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Cytoplasmic sequestration of rel proteins by IkappaBalpha requires CRM1-dependent nuclear export

W F Tam1, L H Lee, L Davis

  • 1Rosenstiel Basic Medical Sciences Research Center, Waltham, Massachusetts 02454, USA.

Molecular and Cellular Biology
|February 25, 2000
PubMed

Insights

The IkappaBalpha protein acts as a nuclear export chaperone, facilitating the movement of Rel proteins like p65 between the nucleus and cytoplasm via CRM1. This nuclear export is crucial for maintaining the cytoplasmic pool of these transcription factors.

Area of Science:

  • Cellular Biology
  • Molecular Biology
  • Protein Interactions

Background:

  • Rel and IkappaB proteins form a complex regulatory network controlling gene transcription.
  • IkappaB proteins are known to retain Rel proteins in the cytoplasm, but nuclear functions have also been proposed.
  • NF-kappaB-dependent gene transcription involves complex regulatory mechanisms.

Purpose of the Study:

  • To investigate the subcellular localization and function of IkappaBalpha.
  • To determine the role of the CRM1 nuclear export pathway in Rel-IkappaB complex dynamics.
  • To elucidate the primary function of IkappaBalpha in the NF-kappaB signaling pathway.

Main Methods:

  • Identification of a CRM1-binding export sequence in IkappaBalpha.
  • Reconstitution of NF-kappaB-IkappaB sequestration in yeast.
  • Inhibition of CRM1 using leptomycin B in mammalian cells (COS and T cells).

Main Results:

  • IkappaBalpha shuttles between the nucleus and cytoplasm via the CRM1 pathway.
  • A specific export sequence in IkappaBalpha mediates CRM1 binding.
  • CRM1-dependent nuclear export is required for cytoplasmic retention of p65 by IkappaBalpha.
  • Inhibition of CRM1 leads to nuclear accumulation of p65 and IkappaBalpha.

Conclusions:

  • IkappaBalpha functions primarily as a nuclear export chaperone, not just a cytoplasmic tether.
  • The nucleus is the main site of p65-IkappaBalpha association.
  • Nuclear export of these complexes is essential for generating the cytoplasmic pool of Rel proteins.

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