Regulation of HTLV-1 Gag budding by Vps4A, Vps4B, and AIP1/Alix

<p>Abstract</p> <p>Background</p> <p>HTLV-1 Gag protein is a matrix protein that contains the PTAP and PPPY sequences as L-domain motifs and which can be released from mammalian cells in the form of virus-like particles (VLPs). The cellular factors Tsg101 and Nedd4.1 interact with PTAP and PPPY, respectively, within the HTLV-1 Gag polyprotein. Tsg101 forms a complex with Vps28 and Vps37 (ESCRT-I complex) and plays an important role in the class E Vps pathway, which mediates protein sorting and invagination of vesicles into multivesicular bodies. Nedd4.1 is an E3 ubiquitin ligase that binds to the PPPY motif through its WW motif, but its function is still unknown. In the present study, to investigate the mechanism of HTLV-1 budding in detail, we analyzed HTLV-1 budding using dominant negative (DN) forms of the class E proteins.</p> <p>Results</p> <p>Here, we report that DN forms of Vps4A, Vps4B, and AIP1 inhibit HTLV-1 budding.</p> <p>Conclusion</p> <p>These findings suggest that HTLV-1 budding utilizes the MVB pathway and that these class E proteins may be targets for prevention of mother-to-infant vertical transmission of the virus.</p

Guanine nucleotide-binding protein in sea urchin eggs serving as the specific substrate of islet-activating protein, pertussis toxin

AbstractA GTP-binding protein serving as the specific substrate of islet-activating protein (IAP), pertussis toxin, was partially purified from Lubrol extract of sea urchin egg membranes. The partially purified protein possessed two polypeptides of 39 and 37 kDa; the 39 kDa polypeptide was specifically ADP-ribosylated by IAP and the 37 kDa protein cross-reacted with the antibody prepared against purified βγ-subunits of αβγ-heterotrimeric IAP substrates from rat brain. Incubation of this sea urchin IAP substrate with a non-hydrolyzable GTP analogue resulted in a reduction of the apparent molecular mass on a column of gel filtration as had been the case with purified rat brain IAP substrates, suggesting that the sea urchin IAP substrate was also a heterooligomer dissociable into two polypeptides in the presence of GTP analogues. Thus, the 39 and 37 kDa polypeptides of the sea urchin IAP substrate correspond to the α- and β-subunits, respectively, of mammalian IAP substrates which are involved in the coupling between membrane receptor and effector systems

BAG-6 is essential for selective elimination of defective proteasomal substrates

The ubiquitin-like protein BAG-6 protects cells from newly synthesized misfolded proteins by tethering them to the proteasome

Activation by hydrodynamics-based injection

The intranuclear disposition of exogenous DNA is quite important for the therapeutic effects of the administered DNA. The expression efficiency from one copy of exogenous DNA delivered by hydrodynamics-based injection dramatically decreases over time, and this ‘silencing’ occurs without CpG methylation. In this study, naked luciferase-plasmid DNA was delivered into mouse liver by hydrodynamics-based injection, and modifications of the histones bound to the plasmid DNA were analyzed by a chromatin immunoprecipitation (ChIP) analysis. In addition, the effects of a second hydrodynamics-based injection on the expression from the plasmid DNA were examined. The ChIP analysis revealed that the modification status of histone H3 remained constant from 4 hr to 4 weeks. Surprisingly, the injection of saline without DNA enhanced the luciferase expression from the preexisting DNA administered 4 and 14 days previously. Our results suggest that histone modification plays no role in the silencing. Instead, our data suggest that the transgene expression is activated by the hydrodynamics-based injection manipulation, and that the return from the activated status causes the silencing

Identification and Herc5-mediated ISGylation of novel target proteins

ISG15, a protein containing two ubiquitin-like domains, is an interferon-stimulated gene product that functions in antiviral response and is conjugated to various cellular proteins (ISGylation) upon interferon stimulation. ISGylation occurs via a pathway similar to the pathway for ubiquitination that requires the sequential action of E1/E2/E3: the E1 (UBE1L), E2 (UbcH8), and E3 (Efp/Herc5) enzymes for ISGylation have been hitherto identified. In this study, we identified six novel candidate target proteins for ISGylation by a proteomic approach. Four candidate target proteins were demonstrated to be ISGylated in UBE1L- and UbcH8-dependent manners, and ISGylation of the respective target proteins was stimulated by Herc5. In addition, Herc5 was capable of binding with the respective target proteins. Thus, these results suggest that Herc5 functions as a general E3 ligase for protein ISGylation

Negative regulation of protein phosphatase 2Cβ by ISG15 conjugation

ISG15, an interferon-upregulated ubiquitin-like protein, is covalently conjugated to various cellular proteins (ISGylation). In this study, we found that protein phosphatase 2Cβ (PP2Cβ), which functions in the nuclear factor κB (NF-κB) pathway via dephosphorylation of TGF-β-activated kinase, was ISGylated, and analysis by NF-κB luciferase reporter assay revealed that PP2Cβ activity was suppressed by co-expression of ISG15, UBE1L, and UbcH8. We determined the ISGylation sites of PP2Cβ and constructed its ISGylation-resistant mutant. In contrast to the wild type, this mutant suppressed the NF-κB pathway even in the presence of ISG15, UBE1L, and UbcH8. Thus, we propose that ISGylation negatively regulates PP2Cβ activity.http://www.elsevier.com/wps/find/journaldescription.cws_home/506085/descriptio

Hemocyte Aggregation in the Solitary Ascidian Halocynthia roretzi: Plasma Factors, Magnesium Ion, and Met-Lys-Bradykinin Induce the Aggregation

Volume: 186Start Page: 247End Page: 25