The receptor tyrosine kinase EphA2 promotes mammary adenocarcinoma tumorigenesis and metastatic progression in mice by amplifying ErbB2 signaling
Dana M. Brantley-Sieders, Guanglei Zhuang, Donna Hicks, Wei Bin Fang, Yoonha Hwang, Justin M.M. Cates, Karen Coffman, Dowdy Jackson, Elizabeth Bruckheimer, Rebecca S. Muraoka-Cook, Jin Chen
Dana M. Brantley-Sieders, Guanglei Zhuang, Donna Hicks, Wei Bin Fang, Yoonha Hwang, Justin M.M. Cates, Karen Coffman, Dowdy Jackson, Elizabeth Bruckheimer, Rebecca S. Muraoka-Cook, Jin Chen
View: Text | PDF
Research Article Oncology

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

Abstract

Overexpression of the receptor tyrosine kinase EPH receptor A2 (EphA2) is commonly observed in aggressive breast cancer and correlates with a poor prognosis. However, while EphA2 has been reported to enhance tumorigenesis, proliferation, and MAPK activation in several model systems, other studies suggest that EphA2 activation diminishes these processes and inhibits the activity of MAPK upon ligand stimulation. In this study, we eliminated EphA2 expression in 2 transgenic mouse models of mammary carcinoma. EphA2 deficiency impaired tumor initiation and metastatic progression in mice overexpressing ErbB2 (also known as Neu) in the mammary epithelium (MMTV-Neu mice), but not in mice overexpressing the polyomavirus middle T antigen in mammary epithelium (MMTV–PyV-mT mice). Histologic and ex vivo analyses of MMTV-Neu mouse mammary epithelium indicated that EphA2 enhanced tumor proliferation and motility. Biochemical analyses revealed that EphA2 formed a complex with ErbB2 in human and murine breast carcinoma cells, resulting in enhanced activation of Ras-MAPK signaling and RhoA GTPase. Additionally, MMTV-Neu, but not MMTV–PyV-mT, tumors were sensitive to therapeutic inhibition of EphA2. These data suggest that EphA2 cooperates with ErbB2 to promote tumor progression in mice and may provide a novel therapeutic target for ErbB2-dependent tumors in humans. Moreover, EphA2 function in tumor progression appeared to depend on oncogene context, an important consideration for the application of therapies targeting EphA2.

Authors

Dana M. Brantley-Sieders, Guanglei Zhuang, Donna Hicks, Wei Bin Fang, Yoonha Hwang, Justin M.M. Cates, Karen Coffman, Dowdy Jackson, Elizabeth Bruckheimer, Rebecca S. Muraoka-Cook, Jin Chen

×

Figure 7

EphA2 deficiency does not affect tumorigenesis, microvascular density, or growth regulatory signaling pathways in MMTV–PyV-mT tumors.

Options: View larger image (or click on image) Download as PowerPoint
EphA2 deficiency does not affect tumorigenesis, microvascular density, o...
(A) Loss of EphA2 protein expression was confirmed by immunohistochemical staining. Scale bar: 50 μm. (B) We detected no change in MMTV–PyV-mT tumor microvascular density based on vWF staining (arrows indicate vWF+ blood vessels). Scale bar: 100 μm. (C) We did not observe any change in levels of GTP-bound active Ras or p-Erk in EphA2–/– MMTV–PyV-mT whole tumor extracts relative to controls, nor did we observe any change in levels of RhoA. Uniform loading was confirmed by immunoblotting for total Ras, total Erk, and tubulin. (D) We observed EphA2 overexpression and elevated phosphorylation in MMTV-Neu and MMTV–PyV-mT tumors relative to normal mammary tissue isolated from control FVB mice, with the highest levels observed in MMTV-Neu tumors. We also observed overexpression of ErbB2 and ephrin-A1 in both tumor types, with comparable ephrin-A1 expression in both tumor types and higher ErbB2 levels in MMTV-Neu tumors. Uniform loading was confirmed by immunoblot for actin. (E) We confirmed EphA2 overexpression specifically in epithelium by comparing EphA2 levels in PMEC lysates versus PMTCs derived from MMTV-Neu and MMTV–PyV-mT mice.