The cause of reduced migration ability in polyamine-deficient cells is not known, but their actin cytoskeleton is clearly abnormal. We depleted polyamines with -difluoromethylornithine (DFMO) in migrating cells with or without stimulation by epidermal growth factor (EGF) and investigated filamentous (F-) actin, monomeric (G-) actin, and thymosin 4 (T4), using immunofluorescent confocal microscopy, DNase assay, and immunoblot analysis. DFMO reduced F-actin in the cell interior, increased it in the cell cortex, redistributed G-actin, and increased nuclear staining of T4. However, DFMO did not affect the amount of T4 mRNA. EGF caused a rapid increase in the staining of F-actin in control cells, but DFMO prevented this response to EGF. Despite the visible changes shown by immunocytochemistry, statistically significant changes in the amount of either actin isoform or of total actin did not occur. We propose that DFMO reduces migration by interfering with the sequestration of G-actin by T4 and the association of F-actin with activated EGF receptors.

epidermal growth factor; -difluoromethylornithine; thymosin 4 messenger ribonucleic acid; monomer sequestration

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