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 alpha(2) (Xu, J., and R.A.F. Clark. 1996, J. Cell Biol. 132:239-249.) and DNA binding activity of a nuclear transcription factor, NF-kappa B (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-kappa B family, and the degradation of an NF-kappa B inhibitor protein, I kappa B-alpha. The inhibition of NF-kappa B activity by SN50, a peptide inhibitor targeted at nuclear translocation of NF-kappa B, significantly reduced the induction of integrin alpha(2) mRNA and protein by the collagen lattice. A region located between -549 and -351 bp in the promoter of integrin alpha(2) gene conferred the inducibility by three-dimensional collagen lattice. The presence of either SN50 or I kappa B-alpha(32,36), a stable mutant of I kappa B-alpha, abrogated this inducibility, indicating that the activation of integrin alpha(2) gene expression was possibly mediated by NF-kappa B through this region. Although there were three DNA-protein binding complexes forming in this region that are sensitive to the inhibition of NF-kappa B nuclear translocation, NF-kappa B was not directly present in the binding complexes. Therefore, an indirect regulatory mechanism by NF-kappa B in integrin alpha(2) gene expression induced by three-dimensional collagen lattice is suggested. The involvement of NF-kappa B in reorganization and contraction of three-dimensional collagen lattice, a process that requires the presence of abundant integrin alpha(2) beta(1), was also examined, The inhibition of NF-kappa B activity by SN50 greatly blocked the contraction, suggesting its critical role in not only the induction of integrin alpha(2) gene expression by three-dimensional collagen lattice, but also alpha(2) beta(1)-mediated tissue-remodeling process.