The role of histone acetyltransferases CBP and GCN5 in the response of cancer and normal breast cells to cellular stress

Breast cancer (BC) is among the most relevant cancer types worldwide. The late diagnosis and the subsequent delay in seeking treatment of BC represents a major issue among female population and attributes to poor prognosis and high mortality. Therefore, the search for new biomarkers with diagnostic, prognostic, and therapeutic purposes is still needed to assist in the clinical management of BC patients. Epigenetic alterations in cancer cells, which accompanied by a plethora of deregulated enzymes like histone acetyltransferase and histone deacetylases, are increasingly recognized to play a critical role in carcinogenesis and in the response of cells to cellular stress induced by cancer therapeutics. The involvement of the histone acetyltransferases CREB-binding protein (CBP) and the General control non-depressible 5 (GCN5) in tumor formation and in regulating cellular response to stress have been previously reported. However, their implications in the cellular response of BC cells to genotoxic stress and in breast tumorigenesis remains poorly understood. Hence, this study aimed to investigate the molecular function of CBP under DNA damage in BC and in breast normal cells as well as to investigate the clinical significance of CBP and GCN5 as molecular markers and/or targets in BC. The cancer and normal breast cell lines were used to examine the expression, stability, activity and interacting proteins of CBP after DNA damage induction. In addition, immunofluorescence, western blot, comet assay, colony formation assay and mass spectrometry analysis were performed after CBP inhibition or downregulation under DNA damage. In order to assess the status of CBP and GCN5 in BC, their expression levels were analyzed in cell lines (by western blot), in patients’ tissues (by immunohistochemistry) and in the publicly available data from BC patients. Our results showed that the depletion of CBP impaired the DNA repair capacity and subsequently increased the sensitivity of BC cells to chemo- and radiotherapy, without influencing the behavior of normal cells. In addition, we report that CBP interacts with and activates ATM, a central regulator of DNA damage response. Furthermore, CBP expression is differentially regulated in BC cells with different hormonal status under DNA damage, in which a strong association between CBP and the expression of Estrogen receptor α (ERα), and the Human epidermal growth factor receptor 2 (HER2) was indicated. Besides, elevated expression of CBP and GCN5 was detected in BC tissues from patients and cell lines more than normal ones. In particular, CBP was more expressed in luminal A and B BC subtypes. In conclusion, our findings aid in further understanding the functional role of CBP in the response of BC and normal cells to DNA damaging agents. The overexpression of CBP in luminal subtypes and its relationship with ERα suggests that targeting CBP could be a potential path for therapy of hormone-positive BC.