Distinct oncogenes drive distinct genome and epigenome alterations in human mammary epithelial cells

Gene expression differences, combined with distinct patterns of genomic rearrangements and epigenetic modifications, have laid the bases of molecular classification of breast cancer. Different molecular subtypes are thought to originate from different cell lineages in the mammary gland, but the early activation of an oncogene could also play a role. It is, however, difficult to discriminate the respective inputs of oncogene activation or cell type of origin in the natural history of the tumor. In this work, we have designed an experimental strategy aiming at determining whether activation of distinct oncogenic pathways in human mammary epithelial cells (HMEC) could lead to different patterns of genetic and epigenetic changes. We show that initial activation of CCNE1, WNT1 and RASv12, which activate distinct oncogenic pathways, in shp53 immortalized HMECs results in different and reproducible profiles of mRNA and miRNA expression, copy number alterations (CNA) and DNA methylation modifications. Noticeably, HMECs transformed by RAS bore very specific profiles of CNAs and DNA methylation, clearly distinct from those shown by CCNE1 and WNT1 transformed HMECs. Genes impacted by CNAs and CpG methylation in the RAS and the CCNE1/WNT1 clusters showed clear differences, illustrating the activation of distinct pathways. Our data show that early activation of distinct oncogenic pathways leads to active adaptive events resulting in specific sets of CNAs and DNA methylation changes. We, thus, propose that activation of different oncogenes could have a role in reshaping the genetic landscape of breast cancer subtypes.