14 The mechanisms involved in apoptosis-dependent cavitation are incompletely understood. 14 It comprises complex cell–cell and cell–matrix recognition, establishment of apical–basal polarity as well as cavitation, which depends on apoptosis of cells situated within the lumen. Lumen formation of different epithelial cell types represents a fundamental step for the proper development of several organs including lungs, pancreas, intestine and kidneys. 13 Knockdown of ANO1 but not ANO6 significantly reduced secretion-dependent cyst growth pointing towards distinct functions of ANO1 and ANO6 in the cyst epithelium. Recently, we have shown that ANO6 is expressed in cyst-forming epithelial cells together with ANO1, which is widely expressed in epithelial cells.

12 Despite the broad expression and function of ANO6, there is only sparse data about the subcellular localization of ANO6. 10 In addition, ANO6 is involved in bone mineralization, cell volume regulation, cell proliferation and apoptosis. 12 Mutations in ANO6 cause the Scott syndrome, which is characterized by a defect in Ca 2+-dependent phospholipid scrambling of plasma membrane phospholipids. ANO6 is the most widely expressed paralogue. 11 However, data about their functional roles are very limited so far. 9, 10 ANO3, 4, 7, 9 may also act as Ca 2+-dependent phospholipid scramblases. 6, 7, 8 Besides its ability to conduct ions ANO6 has also been shown to act as a phospholipid scramblase. 4, 5 In contrast to the other paralogues, the function of ANO1 and ANO2 as Ca 2+-activated chloride channels has been confirmed in vivo and in vitro. 3Īnoctamins (ANO1-ANO10, TMEM16A-K) form a family of 10 proteins that are supposed to act as Ca 2+-activated chloride channels with no homology to other known ion channels. 2 Mutations in genes encoding for proteins that are necessary either for the function or the structure of the primary cilium lead to ciliopathies, systemic disorders that are typically characterized by the development of polycystic kidneys. 1 The ciliary membrane contains receptors and ion channels that link mechanical or chemical stimuli including fluid flow, sonic hedgehog and growth factors to intracellular signaling cascades regulating cell differentiation, migration and growth. Primary cilia are non-motile protrusions of the apical membrane of various cell types. These data identify ANO6 as a cilium-associated protein and suggest its functional relevance in cyst formation. In line with these data, we show that ANO6 is highly expressed in apoptotic cyst epithelial cells of human polycystic kidneys. In the absence of ANO6, apoptosis was reduced and epithelial cells were incompletely removed from the center of cell aggregates, which form in the early phase of cystogenesis. However, knockdown of ANO6 impaired cyst lumen formation of MDCK cells in three-dimensional culture. ANO6 was not essential for cilia formation and had no effect on in vitro cyst expansion. Here we show that anoctamin 6 (ANO6), a member of the anoctamin chloride channel family, is localized in the primary cilium of renal epithelial cells in vitro and in vivo. Functional or structural defects of the cilium lead to systemic disorders comprising polycystic kidneys as a key feature. Primary cilia are antenna-like structures projected from the apical surface of various mammalian cells including renal tubular cells.

Tubular lumen