Cellular and viral oncogenes: the key to unlocking unknowns of Kaposi's sarcoma-associated herpesvirus pathogenesis.

Oncogenic viruses carry an extensive arsenal of oncogenes for hijacking cellular pathways. Notably, variations in oncogenes among tumor-producing viruses give rise to different mechanisms for cellular transformation. Specifically, Kaposi's sarcoma-associated herpesvirus (KSHV) is an oncogenic virus able to infect and transform a variety of cell types. The oncogenicity of KSHV disseminates from the virus' ability to induce and encode a wide variety of both cellular and viral oncogenes. Such an array of cellular and viral oncogenes enables KSHV to induce the malignant phenotype of a KSHV-associated cancer. Evolutionarily, KSHV has acquired many oncogenic homologues capable of inducing cell proliferation, cell differentiation, cell survival, and immune evasion. Integration between inducing and encoding oncogenes plays a vital role in KSHV pathogenicity. KSHV is alleged to harbor the highest number of potential oncogenes by which a virus promotes cellular transformation and malignancy. Many KSHV inducing/encoding oncogenes are mainly expressed during the latent phase of KSHV infection, a period required for virus establishment of malignant cellular transformation. Elucidation of the exact mechanism(s) by which oncogenes promote KSHV pathogenicity would not only give rise to potential novel therapeutic targets/drugs but would also add to our understanding of cancer biology. The scope of this review is to examine the roles of the most important cellular and viral oncogenes involved in KSHV pathogenicity.

Bone Mineral Density and Vitamin D Levels in HIV Treatment-Naïve African American Individuals Randomized to Receive HIV Drug Regimens.

OBJECTIVES: Treatment of human immunodeficiency virus (HIV)-infected patients with tenofovir disoproxil fumarate is associated with a decrease in bone mineral density (BMD). Treatment with efavirenz is associated with vitamin D deficiency. We compared the effects of efavirenz, emtricitabine, and tenofovir disoproxil fumarate (EFV/FTC/TDF) with the effects of raltegravir, darunavir, and ritonavir (RAL/DRV/r) on BMD and 25-hydroxyvitamin D (25[OH]D) levels in HIV-infected, antiretroviral treatment-naïve African American subjects. METHODS: This was a pilot study at a single HIV clinic. Forty HIV treatment-naïve African American subjects were screened, 35 of whom were randomized to receive either EFV/FTC/TDF or RAL/DRV/r. All of the subjects received supplemental vitamin D3 and calcium. CD4 counts, HIV RNA, parathyroid hormone, osteocalcin, N-telopeptide, and 25(OH)D levels were obtained at baseline and at 8, 24, 36, and 48 weeks. Dual-energy x-ray absorptiometry of the spine and hip was performed at baseline and at week 48. RESULTS: Of the 35 subjects enrolled, 10 patients receiving each regimen completed the study. Median baseline 25(OH)D levels were decreased and similar in both groups. All of the patients had plasma HIV RNA <50 copies per milliliter by week 24. By week 48, there was a sustained increase in 25(OH)D in the RAL/DRV/r group (P = 0.0004) but not in the EFV/FTC/TDF group (P = 0.78). There were reductions in BMD of the mean total hip (P = 0.002) and the mean femoral neck (P = 0.004) in the EFV/FTC/TDF group but not in the RAL/DRV/r group. CONCLUSIONS: Treatment of African American patients with HIV using EFV/FTC/TDF is associated with a reduction in BMD of the hip and sustained reductions of 25(OH)D not seen in the group that received RAL/DRV/r. This phenomenon may have long-term consequences on bone integrity in this population.

KSHV gB associated RGD interactions promote attachment of cells by inhibiting the potential migratory signals induced by the disintegrin-like domain.

BACKGROUND: Kaposi's sarcoma-associated herpesvirus (KSHV) glycoprotein B (gB) is not only expressed on the envelope of mature virions but also on the surfaces of cells undergoing lytic replication. Among herpesviruses, KSHV gB is the only glycoprotein known to possess the RGD (Arg-Gly-Asp) binding integrin domain critical to mediating cell attachment. Recent studies described gB to also possess a disintegrin-like domain (DLD) said to interact with non-RGD binding integrins. We wanted to decipher the roles of two individually distinct integrin binding domains (RGD versus DLD) within KSHV gB in regulating attachment of cells over cell migration. METHODS: We established HeLa cells expressing recombinant full length gB, gB lacking a functional RGD (gBΔR), and gB lacking a functionally intact DLD (gBΔD) on their cell surfaces. These cells were tested in wound healing assay, Transwell migration assay, and adhesion assay to monitor the ability of the RGD and DLD integrin recognition motifs in gB to mediate migration and attachment of cells. We also used soluble forms of the respective gB recombinant proteins to analyze and confirm their effect on migration and attachment of cells. The results from the above studies were authenticated by the use of imaging, and standard biochemical approaches as Western blotting and RNA silencing using small interfering RNA. RESULTS: The present report provides the following novel findings: (i) gB does not induce cell migration; (ii) RGD domain in KSHV gB is the switch that inhibits the ability of DLD to induce cellular migration thus promoting attachment of cells. CONCLUSIONS: Independently, RGD interactions mediate attachment of cells while DLD interactions regulate migration of cells. However, when both RGD and DLD are functionally present in the same protein, gB, the RGD interaction-induced attachment of cells overshadows the ability of DLD mediated signaling to induce migration of cells. Furthering our understanding of the molecular mechanism of integrin engagement with RGD and DLD motifs within gB could identify promising new therapeutic avenues and research areas to explore.

Subcellular fractionation method to study endosomal trafficking of Kaposi's sarcoma-associated herpesvirus.

BACKGROUND: Virus entry involves multiple steps and is a highly orchestrated process on which successful infection collectively depends. Entry processes are commonly analyzed by monitoring internalized virus particles via Western blotting, polymerase chain reaction, and imaging techniques that allow scientist to track the intracellular location of the pathogen. Such studies have provided abundant direct evidence on how viruses interact with receptor molecules on the cell surface, induce cell signaling at the point of initial contact with the cell to facilitate internalization, and exploit existing endocytic mechanisms of the cell for their ultimate infectious agenda. However, there is dearth of knowledge in regards to trafficking of a virus via endosomes. Herein, we describe an optimized laboratory procedure to isolate individual organelles during different stages of endocytosis by performing subcellular fractionation. This methodology is established using Kaposi's sarcoma-associated herpesvirus (KSHV) infection of human foreskin fibroblast (HFF) cells as a model. With KSHV and other herpesviruses alike, envelope glycoproteins have been widely reported to physically engage target cell surface receptors, such as integrins, in interactions leading to entry and subsequent infection. RESULTS: Subcellular fractionation was used to isolate early and late endosomes (EEs and LEs) by performing a series of centrifugations steps. Specifically, a centrifugation step post-homogenization was utilized to obtain the post-nuclear supernatant containing intact intracellular organelles in suspension. Successive fractionation via sucrose density gradient centrifugation was performed to isolate specific organelles including EEs and LEs. Intracellular KSHV trafficking was directly traced in the isolated endosomal fractions. Additionally, the subcellular fractionation approach demonstrates a key role for integrins in the endosomal trafficking of KSHV. The results obtained from fractionation studies corroborated those obtained by traditional imaging studies. CONCLUSIONS: This study is the first of its kind to employ a sucrose flotation gradient assay to map intracellular KSHV trafficking in HFF cells. We are confident that such an approach will serve as a powerful tool to directly study intracellular trafficking of a virus, signaling events occurring on endosomal membranes, and dynamics of molecular events within endosomes that are crucial for uncoating and virus escape into the cytosol.

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.

Disintegrin-like domain of glycoprotein B regulates Kaposi's sarcoma-associated herpesvirus infection of cells.

Kaposi's sarcoma-associated herpesvirus (KSHV) glycoprotein B (gB) is a lytic structural protein expressed on the envelope of mature virions and on the membrane of cells supporting lytic infection. In addition to this viral glycoprotein's interaction with integrins via its RGD (Arg-Gly-Asp) motif, KSHV gB possesses a disintegrin-like domain (DLD), which binds integrins as well. Prior to this study, there has been minimal research involving the less common integrin-binding motif, DLD, of gB as it pertains to herpesvirus infection. By using phage display peptide library screening and molecular biology techniques, the DLD of KSHV gB was shown to interact specifically with non-RGD binding α9ß1 integrins. Similarly, monitoring wild-type infection confirmed α9ß1:DLD interactions to be critical to successful KSHV infection of human foreskin fibroblast (HFF) cells and human dermal microvascular endothelial cells (HMVEC-d) compared with 293 cells. To further demonstrate the importance of the DLD of gB in KSHV infection, two recombinant virus constructs were generated using a bacterial artificial chromosome (BAC) system harbouring the KSHV genome (BAC36): BAC36ΔD-KSHV (lacking a functionally intact DLD of gB and containing an introduced tetracycline cassette) and BAC36.T-KSHV (containing an intact DLD sequence and an introduced tetracycline cassette). Accordingly, BAC36ΔD-KSHV presented significantly lower infection rates in HFF and HMVEC-d cells compared with the comparable infection rates achieved by wild-type BAC36-KSHV and BAC36.T-KSHV. Thus, the present report has delineated a critical role for the DLD of gB in KSHV infection, which may lead to a broader knowledge regarding the sophisticated mechanisms utilized by virus-encoded structural proteins in KSHV entry and infection.

Resveratrol inhibits KSHV reactivation by lowering the levels of cellular EGR-1.

In the field of herpesvirus research, the exact molecular mechanism by which such viruses reactivate from latency remains elusive. Kaposi's sarcoma-associated herpesvirus (KSHV) primarily exists in a latent state, while only 1-3% of cells support lytic infection at any specific time. KSHV reactivation from latency is an exceedingly intricate process mediated by the integration of viral and cellular factors. Previously, our lab has described early growth response-1 (Egr-1) as an essential component for the KSHV reactivation process via its ability to mediate transcription of KSHV ORF50, the gene encoding for replication and transcription activator (RTA), a viral component known to control the switch from latent to lytic infection. In here, electrophoretic mobility shift assays (EMSA) and chromatin immunoprecipitation (ChIP) experiments revealed that Egr-1 binds KSHV ORF50 promoter (ORF50P) in at least two different GC-rich binding domains. Expression profiles of cellular egr-1 and KSHV-encoded ORF50 follow a similar pattern during de novo KSHV infection. Over-expressing Egr-1, a signaling component downstream of Raf>MEK>ERK1/2, in KSHV-infected cells activates KSHV lytic replication. Through performing more physiologically relevant experiments, we analyzed the effect of a dietary supplement containing resveratrol on KSHV-infected cells. Our results, for the first time, demonstrate resveratrol to act in lowering ERK1/2 activity and expression of Egr-1 in KSHV-infected cells, resulting in the suppression of virus reactivation from latency. Taken together, these findings will undoubtedly contribute to future studies on not only combating KSHV related disease conditions, but also on other herpesviruses-induced pathogenesis.

Virus reactivation: a panoramic view in human infections.

Viruses are obligate intracellular parasites, relying to a major extent on the host cell for replication. An active replication of the viral genome results in a lytic infection characterized by the release of new progeny virus particles, often upon the lysis of the host cell. Another mode of virus infection is the latent phase, where the virus is 'quiescent' (a state in which the virus is not replicating). A combination of these stages, where virus replication involves stages of both silent and productive infection without rapidly killing or even producing excessive damage to the host cells, falls under the umbrella of a persistent infection. Reactivation is the process by which a latent virus switches to a lytic phase of replication. Reactivation may be provoked by a combination of external and/or internal cellular stimuli. Understanding this mechanism is essential in developing future therapeutic agents against viral infection and subsequent disease. This article examines the published literature and current knowledge regarding the viral and cellular proteins that may play a role in viral reactivation. The focus of the article is on those viruses known to cause latent infections, which include herpes simplex virus, varicella zoster virus, Epstein-Barr virus, human cytomegalovirus, human herpesvirus 6, human herpesvirus 7, Kaposi's sarcoma-associated herpesvirus, JC virus, BK virus, parvovirus and adenovirus.