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IkappaBalpha and p65 regulate the cytoplasmic shuttling of nuclear corepressors: cross-talk between Notch and

Lluís Espinosa1, Julia Inglés-Esteve, Alex Robert-Moreno

  • 1Centre Oncologia Molecular, Institut de Recerca Oncologica, Hospitalet, Barcelona 08907, Spain.

Molecular Biology of the Cell
|February 18, 2003
PubMed

Insights

Nuclear factor-kappa B (NF-kappaB) and Notch pathways regulate cell functions. Cytoplasmic sequestration of p65 by IkappaBalpha upregulates Notch target genes by translocating corepressors, influencing cell differentiation.

Area of Science:

  • Cellular biology
  • Molecular biology
  • Signal transduction

Background:

  • Notch and Nuclear Factor-kappa B (NF-kappaB) pathways are crucial regulators of cellular processes like proliferation, differentiation, and apoptosis.
  • Negative regulation in these pathways often involves the association of effector proteins with nuclear corepressors.
  • Previous work showed a p65-NFkappaB mutant (p65DeltaTA) lacking a transactivation domain induces cytoplasmic translocation of N-CoR, leading to promoter activation.

Purpose of the Study:

  • To investigate if cytoplasmic sequestration of p65 by IkappaBalpha can influence nuclear corepressor localization and Notch-dependent gene transcription.
  • To explore the direct interaction between p65, IkappaBalpha, and SMRT, and the role of coactivators and TNF-alpha treatment in modulating this interaction.
  • To elucidate the mechanism by which this pathway influences cell differentiation, specifically in the 32D myeloid progenitor system.

Main Methods:

  • Studied the effect of p65 sequestration by IkappaBalpha on the cytoplasmic translocation of SMRT/N-CoR.
  • Assessed the impact on the transcription of Notch-dependent genes.
  • Investigated direct binding between p65 and IkappaBalpha with SMRT, and the inhibitory effects of CREB binding protein (CBP) and TNF-alpha treatment.

Main Results:

  • Cytoplasmic sequestration of p65 by IkappaBalpha successfully translocated nuclear corepressors SMRT/N-CoR to the cytoplasm.
  • This sequestration led to the upregulation of transcription of Notch-dependent genes.
  • Direct binding between p65 and IkappaBalpha with SMRT was observed, which was inhibited by CBP and TNF-alpha treatment, suggesting p65 acetylation modulates this interaction. TNF-alpha treatment downregulated Hes1 gene expression.

Conclusions:

  • Cytoplasmic sequestration of p65 by IkappaBalpha is a mechanism for upregulating Notch-dependent gene transcription via SMRT/N-CoR translocation.
  • p65 acetylation, modulated by CBP and TNF-alpha, plays a role in regulating the interaction between p65/IkappaBalpha and SMRT.
  • This newly identified mechanism provides insights into how NF-kappaB signaling can influence cell differentiation, particularly in myeloid progenitor cells.

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