RhoGDIβ affects HeLa cell spindle orientation following UVC irradiation

The molecular signals that regulate mitotic spindle orientation to determine the proper division axis play a critical role in the development and maintenance of tissue homeostasis. However, deregulation of signaling events can result in spindle misorientation, which in turn can trigger developmental defects and cancer progression. Little is known about the cellular signaling pathway involved in the misorientation of proliferating cells that evade apoptosis after DNA damage. In this study, we found that perturbations to spindle orientation were induced in ultraviolet C (UVC)-irradiated surviving cells. N-terminal truncated Rho GDP-dissociation inhibitor β (RhoGDIβ), which is produced by UVC irradiation, distorted the spindle orientation of HeLa cells cultured on Matrigel. The short hairpin RNA-mediated knockdown of RhoGDIβ significantly attenuated UVC-induced misorientation. Subsequent expression of wild-type RhoGDIβ, but not a noncleavable mutant, RhoGDIβ (D19A), again led to a relative increase in spindle misorientation in response to UVC. Our findings revealed that RhoGDIβ impacts spindle orientation in response to DNA damage.     

The mechanism of photosynthetic sulfate reduction by isolated chloroplasts

The reduction of sulfate by isolated spinach chloroplasts was studied. A reconstituted system of broken chloroplasts and of chloroplast extract reduced sulfate to sulfite in the light when ADP, NADP⁺, ferredoxin and glutathione were added. The chloroplast extract reduced sulfate to sulfite in the dark if supplemented with ATP and with reduced glutathione. Neither ferredoxin nor NADPH were needed for this reduction in the dark.

A sulfite reductase was purified from spinach leaves. Broken chloroplasts and sulfite reductase reduced sulfite to sulfide in the light when ferredoxin was added. NADP⁺ was not required for this reduction.

The results suggest that in chloroplasts a sulfate activated by ATP (phosphoadenosine phosphosulfate) is reduced to sulfite by a sulfhydryl compound and that sulfite is reduced to sulfide by a ferredoxin-dependent sulfite reductase.     

Identification of cardiac malformations in mice lacking <Emphasis Type="Italic">Ptdsr</Emphasis>using a novel high-throughput magnetic resonance imaging technique

Background  

Congenital heart defects are the leading non-infectious cause of death in children. Genetic studies in the mouse have been crucial to uncover new genes and signaling pathways associated with heart development and congenital heart disease. The identification of murine models of congenital cardiac malformations in high-throughput mutagenesis screens and in gene-targeted models is hindered by the opacity of the mouse embryo.     

Solution stability and degradation pathway of deoxyribonucleoside phosphoramidites in acetonitrile

The impuritiy profiles of acetonitrile solutions of the four standard O-cyanoethyl-N,N-diisopropyl-phosphoramidites of 5'-O-dimethoxytrityl (DMT) protected deoxyribonucleosides (dG(ib), dA(bz), dC(bz), T) were analyzed by HPLC-MS. The solution stability of the phosphoramidites decreases in the order T, dC>dA>dG. After five weeks storage under inert gas atmosphere the amidite purity was reduced by 2% (T, dC), 6% (dA), and 39% (dG), respectively. The main degradation pathways involve hydrolysis, elimination of acrylonitrile and autocatalytic acrylonitrile-induced formation of cyanoethyl phosphonoamidates. Consequently, the rate of degradation is reduced by reducing the water concentration in solution with molecular sieves and by lowering the amidite concentration. Acid-catalyzed hydrolysis could also be reduced by addition of small amounts of base.     

Activation of heterotrimeric G proteins by a high energy phosphate transfer via nucleoside diphosphate kinase (NDPK) B and Gbeta subunits. Specific activation of Gsalpha by an NDPK B.Gbetagamma complex in H10 cells

Formation of GTP by nucleoside diphosphate kinase (NDPK) can contribute to G protein activation in vitro. To study the effect of NDPK on G protein activity in living cells, the NDPK isoforms A and B were stably expressed in H10 cells, a cell line derived from neonatal rat cardiomyocytes. Overexpression of either NDPK isoform had no effect on cellular GTP and ATP levels, basal cAMP levels, basal adenylyl cyclase activity, and the expression of G(s)alpha and G(i)alpha proteins. However, co-expression of G(s)alpha led to an increase in cAMP synthesis that was largely enhanced by the expression of NDPK B, but not NDPK A, and that was confirmed by direct measurement of adenylyl cyclase activity. Cells expressing an inactive NDPK B mutant (H118N) exhibited a decreased cAMP formation in response to G(s)alpha. Co-immunoprecipitation studies demonstrated a complex formation of the NDPK with Gbetagamma dimers. The overexpression of NDPK B, but not its inactive mutant or NDPK A, increased the phosphorylation of Gbeta subunits. In summary, our data demonstrate a specific NDPK B-mediated activation of a G protein in intact cells, which is apparently caused by formation of NDPK B.Gbetagamma complexes and which appears to contribute to the receptor-independent activation of heterotrimeric G proteins.