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A HIC-5- and KLF4-dependent mechanism transactivates p21(Cip1) in response to anchorage loss

Kazunori Mori1, Hiroyuki Hamanaka, Yukiko Oshima

  • 1Department of Molecular Biology, Division of Cancer Cell Biology, Showa University School of Pharmacy, Tokyo 142-8555, Japan.

The Journal of Biological Chemistry
|September 26, 2012
PubMed

Insights

Cell detachment triggers transcriptional changes to prevent abnormal growth. This study identifies a novel mechanism involving KLF4 and HIC-5 proteins that regulates p21(Cip1) gene expression, crucial for cell cycle arrest in nonadherent cells.

Area of Science:

  • Molecular Biology
  • Cell Biology
  • Gene Regulation

Background:

  • Anchorage loss triggers cellular responses to prevent inappropriate growth in ectopic locations.
  • The precise molecular mechanisms governing these detachment-induced transcriptional changes remain largely unknown.
  • Understanding these mechanisms is vital for comprehending cell cycle control and preventing aberrant proliferation.

Purpose of the Study:

  • To elucidate the transcriptional regulation of cyclin-dependent kinase inhibitor p21(Cip1) during anchorage loss.
  • To identify the key transcription factors and regulatory elements involved in detachment-responsive gene expression.
  • To uncover the role of specific adaptor proteins in mediating these cellular responses.

Main Methods:

  • Investigated the transcriptional up-regulation of p21(Cip1) using anchorage loss models.
  • Identified and characterized a detachment-responsive element (DRE) with binding sites for KLF4 and RUNX1.
  • Employed RNA interference (RNAi) experiments to assess the roles of KLF4 and HIC-5.
  • Analyzed the nuclear localization and oligomerization of HIC-5.
  • Studied the regulatory role of CRP2 at the RUNX1 site.

Main Results:

  • Identified a DRE containing necessary KLF4 and RUNX1 binding sites for p21(Cip1) transactivation.
  • Demonstrated that KLF4 and HIC-5 are critical for DRE transactivation, with HIC-5 tethering KLF4 to DNA upon detachment.
  • Showed that HIC-5 oligomerization and nuclear matrix localization are accelerated by anchorage loss, enhancing its scaffolding function.
  • Revealed that CRP2 negatively regulates transcription at the RUNX1 site, and its removal upon detachment contributes to increased DRE activity.
  • Established a novel detachment-dependent transcriptional mechanism regulating p21(Cip1).

Conclusions:

  • Discovered a novel transcriptional mechanism controlling gene expression in response to anchorage loss.
  • This mechanism involves the coordinated action of KLF4, HIC-5, RUNX1, and CRP2 to regulate p21(Cip1) transcription.
  • The findings contribute to understanding anchorage-dependent cell growth and cell cycle control in nonadherent conditions.

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