Induction of urokinase-type plasminogen activator by UV light in human fetal fibroblasts is mediated through a UV-induced secreted protein.

Abstract

Plasminogen activator was previously shown to be induced by UV light in human cells with low capacity to repair UV-induced DNA lesions. We now show that in human fetal fibroblasts UV light enhanced the two mRNA species coding for the urokinase-type plasminogen activator (uPA) and the tissue-type plasminogen activator, but immunological analysis revealed exclusively uPA activity. Several independent and complementary experiments indicated that induction of uPA was mediated, apparently entirely, through a UV-induced, secreted protein (UVIS) in the growth medium of irradiated cells. First, elevation of uPA mRNA after irradiation was severely blocked by cycloheximide. Second, replacement of conditioned medium in irradiated cells while the rate of plasminogen activator induction was maximal rapidly and completely stopped any further increase in uPA activity. Third, addition of the same removed conditioned medium to nonirradiated cells mimicked UV light in enhancing the level of uPA activity as well as that of uPA mRNA. Fourth, UVIS activity was completely lost by treating the conditioned medium with trypsin but not with nucleases. Kinetic measurements indicated that the accumulation of UVIS rather than the induction of uPA by UVIS conferred the rate-limiting step in the overall process of uPA induction. Both UV light and UVIS acted synergistically with inhibitors of DNA repair for uPA induction. Based on these results, a model is proposed implicating relaxation of DNA torsional stress of an as yet undefined DNA sequence(s) in the induction of UVIS, which is then responsible for activation of the uPA gene.UV light generates pyrimidine dimers in DNA, arresting DNA replication and elongation of transcription in the living cell. Procaryotic and eucaryotic cells counteract the cytotoxic effect of DNA damage through errorproof repair and also via pathways leading to mutagenesis and, in mammalian cells, to neoplastic transformation (36,40,41,60). The bacterial response to DNA damage is inducible and consists of the expression of a set of functions collectively called SOS (40). A key regulatory role in the SOS response is played by the RecA protein, which when activated, probably by binding to single-stranded regions in the DNA, confers a specific proteolytic activity to the lexA gene product, a repressor of many genes, and to the X phage repressor (39). Self-cleavage of the repressors leads to enhanced transcription of the repressor-relieved genes, resulting in coordinate expression of the SOS functions. These include repair and mutagenic activities, X phage activation, and enhanced level of the RecA protein (40).Several activities phenotypically reminiscent of SOS functions are induced by DNA damage in mammalian cells through mechanisms not yet elucidated. These activities include virus reactivation and mutagenesis (6, 57, 58), induction of virus in transformed cells (32), enhancement of postreplication repair (17,18), and induction of the protease plasminogen activator (PA) (5, 47, 48) and of DNA ligase II, an enzyme impl...

UV Irradiation Induces the Murine Urokinase-Type Plasminogen Activator Gene via the c-Jun N-Terminal Kinase Signaling Pathway: Requirement of an AP1 Enhancer Element

“…Moreover, a UV-induced secreted factor was proposed to mediate uPA induction in low-repair-capacity human fetal fibroblasts (72,74). These reports, however, contrast with previously mentioned findings showing that UV activates cytoplasmic kinases through pathways used by growth factors, independently of UV-induced DNA damage (26,27,77).…”

“…5 and 6), suggesting that the uPA gene could be activated, at least in part, by a cytoplasm-transduced signal. These results have to be reconciled with studies showing that UV caused a late (occurring a few days postirradiation) induction of human uPA expression in normal and xeroderma pigmentosum cells after inducing a signal originating from DNA damage (64,74). At present, we can only speculate on these apparently different origins of UV induction.…”

Photoproducts in transcriptionally active DNA induce signal transduction to the delayed U.V.-responsive genes for collagenase and metallothionein

“…We favour U.V.-induced synthesis and secretion of several growth factors (Schorpp et al, 1984;Rotem et al, 1987;Stein et al, 1989a;Yarosh et al, 1993) and their autocrine action as cause of the delayed response. The delay depends on the time required to reach a threshold level in the culture medium.…”

Loss of inducible photorepair in a frog cell line hypersensitive to solar UV light

“…The constitutive EPR in this mutant, however, is the same as in wild-type cells. It has been shown that mammalian cells synthesize a novel class of secretory protein in response to UV damages that effectively transmit UV-specific messages between cells [25,26]. As also seen in frog cells, regulation of EPR is mediated by (a) new protein(s).…”