Gemcitabine resistance in breast cancer cells regulated by PI3K/AKT-mediated cellular proliferation exerts negative feedback via the MEK/MAPK and mTOR pathways

Abstract

Chemoresistance is a major cause of cancer treatment failure and leads to a reduction in the survival rate of cancer patients. Phosphatidylinositol 3-kinase/protein kinase B/mammalian target of rapamycin (PI3K/AKT/mTOR) and mitogen-activated protein kinase (MAPK) pathways are aberrantly activated in many malignant tumors, including breast cancer, which may indicate an association with breast cancer chemoresistance. In this study, we generated a chemoresistant human breast cancer cell line, MDA-MB-231/gemcitabine (simplified hereafter as “231/Gem”), from MDA-MB-231 human breast cancer cells. Flow cytometry studies revealed that with the same treatment concentration of gemcitabine, 231/Gem cells displayed more robust resistance to gemcitabine, which was reflected by fewer apoptotic cells and enhanced percentage of S-phase cells. Through the use of inverted microscopy, Cell Counting Kit-8, and Transwell assays, we found that compared with parental 231 cells, 231/Gem cells displayed more morphologic projections, enhanced cell proliferative ability, and improved cell migration and invasion. Mechanistic studies revealed that the PI3K/AKT/mTOR and mitogen-activated protein kinase kinase (MEK)/MAPK signaling pathways were activated through elevated expression of phosphorylated (p)-extracellular signal-regulated kinase (ERK), p-AKT, mTOR, p-mTOR, p-P70S6K, and reduced expression of p-P38 and LC3-II (the marker of autophagy) in 231/Gem in comparison to control cells. However, there was no change in the expression of Cyclin D1 and p-adenosine monophosphate-activated protein kinase (AMPK). In culture, inhibitors of PI3K/AKT and mTOR, but not of MEK/MAPK, could reverse the enhanced proliferative ability of 231/Gem cells. Western blot analysis showed that treatment with a PI3K/AKT inhibitor decreased the expression levels of p-AKT, p-MEK, p-mTOR, and p-P70S6K; however, treatments with either MEK/MAPK or mTOR inhibitor significantly increased p-AKT expression. Thus, our data suggest that gemcitabine resistance in breast cancer cells is mainly mediated by activation of the PI3K/AKT signaling pathway. This occurs through elevated expression of p-AKT protein to promote cell proliferation and is negatively regulated by the MEK/MAPK and mTOR pathways.

Rg3 inhibits gemcitabine‐induced lung cancer cell invasiveness through ROS‐dependent, NF‐κB‐ and HIF‐1α‐mediated downregulation of PTX3

“…In the present study, we observed that GEM treatment led to a dose-and timedependent increase in PTX3 expression. This result supported our earlier findings where we showed a role of ERK1/2 and PI3K/Akt signaling axis in GEM resistance (X. L. Yang, Lin, Guo, Shao, & Ou, 2014). Our data suggest that the induction of PTX3 on GEM treatment could be as a result of the counter defense mechanism of tumor cells to resist apoptosis by the promotion of PTX3-induced cell survival pathways.…”

Autophagy Protects from Raddeanin A‐Induced Apoptosis in SGC‐7901 Human Gastric Cancer Cells

“…Inhibition of mTOR activity or a decrease of IP3 level can induce autophagy, respectively [10]. In this study, we found that the mTOR pathway was suppressed by RA (Figure 2(c)).…”

Tissue Stiffness and Hypoxia Modulate the Integrin-Linked Kinase ILK to Control Breast Cancer Stem-like Cells

“…Previous work has suggested that ILK regulates cell survival through the PI3K/Akt pathway (32), which has also been implicated in cancer cell (33,34) and CSC survival (35,36), cancer cell proliferation (37,38), and the CSC phenotype (39). We found that knockdown of ILK reduced the phosphorylation of Akt (Figure 4A; Figure S4).…”

“…ILK is well appreciated for its roles in stemness and metastasis (33,34,37) and is known to stimulate tumor angiogenesis through VEGF-A (51). Our data suggest a positive feedback loop in which the signaling activated by ILK induces increased expression of mechanosensors, including β1-integrin and ILK itself.…”