Modulation of the IFN-I/JAK/STAT signaling pathway by the protein HIV-1 Nef accessory

Author(s)

Roger Luiz Rodrigues

• Document type: Doctoral Thesis
• Press: Ribeirão Preto.
• Institution: Universidade de São Paulo (USP). Faculdade de Medicina de Ribeirão Preto (PCARP/BC)
• Defense date: 2024-01-23

Examining board members

Luis Lamberti Pinto da Silva; Luciana Jesus da Costa; Rodrigo de Carvalho Santana

• Advisor: Luis Lamberti Pinto da Silva

Abstract

HIV-1 infects lineages of CD4+ T lymphocytes, monocytes and macrophages that express the CD4 receptor, together with the CCR5 or CXCR4 coreceptors. Although HIV-1 interferes with the ability of these cells to synthesize type I interferon (IFN-I), infected individuals maintain high levels of IFN-α in their serum. IFN-α/β activates the JAK/STAT signaling pathway, stimulates the synthesis of interferon stimulated genes (ISGs) and induces an antiviral state, fundamental in the response and control of infections. However, treatment of patients with IFN-I has low efficiency in containing HIV-1 infection, suggesting a possible viral inhibitory effect on the JAK/STAT pathway. Therefore, we investigated how HIV-1 modulates the JAK/STAT signaling pathway. The HIV-1 accessory protein Nef is critical for infection, promoting viral pathogenesis and immune evasion. Furthermore, HIV-1 infection or isolated expression of the Nef protein reduces the levels of phosphorylated STAT1 in CD4+ T lymphocytes. Therefore, in this work, we investigated how HIV-1 mechanisms by which the HIV-1 Nef modulates the JAK/STAT signaling pathway. For this purpose, CD4+ T lymphocytes, constitutively expressing Nef were stimulated with IFN-α and the activation of the JAK/STAT signaling pathway was evaluated through biochemical assays. We demonstrated that Nef induces proteasomal degradation of STAT1, leading to a strong depletion of total STAT1 levels. This Nef activity prevented the increase in phosphorylated STAT1 levels upon IFN-α stimuli, which is essential for the formation of the ISGF3 complex. In contrast, phosphorylation of the JAK1 and TYK2 kinases, and total STAT2 levels, are not affected by Nef. Induced depletion of STAT1 depends on the association of Nef with cell membranes and is conserved among Nef alleles originating from different HIV-1 strains. Therefore, by depleting STAT1, Nef compromises the expression of ISGs with antiviral activity, mediated by IFN-α, in CD4+ T lymphocytes. These results show a novel activity for the Nef protein, which allows HIV-1 to evade antiviral protection induced by IFN-α by blocking the JAK/STAT signaling pathway. (AU)

• FAPESP's process: 19/15280-5 - Study of molecular mechanisms associated with the modulation of the signaling pathway stimulated by type I interferons (JAK/STAT) by HIV-1
• Grantee: Roger Luiz Rodrigues
• Support Opportunities: Scholarships in Brazil - Doctorate