Loss of Cilia in Uveal Melanoma: Implications for Diagnosis

Abstract

Purpose : The primary cilium is a microtubule-based, finger-like projection on the surface of most cells in the human body. This organelle plays an important role in both cellular proliferation and division. In most mammalian cells, primary cilia are dynamically regulated in the cell cycle by disassembly at the G2/M phase and reassembly after cell division. Previous studies have found depleted or defective cilia in multiple types of cancer cells, including pancreatic and renal cancers. Although there is more focus on the crosstalk between cilia and cancer development, studies about primary cilia in uveal melanoma (UM) remain scarce. The goal of this study was to investigate the ciliation of human UM tissue and cell lines.

Methods : In the present study, we assessed primary cilia in UM (n=3 patients) and basal cell carcinoma (BCC, n=2 patients) paraffin tissue sections by employing two classic ciliary antibodies: Arl13b and IFT88. These antibodies detect the ciliary axonemes and basal bodies respectively. Unstained paraffin-based slides were deparaffinized and boiled in 1mM EDTA +0.05% Tween 20 prior to immunostaining. UM cell lines (UM 92-1 and UM 202) were cultured until confluent and then serum starved for 48 hours before staining with ciliary antibodies. Arl13b signal was counted as a cilium if one end of the signal was adjacent to the IFT88 signal. Statistical analysis was performed using Student's t-test. p < 0.05 was considered statistically significant.

Results : Quantification of immunofluorescently labeled primary cilia indicated that 45 ± 12% of cells were ciliated in BCC tissue (n=658 cells). The ciliation in UM tissue was 0.8 ± 1.2% (n=651 cells), which was significantly reduced compared to BCC tissue (p < 0.001). Quantitative analysis showed that ciliary length is significantly shorter in UM samples compared with BCC samples (p < 0.001). In cultured human UM cell lines, we found similar ciliation compared to UM tissue samples.

Conclusions : This is the first report of loss of cilia in UM tissue in contrast to BCC which more often retain their cilia. These data provide insight into ocular tumor diagnosis and potential cilia-based therapeutic strategies against UM.

This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.