Production of Apolipoprotein C-III Knockout Rabbits using Zinc Finger Nucleases

Apolipoprotein (Apo) C-III (ApoCIII) resides on the surface of plasma chylomicron (CM), very low density lipoprotein (VLDL) and high density lipoproteins ...

University of Michigan Medical Center

Mutations in either the TSC1 or TSC2 tumor suppressor gene are responsible for Tuberous Sclerosis Complex. The gene products of TSC1 and TSC2 form a functional complex and inhibit the phosphorylation of S6K and 4EBP1, two key regulators of translation. Here, we describe that TSC2 is regulated by cellular energy levels and plays an essential role in the cellular energy response pathway. Under energy starvation conditions, the AMP-activated protein kinase (AMPK) phosphorylates TSC2 and enhances its activity. Phosphorylation of TSC2 by AMPK is required for translation regulation and cell size control in response to energy deprivation. Furthermore, TSC2 and its phosphorylation by AMPK protect cells from energy deprivation-induced apoptosis. These observations demonstrate a model where TSC2 functions as a key player in regulation of the common mTOR pathway of protein synthesis, cell growth, and viability in response to cellular energy levels.

TSC2 mediates cellular energy response to control cell growth and survival.

The Ras oncoproteins activate the Raf-MEK-ERK kinase pathway, which plays an important role in cellular transformation. We observed that H-RasV12 exhibited a higher transforming potential than either K-RasV12 or N-RasV12 in both NIH3T3 fibroblasts and RIE-1 rat epithelial cell cultures. Surprisingly N-Ras and K-Ras were more potent than H-Ras in activation of mitogen-activated protein (MAP) kinase activity and ternary complex factor-dependent transcription. In contrast, H-Ras was more effective in activation of phosphatidylinositol 3-kinase (PI3K) and AKT. Co-expression of constitutively active AKT, a downstream target of PI3K, cooperated with H-RasV12, K-RasV12, or N-RasV12 in transformation. Furthermore co-expression of the constitutively active MEK and AKT resulted in focus formation, while neither active MEK1 nor active AKT alone transformed NIH3T3 cells. Our data demonstrated that the transforming potential of Ras was not directly correlated with the ability of Ras to activate the MAP kinase cascade. In contrast, the ability to activate PI3K and AKT correlated with the ability of Ras to induce cellular transformation, suggesting an important role of PI3K-AKT in cellular transformation. Our data also demonstrated that, under these assay conditions, activation of the MAP kinase cascade was not sufficient to induce NIH3T3 cell transformation.

Transformation potential of Ras isoforms correlates with activation of phosphatidylinositol 3-kinase but not ERK.

The semaphorins are a large family of secreted and cell surface proteins that provide attractive and repulsive cues for axon guidance during neuronal development. Semaphorins share a conserved NH(2)-terminal Sema domain with their receptors, the plexins, which mediate neuronal cell adhesion, axon guidance, and maintenance of established neuronal pathways in the adult. Both semaphorins and plexins share structural homology with the extracellular domain of c-Met, a member of the scatter factor family of receptors. However, the highly conserved cytoplasmic region of plexins has no homology with the c-Met tyrosine kinase or with any other known protein. Using a recently developed antibody and RNA analysis, we found that high levels of plexin-B1 are expressed in endothelial cells. Whereas c-Met, with which plexin-B1 can interact, is known to be a potent promoter of angiogenesis, the effects of semaphorin-mediated plexin activation in endothelial cells are still poorly understood. Here, we examined the role of plexin-B1 activation in angiogenesis using a purified, secreted form of its ligand, Semaphorin 4D (Sema4D). Sema4D potently induced chemotaxis and tubulogenesis in endothelial cells and enhanced blood vessel formation in an in vivo mouse model. Interestingly, responses to Sema4D did not require c-Met activation. Instead, the use of chimeric plexin-B1 receptors, Rho inhibitors, and lentiviral gene delivery of interfering molecules revealed that these proangiogenic effects are dependent on a COOH-terminal PDZ-binding motif of plexin-B1, which binds two guanine nucleotide exchange factors for the small GTPase Rho, PDZ-RhoGEF and LARG, and are mediated by the activation of Rho-initiated pathways.

Class IV semaphorins promote angiogenesis by stimulating Rho-initiated pathways through plexin-B.

Tuberous sclerosis complex (TSC) is an autosomal dominant disease characterized by hamartoma formation in various organs. Two genes responsible for the disease, TSC1 and TSC2, have been identified. The TSC1 and TSC2 proteins, also called hamartin and tuberin, respectively, have been shown to regulate cell growth through inhibition of the mammalian target of rapamycin pathway. TSC1 is known to stabilize TSC2 by forming a complex with TSC2, which is a GTPase-activating protein for the Rheb small GTPase. We have identified HERC1 as a TSC2-interacting protein. HERC1 is a 532-kDa protein with an E3 ubiquitin ligase homology to E6AP carboxyl terminus (HECT) domain. We observed that the interaction of TSC1 with TSC2 appears to exclude TSC2 from interacting with HERC1. Disease mutations in TSC2, which result in its destabilization, allow binding to HERC1 in the presence of TSC1. Our study reveals a potential molecular mechanism of how TSC1 stabilizes TSC2 by excluding the HERC1 ubiquitin ligase from the TSC2 complex. Furthermore, these data reveal a possible biochemical basis of how certain disease mutations inactivate TSC2.

TSC1 stabilizes TSC2 by inhibiting the interaction between TSC2 and the HERC1 ubiquitin ligase.

Mutation in the TSC2 tumor suppressor causes tuberous sclerosis complex, a disease characterized by hamartoma formation in multiple tissues. TSC2 inhibits cell growth by acting as a GTPase-activating protein toward Rheb, thereby inhibiting mTOR, a central controller of cell growth. Here, we show that Wnt activates mTOR via inhibiting GSK3 without involving beta-catenin-dependent transcription. GSK3 inhibits the mTOR pathway by phosphorylating TSC2 in a manner dependent on AMPK-priming phosphorylation. Inhibition of mTOR by rapamycin blocks Wnt-induced cell growth and tumor development, suggesting a potential therapeutic value of rapamycin for cancers with activated Wnt signaling. Our results show that, in addition to transcriptional activation, Wnt stimulates translation and cell growth by activating the TSC-mTOR pathway. Furthermore, the sequential phosphorylation of TSC2 by AMPK and GSK3 reveals a molecular mechanism of signal integration in cell growth regulation.

TSC2 integrates Wnt and energy signals via a coordinated phosphorylation by AMPK and GSK3 to regulate cell growth.

Nitro-oleic acid (OA-NO(2)) is a bioactive, nitric-oxide derived fatty acid with physiologically relevant vasculoprotective properties in vivo. OA-NO(2) exerts cell signaling actions as a result of its strong electrophilic nature and mediates pleiotropic cell responses in the vasculature.

Nitro-oleic acid inhibits angiotensin II-induced hypertension.

Zn2+ ions were found to efficiently inhibit activated protein C (APC), suggesting a potential regulatory function for such inhibition. APC activity assays employing a chromogenic peptide substrate demonstrated that the inhibition was reversible and the apparent K I was 13 +/- 2 microM. k cat was seven fold decreased whereas K M was unaffected in the presence of 10 microM Zn2+. The inhibitory effect of Zn2+ on APC activity was also observed when factor Va was used as a substrate in an assay coupled to a prothrombinase assay. The interaction of Zn2+ with APC was accompanied by a reversible approximately 40% decrease in tryptophan fluorescence, consistent with the ion inducing a conformational change in the protein. The apparent K D was 7.4 +/- 1.5 microM and thus correlated well with the apparent K I. In the presence of physiological Ca2+ concentration the K I and K D values were three to four fold enhanced, presumably due to the Ca2+-induced conformational change affecting the conformation of the Zn2+-binding site. The inhibition mechanism was non-competitive both in the absence and presence of Ca2+. Comparisons of sequences and structures suggested several possible sites for zinc binding. The magnitude of the apparent KI in relation to the blood and platelet concentrations of Zn2+ supports a physiological role for this ion in the regulation of anticoagulant activity of APC. These findings broaden the understanding of this versatile serine protease and enable the future development of potentially more efficient anticoagulant APC variants for treatments of thrombotic diseases.

Zinc ions bind to and inhibit activated protein C.

The Hippo-Yap (Yes-associated protein) signaling pathway has emerged as one of the critical pathways regulating cell proliferation, differentiation, and apoptosis in response to environmental and developmental cues. However, Yap1 roles in vascular smooth muscle cell (VSMC) biology have not been investigated. VSMCs undergo phenotypic switch, a process characterized by decreased gene expression of VSMC contractile markers and increased proliferation, migration, and matrix synthesis. The goals of the present studies were to investigate the relationship between Yap1 and VSMC phenotypic switch and to determine the molecular mechanisms by which Yap1 affects this essential process in VSMC biology. Results demonstrated that the expression of Yap1 was rapidly up-regulated by stimulation with PDGF-BB (a known inducer of phenotypic switch in VSMCs) and in the injured vessel wall. Knockdown of Yap1 impaired VSMC proliferation in vitro and enhanced the expression of VSMC contractile genes as well by increasing serum response factor binding to CArG-containing regions of VSMC-specific contractile genes within intact chromatin. Conversely, the interaction between serum response factor and its co-activator myocardin was reduced by overexpression of Yap1 in a dose-dependent manner. Taken together, these results indicate that down-regulation of Yap1 promotes VSMC contractile phenotype by both up-regulating myocardin expression and promoting the association of the serum response factor-myocardin complex with VSMC contractile gene promoters and suggest that the Yap1 signaling pathway is a central regulator of phenotypic switch of VSMCs.

Yap1 protein regulates vascular smooth muscle cell phenotypic switch by interaction with myocardin.

Members of the WUSCHEL-RELATED HOMEOBOX (WOX) gene family have important functions during all stages of plant development and have been implicated in the development of morphological novelties during evolution. Most studies have examined the function of these genes in angiosperms and very little is known from other plant species.

Tianqing Zhu

Center for Advanced Models for Translational Sciences and Therapeutics,
Department of Internal Medicine,
Center for Advanced Models for Translational Sciences and Therapeutics, Department of Internal Medicine

University of Michigan Medical Center

Production of Apolipoprotein C-III Knockout Rabbits using Zinc Finger Nucleases

Tianqing Zhu

.css-o250i3{font-size:18px;font-family:Open Sans,sans-serif;line-height:21.6px;}Center for Advanced Models for Translational Sciences and Therapeutics,Department of Internal Medicine,Center for Advanced Models for Translational Sciences and Therapeutics, Department of Internal Medicine

University of Michigan Medical Center

Production of Apolipoprotein C-III Knockout Rabbits using Zinc Finger Nucleases

Center for Advanced Models for Translational Sciences and Therapeutics,
Department of Internal Medicine,
Center for Advanced Models for Translational Sciences and Therapeutics, Department of Internal Medicine