Using Tsc2-deficient MEFs, human angiomyolipoma-derived 621-101 cells, and xenograft mouse models, it was shown that miR-21 expression was markedly increased in TSC2-deficient cells and was further elevated following rapamycin treatment, despite rapamycin’s role as an mTORC1 inhibitor. The gene discussed is TSC2; the disease is angiomyolipoma.