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 a re involved in the regulation of gene expression of transforming growt h factor-beta (TGF-beta) during epithelial cell migration after woundi ng. Administration of alpha-difluoromethylornithine (DFMO), a specific inhibitor of ornithine decarboxylase (the first rate-limiting enzyme for polyamine synthesis), depleted cellular polyamines putrescine, spe rmidine, and spermine in IEC-6 cells. DFMO also significantly reduced basal levels of TGF-beta mRNA in unwounded cells. Gene expression of T GF-beta was dramatically stimulated after wounding of a monolayer of c ells not treated with DFMO. TGF-beta mRNA levels significantly increas ed from 4 to 12 h after wounding, peaking at 6 h at a level eight time s the prewounding control. Increased levels of TGF-beta mRNA in IEC-6 cells after wounding were paralleled by an increase in TGF-beta conten t. Depletion of intracellular polyamines in DFMO-treated cells signifi cantly inhibited increased expression of the TGF-beta gene in response to wounding. Cell migration also significantly decreased in DFMO-trea ted cells. In the presence of DFMO, exogenous TGF-beta restored cell m igration 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 mig ration. These findings suggest that polyamines are required for epithe lial cell migration in association with their ability to regulate TGF- beta gene expression.