Distinct trafficking pathways mediate Nef-induced and clathrin-dependent major histocompatibility complex class I...

Area of Science:

• Immunology
• Virology
• Cell Biology

Background:

• The human immunodeficiency virus type 1 (HIV-1) Nef protein is known to modulate the surface expression of major histocompatibility complex class I (MHC-I) molecules.
• This modulation is thought to involve alterations in the post-Golgi trafficking of MHC-I, potentially through the unmasking of a tyrosine-based sorting signal (YSQA) in the cytoplasmic tail of HLA-A and -B heavy chains.

Purpose of the Study:

• To investigate the mechanisms by which HIV-1 Nef protein influences MHC-I trafficking.
• To compare the effects of a prototypic sorting motif with those of Nef on MHC-I surface expression and intracellular localization.

Main Methods:

• Genetic modification of HLA-A2 heavy chains by replacing the endogenous YSQA signal with prototypic sorting motifs (YSQI or YSQL), creating A2-endo molecules.
• Analysis of surface expression levels and intracellular localization of modified HLA-A2 molecules in the presence or absence of Nef.
• Utilizing a transdominant-negative mutant of dynamin-1 to assess the role of clathrin-dependent endocytosis in A2-endo trafficking and Nef activity.

Main Results:

• Modified HLA-A2 molecules (A2-endo) exhibited constitutively low surface levels and accumulated near the Golgi apparatus, similar to wild-type HLA-A2 in Nef-expressing cells.
• Internalization of A2-endo was rapid and associated with efficient recycling, distinct from Nef's effect on MHC-I.
• Dynamin-1 inhibition affected A2-endo internalization and CD4 down-regulation by Nef but not Nef's effect on MHC-I, suggesting separate pathways.
• Nef continued to affect A2-endo trafficking, indicating additive effects between prototypic signals and Nef.

Conclusions:

• Distinct cellular trafficking pathways are involved in clathrin-dependent endocytosis and Nef-induced modulation of MHC-I.
• The mechanisms by which prototypic sorting signals and HIV-1 Nef protein regulate MHC-I trafficking differ, despite some overlapping effects.
• These findings contribute to understanding the complex interplay between viral proteins and host cell immune surveillance mechanisms.