Adherens junctions and tight junctions are regulated via different pathways by progastrin in epithelial cells

Adhesion between neighbouring epithelial cells is a crucial and tightly controlled process. In the gastrointestinal tract, the integrity of cell-cell contacts is essential for the regulation of electrolyte absorption and for the prevention of tumour metastasis. We recently showed that migration of the gastric epithelial cell line IMGE-5 is stimulated by the nonamidated form of the hormone gastrin(17). Here, we examine the effect on cell-cell adhesion of the prohormone progastrin, the concentration of which is increased in the plasma of patients with colorectal carcinoma. Progastrin induced the dissociation of both tight junction (TJ) and adherens junction (AJ) complexes in IMGE-5 cells. In progastrin-secreting DLD-1 human colorectal carcinoma cells, expression of an antisense gastrin construct restored membrane localisation of zonula occludens-1 (ZO-1), occludin, beta-catenin and E-cadherin. This restoration was reversed by treatment with exogenous progastrin. Endogenous or exogenous progastrin also increased the paracellular flux of mannitol, and induced cell migration of several gastrointestinal cell lines. In addition, progastrin enhanced Src tyrosine kinase activity and induced a spatial delocalisation of protein kinase C alpha. Using dominant-negative mutants and pharmacological inhibitors, we showed that the stimulation of Src kinase activity was essential for the regulation of TJs. By contrast, the dissociation of AJs involved phosphatidylinositol 3-kinase, partly through the formation of a complex with protein kinase C alpha. We conclude that separate pathways mediate the disruption of AJs and TJs by progastrin. Either pathway may contribute to the co-carcinogenic role of this prohormone in colorectal carcinoma.