Induction of APOBEC3 family proteins, a defensive maneuver underlying interferon-induced anti-HIV-1 activity.

Apolipoprotein B mRNA-editing enzyme-catalytic polypeptide-like 3G (APOBEC3G), a cytidine deaminase, is a recently recognized innate intracellular protein with lethal activity against human immunodeficiency virus (HIV). Packaged into progeny virions, APOBEC3G enzymatic activity leads to HIV DNA degradation. As a counterattack, HIV virion infectivity factor (Vif) targets APOBEC3G for proteasomal proteolysis to exclude it from budding virions. Based on the ability of APOBEC3G to antagonize HIV infection, considerable interest hinges on elucidating its mechanism(s) of regulation. In this study, we provide the first evidence that an innate, endogenous host defense factor has the potential to promote APOBEC3G and rebuke the virus-mediated attempt to control its cellular host. We identify interferon (IFN)-alpha as a potent inducer of APOBEC3G to override HIV Vif neutralization of APOBEC3 proteins that pose a threat to efficient macrophage HIV replication. Our data provide a new dimension by which IFN-alpha mediates its antiviral activity and suggest a means to render the host nonpermissive for viral replication.

Conversion of peripheral CD4+CD25- naive T cells to CD4+CD25+ regulatory T cells by TGF-beta induction of transcription factor Foxp3.

CD4+CD25+ regulatory T cells (Treg) are instrumental in the maintenance of immunological tolerance. One critical question is whether Treg can only be generated in the thymus or can differentiate from peripheral CD4+CD25- naive T cells. In this paper, we present novel evidence that conversion of naive peripheral CD4+CD25- T cells into anergic/suppressor cells that are CD25+, CD45RB-/low and intracellular CTLA-4+ can be achieved through costimulation with T cell receptors (TCRs) and transforming growth factor beta (TGF-beta). Although transcription factor Foxp3 has been shown recently to be associated with the development of Treg, the physiological inducers for Foxp3 gene expression remain a mystery. TGF-beta induced Foxp3 gene expression in TCR-challenged CD4+CD25- naive T cells, which mediated their transition toward a regulatory T cell phenotype with potent immunosuppressive potential. These converted anergic/suppressor cells are not only unresponsive to TCR stimulation and produce neither T helper cell 1 nor T helper cell 2 cytokines but they also express TGF-beta and inhibit normal T cell proliferation in vitro. More importantly, in an ovalbumin peptide TCR transgenic adoptive transfer model, TGF-beta-converted transgenic CD4+CD25+ suppressor cells proliferated in response to immunization and inhibited antigen-specific naive CD4+ T cell expansion in vivo. Finally, in a murine asthma model, coadministration of these TGF-beta-induced suppressor T cells prevented house dust mite-induced allergic pathogenesis in lungs.

Protein engineering of interferon alphas.

Interferon (IFN)-alphas constitute a family of proteins exhibiting high degree of homology in primary, secondary, and tertiary structure and display a high level of species specificity in their biological properties. However, small structural differences in these proteins may be responsible for a significant variety of biological actions. Understanding the structure and function of human IFN-alpha is very important. Recombinant techniques are important tools for the production and modification of IFN proteins. The first IFN hybrid, IFN-alpha1/alpha2 was constructed using recombinant technology in 1981. Subsequently, a number of IFN hybrids and mutants have been constructed, expressed and characterized. These hybrids and mutants have resulted in novel IFNs that either combine different biological properties from the parental proteins or have significantly different biological activity. Therefore, IFN hybrids and mutants have provided a powerful tool for studying the structure and function of these molecules. Also, these engineered IFNs may have important new therapeutic applications and may provide greater sights into understanding of the clinical activities of these molecules.

Myeloid differentiation and susceptibility to HIV-1 are linked to APOBEC3 expression.

HIV-1 recognition by, interaction with, and/or infection of CD4(+)CCR5(+) tissue macrophages and dendritic cells (DCs) play important roles in HIV-1 transmission and pathogenesis. By comparison, circulating CD4(+)CCR5(+) monocytes appear relatively resistant to HIV-1, and a fundamental unresolved question involves deciphering restriction factors unique to this precursor population. Not only do monocytes, relative to macrophages, possess higher levels of the innate resistance factor APOBEC3G, but we uncovered APOBEC3A, not previously associated with anti-HIV activity, as being critical in monocyte resistance. Inversely correlated with susceptibility, silencing of APOBEC3A renders monocytes vulnerable to HIV-1. Differences in promiscuity of monocytes, macrophages, and DCs can be defined, at least partly, by disparities in APOBEC expression, with implications for enhancing cellular defenses against HIV-1.

Gonadotropin-regulated testicular RNA helicase (GRTH/Ddx25) is essential for spermatid development and completion of spermatogenesis.

Gonadotropin-regulated testicular RNA helicase (GRTH/Ddx25), a member of the DEAD-box protein family, is a testis-specific gonadotropin-regulated RNA helicase that is present in Leydig cells and germ cells (meiotic spermatocytes and spermatids). In this study, we observed that GRTH is present in the nucleus, cytoplasm and chromatoid body of germ cells, and is an integral component of messenger ribonuclear protein particles. Male mice with a null mutation in the GRTH gene displayed normal gonadotropin and androgen profiles. However, they were sterile, with azoospermia caused by a complete arrest of spermiogenesis at step 8 of round spermatids and failure to elongate. Round spermatids of the null mice showed marked diminution in the size of chromatoid bodies. The transcription of relevant messages was not altered, but their translation was abrogated in a selective manner. Protein expression of transition proteins 1 and 2 and angiotensin-converting enzyme was completely absent, whereas that of the transcriptional activator cAMP responsive element modulator was intact. These findings indicate that GRTH participates in translational-associated events during germ cell development. Although significant apoptosis was present at the metaphase of meiosis in the GRTH-null mice, spermatogenesis proceeded to step 8 of spermiogenesis when complete arrest occurred. This progression may relate to compensatory gene function(s) and/or the observed up-regulation of DNA repair proteins Rad51 and Dmc1. This study (i) demonstrates that GRTH is essential for completion of spermatogenesis, (ii) provides insights into intrinsic requirements for spermiogenesis, and (iii) establishes a model for studies of male infertility and contraception.