Abstract By inhibiting the α-like DNA polymerase, and therefore nuclear DNA synthesis, aphidicolin induces accumulation of suspension cultured carrot cells at the G1/S boundary of the cell cycle. After a 24-h treatment with the drug the accumulation is complete, affecting all the cycling cells (95% of the population). Upon removal of the inhibitor, all cycling cells immediately resume nuclear DNA synthesis and move synchronously throughout the S-phase.

Abstract A gene named phd1+ encoding a protein highly homologous to the yeast and human histone deacetylases, such as Saccharomyces cerevisiae Rpd3p and human HDAC1, was cloned from Schizosaccharomyces pombe. The immune complex isolated from S. pombe cells expressing Phd1 fused to the FLAG epitope showed histone deacetylase activity, which was inhibited by trichostatin A (TSA), a specific inhibitor of histone deacetylase. The null mutation of phd1+ resulted in a marked decrease in the total cellular histone deacetylase activity and an increase in the sensitivity to TSA. Although the phd1 disruptant showed no obvious defect in the mitotic cell cycle or mating, both homothallic haploid and heterothallic diploid cells failed to form spores in the absence of phd1+. These results indicate that phd1+ encodes a histone deacetylase, which is involved in the meiotic cell cycle in S. pombe.

Abstract L-selectin guides lymphocytes into peripheral lymphoid tissues by recognizing glycoprotein ligands decorated with 6-sulfated sialyl Lewis x (sulfo sLex). Here we have used a rat peripheral lymph node high endothelial cell line (Ax) to study in detail the synthesis, expression and degradation of sLex epitope. We show here that Ax cells possess active α(1,3)fucosyltransferase Fuc-TVII, the enzyme responsible for the final fucosylation of sialyl-N-acetyllactosamine during sLex synthesis, and express sLex on the cell surface. Furthermore, these cells degrade sLex, primarily by desialylating it to neutral Lex epitopes by α(2,3)sialidase(s).

Abstract The role of Ca2+ and protein kinase C (PKC) in the regulation of phosphatidylcholine-hydrolyzing phospholipase D (PLD) was investigated in angiotensin II-stimulated mesangial cells. Elevation of cytosolic free Ca2+ by the calcium ionophore, A23187, or the Ca2+-ATPase inhibitor, thapsigargin, slightly increased PLD-stimulated phosphatidylethanol formation. However, chelation of cytosolic Ca2+ with high concentrations of quin 2 did not attenuate angiotensin II-indueed phosphatidylethanol production, thus suggesting that Ca2+ is not crucially involved in agonist-stimulated PLD activation. Stimulation of PKC by phorbol esters increased PLD activity in mesangial cells. Down-regulation of PKC-α and -δ isoenzymes by 8 h phorbol ester treatment still resulted in full PLD activation. In contrast, a 24 h treatment of mesangial cells with phorbol ester, a regimen that also causes depletion of PKC-ϵ, abolished angiotensin II-evoked phosphatidylethanol formation. In addition, the selective PKC inhibitor, calphostin C, attenuated hormone-induced PLD activity. In summary, these data suggest that angiotensin II stimulation of phospholipase D appears to involve the PKC-ϵ isoenzyme, activated by DAG derived from phosphoinositide hydrolysis.

Abstract We investigated the formation of F2-isoprostanes produced by non-enzymatic peroxidation of arachidonic acid during rabbit aortic endothelial cell-mediated oxidation of low density lipoprotein (LDL). Free and total (sum of free and esterified) levels of F2-isoprostanes were measured using a solid-phase extraction procedure and gas chromatography-mass spectrometry. Free levels of F2-isoprostanes in native LDL were 0.06 ± 0.03 ng/mg protein (n = 4), whereas total levels were 0.28 ± 0.09 ng/mg protein (n = 4). Both free and total levels of the isoprostanes were found to increase during the oxidation. 8-epi-PGF2α was the major isoprostane formed (free and total concentrations after 24 h, 2.50 ± 0.24 and 6.42 ± 1.36 ng/mg protein (n = 4), respectively). The release of F2-isoprostanes during aortic endothelial cell-induced oxidation of LDL could be a contributory factor in the development of atherosclerosis.

Abstract Physiological levels of shear stress alter the genetic program of cultured endothelial cells and reduce endothelial cell turnover in vivo. To test the hypothesis that shear stress interferes with programmed cell death, apoptosis was induced in human umbilical venous endothelial cells by growth factor withdrawal or incubation with tumor necrosis factor α(TNFα) for 18 h. Apoptosis was quantified by ELISA specific for histone-associated DNA fragments and confirmed by demonstrating the specific pattern of internucleosomal DNA fragmentation detected by electrophoresis and immunohistochemical staining. The TNFα (300 U/ml)-mediated increase in DNA fragmentation was completely abrogated by shear stress. Furthermore, shear stress dose-dependently reduced DNA fragmentation induced by growth factor withdrawal with maximal effect at 45 dyn/cm2. Inhibition of the CPP32-like proteases with Ac-DEVD-CHO (100 μM) revealed similar anti-apoptotic effects. In contrast, CPP32-independent induction of endothelial cell apoptosis by C2-ceramide (50 μM) was not prevented by shear stress. Thus, we propose that shear stress interferes with common cell death signal transduction involving the CPP32-like protease family and may contribute to endothelial cell integrity by inhibition of apoptosis.

Abstract Recent studies demonstrated the importance of the mitochondrial ATP in the regulation of a novel long-chain fatty acid generation/export system in mitochondria of diabetic rat heart. In steroidogenic systems, mitochondrial ATP and intramitochondrial arachidonic acid (AA) generation are important for steroidogenesis. Here, we report that mitochondrial ATP is necessary for the generation and export of AA, steroid production and steroidogenic acute regulatory protein induction supported by cyclic 3′–5′-adenosine monophosphate in steroidogenic cells. These results demonstrate that ATP depletion affects AA export and provide new evidence of the existence of the fatty acid generation and export system involved in mitochondrial cholesterol transport.

Abstract The initial steps of heat stress in A431 cells were previously characterized by ligand-independent EGFR transactivation via an unknown mechanism and concomitant secretion of Hsp70. In this work we demonstrate that the depletion of Hsp70 from the conditioned medium of heated cells abolishes EGFR transactivation indicating that secreted Hsp70 is essential for EGFR transactivation during heat shock. This notion is supported by the findings that purified Hsp70 can induce EGFR transactivation and the activation of EGFR-dependent signaling pathways. Both heat stress and pure Hsp70 stimulate activation of TLR2/4 and their association with EGFR. These results suggest that the secreted Hsp70 mediates the cross-communication of TLR and EGFR signaling systems in A431 cells.

Abstract A large (65%) fraction of in vitro cultured rat chromaffin cells exhibit spontaneous [Ca2+]i oscillations, and the rest can be recruited to oscillate by appropriate stimulations. Based on fura-2 single cell [ca2+]i measurements, evidence is provided that these oscillation originate, via the activation of Ca2+-induced Ca2+-release, from intracellular Ca2+ stores in rapid equilibrium with extracellular Ca2+. By combining [Ca2+]i measurements with a specific plaque secretion assay we demonstrate that oscillating cells exhibit a spontaneous exocytic secretory activity whereas the cells with stable [Ca2+]i do not, [Ca2+]i oscillations appear therefore to account for the high unstimulated catecholamine release, an activity typical of the chromaffin cells of the rat.

Abstract We have recently established that the blood concentrations of gallic acid (GA), a polyphenolic component naturally found in food, and its O-methyl derivatives are very low (practically ⩽1 μM) in physiological (postprandial) condition. Using acellular oxidant systems and macrophage-differentiated promonocytes (MDPs) THP-1, we show here that the direct and indirect (through depressing effect on the superoxide cell production) antioxidant properties of these components were not effective at these concentrations. In contrast, 4-O-methyl GA was the most efficient component to depress AT1R and CD36 mRNA expression in Ang II-treated MDPs, suggesting a strong inhibition of Ang II-triggered pro-atherogenic mechanisms of foam cell formation.