PU.1-induced cell growth arrest in L428^tetPU.1 cells is dependent on p21 up-regulation. (A) Stable knockdown of p21 strongly suppressed p21 expression, even after PU.1 induction in L428^tetPU.1 cells. (B) The growth arrest of L428^tetPU.1 cells induced by PU.1 overexpression was reversed by targeted knockdown of p21. PU.1-induced growth arrest in L428^tetPU.1 cells stably transduced with scrambled siRNA (○), whereas PU.1 failed to induce growth arrest in L428^tetPU.1 cells stably transduced with p21 siRNA (▵).