ATM signalling and autophagy cooperate in the regulation of breast cancer stem-like phenotype: a transcriptional profile

In the last past decades, it has been focused the attention on a new emerging concept in the field of cancer research, such as the involvement of a small fraction of cells within many solid tumours that seem to be responsible for tumour initiation, maintenance and, more importantly, for drug resistance, called cancer stem cells (CSCs). According to this hypothesis, this pool of cells could be distinguished from all the other tumour cells, not only because they have different properties, such as the ability to self-renew or to differentiate into different tumour types, but also because they grow in a specific microenvironment, suggesting a different metabolic requirement; understanding this concept and the signalling pathways involved could be be extremely important for the development of new specific therapeutic drugs. Recent studies have underlined the role of the DNA damage response (DDR) as an important mechanism that promotes radio resistance in CSCs, but some aspects need to be clarified. Indeed, the DDR and its major player ATM show a duality in cancer; ATM could act as tumor suppressor, according to its canonical role in response to a DNA damage, or as tumor promoter in specific cancer contexts. Recently, our group identified a new tumorigenic role of ATM in HER2-positive breast cancer (BC), but currently, very little is known about the role of ATM in the regulation of CSCs. Based on literature data and our results, the aim of this study is to identify new possible crosslinks between ATM and other signalling pathways involved in the maintenance of the stem-like phenotype in BC. We characterized cells with stem-like features from BC cell lines as MCF-7 and MCF-7HER2, by using mammosphere assay. We performed a transcriptomic study using Agilent 8x60K whole human genome microarray. Our data show an increase in ATM protein and mRNA levels in cells grown in 3D, and interestingly, the downregulation of ATM expression significantly reduces spheres formation and the activity of ALDH-1, a well-known marker of breast cancer stem cells (BCSCs) features. We analysed different gene expression profiles obtained by microarray analysis in mammospheres with or without ATM and we found a strong correlation with some important pathways for breast cancer stem cells maintenance. Transcriptional profiles of MCF7 and MCF7-HER2 cell lines infected with ATM silencing vectors were compared to the corresponding samples infected with control vectors.