Background: Forkhead Box protein 01 (Foxo1, FKHR) is a transcription factor central to T cell biology. Foxo1 is necessary for the maintenance of T cell quiescence and for the expression of CD62L (L-selectin), an adhesion molecule that controls T cell migration into lymph nodes. TCR stimulation suppresses Foxo1 activity through PI3K/Akt-dependent phosphorylation of Foxo1 and its relocation to the cytoplasm. Foxo1 inactivation results in CD62L transcriptional repression and the activation or repression of a series of genes that regulate T cell activation, migration, survival, growth and differentiation.
Methods: Purified peripheral blood and tonsil CD4 T cells were infected with HIV-1. Blood and tonsil cells were analyzed by flow cytometry. Blood cells were analyzed by ImageStream (Amnis) for Foxo1 and NF-κB localization and TransAM ELISA (Active Motif) for Foxo1 sequence-specific DNA binding activity. Cellular and viral mRNA were analyzed by TaqMan qRT-PCR.
Results: HIV-1 down-modulated CD62L on productively infected naïve and memory (TCM and TEM) resting CD4 T cells. Partial T cell activation was further revealed by upregulation of the mRNA and surface expression of CD69, a Foxo1-suppressed gene. HIV-1-induced CD62L down modulation was inhibited by the PI3K inhibitors LY294002 and PI-103, indicating that activation of the PI3K/Akt pathway contributes to this effect. ImageStream analysis demonstrated relocation of Foxo1 to the cytoplasm in productively infected resting naïve and memory CD4 T cells, and TransAM ELISA demonstrated loss of Foxo1 transactivation activity. A series of Foxo1 regulated mRNA were decreased or increased in productively infected resting CD4 T cells, including CD62L, IL-7rα, Myc, KLF2, CCR5, Fam65b, S1P1 (EDG1), CD52 and Cyclin D2, indicating a profound reprogramming of these cells by HIV-1. Application of the Foxo1 inhibitor AS1842856 prior to or just after infection accelerated de novo viral gene expression and enhanced infected cell viability.
Conclusions: HIV-1 suppression of Foxo1 activity is apparently a strategy to promote its replication in resting CD4 T cells. Dysregulation of Foxo1 may contribute to immune activation, viral load and HIV-1 pathogenesis. As Foxo1 is an investigative cancer therapy target, the ongoing development of Foxo1 interventions may assist the quest to specifically suppress or activate HIV-1 replication in vivo.