Stanich, Jennifer E.

Ano1 is a Ca 2+ activated Cl − channel expressed in several proliferating cell types including various epithelia, gastrointestinal stromal tumors, interstitial cells of Cajal (ICC) and CFPAC‐1 cells. The aim of this study was to determine if Ano1 regulates proliferation. ICC from Ano1 (−/−) and Ano1 (+/+) mice were cultured with Cl − channel inhibitors or in low Cl − media. CFPAC‐1 cells grown in low Cl − media were pulsed with EdU for 1 h. Incorporation was measured by flow cytometry. For immunoblots on mouse jejunum, antibodies to pRb, phospho(Ser773)‐pRb and GAPDH were used. Fewer proliferating ICC were detected in Ano1 (−/−) cultures (15 ± 3.5% Ki67 + ICC vs 25 ± 4% in Ano1 (+/+) , mean ± SEM, n = 4, p < 0.05). Cl − channel inhibitors DIDS (10 μM), niflumate (10 μM) and tamoxifen (1 μM) decreased ICC proliferation by 53, 53 and 59%, respectively ( p < 0.05). This effect was reduced in cultures from Ano1 (−/−) mice (29% and 19 % decrease, 22% increase, p > 0.05). Fewer proliferating ICC and CFPAC‐1 cells were detected in low Cl − media (% EdU + ICC: 120 mM; 19.8 ± 5.3, 12 mM; 8.5 ± 3.2, n = 4, and % EdU + CFPAC‐1: 120 mM; 29.5, 12 mM; 14.3 p < 0.05). Proportionally less Ser773‐phosphorylated pRb was detected in jejunum from Ano1 (−/−) mice (Ano1 (+/+) ; 5.98 ± 0.78, Ano1 (−/−) ; 3.60 ± 0.49, mean ± SEM, n = 7, p < 0.05). In conclusion, Ano1 regulates proliferation possibly by promoting the G 1 /S transition of the cell cycle. Support: DK57061 and DK68055.

Ano1 is a recently discovered Ca2+-activated Cl− channel expressed on interstitial cells of Cajal (ICC) that has been implicated in slow-wave activity in the gut. However, Ano1 is expressed on all classes of ICC, even those that do not contribute to generation of the slow wave, suggesting that Ano1 may have an alternate function in these cells. Ano1 is also highly expressed in gastrointestinal stromal tumors. Mice lacking Ano1 had fewer proliferating ICC in whole mount preparations and in culture, raising the possibility that Ano1 is involved in proliferation. Cl− channel blockers decreased proliferation in cells expressing Ano1, including primary cultures of ICC and in the pancreatic cancer-derived cell line, CFPAC-1. Cl− channel blockers had a reduced effect on Ano1(−/−) cultures, confirming that the blockers are acting on Ano1. Ki67 immunoreactivity, 5-ethynyl-2′-deoxyuridine incorporation, and cell-cycle analysis of cells grown in low-Cl− media showed fewer proliferating cells than in cultures grown in regular medium. We confirmed that mice lacking Ano1 had less phosphorylated retinoblastoma protein compared with controls. These data led us to conclude that Ano1 regulates proliferation at the G1/S transition of the cell cycle and may play a role in tumorigenesis.