Background The different signal transduction pathways of rapidly proliferating cells of the intestine are not clearly understood. We report here a possible signaling pathway that involves regulation of activity of two closely related kinases, MAP-K (mitogen-activated protein kinase) and p34 cdc2 kinase, during hyperplasia of diabetic jejunal mucosa. Our aim was to investigate the activity and phosphorylation of MAP-K and activity and association of p34 cdc2 kinase with cyclin B during diabetes-induced jejunal mucosal hyperplasia in vivo. Methods We studied untreated and difluoromethylornithine (DFMO) treated control rats and rats with streptozotocin-induced type I diabetes. Assays were done 10 days after the induction of diabetes. In diabetic rats there was jejunal hyperplasia as indicated by increases in the jejunal mucosal weight/cm and DNA content as well as increased activities of MAP-K and p34 cdc2 kinase and association of the latter with cyclin B as compared to corresponding values in control rats. Administration of DFMO, an irreversible inhibitor of the proliferation-associated enzyme ornithine decarboxylase (ODC), prevented diabetes-I induced jejunal hyperplasia and decreased all of the above enzymic parameters in both diabetic and control rats. In our previous in vivo study, DFMO administration also blocked diabetic jejunal hyperplasia and in addition decreased ornithine decarboxylase and tyrosine kinase activities jejunal and tyrosine phosphorylation of proteins. Conclusion Thus the jejunal mucosal hyperplasia found in diabetes appears to involve activation of signal transduction pathways involving tyrosine kinases, MAP-K, p34 cdc2 kinase, and cyclin B.
Parekh et al. (Sun,) studied this question.