Inhibition Of Activator Protein-1 Activation Research Articles

Inhibition of activator protein 1 activity by paclitaxel suppresses interleukin-1-induced collagenase and stromelysin expression by bovine chondrocytes.

Cytokine-induced collagenase 1 (matrix metalloproteinase 1 [MMP-1]) and stromelysin 1 (MMP-3) expression is dependent on activator protein 1 (AP-1) activation and have a fundamental role in the pathophysiology of arthritic diseases by degrading connective tissues. This study evaluates the effect of paclitaxel on AP-1 activation and examines its effect on the expression of 2 major matrix metalloproteinases, MMP-1 and MMP-3, and its effect on AP-1 activation. MMP-1, MMP-3, c-fos, and c-jun messenger RNA (mRNA) levels were measured in interleukin-1 (IL-1)-induced primary chondrocytes in the presence and absence of paclitaxel. The effect of paclitaxel on AP-1 promoter activity was studied by chloramphenicol acetyltransferase assays in IL-1-stimulated chondrocytes. The same conditions were applied to studies of the effect of paclitaxel on binding at the AP-1 site by gel-shift mobility assays. The cytotoxicity effect of paclitaxel on chondrocytes was studied by examining cell viability and expression of the matrix molecules aggrecan and type II collagen. IL-1-induced MMP-1 and MMP-3 mRNA levels were markedly reduced in paclitaxel-treated chondrocytes. Further, IL-1-induced AP-1 activation and AP-1 binding were inhibited by paclitaxel. However, there was no effect on the expression of c-fos or c-jun mRNA levels. Chondrocyte viability was not affected by paclitaxel, and there was no effect on the expression of housekeeping genes or the major cartilage matrix molecules aggrecan and type II collagen. These studies demonstrate that paclitaxel is a potent inhibitor of MMP-1 and MMP-3 synthesis through the AP-1 site. However, inhibition of AP-1 activity by paclitaxel does not affect the viability of chondrocytes or the expression of matrix molecules.

AP-1/Jun Is Required for Early Xenopus Development and Mediates Mesoderm Induction by Fibroblast Growth Factor but Not by Activin

In Xenopus, normal mesoderm formation depends on signaling through the fibroblast growth factor (FGF) tyrosine kinase receptor. An important signaling pathway from receptor tyrosine kinases involves Ras/Raf/MAP kinase. However, the downstream pathway that occurs in the nucleus to finally trigger gene expression for mesoderm formation remains unknown. We report here that a high level of activator protein-1 (AP-1)-dependent transcriptional activity is detected during the early development of Xenopus embryos. Injection of a dominant negative mutant jun (DNM-jun or TAM67) RNA into the two-cell stage embryos inhibited endogenous AP-1 activity and blocked normal embryonic development with severe posterior truncation in tadpoles. The inhibition of AP-1 activity and the phenotypic change induced by TAM67 was rescued by co-injection of wild-type c-jun RNA, but not by the control beta-galactosidase RNA. The FGF-stimulated mesoderm induction was markedly inhibited in animal cap explants from the embryos injected with TAM67. Activin induction of mesoderm, on the other hand, was normal in the embryos injected with TAM67 RNA. These findings suggest that AP-1 mediates FGF, but not activin, receptor signaling during mesoderm induction and the AP-1/Jun is a key signaling molecule in the development of posterior structure.

Estradiol increases and anti-estrogens antagonize the growth factor-induced activator protein-1 activity in MCF7 breast cancer cells without affecting c-fos and c-jun synthesis

In estrogen receptor positive human breast cancer cells, anti-estrogens inhibit the mitogenic effect of growth factors in the absence of estrogens. As activator protein-1 (AP-1) activity is one of the first nuclear events following growth factor receptor activation, we studied the effects of estrogens and anti-estrogens on growth factor-induced AP-1 activity using transient transfection of the AP-1-responsive gene (AP-1)4-TK-CAT into MCF7 cells. The growth factor-induced AP-1 response was increased by estradiol and inhibited by anti-estrogens in conditions where growth factor-induced c-fos and c-jun mRNA levels were unchanged by hormone and anti-hormone treatments. The same regulations were obtained when the AP-1 response was directly induced by co-transfection of c-fos and c-jun expression vectors. Co-transfection of the wild-type estrogen receptor HEGO amplified both effects. Inhibition of AP-1 activity by anti-estrogens was unlikely to be explained by the presence of residual estrogens in MCF7 cells. (i) anti-estrogens inhibited AP-1 activity in conditions where they had no effect on basal ERE-mediated activity levels, whereas estradiol was as efficient in stimulating both activities. (ii) The relative efficacy of the two anti-estrogens, OH-tamoxifen and ICI 164,384 in inhibiting these two activities was different; OH-tamoxifen was more efficient in inhibiting ERE-mediated activity, whereas ICI 164,384 was more efficient in trans-repressing AP-1-mediated activity. We conclude that in conditions where c-fos and c-jun syntheses were not affected, the estrogen receptor cooperated with growth factors to stimulate the AP-1 response when activated by estrogens but inhibited AP-1-mediated transcription when occupied by anti-estrogens.