Activation of p70 Ribosomal Protein S6 Kinase Is an Essential Step in the DNA Damage-dependent Signaling Pathway Responsible for the Ultraviolet B-mediated Increase in Interstitial Collagenase (MMP-1) and Stromelysin-1 (MMP-3) Protein Levels in Human Dermal Fibroblasts

Abstract

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 UVBmediated 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 UVBirradiated fibroblasts. By contrast, the interleukin-1␤-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 damagedependent, but not of the interleukin-1/cell membrane receptor-dependent signaling.In past years, two signaling pathways for the mammalian ultraviolet (UV) response have been identified. The first pathway comprises UV irradiation-dependent generation of reactive oxygen species near or within the cell membrane. UVgenerated reactive oxygen species activate receptor tyrosine kinases and protein kinases at the inner surface of the plasma membrane and elicit a signaling cascade, which activates transcription factors and the transcription of defined genes (1-3).The signaling cascade of the second pathway originates in the cell nucleus with indirect (oxidative) (4) or direct DNA damage as the primary signal, followed by passage of secondary "signals" to the cytoplasm, thereby activating specific signaling pathways, which eventually return to the nucleus and induce changes in transcription factors and gene expression (1,5,6).In view of the compelling evidence that the increase in ultraviolet-B (UVB) irradiation (280 -320 nm) on earth due to stratospheric ozone depletion represents a major environmental threat to the skin (7-9), we and others focused our studies on signaling cascades which mediate noxious UVB effects. UVB irradiation has recently been shown to generate lipid peroxides and hydroxyl radicals (HO ⅐ ) (10 -13) in skin cells with detrimental long term effects like cancer formation (9, 14) and premature aging (9, 15, 16). The major types of DNA lesions directly generated by UVB and artificial UVC irradiation predominantly occur at dipyrimidine sites with the formation of cyclobutane pyrimidine dimers (CPD) 1 and py...

Crosslinking of Ribosomal Proteins to RNA in Maize Ribosomes by UV-B and Its Effects on Translation

“…We also found that both ribosomal protein S6 and an S6 kinase are phosphorylated after UV-B exposure. Phosphorylation of these proteins is activated by UV-B in some types of cultured animal cells (Brenneisen et al, 2000;Nomura et al, 2001) where S6 phosphorylation has been implicated in the translational up-regulation of mRNAs containing the 5# TOP motif; exemplar transcripts encode components of the protein synthetic apparatus (Thomas, 2002). One mechanism permitting selective translation of eukaryotic mRNA requires an oligopyrimidine tract at the 5# terminus.…”

“…An increased translation of mRNAs encoding ribosomal proteins and translation factors has been suggested as an additional mechanism for recovery from ribosome damage in animal cells (Meyuhas et al, 1997;Brenneisen et al, 2000). Previously, phosphorylation of the 40S ribosomal protein S6 has been implicated in the translational up-regulation of mRNAs coding for the components of protein synthetic apparatus in specific cultured cell types (Thomas, 2002).…”

“…Selectively translated mRNAs contain an oligopyrimidine tract at their 5# termini (TOP); this 5# TOP motif is essential for increased translation (Meyuhas et al, 1997). Phosphorylation of the ribosomal protein S6 and of the corresponding ribosomal protein S6 kinase signaling pathway occurs upon UV-B irradiation (Brenneisen et al, 2000;Nomura et al, 2001). Brenneisen et al (2000) demonstrated that the activity of p70 ribosomal S6 kinase is increased in cultured human dermal fibroblasts after UV-B irradiation; they hypothesized that the p70 ribosomal S6 kinase is an essential component of a DNA damage-dependent signaling pathway.…”

“…Phosphorylation of the ribosomal protein S6 and of the corresponding ribosomal protein S6 kinase signaling pathway occurs upon UV-B irradiation (Brenneisen et al, 2000;Nomura et al, 2001). Brenneisen et al (2000) demonstrated that the activity of p70 ribosomal S6 kinase is increased in cultured human dermal fibroblasts after UV-B irradiation; they hypothesized that the p70 ribosomal S6 kinase is an essential component of a DNA damage-dependent signaling pathway. Furthermore, Nomura et al (2001) confirmed that UV-B induces activation of ribosomal p70 S6 kinase in cultured mouse epidermal cells.…”

Stress and mTORture signaling

“…UV light exposure initially stimulates S6K activity and within the first half an hour to 7 h after which it decreases and reaches background levels. The stimulating effect upon UV exposure on S6K activity is rapamycin sensitive (Parrott and Templeton, 1999;Brenneisen et al, 2000;Ding et al, 2002;Huang et al, 2002). Interestingly, additional pathways (p38, ERK1/2, JNK and PI3K) may also affect S6K phosphorylation (Zhang et al, 2001).…”