Ultraviolet B (UVB) irradiation has been shown to stimulate the expression of matrix-degrading metalloproteinases via generation of DNA damage and/or reactive oxygen species. Matrix-degrading metalloproteinases promote UVB-triggered detrimental long term effects like cancer formation and premature skin aging. Here, we were interested in identifying components of the signal transduction pathway that causally link UVB-mediated DNA damage and induction of matrix-degrading metalloproteinase (MMP)-1/interstitial collagenase and MMP-3/stromelysin-1 in human dermal fibroblasts in vitro. The activity of p70 ribosomal S6 kinase, a downstream target of the FK506-binding protein-12/rapamycin-associated protein kinase (FRAP) kinase (RAFT1, mTOR), was identified to be 4.8 +/- 0.8-fold, and MMP-1 and MMP-3 protein levels 2.4- and 11.5-fold increased upon UVB irradiation compared with mock-irradiated controls. The FRAP kinase inhibitor rapamycin and the DNA repair inhibitor aphidicolin significantly suppressed the UVB-mediated increase in p70 ribosomal S6 kinase activity by 50-65% and MMP-1 and MMP-3 protein levels by 34-68% and 42-88% compared with UVB-irradiated fibroblasts. By contrast, the interleukin-1beta-mediated increase in MMP-1 and MMP-3 protein levels could not be suppressed by rapamycin. Collectively, our data suggest that the FRAP-controlled p70 ribosomal S6 kinase is an essential component of a DNA damage-dependent, but not of the interleukin-1/cell membrane receptor-dependent signaling.