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Genomic clones coding for human fibroblast collagenase were isolated. By constructing and transfecting mutants with 5' and 3' deletion mutations of the 5' control region of the gene into human or murine cells, we delimited a 32-base-pair sequence at positions -73 to -42 which is required for the induction of transcription by the tumor promoter 12-O-tetradecanoyl-phorbol-13-acetate. The DNA element behaves as a 12-0-tetradecanoyl-phorbol-13-acetate-inducible enhancer: it mediates the stimulation of transcription to the heterologous herpes simplex virus thymidine kinase promoter and acts in a position-and orientationindependent manner. Differences in enhancer efficiency in different cell lines are interpreted to indicate differences in the activity of a trans-acting factor.

Steroid receptors activate and repress genes. An important class of genes that they repress is controlled by the transcription factor AP‐1. The activity of AP‐1 is inhibited by the receptor, a mechanism exploited for the therapy of various forms of pathological hyperproliferation in humans. We show here by point mutations in the DNA binding domain and by the choice of steroid ligands that repression of AP‐1 activity and transactivation functions of the glucocorticoid receptor (GR) are separable entities. While DNA binding and activation of glucocorticoid‐regulated promoters require GR dimerization, we present data that suggest that repression is a function of GR monomers.

Several non‐physiologic agents such as radiation, oxidants and alkylating agents induce ligand‐independent activation of numerous receptor tyrosine kinases (RTKs) and of protein tyrosine kinases at the inner side of the plasma membrane (e.g. Dévary et al., 1992; Sachsenmaier et al., 1994; Schieven et al., 1994; Coffer et al., 1995). Here we show additional evidence for the activation of epidermal growth factor receptor (EGFR), and we show activation of v‐ErbB, ErbB2 and platelet‐derived growth factor receptor. As a common principle of action the inducing agents such as UVC, UVB, UVA, hydrogen peroxide and iodoacetamide inhibit receptor tyrosine dephosphorylation in a thiol‐sensitive and, with the exception of the SH‐alkylating agent, reversible manner. EGFR dephosphorylation can also be modulated by these non‐physiologic agents in isolated plasma membranes in the presence of Triton X‐100. Further, substrate (EGFR) and phosphatase have been separated: a membrane preparation of cells that have been treated with epidermal growth factor (EGF) and whose dephosphorylating enzymes have been permanently destroyed by iodoacetamide can be mixed with a membrane preparation from untreated cells which re‐establishes EGFR dephosphorylation. This dephosphorylation can be modulated in vitro by UV and thiol agents. We conclude that RTKs exhibit significant spontaneous protein kinase activity; several adverse agents target (an) essential SH‐group(s) carried by (a) membrane‐bound protein tyrosine phosphatase(s).

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UV irradiation of human and murine cells enhances the transcription of several genes. Here we report on the primary target of relevant UV absorption, on pathways leading to gene activation, and on the elements receiving the UV-induced signal in the human immunodeficiency virus type 1 (HIV-1) long terminal repeat, in the gene coding for collagenase, and in the cellular oncogenefos. In order to induce the expression of genes, UV radiation needs to be absorbed by DNA and to cause DNA damage of the kind that cannot be repaired by cells from patients with xeroderma pigmentosum group A. UV-induced activation of the three genes is mediated by the major enhancer elements (located between nucleotide positions -105 and -79 of HIV-1, between positions -72 and -65 of the collagenase gene, and between positions -320 and -299 offos). These elements share no apparent sequence motif and bind different trans-acting proteins; a member of the NFKB family binds to the HIV-1 enhancer, the heterodimer of Jun and Fos (AP-1) binds to the collagenase enhancer, and the serum response factors p67 and p62 bind to fos. DNA-binding activities of the factors recognizing the HIIV-1 and collagenase enhancers are augmented in extracts from UV-treated cells. The increase in activity is due to posttranslational modification. While AP-1 resides in the nucleus and must be modulated there, NFKB is activated in the cytoplasm, indicating the existence of a cytoplasmic signal transduction pathway triggered by UV-induced DNA damage. In addition to activation, new synthesis of AP-1 is induced by UV radiation.Under severe stress, e.g., replication arrest by UV-induced DNA damage, many bacteria mount a productive response which involves the new synthesis of a large number of specific gene products (39, 74). The response has been named SOS (51), and it is triggered by the activation of preexisting recA protein and its increased synthesis, probably due to the interaction of recA protein with singlestranded regions of DNA (for a review, see reference 74).Mammalian cells in culture react to UV irradiation with a number of genetic changes resembling those in bacteria (for reviews, see references 29-31, 52, 60). These changes include the altered expression of specific genes (see B. Kaina, B. Stein, A. Schonthal, H. J. Rahmsdorf, H. Ponta, and P. Herrlich, in M. W. Lambert et al., ed., DNA Repair Mechanisms and Their Biological Implications in Mammalian Cells, in press, for a recent list of references). Many genes are induced, e.g., plasminogen activator (46), collagenase and metallothionein genes (2, 4), the cellular oncogene fos (5), and a human retrovirus, the human immunodeficiency virus type 1 (HIV-1) (B. Stein, cited in reference 29; 30, 69, 73).In an attempt to identify the elements of signal transduction to these genes, we show here that UV-induced gene expression is preceded by and requires absorption of UV radiation by DNA and UV-induced covalent DNA changes (photoproducts). Moreover, we define the DNA elements in three of the responsive genes (HIV-1, t...

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