BRD-NUT oncoproteins: a family of closely related nuclear proteins that block epithelial differentiation and maintain the growth of carcinoma cells

Oncogene. 2008 Apr 3;27(15):2237-42. doi: 10.1038/sj.onc.1210852. Epub 2007 Oct 15.

Abstract

An unusual group of carcinomas, here termed nuclear protein in testis (NUT) midline carcinomas (NMC), are characterized by translocations that involve NUT, a novel gene on chromosome 15. In about 2/3rds of cases, NUT is fused to BRD4 on chromosome 19. Using a candidate gene approach, we identified two NMCs harboring novel rearrangements that result in the fusion of NUT to BRD3 on chromosome 9. The BRD3-NUT fusion gene encodes a protein composed of two tandem chromatin-binding bromodomains, an extra-terminal domain, a bipartite nuclear localization sequence, and almost the entirety of NUT that is highly homologous to BRD4-NUT. The function of NUT is unknown, but here we show that NUT contains nuclear localization and export sequences that promote nuclear-cytoplasmic shuttling via a leptomycin-sensitive pathway. In contrast, BRD3-NUT and BRD4-NUT are strictly nuclear, implying that the BRD moiety retains NUT in the nucleus via interactions with chromatin. Consistent with this idea, FRAP studies show that BRD4, BRD4-NUT and BRD3-NUT have significantly slower rates of lateral nuclear diffusion than that of NUT. To investigate the functional role of BRD-NUT fusion proteins in NMCs, we investigated the effects of siRNA-induced BRD3-NUT and BRD4-NUT withdrawal. Silencing of these proteins in NMC cell lines resulted in squamous differentiation and cell cycle arrest. Together, these data suggest that BRD-NUT fusion proteins contribute to carcinogenesis by associating with chromatin and interfering with epithelial differentiation.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Base Sequence
  • Carcinoma / genetics
  • Carcinoma / pathology*
  • Cell Cycle Proteins
  • Cell Differentiation / genetics*
  • Cell Nucleus / metabolism
  • Cell Proliferation*
  • Chromatin / metabolism
  • Epithelial Cells / metabolism
  • Epithelial Cells / physiology*
  • HeLa Cells
  • Humans
  • Male
  • Molecular Sequence Data
  • Multigene Family
  • Nuclear Proteins / genetics
  • Nuclear Proteins / metabolism
  • Nuclear Proteins / physiology*
  • Oncogene Proteins / genetics
  • Oncogene Proteins / metabolism
  • Oncogene Proteins / physiology*
  • Oncogene Proteins, Fusion / metabolism
  • Oncogene Proteins, Fusion / physiology*
  • RNA, Small Interfering / pharmacology
  • RNA-Binding Proteins / genetics
  • RNA-Binding Proteins / metabolism
  • RNA-Binding Proteins / physiology
  • Testicular Neoplasms / genetics
  • Testicular Neoplasms / pathology*
  • Transcription Factors / genetics
  • Transcription Factors / metabolism
  • Transcription Factors / physiology
  • Tumor Cells, Cultured

Substances

  • BRD3 protein, human
  • BRD4 protein, human
  • Cell Cycle Proteins
  • Chromatin
  • NUT protein, human
  • Nuclear Proteins
  • Oncogene Proteins
  • Oncogene Proteins, Fusion
  • RNA, Small Interfering
  • RNA-Binding Proteins
  • Transcription Factors