Basal-like breast cancer: modeling its initiation and characterizing novel EGFR variants
Breast cancer (BC) is now a disease that will affect 1 out of every 8 women worldwide. Due to its highly heterogeneous nature, BC is usually further classified into different subtypes according to gene expression profiling analysis. Basal-like breast cancer (BBC) accounts for 15-20% of all cases of BC. BBC is very aggressive, highly metastatic, and often lethal, mostly due to our poor understanding of the key genetic events that lead to the onset and/or maintain this subtype of BC. As a result, we currently lack targeted therapies that are otherwise very effective in some of the better understood subtypes of BC. Therefore we set to work on deciphering the genetic alterations that when, expressed altogether, would model the onset of sporadic BBC in human cell lines. We already know that patients with BBC often display mutations in the tumor suppressor p53, as well as over-expression of the epidermal growth factor receptor (EGFR) protein by immunohistochemistry, and that loss of PTEN protein is also seen occurring along with the aforementioned lesions. However, there is no model for sporadic BBC that accurately reflects the genetic changes that BBC tumor samples display for studying this BC subtype progression and/or providing a base for which pharmacological studies can be done to find an effective therapy. Thus we used a non-transformed immortalized mammary epithelial cell line, MCF10A, as our model and engineered cells with termed 'triple modified' cells that express the three aforementioned alterations (PTEN, EGFR, p53) that highly observed in BBC. Furthermore, as part of the goal to better understand the genetic underpinnings that occur in BBC progression, we investigated whether variant forms of EGFR existed in cell lines of the basal-like subtype. Prior studies have demonstrated that immunostaining for EGFR in BBC patient tumor samples is elevated, though the molecular mechanisms are not well understood. EGFR is only amplified in BBC in less than 1% of cases thus gene amplification does not account for the high percentage of tumors that express and overexpress EGFR. In the pursuit to better understand the possible contribution of deregulated EGFR in BBC, we discovered a variety of basal-like breast cancer lines containing genetic alterations in EGFR not yet reported in the literature and demonstrated that a portion of them stimulate growth, invasion and transformation in mammary cells. In conclusion, the studies on modeling basal-like tumorigenesis and identifying and characterizing novel variants of EGFR in basal-like breast cancer lines have shed new exciting insights into our current knowledge of BBC. Having a cell line model for the disease provides a new tool for which further genetic and epigenetic manipulations can be exercised to continue asking questions of which other oncogenes and tumor suppressors are important for initiation of BBC. Our data showing that EGFR variants can be found in BBC cell lines and alter breast epithelial growth shows that this is an area that should be further investigated in human tumors so that targeted therapies can be designed to improve patient survival rates and their quality of life.
Biology, Oncology, Breast--Cancer, Tumor suppressor proteins, Carcinogenesis
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