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Cancer Res. 2015 Aug 15;75(16):3327-39. doi: 10.1158/0008-5472.CAN-14-2798. Epub 2015 Jun 30.

Proteolysis of EphA2 Converts It from a Tumor Suppressor to an Oncoprotein.

Author information

1
Division of Cancer Cell Research, Institute of Medical Science, University of Tokyo, Tokyo, Japan.
2
Division of Cancer Cell Research, Institute of Medical Science, University of Tokyo, Tokyo, Japan. Department of Cancer Biology, Vanderbilt University School of Medicine, Nashville, Tennessee.
3
Department of Obstetrics, Fukuoka University, Fukuoka, Japan.
4
Department of Pathology, Fukuoka University, Fukuoka, Japan.
5
Department of Otorhinolaryngology, Faculty of Medicine, Fukuoka University, Fukuoka, Japan.
6
Department of Cancer Biology, Vanderbilt University School of Medicine, Nashville, Tennessee.
7
Division of Cancer Cell Research, Institute of Medical Science, University of Tokyo, Tokyo, Japan. Integrated Center for Advanced Medical Technologies, Kochi Medical School, Kochi, Japan. mseiki@ims.u-tokyo.ac.jp.

Abstract

Eph receptor tyrosine kinases are considered candidate therapeutic targets in cancer, but they can exert opposing effects on cell growth. In the presence of its ligands, Eph receptor EphA2 suppresses signaling by other growth factor receptors, including ErbB, whereas ligand-independent activation of EphA2 augments ErbB signaling. To deploy EphA2-targeting drugs effectively in tumors, the anti-oncogenic ligand-dependent activation state of EphA2 must be discriminated from its oncogenic ligand-independent state. Because the molecular basis for the latter is little understood, we investigated how the activation state of EphA2 can be switched in tumor tissue. We found that ligand-binding domain of EphA2 is cleaved frequently by the membrane metalloproteinase MT1-MMP, a powerful modulator of the pericellular environment in tumor cells. EphA2 immunostaining revealed a significant loss of the N-terminal portion of EphA2 in areas of tumor tissue that expressed MT1-MMP. Moreover, EphA2 phosphorylation patterns that signify ligand-independent activation were observed specifically in these areas of tumor tissue. Mechanistic experiments revealed that processing of EphA2 by MT1-MMP promoted ErbB signaling, anchorage-independent growth, and cell migration. Conversely, expression of a proteolysis-resistant mutant of EphA2 prevented tumorigenesis and metastasis of human tumor xenografts in mice. Overall, our results showed how the proteolytic state of EphA2 in tumors determines its effector function and influences its status as a candidate biomarker for targeted therapy.

PMID:
26130649
PMCID:
PMC4682662
DOI:
10.1158/0008-5472.CAN-14-2798
[Indexed for MEDLINE]
Free PMC Article

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