Laminins and TGF-β maintain cell polarity and functionality of human gastric glandular epithelium

The human gastric glandular epithelium produces a gastric lipase enzyme (HGL) that plays an important role in digestion of dietary triglycerides. To assess the involvement of extracellular matrix components and transforming growth factor-beta1 (TGF-beta1) in the regulation of this enzymic function, normal gastric epithelial cells were cultured on collagen type I, Matrigel, and laminins (LN)-1 and -2 with or without TGF-beta1. Epithelial morphology and HGL expression were evaluated using microscopy techniques, enzymic assays, Western blot, Northern hybridization, and RT-PCR. A correlation was observed between the cell polarity status and the level of HGL expression. TGF-beta1 alone or individual matrix components stimulated cell spreading and caused a downfall of HGL activity and mRNA. By contrast, Matrigel preserved the morphological features of differentiated epithelial cells and maintained HGL expression. The combination of LNs with TGF-beta1 (two constituents of Matrigel) exerted similar beneficial effects on epithelial cell polarity and evoked a 10-fold increase of HGL levels that was blunted by a neutralizing antibody against the alpha(2)-integrin subunit and by mitogen-activated protein kinase (MAPK) inhibitors PD-98059 (p42/p44) or SB-203580 (p38). This investigation demonstrates for the first time that a powerful synergism between a growth factor and basement membrane LNs positively influences cell polarity and functionality of the human gastric glandular epithelium through an activation of the alpha(2)beta(1)-integrin and effectors of two MAPK pathways.