title: Compensation of BRG-1 function by Brm: insight into the role of the core SWI-SNF subunits in retinoblastoma tumor suppressor signaling.
abstract: 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.
authors.affiliation: Department of Cell Biology, University of Cincinnati College of Medicine, Vontz Center for Molecular Studies, Cincinnati, Ohio 45267-0521, USA.
authors.forename: Matthew W
authors.initials: MW
authors.lastname: Strobeck
authors.forename: David N
authors.initials: DN
authors.lastname: Reisman
authors.forename: Ranjaka W
authors.initials: RW
authors.lastname: Gunawardena
authors.forename: Bryan L
authors.initials: BL
authors.lastname: Betz
authors.forename: Steven P
authors.initials: SP
authors.lastname: Angus
authors.forename: Karen E
authors.initials: KE
authors.lastname: Knudsen
authors.forename: Timothy F
authors.initials: TF
authors.lastname: Kowalik
authors.forename: Bernard E
authors.initials: BE
authors.lastname: Weissman
authors.forename: Erik S
authors.initials: ES
authors.lastname: Knudsen
mesh_terms: D000256:Adenoviridae / Q000378:metabolism; D000483:Alleles; D000970:Antineoplastic Agents / Q000494:pharmacology; D001973:Bromodeoxyuridine / Q000378:metabolism; D002945:Cisplatin / Q000494:pharmacology; D019925:Cyclin A / Q000378:metabolism; D004249:DNA Damage; D004265:DNA Helicases; D004268:DNA-Binding Proteins / Q000378:metabolism; D004591:Electrophoresis, Polyacrylamide Gel; D006801:Humans; D018960:Hyaluronan Receptors / Q000096:biosynthesis; D015151:Immunoblotting; D009154:Mutation; D009687:Nuclear Proteins / Q000737:chemistry* / Q000235:genetics*; D010766:Phosphorylation; D010957:Plasmids / Q000378:metabolism; D017434:Protein Structure, Tertiary; D012175:Retinoblastoma / Q000378:metabolism*; D016196:S Phase; D015398:Signal Transduction; D014157:Transcription Factors / Q000737:chemistry* / Q000235:genetics* / Q000378:metabolism / Q000502:physiology*; D014162:Transfection; D014407:Tumor Cells, Cultured
chemical_list: D000970:Antineoplastic Agents; D019925:Cyclin A; D004268:DNA-Binding Proteins; D018960:Hyaluronan Receptors; D009687:Nuclear Proteins; C084011:SMARCA2 protein, human; D014157:Transcription Factors; C084108:SMARCA4 protein, human; D004265:DNA Helicases; D001973:Bromodeoxyuridine; D002945:Cisplatin