Role of Tyrosine Kinase,ODC,and p34cdc2 Kinase and Cyclin B-Associated cdc2 in Jejunal Enterocyte Proliferation,Maturation,and Exfoliation in Diabetic and DFMO-Treated Rats

Abstract

Background

Several signal transduction pathways involved in rapidly proliferating cells of the intestine are currently not well understood. In the jejunum, crypt enterocytes are constantly replicating, lower villi are maturing, and upper villi are constantly shed. Type I diabetes is associated with jejunal mucosal hyperplasia, and administration of diflouromethylornithine (DFMO), an irreversible inhibitor of ornithine decarboxylase (ODC), causes hypoplasia. Phosphorylation of proteins controls cellular proliferation and/or exfoliation. Cell division cycle kinase (p34cdc2) and cyclin B-associated p34cdc2 kinase regulate the cell cycle during the transition from G2-M phase. Our aims were to: 1) investigate the activities of tyrosine kinase, ODC, total p34cdc2 kinase, and cyclin B-associated p34cdc2 kinase and 2) phosphorylate proteins at tyrosine residues in jejunal upper villi, lower villi, and crypt enterocytes of DFMO-treated control and diabetic rats.

Methods

Diabetes was induced by streptozotocin. DFMO was administered in drinking water in both control and diabetic groups for 10 days after the induction of diabetes. Jejunal enterocytes were isolated and kept frozen at -70°C until ready to process.

Results

Diabetic rats showed jejunal mucosal hyperplasia as indicated by increases in the jejunal mucosal weight/cm and DNA content compared to control rats. Diabetic crypt enterocytes showed significant increases in activities of tyrosine kinase, ODC, total p34cdc2 kinase, and cyclin B-associated cdc2 as well as increased phosphorylation of proteins at tyrosine residues compared to control rats. DFMO prevented diabetes-induced jejunal hyperplasia, and decreased the activities of these enzymes and phosphorylation of proteins at tyrosine residues in both diabetic and control rats. Phosphorylation of a 14 kd protein became prominent in crypt, upper villi, and lower villi enterocytes of DFMO-treated diabetic and control groups. Conclusion: Diabetic jejunal mucosal hyperplasia appears to involve activation of complex signal transduction pathways such as tyrosine kinase, ODC, p34cdc2 kinase, and cyclin B. These enzymes are involved in proliferation and/or exfoliation of jejunal enterocytes. Our results also suggest that tyrosine phosphorylation of a 14 kd protein may be involved in cell exfoliation and that jejunal mucosal hypoplasia may be a synergistic effect caused by down regulation of the above enzymes.