Testosterone inhibits tumor necrosis factor-alpha-induced vascular cell adhesion molecule-1 expression in human aortic endothelial cells

It was shown that an increase in the bacteriochlorophyll (BChl) c antenna size observed upon lowering growth light intensities led to enhancement of the hyperchromism of the BChl c Q(y) absorption band of the green photosynthetic bacterium Chloroflexus aurantiacus. With femtosecond difference absorption spectroscopy, it was shown that the amplitude of bleaching of the oligomeric BChl c Q(y) band (as compared to that for monomeric BChl a) increased with increasing BChl c content in chlorosomes. This BChl c bleaching amplitude was about doubled as the chlorosomal antenna size was about trebled. Both sets of findings clearly show that a unit BChl c aggregate in the chlorosomal antenna is variable in size and governed by the grow light intensity, thus ensuring the high efficiency of energy transfer within the BChl c antenna regardless of its size.     

Inhibition of insulin signaling in endothelial cells by protein kinase C-induced phosphorylation of p85 subunit of phosphatidylinositol 3-kinase (PI3K)

The regulation of endothelial function by insulin is consistently abnormal in insulin-resistant states and diabetes. Protein kinase C (PKC) activation has been reported to inhibit insulin signaling selectively in endothelial cells via the insulin receptor substrate/PI3K/Akt pathway to reduce the activation of endothelial nitric-oxide synthase (eNOS). In this study, it was observed that PKC activation differentially inhibited insulin receptor substrate 1/2 (IRS1/2) signaling of insulin's activation of PI3K/eNOS by decreasing only tyrosine phosphorylation of IRS2. In addition, PKC activation, by general activator and specifically by angiotensin II, increased the phosphorylation of p85/PI3K, which decreases its association with IRS1 and activation. Thr-86 of p85/PI3K was identified to be phosphorylated by PKC activation and confirmed to affect IRS1-mediated activation of Akt/eNOS by insulin and VEGF using a deletion mutant of the Thr-86 region of p85/PI3K. Thus, PKC and angiotensin-induced phosphorylation of Thr-86 of p85/PI3K may partially inhibit the activation of PI3K/eNOS by multiple cytokines and contribute to endothelial dysfunction in metabolic disorders.     

EGF rapidly translocates tight junction proteins from the cytoplasm to the cell-cell contact via protein kinase C activation in TMK-1 gastric cancer cells

Tight junctions are commonly disrupted in cancer cells, including gastric cancer. Various growth factors have been reported to affect the localization of tight junction-associated proteins such as ZO-1 and occludin. We investigated the effect of epidermal growth factor (EGF), a growth factor that is often overexpressed in gastric cancer, and fetal bovine serum (FBS) on the localization of ZO-1 and occludin in a gastric cancer cell line. In the poorly differentiated gastric cancer cell line TMK-1, immunohistochemistry demonstrated that ZO-1 and occludin were predominantly localized to the cytoplasm, although there was some weak expression at the cell-cell contact. When the medium was replaced with fresh medium containing 10% FBS, ZO-1 and occludin were rapidly translocated from the cytosol to the cell-cell contact. A similar effect was seen in EGF exposure. These effects induced by FBS or EGF were attenuated in the presence of protein kinase C (PKC) inhibitors calphostin C and bisindolylmaleimide I, but not another PKC inhibitor G?6976, PD98059 (MAPK inhibitor), LY294002 (PI3 kinase inhibitor) or KT5720 (protein kinase A inhibitor). These results suggest that serum-derived factors, including EGF, can rapidly alter the localization of ZO-1 and occludin via a protein kinase C signaling pathway in TMK-1 gastric cancer cells.     

Fumonisin B1-induced apoptosis is associated with delayed inhibition of protein kinase C, nuclear factor-kappaB and tumor necrosis factor alpha in LLC-PK1 cells

Fumonisin B1 (FB1), the most potent of the fumonisin mycotoxins, is a carcinogen and causes a wide range of species-specific toxicoses. FB1 modulates the activity of protein kinase C (PKC), a family of phospholipid-dependent serine/threonine kinases that play important role in modulating a variety of biologic responses ranging from regulation of cell growth to cell death. Although it has been demonstrated that FB1 induces apoptosis in many cell lines, the precise mechanism of apoptosis is not fully understood. In this study, we investigated the membrane localization of various PKC isoforms, PKC enzyme activity, and its downstream targets, namely nuclear factor-kappa B (NF-kappaB), tumor necrosis factor alpha (TNFalpha), and caspase 3, in porcine renal epithelial (LLC-PK1) cells. FB1 repressed cytosol to membrane translocation of PKC-alpha, -delta, -epsilon, and -zeta isoforms over 24-72 h. The FB1-induced membrane PKC repression was corroborated by a concentration-dependent decrease in total PKC activity. Exposure of cells to phorbol 12-myristate 13-acetate (PMA) for this duration also resulted in repressed PKC membrane localization and activity comparable to FB1. Exposure of cells to FB1 (10 microM) was associated with inhibition of cytosol to nuclear translocation of NF-kappaB and NF-kappaB-DNA binding at 72 h. The expression of TNFalpha was significantly inhibited at 24 and 48 h in response to 1 and 10 microM FB1. Increased caspase 3 activity was observed in LLC-PK1 cells exposed to > or =1 microM FB1 at 48 h. PMA also increased the caspase 3 activity at 24 and 48 h. Results suggest that FB1-induced apoptosis involves the activation of caspase 3, which is associated with the repression of PKC and possibly its down-stream effectors, NF-kappaB and TNFalpha.     

Monocarboxylate transporter-1 is required for cell death in mouse chondrocytic ATDC5 cells exposed to interleukin-1beta via late phase activation of nuclear factor kappaB and expression of phagocyte-type NADPH oxidase

Interleukin-1β (IL-1β) induces cell death in chondrocytes in a nitric oxide (NO)- and reactive oxygen species (ROS)-dependent manner. In this study, increased production of lactate was observed in IL-1β-treated mouse chondrocytic ATDC5 cells prior to the onset of their death. IL-1β-induced cell death in ATDC5 cells was suppressed by introducing an siRNA for monocarboxylate transporter-1 (MCT-1), a lactate transporter distributed in plasma and mitochondrial inner membranes. Mct-1 knockdown also prevented IL-1β-induced expression of phagocyte-type NADPH oxidase (NOX-2), an enzyme specialized for production of ROS, whereas it did not have an effect on inducible NO synthase. Suppression of IL-1β-induced cell death by Nox-2 siRNA indicated that NOX-2 is involved in cell death. Phosphorylation and degradation of inhibitor of κBα (IκBα) from 5 to 20 min after the addition of IL-1β was not affected by Mct-1 siRNA. In addition, IκBα was slightly decreased after 12 h of incubation with IL-1β, and the decrease was prominent after 36 h, whereas activation of p65/RelA was observed from 12 to 48 h after exposure to IL-1β. These changes were not seen in Mct-1-silenced cells. Forced expression of IκBα super repressor as well as treatment with the IκB kinase inhibitor BAY 11-7082 suppressed NOX-2 expression. Furthermore, Mct-1 siRNA lowered the level of ROS generated after 15-h exposure to IL-1β, whereas a ROS scavenger, N-acetylcysteine, suppressed both late phase degradation of IκBα and Nox-2 expression. These results suggest that MCT-1 contributes to NOX-2 expression via late phase activation of NF-κB in a ROS-dependent manner in ATDC5 cells exposed to IL-1β.