EGF-R regulates MMP function in fibroblasts through MAPK and AP-1 pathways

EGF-R regulates cell proliferation, migration, and invasion in fibroblasts. However, the connection of EGF-R with downstream signaling pathways mediating these responses has remained elusive. Here we provide genetic and biochemical evidence that EGF-R- and AP-I-mediated signals are required for MMP expression and collagen contraction in fibroblasts. In EGF-R (-/-) mouse embryonal fibroblasts, basal and inducible expression of several MMPs, including MMP-2,-3, and -14 is impaired in comparison to wild-type counterparts. The loss of MMP expression is associated with a suppression of EGF-induced Erk and Jnk activities, and AP-I DNA-binding and transactivation capacities. While inhibition of Jnk mainly prevents EGF-induced phosphorylation of c-Jun, inhibition of Erk pathway suppresses both the expression and phosphorylation of c-Jun and c-Fos proteins. Moreover, the expression of MMP-3 and -14, and collagen contraction is partially prevented by Mek/Erk and Jnk inhibitors. However,Jnk inhibitor also suppresses cell growth independently of EGF-R activity. The central role of AP-I as a mediator of EGF-R signaling in fibroblasts is emphasized by the finding that expression of a dominant negative c-Jun down-regulates the expression of MMP-3. Conversely, expression of a constitutively active Mek I can induce MMP-3 expression independently of upstream signals. The results indicate that ERK pathway and AP-I are downstream effectors of the EGF-R-mediated MMP-3 expression and collagen contraction in fibroblasts.