Potential application of arginine in interaction analysis.

Aqueous solution of 0.1-2 M arginine at mildly acidic to neutral pH is widely used in biotechnology and protein research, including protein refolding, purification, and formulation. This is largely because of its ability to suppress non-specific protein-protein and protein-surface interactions. Here we propose potential applications of arginine in interaction analysis for proteins. One of the important goals of such analysis is discovery of small molecule antagonistic or agonistic ligands that bind to target proteins and thereby modulate their function. Such research is often hampered by the low solubility of the small molecules, the instability of target proteins and the non-specific protein-ligand interactions. Aqueous arginine solution increases the solubility of small molecules, which should give an alternative to conventional dissolution method of small molecules by organic solvents. Arginine may also directly impact on the analysis of protein-protein or protein-ligand interactions by suppressing weak non-specific interactions.

Acute adrenal infection by HSV-1: role of apoptosis in viral replication.

Replication of herpes simplex virus type 1 (HSV-1) in the adrenal gland of mice was observed 12 h after intravenous inoculation, peaked at 48 h (7 x 10(7) PFU/tissue), and was maintained until death. Virus spread to the bilateral intermediolateral column of the thoracic spinal cord. Infected cells appeared in the fascicular zone of the adrenal cortex 12 h after infection, and cell death was evident in lesions found in the adrenal cortex. Lesions involved the medulla 48 h after inoculation. In cortical lesions, cell nuclei were fragmented or shrunken with little damage to the cytoplasm. DNA fragmentation appeared 12 h after inoculation and increased mainly in cortical lesions, which were characterized by apoptosis induced by HSV-1 infection. In the adrenal medulla, cells were fused and formed multinucleated giant cells but rarely displayed cell death. Macrophages, which serve as a frontal barrier to viral infection in the adrenal gland, especially the cortex, were fewer in number than those found in the liver or spleen. It is likely that HSV-1 easily infects the adrenal gland, resulting in suppression of local immunity, and that adrenal cell apoptosis serves as a primitive type of immunity to limit viral replication.

Growth characteristics of SHIV without the vpu gene.

NM-3 is a prototype of chimeric virus between simian and human immunodeficiency viruses (SHIV). It grows in monkey lymphocytic cells in vitro and in vivo as well as in human cells. A mutant designated NM3-E65, which lacks expression of the entire vpu gene, was constructed from NM-3, and monitored for its replication property. Examination of growth properties in simian and human cells of SHIV, HIV, and their vpu mutants revealed that the vpu gene in the genome of the chimeric virus is functional, but non-essential for virus replication.

Lack of apoptosis in Sendai virus-infected HEp-2 cells without participation of viral antiapoptosis gene.

Sendai virus (SeV) has been reported to induce apoptosis in many types of cells. In HEp-2 cells, however, it did not induce apoptosis in most of the infected cells under the conditions in which vesicular stomatitis virus induced massive apoptosis. The use of a novel technique, which allows the detection of viral antiapoptotic activity in the infected cells, showed that SeV does not have any antiapoptotic activity to interfere with the induction of apoptosis. Consistently, vesicular stomatitis virus-induced apoptosis was not interfered with by preinfection with SeV. These results indicate that the observed lack of apoptosis in these SeV-infected cells does not result from the suppression of apoptosis by viral antiapoptotic activity in the infected cells and suggest that, without activating a signaling pathway for the induction of apoptotic response in the infected cells, SeV can escape apoptosis of the cells, allowing long-term survival of the infected cells.

Cyclophilin A-independent replication of a human immunodeficiency virus type 1 isolate carrying a small portion of the simian immunodeficiency virus SIV(MAC) gag capsid region.

Hybrid viruses between human immunodeficiency virus type 1 (HIV-1) and simian immunodeficiency virus strain mac (SIV(MAC)) are invaluable to various fields of HIV-1 research. To date, however, no replication-competent HIV-1 strain containing the gag capsid (CA) region of SIV(MAC) has been reported. To obtain the viable gag gene chimeric virus in an HIV-1 background, seven HIV-1 strains carrying a part of SIV(MAC) CA or a small deletion in the CA region were constructed and examined for their biological and biochemical characteristics. While all the recombinants and mutants were found to express Gag and to produce progeny virions on transfection, only one chimeric virus, which has 18 bp of SIV gag CA sequence in place of the region encoding the HIV-1 CA cyclophilin A (CyPA)-binding loop, was infectious for human cell lines. Although this chimeric virus was unable to grow in monkey lymphocytic cells like wild-type (wt) HIV-1 did, it grew much better than wt virus in the presence of cyclosporin A in a human cell line which supports HIV-1 replication in a CyPA-dependent manner. These results indicate that the transfer of a small portion of the SIV(MAC) CA region to HIV-1 could confer the CyPA-independent replication potential of SIV(MAC) on the virus.

Regulation of cell cycle and apoptosis by human immunodeficiency virus type 1 Vpr.

Biological effects of HIV-1 Vpr on CD4(+) cells were studied by an infection system. High-titered HIV-1 stocks pseudotyped with vesicular stomatitis virus G protein were prepared and used to inoculate into CD4(+ )T cells at high multiplicity of infection. Both cell- and virion-associated Vpr were demonstrated to arrest the cell cycle at the G2/M phase, and to induce cell apoptosis. Of note, morphologically apoptotic cells were shown to be arrested at the G2/M stage. No appreciable effect of Vpr on the anti-Fas antibody-mediated apoptosis was observed in this system.

Physiological significance of apoptosis in animal virus infection.

In contrast to insect viruses, animal viruses can produce considerable amounts of progeny virus in cells undergoing apoptosis. Nevertheless, viruses in general have acquired the ability to escape apoptosis of infected cells. These facts indicate that the role of apoptosis in virus infection is different in insect virus and animal virus, although both viruses need to avoid apoptosis of the infected cells for a viral life cycle in nature. In animal virus infection, the primary role of apoptosis is considered not to be a premature lysis of the infected cells (and the following abortion of virus multiplication) but to allow the dying cells to be phagocytosed by macrophages. This phagocytosis is able to prevent dysregulated inflammatory reactions at the site of virus infection and to initiate a specific immune response against the infected virus.

Mutational analysis of HIV-1 gag proteins (review).

The mature Gag proteins of human immunodeficiency virus type 1 (HIV-1) are major components of infectious virions, and thought to carry out numerous functions throughout the HIV-1 replication cycle. We have recently generated numerous gag gene mutants of HIV-1 to genetically study the functions of the Gag proteins. Through the biological and biochemical analyses, our HIV-1 gag mutants have been grouped into early (defective for uncoating/reverse transcription), late (defective for virion release/maturation), and early/late (defective for both steps) mutants. Many mutants are found to efficiently inhibit the replication of wild-type virus. Worthy of note, there are some early mutants which show host cell-dependent replication potential.

Characterization of apoptosis induced by sorbitol: a unique system for the detection of antiapoptotic activities of viruses.

The treatment of HEp-2 cells with sorbitol induced massive apoptosis rapidly. This method for inducing apoptosis is very useful to detect antiapoptotic activity of viruses as well as viral genes. Commitment to death occurred immediately upon incubation with sorbitol, even in the presence of pancaspase inhibitor, Z-VAD-FMK. Apoptosis is also induced by other polyhydric alcohols with more than four hydroxyl groups, but not induced by glycerol or ethylene glycol. Sorbitol treatment on ice did not induce apoptosis either. These results suggest that this induction of apoptosis does not result simply from high osmotic pressure but probably by the interaction of solutes through their physical nature (such as hydrophobicity) with the plasma membrane of the cells.

Comparison of an antiviral activity of recombinant consensus interferon with recombinant interferon-alpha-2b.

To avoid possible uncertainty in comparing biological activities of interferon samples from different sources where interferon concentrations were determined independently, we prepared chromatographically pure preparations of consensus interferon and interferon-alpha-2b (one of the two commercially available recombinant alpha interferons). We revealed that consensus interferon has a stronger antiviral activity than interferon-alpha-2b, although the effects of these two recombinant interferons on the cellular macromolecule synthesis are at similar levels.

Antiapoptotic activity of herpes simplex virus type 2: the role of US3 protein kinase gene.

In order to determine the ability of herpes simplex virus type 2 (HSV-2) to suppress apoptosis, we examined the effect of HSV-2 infection on apoptosis induced in HEp-2 cells by treatment with 1 M sorbitol. Although a wild-type strain of HSV-2 induced apoptosis in a significant fraction of the infected cells, HSV-2 could suppress sorbitol-induced apoptosis in a manner similar to that of herpes simplex virus type 1 (HSV-1), indicating that HSV-2, like HSV-1, has an antiapoptosis gene. Characterization of the cells infected with a US3-deletion mutant of HSV-2 revealed the necessity of a US3 gene in the antiapoptotic activity of this virus.

Cell-dependent replication potentials of HIV-1 gag mutants.

An infectious molecular clone of human immunodeficiency virus type 1 (HIV-1), designated pNLaiKH, which is tropic for both lymphocytic and monocytic cells, was constructed. To study the early function of HIV-1 Gag proteins in two types of cells, the mutations known to give host cell-dependent early defects were introduced into pNLaiKH, and the replication potentials and defective replication sites in the cells of the resultant mutants were monitored. All mutants grew in some lymphocytic cells, but not at all in monocytic cells. A nucleocapsid mutant was found to be defective at an early replication phase in all the cell lines to various extent, as expected. In contrast, a matrix mutant and a capsid mutant displayed a replication defect in a producer-cell-dependent manner. These results demonstrated that complex interactions of cell factors and Gag proteins are involved in an early process of HIV-1 replication.

Growth characteristics of T-cell tropic HIV-1 vpu gene mutants in human peripheral blood mononuclear cells.

A mutant designated NL-E65, which lacks the expression of entire vpu gene, was constructed from T-cell tropic wild-type (wt) human immunodeficiency virus type 1 (HIV-1) clone and monitored for its replication property in human cells, along with a mutant NL-Ss which expresses a C-terminal truncated Vpu. The mutant NL-Ss could grow in two cell lines and in all peripheral blood mononuclear cell (PBMC) preparations to some extent, with kinetics similar to those of wt virus. Likewise, the mutant NL-E65 exhibited a replication property typical to the vpu mutant in the two cell lines and in all PBMC cultures, growing at a low level. Along with the results previously reported, these data indicate that HIV-1 Vpu is dispensable for virus replication in any of the types of cells so far tested.

Compatibility of Vpu-like activity in the four groups of primate immunodeficiency viruses.

Env-minus mutants of the viruses of major four human and simian immunodeficiency viruses (HIVs and SIVs) were monitored for their progeny virion production upon transfection into the cells, which are dependent on the HIV-1 Vpu for efficient particle release. Of the env mutants of HIV-1 (one mutant), HIV-2/SIVmac (three mutants), SIVagm (one mutant), and SIVmnd (one mutant) examined, the mutant of SIVmnd generated a very low level of progeny virions similar to that by the HIV-1 Vpu-minus mutant. This effect of the mutation was not observed in the cells which are independent on the Vpu for virion release. The Env of SIVmnd efficiently enhanced virion release of heterologous viruses like the HIV-1 Vpu.

Influenza virus overcomes apoptosis by rapid multiplication.

The kinetics of apoptotic fragmentation of the chromosomal DNA was determined in the influenza virus-infected MDCK, HeLa and KB cells, respectively. Comparison of these kinetics with the kinetics of virus multiplication revealed that the multiplication of influenza virus was observed only when apoptosis was induced after the production of progeny virus in the infected cells. The extent of apoptotic response was reversely correlated with the permissiveness of the cells.

Rev-dependent expression of three species of HIV-1 mRNAs (review).

The expression of structural and accessory genes of human immunodeficiency virus type 1 (HIV-1) except for nef requires a viral regulatory protein Rev. Rev-dependency of the expression of structural (gag, pol and env), regulatory (tat and rev), and accessory genes (vif, vpr, vpu and nef) has been investigated by various systems, and it has been demonstrated that unspliced (encodes gag and pol) and singly-spliced (env-vpu, vif and vpr) viral mRNAs are differentially dependent on the function of Rev. In this review, the function of HIV-1 Rev in relation to these findings is discussed.

Activation of HIV-1 enhancer sequence by vaccinia virus.

To investigate whether vaccinia virus (VV) can augment gene expression of human immunodeficiency virus type 1 (HIV-1), co-transfection experiments were carried out in which recombinant plasmids containing various portions of the HIV-1 long terminal repeat (LTR) linked to the chloramphenicol acetyltransferase (CAT) gene were transfected into cultured cells. A high level of enhancement in CAT activity directed by the HIV-1 LTRs containing the enhancer sequence was observed in cells infected with VV, as in the cells infected with type 1 herpes simplex virus (HSV-1). The sequence responsible for this augmentation of CAT activity was different from that recognized by HIV-1 Tat. These data clearly demonstrated that VV transactivates HIV-1 LTR through a mechanism distinct from that of activation by HIV-1 Tat.

Exchangeability of accessory Vif and Vpu proteins between various HIV/SIVs (review).

Representative human and simian immunodeficiency viruses (HIV/SIVs) have been monitored for their Vif and Vpu activities in a wide variety of cells. In contrast to the prototype HIV-1, viruses of the other groups do not necessarily have these activities. Only HIV-2 and SIVmnd were clearly demonstrated to show the Vif and Vpu activities, respectively. The exchangeability of these accessory activities between viruses was then assessed to determine the relatedness of the viruses. Quite different from the results for Tat and Rev trans-activators, the activities are almost fully compatible between viruses. These results may facilitate the functional grouping of various HIV/SIVs.

Role of virus-induced apoptosis in a host defense mechanism against virus infection.

Many animal viruses are known to induce apoptosis in infected cells. This virus-induced apoptosis has been often described as a mechanism of host defense against virus infection, based on the finding that mutants of an insect virus with the ability to induce extensive apoptosis in some cells cannot grow in the same cells. In animal virus infection, we have shown that (1) viruses can somehow overcome this defense mechanism and that (2) virus multiplication in the apoptotic cells is not as completely suppressed as in the insect virus infection. These results suggest that, in the case of animal viruses, the virus-induced apoptosis does not play the same role in the host defense system as in insect cells. However, by examining the virus infection under the conditions comparable to the infection in vivo, we demonstrated the defensive role of apoptosis in animal virus infection.

The non-env tropism of HIV/SIV (Review).

The tropism of human and simian immunodeficiency viruses (HIV and SIV) determined by sequences other than env has been studied. The restriction of HIV-1 replication in monkey cells was demonstrated to be regulated by viral non-env sequence. Likewise, the gag-pol region of SIVagm (virus of the African green monkey) genome was found to be responsible for growth restriction in human cells of the virus. No viral DNA synthesis was detected in cells nonpermissive for the viruses. In addition, a number of HIV-1 gag gene mutants, which have an early defect in viral replication cycle and direct no viral DNA synthesis in some cells, exhibited a phenotype of host range mutant. Taken together, it can be concluded that the viral tropism associated with the uncoating/ reverse transcription process does exist in HIV/SIV replication. Furthermore, many of the accessory gene mutants of HIV/SIV exhibit host cell-dependent replication property. In this review, we summarize these examples of non-env tropism of HIV/SIV.