A connection between transcription and DNA repair was demonstrated previously through the characterization of TFIIH. Using filter binding as well as in vitro transcription challenge competition assays, we now show that the promoter recognition factor TATA boxbinding protein (TBP)/TFIID binds selectively to and is sequestered by cisplatin-or UV-damaged DNA, either alone or in the context of a larger protein complex including TFIIH. Computer-assisted 3D structural analysis reveals a remarkable similarity between the structure of the TATA box as found in its TBP complex and that of either platinated or UV-damaged oligonucleotides. Thus, cisplatin-treated or UV-irradiated DNA could be used as a competing binding site which may lure TBP/TFIID away from its normal promoter sequence, partially explaining the phenomenon of DNA damage-induced inhibition of RNA synthesis. Consistent with an involvement of damaged DNA-specific binding of TBP in inhibiting transcription, we find that microinjection of additional TBP in living human fibroblasts alleviates the reduction in RNA synthesis after UV irradiation. Future anticancer drugs could be designed with the consideration of lesion recognition by TBP and their ability to reduce transcription.

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Endothelin (ET)-1 is a 21-amino-acid peptide that is a potent vasoconstrictor and mitogen. By binding to its G-protein coupled receptor, ET-1 stimulates the proliferation of airway smooth-muscle (ASM) cells, which may be involved in the pathogenesis of asthma. The ETB receptor stimulates activation of the extracellular regulated kinase 2 (ERK2), which is thought to be required for proliferation of ASM cells. Our findings reveal that ET rapidly activates Raf, and that dominant-negative Raf interferes with ET-induced ERK activation in ASM cells. Expression of the amino-terminal Ras-binding domain of Raf inhibited ET-induced ERK activation, suggesting that ET-stimulated Raf activation is a Ras-dependent process. Furthermore, ET-stimulated ERK and Raf activation in ASM cells require calcium influx; chelating extracellular calcium or preventing calcium influx through calcium channels inhibited ET-stimulated, but not phorbol ester-stimulated, ERK and Raf activation.

Endothelin is a 21-amino acid peptide with a striking diversity of important biological responses, including, vasoconstriction, bronchoconstriction, and mitogenesis. Endothelin-1 binding to the endothelin B receptor (ETB), a member of the superfamily of G-protein-coupled receptors, was associated with catalytic activation of the extracellular-regulated kinase 2 (ERK2) and stimulation of AP-1 transcriptional reporter activity. A panel of single point mutations in transmembrane helix 6 (TM6), intracellular loop 3, and transmembrane helix 7 (TM7) were developed to study the structural requirements for ETB activation. Point mutations within highly conserved regions of TM6 and intracellular loop 3 were without effect on agonist-stimulated ERK activation. However, mutations within TM7 of the ETB significantly impacted ligand-stimulated downstream signaling. For example, nine point mutations within TM7 of the ETB were identified that prevented endothelin-stimulated ERK activation. Interestingly, the TM7 mutants fell into two classes; several exhibited greatly decreased AP-1 activity, relative to wild type ETB, whereas others displayed augmented endothelin-stimulated AP-1 transcriptional activity relative to wild type ETB. Our results suggest that TM7 of the ETB is involved in its activation mechanism and regulates agonist-stimulated ERK activation. Endothelin-1 (ET)1 is a 21-amino acid peptide that binds to a G-protein-coupled receptor (GPCR), of which there are two subtypes: endothelin receptor A, and endothelin receptor B (ETB). Receptor binding triggers a diverse spectrum of physiological effects including vasoconstriction, mitogenesis, and embryonic development (1-5).Consistent with the complex biology of endothelin, binding of the peptide to its receptor initiates several important cellular signaling pathways, including increases in cytosolic free calcium, activation of the Src cytosolic tyrosine kinase, tyrosine phosphorylation of the Shc adapter protein, ERK, and c-Jun NH 2 -terminal kinase mitogen-activated protein kinase activation, protein kinase C involvement, activation of phosphatidylinositol 3-kinase, and stimulation of the epidermal growth factor receptor tyrosine kinase activity (3, 6, 7, 9 -14).The endothelin receptors are members of a superfamily of G-protein-coupled receptors that are thought to activate downstream signaling networks through their dynamic interaction with heterotrimeric G-proteins. Mutational studies of the endothelin receptors have defined extracellular loop 2 as being critical for ligand contact and binding, whereas the cytoplasmic tail has been implicated as important for coupling to G-proteins (15-17).The relationship between ligand binding affinity and receptor-G-protein interaction is described by the ternary complex model of receptor activation (18). It is widely thought that a small fraction of receptors reside in the activated conformation and that agonist binding stabilizes this conformation, which results in activation of the associated G-protein. The dynamic interaction ...

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