A Three-dimensional Collagen Lattice Activates NF-κB in Human Fibroblasts: Role in Integrin α₂ Gene Expression and Tissue Remodeling

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. 132:239– 249.) and DNA binding activity of a nuclear transcription factor, NF-κB (Xu, J., and R.A.F. Clark. 1997. J. 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-α^{32, 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.