Focal adhesion kinase signaling is decreased in polyamine-depleted IEC-6 cells

Polyamines are essential to the migration of epithelial cells in the intest inal mucosa. Cells depleted of polyamines do not attach as rapidly to the e xtracellular matrix and do not form the actin stress fibers essential for m igration. Because both attachment and stress fiber formation depend on inte grin signaling and the formation of focal adhesions, we examined these and related processes in polyamine-depleted IEC-6 cells. There was general decr eased tyrosine phosphorylation of focal adhesion kinase (FAK), and, specifi cally, decreased phosphorylation of Tyr-925, the paxillin binding site. In control cells, FAK phosphorylation was rapid after attachment to the extrac ellular matrix, while attached cells depleted of polyamines had significant ly delayed phosphorylation. FAK activity was also significantly inhibited i n polyamine-depleted cells as was the phosphorylation of paxillin. Polyamin e-depleted cells failed to spread normally after attachment, and immunocyto chemistry showed little colocalization of FAK and actin compared with contr ols. Focal adhesion complex formation was greatly reduced in the absence of polyamines. These data suggest that defective integrin signaling may, at l east in part, account for the decreased rates of attachment, actin stress f iber formation, spreading, and migration observed in polyamine-depleted cel ls.