Cholangiocyte primary cilia transduce a fluid shear signal to increase KLF2 via the actin cytoskeleton

Abstract

Cholangiocarcinoma is an aggressive solid tumor formed in the bile duct epithelium. Often this tumor obstructs bile flow, known as cholestasis. Normal cholangiocytes detect bile flow in the ductal lumen with an extension of the apical membrane called the primary cilium. However, these sensory organelles are often lost in malignant cells. Kruppel-like factor 2 (KLF2) is an important flow-sensitive transcription factor involved in shear stress response in endothelial cells, and has anti-proliferative, anti-inflammatory, and anti-angiogenic effects. The potential role of KLF2 in cholangiocyte flow detection and in cholangiocarcinoma is unknown. We hypothesized that reduced bile flow contributes to malignant features in cholangiocarcinoma through regulation of KLF2 signaling. We observed that primary cilia were expressed in normal cholangiocytes but were absent in malignant cells. KLF2 expression was higher in normal cells compared to malignant. Depletion of cilia in normal cells led to a decrease in KLF2 expression and increased cilia number was associated with increased KLF2. Enforced KLF2 expression inhibited cell proliferation, migration, and also decreased cell death induction in malignant cells. Applied media flow over cholangiocytes increased KLF2 and cilia depletion completely blocked flow-induced KLF2 expression. Disruption of filamentous actin decreased KLF2 expression, suggesting the cilium may communicate through a cytoskeletal mechanotransduction pathway. Our studies demonstrate that cilia positively regulated KLF2 protein levels and increased fluid flow induced KLF2 expression for the first time in cholangiocytes, emphasizing the importance of reestablishing bile flow in cholestatic cholangiocarcinoma.