Ligand-independent dimerization and activation of the oncogenic Xmrk receptor by two mutations in the extracellular...

Area of Science:

• Oncology
• Molecular Biology
• Genetics

Background:

• Hereditary malignant melanoma in Xiphophorus fish originates from the overexpression of the oncogenic receptor tyrosine kinase ONC-Xmrk.
• Proto-oncogene INV-Xmrk overexpression alone does not confer oncogenic function, indicating specific activating mutations in ONC-Xmrk are crucial.

Purpose of the Study:

• To identify the specific activating mutations responsible for the oncogenic function of the ONC-Xmrk receptor.
• To elucidate the mechanism by which these mutations lead to receptor activation and influence its processing.

Main Methods:

• Construction and analysis of chimeric and mutant ONC-Xmrk receptors.
• Investigation of mutations within both the intracellular and extracellular domains of the receptor.
• Assessment of receptor dimerization, activation status, and endoplasmic reticulum processing, including glycosylation.

Main Results:

• Mutations in the intracellular domain of ONC-Xmrk were not found to be responsible for receptor activation.
• Two specific mutations in the extracellular domain were identified as critical for ONC-Xmrk activation: C578S (cysteine substitution) and G359R (glycine to arginine exchange in subdomain III).
• Both identified mutations induce constitutive dimer formation, leading to receptor activation, and also impair receptor processing and glycosylation in the endoplasmic reticulum.

Conclusions:

• The oncogenic function of ONC-Xmrk in Xiphophorus melanoma is driven by specific activating mutations in its extracellular domain.
• These mutations promote constitutive dimerization and activation of the receptor tyrosine kinase, contributing to tumor development.
• The identified mutations also impact receptor maturation, suggesting a link between altered processing and oncogenesis.