BBA - Molecular Basis of Disease (v.1782, #3)

Viruses associated with human cancer by Margaret E. McLaughlin-Drubin; Karl Munger (127-150).
It is estimated that viral infections contribute to 15–20% of all human cancers. As obligatory intracellular parasites, viruses encode proteins that reprogram host cellular signaling pathways that control proliferation, differentiation, cell death, genomic integrity, and recognition by the immune system. These cellular processes are governed by complex and redundant regulatory networks and are surveyed by sentinel mechanisms that ensure that aberrant cells are removed from the proliferative pool. Given that the genome size of a virus is highly restricted to ensure packaging within an infectious structure, viruses must target cellular regulatory nodes with limited redundancy and need to inactivate surveillance mechanisms that would normally recognize and extinguish such abnormal cells. In many cases, key proteins in these same regulatory networks are subject to mutation in non-virally associated diseases and cancers. Oncogenic viruses have thus served as important experimental models to identify and molecularly investigate such cellular networks. These include the discovery of oncogenes and tumor suppressors, identification of regulatory networks that are critical for maintenance of genomic integrity, and processes that govern immune surveillance.
Keywords: Human T-cell leukemia virus (HTLV-1); Hepatitis C virus (HCV); Human papillomavirus (HPV); Hepatitis B virus (HBV); Epstein–Barr virus (EBV); Kaposi's sarcoma-associated herpesvirus (KSHV)/human herpes virus 8 (HHV8);

Therapeutic attenuation of mitochondrial dysfunction and oxidative stress in neurotoxin models of Parkinson's disease by Edward C. Stack; Joellyn L. Ferro; Jinho Kim; Steven J. Del Signore; Sarah Goodrich; Samantha Matson; Bonnie B. Hunt; Kerry Cormier; Karen Smith; Wayne R. Matson; Hoon Ryu; Robert J. Ferrante (151-162).
Parkinson's disease (PD) is a progressive neurodegenerative disorder for which there is no current therapy preventing cumulative neuronal loss. There is substantial evidence that mitochondrial dysfunction, oxidative stress, and associated caspase activity underlie the neurodegeneration observed. One potential drug therapy is the potent free radical scavenger and antioxidant cystamine, which has demonstrated significant clinical potential in models of neurodegenerative disorders and human neurological disease. This study examined the oral efficacy of cystamine in the MPTP and 6-hydroxydopamine neurotoxin models of PD. The neuroprotective effects of cystamine treatment significantly ameliorated nigral neuronal loss, preserved striatal dopaminergic projections, and improved striatal dopamine and metabolite levels, as compared to MPTP alone. Cystamine normalized striatal 8-hydroxy-2′-deoxyguanosine levels and ATP concentrations, consistent with reduced oxidative stress and improved mitochondrial function. Cystamine also protected against MPTP-induced mitochondrial loss, as identified by mitochondrial heat shock protein 70 and superoxide dismutase 2, with concomitant reductions in cytochrome c and caspase-3 activities. The neuroprotective value of cystamine was confirmed in the 6-hydroxydopamine model. Together these findings show cystamine's therapeutic benefit to reduce neuronal loss through attenuation of oxidative stress and mitochondrial dysfunction, providing the rationale for human clinical trials in PD patients.
Keywords: Cystamine; MPTP; 6-OHDA; Basal ganglia; ATP; Capsase-3; Dopamine;

Human β2-glycoprotein I (β2GPI) binds to recombinant hepatitis B surface antigen (rHBsAg), but the location of the binding domain on β2GPI is unknown. It has been suggested that the lipid rather than the protein moiety of rHBsAg binds to β2GPI. Since β2GPI binds to anionic phospholipids (PL) through its lipid-binding region in the fifth domain of β2GPI, we predicted that this lipid-binding region may also be involved in binding rHBsAg. In this study, we examined rHBsAg binding to two naturally occurring mutants of β2GPI, Cys306Gly and Trp316Ser, or evolutionarily conserved hydrophobic amino acid sequence, Leu313-Ala314-Phe315 in the fifth domain of β2GPI. The two naturally occurring mutations and two mutagenized amino acids, Leu313Gly or Phe315Ser, disrupted the binding of recombinant β2GPI (rβ2GPI) to both rHBsAg and cardiolipin (CL), an anionic PL. These results suggest that rHBsAg and CL share the same region in the fifth domain of β2GPI. Credence to this conclusion was further provided by competitive ELISA, where CL-bound rβ2GPI was incubated with increasing amounts of rHBsAg. As expected, pre-incubation of rβ2GPI with CL precluded binding to rHBsAg, indicating that CL and rHBsAg bind to the same region on β2GPI. Our data provide evidence that the lipid (PL) rather than the protein moiety of rHBsAg binds to β2GPI and that this binding region is located in the fifth domain of β2GPI, which also binds to anionic PL.
Keywords: Hepatitis B surface antigen; β2-Glycoprotein I; Apolipoprotein H; Anionic phospholipid;

Hsp27 decreases inclusion body formation from mutated GTP-cyclohydrolase I protein by Yu-Wei Chiou; Wuh-Liang Hwu; Yu-May Lee (169-179).
GTP cyclohydrolase I (GCH), an oligomeric protein composed of 10 identical subunits, is required for the synthesis of neurotransmitters; mutations in GCH are associated with dopa-responsive dystonia (DRD) and hyperphenylalaninemia. Mutated GCH proteins are unstable and prone to dominant-negative effect. We show herein that expression of the GCH mutant GCH-201E or the splicing variant GCH-II caused intracellular inclusion bodies. When Hsp27 was expressed together with the GCH mutants, Hsp27 expression decreased the formation of inclusion bodies by GCH (as assessed by immunofluorescence) and decreased the amount of insoluble GCH mutant proteins (as assessed by Western blot). Transfection of pcDNA-Hsp27-S3D, a phosphorylation-mimicry Hsp27 mutant, was more effective at the mutated GCH proteins than transfection with pcDNA-Hsp27, but okadaic acid, a phosphatase inhibitor, enhanced the effect of pcDNA-Hsp27. Hsp27-S3D also abolished the dominant-negative action of GCH-II. The mutated GCH proteins interacted with the wild-type GCH protein; the inclusion bodies were positive for lysosomal marker LAMP1, soluble in 2% SDS, and were not ubiquitinated. Phophorlyated Hsp27 also decreased the inclusion body formation by the huntingtin polyglutamines. Therefore, diseases involving mutated oligomeric proteins would be manageable by chaperone therapies.
Keywords: GTP-cyclohydrolase I; Dopa-responsive dystonia; Inclusion body formation; Chaperone; Heat shock protein 27; Phosphorylation;

Impairment of endothelial nitric oxide synthase causes abnormal fat and glycogen deposition in liver by Lorenz Schild; Frank Dombrowski; Uwe Lendeckel; Carla Schulz; Andreas Gardemann; Gerburg Keilhoff (180-187).
Nitric oxide (NO) affects fatty acid synthesis and biogenesis of fatty acid consuming mitochondria. However, whether NO generated by the endothelial NO synthase isoform (eNOS) has significant impact on the synthesis and deposition of fat in liver remained unclear. We analyzed the quantity and distribution of mitochondria and fat in liver of wild-type (WT) mice and mice lacking eNOS (eNOS-KO). The livers of eNOS-KO mice contained tenfold more fat close (zone 1) and twenty fold more distal (zone 3) to the artery. The fat was deposited as droplets co-localized with mitochondria. Additionally, the livers of eNOS-KO mice contained 1.5-fold more homogenously distributed glycogen. No difference in the quantity of mitochondria was found between liver homogenates of eNOS-KO mice and WT animals. Mitochondria from liver homogenates of eNOS-KO mice exhibited a higher ratio of citrate synthase (CS) and NADH–cytochrome c oxidoreductase (KI+III) activity. We conclude that lack of eNOS-derived NO stimulates citrate- and lipid synthesis in liver thus contributing to the development of overweight. In support of this view, more visceral fat and 70% higher body weight was determined in one year old eNOS-KO mice in comparison to WT animals.
Keywords: Nitric oxide; Endothelial nitric oxide synthase; Liver; Lipid;

Calcium-sensing receptor antagonism or lithium treatment ameliorates aminoglycoside-induced cell death in renal epithelial cells by Claire E. Gibbons; David Maldonado-Pérez; Amish N. Shah; Daniela Riccardi; Donald T. Ward (188-195).
The aminoglycoside antibiotic gentamicin elicits proximal tubular toxicity and cell death. In calcium-sensing receptor (CaR)-transfected HEK-293 (CaR-HEK) cells and CaR-expressing proximal tubule-derived opossum kidney (OK) cells, chronic gentamicin treatment elicits dose-dependent, caspase-mediated apoptotic cell death. Here we investigated whether the renal cell toxicity of the CaR agonist gentamicin could be prevented by CaR antagonism or by lithium cotreatment which may interfere with receptor-mediated signalling. Chronic treatment of OK and CaR-HEK cells with low concentrations of gentamicin elicited cell death, an effect that was ameliorated by cotreatment with the CaR negative allosteric modulator (calcilytic) NPS-89636. This calcilytic also attenuated CaR agonist-induced ERK activation in these cells. In addition, 1 mM LiCl, equivalent to its therapeutic plasma concentration, also inhibited gentamicin-induced toxicity in both cell types. This protective effect of lithium was not due to the disruption of phosphatidylinositol-mediated gentamicin uptake as the cellular entry of Texas red-conjugated gentamicin into OK and CaR-HEK cells was unchanged by lithium treatment. However, the protective effect of lithium was mimicked by glycogen synthase 3β inhibition. Together, these data implicate CaR activation and a lithium-inhibitable signalling pathway in the induction of cell death by gentamicin in renal epithelial cells in culture.
Keywords: Calcium-sensing receptor; Aminoglycoside nephrotoxicity; Lithium; Proximal tubule; Gentamicin;