Phosphorylation of HIV Nef by cAMP-dependent protein kinase

Nef, a multifunctional accessory protein of human immunodeficiency virus (HIV) and simian immunodeficiency virus (SIV), is important for disease progression. Nef downmodulates CD4 and MHC class I expression, alters host-cell signal transduction pathways, and enhances viral replication. We have identified a novel interaction between Nef and cAMP-dependent kinase (PKA). N-terminal serine residues Ser(6,9) of HIVNL4-3 Nef and Ser(10) of SIVmac239 Nef were phosphorylated by PKA in a cell-free system; intracellularly, only Ser(9) of HIVNL4-3 Nef was phosphorylated by PKA. Mutation of Ser(9) to alanine in the context of full-length HIVNL4-3 lowered HIV replication in resting peripheral blood mononuclear cells (PBMC) compared to parental virus. As this mutation played a major role in abrogating the Nef effect on HIV replication in unstimulated primary cells, we postulate that Nef phosphorylation by PKA is an important step in the viral life cycle in resting cells. (C) 2004 Elsevier Inc. All rights reserved.