Aberrations of Chromosomes 1 and 16 in Breast Cancer: A Framework for Cooperation of Transcriptionally Dysregulated Genes

SIMPLE SUMMARY: Classical cytogenetic studies in breast cancer have identified frequent chromosomal aberrations that produce an increased gene copy number in chromosome 1q (1q-gain) and/or a decreased gene copy number in 16q (16q-loss). The understanding of the contribution of such copy number changes to the genesis and progression of cancer is of paramount importance for the design of cancer models and targeted therapies. We exploited molecular data provided by The Cancer Genome Atlas (TCGA) project in order to form different groups of breast cancers bearing 1q-gain and/or 16q-loss or devoid of such aberrations (1,16-chromogroups). An analysis of differential gene expression among 1,16-chromogroups guided the identification of transcriptionally dysregulated 1q and 16q genes. Pathway analysis revealed functional interactions that shed light on novel molecular targets for subtype-specific cancer therapy. ABSTRACT: Derivative chromosome der(1;16), isochromosome 1q, and deleted 16q—producing arm-level 1q-gain and/or 16q-loss—are recurrent cytogenetic abnormalities in breast cancer, but their exact role in determining the malignant phenotype is still largely unknown. We exploited The Cancer Genome Atlas (TCGA) data to generate and analyze groups of breast invasive carcinomas, called 1,16-chromogroups, that are characterized by a pattern of arm-level somatic copy number aberrations congruent with known cytogenetic aberrations of chromosome 1 and 16. Substantial differences were found among 1,16-chromogroups in terms of other chromosomal aberrations, aneuploidy scores, transcriptomic data, single-point mutations, histotypes, and molecular subtypes. Breast cancers with a co-occurrence of 1q-gain and 16q-loss can be distinguished in a “low aneuploidy score” group, congruent to der(1;16), and a “high aneuploidy score” group, congruent to the co-occurrence of isochromosome 1q and deleted 16q. Another three groups are formed by cancers showing separately 1q-gain or 16q-loss or no aberrations of 1q and 16q. Transcriptome comparisons among the 1,16-chromogroups, integrated with functional pathway analysis, suggested the cooperation of overexpressed 1q genes and underexpressed 16q genes in the genesis of both ductal and lobular carcinomas, thus highlighting the putative role of genes encoding gamma-secretase subunits (APH1A, PSEN2, and NCSTN) and Wnt enhanceosome components (BCL9 and PYGO2) in 1q, and the glycoprotein E-cadherin (CDH1), the E3 ubiquitin-protein ligase WWP2, the deubiquitinating enzyme CYLD, and the transcription factor CBFB in 16q. The analysis of 1,16-chromogroups is a strategy with far-reaching implications for the selection of cancer cell models and novel experimental therapies.