The association between increasing levels of O-GlcNAc and galectins in the liver tissue of hibernating thirteen-lined ground squirrels (Ictidomys tridecemlineatus)
CELL AND TISSUE RESEARCH
Authors: Jariwala, Komal A.; Sherazi, Ali A.; Tazhitdinova, Rada; Shum, Kathryn; Guevorguian, Philipp; Karagiannis, Jim; Staples, James F.; Timoshenko, Alexander V.
Abstract
Post-translational glycosylation of proteins with O-linked beta-N-acetylglucosamine (O-GlcNAcylation) and changes of galectin expression profiles are essential in many cellular stress responses. We examine this regulation in the liver tissue of hibernating thirteen-lined ground squirrels (Ictidomys tridecemlineatus) representing a biological model of hypometabolism and physiological stress resistance. The tissue levels of O-GlcNAcylated proteins as well as galectin-1 and galectin-3 proteins detected by immunodot blot assay were significantly lower by 4.6-5.4-, 2.2-2.3- and 2.5-2.9-fold, respectively, in the non-hibernating summer squirrels compared with those in winter, whether hibernating or aroused. However, there were no differences in the expression of genes encoding enzymes involved in O-GlcNAc cycle (O-GlcNAc transferase and O-GlcNAcase) and such galectins as LGALS1, LGALS2, LGALS3, LGALS4 and LGALS9. Only the expression of LGALS8 gene in the liver tissue was significantly decreased by 37.6 +/- 0.1% in hibernating ground squirrels relative to summer animals. Considering that the expression of a proven genetic biomarker ELOVL6 encoding ELOVL fatty acid elongase 6 was readily upregulated in non-hibernating animals by 11.3-32.9-fold, marginal differential changes in the expression of galectin genes cannot be classified as biomarkers of hibernation. Thus, this study provides evidence that hibernation in Ictidomys tridecemlineatus is associated with increasing O-GlcNAcylation of liver proteins and suggests that the contribution of galectins deserves further studies at the protein level.
PLA2G16 represents a switch between entry and clearance of Picornaviridae
NATURE
Authors: Staring, Jacqueline; von Castelmur, Eleonore; Blomen, Vincent A.; van den Hengel, Lisa G.; Brockmann, Markus; Baggen, Jim; Thibaut, Hendrik Jan; Nieuwenhuis, Joppe; Janssen, Hans; van Kuppeveld, Frank J. M.; Perrakis, Anastassis; Carette, Jan E.; Brummelkamp, Thijn R.
Abstract
Picornaviruses are a leading cause of human and veterinary infections that result in various diseases, including polio and the common cold. As archetypical non-enveloped viruses, their biology has been extensively studied(1). Although a range of different cell-surface receptors are bound by different picornaviruses(2-7), it is unclear whether common host factors are needed for them to reach the cytoplasm. Using genome-wide haploid genetic screens, here we identify the lipid-modifying enzyme PLA2G16 (refs 8-11) as a picornavirus host factor that is required for a previously unknown event in the viral life cycle. We find that PLA2G16 functions early during infection, enabling virion-mediated genome delivery into the cytoplasm, but not in any virion-assigned step, such as cell binding, endosomal trafficking or pore formation. To resolve this paradox, we screened for suppressors of the Delta PLA2G16 phenotype and identified a mechanism previously implicated in the clearance of intracellular bacteria(12). The sensor of this mechanism, galectin-8 (encoded by LGALS8), detects permeated endosomes and marks them for autophagic degradation, whereas PLA2G16 facilitates viral genome translocation and prevents clearance. This study uncovers two competing processes triggered by virus entry: activation of a pore-activated clearance pathway and recruitment of a phospholipase to enable genome release.