Induction of luminal apoptosis by PDE4B2 -shRNAs in HCT116 cells grown in 3 DC. (A) mRNA expression levels for PDE4B2 in 3 DC. *, P < 0.005. (B) The amount of cytoplasmic cAMP in HCT 116 cells grown in 2-D or 3-D culture. (C) The ratio of the 3-D structures containing apoptotic cells. *, P < 0.005. mRNA expression levels for PDE4B2 in HCT116 cells with control shRNA (black bar) and PDE4B2-shRNAs (white bar) grown in 3 DC.