The phosphorylation of the serine 10 at histone H3 has been shown to be important for transcriptional activation. Here, we report the molecular mechanism through which H3S10ph triggers transcript elongation of the FOSL1 gene. Serum stimulation induces the PIM1 kinase to phosphorylate the preacetylated histone H3 at the FOSL1 enhancer. The adaptor protein 14-3-3 binds the phosphorylated nucleosome and recruits the histone acetyltransferase MOF, which triggers the acetylation of histone H4 at lysine 16 (H4K16ac). This histone crosstalk generates the nucleosomal recognition code composed of H3K9acS10ph/H4K16ac determining a nucleosome platform for the bromodomain protein BRD4 binding. The recruitment of the positive transcription elongation factor b (P-TEFb) via BRD4 induces the release of the promoter-proximal paused RNA polymerase II and the increase of its processivity. Thus, the single phosphorylation H3S10ph at the FOSL1 enhancer triggers a cascade of events which activate transcriptional elongation.

No abstract

Key Words: cell adhesion Ⅲ endothelial cells Ⅲ angiogenesis Ⅲ biochemistry Ⅲ signaling C rosstalk between integrins and growth factor receptors plays an important role in vascular development and its maintenance. Several examples demonstrated that crosstalk between integrins and tyrosine kinase receptors is required for growth factor-induced biological processes to ensure cell growth, survival, and differentiation in normal and pathological processes. 1 The angiogenic processes require the coordination of signals from the extracellular environment to activates specific tyrosine kinase receptors and integrins. 1,2 Integrins associating with growth factor receptors regulate the capacity of the integrin/receptor complexes to propagate downstream signals. 3,4 Integrin-dependent activation of receptor tyrosine kinases is a general mechanism to enhance growth factor signals, the recruitment of transducing proteins to membrane cytoskeletal complexes as well as nuclear responses. This cooperation has been shown for several signaling pathways including insulin, epidermal growth factor (EGF), platelet-derived growth factor, fibroblast growth factor, and vascular endothelial growth factor (VEGF) signaling. [5][6][7][8][9][10][11][12][13][14][15][16][17][18] Integrins are able to trigger ligand-independent EGF receptor autophosphorylation leading to activation of the downstream pathway. 16 Integrins, c-Src, p130Cas and EGF receptor associate in a macromolecular complex on the cell membrane and integrin-dependent adhesion induces phosphorylation of specific tyrosine residues of EGF receptor, distinct from those obtained by the soluble ligand EGF. 11,19 A large body of evidence demonstrates that the angiogenic process is initiated by mitogenic signals induced by growth factors such as VEGF and the interplay between the tyrosine 34 -36 VEGFR-3, in contrast to its highly related endothelial receptor VEGFR-2 (which, after VEGF stimulation, forms a complex with integrin ␤3 subunit 8,20,21,24,25,37 ), associates selectively with integrin ␤1. 10,12 Cell attachment to fibronectin or collagen induces the phosphorylation of VEGFR-3 in the absence of a ligand and significantly enhances the phosphorylation of the receptor induced by its ligand. 10,12 However, the mechanism of integrin activation of VEGFR-3 has not been clarified.Here, we demonstrate that collagen I-induced activation of VEGFR-3 is independent from the intrinsic catalytic activity of the receptor but it is a direct target of c-Src. c-Src phosphorylates VEGFR-3 at specific tyrosine residues with a pattern of phosphorylation that is distinct from the pattern induced by the ligand. Cell adhesion induces the phosphorylation of the tyrosine residues 1063 and 1337, which are known binding sites for CRKI/II and SHC. Pull-down assays demonstrated that integrin-mediated receptor phosphorylation induces the recruitment of CRKI/II and SHC second messengers to the receptor suggesting that the integrin/receptor complex can activate growth and survival signaling in the absence ...

The inhibition of tumor angiogenesis is one of the main challenges in cancer therapy. With the aim of developing monoclonal antibodies able to inhibit angiogenesis, we immunized mice with proliferating human umbilical vein endothelial cells. We generated a library of monoclonal antibodies able to recognize antigens expressed on endothelial cells and screened the antibodies for their ability to inhibit endothelial cell proliferation, migration, and sprouting in vitro. Here, we show that the antibody, designated as 4E1, is able to neutralize the formation of new vessels both in vitro and in vivo without affecting endothelial cell survival. By mass spectrometry we identified CD93 as the antigen bound by 4E1 and mapped the recognized epitope. CD93 is a transmembrane protein heavily glycosylated preferentially expressed in the vascular endothelium. CD93 silencing by lentiviral-mediated small hairpin RNA expression impairs human endothelial cell proliferation, migration, and sprouting. Altogether these findings reveal 4E1 as a novel antiangiogenic antibody and identify CD93 as a new target suitable for antiangiogenic therapy.