Hypoxia Induces the Acquisition of Cancer Stem-like Phenotype Via Upregulation and Activation of Signal Transducer and Activator of Transcription-3 (STAT3) in MDA-MB-231, a Triple Negative Breast Cancer Cell Line

摘要

The finding that hypoxia can induce cancer stemness in various experimental models is in agreement with the conceptual basis ofcancer cell plasticity. Here, we aimed to gain insights into the molecular basis of hypoxia-induced cancer cell plasticity in triplenegative breast cancer (TNBC). To achieve this goal, we employed our previously published in-vitro model of TNBC, in which asmall subset of stem-like cells can be distinguished from the bulk cell population based on their responsiveness to a Sox2 reporter.In MDA-MB-231, a TNBC cell line, we observed that hypoxia significantly increased the expression of luciferase and greenfluorescence protein (GFP), the readouts of the Sox2 reporter. Upon hypoxic challenge, the bulk, reporter unresponsive (RU) cellsacquired stem-like features, as evidenced by the significant increases in the proportion of CD44high/CD24low cells, colony formationand resistance to cisplatin. Correlating with these phenotypic changes, RU cells exposed to hypoxia exhibited a substantialupregulation of the active/phosphorylated form of STAT3 (pSTAT3). This hypoxia-induced activation of STAT3 correlated withincreased STAT3 transcriptional activity, as evidenced by increased STAT3-DNA binding and an altered gene expression profile.This hypoxia-induced STAT3 activation is biologically significant, since siRNA knockdown of STAT3 in RU cells significantlyattenuated the hypoxia-induced acquisition of Sox2 activity and stem-like phenotypic features. In conclusion, our data haveprovided the proof-of-concept that STAT3 is a critical mediator in promoting the hypoxia-induced acquisition of cancer stemnessin TNBC. Targeting STAT3 in TNBC may be useful in overcoming chemoresistance and decreasing the risk of disease relapse.