Role of nonmuscle myosin II in polyamine-dependent intestinal epithelial cell migration

The current study determines whether nonmuscle myosin II is involved in the process requiring polyamines for the stimulation of cell migration in an in vitro model that mimics the early stages of epithelial restitution. Treatment with alpha-difluoromethylornithine (DFMO), a specific inhibitor of ornithine decarboxylase (ODC), for 4 days totally inhibited ODC activity and depleted intracellular polyamines in the IEC-6 cells. Nonmuscle myosin II concentrations in DFMO-treated cells were decreased by 75%, and stress fibers were sparse or absent. The most striking feature of DFMO-treated cells was the appearance of many small punctate foci of myosin II in the cell interior. Migration of DFMO-treated cells was reduced by 80%. In the presence of DFMO, exogenous putrescine not only returned nonmuscle myosin II levels and distribution toward normal but also restored cell migration to control levels. The administration of wortmannin, an inhibitor of myosin light chain kinase, significantly inhibited cell migration over the denuded area in control cells and in those treated with DFMO + polyamines. These results indicate that 1) polyamine depletion by DFMO is associated with decreased concentration and reorganization of nonmuscle myosin II in IEC-6 cells and 2) exogenous spermidine reverses the inhibitory effects of DFMO.