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Frequent EPHA2 receptor mutations in cholangiocarcinoma disrupt receptor forward signaling supporting a tumor
Evodie Koutouan1, Alejandro Lillo1, Ayano Kabashima2
1Cancer Center, Sanford Burnham Prebys Medical Discovery Institute, La Jolla, CA, 92037, USA.
Abstract:
Although EPHA2 is a receptor tyrosine kinase widely expressed in many cancers, it exhibits a uniquely high frequency of coding sequence mutations in cholangiocarcinoma, a cancer of the biliary tract with dismal prognosis. EPHA2 is extensively studied, but very little is known about the role of EPHA2 cancer mutations. To define the functional significance of EPHA2 mutations in biliary tract cancers, we generated representative EPHA2 mutants and monitored major receptor autophosphorylation sites as indicators of kinase activity-dependent signal transduction (known as forward signaling). We found that missense mutations in the ligand-binding domain abrogate ephrinA ligand binding, while missense mutations in the kinase domain abrogate kinase activity. The effects of missense mutations in other domains were less pronounced and varied depending on the phosphosite. The majority of the EPHA2 mutations are nonsense or frame-shift mutations that introduce early stop codons. They generate EPHA2 truncated forms that lack an intact kinase domain or, in some cases, most of the coding sequence. Several EPHA2 mutants tested inhibited tyrosine phosphorylation of co-expressed EPHA2 wild-type, indicating the ability to exert dominant negative effects. We show that EPHA2 forward signaling in cholangiocytes inhibits the ERK oncogenic pathway and cell proliferation, suggesting that loss-of-function mutations facilitate tumor development in the biliary tract. Indeed, an EPHA2 kinase-inactive mutant, but not EPHA2 wild-type, induced proliferative masses consistent with well differentiated cholangiocarcinoma in a validated mouse model of cholangiocarcinogenesis. Thus, EPHA2 has the attributes of a driver gene with tumor suppressor activity in biliary tract cancers.
Insights
Mutations in EPHA2, a receptor tyrosine kinase, are common in cholangiocarcinoma. Loss-of-function mutations in EPHA2 promote biliary tract cancer development by inhibiting tumor suppressor activity.
Area of Science:
- Oncology
- Molecular Biology
- Biochemistry
Background:
- EPHA2, a receptor tyrosine kinase, is frequently mutated in cholangiocarcinoma, a biliary tract cancer with poor prognosis.
- The functional impact of EPHA2 mutations in cancer remains largely unknown despite extensive research on the receptor.
- Cholangiocarcinoma exhibits a high frequency of EPHA2 coding sequence mutations, suggesting a critical role in tumorigenesis.
Purpose of the Study:
- To investigate the functional significance of EPHA2 mutations in biliary tract cancers.
- To determine how different EPHA2 mutations affect receptor activity, signaling, and tumor development.
- To explore the potential of EPHA2 as a tumor suppressor in cholangiocarcinoma.
Main Methods:
- Generated representative EPHA2 mutants to assess kinase activity and signaling.
- Analyzed missense mutations in ligand-binding and kinase domains for functional impact.
- Investigated the effects of nonsense and frame-shift mutations, including dominant-negative effects.
- Utilized a mouse model of cholangiocarcinogenesis to evaluate EPHA2 mutant function in vivo.
Main Results:
- Missense mutations in the ligand-binding domain abolished ephrinA binding; kinase domain mutations abrogated kinase activity.
- Nonsense and frame-shift mutations generated truncated EPHA2 forms lacking kinase function.
- Some EPHA2 mutants exhibited dominant-negative effects on wild-type EPHA2 signaling.
- EPHA2 forward signaling inhibited the ERK pathway and cell proliferation; a kinase-inactive mutant induced cholangiocarcinoma in mice.
Conclusions:
- EPHA2 mutations significantly impact its function, with loss-of-function mutations promoting biliary tract cancer.
- EPHA2 acts as a tumor suppressor in the biliary tract, with inactivating mutations contributing to cholangiocarcinoma development.
- EPHA2 is a potential driver gene with tumor suppressor activity in biliary tract cancers, offering therapeutic implications.
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