Polymorphisms in Human APOBEC3H Differentially Regulate Ubiquitination and Antiviral Activity

Area of Science:

• Immunology
• Virology
• Genetics

Background:

• The APOBEC3 family provides innate immune defense against viruses like HIV.
• APOBEC3H (A3H) exhibits significant genetic polymorphism, impacting its function.
• Haplotype II is the only antivirally active A3H variant, while others have destabilizing mutations.

Purpose of the Study:

• To investigate the relationship between A3H protein stability, ubiquitination, and antiviral activity.
• To determine if stabilizing destabilized A3H variants restores antiviral function.
• To elucidate the functional consequences of A3H polymorphisms beyond protein stability.

Main Methods:

• Analysis of A3H haplotypes and their correlation with ubiquitination.
• Mutation of lysine residues to inhibit ubiquitination and assess protein expression.
• Construction of fusion chimeras to evaluate the role of specific A3H domains in stability and activity.

Main Results:

• A3H instability correlates with increased ubiquitination; haplotype II is resistant.
• Stabilizing destabilized A3H variants (haplotypes III/IV) via ubiquitination inhibition leads to nuclear localization and loss of antiviral activity.
• Fusion chimeras demonstrate that haplotype III requires haplotype II for stability and virion incorporation, but remains inactive independently.

Conclusions:

• APOBEC3H (A3H) antiviral activity loss in humans involves functional defects beyond protein instability.
• Ubiquitination and protein stability are critical for A3H localization and function.
• Evolutionary loss of A3H activity is multifactorial, involving deficiencies independent of protein degradation pathways.