Cilia can promote or suppress tumor growth, depending on the nature of the tumor-initiating event, as reported by two studies in this week's Nature Medicine.
Primary cilia are specialized appendages that extend from the surface of many cell types and have been implicated in cell signaling. They are crucial during fetal development for signaling pathways mediated by a protein known as Hedgehog. As Hedgehog has also been implicated in cancers, Jeremy Reiter, Arturo Alvarez-Buylla and their respective colleagues explored the possible contribution of primary cilia to tumor formation.
Studying two types of cancer, basal cell carcinoma and medulloblastoma, the two groups independently found that cilia could favor or inhibit tumor formation in mice. If the tumor was triggered by the expression of Smoothened, a well-known activator of Hedgehog, removal of cilia blocked tumor formation. But if the tumor was initiated by the expression of Gli2, a molecule downstream of Hedgehog, then removal of cilia accelerated tumor growth.
These data disclose an unexpected dual role of cilia on cancer. Further analysis of their role may lead to better understanding of tumor development and treatment.