Polyamines are necessary for normal expression of the transforming growth factor-beta gene during cell migration

The current study tests the hypothesis that intracellular polyamines are involved in the regulation of gene expression of transforming growth factor-beta (TGF-beta) during epithelial cell migration after wounding. Administration of alpha-difluoromethylornithine (DFMO), a specific inhibitor of ornithine decarboxylase (the first rate-limiting enzyme for polyamine synthesis), depleted cellular polyamines putrescine, spermidine, and spermine in IEC-6 cells. DFMO also significantly reduced basal levels of TGF-beta mRNA in unwounded cells. Gene expression of TGF-beta was dramatically stimulated after wounding of a monolayer of cells not treated with DFMO. TGF-beta mRNA levels significantly increased from 4 to 12 h after wounding, peaking at 6 h at a level eight times the prewounding control. Increased levels of TGF-beta mRNA in IEC-6 cells after wounding were paralleled by an increase in TGF-beta content. Depletion of intracellular polyamines in DFMO-treated cells significantly inhibited increased expression of the TGF-beta gene in response to wounding. Cell migration also significantly decreased in DFMO-treated cells. In the presence of DFMO, exogenous TGF-beta restored cell migration to normal. These results indicate that 1) polyamine depletion induced by DFMO is associated with decreases in the expression of the TGF-beta gene and cell migration in IEC-6 cells and 2) exogenous TGF-beta reverses the inhibitory effect of polyamine depletion on cell migration. These findings suggest that polyamines are required for epithelial cell migration in association with their ability to regulate TGF-beta gene expression.