Mechanistic Insights Into an Ancient Adenovirus Precursor Protein VII Show Multiple Nuclear Import Receptor Pathways

Area of Science:

• Virology
• Cell Biology
• Molecular Biology

Background:

• Adenoviral pVII proteins are essential for viral genome transport into host cell nuclei.
• The precise mechanisms of nuclear import for pVII proteins, particularly from non-human adenoviruses, remain incompletely understood.

Purpose of the Study:

• To characterize the nuclear import mechanism of precursor pVII (Pre-pVII) protein from frog siadenovirus 1 (FrAdV1).
• To identify and functionally analyze the nuclear localization signals (NLSs) within FrAdV1 Pre-pVII.
• To compare the nuclear import pathways of FrAdV1 Pre-pVII with its human adenovirus counterparts.

Main Methods:

• Structural, functional, and biochemical analyses of FrAdV1 Pre-pVII.
• Identification and characterization of NLSs (NLSa, NLSb, NLSc, NLSd).
• Inhibition studies using specific nuclear import pathway inhibitors.

Main Results:

• FrAdV1 Pre-pVII utilizes two strong NLSs (NLSa, NLSd) interacting with importin (IMP)β1 and IMPα, respectively, as primary drivers for nuclear import.
• A weaker NLS (NLSb) and NLSc contribute to import and nucleolar/intranuclear localization.
• FrAdV1 Pre-pVII nuclear import depends on IMPα/β1 and IMPβ1, but not transportin-1 (IMPβ2), differing from human adenovirus pathways.

Conclusions:

• FrAdV1 Pre-pVII nuclear import is mediated by distinct importin pathways compared to human adenoviruses.
• Adenoviruses have evolved diverse strategies to utilize host cell nuclear transport machinery for pVII proteins.
• This study provides a basis for evolutionary comparisons of adenovirus-host cell interactions in nuclear transport.