Ephrin-A1 Facilitates Mammary Tumor Metastasis through an Angiogenesis-Dependent Mechanism Mediated by EphA Receptor and Vascular Endothelial Growth Factor in Mice

Abstract

Ephrin-A1, the prototypic ligand for EphA receptor tyrosine kinases, is overexpressed in vascularized tumors relative to normal tissue. Moreover, ephrin-A1-Fc fusion proteins induce endothelial cell sprouting, migration, and assembly in vitro, and s.c. vascular remodeling in vivo. Based on these data, we hypothesized that native, membrane-bound ephrin-A1 regulates tumor angiogenesis and progression. We tested this hypothesis using a transplantable mouse mammary tumor model. Small interfering RNA-mediated ephrin-A1 knockdown in metastatic mammary tumor cells significantly diminishes lung metastasis without affecting tumor volume, invasion, intravasation, or lung colonization upon i.v. injection in vivo. Ephrin-A1 knockdown reduced tumor-induced endothelial cell migration in vitro and microvascular density in vivo. Conversely, overexpression of ephrin-A1 in nonmetastatic mammary tumor cells elevated microvascular density and vascular recruitment. Overexpression of ephrin-A1 elevated wild-type but not EphA2-deficient endothelial cell migration toward tumor cells, suggesting that activation of EphA2 on endothelial cells is one mechanism by which ephrin-A1 regulates angiogenesis. Furthermore, ephrin-A1 knockdown diminished, whereas overexpression of ephrin-A1 elevated, vascular endothelial growth factor (VEGF) levels in tumor cell-conditioned medium, suggesting that ephrin-A1-mediated modulation of the VEGF pathway is another mechanism by which membrane-tethered ephrin-A1 regulates angiogenic responses from initially distant host endothelium. These data suggest that ephrin-A1 is a proangiogenic signal, regulating VEGF expression and facilitating angiogenesisdependent metastatic spread. (Cancer Res 2006; 66(21): 10315-24)

The receptor tyrosine kinase EphA2 promotes mammary adenocarcinoma tumorigenesis and metastatic progression in mice by amplifying ErbB2 signaling

“…For rescue experiments, EphA2 -/-MMTV-Neu primary tumor cells were transduced with 1 × 10 8 pfu/ml adenovirus expressing constitutively active RhoA (Q63L) or control β-gal 48 hours prior to transwell assay. Tumor-endothelial cell coculture migration assays were performed as described previously (8,68).…”

Loss of EphA2 receptor tyrosine kinase reduces Apcmin/+ tumorigenesis

“…Eph receptor A2 (EphA2), which maps to human chromosome 1p36.1, is associated with tumor progression, angiogenesis and poor prognosis in breast, pancreatic, ovarian, cervical, mesothelioma, bladder, colon, gastric, lung, melanoma, esophageal, prostate and kidney cancers. [9][10][11][12][13][14][15] In mammary cancers, EphA2 promotes adenocarcinoma development and metastatic progression, [16][17][18][19] in some cases by amplifying ErbB2 signaling. 17 Further, in metastatic breast cancer, EphA2 has been reported to be negatively regulated by estrogen and c-Myc, and EphA2 over-expression decreases estrogen dependence; phenotypes that may explain the antimetastatic functions of estrogen in some cancers.…”

EphA2 protein expression in metastatic renal cell carcinoma treated with VEGF-inhibitors is predictive of patient survival

“…EphA2/ephrin-A1 signaling is one supposed pathway, which contributes to resistance to VEGF-Inhibitors, and mutual modulating activities on expression/activation were observed [2,4,12] . In spite of these new findings the precise mechanisms underlying the interplay of VEGF and EphA2 signaling are still to be uncovered.…”

“…Despite these advancements in therapy the primary and secondary resistances to anti-angiogenic treatment are major problems that could not be overcome to date, and molecular predictive factors that identify responders from non-responders remain to be identified [11] . EphA2/ephrin-A1 and VEGF signaling modulate theexpression/ activation of each other [2,4,12] , and additionally EphA2 signaling is one supposed mechanism, which contributes to resistance to VEGF-Inhibitors [1,13] . These reported associations between EphA2 signaling and the VEGF pathway strongly suggest an influence of EphA2 protein expression on response to VEGF-targeted therapy.…”