Promoter methylation of RASSF1 is common in non-tumor choroid tissue

Abstract

Purpose : RASSF1, located on chromosome 3 (3p21.31), is a known tumor suppressor involved in the tumorigenesis of many cancers. Significant variation in the frequency of epigenetic promoter methylation in RASSF1 have been reported in uveal melanoma (UM), ranging 13-83%. We investigated the frequency of RASSF1 epigenetic inactivation and its role in UM tumorigenesis.

Methods : Promoter methylation status was assessed using methylation-specific PCR. RASSF1 RNA expression was assessed using quantitative-RT PCR. The expression of RASSF1 was also assessed in published UM data from The Cancer Genome Atlas (TCGA).

Results : No promoter methylation was found in the peripheral blood (PB) of UM patients (N=18) and unaffected controls (N=7). Promoter methylation was detected in 3/5 (60%) cadaver choroids; 13/17 (76%) unaffected choroids from eyes with UM; 11/15 (73%) UM tumors; and 3/3 (100%) UM cell lines. Significant downregulation of RASSF1 was detected in UM tumors and unaffected choroids from UM eyes compared to cadaver choroid samples. No genetic alterations, mutations, or deletions of RASSF1 were detected in the 80 UM tumors included in TCGA data. Three tumors showed RASSF1 upregulation and one showed downregulation.

Conclusions : RASSF1 promoter methylation is common in choroidal tissue and is likely not a major driver in UM tumorigenesis. Other mechanisms for downregulation of RASSF1 may be at play. Our results suggest that RASSF1 downregulation is an early and common event in UM tumorigenesis, which may be missed in TCGA analysis because non-tumor tissue is not included.

This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.