HIV Nef disrupts Lck signaling by inducing aberrant phosphorylation of its substrates

Area of Science:

• Immunology
• Molecular Biology
• Virology

Background:

• Human immunodeficiency virus (HIV) Nef protein's role in T-cell receptor (TCR) proximal signaling is complex and debated.
• Previous in vitro studies have not fully elucidated Nef's impact on Lck kinase and its substrates.

Purpose of the Study:

• To investigate the in vivo effects of HIV Nef on tyrosine (Y) phosphorylation of Lck and its substrates, including CD3ζ and Zap-70, in transgenic (Tg) thymocytes.
• To understand the precise mechanisms by which Nef alters Lck activity and substrate phosphorylation.

Main Methods:

• Analysis of tyrosine phosphorylation of Lck, CD3ζ, and Zap-70 in Nef-expressing transgenic thymocytes.
• Investigation of Lck localization and activity using Western blot and phospho-site specific antibodies.
• Assessment of Zap-70 activity and phosphorylation status after various T-cell stimulation protocols (anti-CD3ε, anti-CD3ε+anti-CD4).
• Comparison of Nef Tg thymocytes with LckY505F mutant thymocytes and rescue experiments in double transgenic mice.

Main Results:

• Nef expression led to Lck mis-localization and activation, paradoxically decreasing pY-CD3ζ levels.
• Nef favored Lck hyperphosphorylation at Y505 and accumulation of doubly phosphorylated Lck (Y394, Y505).
• Nef altered Zap-70 phosphorylation and activity, with phenotypes resembling those of mice with semi-active Zap-70 mutants.
• Rescue of CD4+ T-cell loss in double transgenic mice (Nef × LckY505F) correlated with restored Zap-70 phosphorylation and activity.

Conclusions:

• HIV Nef uniquely impacts Lck kinase, causing its mis-localization and aberrant substrate phosphorylation.
• Nef disrupts TCR proximal signaling by inducing qualitative defects in Lck function, contributing to T-cell dysfunction and loss.
• Understanding Nef's interaction with Lck provides insights into HIV pathogenesis and potential therapeutic targets.