Purpose: The purpose of this study was to determine whether YAP/TAZ activation in uveal melanoma (UM) and the susceptibility of melanoma cell lines to YAP/TAZ inhibition by verteporfin (VP) is related to the tumor's genetic background.
Methods: Characteristics of 144 patients with enucleated UM were analyzed together with mRNA expression levels of YAP/TAZ-related genes (80 patients from the The Cancer Genome Atlas [TCGA] project and 64 patients from Leiden, The Netherlands). VP was administered to cell lines 92.1, OMM1, Mel270, XMP46, and MM28 (UM), CRMM1 and CRMM2 (conjunctival melanoma), and OCM3 (cutaneous melanoma). Viability, growth speed, and expression of YAP1-related proteins were assessed.
Results: In TCGA data, high expression of YAP1 and WWTR1 correlated with the presence of monosomy 3 (P = 0.009 and P < 0.001, respectively) and BAP1-loss (P = 0.003 and P = 0.001, respectively) in the primary UM; metastasis development correlated with higher expression of YAP1 (P = 0.05) and WWTR1 (P = 0.003). In Leiden data, downstream transcription factor TEAD4 was increased in cases with M3/BAP1-loss (P = 0.002 and P = 0.006) and related to metastasis (P = 0.004). UM cell lines 92.1, OMM1, and Mel270 (GNAQ/11-mutation, BAP1-positive) and the fast-growing cell line OCM3 (BRAF-mutation) showed decreased proliferation after exposure to VP. Two slow-growing UM cell lines XMP46 and MM28 (GNAQ/11-mutation, BAP1-negative) were not sensitive to VP, and neither were the two conjunctival melanoma cell lines (BRAF/NRAS-mutation).
Conclusions: High risk UM showed an increased expression of YAP/TAZ-related genes. Although most UM cell lines responded in vitro to VP, BAP1-negative and conjunctival melanoma cell lines did not. Not only the mutational background, but also cell growth rate is an important predictor of response to YAP/TAZ inhibition by VP.