Requirement of the MAP kinase cascade for cell cycle progression and differentiation of human intestinal cells

The intracellular signaling pathways responsible for cell cycle arrest and establishment of differentiated cells along the gut axis remain largely unk nown. In the present study we analyzed the regulation of p42/p44 mitogen-ac tivated protein kinase (MAPK) in the process of proliferation and different iation of human intestinal cells. In vitro studies were done in Caco-2/15 c ells, a human colon cancer cell line that spontaneously differentiates into an enterocyte phenotype. In vivo studies were performed on cryostat sectio ns of human fetal intestinal epithelium by indirect immunofluorescence. We found that inhibition of the p42/p44 MAPK signaling by the PD-98059 compoun d or by ectopic expression of the MAPK phosphatase-l strongly attenuated E2 F-dependent transcriptional activity in Caco-2/15 cells. p42/p44 MAPK activ ities dramatically decreased as soon as Caco-2/15 cells reached confluence. However, significant levels of activated p42 MAPK were detected in differe ntiated Caco-2/15 cells. Addition of PD-98059 during differentiation interf ered with sustained activation of p42 MAPK and sucrase-isomaltase expressio n. Although p42/p44 MAPKs were expressed in both the villus tip and crypt c ells, their phosphorylated and active forms were detected in the undifferen tiated crypt cells. Our results indicate that elevated p42/p44 MAPK activit ies stimulate cell proliferation of intestinal cells, whereas low sustained levels of MAPK activities correlated with G(1) arrest and increased expres sion of sucrase-isomaltase.