Biomedical subjects

Kuan-Teh Jeang

Publications and source records attributed to Kuan-Teh Jeang.

At least 19 recordsLinked to original sources

PubMed2007

Heterozygous deletion of mitotic arrest-deficient protein 1 (MAD1) increases the incidence of tumors in mice.

Mitotic arrest-deficient protein 1 (MAD1) is a component of the mitotic spindle assembly checkpoint. We have created a knockout mouse model to examine the physiologic consequence of reduced MAD1 function. Mad1(+/-) mice were successfully generated, but repeated paired mating of Mad1(+/-) with Mad1(+/-) mice failed to produce a single Mad1(-/-) animal, suggesting that the latter genotype is embryonic lethal. In aging studies conducted for >18 months, Mad1(+/-) mice compared with control wild-type (wt) littermates showed a 2-fold higher incidence of constitutive tumors. Moreover, 42% of Mad1(+/-) (P < 0.03), but 0% of wt, mice developed neoplasia after treatment with vincristine, a microtubule depolymerization agent. Mad1(+/-) mouse embryonic fibroblasts (MEF) were found to be more prone than wt cells to become aneuploid; Mad1(+/-), but not wt, MEFs produced fibrosarcomas when explanted into nude mice. Our results indicate an essential MAD1 function in mouse development and correlate Mad1 haploinsufficiency with increased constitutive tumors.

Amino Acid Sequence↗

PubMed2007

HTLV-1 Tax and adult T-cell leukemia.

Human T-lymphotropic virus type I (HTLV-1) is the etiological agent of adult T-cell leukemia/lymphoma (ATL) and HTLV-1 associated myelopathy/tropical spastic paraparesis (HAM/TSP). HTLV-1 viral transactivator/oncoprotein, Tax, activates viral transcription and usurps regulatory mechanisms that are critical for cell growth and division to facilitate viral replication. The effects that Tax exerts on cells include potent NF-k B activation, cell cycle perturbation and cell transformation. How Tax influences ATL development is incompletely understood at present. While Tax-expression is needed at the early stages of cellular transformation, at later times most ATL cells do not express tax; therefore, genetic and epigenetic changes in HTLV-1-infected cells are believed to play an important role in the etiology of ATL. This review attempts to integrate recent literature on the biological activities of Tax and the properties of HTLV-1 transformed T-cells and ATL cells, and speculate on what cellular changes may collaborate with Tax to effect cell transformation and ATL development.

Adult↗

PubMed2006

Libya, HIV, and open communication.

This year-end editorial discusses several points including the recent Libyan verdict sentencing five Bulgarian nurses and a Palestinian doctor to death for allegedly infecting 426 children with HIV. It also comments on the role played by open communication for bridging cultural misunderstandings and summarizes briefly Retrovirology's progress in 2006.

Adult↗

PubMed2006

HIV-1 Tat interaction with Dicer: requirement for RNA.

Dicer is an RNase III which processes two classes of cellular small RNAs: the microRNAs (miRNA) and short interfering RNAs (siRNA). Previously, we observed that over-expressed HIV-1 Tat protein can suppress the processing of small RNAs inside cells. Here, we have investigated the requirements for Tat interaction with Dicer. We report that Tat-Dicer interaction depends on RNA, requires the helicase domain of Dicer, and is independent of Tat's transactivation domain.

Argonaute Proteins↗

PubMed2006

Delivery of 2-5A cargo into living cells using the Tat cell penetrating peptide: 2-5A-tat.

2',5'-Oligoadenylate tetramer (2-5A) has been chemically conjugated to short HIV-1 Tat peptides to provide 2-5A-tat chimeras. Two different convergent synthetic approaches have been employed to provide such 2-5A-tat bioconjugates. One involved generation of a bioconjugate through reaction of a cysteine terminated Tat peptide with a alpha-chloroacetyl derivative of 2-5A. The second synthetic strategy was based upon a cycloaddition reaction of an azide derivative of 2-5A with a Tat peptide bearing an alkyne function. Either bioconjugate of 2-5A-tat was able to activate human RNase L. The union of 2-5A and Tat peptide provided an RNase L-active chimeric nucleopeptide with the ability to be taken up by cells by virtue of the Tat peptide and to activate RNase L in intact cells. This strategy provides a valuable vehicle for the entry of the charged 2-5A molecule into cells and may provide a means for targeted destruction of HIV RNA in vivo.

Adenine Nucleotides↗

PubMed2006

Role of RNA helicases in HIV-1 replication.

Viruses are replication competent genomes which are relatively gene-poor. Even the largest viruses (i.e. Herpesviruses) encode only slightly >200 open reading frames (ORFs). However, because viruses replicate obligatorily inside cells, and considering that evolution may be driven by a principle of economy of scale, it is reasonable to surmise that many viruses have evolved the ability to co-opt cell-encoded proteins to provide needed surrogate functions. An in silico survey of viral sequence databases reveals that most positive-strand and double-stranded RNA viruses have ORFs for RNA helicases. On the other hand, the genomes of retroviruses are devoid of virally-encoded helicase. Here, we review in brief the notion that the human immunodeficiency virus (HIV-1) has adopted the ability to use one or more cellular RNA helicases for its replicative life cycle.

Antiviral Agents↗

PubMed2006

HIV-1 TAR RNA subverts RNA interference in transfected cells through sequestration of TAR RNA-binding protein, TRBP.

TAR RNA-binding protein, TRBP, was recently discovered to be an essential partner for Dicer and a crucial component of the RNA-induced silencing complex (RISC), a critical element of the RNA interference (RNAi) of the cell apparatus. Human TRBP was originally characterized and cloned 15 years ago based on its high affinity for binding the HIV-1 encoded leader RNA, TAR. RNAi is used, in part, by cells to defend against infection by viruses. Here, we report that transfected TAR RNA can attenuate the RNAi machinery in human cells. Our data suggest that TAR RNA sequesters TRBP rendering it unavailable for downstream Dicer-RISC complexes. TAR-induced inhibition of Dicer-RISC activity in transfected cells was partially relieved by exogenous expression of TRBP.

HIV Long Terminal Repeat↗

PubMed2006

The retroviral oncoprotein Tax targets the coiled-coil centrosomal protein TAX1BP2 to induce centrosome overduplication.

Emerging evidence suggests that supernumerary centrosomes drive genome instability and oncogenesis. Human T-cell leukaemia virus type I (HTLV-I) is etiologically associated with adult T-cell leukaemia (ATL). ATL cells are aneuploid, but the causes of aneuploidy are incompletely understood. Here, we show that centrosome amplification is frequent in HTLV-I-transformed cells and that this phenotype is caused by the viral Tax oncoprotein. We also show that the fraction of Tax protein that localizes to centrosomes interacts with TAX1BP2, a novel centrosomal protein composed almost entirely of coiled-coil domains. Overexpression of TAX1BP2 inhibited centrosome duplication, whereas depletion of TAX1BP2 by RNAi resulted in centrosome hyperamplification. Our findings suggest that the HTLV-I Tax oncoprotein targets TAX1BP2 causing genomic instability and aneuploidy.

Aneuploidy↗

PubMed2006

FAT10 plays a role in the regulation of chromosomal stability.

Aneuploidy is a key process in tumorigenesis. Dysfunction of the mitotic spindle checkpoint proteins has been implicated as a cause of aneuploidy in cells. We have previously reported that FAT10, a member of the ubiquitin-like modifier family of proteins, is overexpressed in several gastrointestinal and gynecological cancers. Here we show that FAT10 interacts with MAD2, a spindle checkpoint protein, during mitosis. Notably, we show that localization of MAD2 at the kinetochore during the prometaphase stage of the cell cycle was greatly reduced in FAT10-overexpressing cells. Furthermore, compared with parental HCT116 cells, fewer mitotic cells were observed after double thymidine-synchronized FAT10-overexpressing cells were released into nocodazole for more than 4 h. Nonetheless, when these double thymidine-treated cells were released into media, a similar number of G1 parental and FAT10-overexpressing HCT116 cells was observed throughout the 10-h time course. Additionally, more nocodazole-treated FAT10-overexpressing cells escape mitotic controls and are multinucleate compared with parental cells. Significantly, we observed a higher degree of variability in chromosome number in cells overexpressing FAT10. Hence, our data suggest that high levels of FAT10 protein in cells lead to increased mitotic nondisjunction and chromosome instability, and this effect is mediated by an abbreviated mitotic phase and the reduction in the kinetochore localization of MAD2 during the prometaphase stage of the cell cycle.

Aneuploidy↗

PubMed2006

Role for Akt/protein kinase B and activator protein-1 in cellular proliferation induced by the human T-cell leukemia virus type 1 tax oncoprotein.

Human T-cell leukemia virus type 1 is an oncogenic retrovirus etiologically causal of adult T-cell leukemia. The virus encodes a Tax oncoprotein, which functions in transcriptional regulation, cell cycle control, and transformation. Because adult T-cell leukemia is a highly virulent cancer that is resistant to numerous chemotherapeutic treatments, to understand better this disease it is important to comprehend how human T-cell leukemia virus type 1 promotes cellular growth and survival. Most of the existing data point to Tax activation of NF-kappaB as important for cellular proliferation and transformation. We show here that Tax, in the absence of NF-kappaB signaling, can activate activator protein-1 to promote cellular proliferation and survival. Tax is shown to activate activator protein-1 through the phosphatidylinositol 3-kinase/Akt pathway.

Animals↗

PubMed2006

A peptide-loaded dendritic cell based cytotoxic T-lymphocyte (CTL) vaccination strategy using peptides that span SIV Tat, Rev, and Env overlapping reading frames.

CTL based vaccine strategies in the macaque model of AIDS have shown promise in slowing the progression to disease. However, rapid CTL escape viruses can emerge rendering such vaccination useless. We hypothesized that such escape is made more difficult if the immunizing CTL epitope falls within a region of the virus that has a high density of overlapping reading frames which encode several viral proteins. To test this hypothesis, we immunized macaques using a peptide-loaded dendritic cell approach employing epitopes in the second coding exon of SIV Tat which spans reading frames for both Env and Rev. We report here that autologous dendritic cells, loaded with SIV peptides from Tat, Rev, and Env, induced a distinct cellular immune response measurable ex vivo. However, conclusive in vivo control of a challenge inoculation of SIVmac239 was not observed suggesting that CTL epitopes within densely overlapping reading frames are also subject to escape mutations.

Animals↗

PubMed2006

Transactivation of CCL20 gene by Epstein-Barr virus latent membrane protein 1.

CCL20 is expected to play a crucial role in the initiation of immune responses and tumour growth. However, expression of CCL20 in Epstein-Barr virus (EBV)-associated diseases has not been studied. We examined the contribution of EBV infection and EBV-encoded latent membrane protein (LMP)-1 to CCL20 expression. EBV infection and LMP-1 induced CCL20 mRNA expression in the EBV-negative Burkitt lymphoma (BL) cell lines and the embryonic kidney cell line. Histone deacetylase inhibitor-stimulated endogenous LMP-1 also induced CCL20 expression in an EBV-positive BL cell line. Analysis of the CCL20 promoter showed that it was activated by LMP-1 C-terminal activation region (CTAR)-1 and CTAR-2. Co-expression of IkappaB alpha, IkappaB beta, IkappaB kinase (IKK)alpha, IKKbeta, IKKgamma, nuclear factor (NF)-kappaB-inducing kinase and tumour necrosis factor receptor-associated factor 2 dominant-negative constructs with LMP-1 inhibited the activation of the CCL20 promoter by LMP-1, suggesting that LMP-1 induces CCL20 via NF-kappaB signalling. The requirement for the NF-kappaB-binding site in the CCL20 promoter in LMP-1 responsiveness was established. Our results indicate that activation of the NF-kappaB pathway by LMP-1 is required for the activation of CCL20 expression.

Burkitt Lymphoma↗

PubMed2006

TORC1 and TORC2 coactivators are required for tax activation of the human T-cell leukemia virus type 1 long terminal repeats.

Human T-cell leukemia virus type 1 (HTLV-1) Tax protein activates viral transcription from the long terminal repeats (LTR). Mechanisms through which Tax activates LTR have been established, but coactivators of this process remain to be identified and characterized. Here we show that all three members of the TORC family of transcriptional regulators are coactivators of Tax for LTR-driven expression. TORC coactivation requires CREB, but not ATF4 or other bZIP factors. Tax physically interacts with TORC1, TORC2, and TORC3 (TORC1/2/3), and the depletion of TORC1/2/3 inhibited Tax activity. TORC coactivation can be further enhanced by transcriptional coactivator p300. In addition, coactivators in the p300 family are required for full activity of Tax independently of TORC1/2/3. Thus, both TORC and p300 families of coactivators are essential for optimal activation of HTLV-1 transcription by Tax.

Activating Transcription Factor 4↗

PubMed2006

An alternative splice product of IkappaB kinase (IKKgamma), IKKgamma-delta, differentially mediates cytokine and human T-cell leukemia virus type 1 tax-induced NF-kappaB activation.

NF-kappaB is an inducible transcription factor mediating innate immune responses whose activity is controlled by the multiprotein IkappaB kinase (IKK) "signalsome". The core IKK consists of two catalytic serine kinases, IKKalpha and IKKbeta, and a noncatalytic subunit, IKKgamma. IKKgamma is required for IKK activity by mediating kinase oligomerization and serving to couple the core catalytic subunits to upstream mitogen-activated protein 3-kinase cascades. We have discovered an alternatively spliced IKKgamma mRNA isoform, encoding an in-frame deletion of exon 5, termed IKKgamma-delta. Using a specific reverse transcription-PCR assay, we find that IKKgamma-delta is widely expressed in cultured human cells and normal human tissues. Because IKKgamma-Delta protein is lacking a critical coiled-coil domain important in protein-protein interactions, we sought to determine its signaling properties by examining its ability to self associate, couple to activators of the canonical pathway, and mediate human T-cell leukemia virus type 1 (HTLV-1) Tax-induced NF-kappaB activity. Coimmunoprecipitation and confocal colocalization assays indicate IKKgamma-delta has strong homo- and heterotypic association with wild-type (WT) IKKgamma and, like IKKgamma WT, associates with the IKKbeta kinase. Similarly, IKKgamma-delta mediates IKK kinase activity and downstream NF-kappaB-dependent transcription in response to tumor necrosis factor (TNF) and the NF-kappaB-inducing kinase-IKKalpha signaling pathway. Surprisingly, however, in contrast to IKKgamma WT, IKKgamma-delta is not able to mediate HTLV-1 Tax-induced NF-kappaB-dependent transcription, even though IKKgamma-delta binds and colocalizes with Tax. These observations suggest that IKKgamma-delta is a functionally distinct alternatively spliced mRNA product differentially mediating TNF-induced, but not Tax-induced, signals converging on the IKK signalsome. Differing levels of IKKgamma-delta expression, therefore, may affect signal transduction cascades coupling to IKK.

Alternative Splicing↗

PubMed2006

MicroRNAs in human immunodeficiency virus-1 infection.

Initially reported for Caenorhabditis elegans, microRNA (miRNA) has been shown to regulate gene expression in plants, flies, and mammals . Here, we report on our approaches to investigate the role of miRNAs in human immunodeficiency virus (HIV)-1 infection. Using computer-directed foldings, we first identify potential sequences in HIV-1 that putatively encode miRNAs. Subsequently, we use Northern blotting of RNAs isolated from HIV-infected cells to confirm expression of predicted miRNA sequences. Finally, we use a scanning algorithm to search 3' untranslated regions (UTRs) of human messenger RNAs (mRNAs) in the attempt to predict potential sites targeted by HIV-1 miRNAs.

Algorithms↗

PubMed2006

Replication of human immunodeficiency virus type 1 from entry to exit.

It has been 25 years since the recognition of the disease acquired immunodeficiency syndrome (AIDS) in homosexual men in the United States. Much molecular progress in understanding the replication of the human immunodeficiency virus (HIV) has been advanced. Here, we review in a nonexhaustive manner our current knowledge of the replication of HIV-1 inside human cells from entry to exit of the virus.

HIV Infections↗

PubMed2006

Modulation of nuclear factor-kappaB by human T cell leukemia virus type 1 Tax protein: implications for oncogenesis and inflammation.

Activation of the nuclear factor kappa B (NF-kappaB) transcription factor family by different stimuli, such as inflammatory cytokines, stress inducers, or pathogens, results in innate and adaptive immunity. While the main function of NF-kappaB is to promote the host's immune response, the NF-kappaB pathway is frequently dysregulated by invading viral pathogens. Human T cell leukemia virus type 1 (HTLV-1) is the causative agent of a fatal malignancy known as adult T cell leukemia (ATL) and an inflammatory disease named tropical spastic paraparesis/HTLV-1 associated myelopathy (TSP/HAM). HTLV-1 encodes an oncoprotein, Tax, which plays a significant role in the initiation of cellular transformation and the elicitation of the host's inflammatory responses. Here, we review current thinking on how Tax may affect both diseases through activation of NF-kappaB signaling.

Animals↗

PubMed2005

Changes in microRNA expression profiles in HIV-1-transfected human cells.

MicroRNAs (miRNAs) are small RNAs of 18-25 nucleotides (nt) in length that play important roles in regulating a variety of biological processes. Recent studies suggest that cellular miRNAs may serve to control the replication of viruses in cells. If such is the case, viruses might be expected to evolve the ability to modulate the expression of cellular miRNAs. To ask if expression of HIV-1 genes changes the miRNA profiles in human cells, we employed a high throughput microarray method, termed the RNA-primed Array-based Klenow Enzyme (RAKE) assay. Here, we describe the optimization of this assay to quantify the expression of miRNAs in HIV-1 transfected human cells. We report distinct differences in miRNA profiles in mock-transfected HeLa cells versus HeLa cells transfected with an infectious HIV-1 molecular clone, pNL4-3.

Gene Expression Profiling↗