ITGA6 is directly regulated by hypoxia-inducible factors and enriches for cancer stem cell activity and invasion in metastatic breast cancer models

Abstract

BackgroundHypoxia-inducible factors (HIFs) are well-established mediators of tumor growth, the epithelial to mesenchymal transition (EMT) and metastasis. In several types of solid tumors, including breast cancers, the HIFs play a critical role in maintaining cancer stem cell (CSC) activity. Thus, we hypothesized that HIFs may also regulate transcription of markers of breast CSC activity. One approach to enrich for breast cells with stem-like phenotypes is FACS sorting, in which sub-populations of live cells are gated based on the expression of cell surface antigens, including various integrin subunits. Integrin alpha 6 (ITGA6; CD49f) is routinely used in combination with other integrin subunits to enrich for breast stem cells by FACS. Integrins not only mediate interactions with the extracellular matrix (ECM), but also drive intracellular signaling events that communicate from the tumor microenvironment to inside of the tumor cell to alter phenotypes including migration and invasion.MethodsWe used two models of metastatic breast cancer (MBC), polyoma middle T (MMTV-PyMT) and MDA-MB-231 cells, to compare the expression of ITGA6 in wild type and knockout (KO) or knockdown cells. Chromatin immunoprecipitation (ChIP) and luciferase reporter assays verified that ITGA6 is a direct HIF transcriptional target. We also used FACS sorting to enrich for CD49f + cells to compare tumorsphere formation, tumor initiating cell activity, invasion and HIF activity relative to CD49fneg or low cells. Knockdown of ITGA6 significantly reduced invasion, whereas re-expression of ITGA6 in the context of HIF knockdown partially rescued invasion. A search of public databases also revealed that ITGA6 expression is an independent prognostic factor of survival in breast cancer patients.ResultsWe report that ITGA6 is a HIF-dependent target gene and that high ITGA6 expression enhances invasion and tumor-initiating cell activities in models of MBC. Moreover, cells that express high levels of ITGA6 are enriched for HIF-1α expression and the expression of HIF-dependent target genes.ConclusionsOur data suggest that HIF-dependent regulation of ITGA6 is one mechanism by which sorting for CD49f + cells enhances CSC and metastatic phenotypes in breast cancers. Our results are particularly relevant to basal-like breast cancers which express higher levels of the HIFα subunits, core HIF-dependent target genes and ITGA6 relative to other molecular subtypes.Electronic supplementary materialThe online version of this article (doi:10.1186/s12943-016-0510-x) contains supplementary material, which is available to authorized users.

STROBE-compliant integrin through focal adhesion involve in cancer stem cell and multidrug resistance of ovarian cancer

“…Consistent with our results, ITGA6 overexpression was observed in esophageal cancer [48] and colon cancer, [49] and it not only mediates interaction with the ECM but also drives intracellular signaling events that communicate from the tumor microenvironment to inside of the tumor cell to alter phenotypes including migration and invasion. [50] The associations of the ITGA6 with prognosis in cancer is poorly known, with limited studies reporting that this gene affects the prognosis of prostate cancer by influencing the biological characteristics of CSC, [51] and its high expression exhibited significantly poorer OS, [52] which is consistent with our finding in ovarian cancer (Fig. 5).…”

Identification of potential biomarkers and analysis of prognostic values in head and neck squamous cell carcinoma by bioinformatics analysis

“…As previously reported, silencing of ITGA6 genes significantly inhibited cell migration and invasion in head and neck cancer cells and hepatocellular carcinoma cells 21,22. Similarly high ITGA6 expression was shown to enhance invasion in models of metastatic breast cancer 23. Moreover, Kwon et al24 found ITGA6 is a possible target for antibody-related diagnostic and therapeutic modalities in esophageal squamous cell carcinoma.…”

Integrins in the Spotlight of Cancer

“…Once in the nucleus, these factors can bind to hypoxia response elements (HREs) and regulate at least transcription of 70 different genes [179]. On one side, this leads to an upregulation of specific integrins such as αvβ3 and the β1 and α6 integrin subunits, which mediate the invasive phenotype of tumor cells [180,181,182]. Moreover, a recent study revealed that HIF-1α activates ILK transcription and that the activation of this kinase stimulates HIF-1α expression via the mTOR pathway, creating a sustained feedback loop that promotes EMT [183].…”