Rapid mitogen-activated protein kinase activation by transforming growth factor alpha in wounded rat intestinal epithelial cells.

Abstract

To define signaling events initiating healing after intestinal epithelial injury, activation of mitogen-activated protein kinase (MAPK) pathways was assessed after wounding using an in vitro model. Proteins isolated from wounded monolayers of nontransformed intestinal epithelial cells (IEC-6) were analyzed for tyrosine phosphorylation and MAPK expression by Western blot. Extracellular signal-regulated kinase (ERK) 1, ERK2, and Raf-1 activities were assessed by immune complex kinase assays. Tyrosine phosphorylation of several proteins including ERK1 was substantially increased 5 minutes after injury. Another MAPK, c-Jun-N-terminal protein kinase (JNK), was also activated after wounding. Conditioned medium from wounded but not intact IEC-6 monolayers resulted in increased activity of ERK1, ERK2, and Raf-1 kinase. Wound-conditioned medium stimulated proliferation of subconfluent IEC-6 cells compared with conditioned medium from intact IEC-6 cultures and contained higher amounts of transforming growth factor (TGF)-alpha than supernatants of confluent IEC-6 cultures. Activation of ERK1 and ERK2 was partially inhibited by neutralizing anti-TGF-alpha. Wounding of intestinal epithelial cells results in activation of Raf-1, ERK1, ERK2, and JNK1 MAPKs and subsequent cell proliferation in vitro. Activation of ERK1 and ERK2 is mediated in part by TGF-alpha.