Hypoxia-inducible factor 1-dependent expression of platelet-derived growth factor B promotes lymphatic metastasis of hypoxic breast cancer cells

Abstract

Lymphatic dissemination from the primary tumor is a major mechanism by which breast cancer cells access the systemic circulation, resulting in distant metastasis and mortality. Numerous studies link activation of hypoxia-inducible factor 1 (HIF-1) with tumor angiogenesis, metastasis, and patient mortality. However, the role of HIF-1 in lymphatic dissemination is poorly understood. In this study, we show that HIF-1 promotes lymphatic metastasis of breast cancer by direct transactivation of the gene encoding platelet-derived growth factor B (PDGF-B), which has proliferative and chemotactic effects on lymphatic endothelial cells. Lymphangiogenesis and lymphatic metastasis in mice bearing human breast cancer orthografts were blocked by administration of the HIF-1 inhibitor digoxin or the tyrosine kinase inhibitor imatinib. Immunohistochemical analysis of human breast cancer biopsies demonstrated colocalization of HIF-1α and PDGF-B, which were correlated with lymphatic vessel area and histological grade. Taken together, these data provide experimental support for breast cancer clinical trials targeting HIF-1 and PDGF-B.lymph node | orthotopic transplantation | triple-negative breast cancer M etastasis is the major cause of mortality in breast cancer patients (1). Metastatic dissemination of cancer cells from the primary tumor may occur via blood vessels or lymphatic vessels (LVs). In breast cancer, the most clinically important predictor of distant organ metastasis and patient mortality is the presence and extent of axillary lymph node (LN) metastasis (1). Increased density of peritumoral and intratumoral LVs in breast cancer is significantly associated with LN metastasis and patient mortality (2). Two members of the vascular endothelial growth factor (VEGF) family, VEGF-C and VEGF-D, bind to VEGF receptor 3 on the surface of lymphatic endothelial cells (LECs) to stimulate growth of LVs (lymphangiogenesis) and cancer cell metastasis to LNs and distant sites (3, 4). VEGF-A, which primarily stimulates blood vessel angiogenesis, promotes lymphangiogenesis and LN metastasis, and members of the angiopoietin, FGF, insulin-like growth factor (IGF), and PDGF families also have been reported to promote lymphangiogenesis and metastasis (1, 5).Intratumoral hypoxia is a common finding in breast cancer, and severe hypoxia [pO 2 <10 mm Hg (∼1.5% O 2 )] is associated with a significantly increased risk of metastasis and patient mortality (6). A major mechanism by which hypoxia promotes metastasis is through the hypoxia-inducible factors (HIFs), which activate the transcription of genes that play key roles in many critical aspects of cancer biology, including angiogenesis, metabolic reprogramming, epithelial-mesenchymal transition, and tissue invasion (7). HIFs are heterodimers composed of an O 2 -regulated HIF-1α or HIF-2α subunit and a constitutively expressed HIF-1β subunit (7). HIF-1α is required for vascular metastasis from breast to lung in autochthonous (8) and orthotopic transplantation (9-11) mouse models.Clinical studies h...

Interplay between receptor tyrosine kinases and hypoxia signaling in cancer

“…As discussed in detail in section 2.1., in mice bearing breast cancer orthografts, digoxin was reported to block lymphangiogenesis and lymphatic metastases to a similar extent as PDGFRβ inhibition by imatinib [36]. Interestingly, xenografts derived from cells with HIF-1α enforced expression were resistant to the anti-tumor effect of digoxin, showing that HIF-1α is the critical target of digoxin for cancer therapy [172].…”

“…This second mechanism is indirectly mediated by the HIF system, too. In breast cancer cells, it was specifically shown that HIF-1α binds to a site in intron 3 of the PDGF-B gene to activate its transcription [36]. The PDGF family consists of disulfide-bonded homodimers of A-, B-, C-and D-polypeptide chains as well as the heterodimer PDGF-AB.…”

“…Binding of the PDGF isoforms to α-and β-tyrosine kinase receptors (PDGFRα and PDGFRβ) promotes new vessel formation [36]. Several studies reported correlations between HIF-1α expression and PDGF-B in breast cancer [36] and glioma [37].…”

“…Several studies reported correlations between HIF-1α expression and PDGF-B in breast cancer [36] and glioma [37]. In mice bearing triple negative breast cancer orthografts, lymphangiogenesis and lymphatic metastasis were shown to be blocked by treatment with the cardiac glycoside digoxin [38], which inhibits HIF-1α, or by the tyrosine kinase inhibitor imatinib via PDGFRβ targeting.…”

“…In mice bearing triple negative breast cancer orthografts, lymphangiogenesis and lymphatic metastasis were shown to be blocked by treatment with the cardiac glycoside digoxin [38], which inhibits HIF-1α, or by the tyrosine kinase inhibitor imatinib via PDGFRβ targeting. This suggests that breast cancer patients might benefit from treatment aiming at targeting either HIF-1α or PDGFRβ alone or both together [36].…”