Molecular basis for estrogen receptor alpha deficiency in BRCA1-linked breast cancer.
BACKGROUND
BRCA1-mutant breast tumors are typically estrogen receptor alpha (ER alpha) negative, whereas most sporadic tumors express wild-type BRCA1 and are ER alpha positive. We examined a possible mechanism for the observed ER alpha-negative phenotype of BRCA1-mutant tumors.


METHODS
We used a breast cancer disease-specific microarray to identify transcripts that were differentially expressed between paraffin-embedded samples of 17 BRCA1-mutant and 14 sporadic breast tumors. We measured the mRNA levels of estrogen receptor 1 (ESR1) (the gene encoding ER alpha), which was differentially expressed in the tumor samples, by quantitative polymerase chain reaction. Regulation of ESR1 mRNA and ER alpha protein expression was assessed in human breast cancer HCC1937 cells that were stably reconstituted with wild-type BRCA1 expression construct and in human breast cancer T47D and MCF-7 cells transiently transfected with BRCA1-specific short-interfering RNA (siRNA). Chromatin immunoprecipitation assays were performed to determine if BRCA1 binds the ESR1 promoter and to identify other interacting proteins. Sensitivity to the antiestrogen drug fulvestrant was examined in T47D and MCF-7 cells transfected with BRCA1-specific siRNA. All statistical tests were two-sided.


RESULTS
Mean ESR1 gene expression was 5.4-fold lower in BRCA1-mutant tumors than in sporadic tumors (95% confidence interval [CI] = 2.6-fold to 40.1-fold, P = .0019). The transcription factor Oct-1 recruited BRCA1 to the ESR1 promoter, and both BRCA1 and Oct-1 were required for ER alpha expression. BRCA1-depleted breast cancer cells expressing exogenous ER alpha were more sensitive to fulvestrant than BRCA1-depleted cells transfected with empty vector (T47D cells, the mean concentration of fulvestrant that inhibited the growth of 40% of the cells [IC40] for empty vector versus ER alpha: >10(-5) versus 8.0 x 10(-9) M [95% CI = 3.1 x 10(-10) to 3.2 x 10(-6) M]; MCF-7 cells, mean IC40 for empty vector versus ER alpha: >10(-5) versus 4.9 x 10(-8) M [95% CI = 2.0 x 10(-9) to 3.9 x 10(-6) M]).


CONCLUSIONS
BRCA1 alters the response of breast cancer cells to antiestrogen therapy by directly modulating ER alpha expression.
Hosey
Alison M
AM
Centre for Cancer Research and Cell Biology, Queen's University Belfast, 97 Lisburn Rd, Belfast, Northern Ireland, BT9 7BL, UK.
Gorski
Julia J
JJ
Murray
Margaret M
MM
Quinn
Jennifer E
JE
Chung
Wen Y
WY
Stewart
Gail E
GE
James
Colin R
CR
Farragher
Susan M
SM
Mulligan
Jude M
JM
Scott
Alistair N
AN
Dervan
Peter A
PA
Johnston
Patrick G
PG
Couch
Fergus J
FJ
Daly
Peter A
PA
Kay
Elaine
E
McCann
Amanda
A
Mullan
Paul B
PB
Harkin
D Paul
DP
D018931:Antineoplastic Agents, Hormonal / Q000494:pharmacology*; D015152:Blotting, Northern; D001943:Breast Neoplasms / Q000737:chemistry* / Q000188:drug therapy / Q000235:genetics*; D045744:Cell Line, Tumor; D004958:Estradiol / Q000031:analogs & derivatives* / Q000494:pharmacology; D020847:Estrogen Receptor Modulators / Q000494:pharmacology*; D047628:Estrogen Receptor alpha / Q000172:deficiency* / Q000235:genetics; D005260:Female; D000077267:Fulvestrant; D020869:Gene Expression Profiling; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D020868:Gene Silencing; D019398:Genes, BRCA1; D006801:Humans; D015151:Immunoblotting; D047468:Immunoprecipitation; D009154:Mutation; D012333:RNA, Messenger / Q000032:analysis; D034741:RNA, Small Interfering; D012107:Research Design; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014158:Transcription, Genetic
D018931:Antineoplastic Agents, Hormonal; D020847:Estrogen Receptor Modulators; D047628:Estrogen Receptor alpha; D012333:RNA, Messenger; D034741:RNA, Small Interfering; D000077267:Fulvestrant; D004958:Estradiol