A novel homologous recombination system to study 92 kDa type IV collagenase transcription demonstrates that the NF-kappaB motif drives the transition from a repressed to an activated state of gene expression.

The 92-kDa type IV collagenase (MMP-9) contributes to tissue remodeling in both physiology and pathology. Previous studies on the transcriptional regulation of this gene have used transiently transfected promoter-reporter constructs. However, this approach suffers from several limitations including (a) multiple copies of the plasmid and (b) the plasmid is not genomically integrated and consequently poorly chromatinized. We developed a novel system for studying MMP-9 transcription in which a single copy of a MMP-9 promoter-luciferase construct(s) is integrated at an identical genomic locus in HT1080 cells by homologous recombination. We report that the activity of a genomic-integrated 2.2 kb MMP-9 promoter sequence mirrors expression of the endogenous MMP-9 gene in response to both physiological and pharmacological (curcumin) cues. Further, when constrained into chromatin, the integrated NF-kappaB-mutated MMP-9 promoter is repressed by PMA, a situation not apparent using nonintegrated plasmids. Thus, we have developed a novel method for studying MMP-9 expression that overcomes some of the limitations associated with transient transfection approaches and which may be of utility in screening for agents that repress the expression of this gene.