HTLV x gene mutants exhibit novel transcriptional regulatory phenotypes

Antiproliferative and proapoptotic activities of Sea Cucumber H. Leucospilota extract on breast carcinoma cell line (SK-BR-3)

BACKGROUND

Sea cucumber is a natural resource rich in many important pharmacological compounds. this study aimed to investigate the effect of H. leucospilota extract on the induction of cell death and and Proapoptotic Activities.

METHODS AND RESULTS

H. leucospilota was collected, the methanolic extract was prepared and in vitro cytotoxicity of H. leucospilota extract in the range of 12.5, 25, 50, 100, and 200 μg/mL concentrations for 48 hours on SK-BR-3 and MCR5 cells was determined. Analysis of apoptosis and cell cycle stages were performed using flow cytometry. the expressions of several apoptotic-related proteins in SK-BR-3 cells were evaluated using Western blot analysis. ROS formation and caspase activity were determined. GC-MS (involving a multistep temperature gradient and trimethylsilyl derivatives) and phytochemical analysis were used for identification of bioactive compounds. Methanolic extract inhibited the proliferation of the SK-BR-3 cell line in a dose- and time-dependent manner. As it was observed, exposure of the H. leucospilota extract triggered the apoptosis of the SK-BR-3 cells, induced DNA fragmentation, and arrested the cells in G2/M phase. treatment of the methanolic extract induced the downregulation of antiapoptotic Bcl-2 protein as well as the upregulation of Bax, caspase-3, caspase-7 proteins in SK-BR-3 cells. Methanolic extract-elicited apoptosis was accompanied with the elevated level of ROS. The GC-MS and phytochemical analysis revealed 30 compounds and the extract contained alkaloids, flavonoids, steroids, terpenoids, phenols, and saponins.

CONCLUSIONS

The antiproliferative and proapoptotic activities of the tested extract suggested the pharmacologic potential of H. leucospilota. Correspondingly, further characterizations of the identified compounds are in progress.

HER2-low status and response to neoadjuvant chemotherapy in HER2 negative early breast cancer

PURPOSE

Knowledge on whether low expressions of HER2 have prognostic impact in early-stage breast cancer (BC) and on its response to current chemotherapy protocols can contribute to medical practice and development of new drugs for this subset of patients, changing treatment paradigms. This study aims to evaluate the impact of HER2-low status on response to neoadjuvant chemotherapy (NACT) and survival outcomes in early-stage HER2-negative BC.

METHODS

Records from all BC patients treated with NACT from January 2007 to December 2018 in a single cancer center were retrospectively reviewed. HER2-negative (immunohistochemistry [IHC] 0, + 1, or + 2 non-amplified by in situ hybridization [ISH]) patients were included. HER2-low was defined by IHC + 1 or + 2 ISH non-amplified and HER2-0 by IHC 0. The coprimary objectives were to compare pathological complete response (pCR) and relapse-free survival (RFS) between luminal/HER2-low versus luminal/HER2-0 populations and between triple negative (TNBC)/HER2-low versus TNBC/HER2-0.

RESULTS

In total, 855 HER2-negative patients were identified. The median follow-up was 59 months. 542 patients had luminal subtype (63.4%) and 313 had TNBC (36.6%). 285 (33.3%) were HER2-low. Among luminal patients, 145 had HER2 IHC + 1 (26.8%) and 91 had IHC + 2/ISH non-amplified (16.8%). In TNBC, 36 had HER2 IHC + 1 (11.5%) and 13 had IHC + 2/ISH non-amplified (4.2%). Most patients had locally advanced tumors, regardless of subtype or HER2-low status. For luminal disease, pCR was achieved in 13% of HER2-low tumors versus 9.5% of HER2-0 (p = 0.27). Similarly, there was no difference in pCR rates among TNBC: 51% versus 47% in HER2-low versus HER2-0, respectively (p = 0.64). HER2-low was also not prognostic for RFS, with 5-year RFS rates of 72.1% versus 71.7% (p = 0.47) for luminal HER2-low/HER2-0, respectively, and 75.6% versus 70.8% (p = 0.23) for TNBC HER2-low/HER2-0.

CONCLUSION

Our data does not support HER2-low as a biologically distinct BC subtype, with no prognostic value on survival outcomes and no predictive effect for pCR after conventional NACT.

Notch-1-PTEN-ERK1/2 signaling axis promotes HER2+ breast cancer cell proliferation and stem cell survival

Trastuzumab targets the HER2 receptor on breast cancer cells to attenuate HER2-driven tumor growth. However, resistance to trastuzumab-based therapy remains a major clinical problem for women with HER2+ breast cancer. Breast cancer stem cells (BCSCs) are suggested to be responsible for drug resistance and tumor recurrence. Notch signaling has been shown to promote BCSC survival and self-renewal. Trastuzumab-resistant cells have increased Notch-1 expression. Notch signaling drives cell proliferation in vitro and is required for tumor recurrence in vivo. We demonstrate herein a mechanism by which Notch-1 is required for trastuzumab resistance by repressing PTEN expression to contribute to activation of ERK1/2 signaling. Furthermore, Notch-1-mediated inhibition of PTEN is necessary for BCSC survival in vitro and in vivo. Inhibition of MEK1/2-ERK1/2 signaling in trastuzumab-resistant breast cancer cells mimics effects of Notch-1 knockdown on bulk cell proliferation and BCSC survival. These findings suggest that Notch-1 contributes to trastuzumab resistance by repressing PTEN and this may lead to hyperactivation of ERK1/2 signaling. Furthermore, high Notch-1 and low PTEN mRNA expression may predict poorer overall survival in women with breast cancer. Notch-1 protein expression predicts poorer survival in women with HER2+ breast cancer. These results support a potential future clinical trial combining anti-Notch-1 and anti-MEK/ERK therapy for trastuzumab-resistant breast cancer.

Mutational analysis of bovine leukemia virus Rex: identification of a dominant-negative inhibitor

The Rex proteins of the delta-retroviruses act to facilitate the export of intron-containing viral RNAs. The Rex of bovine leukemia virus (BLV) is poorly characterized. To gain a better understanding of BLV Rex, we generated a reporter assay to measure BLV Rex function and used it to screen a series of point and deletion mutations. Using this approach, we were able to identify the nuclear export signal of BLV Rex. Further, we identified a dominant-negative form of BLV Rex. Protein localization analysis revealed that wild-type BLV Rex had a punctate nuclear localization and was associated with nuclear pores. In contrast, the dominant-negative BLV Rex mutation had a diffuse nuclear localization and no nuclear pore association. Overexpression of the dominant-negative BLV Rex altered the localization of the wild-type protein. This dominant-negative derivative of BLV Rex could be a useful tool to test the concept of intracellular immunization against viral infection in a large animal model.

A 10-amino acid domain within human T-cell leukemia virus type 1 and type 2 tax protein sequences is responsible for their divergent subcellular distribution

Human T-cell leukemia virus type 1 and type 2 (HTLV-1/2) are related retroviruses that infect T-lymphocytes. Whereas HTLV-1 infection can cause leukemia, HTLV-2 has not been demonstrated to be the agent of a hematological malignant disease. Nevertheless, the virally encoded Tax-1 and Tax-2 transactivators display a high percentage of similarity. Tax-1 is a shuttling protein that contains a noncanonical nuclear localization signal as well as a nuclear export signal. The presence of the nuclear localization signal and the nuclear export signal domains in the Tax-2 sequence has not been determined. The distribution of Tax-2 in infected cells is not known but has been assumed to be similar to that of Tax-1. By using a Tax-2-specific antibody, we report here that Tax-2 is located predominantly in the cytoplasm of the HTLV-2 immortalized or transformed infected T-cells. These results were confirmed after transient transfection of untagged Tax-1 and Tax-2 constructs, histidine tag Tax1/Tax2, GFP-Tax, and Tax-GFP fusion constructs in several cell lines. We show that this unanticipated localization is not due to a default in the Tax-2 nuclear localization signal functions nor to major differences in Tax-2 versus Tax-1 binding to the IKKgamma/NEMO protein. In addition, we demonstrate that inhibiting the proteasome results in a relocalization of Tax-1 in the cytoplasm, similar to that of Tax-2. By using a series of Tax-1/Tax-2 chimeras, we determined that the minimal domain that is necessary for Tax-2 peculiar distribution encompasses amino acids 90-100. Finally, we show a high correlation between intracellular localization of Tax and their NF-kappaB or CREB transactivating ability.

Tremblay M, Olivier M. The Lipophosphoglycan of Leishmania donovani Up-Regulates HIV-1 Transcription in T Cells Through the Nuclear Factor-κB Elements

We have recently demonstrated that the parasite Leishmania donovani and its surface molecule, lipophosphoglycan (LPG), can activate HIV-1 replication in monocytoid cells. Our present interest was to determine whether LPG could also up-regulate HIV-1 transcription in T cells. Using a CD4-positive human lymphoid T cell line (1G5) containing a stably integrated HIV-1 long terminal repeat (LTR)-luciferase construct, we found that LPG is a potent inducer of HIV-1 LTR activity. Treatment of 1G5 cells with signaling antagonists revealed that protein tyrosine kinase- and protein kinase A-dependent pathways were actively participating in the LPG-induced enhancement of HIV-1 LTR-driven activity. Transfection of Jurkat E6.1 cells with plasmids containing wild-type and nuclear factor-κB (NF-κB)-mutated HIV-1 LTR-luciferase constructs has suggested a role for NF-κB binding sites in the LPG-mediated induction of HIV-1 LTR activity. An LPG-induced binding factor specific to the NF-κB consensus sequences could be observed using electrophoretic mobility shift assay. Finally, transfection experiments performed with a vector containing HIV-1 κB binding sites only showed similar LPG-mediated induction, which was abrogated by sodium salicylate, a known NF-κB inhibitor. We thus demonstrate that the LPG-mediated induction of HIV-1 LTR activity in T cells involves several second messengers culminating in activation of HIV-1 LTR-driven transcription via NF-κB-binding consensus sequences. In conclusion, these results reinforce the idea that L. donovani is a putative cofactor in HIV-1 pathogenesis.

Mechanisms of Tax Regulation of Human T Cell Leukemia Virus Type I Gene Expression

During the last several years, the human T cell leukemia virus type I (HTLV-I) has become recognized as an important cause for public health concern throughout the world. HTLV-I is the causative agent of a variety of clinical diseases, including an aggressive lymphoproliferative disorder named adult T cell leukemia. HTLV-I induces pathogenicity in the infected host cell through the synthesis of a virally encoded protein called Tax. Expression of Tax is critical to the life cycle of the virus, as the protein greatly increases the efficiency of HTLV-I gene transcription and replication. Furthermore, Tax has been shown to deregulate the transcription of many cellular genes, leading to the hypothesis that the presence of Tax promotes unchecked growth in the HTLV-I-infected cell. The mechanism of Tax trans-activation of HTLV-I gene expression is not known. Tax does not bind directly to the Tax-responsive promoter elements of the virus, but appears to function through interaction with certain cellular DNA binding proteins, including activating transcription factor 2 and cAMP response element binding protein that recognize these sequences. This review summarizes some of the recent work in the field aimed at elucidating the mechanism of Tax trans-activation of HTLV-I gene expression. Copyright 1995 S. Karger AG, Basel

trans-dominant mutants of E1A provide genetic evidence that the zinc finger of the trans-activating domain binds a transcription factor

The 289R E1A protein of adenovirus stimulates transcription of early viral and certain cellular genes. trans-Activation requires residues 140 to 188, which encompass a zinc finger. Several studies have indicated that trans-activation by E1A is mediated through cellular transcription factors. In particular, the ability of the trans-dominant E1A point mutant hr5 (Ser-185 to Asn) to inhibit wild-type E1A trans-activation was proposed to result from the sequestration of a cellular factor. Using site-directed mutagenesis, we individually replaced every residue within and flanking the trans-activating domain with a conservative amino acid, revealing 16 critical residues. Six of the individual substitutions lying in a contiguous stretch C terminal to the zinc finger (carboxyl region183-188) imparted a trans-dominant phenotype. trans-Dominance was even produced by deletion of the entire carboxyl region183-188. Conversely, an intact finger region147-177 was absolutely required for trans-dominance, since second-site substitution of every critical residue in this region abrogated the trans-dominant phenotype of the hr5 protein. These data indicate that the finger region147-177 bind a limiting cellular transcription factor and that the carboxyl region183-188 provides a separate and essential function. In addition, we show that four negatively charged residues within the trans-activating domain do not comprise a distinct acidic activating region. We present a model in which the trans-activating domain of E1A binds to two different cellular protein targets through the finger and carboxyl regions.

trans-dominant mutants of E1A provide genetic evidence that the zinc finger of the trans-activating domain binds a transcription factor

The 289R E1A protein of adenovirus stimulates transcription of early viral and certain cellular genes. trans-Activation requires residues 140 to 188, which encompass a zinc finger. Several studies have indicated that trans-activation by E1A is mediated through cellular transcription factors. In particular, the ability of the trans-dominant E1A point mutant hr5 (Ser-185 to Asn) to inhibit wild-type E1A trans-activation was proposed to result from the sequestration of a cellular factor. Using site-directed mutagenesis, we individually replaced every residue within and flanking the trans-activating domain with a conservative amino acid, revealing 16 critical residues. Six of the individual substitutions lying in a contiguous stretch C terminal to the zinc finger (carboxyl region183-188) imparted a trans-dominant phenotype. trans-Dominance was even produced by deletion of the entire carboxyl region183-188. Conversely, an intact finger region147-177 was absolutely required for trans-dominance, since second-site substitution of every critical residue in this region abrogated the trans-dominant phenotype of the hr5 protein. These data indicate that the finger region147-177 bind a limiting cellular transcription factor and that the carboxyl region183-188 provides a separate and essential function. In addition, we show that four negatively charged residues within the trans-activating domain do not comprise a distinct acidic activating region. We present a model in which the trans-activating domain of E1A binds to two different cellular protein targets through the finger and carboxyl regions.

Transdominant human T-cell lymphotropic virus type I TAX1 mutant that fails to localize to the nucleus

Human T-cell lymphotropic virus type I (HTLV-I) encodes a 40-kDa nuclear transactivating phosphoprotein, TAX1. The results presented in this study demonstrate that deletion of amino acids 2 through 59 of TAX1 (delta 58 TAX1) decreased transactivation of the HTLV-I long terminal repeat 10- to 20-fold. S1 nuclease analysis revealed that the decrease in transactivation of the HTLV-I long terminal repeat was associated with a lack of RNA synthesis. In contrast to the nuclear localization of the wild-type TAX1 protein, indirect immunofluorescence analysis demonstrated that delta 58 TAX1 failed to localize to the nucleus, indicating that the TAX1 nuclear localization sequence is present in amino acids 2 through 59. Cotransfection of wild-type and mutant TAX1 DNAs resulted in the cytoplasmic accumulation of TAX1 and a 25-fold decrease in transactivation. Although several possibilities which may account for this transdominant effect exist, we favor a model in which delta 58 TAX1 interferes with the nuclear localization of wild-type TAX1 protein, perhaps by forming heterodimer complexes.

Identification of HTLV-I tax trans-activator mutants exhibiting novel transcriptional phenotypes

The type I human T-cell leukemia virus (HTLV-I) encodes a 40-kD nuclear trans-regulatory protein termed Tax that transcriptionally activates the HTLV-I long terminal repeat (LTR), as well as select [corrected] cellular and heterologous viral promoters. Tax does not bind DNA specifically but, rather, acts in a more indirect manner. Tax activation of the HTLV-I LTR is mediated through constitutively expressed cellular factors that bind to cAMP response elements (CREs) present within the 21-bp enhancers of the LTR. In contrast, Tax transactivation of the interleukin-2 receptor-alpha gene (IL-2R alpha) and LTR of the type 1 human immunodeficiency virus (HIV-1) involves the induced nuclear expression of NF-kappa B. We now report the identification of missense mutations within the tax gene that functionally segregate these two pathways of trans-activation. Additionally, we demonstrate that the carboxyl terminus of the Tax protein, despite its acidic and predicted alpha-helical structure, is completely dispensable for trans-activation through either of these transcription factor pathways. Finally, we demonstrate that mutations within a putative zinc finger domain disrupt the nuclear localization of Tax and abolish trans-activation. These results demonstrate that Tax trans-activation of viral and cellular promoters involves at least two mechanisms of host transcription factor activation and suggest that this activation is likely mediated through distinct functional domains.

A transdominant tat mutant that inhibits tat-induced gene expression from the human immunodeficiency virus long terminal repeat

Regulation of human immunodeficiency virus (HIV) gene expression is dependent on specific regulatory regions in the long terminal repeat. These regions include the enhancer, SP1, "TATA," and trans-activating (TAR) regions. In addition, viral regulatory proteins such as tat and rev are important in regulating HIV gene expression. The mechanism of tat activation remains the subject of investigation, but effects at both transcriptional and posttranscriptional levels seem likely. Previous mutagenesis of the tat protein revealed that the amino terminus, the cysteine-rich domain, and the basic domain were all required for complete tat activation. Mutants of other viral trans-acting regulatory proteins, including E1A, tax, and VM65, have been identified that were capable of antagonizing the activity of their corresponding wild-type proteins. We wished to determine whether mutants of the tat protein could be identified that exhibited a similar phenotype. One mutant (delta tat) that truncated the basic domain of tat resulted in a transdominant phenotype inhibiting tat-induced gene expression of the HIV long terminal repeat but not other viral promoters. This mutant exhibited its maximal phenotype in cotransfection experiments when present in an 8- to 30-fold molar excess over the wild-type tat gene. Trans-activation of the HIV long terminal repeat by delta tat was very defective at the DNA concentrations used in these experiments. RNase protection analysis indicated that this mutant decreased tat-induced steady-state mRNA levels of the HIV long terminal repeat. Second-site mutations of the delta tat gene in either the amino terminus or cysteine region eliminated the transdominant phenotype. In contrast to tat, which was localized predominantly to the nucleolus, delta tat was present in both the nucleus and cytoplasm, suggesting that it may inhibit tat function by preventing nucleolar localization. Transdominant mutants of tat may have a role in potentially inhibiting HIV gene expression.

Trans-dominant inactivation of HTLV-I and HIV-1 gene expression by mutation of the HTLV-I Rex transactivator

The rex gene of the type I human T-cell leukaemia virus (HTLV-I) encodes a phosphorylated nuclear protein of relative molecular mass 27,000 which is required for viral replication. The Rex protein acts by promoting the cytoplasmic expression of the incompletely spliced viral messenger RNAs that encode the virion structural proteins. To identify the biologically important peptide domains within Rex, we introduced a series of mutations throughout its sequence. Two distinct classes of mutations lacking Rex biological activity were identified. One class corresponds to trans-dominant repressors as they inhibit the function of the wild-type Rex protein. The second class of mutants, in contrast, are recessive negative, rather than dominant negative, as they are not appropriately targeted to the cell nucleus. These results indicate the presence of at least two functionally distinct domains within the Rex protein, one involved in protein localization and a second involved in effector function. The trans-dominant Rex mutants may represent a promising new class of anti-viral agents.

Structural and functional characterization of mutants of the bovine leukemia virus transactivator protein p34

Mutants of the bovine leukemia virus (BLV) transactivator protein (tat, tax, p34, the XLOR gene product) were constructed by site-directed deletions, in-phase linker insertions, or fragment replacements (swapping) among BLV variants. The mutant constructs were transfected into cos cells and transiently expressed. Western blot analysis using a mixture of monoclonal antibodies to wild-type p34 revealed the presence of mutated XLOR gene products in all the mutants tested. The transactivating activity of 11 tax mutants containing site-directed deletions and in-phase linker insertions was completely abolished. Only the swapping mutant tested, a hybrid between two BLV variants, transactivated LTR-directed gene expression at wild-type levels. These data illustrate the narrow range of structural variations that allow full activity of the BLV tax product and suggest that the present molecular structure of the transactivator protein results from heavy evolutionary constraints.

Functional dissection of the HIV-1 Rev trans-activator--derivation of a trans-dominant repressor of Rev function

Human immunodeficiency virus type 1 (HIV-1) encodes a nuclear trans-activator, termed Rev, that is required for the expression of the viral structural proteins and, hence, for viral replication. The Rev protein acts posttranscriptionally to induce the sequence-specific nuclear export of unspliced HIV-1 mRNA species that are otherwise excluded from the cell cytoplasm. We have used site-directed mutagenesis to identify two distinct regions of the HIV-1 Rev protein that are required for in vivo biological activity. The larger and more N-terminal of these two regions includes, but extends beyond, an arginine-rich sequence element required for nuclear localization. Mutation of a second, more C-terminal Rev protein sequence element was found to yield defective Rev proteins that act as trans-dominant inhibitors of Rev function. These Rev mutants are shown to inhibit HIV-1 replication when expressed in transfected cells and may have potential application in the treatment of HIV-1 related disease.

Mutational analysis of HIV-1 Tat minimal domain peptides: identification of trans-dominant mutants that suppress HIV-LTR-driven gene expression

The HIV-1 Tat protein is a potent trans-activator essential for virus replication. We reported previously that HIV-1 Tat peptides containing residues 37-48 (mainly region II), a possible activating region, and residues 49-57 (region III), a nuclear targeting and putative nucleic acid binding region, possess minimal but distinct trans-activator activity. The presence of residues 58-72 (region IV) greatly enhances trans-activation. We postulate that Tat mutant peptides with an inactive region II and a functional region III can behave as dominant negative mutants. We synthesized minimal domain peptides containing single amino substitutions for amino acid residues within region II that are conserved among different HIV isolates. We identify four amino acid residues whose substitution within Tat minimal domain peptides leads to defects in transactivation. Some of these mutants are trans-dominant in several peptide backbones, since they strongly inhibit trans-activation by wild-type Tat protein added to cells or expressed from microinjected plasmid. Significantly, trans-activation of integrated HIV-LTRCAT is blocked by some trans-dominant mutant peptides. These results suggest an attractive approach for the development of an AIDS therapy.

In vitro mutagenesis of the human T-cell leukemia virus types I and II tax genes

The tax gene of the human T-cell leukemia virus types I and II (HTLV-I and HTLV-II) is essential for viral replication and acts by increasing the level of RNA transcription. The tax genes of HTLV-I and HTLV-II encode proteins of 40 and 37 kilodaltons, respectively. By in vitro mutagenesis of the tax gene, we have investigated those regions of the protein which are essential for its function. Mutation of either the amino- or carboxy-terminal domain of the protein resulted in loss of trans-activation ability. In addition, specificity of its activity with regard to trans-activation of either the HTLV-I or HTLV-II long terminal repeats was conferred by the first 59 amino acids.

Functional inactivation of genes by dominant negative mutations

Molecular biologists are increasingly faced with the problem of assigning a function to genes that have been cloned. A new approach to this problem involves the manipulation of the cloned gene to create what are known as 'dominant negative' mutations. These encode mutant polypeptides that when overexpressed disrupt the activity of the wild-type gene. There are many precedents for this kind of behaviour in the literature--some oncogenes might be examples of naturally occurring dominant negative mutations.