Dynamic Expression of Primary Cilia Across Diverse Human Cancers

Abstract

Primary cilia are highly conserved organelles that are best known for their role in signal transduction in development. However, their significance in cancer biology is unclear, with some studies reporting that cilia are lost in cancer while others suggest that cilia promote tumor growth and metastasis. Using immunohistochemistry against the ciliary membrane protein ARL13b, we systematically quantified the cilia found across a diverse spectrum of over 2,000 human tumors. We found that the vast majority of human tumor types were capable of producing cilia, with some tumor types containing more than 50% cells with cilia. Using electron microscopy and live cell imaging, we observed that cilia on tumor cells have atypical ultrastructural features and are highly dynamic, with cilia disassembly immediately before mitosis and re-assembly in the daughter cells. To further investigate the role of cilia in tumor cells, we performed CRISPR/Cas9-mediated knockout of KIF3A in an ovarian cancer cell line. KIF3A knockout resulted in loss of cilia, but without major transcriptomic changes or loss of cell viability. Because cilia have been thought to be features of quiescent or G0/G1 cells, we used multiplexed cyclic immunofluorescence on human tumor samples to characterize the proliferation status of ciliated tumor cells, and found that both proliferating and non-cycling tumor cells were capable of forming cilia.