Transcriptional repression of IL-2 and MMP-1 and anti-invasive activity of p21(SNFT)

p21SNFT is a human basic leucine zipper transcription factor that has been shown to repress AP-1 mediated transcription by replacing Fos in the AP-1 (Fos/Jun) heterodimer. Overexpression of p21SNFT leads to the significant and specific repression of transcription from the interleukin-2 (IL-2) promoter as well as from several of the promoter's essential AP-1-driven composite promoter elements. One example is the distal NF-AT/AP-1 enhancer, where AP-1 interacts with members of the nuclear factor of activated T cells (NF-AT) family. p21SNFT formed dimers with Jun on a consensus AP-1 binding site (TRE) and interacted with Jun and NF-AT at the distal NF-AT/AP-1 enhancer. A detailed biochemical analysis compared interactions involving p21SNFT with those involving Fos. The results demonstrated that a p21SNFT/Jun dimer binds a TRE similarly to AP-1 and, like AP-1, binds cooperatively with NF-AT at the NF-AT/AP-1 composite element. However, Fos interacted much more efficiently than p21SNFT with Jun and NF-AT, and the replacement of Fos by p21SNFT in the trimolecular complex drastically altered protein:DNA contacts. The data suggested that p21SNFT may repress transcriptional activity by inducing a unique conformation in the ternary complex. Consequently, we hypothesized that p21SNFT may be able to repress other promoters at which interactions between AP-1 and another transcription factor on DNA at composite elements are required. Indeed, overexpression of p21SNFT in HepG2 hepatocarcinoma cells led to transcriptional repression of matrix metalloproteinase I (MMP-1) by approximately 40–60%. p21SNFT interacted with the MMP-1 promoter by replacing Fos in the AP-1 complex at the -88Ets/AP-1 composite enhancer element, forming instead an Ets/p21SNFT/Jun/DNA quatramolecular complex. This complex was shown to footprint DNA differently than an Ets/AP-1 complex, suggesting a difference in overall conformation that may be responsible for the repressive effects of p21SNFT. Finally, overexpression of p21SNFT and inhibition of MMP-1 led to a reduction in invasiveness of HepG2 cells through type I collagen in tissue culture, and p21SNFT was sufficient to inhibit invasion through reconstituted basement membrane as well. The results suggest that repression of MMP-1 by p21SNFT may be a mechanism for inhibiting pathological matrix remodeling during cancer progression in vivo.