Interplay between Desmoglein2 and hypoxia controls intravasation and circulating tumor cell clustering in breast cancer metastasis
Metastasis is the major cause of cancer death. An increased level of circulating tumor cells (CTCs), metastatic cancer cells that have intravasated into the circulatory system, is particularly associated with colonization of distant organs and poor prognosis. However, the key factors required for tumor cell dissemination and colonization remain elusive. We found that high expression of Desmoglein2 (DSG2), a component of desmosome-mediated intercellular adhesion complexes, promoted tumor growth, increased the prevalence of CTC clusters and facilitated distant organ colonization. The dynamic regulation of DSG2 by hypoxia was key to this process as downregulation of DSG2 in hypoxic regions of primary tumors led to elevated epithelial-mesenchymal transition (EMT) gene expression, allowing cells to detach from the primary tumor and undergo intravasation. Subsequent derepression of DSG2 after intravasation and release of hypoxic stress was associated with an increased ability to colonize distant organs. This dynamic regulation of DSG2 was mediated by Hypoxia-Induced Factor1 (HIF1). In contrast to its more widely observed function to promote expression of hypoxia-inducible genes, HIF1 repressed DSG2 by recruitment of the Polycomb Repressive Complex 2 components, EZH2 and SUZ12, to the DSG2 promoter in hypoxic cells. Consistent with our experimental data, DSG2 expression level correlated with poor prognosis and recurrence risk in breast cancer patients. Together, these results demonstrated the importance of DSG2 expression in metastasis and revealed a new mechanism by which hypoxia drives metastasis. Significance StatementDuring metastasis, hypoxia is a major force driving primary tumor cells to disseminate into the circulatory system. The key factors that promote circulating tumor cells (CTC) dissemination and allow them to successfully colonize distal sites are still incompletely known. We found that downregulation of DSG2 in hypoxic tumor allowed single tumor cell dissemination while DSG2 expressing tumors generated more CTC clusters. Re-induction of DSG2 expression in single CTCs may contribute to CTC survival and colonization in distant organs. These findings highlight the importance of DSG2 in breast cancer progression and metastasis.