A three-dimensional collagen lattice activates NF-κB in human fibroblasts: Role in integrin α2 gene expression and tissue remodeling

Abstract

Normal adult human dermal fibroblasts grown in a three-dimensional collagen lattice increase mRNA level of collagen receptor integrin subunit α2 (Xu, J, and R.A.F. Clark. 1996. J. Cell Biol. 132:239249.) and DNA binding activity of a nuclear transcription factor, NF-κB (Xu, J., and R.A.F. Clark. 1997. Z Cell Biol. 136:473-483.). Here we present evidence that the collagen lattice induced the nuclear translocation of p50, one member of NF-κB family, and the degradation of an NF-κB inhibitor protein, IκB-α. The inhibition of NF-κB activity by SN50, a peptide inhibitor targeted at nuclear translocation of NF-κB, significantly reduced the induction of integrin α2 mRNA and protein by the collagen lattice. A region located between -549 and -351 bp in the promoter of integrin α2 gene conferred the inducibility by three-dimensional collagen lattice. The presence of either SN50 or IκB-α32,36, a stable mutant of IκB-α, abrogated this inducibility, indicating that the activation of integrin α2 gene expression was possibly mediated by NF-κB through this region. Although there were three DNA-protein binding complexes forming in this region that are sensitive to the inhibition of NF-κB nuclear translocation, NF-κB was not directly present in the binding complexes. Therefore, an indirect regulatory mechanism by NF-κB in integrin α2 gene expression induced by three-dimensional collagen lattice is suggested. The involvement of NF-κB in reorganization and contraction of three-dimensional collagen lattice, a process that requires the presence of abundant integrin α2β1, was also examined. The inhibition of NF-κB activity by SN50 greatly blocked the contraction, suggesting its critical role in not only the induction of integrin α2 gene expression by three- dimensional collagen lattice, but also α2β1-mediated tissue-remodeling process.