Both cell-cell and cell-extracellular matrix interactions are critically involved in developmental programs and provide three-dimensional (3-D) architectures in vivo, and deregulation of these interactions is frequently observed in cancer . Human cancers are derived from epithelial tissues characterized by specific cellular architectures including epithelial cell-cell junctions, which allow the separation of apical and basolateral membranes. This apical-basal cell polarity is crucial in normal cell functions, and loss of cell polarity is a critical step in tumorigenesis .
We recently demonstrated that HKe3 cell line, which is a human colorectal cancer (CRC) HCT116 cell line disrupted at oncogenic KRAS, in 3-D Matrigel culture (3 DC) manifests an organized structure resembling a colonic crypt . In this model, oncogenic KRAS was found to be involved in the inhibition of luminal apoptosis, impairment of epithelial cell polarity and downregulation of DNA repair genes including TP53 and BRCA2 in a 3-D specific manner , suggesting that this model could mimic the in vivo growth of the colonic epithelium and would be useful for determining the critical genes involved in CRC development through oncogenic KRAS-mediated signals in vivo.
We previously identified phosphodiesterase 4B (PDE4B) as one of the differentially expressed between HCT116 cells and HKe3 cells in this model . PDE4 cyclic AMP (cAMP)-specific phosphodiesterase family members are hydrolytic enzymes responsible for the degradation of the second messenger cAMP in many cell types, and the family consists of four genes (PDE4A, PDE4B, PDE4C and PDE4D) encoding multiple isoforms [6–8]. These isoforms can have unique functional roles by their targeting to specific signaling complexes where they underpin the compartmentalization of cAMP signaling . Notably, particular PDE4 isoforms are subject to different regulatory influences, such as phosphorylation , ubiquitination  and activity changes induced by interacting proteins . For example, the interaction of the disrupted in schizophrenia 1 (DISC1) with PDE4B1 or PDE4B3 and mutations in DISC1 associates with schizophrenia .
PDE4 is ubiquitously expressed in inflammatory cells and PDE4 inhibitors have a therapeutic potential for inflammatory diseases, including asthma, chronic obstructive pulmonary diseases, inflammatory bowel disease and psoriasis . A recent study suggests that overexpression of PDE4 enzymes is critical for the MAPK activation by oncogenic-RAS in melanoma cells , indicating the novel strategy targeting PDE4 activity in melanoma cells with oncogenic KRAS. However, the precise mechanism of PDE4B in 3-D microenvironment of CRC with oncogenic KRAS has not been addressed so far.
In this study, we used a selective inhibitor of all PDE4 sub-families, rolipram [9, 14, 16] or PDE4B2- shRNAs, and found that rolipram and PDE4B2-shRNAs revert the disorganization of CRC into the normal physiologic state of the epithelial cell in 3 DC.