Identification of new cancer stem cell markers and signaling pathways in HER-2-positive breast cancer by transcriptome sequencing

Human epidermal growth factor receptor (HER)-2-positive breast cancer accounts for similar to 25% of all breast cancer cases, has a high propensity for relapse, metastasis and drug resistance, and is associated with a poor prognosis. Therefore, it is necessary to develop more effective therapeutic targets for the treatment of HER-2-positive breast cancer. CD44(+)/CD24(-/low) is currently the most commonly used marker for breast cancer stem cells (CSCs), which are considered the main cause of drug resistance, relapse and metastasis. In the present study, the ratio of CD44(+)/CD24(-/low) cells was almost zero in SK-BR-3 cells; however, it was >90% in MDA-MB-231 cells, as determined by flow cytometry. Since SK-BR-3 and MDA-MB-231 cells both exhibit a strong propensity for invasion and migration, it was hypothesized that there may be other markers of CSCs in SK-BR-3 cells. Therefore, transcriptome sequencing was performed for SK-BR-3 and MDA-MB-231 cells. It was observed that several leukocyte differentiation antigens and other CSC markers were significantly more highly expressed in SK-BR-3 cells. Furthermore, the expression of aldehyde dehydrogenase (ALDH)1A3, CD164 and epithelial cell adhesion molecule (EpCAM) was higher in SK-BR-3 cells compared with in other subtypes of breast cell lines, as determined by reverse transcription-polymerase chain reaction and western blot analysis. In addition, the expression levels of ALDH1A3, ALDH3B2 and EpCAM were higher in HER-2-positive breast cancer compared with in paracancerous tissues and other subtypes of breast cancer, as determined by immunohistochemistry. The expression of beta-catenin in the Wnt signaling pathway was lower in SK-BR-3 cells compared with in MDA-MB-231 cells, which may be used as a prognostic indicator for breast cancer. These findings may help identify novel CSC markers and therapeutic targets for HER-2-positive breast cancer.