Biochemical characterization of casein kinase II as a protein kinase responsible for stimulation of HIV-1 protease in vitro

Where all the Roads Meet? A Crossover Perspective on Host Factors Regulating SARS-CoV-2 infection

COVID-19 caused by SARS-CoV-2 is the latest pandemic which has thrown the world into an unprecedented social and economic uncertainties along with huge loss to humanity. Identification of the host factors regulating the replication of SARS-CoV-2 in human host may help in the development of novel anti-viral therapies to combat the viral infection and spread. Recently, some research groups used genome-wide CRISPR/Cas screening to identify the host factors critical for the SARS-CoV-2 replication and infection. A comparative analysis of these significant host factors (p < 0.05) identified fifteen proteins common in these studies. Apart from ACE2 (receptor for SARS-CoV-2 attachment), other common host factors were CSNK2B, GDI2, SLC35B2, DDX51, VPS26A, ARPP-19, C1QTNF7, ALG6, LIMA1, COG3, COG8, BCOR, LRRN2 and TLR9. Additionally, viral interactome of these host factors revealed that many of them were associated with several SARS-CoV-2 proteins as well. Interestingly, some of these host factors have already been shown to be critical for the pathogenesis of other viruses suggesting their crucial role in virus-host interactions. Here, we review the functions of these host factors and their role in other diseases with special emphasis on viral diseases.

Flavone inspired discovery of benzylidenebenzofuran-3(2H)-ones (aurones) as potent inhibitors of human protein kinase CK2

In this work, we describe the design, synthesis and SAR studies of 2-benzylidenebenzofuran-3-ones (aurones), a new family of potent inhibitors of CK2. A series of aurones have been synthesized. These compounds are structurally related to the synthetic flavones and showed nanomolar activities towards CK2. Biochemical tests revealed that 20 newly synthesized compounds inhibited CK2 with IC₅₀ values in the nanomolar range. Further property-based optimization of aurones was performed, yielding a series of CK2 inhibitors with enhanced lipophilic efficiency. The most potent compound 12m (BFO13) has CLipE = 4.94 (CLogP = 3.5; IC₅₀ = 3.6 nM) commensurable with the best known inhibitors of CK2.

Epigenetics, N-myrystoyltransferase-1 and casein kinase-2-alpha modulates the increased replication of HIV-1 CRF02_AG, compared to subtype-B viruses

HIV subtypes distribution varies by geographic regions; this is likely associated with differences in viral fitness but the predictors and underlying mechanisms are unknown. Using in-vitro, in-vivo, and ex-vivo approaches, we found significantly higher transactivation and replication of HIV-1-CRF02_AG (prevalent throughout West-Central Africa), compared to subtype-B. While CRF02_AG-infected animals showed higher viremia, subtype-B-infected animals showed significantly more weight loss, lower CD4+ T-cells and lower CD4/CD8 ratios, suggesting that factors other than viremia contribute to immunosuppression and wasting syndrome in HIV/AIDS. Compared to HIV-1-subtype-B and its Tat proteins(Tat.B), HIV-1-CRF02_AG and Tat.AG significantly increased histone acetyl-transferase activity and promoter histones H3 and H4 acetylation. Silencing N-myrystoyltransferase(NMT)-1 and casein-kinase-(CK)-II-alpha prevented Tat.AG- and HIV-1-CRF02_AG-mediated viral transactivation and replication, but not Tat.B- or HIV-1-subtype-B-mediated effects. Tat.AG and HIV-1-CRF02_AG induced the expression of NMT-1 and CKII-alpha in human monocytes and macrophages, but Tat.B and HIV-1-subtype-B had no effect. These data demonstrate that NMT1, CKII-alpha, histone acetylation and histone acetyl-transferase modulate the increased replication of HIV-1-CRF02_AG. These novel findings demonstrate that HIV genotype influence viral replication and provide insights into the molecular mechanisms of differential HIV-1 replication. These studies underline the importance of considering the influence of viral genotypes in HIV/AIDS epidemiology, replication, and eradication strategies.

Herbal Gel Formulation Developed for Anti-Human Immunodeficiency Virus (HIV)-1 Activity Also Inhibits In Vitro HSV-2 Infection

Herpes simplex virus-2 (HSV-2) infection is the most common cause of genital ulcers. The impact of ulcers also demonstrates a strong link to the human immunodeficiency virus (HIV) infection. Complications, drug resistance, and side-effects of anti-viral drugs make the treatment of HSV-2 infection challenging. Herbal medicines have shown potential against HSV-2 and HIV infections. In this context, polyherbal gel formulation comprising 50% ethanolic extracts from Acacia catechu, Lagerstroemia speciosa, Terminalia chebula and Phyllanthus emblica has been developed. The gel formulation significantly exhibited virucidal activity against both HIV-1 and HSV-2 infections with IC₅₀, 55.93 ± 5.30 µg/mL and 27.26 ± 4.87 µg/mL, respectively. It also inhibited HSV-2 attachment and penetration to the Vero cells with an IC₅₀ = 46.55 ± 1.25 µg/mL and 54.94 ± 2.52 µg/mL respectively, which were significantly lower than acyclovir. However, acyclovir is more potent in post-infection assay with an IC₅₀ = 0.065 ± 0.01 µg/mL whereas gel formulation showed an IC₅₀ = 469.05 ± 16.65 µg/mL under similar conditions. Gel formulation showed no inhibitory effect on the viability of lactobacilli, human vaginal keratinocyte cells (Vk2/E6E7), and the integrity of the Caco-2 cells monolayer. Gel formulation did not lead to any significant increase in the secretion of pro-inflammatory cytokines and mutagenic index. The proposed gel formulation may be a promising candidate microbicide for the prevention of sexually transmitted HIV-1 and HSV-2.

Molecular and Genetic Characterization of HIV-1 Tat Exon-1 Gene from Cameroon Shows Conserved Tat HLA-Binding Epitopes: Functional Implications

HIV-1 Tat plays a critical role in viral transactivation. Subtype-B Tat has potential use as a therapeutic vaccine. However, viral genetic diversity and population genetics would significantly impact the efficacy of such a vaccine. Over 70% of the 37-million HIV-infected individuals are in sub-Saharan Africa (SSA) and harbor non-subtype-B HIV-1. Using specimens from 100 HIV-infected Cameroonians, we analyzed the sequences of HIV-1 Tat exon-1, its functional domains, post-translational modifications (PTMs), and human leukocyte antigens (HLA)-binding epitopes. Molecular phylogeny revealed a high genetic diversity with nine subtypes, CRF22_01A1/CRF01_AE, and negative selection in all subtypes. Amino acid mutations in Tat functional domains included N24K (44%), N29K (58%), and N40K (30%) in CRF02_AG, and N24K in all G subtypes. Motifs and phosphorylation analyses showed conserved amidation, N-myristoylation, casein kinase-2 (CK2), serine and threonine phosphorylation sites. Analysis of HLA allelic frequencies showed that epitopes for HLAs A*0205, B*5301, Cw*0401, Cw*0602, and Cw*0702 were conserved in 58%-100% of samples, with B*5301 epitopes having binding affinity scores > 100 in all subtypes. This is the first report of N-myristoylation, amidation, and CK2 sites in Tat; these PTMs and mutations could affect Tat function. HLA epitopes identified could be useful for designing Tat-based vaccines for highly diverse HIV-1 populations, as in SSA.

HIV-1 Protease in the Fission Yeast Schizosaccharomyces pombe

BACKGROUND

HIV-1 protease (PR) is an essential viral enzyme. Its primary function is to proteolyze the viral Gag-Pol polyprotein for production of viral enzymes and structural proteins and for maturation of infectious viral particles. Increasing evidence suggests that PR cleaves host cellular proteins. However, the nature of PR-host cellular protein interactions is elusive. This study aimed to develop a fission yeast (Schizosaccharomyces pombe) model system and to examine the possible interaction of HIV-1 PR with cellular proteins and its potential impact on cell proliferation and viability.

RESULTS

A fission yeast strain RE294 was created that carried a single integrated copy of the PR gene in its chromosome. The PR gene was expressed using an inducible nmt1 promoter so that PR-specific effects could be measured. HIV-1 PR from this system cleaved the same indigenous viral p6/MA protein substrate as it does in natural HIV-1 infections. HIV-1 PR expression in fission yeast cells prevented cell proliferation and induced cellular oxidative stress and changes in mitochondrial morphology that led to cell death. Both these PR activities can be prevented by a PR-specific enzymatic inhibitor, indinavir, suggesting that PR-mediated proteolytic activities and cytotoxic effects resulted from enzymatic activities of HIV-1 PR. Through genome-wide screening, a serine/threonine kinase, Hhp2, was identified that suppresses HIV-1 PR-induced protease cleavage and cell death in fission yeast and in mammalian cells, where it prevented PR-induced apoptosis and cleavage of caspase-3 and caspase-8.

CONCLUSIONS

This is the first report to show that HIV-1 protease is functional as an enzyme in fission yeast, and that it behaves in a similar manner as it does in HIV-1 infection. HIV-1 PR-induced cell death in fission yeast could potentially be used as an endpoint for mechanistic studies, and this system could be used for developing a high-throughput system for drug screenings.

Subtype-specific patterns in HIV Type 1 reverse transcriptase and protease in Oyo State, Nigeria: implications for drug resistance and host response

As the use of antiretroviral therapy becomes more widespread across Africa, it is imperative to characterize baseline molecular variability and subtype-specific peculiarities of drug targets in non-subtype B HIV-1 infection. We sequenced and analyzed 35 reverse transcriptase (RT) and 43 protease (PR) sequences from 50 therapy-naive HIV-1-infected Nigerians. Phylogenetic analyses of RT revealed that the predominant viruses were CRF02_AG (57%), subtype G (26%), and CRF06_cpx (11%). Six of 35 (17%) individuals harbored primary mutations for RT inhibitors, including M41L, V118I, Y188H, P236L, and Y318F, and curiously three of the six were infected with CRF06_cpx. Therefore, CRF06_cpx drug-naive individuals had significantly more drug resistance mutations than the other subtypes (p = 0.011). By combining data on quasisynonymous codon bias with the influence of the differential genetic cost of mutations, we were able to predict some mutations, which are likely to predominate by subtype, under drug pressure. Some subtype-specific polymorphisms occurred within epitopes for HLA B7 and B35 in the RT, and HLA A2 and A*6802 in PR, at positions implicated in immune evasion. Balanced polymorphism was also observed at predicted serine-threonine phosphorylation sites in the RT of subtype G viruses. The subtype-specific codon usage and polymorphisms observed suggest the involvement of differential pathways for drug resistance and host-driven viral evolution in HIV-1 CRF02_AG, subtype G, and CRF06_cpx, compared to subtype B. Subtype-specific responses to HIV therapy may have significant consequences for efforts to provide effective therapy to the populations infected with these HIV-1 subtypes.

Protein kinase CK2 phosphorylates the Nef protein from a neurovirulent simian immunodeficiency virus

The Nef protein of Human Immunodeficiency Virus (HIV) and Simian Immunodeficiency Virus (SIV) is a pluripotent accessory protein that plays a critical role in disease progression. One analogous characteristic of Nef proteins from SIV and HIV is the ability to associate with cellular kinases. We have previously reported that the Nef protein from a macrophage-tropic neurovirulent SIV clone, SIV/17E-Fr, is associated with an unknown kinase activity that is distinct from the p21-associated kinase that interacts with SIVmac239 Nef. Using site-directed mutagenesis and kinase-specific inhibitors, we have identified this kinase as the ubiquitous serine/threonine kinase, protein kinase CK2.

Purification and biochemical characterization of a fibroblast growth factor-binding protein (FGF-BP) from the lactoferrin fraction of bovine milk

By means of gel filtration on a TSK-gel HPLC column in the presence of 8 M urea, a 37-kDa polypeptide (p37) was completely separated from lactoferrin (LF) in the heparin HII fraction of the partially purified LF fraction prepared from bovine milk. Purified p37 was identified as a fibroblast growth factor-binding protein (FGF-BP), since its N-terminal 14 amino acid residues (KKEGRNRRGSKASA) were 100% identical to the corresponding sequence of bovine FGF-BP. It was found, in vitro, that (i) p37 had a higher binding affinity with bFGF than bLF; (ii) p37 functioned as a phosphate acceptor for at least three protein kinases (PKA, CK1 and CK2); (iii) bLF stimulated about 3-fold the PKA-mediated phosphorylation of p37, but suppressed its phosphorylation by CK1; and (iv) galloyl pedunculagin was an effective inhibitor for the phosphorylation of p37 by PKA and CK1. Furthermore, the physiological correlation between p37 and bLF may be regulated through specific phosphorylation of p37 by PKA, since p37 fully phosphorylated by PKA did not bind to bLF in vitro. The sulfatide-induced conformational changes in p37 enabled the phosphorylation of p37 by CK1 and also reduced its ability to bind with bLF in vitro. From these results presented here, it is concluded that (i) p37 (FGF-BP) may be tightly associated with bLF in bovine milk; and (ii) the physiological correlation between p37 and bLF may be regulated by the PKA-mediated full phosphorylation of p37 or by the direct binding of sulfatide to p37 in vivo.

High phosphorylation of HBV core protein by two alpha-type CK2-activated cAMP-dependent protein kinases in vitro

Two alpha-type CK2-activated PKAs (CK2-aPKAIalpha and CK2-aPKAIIalpha) were biochemically characterized in vitro using GST-HBV core fusion protein (GST-Hcore) and GST-Hcore157B as phosphate acceptors. It was found that (i), in the absence of cAMP, these two CK2-aPKAs phosphorylated both Ser-170 and Ser-178 on GST-Hcore and Hcore157B; (ii) this phosphorylation was approx. 4-fold higher than their phosphorylation by cAMP-activated PKAs; and (iii) suramin effectively inhibited the phosphorylation of Hcore157B by CK2-aPKAIIalpha through its direct binding to Hcore157B in vitro. These results suggest that high phosphorylation of HBV-CP by two CK2-aPKAs, in the absence of cAMP, may be involved in the pregenomic RNA (pgRNA) encapsidation and DNA-replication in HBV-infected cells.

Inhibitory effects of epigallocatechin gallate on the propagation of bovine coronavirus in Madin-Darby bovine kidney cells

Epigallocatechin gallate (EGCg) is the main active component of tea polyphenol and shows several biological activities, such as antimicrobial, antitumor‐promoting, anti‐inflammatory and anti‐oxidative activities. In the present study, the inhibitory effect of EGCg on bovine coronavirus (BCV) propagation in Madin‐Darby bovine kidney (MDBK) cells was investigated. EGCg at concentrations of less than 10 µg/mL did not show any cytotoxicity to MDBK cells. BCV propagation was significantly inhibited by pretreatment of the virus with EGCg (0.5–10 µg/mL) before virus inoculation in dose‐dependent, incubation time‐dependent and temperature‐dependent manners. The antiviral effect of pretreating MDBK cells with EGCg on BCV propagation was much weaker than that of pretreating BCV with EGCg. The hemagglutination activity of BCV was also reduced by EGCg in a dose‐dependent manner. These results demonstrate that EGCg possesses a distinct anti‐BCV activity and strongly suggest that EGCg interferes with the adsorption of BCV to MDBK cells by the interaction of EGCg with BCV particles. EGCg may therefore be a useful candidate for controlling BCV infection more effectively.

Biochemical characterization of an effective substrate and potent activators of CK2 copurified with Bowman-Birk-type proteinase inhibitor from soybean seeds in vitro

By means of Mono P column chromatography, an effective phosphate acceptor (EPA) of casein kinase 2 (CK2) was purified from the Bowman-Birk-type proteinase inhibitor (BBI) fraction of soybean seeds. The most acidic EPA (aEPA, pI=approx. 3.7) was heavily phosphorylated when incubated with CK2 and 5 microM [gamma-(32)P]ATP in the presence of poly-Arg (a CK2 activator) in vitro. However, aEPA was slightly phosphorylated by casein kinase 1 (CK1) as effective as C-kinase and not at all by A-kinase in vitro. The 13 N-terminal amino acid residues (SDHSSSDDESSKP) of aEPA were 100% homologous to the corresponding sequence of soybean BBI-type proteinase inhibitor CII (SBI CII). Polyamine at 3 mM stimulated 4.6-fold the CK2-mediated phosphorylation of aEPA, and this phosphorylation was sensitive to quercetin (ID(50)=approx. 0.1 microM) in vitro. Furthermore, two basic proteins [Mr=29,000 (p29) and 17,000 (p17)] copurified with BBI were identified as proteolytic cleavage products of basic 7S globulin and functioned as potent CK2 activators in vitro. aEPA fully phosphorylated by CK2 in the presence of poly-Arg or basic proteins formed a complex with trypsin, whereas unphosphorylated aEPA was digested by trypsin in vitro. These results suggest that (i) aEPA (a BBI isoform) may coexist with two basic proteins (p29 and p17) generated from basic 7S globulin; and (ii) the physiological interaction between aEPA and its binding trypsin-like proteinases may be regulated through specific phosphorylation of aEPA by CK2 activated with the two basic proteins in legume seeds.

Casein kinase 2 (CK2)-mediated reduction of the activities of Src family tyrosine kinases in vitro

The physiological correlation between casein kinase 2 (CK2) and two Src family tyrosine kinases (Src-TKs, Fyn and Src) was mainly investigated in vitro. It was found that (i) Thr-residues of these two Src-TKs were preferentially phosphorylated by CK2 using [gamma-32P]GTP as a phosphate donor; (ii) this phosphorylation was highly stimulated in the presence of poly-Arg; (iii) full phosphorylation of two Src-TKs by CK2 resulted in significant reduction of their TK activities; and (iv) quercetin (a CK2 inhibitor) inhibited the CK2-mediated reduction of their Src-TK activities in vitro. Under the same experimental conditions, similar results were obtained with Yes. These results suggest that CK2 may be a protein kinase responsible for the suppression of at least three Src-TKs (Fyn, Src and Yes) through the specific phosphorylation of their Thr-residues at the cellular level.

Theaflavin derivatives in black tea and catechin derivatives in green tea inhibit HIV-1 entry by targeting gp41

Theaflavin derivatives and catechin derivatives are the major polyphenols in black tea and green tea, respectively. Several tea polyphenols, especially those with galloyl moiety, can inhibit HIV-1 replication with multiple mechanisms of action. Here we showed that the theaflavin derivatives had more potent anti-HIV-1 activity than catechin derivatives. These tea polyphenols could inhibit HIV-1 entry into target cells by blocking HIV-1 envelope glycoprotein-mediated membrane fusion. The fusion inhibitory activity of the tea polyphenols was correlated with their ability to block the formation of the gp41 six-helix bundle, a fusion-active core conformation. Computer-aided molecular docking analyses indicate that these tea polyphenols, theaflavin-3,3'-digallate (TF3) as an example, may bind to the highly conserved hydrophobic pocket on the surface of the central trimeric coiled coil formed by the N-terminal heptad repeats of gp41. These results indicate that tea, especially black tea, may be used as a source of anti-HIV agents and theaflavin derivatives may be applied as lead compounds for developing HIV-1 entry inhibitors targeting gp41.

Plant substances as anti-HIV agents selected according to their putative mechanism of action

Despite the continuous advances made in antiretroviral combination therapy, AIDS has become the leading cause of death in Africa and the fourth worldwide. Today, many research groups are exploring the biodiversity of the plant kingdom to find new and better anti-HIV drugs with novel mechanisms of action. In this review, plant substances showing a promising anti-HIV activity are discussed according to the viral targets with which they interact. Most of these compounds, however, interfere with early steps in the HIV replication, such as the virus entry steps and the viral enzymes reverse transcriptase and integrase, whereas until now almost no plant compounds have been found to interact with the many other viral targets. Since some plant substances are known to modulate several cellular factors, such as NF-kappa B and TNF-alpha, which are also involved in the replication of HIV, their role as potential anti-HIV products is also discussed. In conclusion, several plant-derived antiviral agents are good candidates to be further studied for their potential in the systemic therapy and/or prophylaxis of HIV infections, most probably in combination with other anti-HIV drugs.

A novel CK2-mediated activation of type II cAMP-dependent protein kinase through specific phosphorylation of its regulatory subunit (RIIα) in vitro

The physiological significance of the casein kinase 2 (CK2)-mediated phosphorylation of type II cAMP-dependent protein kinase (PKAIIalpha) and free type II regulatory (R) subunit (RIIalpha) on their activities was mainly investigated in vitro. In these experiments, [gamma-32P]GTP was used as a phosphate donor for the CK2-mediated phosphorylation of free RIIalpha and PKAIIalpha (bovine heart) in vitro. It was found that: (i). CK2 phosphorylated only threonine (Thr)-residues of free RIIalpha and phosphorylated preferentially Thr-residues of the R subunit (RIIalpha) of PKAIIalpha (PKA RIIalpha) in vitro; (ii). this phosphorylation was selectively inhibited by quercetin (an CK2 inhibitor); and (iii). the phosphorylation of free RIIalpha by CK2 resulted in the reduction of its suppressive effect on the activity (phosphorylation of histone H2B) of the catalytic (C) subunit and in the reduction of its ability to form a complex with the C subunit in vitro. As expected, the activity of PKAIIalpha was approx. 3.5-fold enhanced after its R subunit was fully phosphorylated by CK2 in vitro. cAMP synergistically stimulated the activity of PKAIIalpha phosphorylated by CK2 in vitro. These results strongly suggest that CK2 may be a protein kinase responsible for the activation of PKAIIalpha through specific phosphorylation of its R subunit at the cellular level.

Was it there all the time?

The complement system is old, yet it may still have something new to teach us. For many years, research has existed which shows that C3d, in addition to its established role as an adjuvant, could have an immunosuppressive activity. Being true, it suggests that a common mechanism may be used both by organisms and by their pathogens to prevent unwanted immune responses.

Inhibition of adenovirus infection and adenain by green tea catechins

Green tea catechins have been reported to inhibit proteases involved in cancer metastasis and infection by influenza virus and HIV. To date there are no effective anti-adenoviral therapies. Consequently, we studied the effect of green tea catechins, and particularly the predominant component, epigallocatechin-3-gallate (EGCG), on adenovirus infection and the viral protease adenain, in cell culture. Adding EGCG (100 microM) to the medium of infected cells reduced virus yield by two orders of magnitude, giving and IC(50) of 25 microM and a therapeutic index of 22 in Hep2 cells. The agent was the most effective when added to the cells during the transition from the early to the late phase of viral infection suggesting that EGCG inhibits one or more late steps in virus infection. One of these steps appears to be virus assembly because the titer of infectious virus and the production of physical particles was much more affected than the synthesis of virus proteins. Another step might be the maturation cleavages carried out by adenain. Of the four catechins tested on adenain, EGCG was the most inhibitory with an IC(50) of 109 microM, compared with an IC(50) of 714 microM for PCMB, a standard cysteine protease inhibitor. EGCG and different green teas inactivated purified adenovirions with IC(50) of 250 and 245-3095, respectively. We conclude that the anti-adenoviral activity of EGCG manifests itself through several mechanisms, both outside and inside the cell, but at effective drug concentrations well above that reported in the serum of green tea drinkers.

Further characterization of galloyl pedunculagin as an effective autophosphorylation inhibitor of C-kinase in vitro

The inhibitory effect of galloyl pedunculagin (GP) isolated from Platycarya strobilacea on the activity and autophosphorylation of Ca(2+)- and phospholipid-dependent protein kinase (C-kinase) was examined in vitro. It was found that (i). GP inhibited the activity (phosphorylation of complement C3 from guinea pig) of C-kinase alpha (rat brain) in a dose-dependent manner with an ID(50) of approx. 0.12 micro M (ii). GP at lower doses (ID(50)=approx. 6 nM) inhibited autophosphorylation of C-kinase alpha; and (iii). the GP-induced inhibition of autophosphorylation of C-kinase alpha and its enzyme activity was a manner non-competitive to ATP. Similar inhibitory effect of GP on autophosphorylation of recombinant human C-kinase eta (rhC-kinase eta) and its phosphorylating activity was observed. These results suggest that GP is an effective autophosphorylation inhibitor of these two C-kinase isoforms (alpha and eta) in vitro. In addition, the CD analysis suggests that the proline-containing six amino acid residues (PVLTPP) including a threonine residue (autophosphorylation site) at the C-terminal region (positions 635-640) of C-kinase alpha may be one of the GP-binding sites.

Mayaro virus infection cycle relies on casein kinase 2 activity

Replication of Mayaro virus in Vero cells induces dramatic cytopathic effects and cell death. In this study, we have evaluated the role of casein kinase 2 (CK2) during Mayaro virus infection cycle. We found that CK2 was activated during the initial stages of infection ( approximately 36% after 4h). This activation was further confirmed when the enzyme was partially purified from the cellular lysate either by Mono Q 5/5Hr column or heparin-agarose column. Using this later column, we found that the elution profile of CK2 activity from infected cells was different from that obtained for control cell enzyme, suggesting a structural modification of CK2 after infection. Treatment of infected cells with a cell-permeable inhibitor of CK2, dichloro-1-(beta-D-ribofuranosyl)benzimidazole (DRB), abolished the cytopathic effect in a dose-dependent manner. Together this set of data demonstrates for the first time that CK2 activity in host cells is required in Mayaro virus infection cycle.

Polyphenolic antioxidant (-)-epigallocatechin-3-gallate from green tea as a candidate anti-HIV agent

Epigallocatechin-3-gallate (EGCG), one of the components of green tea, has been suggested to have antiviral activity. To determine the effects of EGCG on HIV infection, peripheral blood lymphocytes were incubated with either LAI/IIIB or Bal HIV strains and increasing concentrations of EGCG. EGCG strongly inhibited the replication of both virus strains as determined by reverse transcriptase and p24 assays on the cell supernatants.

Rotavirus NSP5: mapping phosphorylation sites and kinase activation and viroplasm localization domains

Rotavirus NSP5 is a nonstructural protein that localizes in cytoplasmic viroplasms of infected cells. NSP5 interacts with NSP2 and undergoes a complex posttranslational hyperphosphorylation, generating species with reduced polyacrylamide gel electrophoresis mobility. This process has been suggested to be due in part to autophosphorylation. We developed an in vitro phosphorylation assay using as a substrate an in vitro-translated NSP5 deletion mutant that was phosphorylated by extracts from MA104 cells transfected with NSP5 mutants but not by extracts from mock-transfected cells. The phosphorylated products obtained showed shifts in mobility similar to what occurs in vivo. From these and other experiments we concluded that NSP5 activates a cellular kinase(s) for its own phosphorylation. Three NSP5 regions were found to be essential for kinase(s) activation. Glutathione S-transferase-NSP5 mutants were produced in Escherichia coli and used to determine phosphoacceptor sites. These were mapped to four serines (Ser(153), Ser(155), Ser(163), and Ser(165)) within an acidic region with homology to casein kinase II (CKII) phosphorylation sites. CKII was able to phosphorylate NSP5 in vitro. NSP5 and its mutants fused to enhanced green fluorescent protein were used in transfection experiments followed by virus infection and allowed the determination of the domains essential for viroplasm localization in the context of virus infection.

Characterization of secretory type IIA phospholipase A2 (sPLA2-IIA) as a glycyrrhizin (GL)-binding protein and the GL-induced inhibition of the CK-II-mediated stimulation of sPLA2-IIA activity in vitro

By means of heparin-affinity and glycyrrhizin (GL)-affinity column chromatographies (HPLC), a GL-binding phospholipase A2 (gbPLA2) was selectively purified from the synovial fluids of patients with rheumatoid arthritis. This purified gbPLA2 was identified as a secretory type IIA PLA2 (sPLA2-IIA) since it was crossreacted with anti-sPLA2-IIA serum. The activity of purified sPLA2-IIA was inhibited by glycyrrhetinic acid (GA) and a GA derivative (oGA) in a dose-dependent manner, but it was more sensitive to GA than GL. Furthermore, it was found that (i) purified sPLA2-IIA is phosphorylated by casein kinase II (CK-II) in vitro; (ii) this phosphorylation induces in a significant stimulation of PLA2 activity; and (iii) oGA at one-tenth the concentration of GL inhibits the CK-II-mediated stimulation of sPLA2-IIA activity. These results show that (i) sPLA2-IIA is a GL-binding protein; and (ii) CK-II mediates stimulation of its PLA2 activity in vitro.

Inhibitory effect of glycyrrhizin on the phosphorylation and DNA-binding abilities of high mobility group proteins 1 and 2 in vitro

The physiological correlation between glycyrrhizin (GL) and high mobility group proteins I and 2 (HMG1/2) and the inhibitory effect of GL on their phosphorylation by three protein kinases (CK-I, CK-II and PKC) were investigated biochemically in vitro. It was found that GL binds directly to HMG1/2, because (i) HMG1/2 have a high affinity with a GL-affinity column; and (ii) GL induces the conformational changes in HMG1/2. Both purified HMG1/2 functioned as phosphate acceptors for these two protein kinases (CK-I and PKC), but not phosphorylated by CK-II. Phosphorylation of HMG1/2 by two protein kinases (CK-I and PKC) was completely inhibited by a glycyrrhetinic acid derivative (oGA) at one-tenth the concentration of GL. Also, the DNA-binding abilities of HNG1/2 were reduced by GL in a dose-dependent manner. These results show that the binding of GL to HMG1/2 results in the inhibition of their physiological activities (DNA-binding ability and phosphorylation by PKC or CK-I) in vitro. The GL-induced inhibition of the physiological activities of HMG1/2 may be involved in the anti-inflammatory effect of GL in vivo.