Changes in cell function occur by specific patterns of intracellular Ca2+, activating Ca2+-sensitive proteins. The anoctamin (TMEM16) protein family has Ca2+-dependent ion channel activity, which provides transmembrane ion transport, and/or Ca2+-dependent phosphatidyl-scramblase activity. Using amino acid sequence analysis combined with measurements of ion channel function, we clarified the so far unknown Ano4 function as Ca2+-dependent, non-selective monovalent cation channel; heterologous Ano4 expression in HEK293 cells elicits Ca2+ activated conductance with weak selectivity of K+ > Na+ > Li+. Endogenously expressed Ca2+-dependent cation channels in the retinal pigment epithelium were identified as Ano4 by KO mouse-derived primary RPE cells and siRNA against Ano4. Exchanging a negatively charged amino acid in the putative pore region (AA702–855) into a positive one (E775K) turns Ano4-elicited currents into Cl− currents evidencing its importance for ion selectivity. The molecular identification of Ano4 as a Ca2+-activated cation channel advances the understanding of its role in Ca2+ signaling.

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PURPOSE. Posterior capsule opacification (PCO) is a complication after cataract surgery, particularly in children. Epithelial-mesenchymal transition (EMT) of lens epithelial cells, mediated by transforming growth factor beta (TGFb), contributes to PCO. However, its pathogenesis in children is poorly understood. We correlated cell growth in culture with patient characteristics, studied gene expression of pediatric lens epithelial cells (pLEC), and examined the effects of TGFb-2 on these cells in vitro. METHODS. Clinical characteristics of children with cataracts correlated with growth behavior of pLEC in vitro. mRNA expression of epithelial (aB-crystallin, connexin-43) and mesenchymal (a V-integrin, a-smooth muscle actin, collagen-Ia2, fibronectin-1) markers was quantified in pLEC and in cell line HLE-B3 in the presence and absence of TGFb-2. RESULTS. Fifty-four anterior lens capsules from 40 children aged 1 to 180 months were obtained. Cell outgrowth occurred in 44% of the capsules from patients 12 months and in 33% of capsules from children aged 13 to 60 months, but in only 6% of capsules from children over 60 months. TGFb-2 significantly upregulated expression of aB-crystallin (HLE-B3), a V-integrin (HLE-B3), collagen-Ia2, and fibronectin-1 (in pLEC and HLE-B3 cells). CONCLUSIONS. Patient characteristics correlated with growth behavior of pLEC in vitro, paralleling a higher clinical incidence of PCO in younger children. Gene expression profiles of pLEC and HLE-B3 suggest that upregulation of a V-integrin, collagen-Ia2, and fibronectin-1 are involved in EMT.