Somatic Hypermutation of the YAP Oncogene in a Human Cutaneous Melanoma

Area of Science:

• Oncology
• Molecular Biology
• Signaling Pathways

Background:

• Melanoma progression is often driven by MAPK signaling pathway mutations (BRAF, NRAS), but MAPK-targeted therapies lack sustained efficacy.
• The Hippo signaling pathway, regulated by YAP and TAZ oncoproteins, is implicated in cancer progression but rarely directly mutated.
• YAP hyperactivation is observed in uveal melanoma, prompting investigation into its role in cutaneous melanoma.

Purpose of the Study:

• To investigate the role of the YAP oncoprotein in cutaneous melanoma progression.
• To identify novel mechanisms driving melanoma beyond classical BRAF/NRAS mutations.
• To explore YAP as a potential therapeutic target in melanoma.

Main Methods:

• Analysis of YAP protein expression in benign nevi, primary cutaneous melanomas, and normal melanocytes.
• Assessment of cell viability dependence on Hippo pathway signaling in patient-derived xenografts and melanoma cell lines.
• Genotyping studies to identify mutations in melanoma samples.

Main Results:

• Elevated YAP protein expression was found in most nevi and primary melanomas compared to normal melanocytes.
• Melanoma cell viability showed variable dependence on Hippo pathway signaling, independent of TAZ and BRAF/NRAS mutations.
• The first hyperactivating YAP mutations in human cancer were identified in melanoma, comprising seven distinct missense mutations affecting key serine residues, leading to YAP hyperactivation.

Conclusions:

• The YAP oncoprotein is implicated in cutaneous melanoma progression and represents a potential therapeutic target in specific patient subgroups.
• Successful anti-YAP therapies will require biomarkers beyond YAP protein expression to identify suitable patient populations.