CLDN4 and breast cancer: It is noteworthy that, upon cholesterol addition, the relative cell numbers in T47D:dKO:CLDN4:LXRβS432A cells were also significantly elevated, and the increased level was similar to that in T47D:dKO:CLDN4:LXRβ cells (Additional file 1: Fig. S10B), suggesting that the CLDN4–LXRβS432 signaling regulates breast cancer cell proliferation by increasing the intracellular cholesterol levels.