HIV-1 Nef triggers Vav-mediated signaling pathway leading to functional and morphological differentiation of dendritic cells

Elucidating effects of long-term expression of HIV-1 Nef on astrocytes by microarray, promoter, and literature analyses

The challenge of microarray analysis is to unveil the biological mechanisms behind the chip data. Due to the sometimes counteracting influences of de novo transcription, RNA processing and degradation, the discovery of any particular mechanism is difficult. Therefore, a combination of data- and knowledge-driven analysis appears to be the best way to attack the problem. We analyzed human astrocytes stably expressing the HIV-1 nef gene by microarray analyses to elucidate the effects of constitutive HIV-1 Nef expression on the transcriptome of astrocytes. Statistical evaluation of microarray results revealed small clusters of genes specifically up-regulated by native Nef protein in contrast to astrocytes expressing a non-myristoylated Nef variant. At least three significantly overrepresented gene ontology groups (small GTPase signaling, regulation of apoptosis and lipid metabolism) were detected. The JAK/STAT pathway was clearly associated with those genes. This finding agreed well with a literature-based approach, where a network was derived by combined literature and promoter sequence analysis. Promoter organization suggested potentially coordinated transcriptional regulation of some of these genes. Both results were in line with previously reported phenotypic changes.

Human immunodeficiency virus (HIV)-1 proteins and cytoskeleton: partners in viral life and host cell death

Cytoskeletal components play a major role in the human immunodeficiency virus-1 (HIV-1) infection. A wide variety of molecules belonging to the microfilament system, including actin filaments and actin binding proteins, as well as microtubules have a key role in regulating both cell life and death. Cell shape maintenance, cell polarity and cell movements as well as cytoplasmic trafficking of molecules determining cell fate, including apoptosis, are in fact instructed by the cytoskeleton components. HIV infection and viral particle production seem to be controlled by cytoskeleton as well. Furthermore, HIV-associated apoptosis failure can also be regulated by the actin network function. In fact, HIV protein gp120 is able to induce cytoskeleton-driven polarization, thus sensitizing T cells to CD95/Fas-mediated apoptosis. The microfilament system seems thus to be a sort of cytoplasmic supervisor of the viral particle, the host cell and the bystander cell's very fate.

Chimeric human immunodeficiency virus type 1 virions that contain the simian immunodeficiency virus nef gene are cyclosporin A resistant

We have previously shown that human immunodeficiency virus type 1 (HIV-1) virions which have their own nef gene deleted and are trans complemented to contain HIV-2 or simian immunodeficiency virus (SIV) Nef become resistant to treatment with cyclosporin A. To expand and confirm these studies, we have tested an HIV-1 isolate in which the HIV-1 nef gene has been replaced by the nef gene from SIV in a multiround infectivity assay using more physiologically relevant cell types. Our results confirm that HIV-1 virions that contain SIV nef can replicate in a cyclophilin-independent fashion.

Role of cytokines and chemokines in the regulation of innate immunity and HIV infection

The earliest defense against microbial infection is represented by the responses of the innate (or natural) immune system, that also profoundly regulates the adaptive (or acquired) T- and B-cell immune responses. Activation of the innate immune system is primed by microbial invasion in response to conserved structures present in large groups of microorganisms (LPS, peptidoglycan, double-stranded RNA), and is finely tuned by different cell types (including dendritic cells, macrophages, natural killer cells, natural killer T cells, and gammadelta T cells). In addition, several soluble factors (complement components, defensins, mannose-binding lectins, interferons, cytokines and chemokines) can play a major role in the regulation of both the innate and adaptive immunity. In this review, we will briefly overview the regulation of some cellular subsets of the innate immune system particularly involved in human immunodeficiency virus (HIV) infection and then focus our attention on those cytokines and chemokines whose levels of expression are more profoundly affected by HIV infection and that, conversely, can modulate virus infection and replication.

HIV-1 and the hijacking of dendritic cells: a tug of war

Dendritic cells are critical for host immunity and are involved both in the innate and adaptive immune responses. They are among the first cells targeted by HIV-1 in vivo at mucosal sites. Dendritic cells can sequester HIV-1 in endosomal compartments for several days and transmit infectious HIV-1 to interacting T cells in the lymph node, which is the most important site for viral replication and spread. Initially, the cellular immune response developed against HIV-1 is strong, but eventually it fails to control and resolve the infection. The most dramatic effect seen on the immune system during untreated HIV-1 infection is the destruction of helper CD4(+) T cells, which leads to subsequent immune deficiency. However, the immunomodulatory effects of HIV-1 on different dendritic cell subpopulations may also play an important role in the pathogenesis of HIV-1. This review discusses the effects HIV-1 exerts on dendritic cells in vivo and in vitro, including the binding and uptake of HIV by dendritic cells, the formation of infectious synapses, infection, and the role of dendritic cells in HIV-1 pathogenesis.

HIV‐1 Nef equips dendritic cells to reduce survival and function of CD8 + T cells: a mechanism of immune evasion

The accessory HIV-1 Nef protein is a crucial determinant for viral replication and pathogenesis. During HIV infection, loss of immune control in the setting of a strong and broad HIV-specific T-lymphocyte response, leads to a lethal outcome through AIDS. Moreover, dysfunction of dendritic cells (DCs) may contribute to the immune suppression associated with AIDS progression. We recently demonstrated that exogenous Nef selectively activates immature DCs manipulating their phenotypical, morphological, and functional developmental program. Here, we tracked whether Nef, targeting DCs, could be involved in the dysregulation of CD8+ T cell responses. We found that Nef inhibits the capacity of DCs to prime alloreactive CD8+ T cell responses down-regulating their proliferation and functional competence. This coincides with the induction of CD8+ T cell apoptosis. Nef oversees apoptotic killing of CD8+ T cells up-regulating TNF-alpha and FasL production by DCs and interfering with the death receptor pathway in CD8+ T cells and thus activating caspase 8. Our findings suggest that Nef may contribute to the immune evasion associated with HIV-1 infection, subverting DC biology. This may help explain the pleiotropic function that Nef plays during infection and makes this protein an attractive target for preventive and therapeutic intervention.