Expression of the Brn-3b transcription factor correlates with expression of HSP-27 in breast cancer biopsies and is required for maximal activation of the HSP-27 promoter.
In breast cancer, overexpression of the small heat shock protein, HSP-27, is associated with increased anchorage-independent growth, increased invasiveness, and resistance to chemotherapeutic drugs and is associated with poor prognosis and reduced disease-free survival. Therefore, factors that increase the expression of HSP-27 in breast cancer are likely to affect the prognosis and outcome of treatment. In this study, we show a strong correlation between elevated levels of the Brn-3b POU transcription factor and high levels of HSP-27 protein in manipulated MCF-7 breast cancer cells as well as in human breast biopsies. Conversely, HSP-27 is decreased on loss of Brn-3b. In cotransfection assays, Brn-3b can strongly transactivate the HSP-27 promoter, supporting a role for direct regulation of HSP-27 expression. Brn-3b also cooperates with the estrogen receptor (ER) to facilitate maximal stimulation of the HSP-27 promoter, with significantly enhanced activity of this promoter observed on coexpression of Brn-3b and ER compared with either alone. RNA interference and site-directed mutagenesis support the requirement for the Brn-3b binding site on the HSP-27 promoter, which facilitates maximal transactivation either alone or on interaction with the ER. Chromatin immunoprecipitation provides evidence for association of Brn-3b with the HSP-27 promoter in the intact cell. Thus, Brn-3b can, directly and indirectly (via interaction with the ER), activate HSP-27 expression, and this may represent one mechanism by which Brn-3b mediates its effects in breast cancer cells.
Lee
Sonia A
SA
Medical Molecular Biology Unit, Institute of Child Health, University College London, 30 Guilford Street, London WC1N 1EH, UK.
Ndisang
Daniel
D
Patel
Chandrakant
C
Dennis
Jonathan H
JH
Faulkes
David J
DJ
D'Arrigo
Corrado
C
Samady
Laila
L
Farooqui-Kabir
Saleha
S
Heads
Richard J
RJ
Latchman
David S
DS
Budhram-Mahadeo
Vishwanie S
VS
D001483:Base Sequence; D001706:Biopsy; D001943:Breast Neoplasms / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D045744:Cell Line, Tumor; D047369:Chromatin Immunoprecipitation; D004268:DNA-Binding Proteins / Q000096:biosynthesis* / Q000235:genetics; D015972:Gene Expression Regulation, Neoplastic; D018841:HSP90 Heat-Shock Proteins / Q000096:biosynthesis / Q000235:genetics; D006360:Heat-Shock Proteins / Q000096:biosynthesis* / Q000235:genetics; D006801:Humans; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D011401:Promoter Regions, Genetic; D034622:RNA Interference; D011960:Receptors, Estrogen / Q000096:biosynthesis / Q000235:genetics; D050818:Transcription Factor Brn-3; D050820:Transcription Factor Brn-3B; D014157:Transcription Factors / Q000096:biosynthesis* / Q000235:genetics; D015533:Transcriptional Activation; D014162:Transfection
D004268:DNA-Binding Proteins; D018841:HSP90 Heat-Shock Proteins; D006360:Heat-Shock Proteins; D011960:Receptors, Estrogen; D050818:Transcription Factor Brn-3; D050820:Transcription Factor Brn-3B; D014157:Transcription Factors