Compensation of BRG-1 function by Brm: insight into the role of the core SWI-SNF subunits in retinoblastoma tumor suppressor signaling

J Biol Chem. 2002 Feb 15;277(7):4782-9. doi: 10.1074/jbc.M109532200. Epub 2001 Nov 21.


The BRG-1 subunit of the SWI-SNF complex is involved in chromatin remodeling and has been implicated in the action of the retinoblastoma tumor suppressor (RB). Given the importance of BRG-1 in RB function, germ line BRG-1 mutations in tumorigenesis may be tantamount to RB inactivation. Therefore, in this study we assessed the behavior of cells harboring discrete BRG-1 alleles for the RB-signaling pathway. Using p16ink4a, an upstream activator of endogenous RB, or a constitutively active RB construct (PSM-RB), we determined that the majority of tumor lines with germ line defects in BRG-1 were sensitive to RB-mediated cell cycle arrest. By contrast, A427 (lung carcinoma) cells were resistant to expression of p16ink4a and PSM-RB. Analysis of the SWI-SNF subunits in the different tumor lines revealed that A427 are deficient for BRG-1 and its homologue, Brm, whereas RB-sensitive cell lines retained Brm expression. Similarly, the RB-resistant SW13 and C33A cell lines were also deficient for both BRG-1/Brm. Reintroduction of either BRG-1 or Brm into A427 or C33A cells restored RB-mediated signaling to cyclin A to cause cell cycle arrest. Consistent with this compensatory role, we observed that Brm could also drive expression of CD44. We also determined that loss of these core SWI-SNF subunits renders SW13 cells resistant to activation of the RB pathway by the chemotherapeutic agent cisplatin, since reintroduction of either BRG-1 or Brm into SW13 cells restored the cisplatin DNA-damage checkpoint. Together, these data demonstrate that Brm can compensate for BRG-1 loss as pertains to RB sensitivity.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Adenoviridae / metabolism
  • Alleles
  • Antineoplastic Agents / pharmacology
  • Bromodeoxyuridine / metabolism
  • Cisplatin / pharmacology
  • Cyclin A / metabolism
  • DNA Damage
  • DNA Helicases
  • DNA-Binding Proteins / metabolism
  • Electrophoresis, Polyacrylamide Gel
  • Humans
  • Hyaluronan Receptors / biosynthesis
  • Immunoblotting
  • Mutation
  • Nuclear Proteins / chemistry*
  • Nuclear Proteins / genetics*
  • Phosphorylation
  • Plasmids / metabolism
  • Protein Structure, Tertiary
  • Retinoblastoma / metabolism*
  • S Phase
  • Signal Transduction*
  • Transcription Factors / chemistry*
  • Transcription Factors / genetics*
  • Transcription Factors / metabolism
  • Transcription Factors / physiology*
  • Transfection
  • Tumor Cells, Cultured


  • Antineoplastic Agents
  • Cyclin A
  • DNA-Binding Proteins
  • Hyaluronan Receptors
  • Nuclear Proteins
  • SMARCA2 protein, human
  • Transcription Factors
  • SMARCA4 protein, human
  • DNA Helicases
  • Bromodeoxyuridine
  • Cisplatin