Breast cancer-associated NEAT1 in cellular stress response pathways

Abstract

In this thesis, we investigated the role of NEAT1 in stress, cancer, and autophagy in breast cancer. In paper I, we studied NEAT1 in oxidative stress and heat shock. In the heat shock response, HSF1 translocates into the nucleus in order to activate its target gene, and we discovered a novel binding site for HSF1 in the promoter of NEAT1. The expression of NEAT1, as well as paraspeckle formation, were induced by both SFN and heat shock. The study further displayed that the proliferation of breast cancer cells is highly dependent on NEAT1 expression, in line with what previous studies have shown. In paper II, we have continued to study NEAT1 in breast cancer tumors and also breast cancer cell lines. From analyses of four different breast cancer cohorts, we found that NEAT1_2 expression was positively correlated with HER2-positive breast cancer tumor, whereas, it was negatively associated with ER-positive luminal A breast cancer. Interestingly, high levels of NEAT1_2 was observed in lactating tissue as well as in breast tissue of a pregnant female. As repeatedly reported, NEAT1 expression resulted in chemoresistance, and we also showed that NEAT1_2-depletion increased apoptosis in HER2-positive breast cancer cells, when treated with the dual HER2 and EGFR inhibitor lapatinib. Finally, according to the results in paper I, we hypothesized that NEAT1 might affect the autophagy in breast cancer cell line. Therefore, we decided to investigate the role of this lncRNA in autophagy in paper III. Interestingly, our data revealed that NEAT1-depletion induce basal autophagy in breast cancer cell lines. Further, the results suggesting a role for NEAT1 in normal functionality of lysosome in cancer cells. Finally, we illustrated that the induction of autophagy was regulated by AMPK, but not mTOR. Activated AMPK bypasses mTOR and activates Ulk1 in our model.