Functional role of bone morphogenetic protein-4 in isolated canine parietal cells

Bone morphogenetic protein (BMP)-4 is an important regulator of cellular growth and differentiation. Expression of BMP-4 has been documented in the gastric mucosa. We reported that incubation of canine parietal cells with EGF for 72 h induced both parietal cell morphological transformation and inhibition of H⁺/K⁺-ATPase gene expression through MAPK-dependent mechanisms. We explored the role of BMP-4 in parietal cell maturation and differentiation. Moreover, we investigated if BMP-4 modulates the actions of EGF in parietal cells. H⁺/K⁺-ATPase gene expression was examined by Northern blots and quantitative RT-PCR. Acid production was assessed by measuring the uptake of [¹⁴C]aminopyrine. Parietal cell apoptosis was quantitated by Western blots with anticleaved caspase 3 antibodies and by counting the numbers of fragmented, propidium iodide-stained nuclei. MAPK activation and Smad1 phosphorylation were measured by Western blots with antiphospho-MAPK and anti-phospho-Smad1 antibodies. Parietal cell morphology was examined by immunohistochemical staining of cells with anti-H ⁺/K⁺-ATPase α-subunit antibodies. BMP-4 stimulated Smad1 phosphorylation and induced H⁺/K⁺-ATPase gene expression. BMP-4 attenuated EGF-mediated inhibition of H⁺/K ⁺-ATPase gene expression and blocked EGF induction of both parietal cell morphological transformation and MAPK activation. Incubation of cells with BMP-4 enhanced histamine-stimulated [¹⁴C]aminopyrine uptake. BMP-4 had no effect on parietal cell apoptosis, whereas TGF-β stimulated caspase-3 activation and nuclear fragmentation. In conclusion, BMP-4 promotes the induction and maintenance of a differentiated parietal cell phenotype. These findings may provide new clues for a better understanding of the mechanisms that regulate gastric epithelial cell growth and differentiation.