oa Akt-activated Vascular Endothelial Cells Enhance Breast Cancer Stemness

Breast cancer is a major disease leading in both incidence and mortality in women. Although the mortality has been reduced by various therapy approaches, recurrence still occurs in many patients. Evidence indicates that tumor-initiating (cancer stem) cells may contribute to disease relapse, suggesting the importance of effective targeting of this cell population. Recently, it has been shown that the components of the tumor microenvironment, including tumor vascular endothelium, interact with cancer stem cells through intracellular signaling pathways. However, the exact mechanism underlying this interaction is not known. In this study, we intend to investigate how the Akt-activated vascular endothelial cells (E4ORF1) communicate with defined populations of breast tumor. Moreover, we are interested to find out if notch pathway is regulating this crosstalk.

The cancer stem cells were enriched under serum-free conditions in 3D media to obtain mammospheres. To investigate how E4ORF1 maintains breast tumor cells and cancer stem cell in the absence of serum and cytokines, breast cancer MDA-MB231 and MCF-7 cells were co-cultivated with E4ORF1, its conditioned media, or in 3D media. In addition, the expression of pluripotency markers was assessed by real-time PCR in cancer cells after contact with E4ORF1 cells. Besides, the involvement of notch pathway in E4ORF1 interaction with mammospheres was studied by using RNAi against Jagged-1.

Our preliminary results demonstrated that E4ORF1 cells were able to maintain cancer cells under serum-free conditions and in a contact-dependent manner. Also,they were able to enrich mammospheres in contact or after temporary exposure. Moreover, the expression of some pluripotency markers displayed a 1.5-fold increase in cancer cells co-cultured with E4ORF1 cells. Besides, Notch pathway activation seemed to be necessary for E4ORF1 to support mammosphere growth since there was a 3-fold decrease in sphere numbers in Jag-1-/MDA-MB231 cells.

These results suggest that E4ORF1 cells are capable of maintaining cancer stem cell population. Since this interaction is contact dependent, it might indicate the involvement of some intracellular signaling pathways. Our results show that notch might be involved in this crosstalk, which makes it a target for therapy in order to inhibit the cancer stem cell population to prevent breast cancer reappearance.