Hypoxia potentiates Notch signaling in breast cancer leading to decreased E-cadherin expression and increased cell migration and invasion

Abstract

BACKGROUND: Epithelial-to-mesenchymal transition (EMT) is associated with decreased adhesion and acquisition of metastatic potential of breast cancer cells. Epithelial-to-mesenchymal transition is mediated, in part, by two transcription repressors, Snail and Slug, that are known to be targets of the Notch signaling pathway, and JAGGED1-induced Notch activation increases EMT. However, the events that lead to increased Notch activity during EMT of breast cancer cells are unknown. METHODS: The accumulation of hypoxia inducible factors (HIFs) under hypoxia was detected by western blot analysis, and their effects on Notch signaling were measured by an in vitro Notch reporter assay. The expression of Notch target genes under hypoxia was tested by real-time PCR. The knockdown of HIF-1a was mediated by retroviral delivery of shRNA. The expression of Slug and Snail under hypoxia was measured by real-time PCR. Breast cancer cell migration and invasion under hypoxia were tested with cell migration and invasion kits. RESULTS: Hypoxia increased the expression of Notch target genes such as HES1 and HEY1 in breast cancer cells, as was expression of Notch receptors and ligands. The mechanism is likely to involve the accumulation of HIF-1a and HIF-2a in these cells by hypoxia, which synergised with the Notch co-activator MAML1 in potentiating Notch activity. Hypoxia inducible factor-1a was found to bind to HES1 promoter under hypoxia. Knockdown of HIF-1a with shRNA inhibited both HES1 and HEY1 expression under hypoxia. Hypoxia increased the expression of Slug and Snail, and decreased the expression of E-cadherin, hallmarks of EMT. Notch pathway inhibition abrogated the hypoxia-mediated increase in Slug and Snail expression, as well as decreased breast cancer cell migration and invasion. CONCLUSION: Hypoxia-mediated Notch signaling may have an important role in the initiation of EMT and subsequent potential for breast cancer metastasis.

Notch1‐Snail1‐E‐cadherin pathway in metastatic hepatocellular carcinoma

“…37,40 Our results show that Snail1 is the downstream target gene of Notch1 and further regulates E-cadherin expression in the following evidence: (i) knocking-down Notch1 reduced and abolished Snail1 expression in metastatic HCC cells (Figs. 3a-3c); (ii) a reduction in the Snail1 level by shNotch1 correlated with the re-establishment of E-cadherin (Fig.…”

“…during normal development, and tumor metastasis has been reported to occur through the control of Slug (Snail2) 39,40 and Snail1 under hypoxic conditions. 37,40 Our results show that Snail1 is the downstream target gene of Notch1 and further regulates E-cadherin expression in the following evidence: (i) knocking-down Notch1 reduced and abolished Snail1 expression in metastatic HCC cells (Figs.…”

The Inflammatory Tumor Microenvironment, Epithelial Mesenchymal Transition and Lung Carcinogenesis

“…In addition to HIF-1α and HIF-2α binding to the HRE in its promoter region, expression of SNAI1 can be upregulated during hypoxia via other mechanisms, namely, Notch signaling. In a range of tumor cell lines, hypoxic activation of Notch signaling induced EMT and promoted cell migration, invasion and survival, effects that were attributed to direct upregulation of Snail and Slug expression, as well as the lysyl oxidase (LOX)-dependent stabilization of Snail protein [75,76].…”

JAG2 Induction in Hypoxic Tumor Cells Alters Notch Signaling and Enhances Endothelial Cell Tube Formation

“…Several mechanisms have been proposed including direct icN1 stabilization by interaction with HIF proteins (8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18). As of yet, little attention has been given to Notch ligand regulation and the effects this may have on Notch activation under hypoxia.…”