Transformation Of Infected Cells Research Articles

Alternative RNA splicing in cancer: what about adult T-cell leukemia?

Eukaryotic cells employ a broad range of mechanisms to regulate gene expression. Among others, mRNA alternative splicing is a key process. It consists of introns removal from an immature mRNA (pre-mRNA) via a transesterification reaction to create a mature mRNA molecule. Large-scale genomic studies have shown that in the human genome, almost 95% of protein-encoding genes go through alternative splicing and produce transcripts with different exons combinations (and sometimes retained introns), thus increasing the proteome diversity. Considering the importance of RNA regulation in cellular proliferation, survival, and differentiation, alterations in the alternative splicing pathway have been linked to several human cancers, including adult T-cell leukemia/lymphoma (ATL). ATL is an aggressive and fatal malignancy caused by the Human T-cell leukemia virus type 1 (HTLV-1). HTLV-1 genome encodes for two oncoproteins: Tax and HBZ, both playing significant roles in the transformation of infected cells and ATL onset. Here, we review current knowledge on alternative splicing and its link to cancers and reflect on how dysregulation of this pathway could participate in HTLV-1-induced cellular transformation and adult T-cell leukemia/lymphoma development.

NF-κB and MicroRNA Deregulation Mediated by HTLV-1 Tax and HBZ.

The risk of developing adult T-cell leukemia/lymphoma (ATLL) in individuals infected with human T-cell lymphotropic virus 1 (HTLV-1) is about 3–5%. The mechanisms by which the virus triggers this aggressive cancer are still an area of intensive investigation. The viral protein Tax-1, together with additional regulatory proteins, in particular HTLV-1 basic leucine zipper factor (HBZ), are recognized as relevant viral factors required for both viral replication and transformation of infected cells. Tax-1 deregulates several cellular pathways affecting the cell cycle, survival, and proliferation. The effects of Tax-1 on the NF-κB pathway have been thoroughly studied. Recent studies also revealed the impact of Tax-1 and HBZ on microRNA expression. In this review, we summarize the recent progress in understanding the contribution of HTLV-1 Tax- and HBZ-mediated deregulation of NF-κB and the microRNA regulatory network to HTLV-1 pathogenesis.

Transformation of Primary Conjunctival Cells Transfected with Papilloma and Herpesvirus Oncogenes

<p class="cco-body"><span lang="EN-GB">Ocular surface squamous neoplasia (OSSN) is a common cancer that has recently increased in incidence in HIV-1 infected patients. The rise has been more transparent in sub-Sahara Africa. Our recent publications showed the association of OSSN with multiple viral, bacterial and parasitic infections. Here we show through transfection with different viral constructs, the changes taking place in the primary conjunctival cells which involve some of the important markers associated with initiation and maintenance of the cancer.</span></p><p class="cco-body"><span lang="EN-GB">We transfected primary conjunctival cells with different oncogenic viral genes (HPV16-E6, HPV16-E7, HPV16-E6/E7, KSHV-LANA, and EBV-EBNA1) that have been associated with transformation of infected cells. The cells were tested for expression of different markers linked to oncogenesis. We used RT PCR to determine the expression of the markers. The level of expression was determined in each case. We also performed immunohistochemistry (IHC) on the primary cells using specific antibodies.</span></p><p class="cco-body"><span lang="EN-GB">The transfected conjunctival cells were demonstrated to be epitheliod as determined by expression of Cytokeratin-19 (C-19) and Vimentin markers. The primary conjunctival cells were efficiently transfected with the specific viral oncogenes resulting in expression of different cytokines, chemokine, cell cycle markers, and growth factors. The different constructs elicited expression and/or suppression of p53, p21, pRB, IL-10, IL-13, cyclinD1, TNF, TNF13B, and VEGF in specific transfected conjunctival primary cells. </span></p><p class="cco-body"><span lang="EN-GB">Our findings indicate that the viral oncogene expression in primary conjunctival cells contributed to the production of inflammatory cytokines, chemokines and dysregulation of cell cycle proteins in primary conjunctival tissues. This mirrors the transformation process in OSSN pathogenesis. Further studies should follow to identify pathways dysregulated that can be targeted for therapy or vaccine development. </span></p>

Examination of the interactions between the HTLV-1-encoded Tax oncoprotein and the cellular coactivators CBP/p300

Human T-cell Leukemia virus type-1 (HTLV-1) causes several diseases including aggressive Adult T-cell Leukemia (ATL). A major player in the malignant transformation of infected cells is expression of Tax, the virally-encoded oncoprotein. Tax is a potent activator of HTLV-1 transcription. To activate viral transcription, Tax, together with the cellular protein CREB, bind to the viral CRE enhancer elements located in the HTLV-1 promoter. Together, these activators recruit the homologous coactivator proteins CBP to initiate strong transcription of the provirus. Both CBP/p300 are involved in multiple cellular pathways, and deregulation of these proteins is associated with numerous pathologies. Despite extensive work on Tax-stimulated recruitment of CBP/p300 to the HTLV-1 promoter, primarily via their KIX domain, potential interactions between Tax and other domains of CBP/p300 have not been fully investigated. Recently, we have found that Tax interacts with several additional domains of the coactivators, however the significance of these interactions remains incompletely understood. We hypothesize that Tax interaction with various domains of CBP/p300 stimulates the potency of the coactivators and enhanced transcription. Our studies utilize protein-protein and protein-DNA interaction assays using individual domains of the coactivators, together with mutations and deletions that specifically target the Tax-CBP/p300 interface. Competition and activity assays enable us to functionally and biophysically characterize Tax-coactivator interactions. These studies have implications for both viral and cellular mechanisms of gene expression, and expand our understanding of the role of Tax and the cellular coactivators in HTLV-1 transcription and replication.

Molecular and Cellular Mechanism of Leukemogenesis of ATL: Emergent Evidence of a Significant Role for HBZ in HTLV-1-Induced Pathogenesis

Adult T-cell leukemia (ATL) is a leukemia derived from mature CD4+ T cells and induced by human T-cell leukemia virus type 1 (HTLV-1) infection. Previous studies have revealed many possible molecular and cellular mechanisms of HTLV-1-induced leukemogenesis, but it still remains unknown how HTLV-1 transforms peripheral CD4 T cells in infected individuals. Given the fact that only 2–5% of infected individuals develop ATL, HTLV-1 infection alone is not sufficient for the transformation of infected cells. Host genetic and epigenetic abnormalities and host immunological status should be considered in attempting to understand the mechanism of the oncogenesis of ATL. Nonetheless, it is obvious that HTLV-1 infection dramatically increases the risk of leukemia generation from peripheral CD4 T-cells, in which the incidence of leukemia is quite low. Furthermore, the evidence that all ATL cases retain the HTLV-1 provirus, especially the 3′ region, indicates that HTLV-1-encoded genes play a critical role in leukemogenesis. Since increasing evidence indicates that the HTLV-1 bZIP factor (HBZ) gene plays a significant role in the pathogenesis of HTLV-1, we will discuss the cellular and molecular mechanism of ATL generation from the virological point of view, particularly focusing on HBZ.

Features of HTLV-1 transcriptional and chromatin remodeling dynamics emerge from ChIP-chip analysis

Human T-lymphotropic virus type 1 (HTLV-1) is the etiological agent of adult T cell leukemia (ATL), a lymphoproliferative disease that primarily affects CD4+ T cells. Cellular transformation of infected cells is mediated through Tax, a multifaceted viral-encoded transactivator protein, which exerts regulatory effects in gene expression and cell cycle dysregulation. Vast differential cellular gene expression changes have been documented in the presence of Tax. We have performed ChIP-chip experiments and confirmation of gene expression dysregulation in uninfected and infected cell lines and performed analysis on selected microarray data from published literature (Tesi cells). We have characterized the resulting changes into seven categories according to the absence or presence of transcriptional machinery and core chromatin remodeling complex components RNA polymerase II (Pol II), CREB, BRG1, NFκB, and Tax, on the HTLV-1 long terminal repeat (LTR). Our data set suggests that gene expression regulation upon infection results in activation, de-repression, suppression (elongation block), suppression (block in factor occupancy), suppression (initiation block) and possible Pol II-independent gene expression in the presence of Tax. We have previously shown the essential Tax-BRG1 interaction for Tax transactivation and viral production, and that additional recruitment of transcriptional machinery and chromatin remodeling complexes to the viral LTR results in differential gene modulation.

The Human T-Cell Leukemia Virus Type 1 Oncoprotein Tax Controls Forkhead Box O4 Activity through Degradation by the Proteasome

Activation of the phosphatidylinositol 3-kinase (PI3K)/protein kinase B (Akt) signaling pathway by the viral Tax oncoprotein plays a pivotal role in clonal expansion of human T-cell leukemia virus type 1 (HTLV-1)-infected cells. As the Forkhead box O (FoxO) tumor suppressors act as downstream effectors of PI3K/Akt, they represent good candidate targets whose dysregulation by Tax might be involved in HTLV-1-mediated activation and transformation of infected cells. In this report, we provide evidence showing that Tax induces a dose-dependent degradation of FoxO4 by the ubiquitin-proteasome pathway. Consistent with that, we demonstrate that Tax expression increases the interaction between FoxO4 and Mdm2 E3 ligase, leading to a strong FoxO4 polyubiquitination. These processes require the phosphorylation of FoxO4 by Akt, since a mutant of FoxO4 with mutations on its three Akt phosphorylation sites appears to be resistant to Tax-mediated degradation and ubiquitination. In addition, we show that Tax expression is associated with degradation and phosphorylation of endogenous FoxO4 in Jurkat T cells. Finally, we demonstrate that Tax represses FoxO4 transcriptional activity. Our study demonstrates that Tax can control FoxO4 protein stability and transcriptional activity and provides new insight into the subversion of cell signaling pathways during HTLV-1 infection.

Aspects virologiques et carcinologiques des papillomavirus humains HPV

Human papillomaviruses are small viruses belonging to the Papillomaviridae. More than 100 genotypes have been identified, causing benign (low-risk HPV) or malignant (high-risk HPV) cutaneous or mucosal lesions. The low-risk HPV6 and HPV11 provoke genital warts, while the high-risk HPV16 and HPV18 can cause cervical cancer. The HPVgenome includes several open reading frames that encode proteins involved in viral DNA replication (E1 and E2), viral gene expression regulation (E2), virus assembly (E4) and the immortalisation and transformation of infected epithelial cells (E5, E6 and E7; high-risk HPV only). The open reading frames L1 and L2 encode the two capsid proteins. HPV target stem cells of the squamous epithelium. The complete life cycle involves three phases, with sequential expression of viral genes leading to viral DNA replication and to the production of highly infectious virions. Viral DNA integration occurs with high-risk types and leads to the overexpression of two viral oncoproteins, E6 and E7. These proteins, in combination with E5, promote the immortalisation and transformation of infected cells.

Hepatitis C and B virus infection in Chinese patients with extrahepatic bile duct carcinoma

Objective In China, the incidence of extrahepatic bile duct carcinoma (EBDC) tends to increase over the past decades. The etiology of the noted increase in EBDC is not identified. Approximately, in a half of the overall Chinese patients with EBDC, the causative factors in the development of EBDC have not been demonstrated. There is a high prevalence of hepatitis C virus (HCV) or hepatitis B virus (HBV) in China, both of which can induce malignant transformation of infected cells and strongly associated with hepatocellular carcinoma (HCC). In this study, EBDC tissues from Chinese patients were examined for the presence of HCV and HBV infection to investigate further the potential causes of EBDC.

HTLV-1 proviruses encoding non-functional TAX in adult T-cell leukemia.

Adult T-cell leukemia (ATL) is associated with prior infection with human T-cell leukemia virus type 1 (HTLV-1). TAX, the major transactivator of HTLV-1, has been implicated in the immortalization of infected T-cells, but molecular mechanisms of in vivo malignant cell transformation induced by HTLV-1 remain unclear. To investigate the role of TAX in the monoclonal proliferation of ATL cells, we determined the nucleotide sequence of tax DNA clones obtained from 6 ATL patients and analysed the biological function of their products. We found that ATL cells from 2 of these patients possessed tax with a nonsense or frame-shift mutation resulting in the premature termination of its protein product, which was no longer functional. This strongly argued against an indispensable role of TAX for the maintenance of ATL cells in vivo. On the other hand, the frequency of nucleotide substitutions found in non-functional tax DNA clones from these patients was significantly lower than those in functional tax DNA clones from the others, suggesting a role for TAX in the genome instability of infected cells. Although mismatch repair defects in the microsatellite markers, including those in hMSH3, hMSH6, BAX, TGF-beta RII, and E2F4 genes, were infrequent, we found an increase in the number of CAG repeats of the E2F4 microsatellite marker in 1 patient. These findings indicate that while TAX may be a necessary prerequisite for malignant transformation of infected cells, it is not essential for the maintenance of ATL cells in vivo.

Defective DNA repair in cells with human T-cell leukemia/bovine leukemia viruses: role of tax gene.

Human T-cell leukemia virus (HTLV)/bovine leukemia virus (BLV) group retroviruses, which cause hematopoietic cancers, encode a unique protein, Tax, involved in the transformation of infected cells. Our purpose was to determine whether the mechanism by which Tax protein induces transformation in HTLV- or BLV-infected cells involves DNA damage. We used a micronucleus assay to measure chromosomal damage and alkali denaturation analysis to test host-cell DNA integrity in cells infected with HTLV, BLV, or simian T-lymphotropic virus or in cells transfected with the tax gene of HTLV or BLV. Controls included uninfected cells and cells infected with other oncogenic retroviruses or oncogenic DNA viruses. We used a plasmid reactivation assay to examine whether the damage might be due to the inhibition of DNA repair. To ascertain which of several repair pathways might be inhibited, chemical methods were used to selectively introduce lesions repaired by specific pathways into the reporter plasmid. The presence of Tax was associated with DNA damage. HTLV- or BLV-infected or tax-transfected cells showed normal ability to repair damage induced by deoxyribonuclease I or psoralen but markedly decreased ability to repair damage induced by UV light, quercetin, or hydrogen peroxide. These data suggest that the DNA repair pathway most inhibited by Tax is base-excision repair of oxidative damage. To our knowledge, this is the first report demonstrating inhibition of DNA repair by any retrovirus and suggests that this inhibition of DNA repair may contribute to the mechanism of cell transformation by the HTLV/BLV group of viruses.

Genital Infection With Type 2 Herpes Simplex Virus

Current evidence leaves little doubt that genital herpes is primarily a venereal disease. Like gonorrhea, it is frequently subclinical or asymptomatic. A high rate of infection is found among patients attending venereal disease clinics and among persons of low socioeconomic status. The infection (primary or recurrent) is generally self-limiting, but in a pregnant woman it poses a significant risk to the fetus. It also has been linked to an increased risk of cervical cancer. The Papanicolaou smear is a useful tool for early detection. Effective antiviral therapy for genital herpes is unavailable. Photodynamic inactivation appears promising in recurrent herpes but may be hazardous; malignant transformation of infected cells subjected to this process has been demonstrated in vitro.

EFFECT OF 5-IODO-2'-DEOXYURIDINE ON MULTIPLICATION OF ROUS SARCOMA VIRUS IN VITRO.

SummaryIUdR, added to primary chick fibroblast cultures at the time of RSV infection, not only inhibits virus multiplication but also appears to suppress the malignant transformation of infected cells.