Cell cycle regulation (G1) by autocrine interferon and dissociation between autocrine interferon and 2',5'-oligoadenylate synthetase expression

Lupus-Associated Functional Polymorphism in PNP Causes Cell Cycle Abnormalities and Interferon Pathway Activation in Human Immune Cells

OBJECTIVE

Systemic lupus erythematosus (SLE) is frequently characterized by activation of the type I interferon (IFN) pathway. We previously observed that a missense single-nucleotide polymorphism (rs1049564) in the purine nucleoside phosphorylase (PNP) gene was associated with high levels of IFN in SLE. PNP is a key enzyme involved in purine metabolism. In this study, we performed functional follow-up of this polymorphism in human cells.

METHODS

Type I IFN was measured in patient sera, using a reporter cell assay. Structural modeling of the PNP variant was performed using PyMOL software. PNP messenger RNA (mRNA) and protein levels and type I IFN-induced gene expression were measured in lymphoblastoid cell lines with known PNP rs1049564 genotypes. The cell cycle was assayed using flow cytometry.

RESULTS

Structural modeling indicated no major disruption in folding related to rs1049564. We observed that homozygous rs1049564 TT lymphoblastoid cells had decreased PNP mRNA expression and protein levels, and that cells with the TT genotype had reduced PNP enzymatic activity even when the amount of PNP was controlled. Cells with the TT genotype had a 2-fold increase in S-phase block as compared with cells with the homozygous CC phenotype. The S-phase block could be pharmacologically reversed with hypoxanthine and adenosine, supporting the notion that relative PNP deficiency is the cause of the S-phase block. Type I IFN-induced transcripts were increased in a dose-response manner related to the rs1049564 T allele, at both baseline and after type I IFN stimulation.

CONCLUSION

The PNP rs1049564 T allele is a loss-of-function variant that induces S-phase block and IFN pathway activation in lymphocytes. The S-phase block could be rescued in our in vitro experiments, suggesting the potential for personalized treatment.

Transplacental RNAi: deciphering gene function in the postimplantation-staged embryo

RNAi offers the opportunity to examine the role in postimplantation development of genes that cause preimplantation lethality and to create allelic series of targeted embryos. We have delivered constituitively expressed short hairpin (sh) RNAs to pregnant mice during the early postimplantation period of development and observed gene knockdown and defects that phenocopy the null embryo. We have silenced genes that have not yet been “knocked out” in the mouse (geminin and Wnt8b), those required during earlier cleavage stages of development (nanog), and genes required at implantation (Bmp4, Bmp7) singly and in combination (Bmp4 + Bmp7), and obtained unique phenotypes. We have also determined a role in postimplantation development of two transcripts identified in a differential display RT-PCR screen of genes induced in ES cells by noggin exposure, Aggf1 and an Est (GenBank AK008955). Systemic delivery of shRNAs provides a valuable approach to gene silencing in the embryo.

Growth inhibition of subcutaneous mouse melanoma and induction of natural killer cells by liposome-mediated interferon-beta gene therapy

In this study we investigated the antitumour effect and mechanism of action of cationic liposome-mediated murine interferon-beta (IFNbeta) gene therapy in mouse B16F1 melanoma cells in vitro and in vivo. Murine IFNbeta gene transfer by cationic liposome resulted in substantial growth inhibition of B16F1 melanoma cells in culture when compared with phosphate buffered saline or recombinant murine IFNbeta treatment, or lacZ control gene transfer. Use of video-enhanced contrast-differential interference contrast (VEC-DIC) microscopy revealed that liposomes containing the murine IFNbeta gene [lip(pSV2muIFNbeta)], but not recombinant murine IFNbeta, induced dramatic morphological changes that characterize apoptosis, including bleb formation, shrinkage of cells, nuclear condensation and 'ballooning', in approximately 30% of the cells treated. Intratumoral administration of lip(pSV2muIFNbeta) resulted in a 5.5-fold reduction in the mean volume of subcutaneous melanoma lesions in syngeneic mice 15 days after treatment and eradicated the tumour in 18% of the mice treated. Immunocytochemical analysis demonstrated that a larger number of natural killer (NK) cells infiltrated the tumour following lip(pSV2muIFNbeta) treatment than in controls. In vivo depletion of NK cells using the anti-asialoGM1 antibody reduced the efficacy of lip(pSV2muIFNbeta) treatment. Taken together, our data suggest that cationic liposome-mediated IFNbeta gene therapy could be effective against melanoma by directly inducing cell death and stimulating NK cells.

IFN-beta gene therapy induces systemic antitumor immunity against malignant glioma

We previously demonstrated that intratumoral administration of liposomes containing the murine interferon beta (IFN-beta) gene [lip(pSV2muIFN-beta)] resulted in stronger growth-inhibitory effect on GL261 (H-2b) mouse glioma inoculated in brains of syngeneic C57BL/6 mice than conventional exogenous IFN-beta administration, and histologic evaluation revealed the massive infiltration of T lymphocytes (CD8 > CD4) within the residual tumor. The present study was aimed at determining whether such tumor-infiltrating lymphocytes (TIL) have any tumor-specific cytotoxic effects. Intratumoral administration of lip(pSV2muIFN-beta) resulted in prolonged survival time and a 50% tumor-free incidence in the mice treated. The surviving animals were subsequently re-challenged with either subcutaneous or intracranial injection of GL261 cells, and no tumors were found to develop over a 50-day period. In vivo depletion of CD8, but not CD4 cells decreased the efficacy of lip(pSV2muIFN-beta). Specific cytotoxic T lymphocytes (CTL) against GL261 cells were generated from both TIL and spleen cells of the mice treated. The results of flow cytometric analysis and antibody blocking test revealed that the bulk CTL lines thus prepared were T cell receptor (TCR) alphabeta, CD8 T lymphocytes with H-2b restriction. These findings suggest that, in addition to direct growth-inhibitory effects by the IFN-beta gene on the tumor cells, activation of systemic cellular immunity may participate in antitumor effects in vivo, despite the fact that central nervous system is generally regarded as an immunologically privileged site.

Antitumor effect and cellular immunity activation by murine interferon-beta gene transfer against intracerebral glioma in mouse

Cationic liposomes containing the human interferon-beta (IFN-beta) gene induce marked growth inhibition in human glioma cells. In vivo experiments using an human glioma implanted into the brains of nude mice have demonstrated a definite growth-inhibitory effect, achieving complete tumor regression with multiple intratumoral injections of the gene. However, nude mouse studies are inadequate to evaluate antitumor effects fully, especially those related to activation of the host immune response. This article aimed to investigate antitumor effects and immune response activation by murine IFN-beta gene transfer in syngeneic mice. In vitro experiments demonstrated a stronger growth-inhibitory effect of liposomes containing the murine IFN-beta gene on a GL261 mouse glioma cell line than exogenously added murine IFN-beta. In in vivo experiments, intratumoral administration of liposomes containing the murine IFN-beta gene resulted in a 16-fold reduction in the mean volume of residual gliomas in the brains of C57BL/6 mice and massive infiltration of cytotoxic T lymphocytes (CTL) within the residual tumor, while few CTL were infiltrated in controls including murine IFN-beta, empty liposomes, naked plasmid expressing murine IFN-beta, and liposomes containing beta-galactosidase gene. In addition, 40% of mice treated with liposomes containing the murine IFN-beta gene were completely cured. These findings indicated that activation of cellular immunity participates in antitumor effects in vivo together with direct effects of the IFN-beta gene.

Negative cell cycle control of human T cells by beta-galactoside binding protein (beta GBP): induction of programmed cell death in leukaemic cells

The cell cycle is negatively regulated by diverse molecular events which originate in part from the interaction of secreted proteins with specific cell surface receptors. By exerting negative control on cell proliferation, these factors can help maintain cell number balance both through growth restraints and the induction of apoptosis and may thus contribute to prevent or control tumourigenesis. Here we report that betaGBP, a negative growth factor which controls transition from S phase into G2, causes an S/G2 growth arrest in both normal and leukaemic T cells. However, in leukaemic T cells but not in normal T lymphocytes, growth arrest is followed by apoptosis. Analysis of possible mechanisms of induction of apoptosis does not support Fas and Fas L as having a main role but points instead to Bcl-2 and Bax. The induction of apoptosis in leukaemic T cells is characterised by the decrease of Bcl-2 and consequent predominance of Bax. By contrast, in the normal T cells, which do not enter apoptosis, the quantitative relationship of Bcl-2 to Bax remains unchanged. The ability of betaGBP to selectively induce apoptosis in leukaemic cells suggests that betaGBP may play a role in cancer surveillance and that its use has potential therapeutic implications.

The 2-5A system: modulation of viral and cellular processes through acceleration of RNA degradation

The 2-5A system is an RNA degradation pathway that can be induced by the interferons (IFNs). Treatment of cells with IFN activates genes encoding several double-stranded RNA (dsRNA)-dependent synthetases. These enzymes generate 5'-triphosphorylated, 2',5'-phosphodiester-linked oligoadenylates (2-5A) from ATP. The effects of 2-5A in cells are transient since 2-5A is unstable in cells due to the activities of phosphodiesterase and phosphatase. 2-5A activates the endoribonuclease 2-5A-dependent RNase L, causing degradation of single-stranded RNA with moderate specificity. The human 2-5A-dependent RNase is an 83.5 kDa polypeptide that has little, if any, RNase activity, unless 2-5A is present. 2-5A binding to RNase L switches the enzyme from its off-state to its on-state. At least three 2',5'-linked oligoadenylates and a single 5'-phosphoryl group are required for maximal activation of the RNase. Even though the constitutive presence of 2-5A-dependent RNase is observed in nearly all mammalian cell types, cellular amounts of 2-5A-dependent mRNA and activity can increase after IFN treatment. One well-established role of the 2-5A system is as a host defense against some types of viruses. Since virus infection of cells results in the production and secretion of IFNs, and since dsRNA is both a frequent product of virus infection and an activator of 2-5A synthesis, the replication of encephalomyocarditis virus, which produces dsRNA during its life cycle, is greatly suppressed in IFN-treated cells as a direct result of RNA decay by the activated 2-5A-dependent RNase. This review covers the organic chemistry, enzymology, and molecular biology of 2-5A and its associated enzymes. Additional possible biological roles of the 2-5A system, such as in cell growth and differentiation, human immunodeficiency virus replication, heat shock, atherosclerotic plaque, pathogenesis of Type I diabetes, and apoptosis, are presented.

Inhibition of HIV-1 replication and activation of RNase L by phosphorothioate/phosphodiester 2',5'-oligoadenylate derivatives

2',5'-Oligoadenylate (2-5A) derivatives have been designed to act distal to the human immunodeficiency virus-1 (HIV-1)-induced blockade in the 2-5A synthetase/RNase L antiviral pathway. Stereochemical modification of individual internucleotide linkages of the 2-5A molecule was accomplished by phosphoramidite and phosphotriester chemical syntheses. Phosphorothioate/phosphodiester trimer and tetramer 2-5A derivatives revealed differences in the stereodynamics of activation of RNase L and inhibition of HIV-1 replication. The first and second internucleotide linkages are critical for activation of recombinant, human RNase L; A(Rp)ApA, A(Sp)ApA and ApA(Rp)A are agonists (IC50 = 2 x 10(-7), 2 x 10(-6) and 8 x 10(-6) M); ApA(Sp)A is an antagonist. The second and third internucleotide linkages are crucial for activation of murine RNase L; ApA(Rp)A, ApA(Rp)ApA, and ApApA(Rp)A are agonists (IC50 = 5 x 10(-7) M); ApA(Sp)A, ApA(Sp)ApA, and ApApA(Sp)A are antagonists. Inhibition of HIV-1-induced syncytia formation by the phosphorothioate/phosphodiester derivatives is specific for derivatives with substitution at the 2',3'-terminus. ApA(Rp)A, ApA(Sp)A, ApApA(Rp)A, and ApApA(Sp)A are potent inhibitors of HIV-1-induced syncytia formation (80-, 10-, 40-, and 15-fold more inhibitory, respectively, than solvent control). HIV-1 infection results in enhanced uptake and accumulation of ApA(Rp)A and ApA(Sp)A (7- and 10-fold, respectively). These stereochemically modified 2-5A derivatives are taken up preferentially by HIV-1-infected cells and show promise in anti-HIV-1 chemotherapy.

Role of interferons in the regulation of cell proliferation, differentiation, and development

There now appears to be evidence to support the view that the type I IFNs are naturally produced negative regulators of growth that also modify cell differentiation. Consistent with this, it appears that the ability to produce and respond to IFN is suppressed in early embryonic development when cell proliferation and differentiation are essential. In the later stages of fetal development, IFN production is de-repressed, and cells show increased sensitivity to IFN, which may be important in regulating cell proliferation and/or differentiation processes or the interaction between fetal and maternal tissues. Interestingly, the IFN system can also be suppressed in disease states such as the development of tumours or in the establishment of a (chronic) viral infection. Therefore, understanding the developmental regulation of the IFN system may be important to understanding and controlling the IFN system in disease. More extensive studies of the developmental stage and tissue-specific expression of type I IFNs and their receptors are necessary, as well as more direct in vivo experiments to further elucidate the role of the IFN system in reproduction and development.

Chemical synthesis and biological characterization of phosphorothioate analogs of 2', 5'-3'-deoxyadenylate trimer

In continued studies to elucidate the requirements for binding to and activation of the 2',5'-oligoadenylate (2-5A) dependent endoribonuclease (RNase L), four 2-5A trimer analogs were examined to evaluate the effect of chirality of phosphorothioate substitution on biological activity. The chemical syntheses and purification of the four isomers of P-thio-3'-deoxyadenylyl-(2'-5')-P-thio-3'- deoxyadenylyl-(2'-5')-3'-deoxyadenosine, by the phosphoramidite approach, is described. The isolated intermediates were characterized by elemental and spectral analyses. The fully deblocked compounds were characterized by 1H and 31P NMR and HPLC analyses. The 2',5'-(3'dA)3 cores with either Rp or Sp chirality in the 2',5'-internucleotide linkages will bind to but will not activate RNase L. This is in contrast to 2',5'-A3 core analogs with either RpRp or SpRp phosphorothioate substitution in the 2',5'-internucleotide linkages which can bind to and activate RNase L. There are also marked differences in the ability of the 2',5'-A3 analogs to activate RNase L following introduction of the 5'-monophosphate. For example, the 5'monophosphates of 2',5'-(3'dA)3-RpRp and 2',5'-(3'dA)3-SpRp can bind to and activate RNase L, whereas the 5'-monophosphates of 2',5'-(3'dA)3-RpSp and 2',5'-(3'dA)3-SpSp can bind to but can not activate RNase L.

Molecular expression of the negative growth factor murine beta-galactoside binding protein (mGBP)

Characterisation of the negative growth factor mGBP at molecular and biological levels indicates that the protein has no lectin nature and suggests instead a participation in the cytokine network. The protein is shown to be expressed as a monomer in two forms, one of which is non-covalently linked to a glycan complex. This confers greater efficiency to the inhibitor and may favour a paracrine role. The two monomeric forms may oxidise into tetramers which retain biological activity, but lack ability to link to specific saccharide residues.

A proliferation-related constraint on endogenous and interferon-induced 2-5A synthetase activity in normal and neoplastic Syrian hamster cells

2-5A Synthetase is one of the most extensively characterized enzymes induced by interferon (IFN) and is the central enzyme in a pathway that may be involved in the control of cellular proliferation. We examined the activity of this enzyme in normal diploid Syrian hamster cells (FC13) and their neoplastically transformed derivatives (BP6T); the former cell strain possesses regulated proliferative control, while the latter cell line has escaped from this control. A significant threefold increase in 2-5A synthetase activity was observed in density-arrested versus proliferating FC13 cells, whereas endogenous enzyme activity was uniformly low in BP6T cultures. The increase in enzyme activity in FC13 cultures was not accompanied by the production of IFN at a detectable level, but was parallelled by an increase in the intracellular level of 2',5'-oligoadenylate. IFN treatment resulted in a differential induction of enzyme activity depending on the proliferative state of FC13 cells. After IFN treatment, BP6T cells and subconfluent FC13 cells responded similarly with a fivefold increase in enzyme activity, whereas confluent FC13 cells displayed only a 1.4-fold increase. 2-5A Synthetase enzyme activity reflected steady-state mRNA levels in BP6T and subconfluent FC13 cells. In contrast, a noncoordinate regulation of 2-5A synthetase mRNA expression and enzyme activity was detected in confluent FC13 cells, suggesting that posttranscriptional mechanisms may be involved. The different patterns of endogenous and IFN-induced 2-5A synthetase enzyme activity in FC13 and BP6T cells found in this comparative study may represent an alteration fundamental to the loss of proliferative control in transformed cells.

Structure and expression of the negative growth factor mouse beta-galactoside binding protein gene

Following the identification of murine beta-galactoside binding protein (mGBP) as an autocrine negative growth factor we have now isolated and characterized the genomic region spanning the mGBP gene and have determined the 5' end of the transcript by primer extension, S1 mapping and mRNA sequence. The gene is found to be contained within 4 kilobases and composed of four exons of 79, 80, 171 and 197 nucleotides separated by three introns of 1200, 1600 and 193 nucleotides. The DNA region upstream of the 5' end of the transcript contains canonical sequences for eukaryotic promoter elements including CAT and TATA boxes and several DNA motifs for potential transcription regulation. The gene is differentially expressed in a variety of normal tissues.

Identification of an autocrine negative growth factor: mouse beta-galactoside-binding protein is a cytostatic factor and cell growth regulator

Murine beta-galactoside-binding protein, a protein classified as a soluble lectin, is shown to be a cell growth-regulatory molecule and a cytostatic factor. The growth-inhibitory effect is not related to lectin properties, and competition assays indicate that the protein binds to specific cell surface receptors with high affinity. It exerts control in G0 and at G2, both as a regulator of cell replication and as a cytostatic factor.