The Ephrin-A1/EPHA2 Signaling Axis Regulates Glutamine Metabolism in HER2-Positive Breast Cancer

Abstract

Dysregulation of receptor tyrosine kinases (RTKs) contributes to cellular transformation and cancer progression by disrupting key metabolic signaling pathways. The EPHA2 RTK is overexpressed in aggressive forms of breast cancer, including the HER2+ subtype, and correlates with poor prognosis. However, the role of EPHA2 in tumor metabolism remains unexplored. In this study, we used in vivo and in vitro models of HER2-overexpressing breast cancer to investigate the mechanisms by which EPHA2 ligand-independent signaling promotes tumorigenesis in the absence of its prototypic ligand, ephrin-A1. We demonstrate ephrin-A1 loss leads to upregulated glutamine metabolism and lipid accumulation that enhanced tumor growth. Global metabolic profiling of ephrin-A1-null, HER2-overexpressing mammary tumors revealed a significant increase in glutaminolysis, a critical metabolic pathway that generates intermediates for lipogenesis. Pharmacologic inhibition of glutaminase activity reduced tumor growth in both ephrin-A1-depleted and EPHA2-overexpressing tumor allografts in vivo. Mechanistically, we show that the enhanced proliferation and glutaminolysis in the absence of ephrin-A1 was attributed to increased RhoA-dependent glutaminase activity. EPHA2 depletion or pharmacologic inhibition of Rho, glutaminase, or fatty acid synthase abrogated the increased lipid content and proliferative effects of ephrin-A1 knockdown. Together, these findings highlight a novel, unsuspected connection between the EPHA2/ephrin-A1 signaling axis and tumor metabolism, and suggest potential new therapeutic targets in cancer subtypes exhibiting glutamine dependency.

The receptor tyrosine kinase EphA2 promotes glutamine metabolism in tumors by activating the transcriptional coactivators YAP and TAZ

“…2A). As expected, EphA2 expression was significantly increased in ephrin-A1 knockout tumors (2). While YAP and TAZ were primarily observed in the cytoplasm of wild-type tumors, nuclear localization was significantly increased in ephrin-A1 knockout tumors (Fig.…”

“…Although Rho activation can lead to increased glutaminase activity (2, 40), the mechanism has not been elucidated. As RhoA can activate the transcriptional cofactors YAP and TAZ (41), we reasoned that increased glutaminolysis induced by EphA2 could be mediated by RhoA-dependent YAP and TAZ activation.…”

“…To determine if EphA2 increases YAP and TAZ activity in vivo, we utilized an ephrin-A1 ( EFNA1 ) knockout MMTV-NeuT breast cancer mouse model, which has been demonstrated to overexpress EphA2 (2). Mammary tumors were collected from wild-type ( EFNA1 +/+ ) or ephrin-A1 knockout ( EFNA1 −/− ) mice, and YAP and TAZ subcellular localization were determined by immunohistochemistry (Fig.…”

“…As a member of the largest family of RTKs, the Eph receptors, EphA2 is frequently overexpressed in human cancer, with enhanced EphA2 activity correlating with tumor progression and reduced survival (2–5). However, unlike other RTKs, cumulative evidence supports two modes of EphA2 signaling.…”

“…Among breast cancer subtypes, the HER2-positive subtype is one of the most reliant on glutamine metabolism, likely resulting from HER2-dependent upregulation of GLS and SLC1A5 (38, 39). We have previously shown that EphA2 promotes glutamine metabolism to support tumor growth in a HER2-positive breast cancer model (2); however, the mechanism of EphA2-dependent metabolism has not been elucidated.…”