HIF-1α/GPER signaling mediates the expression of VEGF induced by hypoxia in breast cancer associated fibroblasts (CAFs)

Abstract

IntroductionCarcinoma-associated fibroblasts (CAFs) play a pivotal role in cancer progression by contributing to invasion, metastasis and angiogenesis. Solid tumors possess a unique microenvironment characterized by local hypoxia, which induces gene expression changes and biological features leading to poor outcomes. Hypoxia Inducible Factor 1 (HIF-1) is the main transcription factor that mediates the cell response to hypoxia through different mechanisms that include the regulation of genes strongly associated with cancer aggressiveness. Among the HIF-1 target genes, the G-protein estrogen receptor (GPER) exerts a stimulatory role in diverse types of cancer cells and in CAFs.MethodsWe evaluated the regulation and function of the key angiogenic mediator vascular endothelial growth factor (VEGF) in CAFs exposed to hypoxia. Gene expression studies, Western blotting analysis and immunofluorescence experiments were performed in CAFs and breast cancer cells in the presence of cobalt chloride (CoCl2) or cultured under low oxygen tension (2% O2), in order to analyze the involvement of the HIF-1α/GPER signaling in the biological responses to hypoxia. We also explored the role of the HIF-1α/GPER transduction pathway in functional assays like tube formation in human umbilical vein endothelial cells (HUVECs) and cell migration in CAFs.ResultsWe first determined that hypoxia induces the expression of HIF-1α and GPER in CAFs, then we ascertained that the HIF-1α/GPER signaling is involved in the regulation of VEGF expression in breast cancer cells and in CAFs exposed to hypoxia. We also assessed by ChIP assay that HIF-1α and GPER are both recruited to the VEGF promoter sequence and required for VEGF promoter stimulation upon hypoxic condition. As a biological counterpart of these findings, conditioned medium from hypoxic CAFs promoted tube formation in HUVECs in a HIF-1α/GPER dependent manner. The functional cooperation between HIF-1α and GPER in CAFs was also evidenced in the hypoxia-induced cell migration, which involved a further target of the HIF-1α/GPER signaling like connective tissue growth factor (CTGF).ConclusionsThe present results provide novel insight into the role elicited by the HIF-1α/GPER transduction pathway in CAFs towards the hypoxia-dependent tumor angiogenesis. Our findings further extend the molecular mechanisms through which the tumor microenvironment may contribute to cancer progression.

Effects of thalidomide on growth and VEGF-A expression in SW480 colon cancer cells

“…However, studies have also reported that THD has anti-inflammatory, immunomodulatory, and anti angiogenic effects (16). The effects of THD on proliferation of colon cancer cells are rarely reported.…”

“…VEGF is one of the target genes of HIF-1α. HIF-1α promotes the transcription of target gene VEGF, and regulates angiogenesis in tumors under hypoxic conditions (15,16). Therefore, HIF-1α may reduce the possibility of recurrence and metastasis of tumor cells if the formation of new blood vessels in tumor tissue can be suppressed.…”

Aspirin may inhibit angiogenesis and induce autophagy by inhibiting mTOR signaling pathway in murine hepatocarcinoma and sarcoma models

“…Decreased expression of HIF-1α is associated with slower cell growth and tumor angiogenesis (12,31). HIF-1α and VEGF-A expression are strongly associated with cancer progression and angiogenesis (12)(13)(14).…”

“…Decreased expression of HIF-1α is associated with slower cell growth and tumor angiogenesis (12,31). HIF-1α and VEGF-A expression are strongly associated with cancer progression and angiogenesis (12)(13)(14). In our study, the control group demonstrated marked expression of p-mTOR, which is the activated form of mTOR and its downstream protein, HIF-1α and VEGF-A, while the high and low-dose aspirin and everolimus groups effectively inhibited the expression of p-mTOR, HIF-1α and VEGF-A.…”

“…Tumor tissue is usually accompanied by hypoxia, which promotes HIF-1α production. HIF-1α and its downstream target, VEGF-A, play critical roles in tumor angiogenesis and represent an attractive chemotherapeutic target (11)(12)(13). Ruan et al revealed that the phosphatidylinositol 3-kinase (PI3K)/AKT/mTOR signaling pathway as 'the regulation center of angiogenesis' could regulate the expression of VEGF-A by hypoxia and HIF-1α, cancer genes, hormones, growth factors and cytokines and other factors (14).…”