The Akt and MAPK signal-transduction pathways regulate growth factor actions in isolated gastric parietal cells.
OBJECTIVE
Incubation of purified (>95%) canine parietal cells in primary culture with epidermal growth factor for 7-16 hours stimulates H(+)K(+)-adenosine triphosphatase gene expression. In this study, we examined the effect of prolonged stimulation (72 hours) of the parietal cells with epidermal growth factor.


METHODS
H(+)K(+)-adenosine triphosphatase protein and gene expression were assessed by immunohistochemistry and Northern blots. Mitogen-activated protein kinase and Akt activation were quantitated by kinase assays and Western blots with specific antiphospho antibodies. Akt overexpression was achieved by adenovirus-mediated gene transfer of a constitutively active Akt gene.


RESULTS
Epidermal growth factor changed the morphology of the cultured cells, which acquired the appearance of fusiform cells, and it inhibited H(+)K(+)-adenosine triphosphatase gene expression. Staining of the cells both with anti-H(+)K(+)-adenosine triphosphatase antibodies and with Texas Red-labeled Dolichos biflorus lectin confirmed that the fusiform cells expressed markers of parietal cell differentiation. Epidermal growth factor stimulated mitogen-activated protein kinase with 2 peaks of activation, observed after 5 minutes and 72 hours, whereas it activated Akt after 5 minutes but not 72 hours of incubation. Overexpression of Akt blocked both epidermal growth factor-induced morphological transformation and inhibition of H + K + -adenosine triphosphatase gene expression. Identical results were observed in the presence of the mitogen-activated protein kinase inhibitor PD98059.


CONCLUSIONS
Activation of the Akt signal-transduction pathway seems to be a crucial event for the induction of parietal cell maturation and differentiation.
Department of Internal Medicine, University of Michigan Medical School, Ann Arbor 48109-0682, USA.
Vinzenz
V
Stepan
Nonthalee
N
Pausawasdi
Saravanan
S
Ramamoorthy
Andrea
A
Todisco
D000818:Animals; D002454:Cell Differentiation; D002478:Cells, Cultured; D004285:Dogs; D004815:Epidermal Growth Factor / Q000494:pharmacology*; D017506:H(+)-K(+)-Exchanging ATPase / Q000235:genetics; D020935:MAP Kinase Signaling System / Q000502:physiology*; D010295:Parietal Cells, Gastric / Q000166:cytology*; D017346:Protein Serine-Threonine Kinases / Q000502:physiology*; D021122:Protein Subunits; D011518:Proto-Oncogene Proteins / Q000502:physiology*; D051057:Proto-Oncogene Proteins c-akt; D015398:Signal Transduction / Q000502:physiology*
D021122:Protein Subunits; D011518:Proto-Oncogene Proteins; D004815:Epidermal Growth Factor; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D017506:H(+)-K(+)-Exchanging ATPase