Clarifying the role of G protein signaling in HIV infection: new approaches to an old question.

Whether or not HIV gp120-elicited signal transduction through the coreceptors CCR5 and CXCR4 is required for productive viral replication has long been a subject of controversy. The complexity and diversity of G protein signal transduction initiated by chemokine receptor activation has hindered efforts to understand the contributions of these pathways to the HIV life cycle. Several recent studies have demonstrated an important role for G proteins in mediating signaling events through both CCR5 and CXCR4 that are necessary for productive HIV infection. In addition to gp120-mediated G protein activation, there is still much to learn about the impact of G protein signaling during HIV infection, including the role of T-cell receptor/CXCR4 cross-talk, regulation of G protein expression during infection and the contribution of G protein subunit genetic polymorphisms to disease progression. This review will describe the effects of G protein signaling in immune cells, summarize the current understanding of CCR5 and CXCR4-initiated signal transduction in HIV replication, and discuss important gaps that still remain in our understanding of G protein signaling and its contribution to HIV pathogenesis.