Ontogeny of MAP kinases in rat small intestine: premature stimulation by insulin of BBM hydrolases is regulated by ERKs but not by p-38 MAP kinase.
Although mitogen-activating protein (MAP) kinases are crucial signal transduction molecules regulating cellular proliferation, differentiation, and morphology, their ontogenic changes in the small intestine have not been analyzed. Also, it remains unknown which pathway of activated MAP kinases regulates the expression of brush border membrane hydrolases during growth. Therefore, we have analyzed the mucosal distribution, ontogeny, and responses to insulin and to inhibitors of p44, p42, and p38 MAP kinases in immature and mature enterocytes using Western blot analysis and autoradiography after immunoprecipitation, immunohistochemistry, and in vitro phosphorylation assays. Between d 10 and 40 postpartum, diphosphorylated active p44/p42 extracellular regulated protein kinases (ERKs) increased in abundance compared with total immunoprecipitated ERKs, and were highly responsive to exogenous insulin. In concordance, ERK total activity increased by 4-fold during the same period of growth and was further enhanced 2-fold by exogenous insulin. In weaning rats, ERKs were mainly located in membranes of villus cells and with less intensity in crypt cells. By contrast, p38 MAP kinase was unresponsive to insulin and was confined to nuclei. Administration to sucklings of PD 098059, a specific inhibitor of ERKs, not only inhibited the premature stimulation of sucrase, lactase, and maltase total activities in response to exogenous insulin, but also depressed the natural expression of these brush border membrane enzymes in the absence of insulin stimulation. In concordance, administration of SB 203580, a specific inhibitor of p38 MAP kinase, failed to inhibit both the response of brush border membrane hydrolases to insulin and their natural expression in the absence of insulin stimulation. We conclude that the ontogenic expression of brush border membrane hydrolases and their premature stimulation by insulin are regulated at least in part by the activation of p44/p42 ERKs but not by p38 MAP kinase.
Marandi
Soheila
S
Laboratories of Pediatric Gastroenterology and Nutrition, Faculty of Medicine, Université Catholique de Louvain, B-1200 Brussels, Belgium.
De Keyser
Nadine
N
Stilmant
Catherine
C
Saliez
Alain
A
Sokal
Etienne Marc
EM
Guiot
Yves
Y
Buts
Jean-Paul
JP
D000818:Animals; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D005419:Flavonoids / Q000494:pharmacology; D006867:Hydrolases / Q000378:metabolism*; D007004:Hypoglycemic Agents / Q000494:pharmacology*; D007328:Insulin / Q000494:pharmacology*; D007413:Intestinal Mucosa / Q000201:enzymology / Q000254:growth & development; D007421:Intestine, Small / Q000201:enzymology* / Q000254:growth & development; D020935:MAP Kinase Signaling System / Q000187:drug effects / Q000502:physiology; D008871:Microvilli / Q000201:enzymology; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D010766:Phosphorylation; D051381:Rats; D048051:p38 Mitogen-Activated Protein Kinases
D004791:Enzyme Inhibitors; D005419:Flavonoids; D007004:Hypoglycemic Agents; D007328:Insulin; D020928:Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases; D006867:Hydrolases; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one