Upregulation of the apoptosis-associated protein Grb3-3 in HIV-1-infected human CD4(+) lymphocytes

The Grb2 splice variant, Grb3-3, is a negative regulator of RAS activation

Activation of RAS is crucial in driving cellular outcomes including proliferation, differentiation, migration and apoptosis via the MAPK pathway. This is initiated on recruitment of Grb2, as part of a Grb2-Sos complex, to an up-regulated receptor tyrosine kinase (RTK), enabling subsequent interaction of Sos with the plasma membrane-localised RAS. Aberrant regulation at this convergence point for RTKs in MAPK signalling is a key driver of multiple cancers. Splicing of the GRB2 gene produces a deletion variant, Grb3-3, that is incapable of binding to RTKs. We show that, despite maintaining the ability to bind to Sos, the Grb3-3-Sos complex remains in the cytoplasm, unable to engage with RAS. Competition between Grb2 and Grb3-3 for binding to C-terminal proline-rich sequences on Sos modulates MAPK signalling. Additionally, we demonstrate that splicing is regulated by heterogenous nuclear riboproteins C1/C2, and that normal and malignant colon tissue show differential Grb3-3 expression.

First evidence of overlaps between HIV-Associated Dementia (HAD) and non-viral neurodegenerative diseases: proteomic analysis of the frontal cortex from HIV+ patients with and without dementia

Background

The pathogenesis of HIV-associated dementia (HAD) is poorly understood. To date, detailed proteomic fingerprinting directly from autopsied brain tissues of HAD and HIV non-dementia patients has not been performed.

Result

Here, we have analyzed total proteins from the frontal cortex of 9 HAD and 5 HIV non-dementia patients. Using 2-Dimensional differential in-gel electrophoresis (2-DIGE) to analyze the brain tissue proteome, 76 differentially expressed proteins (p < 0.05; fold change>1.25) were identified between HAD and HIV non-dementia patients, of which 36 protein spots (based on 3D appearance of spots on the images) were chosen for the mass spectrometry analysis. The large majority of identified proteins were represented in the energy metabolic (mitochondria) and signal transduction pathways. Furthermore, over 90% of the protein candidates are common to both HAD and other non-viral neurodegenerative disease, such as Alzheimer's disease. The data was further validated using specific antibodies to 4 proteins (CA2, GS, CKMT and CRMP2) by western blot (WB) in the same samples used for 2D-DIGE, with additional confirmation by immunohistochemitsry (IHC) using frontal lobe tissue from different HAD and HIV+ non-dementia patients. The validation for all 4 antibodies by WB and IHC was in concordance with the DIGE results, lending further credence to the current findings.

Conclusion

These results suggest not only convergent pathogenetic pathways for the two diseases but also the possibility of increased Alzheimer's disease (AD) susceptibility in HAD patients whose life expectancy has been significantly increased by highly active antiretroviral therapy.

Human Immunodeficiency virus type 1 Nef potently induces apoptosis in primary human brain microvascular endothelial cells via the activation of caspases

The lentiviral protein Nef plays a major role in the pathogenesis of human immunodeficiency virus type I (HIV-1) infection. Although the exact mechanisms of its actions are not fully understood, Nef has been shown to be essential for the maintenance of high-titer viral replication and disease pathogenesis in in vivo models of simian immunodeficiency virus infection of monkeys. Nef has also been suggested to play a pivotal role in the depletion of T cells by promoting apoptosis in bystander cells. In this context, we investigated the ability of extracellular and endogenously expressed HIV-1 Nef to induce apoptosis in primary human brain microvascular endothelial cells (MVECs). Human brain MVECs were exposed to baculovirus-expressed HIV-1 Nef protein, an HIV-1-based vector expressing Nef, spleen necrosis virus (SNV)-Nef virus (i.e., SNV vector expressing HIV-1 Nef as a transgene), and the HIV-1 strain ADA and its Nef deletion mutant, ADADeltaNef. We observed that ADA Nef, the HIV-1 vector expressing Nef, and SNV-Nef were able to induce apoptosis in a dose-dependent manner. The mutant virus with a deletion in Nef was able to induce apoptosis in MVECs to modest levels, but the effects were not as pronounced as with the wild-type HIV-1 strain, ADA, the HIV-1-based vector expressing Nef, or SNV-Nef viruses. We also demonstrated that relatively high concentrations of exogenous HIV-1 Nef protein were able to induce apoptosis in MVECs. Gene microarray analyses showed increases in the expression of several specific proapoptotic genes. Western blot analyses revealed that the various caspases involved with Nef-induced apoptosis are processed into cleavage products, which occur only during programmed cell death. The results of this study demonstrate that Nef likely contributes to the neuroinvasion and neuropathogenesis of HIV-1, through its effects on select cellular processes, including various apoptotic cascades.

T-cell and neuronal apoptosis in HIV infection: implications for therapeutic intervention

The pathogenesis of HIV infection involves the selective loss of CD4+ T cells contributing to immune deficiency. Although loss of T cells leading to immune dysfunction in HIV infection is mediated in part by viral infection, there is a much larger effect on noninfected T cells undergoing apoptosis in response to activation stimuli. In the subset of patients with HIV dementia complex, neuronal injury, loss, and apoptosis are observed. Viral proteins, gp120 and Tat, exhibit proapoptotic activities when applied to T cell and neuronal cultures by direct and indirect mechanisms. The pathways leading to cell death involve the activation of one or more death receptor pathways (i.e., TNF-alpha, Fas, and TRAIL receptors), chemokine receptor signaling, cytokine dysregulation, caspase activation, calcium mobilization, and loss of mitochondrial membrane potential. In this review, the mechanisms involved in T-cell and neuronal apoptosis, as well as antiapoptotic pathways potentially amenable to therapeutic application, are discussed.

Ethanol strongly potentiates apoptosis induced by HIV-1 proteins in primary human brain microvascular endothelial cells

Ethanol may have significant effects on human immunodeficiency virus type I (HIV-1) pathogenesis in vivo. As such, the effects of ethanol treatment were studied on the proapoptotic potential of various HIV-1 proteins in primary isolated human brain microvascular endothelial cells (MVECs), a major cellular component of the blood-brain barrier. Low-passage primary brain MVECs were treated with recombinant HIV-1 proteins Nef, Vpr, Tat and gp120 proteins from X4, R5, and X4R5 viral strains, with and without ethanol at various relevant concentrations. The apoptotic potential of each HIV-1 protein with and without ethanol was compared with cells treated with ethanol alone or GST protein as a control, under similar conditions. Specific HIV-1 proteins induced apoptosis in primary isolated human brain MVECs, which was potentiated on treatment with 0.1 and 0.3% (v/v) ethanol. Cotreatment with ethanol and specific HIV-1 proteins showed enhanced lactate dehydrogenase release, compared with MVECs treated with ethanol alone. The presence of ethanol in in vitro culture medium also enhanced HIV-1 protein-mediated tumor necrosis factor-alpha production, compared with cells treated with ethanol alone or GST protein. Thus, these studies demonstrate ethanol's potential for inducing apoptosis of human MVECs with relevant HIV-1-specific proteins and suggest a potential synergistic effect in augmenting HIV-1 neuroinvasion and neuropathogenesis in vivo.