High-resolution genomic profiles of breast cancer cell lines

A BAC-array platform for comparative genomic hybridization was constructed from a library of 32,433 clones providing complete genome coverage, and evaluated by screening for DNA copy number changes in 11 breast cell lines (BT474, MCF7, HCC1937, SK-BR-3, L56Br-C1, ZR-75-1, MCF10A, JIMT1, MDA-MB-231, MDA-MB-361 and HCC2218). These were also characterized by gene expression analysis and found to represent all five recently described breast cancer subtypes using the ‘intrinsic gene set’ and centroid correlation. Three cell lines, HCC1937 and L56BrC1 derived from BRCA1 mutation carriers and MDA-MB-231, were of basal-like subtype and characterized by a high frequency of low-level gains and losses of typical pattern, including limited deletions on 5q. Four estrogen receptor positive cell lines were of luminal A subtype and characterized by a different pattern of aberrations and high-level amplifications, including ERBB2 and other 17q amplicons in BT474 and MDA-MB-361. SK-BR-3 cells, characterized by a complex genome including ERBB2 amplification, massive high-level amplifications on 8q and a homozygous deletion of CDH1 at 16q22, had an expression signature closest to luminal B subtype. The effects of gene amplifications were verified by gene expression analysis to distinguish targeted genes from silent amplicon passengers. JIMT1, derived from an ERBB2 amplified trastuzumab resistant tumor, was of the ERBB2 subtype. Homozygous deletions included other known targets such as PTEN (HCC1937) and CDKN2A (MDA-MB-231, MCF10A), but also new candidate suppressor genes such as FUSSEL18 (HCC1937) and WDR11 (L56Br-C1) as well as regions without known genes. The tiling BAC arrays constitute a powerful tool for high-resolution genomic profiling suitable for cancer research and clinical diagnostics. Keywords: comparative genomic hybridization Genomic DNA was extracted from 11 breast cancer cell lines. The DNA was labeled using Bioprime array CGH labeling kit (Invitrogen). Promega pooled male DNA was used as reference. Dye-swaps were performed for L56Br-C1 and HCC2218. Labeled DNA was hybridized onto BAC arrays containing ~32 000 BAC clones printed in singlets. BAC arrays were produced at the SWEGENE DNA Microarray Facility at Lund University.