediator of well-defined gp120-mediated effects in MDM unravels a novel mechanism involved in bystander activation and may contribute to define potential therapeutic targets to block Env-triggered pathologic responses.
