HIV-1 Tat regulates endothelial cell cycle progression via activation of the Ras/ERK MAPK signaling pathway

Fentanyl dysregulates neuroinflammation and disrupts blood-brain barrier integrity in HIV-1 Tat transgenic mice

Opioid overdose deaths have dramatically increased by 781% from 1999 to 2021. In the setting of HIV, opioid drug abuse exacerbates neurotoxic effects of HIV in the brain, as opioids enhance viral replication, promote neuronal dysfunction and injury, and dysregulate an already compromised inflammatory response. Despite the rise in fentanyl abuse and the close association between opioid abuse and HIV infection, the interactive comorbidity between fentanyl abuse and HIV has yet to be examined in vivo. The HIV-1 Tat-transgenic mouse model was used to understand the interactive effects between fentanyl and HIV. Tat is an essential protein produced during HIV that drives the transcription of new virions and exerts neurotoxic effects within the brain. The Tat-transgenic mouse model uses a glial fibrillary acidic protein (GFAP)-driven tetracycline promoter which limits Tat production to the brain and this model is well used for examining mechanisms related to neuroHIV. After 7 days of fentanyl exposure, brains were harvested. Tight junction proteins, the vascular cell adhesion molecule, and platelet-derived growth factor receptor-β were measured to examine the integrity of the blood brain barrier. The immune response was assessed using a mouse-specific multiplex chemokine assay. For the first time in vivo, we demonstrate that fentanyl by itself can severely disrupt the blood-brain barrier and dysregulate the immune response. In addition, we reveal associations between inflammatory markers and tight junction proteins at the blood-brain barrier.

Deciphering the complete human-monkeypox virus interactome: Identifying immune responses and potential drug targets

Monkeypox virus (MPXV) is a dsDNA virus, belonging to Poxviridae family. The outbreak of monkeypox disease in humans is critical in European and Western countries, owing to its origin in African regions. The highest number of cases of the disease were found in the United States, followed by Spain and Brazil. Understanding the complete infection mechanism of diverse MPXV strains and their interaction with humans is important for therapeutic drug development, and to avoid any future epidemics. Using computational systems biology, we deciphered the genome-wide protein-protein interactions (PPIs) between 22 MPXV strains and human proteome. Based on phylogenomics and disease severity, 3 different strains of MPXV: Zaire-96-I-16, MPXV-UK_P2, and MPXV_USA_2022_MA001 were selected for comparative functional analysis of the proteins involved in the interactions. On an average, we predicted around 92,880 non-redundant PPIs between human and MPXV proteomes, involving 8014 host and 116 pathogen proteins from the 3 strains. The gene ontology (GO) enrichment analysis revealed 10,624 common GO terms in which the host proteins of 3 strains were highly enriched. These include significant GO terms such as platelet activation (GO:0030168), GABA-A receptor complex (GO:1902711), and metalloendopeptidase activity (GO:0004222). The host proteins were also significantly enriched in calcium signaling pathway (hsa04020), MAPK signaling pathway (hsa04010), and inflammatory mediator regulation of TRP channels (hsa04750). These significantly enriched GO terms and KEGG pathways are known to be implicated in immunomodulatory and therapeutic role in humans during viral infection. The protein hubs analysis revealed that most of the MPXV proteins form hubs with the protein kinases and AGC kinase C-terminal domains. Furthermore, subcellular localization revealed that most of the human proteins were localized in cytoplasm (29.22%) and nucleus (26.79%). A few drugs including Fostamatinib, Tamoxifen and others were identified as potential drug candidates against the monkeypox virus disease. This study reports the genome-scale PPIs elucidation in human-monkeypox virus pathosystem, thus facilitating the research community with functional insights into the monkeypox disease infection mechanism and augment the drug development.

HIV-1 Proteins gp120 and Tat Promote Epithelial-Mesenchymal Transition and Invasiveness of HPV-Positive and HPV-Negative Neoplastic Genital and Oral Epithelial Cells

The incidence of human papillomavirus (HPV)-associated anogenital and oropharyngeal cancer in human immunodeficiency virus (HIV)-infected individuals is substantially higher than in HIV-uninfected individuals. HIV may also be a risk factor for the development of HPV-negative head and neck, liver, lung, and kidney cancer. However, the molecular mechanisms underlying HIV-1-associated increase of epithelial malignancies are not fully understood. Here, we showed that HPV-16-immortalized anal AKC-2 and cervical CaSki epithelial cells that undergo prolonged exposure to cell-free HIV-1 virions or HIV-1 viral proteins gp120 and tat respond with the epithelial-mesenchymal transition (EMT) and increased invasiveness. Similar responses were observed in HPV-16-infected SCC-47 and HPV-16-negative HSC-3 oral epithelial cancer cells that were cultured with these viral proteins. EMT induced by gp120 and tat led to detachment of poorly adherent cells from the culture substratum; these cells remained capable of reattachment, upon which they coexpressed both E-cadherin and vimentin, indicative of an intermediate stage of EMT. The reattached cells also expressed stem cell markers CD133 and CD44, which may play a critical role in cancer cell invasion and metastasis. Inhibition of transforming growth factor (TGF)-β1 and MAPK signaling and vimentin expression, and restoration of E-cadherin expression reduced HIV-induced EMT and the invasive activity of HPV-16-immortalized anal and cervical epithelial cells. Collectively, our results suggest that these approaches along with HIV viral suppression with antiretroviral therapy (ART) might be useful to limit the role of HIV-1 infection in the acceleration of HPV-associated or HPV-independent epithelial neoplasia. IMPORTANCE HPV-16-immortalized genital and oral epithelial cells and HPV-negative oral cancer cells that undergo prolonged contact with cell-free HIV-1 virions or with viral proteins gp120 and tat respond by becoming more invasive. EMT cells induced by HIV-1 in cultures of HPV-16-immortalized anal and cervical epithelial cells express the stem cell markers CD133 and CD44. These results suggest that the interaction of HIV-1 with neoplastic epithelial cells may lead to their de-differentiation into cancer stem cells that are resistant to apoptosis and anti-cancer drugs. Thus, this pathway may play a critical role in the development of invasive cancer. Inhibition of TGF-β1 and MAPK signaling and vimentin expression, and restoration of E-cadherin expression reduced HIV-induced EMT and the invasiveness of HPV-16-immortalized anal and cervical epithelial cells. Taken together, these results suggest that these approaches might be exploited to limit the role of HIV-1 infection in the acceleration of HPV-associated or HPV-independent epithelial neoplasia.

Human Immunodeficiency Virus (HIV) and Human Cytomegalovirus (HCMV) Coinfection of Infant Tonsil Epithelium May Synergistically Promote both HIV-1 and HCMV Spread and Infection

Mother-to-child transmission (MTCT) of human immunodeficiency virus type 1 (HIV-1) and human cytomegalovirus (HCMV) may occur during pregnancy, labor, or breastfeeding. These viruses from amniotic fluid, cervicovaginal secretions, and breast milk may simultaneously interact with oropharyngeal and tonsil epithelia; however, the molecular mechanism of HIV-1 and HCMV cotransmission through the oral mucosa and its role in MTCT are poorly understood. To study the molecular mechanism of HIV-1 and HCMV MTCT via oral epithelium, we established polarized infant tonsil epithelial cells and polarized-oriented ex vivo tonsil tissue explants. Using these models, we showed that cell-free HIV-1 and its proteins gp120 and tat induce the disruption of tonsil epithelial tight junctions and increase paracellular permeability, which facilitates HCMV spread within the tonsil mucosa. Inhibition of HIV-1 gp120-induced upregulation of mitogen-activated protein kinase (MAPK) and NF-κB signaling in tonsil epithelial cells, reduces HCMV infection, indicating that HIV-1-activated MAPK and NF-κB signaling may play a critical role in HCMV infection of tonsil epithelium. HCMV infection of tonsil epithelial cells also leads to the disruption of tight junctions and increases paracellular permeability, facilitating HIV-1 paracellular spread into tonsil mucosa. HCMV-promoted paracellular spread of HIV-1 increases its accessibility to tonsil CD4 T lymphocytes, macrophages, and dendritic cells. HIV-1-enhanced HCMV paracellular spread and infection of epithelial cells subsequently leads to the spread of HCMV to tonsil macrophages and dendritic cells. Our findings revealed that HIV-1- and HCMV-induced disruption of infant tonsil epithelial tight junctions promotes MTCT of these viruses through tonsil mucosal epithelium, and therapeutic intervention for both HIV-1 and HCMV infection may substantially reduce their MTCT. IMPORTANCE Most HIV-1 and HCMV MTCT occurs in infancy, and the cotransmission of these viruses may occur via infant oropharyngeal and tonsil epithelia, which are the first biological barriers for viral pathogens. We have shown that HIV-1 and HCMV disrupt epithelial junctions, reducing the barrier functions of epithelia and thus allowing paracellular penetration of both viruses via mucosal epithelia. Subsequently, HCMV infects epithelial cells, macrophages, and dendritic cells, and HIV-1 infects CD4⁺ lymphocytes, macrophages, and dendritic cells. Infection of these cells in HCMV- and HIV-1-coinfected tonsil tissues is much higher than that by HCMV or HIV-1 infection alone, promoting their MTCT at its initial stages via infant oropharyngeal and tonsil epithelia.

Impact of human immunodeficiency virus on pulmonary vascular disease

With the advent of anti-retroviral therapy, non-AIDS-related comorbidities have increased in people living with HIV. Among these comorbidities, pulmonary hypertension (PH) is one of the most common causes of morbidity and mortality. Although chronic HIV-1 infection is independently associated with the development of pulmonary arterial hypertension, PH in people living with HIV may also be the outcome of various co-morbidities commonly observed in these individuals including chronic obstructive pulmonary disease, left heart disease and co-infections. In addition, the association of these co-morbidities and other risk factors, such as illicit drug use, can exacerbate the development of pulmonary vascular disease. This review will focus on these complex interactions contributing to PH development and exacerbation in HIV patients. We also examine the interactions of HIV proteins, including Nef, Tat, and gp120 in the pulmonary vasculature and how these proteins alter the endothelial and smooth muscle function by transforming them into susceptible PH phenotype. The review also discusses the available infectious and non-infectious animal models to study HIV-associated PAH, highlighting the advantages and disadvantages of each model, along with their ability to mimic the clinical manifestations of HIV-PAH.

Hedgehog Signaling: Implications in Cancers and Viral Infections

The hedgehog (SHH) signaling pathway is primarily involved in embryonic gut development, smooth muscle differentiation, cell proliferation, adult tissue homeostasis, tissue repair following injury, and tissue polarity during the development of vertebrate and invertebrate organisms. GLIoma-associated oncogene homolog (GLI) family of zinc-finger transcription factors and smoothened (SMO) are the signal transducers of the SHH pathway. Both SHH ligand-dependent and independent mechanisms activate GLI proteins. Various transcriptional mechanisms, posttranslational modifications (phosphorylation, ubiquitination, proteolytic processing, SUMOylation, and acetylation), and nuclear-cytoplasmic shuttling control the activity of SHH signaling pathway proteins. The dysregulated SHH pathway is associated with bone and soft tissue sarcomas, GLIomas, medulloblastomas, leukemias, and tumors of breast, lung, skin, prostate, brain, gastric, and pancreas. While extensively studied in development and sarcomas, GLI family proteins play an essential role in many host-pathogen interactions, including bacterial and viral infections and their associated cancers. Viruses hijack host GLI family transcription factors and their downstream signaling cascades to enhance the viral gene transcription required for replication and pathogenesis. In this review, we discuss a distinct role(s) of GLI proteins in the process of tumorigenesis and host-pathogen interactions in the context of viral infection-associated malignancies and cancers due to other causes. Here, we emphasize the potential of the Hedgehog (HH) pathway targeting as a potential anti-cancer therapeutic approach, which in the future could also be tested in infection-associated fatalities.

Hippocampal blood-brain barrier of methamphetamine self-administering HIV-1 transgenic rats

Combined antiretroviral therapy for HIV infection reduces plasma viral load and prolongs life. However, the brain is a viral reservoir, and pathologies such as cognitive decline and blood-brain barrier (BBB) disruption persist. Methamphetamine abuse is prevalent among HIV-infected individuals. Methamphetamine and HIV toxic proteins can disrupt the BBB, but it is unclear if there exists a common pathway by which HIV proteins and methamphetamine induce BBB damage. Also unknown are the BBB effects imposed by chronic exposure to HIV proteins in the comorbid context of chronic methamphetamine abuse. To evaluate these scenarios, we trained HIV-1 transgenic (Tg) and non-Tg rats to self-administer methamphetamine using a 21-day paradigm that produced an equivalency dose range at the low end of the amounts self-titrated by humans. Markers of BBB integrity were measured for the hippocampus, a brain region involved in cognitive function. Outcomes revealed that tight junction proteins, claudin-5 and occludin, were reduced in Tg rats independent of methamphetamine, and this co-occurred with increased levels of lipopolysaccharide, albumin (indicating barrier breakdown) and matrix metalloproteinase-9 (MMP-9; indicating barrier matrix disruption); reductions in GFAP (indicating astrocytic dysfunction); and microglial activation (indicating inflammation). Evaluations of markers for two signaling pathways that regulate MMP-9 transcription, NF-κB and ERK/∆FosB revealed an overall genotype effect for NF-κB. Methamphetamine did not alter measurements from Tg rats, but in non-Tg rats, methamphetamine reduced occludin and GFAP, and increased MMP-9 and NF-κB. Study outcomes suggest that BBB dysregulation resulting from chronic exposure to HIV-1 proteins or methamphetamine both involve NF-κB/MMP-9.

Human immunodeficiency virus interaction with oral and genital mucosal epithelia may lead to epithelial-mesenchymal transition and sequestration of virions in the endosomal compartments

Oral and genital mucosal epithelia are multistratified epithelial barriers with well-developed tight and adherens junctions. These barriers serve as the first line of defense against many pathogens, including human immunodeficiency virus (HIV). HIV interaction with the surface of mucosal epithelial cells, however, may activate transforming growth factor-beta (TGF-β) and mitogen-activated protein kinase signaling pathways. When activated, these pathways may lead to the disruption of epithelial junctions and epithelial-mesenchymal transition (EMT). HIV-induced impairment of the mucosal barrier may facilitate the spread of pathogenic viral, bacterial, fungal, and other infectious agents. HIV-induced EMT promotes highly motile/migratory cells. In oral and genital mucosa, if EMT occurs within a human papillomavirus (HPV)-infected premalignant or malignant cell environment, the HPV-associated neoplastic process could be accelerated by promoting viral invasion of malignant cells. HIV also internalizes into oral and genital mucosal epithelial cells. The majority (90%) of internalized virions do not cross the epithelium, but are retained in endosomal compartments for several days. These sequestered virions are infectious. Upon interaction with activated peripheral blood mononuclear cells and CD4+ T lymphocytes, epithelial cells containing the virus can be transferred. The induction of HIV-1 release and the cell-to-cell spread of virus from epithelial cells to lymphocytes is mediated by interaction of lymphocyte receptor function-associated antigen-1 with the epithelial cell receptor intercellular adhesion molecule-1. Thus, mucosal epithelial cells may serve as a transient reservoir for HIV, which could play a critical role in viral transmission.

HIV-1 proteins gp120 and tat induce the epithelial-mesenchymal transition in oral and genital mucosal epithelial cells

The oral, cervical, and genital mucosa, covered by stratified squamous epithelia with polarized organization and strong tight and adherens junctions, play a critical role in preventing transmission of viral pathogens, including human immunodeficiency virus (HIV). HIV-1 interaction with mucosal epithelial cells may depolarize epithelia and disrupt their tight and adherens junctions; however, the molecular mechanism of HIV-induced epithelial disruption has not been completely understood. We showed that prolonged interaction of cell-free HIV-1 virions, and viral envelope and transactivator proteins gp120 and tat, respectively, with tonsil, cervical, and foreskin epithelial cells induces an epithelial-mesenchymal transition (EMT). EMT is an epigenetic process leading to the disruption of mucosal epithelia and allowing the paracellular spread of viral and other pathogens. Interaction of cell-free virions and gp120 and tat proteins with epithelial cells substantially reduced E-cadherin expression and activated vimentin and N-cadherin expression, which are well-known mesenchymal markers. HIV gp120- and tat-induced EMT was mediated by SMAD2 phosphorylation and activation of transcription factors Slug, Snail, Twist1 and ZEB1. Activation of TGF-β and MAPK signaling by gp120, tat, and cell-free HIV virions revealed the critical roles of these signaling pathways in EMT induction. gp120- and tat-induced EMT cells were highly migratory via collagen-coated membranes, which is one of the main features of mesenchymal cells. Inhibitors of TGF-β1 and MAPK signaling reduced HIV-induced EMT, suggesting that inactivation of these signaling pathways may restore the normal barrier function of mucosal epithelia.

HIV Proteins and Endothelial Dysfunction: Implications in Cardiovascular Disease

With the success of antiretroviral therapy (ART), a dramatic decrease in viral burden and opportunistic infections and an increase in life expectancy has been observed in human immunodeficiency virus (HIV) infected individuals. However, it is now clear that HIV- infected individuals have enhanced susceptibility to non-AIDS (Acquired immunodeficiency syndrome)-related complications such as cardiovascular disease (CVD). CVDs such as atherosclerosis have become a significant cause of morbidity and mortality in individuals with HIV infection. Though studies indicate that ART itself may increase the risk to develop CVD, recent studies suggest a more important role for HIV infection in contributing to CVD independently of the traditional risk factors. Endothelial dysfunction triggered by HIV infection has been identified as a critical link between infection, inflammation/immune activation, and atherosclerosis. Considering the inability of HIV to actively replicate in endothelial cells, endothelial dysfunction depends on both HIV-encoded proteins as well as inflammatory mediators released in the microenvironment by HIV-infected cells. Indeed, the HIV proteins, gp120 (envelope glycoprotein) and Tat (transactivator of transcription), are actively secreted into the endothelial cell micro-environment during HIV infection, while Nef can be actively transferred onto endothelial cells during HIV infection. These proteins can have significant direct effects on the endothelium. These include a range of responses that contribute to endothelial dysfunction, including enhanced adhesiveness, permeability, cell proliferation, apoptosis, oxidative stress as well as activation of cytokine secretion. This review summarizes the current understanding of the interactions of HIV, specifically its proteins with endothelial cells and its implications in cardiovascular disease. We analyze recent in vitro and in vivo studies examining endothelial dysfunction in response to HIV proteins. Furthermore, we discuss the multiple mechanisms by which these viral proteins damage the vascular endothelium in HIV patients. A better understanding of the molecular mechanisms of HIV protein associated endothelial dysfunction leading to cardiovascular disease is likely to be pivotal in devising new strategies to treat and prevent cardiovascular disease in HIV-infected patients.

Notch3/VEGF-A axis is involved in TAT-mediated proliferation of pulmonary artery smooth muscle cells: Implications for HIV-associated PAH

The incidence of pulmonary arterial hypertension (PAH) is a significant co-morbidity observed in HIV (+) individuals. Pulmonary artery smooth muscle cells (PASMCs)—key components of the arterial vessel wall that regulate vessel diameter, demonstrate increased proliferation and hypertrophy in the lungs of HIV infected individuals, underscoring the role of these cells in the pathogenesis of HIV-associated PAH. While several pathways have been implicated in enhanced proliferation of PASMCs, detailed molecular mechanism(s) underlying HIV-associated PASMC proliferation still remain elusive. In the current study, we sought to investigate the effects HIV protein transactivator of transcription (TAT)-mediated proliferation on PASMCs. In agreement with earlier findings, our results also demonstrated TAT-mediated proliferation of human PASMCs. We identified activation of a novel Notch3 signaling pathway in TAT-mediated proliferation of PASMCs. Further validation of the Notch 3 pathway was demonstrated using both pharmacological (γ-secretase inhibitor, DAPT), as well as genetic approaches (Notch3 siRNA). Vascular endothelial growth factor A (VEGF-A) was identified as a novel downstream molecule that was induced following Notch activation. Findings from in vitro studies were further validated in archived simian immunodeficiency virus (SIV)-infected monkey lung tissues. There was increased activation of Notch3 signaling as well as enhanced expression of VEGF-A in the lungs of SIV-infected macaques compared with the lungs of SIV(−) controls. Taken together, we demonstrated that HIV-TAT increased the proliferation of PASMCs via the Notch3/VEGF-A axis. Targeting the Notch3/VEGF-A axis could thus be considered a potential therapeutic approach for the treatment of HIV-associated PAH.

Region-specific changes in markers of neuroplasticity revealed in HIV-1 transgenic rats by low-dose methamphetamine

Methamphetamine abuse co-occurring with HIV infection presents neuropathology in brain regions that mediate reward and motivation. A neuronal signaling cascade altered acutely by meth and some HIV-1 proteins is the mitogen-activated protein kinase (MAPK) pathway. It remains unknown if chronic co-exposure to meth and HIV-1 proteins converge on MAPK in vivo. To make this determination, we studied young adult Fischer 344 HIV-1 transgenic (Tg) and non-Tg rats that self-administered meth (0.02-0.04 mg/kg/0.05 ml iv infusion, 2 h/day for 21 days) and their saline-yoked controls. One day following the operant task, rats were killed. Brain regions involved in reward-motivation [i.e., nucleus accumbens (NA) and ventral pallidum (VP)], were assayed for a MAPK cascade protein, extracellular signal-regulated kinase (ERK), and a downstream transcription factor, ΔFosB. In the NA, activated (phosphorylated; p) ERK-to-ERK ratio (pERK/ERK) was increased in meth-exposed Tg rats versus saline Tg controls, and versus meth non-Tg rats. ΔFosB was increased in meth Tg rats versus saline and meth non-Tg rats. Assessment of two targets of ΔFosB-regulated transcription revealed (1) increased dopamine D1 receptor (D1R) immunoreactivity in the NA shell of Tg-meth rats versus saline Tg controls, but (2) no changes in the AMPA receptor subunit, GluA2. No changes related to genotype or meth occurred for ERK, ΔFosB or D1R protein in the VP. Results reveal a region-specific activation of ERK, and increases in ΔFosB and D1R expression induced by HIV-1 proteins and meth. Such effects may contribute to the neuronal and behavioral pathology associated with meth/HIV comorbidity.

HIV-induced matrix metalloproteinase-9 activation through mitogen-activated protein kinase signalling promotes HSV-1 cell-to-cell spread in oral epithelial cells

We have shown that cell-free HIV-1 and viral proteins tat and gp120 activate mitogen-activated protein kinases (MAPKs) in tonsil epithelial cells, disrupting their tight and adherens junctions. This causes liberation of the HSV-1 receptor nectin-1 from assembled adherens junctions, leading to promotion of HSV-1 infection and spread. In the present study, we show that HIV-associated activation of MAPK leads to upregulation of transcription factor NF-κB and matrix metalloproteinase-9 (MMP-9). This induces the disruption of tight and adherens junctions, increasing HSV-1 cell-to-cell spread. Inhibition of HIV-associated MAPK activation by U0126 abolishes NF-κB and MMP-9 upregulation and reduces HSV-1 spread. Inactivation of MMP-9 also reduced HIV-promoted HSV-1 spread. These results indicate that HIV-1-activated MAPK/NF-κB and MMP-9 play a critical role in the disruption of oral epithelial junctions and HSV-1 cell-to-cell spread. Inhibition of MMP-9 expression in the oral epithelium of HIV-infected individuals may prevent the development of diseases caused by HSV-1, such as ulcers, necrotic lesions and gingivostomatitis.

Clinically significant mutations in HIV-infected patients with lung adenocarcinoma

BACKGROUND

Lung cancer is a major cause of death in HIV-infected (HIV+) persons. In this study, we compared the prevalence of tumour EGFR and KRAS mutations in a cohort of lung adenocarcinoma patients by HIV status.

METHODS

We collected data from 55 HIV+ patients with lung adenocarcinoma matched to 136 uninfected comparators. We compared the prevalence of EGFR and KRAS mutations by HIV status. We then compared survival by HIV status and by cancer mutation status among HIV+ subjects.

RESULTS

Presence of KRAS and EGFR genetic alterations did not vary by HIV status (all P>0.1). There was no difference in overall survival by HIV status or by mutation status among HIV+ subjects.

CONCLUSIONS

We found no major differences in the prevalence of EGFR or KRAS lung adenocarcinoma mutations by HIV status, suggesting that mutational testing should be conducted similarly regardless of the HIV status.

HIV Tat Impairs Neurogenesis through Functioning As a Notch Ligand and Activation of Notch Signaling Pathway

Alterations in adult neurogenesis have been noted in the brain of HIV-infected individuals and are likely linked to HIV-associated neurocognitive deficits, including those in learning and memory. But the underlying molecular mechanisms are not fully understood. In the study, we took advantage of doxycycline-inducible and astrocyte-specific HIV-1 Tat transgenic mice (iTat) and determined the relationship between Tat expression and neurogenesis. Tat expression in astrocytes was associated with fewer neuron progenitor cells (NPCs), fewer immature neurons, and fewer mature neurons in the dentate gyrus of the hippocampus of the mouse brain. In vitro NPC-derived neurosphere assays showed that Tat-containing conditioned media from astrocytes or recombinant Tat protein inhibited NPC proliferation and migration and altered NPC differentiation, while immunodepletion of Tat from Tat-containing conditioned media or heat inactivation of recombinant Tat abrogated those effects. Notch signaling downstream gene Hes1 promoter-driven luciferase reporter gene assay and Western blotting showed that recombinant Tat or Tat-containing conditioned media activated Hes1 transcription and protein expression, which were abrogated by Tat heat inactivation, immunodepletion, and cysteine mutation at position 30. Last, Notch signaling inhibitor N-[N-(3,5-difluorophenacetyl)-l-alanyl]-S-phenylglycine t-butyl ester (DAPT) significantly rescued Tat-impaired NPC differentiation in vitro and neurogenesis in vivo Together, these results show that Tat adversely affects NPCs and neurogenesis through Notch signaling and point to the potential of developing Notch signaling inhibitors as HIV/neuroAIDS therapeutics.

SIGNIFICANCE STATEMENT

HIV infection of the CNS causes cognitive and memory deficits, which have become more prevalent in the era of combination antiretroviral therapy (cART). Neurogenesis is impaired in HIV-infected individuals. But the underlying molecular mechanisms remain largely unknown. In this study, we have discovered that HIV Tat impairs neurogenesis through the Notch signaling pathway. These findings are particularly important because Tat protein has recently been detected in the brain of HIV-infected individuals with HIV replication in the periphery being effectively controlled by cART. The current study not only further highlights the importance of HIV Tat protein in HIV/neuroAIDS, but also presents a new strategy to develop novel HIV/neuroAIDS therapeutics, particularly in the era of cART.

Involvement of PUMA in pericyte migration induced by methamphetamine

Mounting evidence indicates that methamphetamine causes blood-brain barrier damage, with emphasis on endothelial cells. The role of pericytes in methamphetamine-induced BBB damage remains unknown. Our study demonstrated that methamphetamine increased the migration of pericytes from the endothelial basement membrane. However, the detailed mechanisms underlying this process remain poorly understood. Thus, we examined the molecular mechanisms involved in methamphetamine-induced pericyte migration. The results showed that exposure of C3H/10T1/2 cells and HBVPs to methamphetamine increased PUMA expression via activation of the sigma-1 receptor, MAPK and Akt/PI3K pathways. Moreover, methamphetamine treatment resulted in the increased migration of C3H/10T1/2 cells and HBVPs. Knockdown of PUMA in pericytes transduced with PUMA siRNA attenuated the methamphetamine-induced increase in cell migration through attenuation of integrin and tyrosine kinase mechanisms, implicating a role of PUMA in the migration of C3H/10T1/2 cells and HBVPs. This study has demonstrated that methamphetamine-mediated pericytes migration involves PUMA up-regulation. Thus, targeted studies of PUMA could provide insights to facilitate the development of a potential therapeutic approach for alleviation of methamphetamine-induced pericyte migration.

Confusion in the Study of Immune Reconstitution Inflammatory Syndrome

As a consequence of late presentation for HIV care, a significant proportion of individuals develop immune reconstitution inflammatory syndrome (IRIS) soon after initiation of antiretroviral therapy. Incidence, predictors, and models of pathogenesis of IRIS vary in the literature. Here we discuss factors that may contribute to this lack of consensus. We propose that different pathogens drive different types of IRIS and suggest that these clinical conditions should be studied individually and not grouped under the general heading of "IRIS."

HIV-Tat immunization induces cross-clade neutralizing antibodies and CD4(+) T cell increases in antiretroviral-treated South African volunteers: a randomized phase II clinical trial

BACKGROUND

Although combined antiretroviral therapy (cART) has saved millions of lives, it is incapable of full immune reconstitution and virus eradication. The transactivator of transcription (Tat) protein is a key human immunodeficiency virus (HIV) virulence factor required for virus replication and transmission. Tat is expressed and released extracellularly by infected cells also under cART and in this form induces immune dysregulation, and promotes virus reactivation, entry and spreading. Of note, anti-Tat antibodies are rare in natural infection and, when present, correlate with asymptomatic state and reduced disease progression. This suggested that induction of anti-Tat antibodies represents a pathogenesis-driven intervention to block progression and to intensify cART. Indeed Tat-based vaccination was safe, immunogenic and capable of immune restoration in an open-label, randomized phase II clinical trial conducted in 168 cART-treated volunteers in Italy. To assess whether B-clade Tat immunization would be effective also in patients with different genetic background and infecting virus, a phase II trial was conducted in South Africa.

METHODS

The ISS T-003 was a 48-week randomised, double-blinded, placebo-controlled trial to evaluate immunogenicity (primary endpoint) and safety (secondary endpoint) of B-clade Tat (30 μg) given intradermally, three times at 4-week intervals, in 200 HIV-infected adults on effective cART (randomised 1:1) with CD4(+) T-cell counts ≥200 cells/µL. Study outcomes also included cross-clade anti-Tat antibodies, neutralization, CD4(+) T-cell counts and therapy compliance.

RESULTS

Immunization was safe and well-tolerated and induced durable, high titers anti-Tat B-clade antibodies in 97 % vaccinees. Anti-Tat antibodies were cross-clade (all vaccinees tested) and neutralized Tat-mediated entry of oligomeric B-clade and C-clade envelope in dendritic cells (24 participants tested). Anti-Tat antibody titers correlated positively with neutralization. Tat vaccination increased CD4(+) T-cell numbers (all participants tested), particularly when baseline levels were still low after years of therapy, and this had a positive correlation with HIV neutralization. Finally, in cART non-compliant patients (24 participants), vaccination contained viral load rebound and maintained CD4(+) T-cell numbers over study entry levels as compared to placebo.

CONCLUSIONS

The data indicate that Tat vaccination can restore the immune system and induces cross-clade neutralizing anti-Tat antibodies in patients with different genetic backgrounds and infecting viruses, supporting the conduct of phase III studies in South Africa. Trial registration ClinicalTrials.gov NCT01513135, 01/23/2012.

Human immunodeficiency virus-associated disruption of mucosal barriers and its role in HIV transmission and pathogenesis of HIV/AIDS disease

Oral, intestinal and genital mucosal epithelia have a barrier function to prevent paracellular penetration by viral, bacterial and other pathogens, including human immunodeficiency virus (HIV). HIV can overcome these barriers by disrupting the tight and adherens junctions of mucosal epithelia. HIV-associated disruption of epithelial junctions may also facilitate paracellular penetration and dissemination of other viral pathogens. This review focuses on possible molecular mechanisms of HIV-associated disruption of mucosal epithelial junctions and its role in HIV transmission and pathogenesis of HIV and acquired immune deficiency syndrome (AIDS).

Beyond RGD: virus interactions with integrins

Viruses successfully infect host cells by initially binding to the surfaces of the cells, followed by an intricate entry process. As multifunctional heterodimeric cell-surface receptor molecules, integrins have been shown to usefully serve as entry receptors for a plethora of viruses. However, the exact role(s) of integrins in viral pathogen internalization has yet to be elaborately described. Notably, several viruses harbor integrin-recognition motifs displayed on viral envelope/capsid-associated proteins. The most common of these motifs is the minimal peptide sequence for binding integrins, RGD (Arg-Gly-Asp), which is known for its role in virus infection via its ability to interact with over half of the more than 20 known integrins. Not all virus-integrin interactions are RGD-dependent, however. Non-RGD-binding integrins have also been shown to effectively promote virus entry and infection as well. Such virus-integrin binding is shown to facilitate adhesion, cytoskeleton rearrangement, integrin activation, and increased intracellular signaling. Also, we have attempted to discuss the role of carbohydrate moieties in virus interactions with receptor-like host cell surface integrins that drive the process of internalization. As much as possible, this article examines the published literature regarding the role of integrins in terms of virus infection and virus-encoded glycosylated proteins that mediate interactions with integrins, and it explores the idea of targeting these receptors as a therapeutic treatment option.

Rosiglitazone suppresses HIV-1 Tat-induced vascular inflammation via Akt signaling

Peroxisome proliferator-activated receptor gamma (PPARƔ) contributes to human immunodeficiency virus (HIV)-1-induced dysfunction of brain endothelial cells. The aim of the present study was to evaluate the protection mechanism of PPARƔ against Tat-induced responses of adhesion molecules. We measured the protein expressions of intercellular adhesion molecule (ICAM)-1 and vascular cell adhesion molecule (VCAM)-1 in human brain microvascular endothelial cells (hCMEC/D3) and C57BL/6J mouse brain microvessels with Western blotting and immunofluorescent labeling. The mRNA levels of ICAM-1 and VCAM-1 were determined by real-time reverse-transcriptase polymerase chain reaction. HIV-1 Tat induced overexpression of ICAM-1 but not VCAM-1 in both hCMEC/D3 and brain microvessels, this response was attenuated by treatment with the PPARƔ agonist rosiglitazone. Tat-mediated upregulation of ICAM-1 and VCAM-1 levels were abolished by the addition of PPARƔ antagonist GW9662 and the Akt inhibitor KP3721, indicating that Akt signaling is involved in the PPARƔ-mediated protection of Tat-induced adhesion molecule upregulation. These results show that Akt signaling plays a key role in PPARƔ's vascular inflammatory effects that contribute to blood-brain barrier damage.

HIV-1 Tat affects the programming and functionality of human CD8⁺ T cells by modulating the expression of T-box transcription factors

OBJECTIVE

HIV infection is characterized by several immune dysfunctions of both CD8⁺ and CD4⁺ T cells as hyperactivation, impairment of functionality and expansion of memory T cells. CD8⁺ T-cell dysfunctions have been associated with increased expression of T-bet, Eomesdermin and pro-inflammatory cytokines, and with down-regulation of CD127. The HIV-1 trans-activator of transcription (Tat) protein, which is released by infected cells and detected in tissues of HIV-positive individuals, is known to contribute to the dysregulation of CD4⁺ T cells; however, its effects on CD8⁺ T cells have not been investigated. Thus, in this study, we sought to address whether Tat may affect CD8⁺ T-cell functionality and programming.

METHODS

CD8⁺ T cells were activated by T-cell receptor engagement in the presence or absence of Tat. Cytokine production, killing capacity, surface phenotype and expression of transcription factors important for T-cell programming were evaluated.

RESULTS

Tat favors the secretion of interleukin-2, interferon-γ and granzyme B in CD8⁺ T cells. Behind this functional modulation we observed that Tat increases the expression of T-bet, Eomesdermin, Blimp-1, Bcl-6 and Bcl-2 in activated but not in unstimulated CD8⁺ T lymphocytes. This effect is associated with the down-regulation of CD127 and the up-regulation of CD27.

CONCLUSION

Tat deeply alters the programming and functionality of CD8⁺ T lymphocytes.

Some mechanisms of FLIP expression in inhibition of HIV-1 replication in Jurkat cells, CD4+ T cells and PBMCs

HIV-1 infection and replication are affected by host factors. Recent studies demonstrate that molecules from apoptotic pathways regulate HIV-1 replication. Therefore, studies on effects of host factors that maintain host cell survival and influence HIV-1 replication are critical to understanding the mechanisms of HIV-1 replicative cycle. Using the susceptible Jurkat cell line, CD4(+) T cells, and peripheral blood mononuclear cells (PBMCs), we studied the role of FLIP, an inhibitor of caspase-8, in HIV-1 production. Full length cellular FLIP (cFLIP) inhibited HIV-1 replication in these cells. cFLIP upregulated the expression of viral restriction factors, such as TRIM5, Apobec3G, and Bst2/tetherin, decreased nuclear factor 1C expression and inactivated ERK and p38 induced by HIV-1 in Jurkat cells. cFLIP blocked the trafficking of gp120 and Gag p24 capsid protein into lipid rafts with inhibition of Tsg101 and Alix in ESCRT signaling pathway. cFLIP also promoted Bst2/tetherin trafficking into lipid rafts. These results indicate that cFLIP may inhibit the HIV-1 replication cycle at multiple steps, including viral RNA release, transcription, traffic and assembly. We also found that cFLIP expression downregulated Fas expression and inactivated FADD in the Fas-mediated apoptotic pathway. The inactivated FADD also inhibited HIV-1 replication.

HIV-associated disruption of tight and adherens junctions of oral epithelial cells facilitates HSV-1 infection and spread

Herpes simplex virus (HSV) types 1 and 2 are the most common opportunistic infections in HIV/AIDS. In these immunocompromised individuals, HSV-1 reactivates and replicates in oral epithelium, leading to oral disorders such as ulcers, gingivitis, and necrotic lesions. Although the increased risk of HSV infection may be mediated in part by HIV-induced immune dysfunction, direct or indirect interactions of HIV and HSV at the molecular level may also play a role. In this report we show that prolonged interaction of the HIV proteins tat and gp120 and cell-free HIV virions with polarized oral epithelial cells leads to disruption of tight and adherens junctions of epithelial cells through the mitogen-activated protein kinase signaling pathway. HIV-induced disruption of oral epithelial junctions facilitates HSV-1 paracellular spread between the epithelial cells. Furthermore, HIV-associated disruption of adherens junctions exposes sequestered nectin-1, an adhesion protein and critical receptor for HSV envelope glycoprotein D (gD). Exposure of nectin-1 facilitates binding of HSV-1 gD, which substantially increases HSV-1 infection of epithelial cells with disrupted junctions over that of cells with intact junctions. Exposed nectin-1 from disrupted adherens junctions also increases the cell-to-cell spread of HSV-1 from infected to uninfected oral epithelial cells. Antibodies to nectin-1 and HSV-1 gD substantially reduce HSV-1 infection and cell-to-cell spread, indicating that HIV-promoted HSV infection and spread are mediated by the interaction of HSV gD with HIV-exposed nectin-1. Our data suggest that HIV-associated disruption of oral epithelial junctions may potentiate HSV-1 infection and its paracellular and cell-to-cell spread within the oral mucosal epithelium. This could be one of the possible mechanisms of rapid development of HSV-associated oral lesions in HIV-infected individuals.

HIV-associated disruption of mucosal epithelium facilitates paracellular penetration by human papillomavirus

The incidence of human papillomavirus (HPV)-associated epithelial lesions is substantially higher in human immunodeficiency virus (HIV)-infected individuals than in HIV-uninfected individuals. The molecular mechanisms underlying the increased risk of HPV infection in HIV-infected individuals are poorly understood. We found that HIV proteins tat and gp120 were expressed within the oral and anal mucosal epithelial microenvironment of HIV-infected individuals. Expression of HIV proteins in the mucosal epithelium was correlated with the disruption of epithelial tight junctions (TJ). Treatment of polarized oral, cervical and anal epithelial cells, and oral tissue explants with tat and gp120 led to disruption of epithelial TJ and increased HPV pseudovirion (PsV) paracellular penetration in to the epithelium. PsV entry was observed in the basal/parabasal cells, the cells in which the HPV life cycle is initiated. Our data suggest that HIV-associated TJ disruption of mucosal epithelia may potentiate HPV infection and subsequent development of HPV-associated neoplasia.

Nonmuscle myosin light-chain kinase mediates microglial migration induced by HIV Tat: involvement of β1 integrins

One of the hallmark features of HIV-associated neurological disease is increased activation and migration of microglia. HIV transactivator of transcription (Tat) is released from infected cells and has the ability to recruit microglia. The purpose of this study was to investigate molecular mechanisms by which recombinant Tat₁₋₇₂, but not heated-inactive Tat₁₋₇₂,induces migration of rat primary microglia. Using primary microglia in Boyden chambers, we demonstrated the role of nonmuscle myosin light-chain kinase (nmMYLK) in Tat₁₋₇₂ (14.4 nM)-mediated increased microglial migration (up to 171.85%). These findings were validated using microglia isolated from wild-type (WT) or nmMYLK(-/-) mice in Dunn chamber assays. Tat₁₋₇₂-mediated activation of nmMYLK resulted in "inside-out" activation of β1 integrin, followed by "outside-in" activation of c-Src, Pyk2, and Cdc42-GTP (using G-LISA in primary and nmMYLK(-/-) microglia) and, subsequently, actin polymerization (flow cytometry and Western blot assays). In vivo corroboration of these findings demonstrated decreased migration of nmMYLK(-/-) microglia (2 × 10(5) cells transplanted into corpus callosum) compared with WT microglia toward microinjected Tat₁₋₇₂ (2 μg/mouse) in hippocampus. Up-regulation of nmMYLK in microglia was also detected in sections of basal ganglia from humans with HIV-encephalitis compared with uninfected controls. nmMYLK is thus critical for eliciting microglial migration during the innate immune response.

Varicella-Zoster virus ORF12 protein triggers phosphorylation of ERK1/2 and inhibits apoptosis

Mitogen-activated protein kinases (MAPKs) are a family of serine-threonine protein kinases involved in many cellular processes, including cell proliferation, differentiation, inflammation, and cell death. Activation of several MAPKs, including extracellular signal-regulated kinase 1 and 2 (ERK1/2), p38, and c-Jun N-terminal kinase (JNK), results in stimulation of activator protein 1 (AP-1), which promotes gene transcription. Previous studies have demonstrated that varicella-zoster virus (VZV) infection activates ERK1/2, p38, and JNK to promote viral replication, but the underlying mechanism(s) is unclear. To identify viral proteins responsible for the activation of MAPK, we used a proteomic approach to screen viral proteins for AP-1 promoter activation by an AP-1-luciferase reporter assay. We found that VZV ORF12 protein, located in the tegument of virions, enhances AP-1 reporter activity. This effect of ORF12 protein was markedly inhibited by a MAPK/ERK kinase 1 and 2 (MEK1/2) inhibitor (U0126), partially blocked by a p38 inhibitor (SB202190), but not inhibited by a JNK inhibitor (SP600125). Expression of VZV ORF12 protein in cells resulted in phosphorylation of ERK1/2 and p38 but not JNK. Infection of cells with a VZV ORF12 deletion mutant resulted in reduced levels of phosphorylated ERK1/2 (p-ERK1/2) compared to infection with wild-type VZV. Furthermore, deletion of ORF12 rendered VZV-infected cells more susceptible to staurosporine-induced apoptosis. In conclusion, VZV ORF12 protein activates the AP-1 pathway by selectively triggering the phosphorylation of ERK1/2 and p38. Cells infected with a VZV ORF12 deletion mutant have reduced levels of p-ERK1/2 and are more susceptible to apoptosis than cells infected with wild-type VZV.

Exploring transduction mechanisms of protein transduction domains (PTDs) in living cells utilizing single-quantum dot tracking (SQT) technology

Specific protein domains known as protein transduction domains (PTDs) can permeate cell membranes and deliver proteins or bioactive materials into living cells. Various approaches have been applied for improving their transduction efficacy. It is, therefore, crucial to clarify the entry mechanisms and to identify the rate-limiting steps. Because of technical limitations for imaging PTD behavior on cells with conventional fluorescent-dyes, how PTDs enter the cells has been a topic of much debate. Utilizing quantum dots (QDs), we recently tracked the behavior of PTD that was derived from HIV-1 Tat (TatP) in living cells at the single-molecule level with 7-nm special precision. In this review article, we initially summarize the controversy on TatP entry mechanisms; thereafter, we will focus on our recent findings on single-TatP-QD tracking (SQT), to identify the major sequential steps of intracellular delivery in living cells and to discuss how SQT can easily provide direct information on TatP entry mechanisms. As a primer for SQT study, we also discuss the latest findings on single particle tracking of various molecules on the plasma membrane. Finally, we discuss the problems of QDs and the challenges for the future in utilizing currently available QD probes for SQT. In conclusion, direct identification of the rate-limiting steps of PTD entry with SQT should dramatically improve the methods for enhancing transduction efficiency.

Phosphorylation events during viral infections provide potential therapeutic targets

For many medically relevant viruses, there is now considerable evidence that both viral and cellular kinases play important roles in viral infection. Ultimately, these kinases, and the cellular signaling pathways that they exploit, may serve as therapeutic targets for treating patients. Currently, small molecule inhibitors of kinases are under investigation as therapy for herpes viral infections. Additionally, a number of cellular or host-directed tyrosine kinase inhibitors that have been previously FDA approved for cancer treatment are under study in animal models and clinical trials, as they have shown promise for the treatment of various viral infections as well. This review will highlight the wide range of viral proteins phosphorylated by viral and cellular kinases, and the potential for variability of kinase recognition sites within viral substrates to impact phosphorylation and kinase prediction. Research studying kinase-targeting prophylactic and therapeutic treatments for a number of viral infections will also be discussed.

Fractalkine/CX3CL1 protects striatal neurons from synergistic morphine and HIV-1 Tat-induced dendritic losses and death

BACKGROUND

Fractalkine/CX3CL1 and its cognate receptor CX3CR1 are abundantly expressed in the CNS. Fractalkine is an unusual C-X3-C motif chemokine that is important in neuron-microglial communication, a co-receptor for HIV infection, and can be neuroprotective. To assess the effects of fractalkine on opiate-HIV interactive neurotoxicity, wild-type murine striatal neurons were co-cultured with mixed glia from the striata of wild-type or Cx3cr1 knockout mice ± HIV-1 Tat and/or morphine. Time-lapse digital images were continuously recorded at 20 min intervals for up to 72 h using computer-aided microscopy to track the same cells repeatedly.

RESULTS

Co-exposure to Tat and morphine caused synergistic increases in neuron death, dendritic pruning, and microglial motility as previously reported. Exogenous fractalkine prevented synergistic Tat and morphine-induced dendritic losses and neuron death even though the inflammatory mediator TNF-α remained significantly elevated. Antibody blockade of CX3CR1 mimicked the toxic effects of morphine plus Tat, but did not add to their toxicity; while fractalkine failed to protect wild-type neurons co-cultured with Cx3cr1-/--null glia against morphine and Tat toxicity. Exogenous fractalkine also normalized microglial motility, which is elevated by Tat and morphine co-exposure, presumably limiting microglial surveillance that may lead to toxic effects on neurons. Fractalkine immunofluorescence was expressed in neurons and to a lesser extent by other cell types, whereas CX3CR1 immunoreactivity or GFP fluorescence in cells cultured from the striatum of Cx3cr1-/- (Cx3cr1GFP/GFP) mice were associated with microglia. Immunoblotting shows that fractalkine levels were unchanged following Tat and/or morphine exposure and there was no increase in released fractalkine as determined by ELISA. By contrast, CX3CR1 protein levels were markedly downregulated.

CONCLUSIONS

The results suggest that deficits in fractalkine-CX3CR1 signaling contribute to the synergistic neurotoxic effects of opioids and Tat. Importantly, exogenous fractalkine can selectively protect neurons from the injurious effects of chronic opioid-HIV-1 Tat co-exposure, and this suggests a potential therapeutic course for neuroAIDS. Although the cellular mechanisms underlying neuroprotection are not certain, findings that exogenous fractalkine reduces microglial motility and fails to protect neurons co-cultured with Cx3cr1-/- mixed glia suggest that fractalkine may act by interfering with toxic microglial-neuron interactions.

HIV-1-induced alterations of claudin-5 expression at the blood-brain barrier level

HIV-1 crosses the blood-brain barrier (BBB) early in the course of systemic infection and resides in brain macrophages and microglia. The integrity of the brain endothelium is regulated by intercellular tight junctions, which also play a critical role in HIV-1-entry into the brain. Disruption of tight junctions, including changes in claudin-5 expression, is common in HIV-1-infected patients. Recent evidence indicates that both exposure to HIV-1 and HIV-1 specific proteins, such as Tat protein, can contribute to alterations of expression and distribution of claudin-5 in brain endothelial cells and brain microvessels.

The ins and outs of HIV-1 Tat

HIV-1 encodes for the small basic protein Tat (86-101 residues) that drastically enhances the efficiency of viral transcription. The mechanism enabling Tat nuclear import is not yet clear, but studies using reporter proteins fused to the Tat basic domain indicate that Tat could reach the nucleus by passive diffusion. Tat also uses an unusual transcellular transport pathway. The first step of this pathway involves high-affinity binding of Tat to phosphatidylinositol (4,5) bisphosphate (PI(4,5)P(2)), a phospholipid that is concentrated in the inner leaflet of the plasma membrane and enables Tat recruitment at this level. Tat then crosses the plasma membrane to reach the outside medium. Although unconventional, Tat secretion by infected cells is highly active, and export is the major destination for HIV-1 Tat. Secreted Tat can bind to a variety of cell types using several different receptors. Most of them will allow Tat endocytosis. Upon internalization, low endosomal pH triggers a conformational change in Tat that results in membrane insertion. Later steps of Tat translocation to the target-cell cytosol are assisted by Hsp90, a general cytosolic chaperone. Cytosolic Tat can trigger various cell responses. Indeed, accumulating evidence suggests that extracellular Tat acts as a viral toxin that affects the biological activity of different cell types and has a key role in acquired immune-deficiency syndrome development. This review focuses on some of the recently identified molecular details underlying the unusual transcellular transport pathway used by Tat, such as the role of the single Trp in Tat for its membrane insertion and translocation.

Fibroblast Growth Factor-2 and the HIV-1 Tat Protein Synergize in Promoting Bcl-2 Expression and Preventing Endothelial Cell Apoptosis: Implications for the Pathogenesis of AIDS-Associated Kaposi's Sarcoma

Kaposi's sarcoma (KS) is a vascular tumor frequently occurring in Human Immunodeficiency Virus- (HIV-) 1-infected individuals. Our previous work indicated that the angiogenic fibroblast growth factor (FGF)-2 and the Tat protein of HIV-1, both expressed in KS lesions of HIV-infected patients, synergize at inducing angioproliferative, KS-like lesions in mice. Here we show that the development of angioproliferative lesions promoted in mice by combined Tat and FGF-2 associates with an increase in the levels of expression of the antiapoptotic Bcl-2 protein. Upregulation of Bcl-2 expression by combined FGF-2 and Tat occurs also in vitro, and this protects human primary endothelial cells from programmed cell death. As Bcl-2 is expressed in human KS lesions in a fashion paralleling the progression of the disease, these findings suggest a molecular mechanism by which Tat and FGF-2 cooperate in KS maintenance and progression in HIV-infected individuals.

Viruses as key regulators of angiogenesis

Angiogenesis is an important physiological process that is controlled by a precise balance of growth and inhibitory factors in healthy tissues. However, environmental and genetic factors may disturb this delicate balance, resulting in the development of angiogenic diseases, tumour growth and metastasis. During the past decades, extensive research has led to the identification and characterization of genes, proteins and signalling pathways that are involved in neovascularization. Moreover, increasing evidence indicates that viruses may also regulate angiogenesis either directly, by (i) producing viral chemokines, growth factors and/or receptors or (ii) activating blood vessels as a consequence of endothelial cell tropism, or indirectly, by (iii) modulating the activity of cellular proteins and/or (iv) inducing a local or systemic inflammatory response, thereby creating an angiogenic microenvironment. As such, viruses may modulate several signal transduction pathways involved in angiogenesis leading to changes in endothelial cell proliferation, migration, adhesion, vascular permeability and/or protease production. Here, we will review different mechanisms that may be applied by viruses to deregulate the angiogenic balance in healthy tissues and/or increase the angiogenic potential of tumours.

HIV-1 Tat binds to SH3 domains: cellular and viral outcome of Tat/Grb2 interaction

The Src-homology 3 (SH3) domain is one of the most frequent protein recognition modules (PRMs), being represented in signal transduction pathways and in several pathologies such as cancer and AIDS. Grb2 (growth factor receptor-bound protein 2) is an adaptor protein that contains two SH3 domains and is involved in receptor tyrosine kinase (RTK) signal transduction pathways. The HIV-1 transactivator factor Tat is required for viral replication and it has been shown to bind directly or indirectly to several host proteins, deregulating their functions. In this study, we show interaction between the cellular factor Grb2 and the HIV-1 trans-activating protein Tat. The binding is mediated by the proline-rich sequence of Tat and the SH3 domain of Grb2. As the adaptor protein Grb2 participates in a wide variety of signaling pathways, we characterized at least one of the possible downstream effects of the Tat/Grb2 interaction on the well-known IGF-1R/Raf/MAPK cascade. We show that the binding of Tat to Grb2 impairs activation of the Raf/MAPK pathway, while potentiating the PKA/Raf inhibitory pathway. The Tat/Grb2 interaction affects also viral function by inhibiting the Tat-mediated transactivation of HIV-1 LTR and viral replication in infected primary microglia.

Down-regulation of HIV-1 infection by inhibition of the MAPK signaling pathway

The human immunodeficiency virus type 1 (HIV-1) can interact with and exploit the host cellular machinery to replicate and propagate itself. Numerous studies have shown that the Mitogen-activated protein kinase (MAPK) signal pathway can positively regulate the replication of HIV-1, but exactly how each MAPK pathway affects HIV-1 infection and replication is not understood. In this study, we used the Extracellular signal-regulated kinase (ERK) pathway inhibitor, PD98059, the Jun N-terminal kinase (JNK) pathway inhibitor, SP600125, and the p38 pathway inhibitor, SB203580, to investigate the roles of these pathways in HIV-1 replication. We found that application of PD98059 results in a strong VSV-G pseudotyped HIV-1(NL4-3) luciferase reporter virus and HIV-1(NL4-3) virus inhibition activity. In addition, SB203580 and SP600125 also elicited marked VSV-G pseudotyped HIV-1(NL4-3) luciferase reporter virus inhibition activity but no HIV-1(NL4-3) virus inhibition activity. We also found that SB203580 and SP600125 can enhance the HIV-1 inhibition activity of PD98059 when cells were treated with all three MAPK pathway inhibitors in combination. Finally, we show that HIV-1 virus inhibition activity of the MAPK pathway inhibitors was the result of the negative regulation of HIV-1 LTR promoter activity.

Single particle tracking confirms that multivalent Tat protein transduction domain-induced heparan sulfate proteoglycan cross-linkage activates Rac1 for internalization

The mechanism by which HIV-1-Tat protein transduction domain (TatP) enters the cell remains unclear because of an insufficient understanding of the initial kinetics of peptide entry. Here, we report the successful visualization and tracking of TatP molecular kinetics on the cell surface with 7-nm spatial precision using quantum dots. Strong cell binding was only observed with a TatP valence of ≥8, whereas monovalent TatP binding was negligible. The requirement of the cell-surface heparan sulfate (HS) chains of HS proteoglycans (HSPGs) for TatP binding and intracellular transport was demonstrated by the enzymatic removal of HS and simultaneous observation of two individual particles. Multivalent TatP induces HSPG cross-linking, recruiting activated Rac1 to adjacent lipid rafts and thereby enhancing the recruitment of TatP/HSPG to actin-associated microdomains and its internalization by macropinocytosis. These findings clarify the initial binding mechanism of TatP to the cell surface and demonstrate the importance of TatP valence for strong surface binding and signal transduction. Our data also shed light on the ability of TatP to exploit the machinery of living cells, using HSPG signaling to activate Rac1 and alter TatP mobility and internalization. This work should guide the future design of TatP-based peptides as therapeutic nanocarriers with efficient transduction.

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.

Intact lipid rafts regulate HIV-1 Tat protein-induced activation of the Rho signaling and upregulation of P-glycoprotein in brain endothelial cells

The Rho signaling has an essential function in human immunodeficiency virus (HIV)-1-mediated disruption of the integrity of the blood-brain barrier (BBB). However, it is unknown how membrane domains, such as lipid rafts, can influence HIV-1-mediated activation of the Rho pathway and how these processes can affect the expression of the efflux transporters at the BBB level. This study is focused on the function of HIV-1 protein Tat in activation of the Rho signaling and upregulation of P-glycoprotein (P-gp) in human brain endothelial cells. Treatment with Tat markedly elevated GTP-RhoA levels and the potential downstream effectors, such as myosin phosphatase target subunit 1 and myosin light chain. In addition, Tat upregulated expression and promoter activity of P-gp as well as its efflux function. Inhibition of the Rho signaling cascade effectively blocked P-gp overexpression at the level of promoter activity. Disruption of lipid rafts by depletion of membrane cholesterol by methyl-beta-cyclodextrin, but not caveolin-1 silencing, also abolished Tat-mediated RhoA activation and P-gp upregulation. The present data indicate the critical function of intact lipid rafts and the Rho signaling in HIV-1-mediated upregulation of P-gp and potential development of drug resistance in brain endothelial cells.

Inhibition of telomerase activity alters tight junction protein expression and induces transendothelial migration of HIV-1-infected cells

Telomerase, via its catalytic component telomerase reverse transcriptase (TERT), extends telomeres of eukaryotic chromosomes. The importance of this reaction is related to the fact that telomere shortening is a rate-limiting mechanism for human life span that induces cell senescence and contributes to the development of age-related pathologies. The aim of the present study was to evaluate whether the modulation of telomerase activity can influence human immunodeficiency virus type 1 (HIV-1)-mediated dysfunction of human brain endothelial cells (hCMEC/D3 cells) and transendothelial migration of HIV-1-infected cells. Telomerase activity was modulated in hCMEC/D3 cells via small interfering RNA-targeting human TERT (hTERT) or by using a specific pharmacological inhibitor of telomerase, TAG-6. The inhibition of hTERT resulted in the upregulation of HIV-1-induced overexpression of intercellular adhesion molecule-1 via the nuclear factor-kappaB-regulated mechanism and induced the transendothelial migration of HIV-1-infected monocytic U937 cells. In addition, the blocking of hTERT activity potentiated a HIV-induced downregulation of the expression of tight junction proteins. These results were confirmed in TERT-deficient mice injected with HIV-1-specific protein Tat into the cerebral vasculature. Further studies revealed that the upregulation of matrix metalloproteinase-9 is the underlying mechanisms of disruption of tight junction proteins in hCMEC/D3 cells with inhibited TERT and exposed to HIV-1. These results indicate that the senescence of brain endothelial cells may predispose to the HIV-induced upregulation of inflammatory mediators and the disruption of the barrier function at the level of the brain endothelium.

Sequence alignment reveals possible MAPK docking motifs on HIV proteins

Over the course of HIV infection, virus replication is facilitated by the phosphorylation of HIV proteins by human ERK1 and ERK2 mitogen-activated protein kinases (MAPKs). MAPKs are known to phosphorylate their substrates by first binding with them at a docking site. Docking site interactions could be viable drug targets because the sequences guiding them are more specific than phosphorylation consensus sites. In this study we use multiple bioinformatics tools to discover candidate MAPK docking site motifs on HIV proteins known to be phosphorylated by MAPKs, and we discuss the possibility of targeting docking sites with drugs. Using sequence alignments of HIV proteins of different subtypes, we show that MAPK docking patterns previously described for human proteins appear on the HIV matrix, Tat, and Vif proteins in a strain dependent manner, but are absent from HIV Rev and appear on all HIV Nef strains. We revise the regular expressions of previously annotated MAPK docking patterns in order to provide a subtype independent motif that annotates all HIV proteins. One revision is based on a documented human variant of one of the substrate docking motifs, and the other reduces the number of required basic amino acids in the standard docking motifs from two to one. The proposed patterns are shown to be consistent with in silico docking between ERK1 and the HIV matrix protein. The motif usage on HIV proteins is sufficiently different from human proteins in amino acid sequence similarity to allow for HIV specific targeting using small-molecule drugs.

Functions of Tat: the versatile protein of human immunodeficiency virus type 1

Human immunodeficiency virus type 1 (HIV-1) Tat is a multifunctional protein that contributes to several pathological symptoms of HIV-1 infection as well as playing a critical role in virus replication. Tat is a robust transactivating protein that induces a variety of effects by altering the expression levels of cellular and viral genes. The functions of Tat are therefore primarily related to its role in modulation of gene expression. In this review the functions of HIV-1 Tat that have been well documented, as well as a number of novel functions that have been proposed for this protein, are discussed. Since some of the functions of Tat vary in different cell types in a concentration-dependent manner and because Tat sometimes exerts the same activity through different pathways, study of this protein has at times yielded conflicting and controversial results. Due to its pivotal role in viral replication and in disease pathogenesis, Tat and the cellular pathways targeted by Tat are potential targets for new anti-HIV drugs.

Proteomic characterization of HIV-modulated membrane receptors, kinases and signaling proteins involved in novel angiogenic pathways

Background

Kaposi's sarcoma (KS), hemangioma, and other angioproliferative diseases are highly prevalent in HIV-infected individuals. While KS is etiologically linked to the human herpesvirus-8 (HHV8) infection, HIV-patients without HHV-8 and those infected with unrelated viruses also develop angiopathies. Further, HIV-Tat can activate protein-tyrosine-kinase (PTK-activity) of the vascular endothelial growth factor receptor involved in stimulating angiogenic processes. However, Tat by itself or HHV8-genes alone cannot induce angiogenesis in vivo unless specific proteins/enzymes are produced synchronously by different cell-types. We therefore tested a hypothesis that chronic HIV-replication in non-endothelial cells may produce novel factors that provoke angiogenic pathways.

Methods

Genome-wide proteins from HIV-infected and uninfected T-lymphocytes were tested by subtractive proteomics analyses at various stages of virus and cell growth in vitro over a period of two years. Several thousand differentially regulated proteins were identified by mass spectrometry (MS) and >200 proteins were confirmed in multiple gels. Each protein was scrutinized extensively by protein-interaction-pathways, bioinformatics, and statistical analyses.

Results

By functional categorization, 31 proteins were identified to be associated with various signaling events involved in angiogenesis. 88% proteins were located in the plasma membrane or extracellular matrix and >90% were found to be essential for regeneration, neovascularization and angiogenic processes during embryonic development.

Conclusion

Chronic HIV-infection of T-cells produces membrane receptor-PTKs, serine-threonine kinases, growth factors, adhesion molecules and many diffusible signaling proteins that have not been previously reported in HIV-infected cells. Each protein has been associated with endothelial cell-growth, morphogenesis, sprouting, microvessel-formation and other biological processes involved in angiogenesis (p = 10^-4 to 10^-12). Bioinformatics analyses suggest that overproduction of PTKs and other kinases in HIV-infected cells has suppressed VEGF/VEGFR-PTK expression and promoted VEGFR-independent pathways. This unique mechanism is similar to that observed in neovascularization and angiogenesis during embryogenesis. Validation of clinically relevant proteins by gene-silencing and translational studies in vivo would identify specific targets that can be used for early diagnosis of angiogenic disorders and future development of inhibitors of angiopathies. This is the first comprehensive study to demonstrate that HIV-infection alone, without any co-infection or treatment, can induce numerous "embryonic" proteins and kinases capable of generating novel VEGF-independent angiogenic pathways.

Coxsackie adenovirus receptor (CAR) regulates integrin function through activation of p44/42 MAPK

The coxsackie B virus and adenovirus receptor (CAR) is an attachment receptor for Adenovirus serotype 5 (Ad5) and in many cell types forms homodimers with neighbouring cells as part of a cell adhesion complex. CAR co-operates with cell surface integrin receptors to enable efficient viral entry, but little is known about the mechanism of crosstalk between these two receptor types. Here we show that overexpression of CAR in human epithelial cells leads to increased basal activation of p44/42 MAPK and this is required for efficient Ad5 infection. We demonstrate that CAR forms homodimers in cis and that this dimerisation is enhanced in the presence of Ad5 in a phospho-p44/42-dependent manner. CAR-induced p44/42 activation also leads to increased activation of beta1 and beta3 integrins. Analysis of CAR mutants demonstrates that the cyto domain of CAR is required for CAR-induced p44/42 activation, integrin activation and localisation to cell junctions. This data for the first time demonstrates that signalling downstream of CAR can have a dual effect on integrins and CAR itself in order to promote efficient viral binding to cell membranes.

Glioma-associated endothelial cells are chemoresistant to temozolomide

Temozolomide is considered the standard of care and drug of choice for the treatment of initially diagnosed malignant gliomas. Although well tolerated, temozolomide still has limited clinical efficacy. Following drug treatment, patient prognosis still remains poor; tumor recurrence is almost universal. We hypothesized that this lack of effectiveness with temozolomide is because this drug does not target the glioma microenvironment, which is highly vascular in malignant gliomas. To test this hypothesis we analyzed the effects of temozolomide on the tumor vasculature in vitro and in vivo. We found that this drug did not affect the viability or proliferation rate of endothelial cells isolated from human glioma specimens, although temozolomide was highly cytotoxic to the glioma cell lines U87MG and U251. Furthermore, temozolomide did not inhibit the migration of these glioma-associated endothelial cells, a key mechanism responsible for tumor angiogenesis. In in vivo studies, using the intracranial glioma mouse model, temozolomide did not cause a pronounced effect on microvessel density. Our findings show that temozolomide has no apparent effect on the glioma vascular microenvironment. Thus combination therapy with anti-vascular agents may enhance temozolomide effectiveness as glioma therapeutic protocol.

RNA viruses and the mitogenic Raf/MEK/ERK signal transduction cascade

The Raf/MEK/ERK signal transduction cascade belongs to the mitogen-activated protein kinase (MAPK) cascades. Raf/MEK/ERK signaling leads to stimulus-specific changes in gene expression, alterations in cell metabolism or induction of programmed cell death (apoptosis), and thus controls cell differentiation and proliferation. It is induced by extracellular agents, including pathogens such as RNA viruses. Many DNA viruses are known to induce cellular signaling via this pathway. As these pathogens partly use the DNA synthesis machinery for their replication, they aim to drive cells into a proliferative state. In contrast, the consequences of RNA virus-induced Raf/MEK/ERK signaling were less clear for a long time, but since the turn of the century the number of publications on this topic has rapidly increased. Research on this virus/host-interaction will broaden our understanding of its relevance in viral replication. This important control center of cellular responses is differently employed to support the replication of several important human pathogenic RNA viruses including influenza, Ebola, hepatitis C and SARS corona viruses.

Molecular mechanism(s) involved in the synergistic induction of CXCL10 by human immunodeficiency virus type 1 Tat and interferon-gamma in macrophages

Synergistic interactions between viral proteins and soluble host factors released from infected mononuclear phagocytes play a critical role in the pathogenesis of human immunodeficiency virus (HIV)-associated dementia (HAD). The chemokine CXCL10 has been found to be closely associated with the progression of HIV-1-related central nervous system (CNS) disease and its related neuropsychiatric impairment. In this report the authors demonstrate that the HIV-1 protein Tat can interact with the proinflammatory cytokine interferon (IFN)-gamma to dramatically induce the expression of CXCL10 in macrophages. Synergistic induction of CXCL10 by both Tat and IFN-gamma was susceptible to inhibition by the MEK1/2 inhibitor U0126 and the p38 mitogen-activated protein kinase (MAPK) inhibitor SB203580. In addition, JAK/STAT pathway plays a major role in Tat/gamma-mediated CXCL10 induction in macrophages because pretreatment of stimulated macrophages with JAK inhibitor completely abrogated the synergistic induction of the chemokine. Functionality of the synergistically induced CXCL10 was further demonstrated by its chemotactic activity for peripheral blood lymphocytes. Taken together, these findings demonstrate that the cooperative interaction of Tat and IFN-gamma results in enhanced chemokine expression, which in turn can amplify the inflammatory responses within the CNS of HAD patients by recruiting more lymphocytes in the brain.

Caveolin-1 regulates human immunodeficiency virus-1 Tat-induced alterations of tight junction protein expression via modulation of the Ras signaling

The blood-brain barrier (BBB) is the critical structure for preventing human immunodeficiency virus (HIV) trafficking into the brain. Specific HIV proteins, such as Tat protein, can contribute to the dysfunction of tight junctions at the BBB and HIV entry into the brain. Tat is released by HIV-1-infected cells and can interact with a variety of cell surface receptors activating several signal transduction pathways, including those localized in caveolae. The present study focused on the mechanisms of Tat-induced caveolae-associated Ras signaling at the level of the BBB. Treatment with Tat activated the Ras pathway in human brain microvascular endothelial cells (HBMECs). However, caveolin-1 silencing markedly attenuated these effects. Because the integrity of the brain endothelium is regulated by intercellular tight junctions, these structural elements of the BBB were also evaluated in the present study. Exposure to Tat diminished the expression of several tight junction proteins, namely, occludin, zonula occludens (ZO)-1, and ZO-2 in the caveolar fraction of HBMECs. These effects were effectively protected by pharmacological inhibition of the Ras signaling and by silencing of caveolin-1. The present data indicate the importance of caveolae-associated signaling in the disruption of tight junctions on Tat exposure. They also demonstrate that caveolin-1 may constitute an early and critical modulator that controls signaling pathways leading to the disruption of tight junction proteins. Thus, caveolin-1 may provide an effective target to protect against Tat-induced HBMEC dysfunction and the disruption of the BBB in HIV-1-infected patients.