Analysis of components of the G2 block. Western blot of CD44high and CD44low fractions showing low baseline levels of phosphorylated Chk1 and Chk2 in the unstimulated Cal cell line (A). After 24 hours of exposure to 100 ng/ml NCZ levels increase, especially for CD44high cells (A). Cells of the Ca1 cell line before and after inhibition of Chk1/2 with DBH show increased cell death associated with partial release from the G2 block (p < 0.01) (B). Rates of cell death and proportion of CD44high cells after independent knockdown with siRNAs of Chk1 and Chk2 in CaLH3 cells show an effect mainly via Chk1 (C). Message levels for Wee1 and Myt1 in CD44high and CD44low cells of the Ca1 cell line. The CD44high cells of both cell types show higher levels of Myt1 and CD44high Ca1 cells higher levels of Wee1 (D).