Background/aim: Uveal melanoma (UM) is the deadliest form of adult eye cancers due to frequent metastasis to the liver and poor therapeutic responses by the metastatic tumours. Mutations in the BAP1 gene which leads to deficiency of BAP1 function and expression are associated with elevated risks of UM metastasis and poor disease prognosis. BAP1-deficient UM cell lines survive better in amino acid depleted conditions but mechanisms associated with better cell survival are unclear. This study aims to identify these mechanisms that may lead to uncovering therapeutic strategies to effectively target BAP1-deficient and metastatic UM.
Methods: A reverse phase protein array was performed to screen the expression of approximately 500 proteins following exposure of BAP1-deficient UM and BAP1 wild-type (WT) UM cells to amino acid-free culture media.
Results: The expression levels of five proteins were significantly different between BAP1-deficient and BAP1 WT UM cells following incubation in amino acid-free media. Insulin-like growth factor-binding protein 2 (IGFBP2) expression was validated by Western blotting. IGFBP2 levels decreased markedly following amino acid depletion in BAP1-deficient UM cells but not in BAP1 WT cells. The basal expression level of IGFBP2 was found to be elevated in BAP1-deficient cells. Consistently, IGFBP2 mRNA levels are higher in BAP1 mutant UM patient specimens within The Cancer Genome Atlas (TCGA) dataset compared to BAP1 WT UM and silencing of BAP1 in BAP1 WT UM cell lines decreased IGFBP2 protein levels. To link IGFBP2 levels to survival under amino acid starvation, siRNA-mediated knockdown of IGFBP2 was performed and found to decrease the survival of BAP1-deficient UM cells under amino acid depletion. Studies are ongoing to elucidate the roles of IGFBP2 in UM and mechanisms mediating IGFBP2, and whether better cell survival in amino acid depleted conditions such as in the blood circulation promotes metastasis.
Conclusions: Findings from this study show that IGFBP2 is elevated in BAP1-deficient UM and is associated with protection of BAP1-deficient UM cells against the growth inhibitory effects of amino acid-depletion. This highlights the potential of IGFBP2 as a therapeutic target and likely as part of strategies to prevent metastasis and/or to effectively control metastatic UM.