Primary cilia are hair-like projections that protrude on most of mammalian cells and mediate reception of extracellular signals. Numerous studies have demonstrated that a variety of cancer cells including pancreatic ductal adenocarcinoma (PDAC) fail to form primary cilia. The loss of primary cilia is thought to cause carcinogenesis and progressive cell proliferation. However, the relationship of the primary cilia loss with carcinogenesis and/or cancer malignancy remains arguable. We herein examined whether ciliogenesis was increased in a model of more progressive PDAC and investigated effects of ciliogenesis on growth of PDAC using a pancreatic cancer cell line, PANC-1. The majority of PANC-1 cells in a cell cluster grown from a solitary cell possessed primary cilia. The rate of ciliogenesis was higher in cells grown from low density than in cells grown from high density. Almost all clones passing limiting dilution culture had abilities to grow primary cilia. Compared to the parental PANC-1 cells, clones that proliferated from a solitary cell showed increase in the ciliogenesis rate. Blocking ciliogenesis suppressed cell cluster formation. Our results suggest that pancreatic cancer cells that are more resistant to a solitary condition have abilities of ciliogenesis and form tumor-like cell clusters in a primary cilia-dependent manner.
