A direct signaling role for phosphatidylinositol 4,5-bisphosphate (PIP2) in the visual excitation process of microvillar receptors

Author Posting. © American Society for Biochemistry and Molecular Biology, 2005. This article is posted here by permission of American Society for Biochemistry and Molecular Biology for personal use, not for redistribution. The definitive version was published in Journal of Biological Chemistry 280 (2005): 16784-16789, doi:10.1074/jbc.M414538200.In microvillar photoreceptors the pivotal role of phospholipase C in light transduction is undisputed, but previous attempts to account for the photoresponse solely in terms of downstream products of phosphatidylinositol 4,5-bisphosphate (PIP2) hydrolysis have proved wanting. In other systems PIP2 has been shown to possess signaling functions of its own, rather than simply serving as a precursor molecule. Because illumination of microvillar photoreceptors cells leads to PIP2 break-down, a potential role for this phospholipid in phototransduction would be to help maintain some element(s) of the transduction cascade in the inactive state. We tested the effect of intracellular dialysis of PIP2 on voltage-clamped molluscan photoreceptors and found a marked reduction in the amplitude of the photocurrent; by contrast, depolarization-activated calcium and potassium currents were unaffected, thus supporting the notion of a specific effect on light signaling. In the dark, PIP2 caused a gradual outward shift of the holding current; this change was due to a decrease in membrane conductance and may reflect the suppression of basal openings of the light-sensitive conductance. The consequences of depleting PIP2 were examined in patches of light-sensitive microvillar membrane screened for the exclusive presence of light-activated ion channels. After excision, superfusion with anti-PIP2 antibodies induced the appearance of single-channel currents. Replenishment of PIP2 by exogenous application reverted the effect. These data support the notion that PIP2, in addition to being the source of inositol trisphosphate and diacylglycerol, two messengers of visual excitation, may also participate in a direct fashion in the control of the light-sensitive conductanceThis work was supported by National Institutes of Health Grant EY07559

Oridonin induces apoptosis and senescence in colorectal cancer cells by increasing histone hyperacetylation and regulation of p16, p21, p27 and c-myc

<p>Abstract</p> <p>Background</p> <p>Oridonin, a tetracycline diterpenoid compound, has the potential antitumor activities. Here, we evaluate the antitumor activity and action mechanisms of oridonin in colorectal cancer.</p> <p>Methods</p> <p>Effects of oridonin on cell proliferation were determined by using a CCK-8 Kit. Cell cycle distribution was determined by flow cytometry. Apoptosis was examined by analyzing subdiploid population and terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling assay. Senescent cells were determined by senescence-associated β-galactosidase activity analysis. Semi-quantitative RT-PCR was used to examine the changes of mRNA of p16, p21, p27 and c-myc. The concomitant changes of protein expression were analyzed with Western blot. Expression of AcH3 and AcH4 were examined by immunofluorescence staining and Western blots. Effects of oridonin on colony formation of SW1116 were examined by Soft Agar assay. The in vivo efficacy of oridonin was detected using a xenograft colorectal cancer model in nude mice.</p> <p>Results</p> <p>Oridonin induced potent growth inhibition, cell cycle arrest, apoptosis, senescence and colony-forming inhibition in three colorectal cancer cell lines in a dose-dependent manner in vitro. Daily i.p. injection of oridonin (6.25, 12.5 or 25 mg/kg) for 28 days significantly inhibited the growth of SW1116 s.c. xenografts in BABL/C nude mice. With western blot and reverse transcription-PCR, we further showed that the antitumor activities of oridonin correlated with induction of histone (H3 and H4) hyperacetylation, activation of p21, p27 and p16, and suppression of c-myc expression.</p> <p>Conclusion</p> <p>Oridonin possesses potent in vitro and in vivo anti-colorectal cancer activities that correlated with induction of histone hyperacetylation and regulation of pathways critical for maintaining growth inhibition and cell cycle arrest. Therefore, oridonin may represent a novel therapeutic option in colorectal cancer treatment.</p

Evidence of accelerated ageing in clinical drug addiction from immune, hepatic and metabolic biomarkers

Background: Drug addiction is associated with significant disease and death, but its impact on the ageing process has not been considered. The recent demonstration that many of the items available in routine clinical pathology have applicability as biomarkers of the ageing process implies that routine clinical laboratory parameters would be useful as an initial investigation of this possibility. Methods: 12,093 clinical laboratory results 1995-2006 were reviewed. To make the age ranges of the medical and addicted groups comparable the age range was restricted to 15-45 years. Results: 739 drug addicted (DA) and 5834 general medical (GM) age matched blood samples were compared. Significant elevation of immune parameters was noted in the C-reactive protein, erythrocyte sedimentation rate, total lymphocyte count, serum globulins and the globulin:albumin ratio (P < 0.01). Alanine aminotranferase, creatinine, urea, and insulin like growth factor-1 were also significantly higher (P < 0.01) in the DA group. Albumin, body mass index and dihydroepiandrosterone sulphate were unchanged and cholesterol was lower (all P < 0.05). Conclusion: These data demonstrate for the first time that addiction is associated with an altered profile of common biomarkers of ageing raising the possibility that the ageing process may be altered in this group. Infective and immune processes may be centrally involved. They suggest that addiction forms an interesting model to further examine the contribution of immune suppression and hyperstimulation to the ageing process

Dysregulated Expression of Glycolipids in Tumor Cells: From Negative Modulator of Anti-tumor Immunity to Promising Targets for Developing Therapeutic Agents

Glycolipids are complex molecules consisting of a ceramide lipid moiety linked to a glycan chain of variable length and structure. Among these are found the gangliosides, which are sialylated glycolipids ubiquitously distributed on the outer layer of vertebrate plasma membranes. Changes in the expression of certain species of gangliosides have been described to occur during cell proliferation, differentiation and ontogenesis. However, the aberrant and elevated expression of gangliosides has been also observed in different types of cancer cells, thereby promoting tumor survival. Moreover, gangliosides are actively released from the membrane of tumor cells, having a strong impact on impairing anti-tumor immunity. Beyond the undesirable effects of gangliosides in cancer cells, a substantial number of cancer immunotherapies have been developed in recent years that have used gangliosides as the main target. This has resulted in successful immune cell- or antibody-responses against glycolipids, with promising results having been obtained in clinical trials. In this review, we provide a general overview on the metabolism of glycolipids, both in normal and tumor cells, as well as examining glycolipid-mediated immune modulation and the main successes achieved in immunotherapies using gangliosides as molecular targets

MRI of atherosclerosis and fatty liver disease in cholesterol fed rabbits

Abstract Background The globally rising obesity epidemic is associated with a broad spectrum of diseases including atherosclerosis and non-alcoholic fatty liver (NAFL) disease. In the past, research focused on the vasculature or liver, but chronic systemic effects and inter-organ communication may promote the development of NAFL. Here, we investigated the impact of confined vascular endothelial injury, which produces highly inflamed aortic plaques that are susceptible to rupture, on the progression of NAFL in cholesterol fed rabbits. Methods Aortic atherosclerotic inflammation (plaque Gd-enhancement), plaque size (vessel wall area), and composition, were measured with in vivo magnetic resonance imaging (MRI) in rabbits fed normal chow or a 1% cholesterol-enriched atherogenic diet. Liver fat was quantified with magnetic resonance spectroscopy (MRS) over 3 months. Blood biomarkers were monitored in the animals, with follow-up by histology. Results Cholesterol-fed rabbits with and without injury developed hypercholesterolemia, NAFL, and atherosclerotic plaques in the aorta. Compared with rabbits fed cholesterol diet alone, rabbits with injury and cholesterol diets exhibited larger, and more highly inflamed plaques by MRI (P < 0.05) and aggravated liver steatosis by MRS (P < 0.05). Moreover, after sacrifice, damaged (ballooning) hepatocytes and extensive liver fibrosis were observed by histology. Elevated plasma gamma-glutamyl transferase (GGT; P = 0.014) and the ratio of liver enzymes aspartate and alanine aminotransferases (AST/ALT; P = 0.033) indicated the progression of steatosis to non-alcoholic steatohepatitis (NASH). Conclusions Localized regions of highly inflamed aortic atherosclerotic plaques in cholesterol-fed rabbits may contribute to progression of fatty liver disease to NASH with fibrosis