Adducin family proteins possess different nuclear export potentials.

Area of Science:

• Cell Biology
• Molecular Biology

Background:

• Adducin (ADD) proteins (ADD1, ADD2, ADD3) are actin-binding proteins crucial for membrane cytoskeleton and cell-cell junction stability.
• All ADD proteins possess a nuclear localization signal (NLS), yet only ADD1 localizes to the nucleus, a discrepancy requiring investigation.

Purpose of the Study:

• To elucidate the reasons behind the differential subcellular localization of ADD protein isoforms.
• To investigate the nuclear import and export mechanisms of ADD proteins.

Main Methods:

• Transient expression of HA-tagged ADD proteins and mutants in NIH3T3 fibroblasts.
• Immunofluorescence staining to examine cytoplasmic and nuclear distribution.
• Mass spectrometry and co-immunoprecipitation to identify interacting nuclear proteins.

Main Results:

• ADD1 localized to both cytoplasm and nucleus, while ADD2 and ADD3 were primarily cytoplasmic.
• ADD2 and ADD3 showed partial nuclear sequestration (~40%) upon inhibition of CRM1/exportin1, indicating functional NLS and rapid cytoplasmic export.
• ADD2 and ADD3 exhibited stronger counteraction of a Simian virus 40 large T-antigen NLS compared to ADD1, suggesting distinct nuclear transport dynamics.
• ADD1's nuclear retention facilitated interactions with RNA polymerase II and zinc-finger protein 331.

Conclusions:

• ADD2 and ADD3 possess functional NLS and actively shuttle between the cytoplasm and nucleus.
• Differential nuclear export capabilities are responsible for the distinct subcellular localization patterns of ADD isoforms.
• ADD1's interaction with RNA polymerase II and zinc-finger protein 331 suggests a potential role in transcriptional regulation.