Endothelial specific YY1 deletion restricts tumor angiogenesis and tumor growth.

Angiogenesis is a physiological process for the formation of new blood vessels from the pre-existing vessels and it has a vital role in the survival and growth of neoplasms. During tumor angiogenesis, the activation of the gene transcriptions in vascular endothelial cells (ECs) plays an essential role in the promotion of EC proliferation, migration, and vascular network development. However, the molecular mechanisms underlying transcriptional regulation of EC and tumor angiogenesis remains to be fully elucidated. Here we report that the transcription factor Yin Yang 1 (YY1) in ECs is critically involved in tumor angiogenesis. First, we utilized a tamoxifen-inducible EC-specific YY1 deficient mouse model and showed that YY1 deletion in ECs inhibited the tumor growth and tumor angiogenesis. Using the in vivo matrigel plug assay, we then found that EC-specific YY1 ablation inhibited growth factor-induced angiogenesis. Furthermore, vascular endothelial growth factor (VEGF)-induced EC migration was diminished in YY1-depleted human umbilical vein endothelial cells (HUVECs). Finally, a rescue experiment revealed that YY1-regulated BMP6 expression in ECs was involved in EC migration. Collectively, our results demonstrate that endothelial YY1 has a crucial role in tumor angiogenesis and suggest that targeting endothelial YY1 could be a potential therapeutic strategy for cancer treatment.

Endothelial-specific YY1 governs sprouting angiogenesis through directly interacting with RBPJ.

Angiogenesis, the formation of new blood vessels, is tightly regulated by gene transcriptional programs. Yin Ying 1 (YY1) is a ubiquitously distributed transcription factor with diverse and complex biological functions; however, little is known about the cell-type-specific role of YY1 in vascular development and angiogenesis. Here we report that endothelial cell (EC)-specific YY1 deletion in mice led to embryonic lethality as a result of abnormal angiogenesis and vascular defects. Tamoxifen-inducible EC-specific YY1 knockout (YY1iΔEC ) mice exhibited a scarcity of retinal sprouting angiogenesis with fewer endothelial tip cells. YY1iΔEC mice also displayed severe impairment of retinal vessel maturation. In an ex vivo mouse aortic ring assay and a human EC culture system, YY1 depletion impaired endothelial sprouting and migration. Mechanistically, YY1 functions as a repressor protein of Notch signaling that controls EC tip-stalk fate determination. YY1 deficiency enhanced Notch-dependent gene expression and reduced tip cell formation. Specifically, YY1 bound to the N-terminal domain of RBPJ (recombination signal binding protein for Ig Kappa J region) and competed with the Notch coactivator MAML1 (mastermind-like protein 1) for binding to RBPJ, thereby impairing the NICD (intracellular domain of the Notch protein)/MAML1/RBPJ complex formation. Our study reveals an essential role of endothelial YY1 in controlling sprouting angiogenesis through directly interacting with RBPJ and forming a YY1-RBPJ nuclear repression complex.

Myofibroblast-specific YY1 promotes liver fibrosis.

Liver fibrosis is a common consequence of various chronic hepatitis and liver injuries. The myofibroblasts, through the accumulation of extracellular matrix (ECM) proteins, are closely associated with the progression of liver fibrosis. However, the molecular mechanisms underlying transcriptional regulation of fibrogenic genes and ECM proteins in myofibroblasts remain largely unknown. Using tamoxifen inducible myofibroblast-specific Cre-expressing mouse lines with selective deletion of the transcription factor Yin Yang 1 (YY1), here we show that YY1 deletion in myofibroblasts mitigates carbon tetrachloride-induced liver fibrosis. This protective effect of YY1 ablation on liver fibrosis was accompanied with reduced expression of profibrogenic genes and ECM proteins, including TNF-α, TGF-ß, PDGF, IL-6, α-SMA and Col1α1 in liver tissues from YY1 mutant mice. Moreover, using the human hepatic stellate cell (HSC) line LX-2, we found that knockdown of YY1 in myofibroblasts by siRNA treatment diminished myofibroblast proliferation, α-SMA expression, and collagen deposition. Collectively, our findings reveal a specific role of YY1 in hepatic myofibroblasts and suggest a new therapeutic strategy for hepatic fibrosis-associated liver diseases.

Tannic acid as a plant-derived polyphenol exerts vasoprotection via enhancing KLF2 expression in endothelial cells.

The transcription factor Kruppel-like factor 2 (KLF2) is a critical anti-inflammatory and anti-atherogenic molecule in vascular endothelium. Enhancing KLF2 expression and activity improves endothelial function and prevents atherosclerosis. However, the pharmacological and molecular regulators for KLF2 are scarce. Using high-throughput luciferase reporter assay to screen for KLF2 activators, we have identified tannic acid (TA), a polyphenolic compound, as a potent KLF2 activator that attenuates endothelial inflammation. Mechanistic studies suggested that TA induced KLF2 expression in part through the ERK5/MEF2 pathway. Functionally, TA markedly decreased monocyte adhesion to ECs by reducing expression of adhesion molecule VCAM1. Using lung ECs isolated from Klf2 +/+ and Klf2 +/- mice, we showed that the anti-inflammatory effect of TA is dependent on KLF2. Collectively, our results demonstrate that TA is a potent KLF2 activator and TA attenuated endothelial inflammation through upregulation of KLF2. Our findings provide a novel mechanism for the well-established beneficial cardiovascular effects of TA and suggest that KLF2 could be a novel therapeutic target for atherosclerotic vascular disease.

Cryptotanshinone, an orally bioactive herbal compound from Danshen, attenuates atherosclerosis in apolipoprotein E-deficient mice: role of lectin-like oxidized LDL receptor-1 (LOX-1).

BACKGROUND AND PURPOSE: Cryptotanshinone (CTS) is a major bioactive diterpenoid isolated from Danshen, an eminent medicinal herb that is used to treat cardiovascular disorders in Asian medicine. However, it is not known whether CTS can prevent experimental atherosclerosis. The present study was designed to investigate the protective effects of CTS on atherosclerosis and its molecular mechanisms of action. EXPERIMENTAL APPROACH: Apolipoprotein E-deficient (ApoE(-/-)) mice, fed an atherogenic diet, were dosed daily with CTS (15, 45 mg kg(-1) day(-1)) by oral gavage. In vitro studies were carried out in oxidized LDL (oxLDL)-stimulated HUVECs treated with or without CTS. KEY RESULTS: CTS significantly attenuated atherosclerotic plaque formation and enhanced plaque stability in ApoE(-/-) mice by inhibiting the expression of lectin-like oxLDL receptor-1 (LOX-1) and MMP-9, as well as inhibiting reactive oxygen species (ROS) generation and NF-κB activation. CTS treatment significantly decreased the levels of serum pro-inflammatory mediators without altering the serum lipid profile. In vitro, CTS decreased oxLDL-induced LOX-1 mRNA and protein expression and, thereby, inhibited LOX-1-mediated adhesion of monocytes to HUVECs, by reducing the expression of adhesion molecules (intracellular adhesion molecule 1 and vascular cellular adhesion molecule 1). Furthermore, CTS inhibited NADPH oxidase subunit 4 (NOX4)-mediated ROS generation and consequent activation of NF-κB in HUVECs. CONCLUSIONS AND IMPLICATIONS: CTS was shown to have anti-atherosclerotic activity, which was mediated through inhibition of the LOX-1-mediated signalling pathway. This suggests that CTS is a vasculoprotective drug that has potential therapeutic value for the clinical treatment of atherosclerotic cardiovascular diseases.

Flow shear stress stimulates Gab1 tyrosine phosphorylation to mediate protein kinase B and endothelial nitric-oxide synthase activation in endothelial cells.

Fluid shear stress generated by blood flow modulates endothelial cell function via specific intracellular signaling events. We showed previously that flow activated the phosphatidylinositol 3-kinase (PI3K), Akt, and endothelial nitric-oxide synthase (eNOS) via Src kinase-dependent transactivation of vascular endothelial growth factor receptor 2 (VEGFR2). The scaffold protein Gab1 plays an important role in receptor tyrosine kinase-mediated signal transduction. We found here that laminar flow (shear stress = 12 dynes/cm2) rapidly stimulated Gab1 tyrosine phosphorylation in both bovine aortic endothelial cells and human umbilical vein endothelial cells, which correlated with activation of Akt and eNOS. Gab1 phosphorylation as well as activation of Akt and eNOS by flow was inhibited by the Src kinase inhibitor PP2 (4-amino-5-(4-chlorophenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine) and VEGFR2 kinase inhibitors SU1498 and VTI, suggesting that flow-mediated Gab1 phosphorylation is Src kinase-dependent and VEGFR2-dependent. Tyrosine phosphorylation of Gab1 by flow was functionally important, because flow stimulated the association of Gab1 with the PI3K subunit p85 in a time-dependent manner. Furthermore, transfection of a Gab1 mutant lacking p85 binding sites inhibited flow-induced activation of Akt and eNOS. Finally, knockdown of endogenous Gab1 by small interference RNA abrogated flow activation of Akt and eNOS. These data demonstrate a critical role of Gab1 in flow-stimulated PI3K/Akt/eNOS signal pathway in endothelial cells.