Enhanced expression of matrix metalloproteinase (MMP)-1/interstitial collagenase and MMP-3/stromelysin-1 in skin fibroblasts and subsequent damage of dermal connective tissue in the context of sun-induced premature aging and skin tumour progression is causally linked to UVB irradiation. Here, we were interested in identifying components of the complex signal-transduction pathway underlying UVB-mediated up-regulation of these delayed UV-responsive genes and focused on components maximally activated early after irradiation. A 2.3-fold increase in protein kinase CK2 activity was measured at 20-40 min after low-dose UVB irradiation (at 10 mJ/cm2) of dermal fibroblasts. This UVB-mediated increase in CK2 activity was abrogated by pharmacological approaches using non-toxic concentrations of the CK2 inhibitor 5,6-dichloro-1-beta-d-ribofuranosylbenzimidazole (DRB). Preincubation of fibroblasts with DRB prior to UVB irradiation lowered MMP-1 by 49-69% and MMP-3 protein levels by 55-63% compared with UVB-irradiated controls. By contrast, the CK2 inhibitor did not affect the UVB-triggered transcription of MMPs. Furthermore, UVB irradiation of fibroblasts overexpressing a kinase-inactive mutant of CK2 (CK2alpha-K68A-HA) resulted in lowering of the protein levels of MMP-1 by 25% and MMP-3 by 22% compared with irradiated fibroblasts transfected with the vector control. This reduction in MMP protein levels correlated with the transfection efficiency. Taken together, we describe a novel aspect of protein kinase CK2, namely its inducible activity by UVB irradiation, and provide evidence that CK2 is an early mediator of the UVB-dependent up-regulation of MMP-1 and MMP-3 translation, whereas their major tissue inhibitor of matrix metalloproteinase-1 is not affected by CK2.

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