ETS Proto-oncogene 1 Transcriptionally Up-regulates the Cholangiocyte Senescence-associated Protein Cyclin-dependent Kinase Inhibitor 2A.

Primary sclerosing cholangitis (PSC) is a chronic, fibroinflammatory cholangiopathy (disease of the bile ducts) of unknown pathogenesis. We reported that cholangiocyte senescence features prominently in PSC and that neuroblastoma RAS viral oncogene homolog (NRAS) is activated in PSC cholangiocytes. Additionally, persistent microbial insult (e.g. LPSs) induces cyclin-dependent kinase inhibitor 2A (CDKN2A/p16INK4a) expression and senescence in cultured cholangiocytes in an NRAS-dependent manner. However, the molecular mechanisms involved in LPS-induced cholangiocyte senescence and NRAS-dependent regulation of CDKN2A remain unclear. Using our in vitro senescence model, we found that LPS-induced CDKN2A expression coincided with a 4.5-fold increase in ETS1 (ETS proto-oncogene 1) mRNA, suggesting that ETS1 is involved in regulating CDKN2A This idea was confirmed by RNAi-mediated suppression or genetic deletion of ETS1, which blocked CDKN2A expression and reduced cholangiocyte senescence. Furthermore, site-directed mutagenesis of a predicted ETS-binding site within the CDKN2A promoter abolished luciferase reporter activity. Pharmacological inhibition of RAS/MAPK reduced ETS1 and CDKN2A protein expression and CDKN2A promoter-driven luciferase activity by ∼50%. In contrast, constitutively active NRAS expression induced ETS1 and CDKN2A protein expression, whereas ETS1 RNAi blocked this increase. Chromatin immunoprecipitation-PCR detected increased ETS1 and histone 3 lysine 4 trimethylation (H3K4Me3) at the CDKN2A promoter following LPS-induced senescence. Additionally, phospho-ETS1 expression was increased in cholangiocytes of human PSC livers and in the Abcb4 (Mdr2)-/- mouse model of PSC. These data pinpoint ETS1 and H3K4Me3 as key transcriptional regulators in NRAS-induced expression of CDKN2A, and this regulatory axis may therefore represent a potential therapeutic target for PSC treatment.

Primary Cilia in Tumor Biology: The Primary Cilium as a Therapeutic Target in Cholangiocarcinoma.

Cilia are microtubule-based organelles, which are ubiquitously expressed in epithelial cells. Cholangiocytes, the epithelial cells lining the biliary tree, have primary cilia extending from their apical plasma membrane into the ductal lumen, where the cilia function as multisensory organelles transducing environmental cues into the cell interior. The decrease or loss of primary cilia has been described in several malignancies, including cholangiocarcinoma, suggesting that the loss of cilia is a common occurrence in neoplastic transformation. In this short review, we describe the expression of cilia in several cancers, explore the mechanisms and consequences of ciliary loss, and discuss the potential use of the primary cilia as therapeutic targets.