Members of the POU and SOX transcription factor families exemplify the partnerships established between various transcriptional regulators during early embryonic development. Although functional cooperativity between key regulator proteins is pivotal for milestone decisions in mammalian development, little is known about the underlying molecular mechanisms. In this study, we focus on two transcription factors, Oct4 and Sox2, as their combination on DNA is considered to direct the establishment of the first three lineages in the mammalian embryo. Using experimental high-resolution structure determination, followed by model building and experimental validation, we found that Oct4 and Sox2 were able to dimerize onto DNA in distinct conformational arrangements. We demonstrate that the DNA enhancer region of their target genes is responsible for the correct spatial alignment of glue-like interaction domains on their surface. Interestingly, these surfaces frequently have redundant functions and are instrumental in recruiting various interacting protein partners.[Keywords: Oct4; Sox2; POU domain; HMG domain; FGF4 and UTF1 enhancers; crystal structure] Supplemental material is available online at http://www.genesdev.org.

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Lymphangiogenesis is an important process that contributes to the spread of cancer. Here we show that insulin-like growth factors 1 (IGF-1) and 2 (IGF-2) induce lymphangiogenesis in vivo. In a mouse cornea assay, IGF-1 and IGF-2 induce lymphangiogenesis as detected with LYVE-1, a specific marker for lymphatic endothelium. angiogenesis ͉ insulin-like ͉ growth factor family ͉ vascularization ͉ tumor growth ͉ metastasis

Besides lung, postnatal human epidermis is the only epithelium in direct contact with atmospheric oxygen. Skin epidermal oxygenation occurs mostly through atmospheric oxygen rather than tissue vasculature, resulting in a mildly hypoxic microenvironment that favors increased expression of hypoxia-inducible factor-1α (HIF-1α). Considering the wide spectrum of biological processes, such as angiogenesis, inflammation, bioenergetics, proliferation, motility, and apoptosis, that are regulated by this transcription factor, its high expression level in the epidermis might be important to HIF-1α in skin physiology and pathophysiology. Here, we review the role of HIF-1α in cutaneous angiogenesis, skin tumorigenesis, and several skin disorders.

The crystal structure of the dimeric anthranilate phosphoribosyltransferase (AnPRT) reveals a new category of phosphoribosyltransferases, designated as class III. The active site of this enzyme is located within the¯exible hinge region of its two-domain structure. The pyrophosphate moiety of phosphoribosylpyrophosphate is co-ordinated by a metal ion and is bound by two conserved loop regions within this hinge region. With the structure of AnPRT available, structural analysis of all enzymatic activities of the tryptophan biosynthesis pathway is complete, thereby connecting the evolution of its enzyme members to the general development of metabolic processes. Its structure reveals it to have the same fold, topology, active site location and type of association as class II nucleoside phosphorylases. At the level of sequences, this relationship is mirrored by 13 structurally invariant residues common to both enzyme families. Taken together, these data imply common ancestry of enzymes catalysing reverse biological processesÐthe ribosylation and deribosylation of metabolic pathway intermediates. These relationships establish new links for enzymes involved in nucleotide and amino acid metabolism. Keywords: enzyme evolution/nucleoside phosphorylase/ nucleotide salvage/phosphoribosyltransferase/tryptophan biosynthesis IntroductionThe transfer of a ribosyl group between an aromatic base and phosphate groups is one of the most fundamental biochemical reactions in the metabolism of nucleotides and amino acids (Craig and Eakin, 2000;Pugmire and Ealick, 2002). This transfer is generally reversible, leading to either the addition or the removal of a ribosyl unit from metabolic compounds. The addition of ribosyl groups is catalysed by phosphoribosyltransferases (PRTs), which displace the 1¢-pyrophosphate moiety from the substrate 5-phosphoribosyl-1¢-pyrophosphate (PRPP), forming a 1¢-glycosidic±nitrogen bond between a nitrogenated base and a phosphoribosyl group. The reverse process is catalysed by nucleoside phosphorylases (NPs) and is associated speci®cally with the removal of ribose from nucleosides by the phosphorolytic cleavage of the N-1¢-glycosidic bond (Figure 1). PRT catalysis generally requires the presence of a divalent metal ion, whereas no metal ion is needed for NP catalysis. Both types of reactions are believed to follow a sequential S N 1 mechanism, although alternative mechanisms are not ruled out (Craig and Eakin, 2000;Pugmire and Ealick, 2002).PRTs are known to be involved in nucleotide salvage and synthesis pathways as well as in the biosynthesis of the amino acids histidine and tryptophan, and the co-factor NAD. Most of the PRTs with known three-dimensional structure share the same two-domain architecture, known as the PRT-I fold (Craig and Eakin, 2000;Sinha and Smith, 2001), the only exception being quinolate PRT, which has been classi®ed as the PRT-II fold (Eads et al., 1997). The currently available NP structures are also categorized into two unrelated folds. The ®rst class is involved in the cleavage of...

Proliferative signals lead to the rapid and transient induction of the c-fos proto-oncogene by targeting the ternary complex assembled on the serum response element (SRE). Transactivation by both components of this complex, serum response factor (SRF) and the ternary complex factor Elk-1, can be potentiated by the coactivator CREB-binding protein (CBP). We report a novel interaction between the bromodomain of CBP, amino acids 1100 -1286, and Elk-1. DNA binding and glutathione S-transferase pull-down assays demonstrate that binding requires Elk-1 1-212 but not the C-terminal transactivation domain. Competition and antibody controls show that the bromocomplex involves both SRF and Elk-1 on the c-fos SRE and uniquely Elk-1 on the E74 Ets binding site. Interestingly, methylation interference and DNA footprinting analyses show almost indistinguishable patterns between ternary and bromocomplexes, suggesting that CBP-(1100 -1286) interacts via Elk-1 and does not require specific DNA contacts. Functionally, the bromocomplex blocks activation, because cotransfection of CBP-(1100 -1286) reduces RasV12-driven activation of SRE and E74 luciferase reporters. Repression is relieved moderately or strongly by linking the bromodomain to the N-or C-terminal transactivation domains of CBP, respectively. These results are consistent with a model in which CBP is constitutively bound to the SRE in a higher order complex that would facilitate the rapid transcriptional activation of c-fos by signaling-driven phosphorylation.

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