Cytochalasin D disruption of actin filaments in 3T3 cells produces an anti-apoptotic response by activating gelatinase A extracellularly and initiating intracellular survival signals

AbstractDisruption of actin filaments affects multiple cell functions including motility, signal transduction and cell division, ultimately culminating in cell death. Although this is the usual sequence of events, we have made the interesting observation that disruption of actin filaments by the potent toxin cytochalasin D (Cyto D) causes one cell type, mouse mesangial cells (MMC), to undergo apoptosis, while in another cell type (NIH 3T3), it has the opposite effect, resulting in production of survival signals. The purpose of this study was to investigate the molecular basis for these observed differences. In the present communication, we demonstrate that exposure to Cyto D induces the pro-apoptotic pathways, p38 and stress-activated protein kinase (SAPK)/jun amino-terminal kinase (JNK), in both cell types. However, in 3T3, but not MMC, the extracellular signal regulated kinase (ERK) 1/2 pathway is protected from inhibition following treatment with Cyto D—leading to phosphorylation of Bclxi/Bcl 2-associated death promoter (BAD). Inhibition of Cyto D-induced secretion and activation of gelatinase A in 3T3 cells reverses the production of survival signals by Cyto-D. To investigate this effect further we employed CS-1 cells, a well-characterized melanoma cell line that lacks integrin β3, and also does not secrete gelatinase A. Co-transfection of CS-1 cells with integrin β3 and a gelatinase A transgene, which enables the cells to secrete constituitively active gelatinase A, enhances CS-1 cell survival signals. Together, our findings suggest that extracellularly activated gelatinase A, through interaction with integrin αVβ3, elicits survival signals mediated through ERK 1/2 that override activation of p38 and SAPK/JNK stress pathways

Description of a PCR-based technique for DNA splicing and mutagenesis by producing 5' overhangs with run through stop DNA synthesis utilizing Ara-C

BACKGROUND: Splicing of DNA molecules is an important task in molecular biology that facilitates cloning, mutagenesis and creation of chimeric genes. Mutagenesis and DNA splicing techniques exist, some requiring restriction enzymes, and others utilize staggered reannealing approaches. RESULTS: A method for DNA splicing and mutagenesis without restriction enzymes is described. The method is based on mild template-dependent polymerization arrest with two molecules of cytosine arabinose (Ara-C) incorporated into PCR primers. Two rounds of PCR are employed: the first PCR produces 5' overhangs that are utilized for DNA splicing. The second PCR is based on polymerization running through the Ara-C molecules to produce the desired final product. To illustrate application of the run through stop mutagenesis and DNA splicing technique, we have carried out splicing of two segments of the human cofilin 1 gene and introduced a mutational deletion into the product. CONCLUSION: We have demonstrated the utility of a new PCR-based method for carrying out DNA splicing and mutagenesis by incorporating Ara-C into the PCR primers

Accretion and star formation rates in low redshift type-II active galactic nuclei

Accretion and star formation (SF) rates in low redshift SDSS type-II active galactic nuclei (AGN) are critically evaluated. Comparison with photoionization models indicates that bolometric luminosity (Lbol) estimates based on L(oiii 5007A) severely underestimate Lbol in low ionization sources such as LINERs. An alternative method based on L(hb) is less sensitive to ionization level and a novel method, based on a combination of L(oiii 5007A) and L(oi 6300A), is erhaps the best. Using this method I show that low ionization AGN are accreting faster than assumed until now. Significant related other findings are: 1. Any type-II AGN property related to the black hole (BH) mass is more reliably obtained by removing blue galaxies from the sample. 2. Seyfert 2s and LINER 2s form a continuous sequence of L/Ledd with no indication for a change in accretion mechanism, or mode of mass supply. There are very few, if any, LINERs in all type-I samples which results in a much arrower L/Ledd distribution compared with type-II samples. 3. There is a strong correlation between SF luminosity, Lsf, and Lbol over more than five orders of magnitude in luminosity. This leads to a simple relationship between bulge and BH growth rates, g(bulge)/g(BH) propto Lbol^(-0.2), where g(bulge)/g(BH) = 115 for Lbol=10^42 erg/sec. Seyfert 2s and LINER 2s follow the same Lsf-Lbol correlation for all sources with a stellar age indicator, D4000, smaller than 1.8. This suggests that a similar fraction of SF gas finds its way to the center in all AGN. 4. Lbol, Lsf, L/Ledd and the specific SF rate follow D4000 in a similar way.Comment: 16 pages, 16 figures, accepted for publication in MNRA

MUNC13 REGULATES SECRETION AT THE GOLGI IN A LOCALIZATION-DEPENDENT MANNER

Background: Constitutive secretion is critical for the maintenance of eukaryotic cell structure and function. Our lab has shown that Rab34 is required for secretion at the Golgi^1, and that the C1 domain-containing protein, Munc13, is an effector of Rab34^2. Current studies seek to elucidate potential roles for Munc13in secretion at the Golgi. Methods: Using a temperature-sensitive mutant of the Vesicular Stomatitis G-protein fused to GFP (VSVG-GFP) to monitor secretion, we examinedthe role of Munc13 in secretion in HeLa cells. Cells transfected with VSVG-GFP were treated with Munc13, amutant lacking the C1 domain (C1-less), and the phorbol esters TPA andPDBu. The rate of VSVG-GFP secretion was monitored using surface labelling of plasmalemmal VSVG-GFP and spinning disc confocal microscopy. Results: TPA treatment resulted in an increase in the rate of VSVG-GFP appearance at the plasma membrane. Co-transfection of either Munc13 or C1-less alone also resulted in an increased rate of VSVG-GFP transport. Transfection of Munc13 plus TPA treatment resulted in amarked decrease in the rate of VSVG-GFP transport. Since TPA treatment relocalizes Munc13 to the plasma membrane, this result suggests that the availability of Munc13 in the cytosol is required for its effect on VSVG-GFP secretion. Conclusions: Munc13 over-expression increases the rate of VSVG-GFP secretion to the plasma membrane. Sequestration of Munc13 at the plasma membrane with TPA abrogates thiseffect, and reduces the rate of VSVG-GFP secretion. We propose that Munc13 effects VSVG-GFP secretion via its interaction with Rab34 at the Golgi. References: 1. Goldenberg, NM, S. Grinstein, M. Silverman. Golgi-bound Rab34 is a Novel Member ofthe Secretory Pathway. Mol BiolCell. 18(12):4762-4771 (2007). 2. Speight, P, M. Silverman.Diacylglycerol-Activated Hmunc13 Serves as an Effector of the GTPaseRab34. Traffic.6(10):858-865 (2005)