Primary cilia and aberrant cell signaling in human ovarian cancer

Human ovarian cancer is linked to defects in assembly and function of primary cilia. Human ovarian cancer cells have increased expression and activity of centriolar Aurora A kinase (AurA) that inhibits formation of primary cilia and cause aberrant Hedgehog (Hh) signaling.
Ovarian cancer is the fourth leading cause of death among women in industrialized countries. Around 80-90% of these cancers stem from the ovarian surface epithelium (OSE). Here we show that cancer OSE cells have defects in assembly of primary cilia, which may cause malignant transformation of OSE.
Isolation and culturing of human wt and cancer OSE cells from patients. Immunofluorescence microscopy, SDS-PAGE, Western blotting, quantitative PCR, immunohistochemical analysis of OSE sections, AurA inhibition assays.

We investigated the relationship between primary cilia in cultures of normal human OSE cells isolated from 20-34 year old women and in human ovarian adenocarcinoma cell lines (OVCAR3 and SKOV3), which are derived from human OSE of ovarian cancer patients. Initially we show by immunofluorescence microscopy (IFM) analysis that primary cilia protrude from normal OSE, and that about 80% of human OSE cells in culture form primary cilia after serum starvation to induce growth arrest. In contrast, only about 20% of OVCAR3 and SKOV3 cells were ciliated during growth arrest, indicating that defects in ciliogenesis are linked to ovarian cancer. Induction of quiescence was verified by dephosphorylation of retinoblastoma protein and nuclear loss of PCNA and KI67, such that growth-arrested cells were e.g. KI67 negative. In normal OSE cells, components in signaling pathways that are defective in tumor cell formation and invasion localized to primary cilia, including Hh components. Hh signaling measured by Ptc-1 expression was greatly up-regulated in cancer cells compared to normal cells. IFM and Western blot analysis further showed that AurA is up-regulated and strongly localized to centrioles in cancer cells, and that this localization is reduced in wt OSE cells forming primary cilia. Inhibition of AurA in cancer partly restored ciliary assembly.
Our results support the model by which primary cilia are associated with malignant transformation of OSE that may represent a novel drug target with therapeutic potential in epithelial cancers. Further analysis will be required to understand the importance of AurA and its upstream regulators in ciliary disassembly and regulation of signaling pathways in malignant cell transformation.

No relevant conflicts of interest declared.