Expression profiling of familial breast cancers demonstrates higher expression of FGFR2 in BRCA2-associated tumors

Abstract

Background: BRCA1- and BRCA2-associated tumors appear to have distinct molecular signatures. BRCA1-associated tumors are predominantly basal-like cancers, whereas BRCA2-associated tumors have a predominant luminal-like phenotype. These two molecular signatures reflect in part the two cell types found in the terminal duct lobular unit of the breast. To elucidate novel genes involved in these two spectra of breast tumorigenesis we performed global gene expression analysis on breast tumors from germline BRCA1 and BRCA2 mutation carriers.

Methodology: Breast tumor RNAs from 7 BRCA1 and 6 BRCA2 mutation carriers were profiled using UHN human 19K cDNA microarrays. Supervised univariate analyses were conducted to identify genes differentially expressed between BRCA1 and BRCA2-associated tumors. Selected discriminatory genes were validated using real time reverse transcription polymerase chain reaction in the tumor RNAs, and/or by immunohistochemistry (IHC) or by in situ hybridization (ISH) on tissue microarrays (TMAs) containing an independent set of 58 BRCA1 and 64 BRCA2-associated tumors.

Results: Genes more highly expressed in BRCA1-associated tumors included stathmin, osteopontin, TGFbeta2 and Jagged 1 in addition to genes previously identified as characteristic of basal-like breast cancers. BRCA2-associated cancers were characterized by the higher relative expression of FGF1 and FGFR2. FGFR2 protein was also more highly expressed in BRCA2-associated cancers (P = 0.004).

Significance: BRCA1-associated tumours demonstrated increased expression of component genes of the Notch and TGFbeta pathways whereas the higher expression of FGFR2 and FGF1 in BRCA2-associated cancers suggests the existence of an autocrine stimulatory loop.

Fig. 1

Unsupervised two dimensional cluster analysis of 7 BRCA1-associated and 6 BRCA2-associated breast tumors. Two dimensional presentation of transcript ratios for 13 tumors. The top 150 significant genes differentially expressed between the two tumor groups from SAM Moderated t-test are shown. Each column represents a tumor and each row a gene. As shown in the color bar, red indicates up regulation, green down regulation and black no change

Fig. 2

Scatter plots comparing the expression ratios of 6 genes obtained using both cDNA microarrays and RT-PCR in BRCA1-associated and BRCA2-associated tumors. The log2 expression ratios from RT-PCR (y-axis) and log2 expression ratios from cDNA microarrays (x-axis) for 6 genes from BRCA1-associated (red spots) and BRCA2-associated (purple spots) tumors are illustrated in the scatter plots. The relative expression ratios for both modalities for each tumor correlate positively i.e., RT-PCR and expression data go in the same direction (up regulated or down regulated) for the two tumor groups

Fig. 3

Immunohistochemical and ISH studies on representative BRCA2-associated and BRCA1-associated tumors. Tumor (a) and (b) are a representative BRCA2-associated and BRCA1-associated tumor stained for FGFR2. The cytoplasmic stain is positive in tumor (a) as evidenced by the intense brown staining and negative in tumor (b). Tumors represented in (c) and (d) are representative BRCA2-associated and BRCA1-associated tumors following ISH for Jagged1 mRNA. Tumor (c) is negative, with a vessel acting as a positive internal control whereas tumor (d) is positive