Modulation of E2F activity is linked to interferon-induced growth suppression of hematopoietic cells

Expression of different genotypes of bovine TRDMT1 gene and its polymorphisms association with body measures in Qinchuan cattle (Bos Taurus)

DNA methyltransferase 2 (DNMT2) was renamed as tRNA aspartic acid methyltransferase 1 (TRDMT1) by catalyzing the methylation of tRNA^Asp anti-codon loop C38. The development of sequencing of nucleic acids and protein detection techniques have prompted the demonstration that TRDMT1 mediated tRNA modification affects protein synthesis efficiency. This process affects the growth and development of animals. The DNA of 224 Qinchuan cattles aged 2-4 years old was collected in this experiment. The genetic variations of TRDMT1 exon and some intron regions were detected by mixed pool sequencing technology. qRT-PCR and Western Blot were used to detect the expression levels of mRNA and protein produced with the combination of different genetic variant loci. Three haplotypes were detected and the distribution ratios were different. Muscle tissue mRNA and protein testing showed that there were differences in mRNA expression levels among different genotypes (P < 0.05) and the protein expression levels between different genotypes show the same trend as mRNA. This study provides potential molecular materials for the improvement of Qinchuan cattle reproductivity and provides theoretical support for studying the effects of livestock TRDMT1 on animal growth and development.

E2F1 transcription factor and its impact on growth factor and cytokine signaling

E2F1 is a transcription factor involved in cell cycle regulation and apoptosis. The transactivation capacity of E2F1 is regulated by pRb. In its hypophosphorylated form, pRb binds and inactivates DNA binding and transactivating functions of E2F1. The growth factor stimulation of cells leads to activation of CDKs (cyclin dependent kinases), which in turn phosphorylate Rb and hyperphosphorylated Rb is released from E2F1 or E2F1/DP complex, and free E2F1 can induce transcription of several genes involved in cell cycle entry, induction or inhibition of apoptosis. Thus, growth factors and cytokines generally utilize E2F1 to direct cells to either fate. Furthermore, E2F1 regulates expressions of various cytokines and growth factor receptors, establishing positive or negative feedback mechanisms. This review focuses on the relationship between E2F1 transcription factor and cytokines (IL-1, IL-2, IL-3, IL-6, TGF-beta, G-CSF, LIF), growth factors (EGF, KGF, VEGF, IGF, FGF, PDGF, HGF, NGF), and interferons (IFN-α, IFN-β and IFN-γ).

Gene activity in primary T cells infected with HIV89.6: intron retention and induction of genomic repeats

Background

HIV infection has been reported to alter cellular gene activity, but published studies have commonly assayed transformed cell lines and lab-adapted HIV strains, yielding inconsistent results. Here we carried out a deep RNA-Seq analysis of primary human T cells infected with the low passage HIV isolate HIV_89.6.

Results

Seventeen percent of cellular genes showed altered activity 48 h after infection. In a meta-analysis including four other studies, our data differed from studies of HIV infection in cell lines but showed more parallels with infections of primary cells. We found a global trend toward retention of introns after infection, suggestive of a novel cellular response to infection. HIV_89.6 infection was also associated with activation of several human endogenous retroviruses (HERVs) and retrotransposons, of interest as possible novel antigens that could serve as vaccine targets. The most highly activated group of HERVs was a subset of the ERV-9. Analysis showed that activation was associated with a particular variant of ERV-9 long terminal repeats that contains an indel near the U3-R border. These data also allowed quantification of >70 splice forms of the HIV_89.6 RNA and specified the main types of chimeric HIV_89.6-host RNAs. Comparison to over 100,000 integration site sequences from the same infected cell populations allowed quantification of authentic versus artifactual chimeric reads, showing that 5′ read-in, splicing out of HIV_89.6 from the D4 donor and 3′ read-through were the most common HIV_89.6-host cell chimeric RNA forms.

Conclusions

Analysis of RNA abundance after infection of primary T cells with the low passage HIV_89.6 isolate disclosed multiple novel features of HIV-host interactions, notably intron retention and induction of transcription of retrotransposons and endogenous retroviruses.

Electronic supplementary material

The online version of this article (doi:10.1186/s12977-015-0205-1) contains supplementary material, which is available to authorized users.

Biological rationale and clinical use of interferon in the classical BCR-ABL-negative myeloproliferative neoplasms

Because of its antiapoptotic, antiproliferative, and immunomodulatory properties, interferon (IFN) has been broadly used as an antiviral and antineoplastic agent. These properties are particularly suitable for the treatment of the classical BCR-ABL-negative myeloproliferative neoplasms (MPN), including essential thrombocytosis (ET), polycythemia vera (PV), and myelofibrosis (MF). In the MPN, IFN has been shown to suppress megakaryopoiesis, inhibit erythroid colony-forming cells, suppress bone marrow fibroblast progenitors, induce cytogenetic remission, and reduce the JAK2 V617F allele burden, sometimes completely. Although efficacy has long been demonstrated in the MPN, toxicities were frequent with recombinant IFN, tempering enthusiasm. However, with pegylated-IFN, because of less toxicity, there has been renewed interest, and recent studies in the MPN have shown hematologic and molecular response or remission in ET and PV; a smaller study in early MF has shown IFN's potential to retard fibrosis. The role of IFN in the treatment of MPN is being re-evaluated on the basis of these studies, and will be better defined as results return from an ongoing international study.

E2F4 plays a key role in Burkitt lymphoma tumorigenesis

Sporadic Burkitt lymphoma (sBL) is a rapidly growing B-cell non-Hodgkin's lymphoma whose treatment requires highly aggressive therapies that often result severely toxic. Identification of proteins whose expression or function is deregulated in sBL and play a role in its formation could facilitate development of less toxic therapies. We have previously shown that E2F1 expression is deregulated in sBL. We have now investigated the mechanisms underlying E2F1 deregulation and found that the E2F sites in its promoter fail to repress its transcriptional activity in BL cells and that the transcriptional repressor E2F4 barely interacts with these sites. We also have found that E2F4 protein levels, but not those of its mRNA, are reduced in sBL cell lines relative to immortal B-cell lines. E2F4 protein expression is also decreased in 24 of 26 sBL tumor samples from patients compared with control tissues. Our data demonstrate that enforced E2F4 expression in BL cells not only diminishes E2F1 levels, but also reduces selectively the tumorigenic properties and proliferation of BL cells, while increasing their accumulation in G(2)/M. Our results therefore point to E2F4 as a target for developing novel and less toxic treatments for sBL.

Genome-wide analysis of target genes regulated by HoxB4 in hematopoietic stem and progenitor cells developing from embryonic stem cells

Forced expression of the transcription factor HoxB4 has been shown to enhance the self-renewal capacity of mouse bone marrow hematopoietic stem cells (HSCs) and confer a long-term repopulating capacity to yolk sac and embryonic stem (ES) cell-derived hematopoietic precursors. The fact that ES cell-derived precursors do not repopulate bone marrow without HoxB4 underscores an important role for HoxB4 in the maturation of ES-derived hematopoietic precursors into long-term repopulating HSCs. However, the precise molecular mechanism underlying this process is barely understood. In this study, we performed a genome-wide analysis of HoxB4 using ES cell-derived hematopoietic stem/progenitor cells. The results revealed many of the genes essential for HSC development to be direct targets of HoxB4, such as Runx1, Scl/Tal1, Gata2, and Gfi1. The expression profiling also showed that HoxB4 indirectly affects the expression of several important genes, such as Lmo2, Erg, Meis1, Pbx1, Nov, AhR, and Hemgn. HoxB4 tended to activate the transcription, but the down-regulation of a significant portion of direct targets suggested its function to be context-dependent. These findings indicate that HoxB4 reprograms a set of key regulator genes to facilitate the maturation of developing HSCs into repopulating cells. Our list of HoxB4 targets also provides novel candidate regulators for HSCs.

Disruption of mutually negative regulatory feedback loop between interferon-inducible p202 protein and the E2F family of transcription factors in lupus-prone mice

Studies have identified IFN-inducible Ifi202 gene as a lupus susceptibility gene (encoding p202 protein) in mouse models of lupus disease. However, signaling pathways that regulate the Ifi202 expression in cells remain to be elucidated. We found that steady-state levels of Ifi202 mRNA and protein were high in mouse embryonic fibroblasts (MEFs) from E2F1 knockout (E2F1(-/-)) and E2F1 and E2F2 double knockout (E2F1(-/-)E2F2(-/-)) mice than isogenic wild-type MEFs. Moreover, overexpression of E2F1 in mouse fibroblasts decreased expression of p202. Furthermore, expression of E2F1, but not E2F4, transcription factor in mouse fibroblasts repressed the activity of 202-luc-reporter in promoter-reporter assays. Interestingly, the E2F1-mediated transcriptional repression of the 202-luc-reporter was independent of p53 and pRb expression. However, the repression was dependent on the ability of E2F1 to bind DNA. We have identified a potential E2F DNA-binding site in the 5'-regulatory region of the Ifi202 gene, and mutations in this E2F DNA-binding site reduced the E2F1-mediated transcriptional repression of 202-luc-reporter. Because p202 inhibits the E2F1-mediated transcriptional activation of genes, we compared the expression of E2F1 and its target genes in splenic cells from lupus-prone B6.Nba2 congenic mice, which express increased levels of p202, with age-matched C57BL/6 mice. We found that increased expression of Ifi202 in the congenic mice was associated with inhibition of E2F1-mediated transcription and decreased expression of E2F1 and its target genes that encode proapoptotic proteins. Our observations support the idea that increased Ifi202 expression in certain strains of mice contributes to lupus susceptibility in part by inhibiting E2F1-mediated functions.

E2F-6 suppresses growth-associated apoptosis of human hematopoietic progenitor cells by counteracting proapoptotic activity of E2F-1

E2F-6 is a dominant-negative transcriptional repressor against other members of the E2F family. In this study, we investigated the expression and function of E2F-6 in human hematopoietic progenitor cells to clarify its role in hematopoiesis. We found that among E2F subunits, E2F-1, E2F-2, E2F-4, and E2F-6 were expressed in CD34(+) human hematopoietic progenitor cells. The expression of E2F-6 increased along with proliferation and decreased during differentiation of hematopoietic progenitors, whereas the other three species were upregulated in CD34(-) bone marrow mononuclear cells. Overexpression of E2F-6 did not affect the growth of immature hematopoietic cell line K562 but suppressed E2F-1-induced apoptosis, whereas it failed to inhibit apoptosis induced by differentiation inducers and anticancer drugs. Among E2F-1-dependent apoptosis-related molecules, E2F-6 specifically inhibited upregulation of Apaf-1 by competing with E2F-1 for promoter binding. E2F-6 similarly suppressed apoptosis and Apaf-1 upregulation in primary hematopoietic progenitor cells during cytokine-induced proliferation but had no effect when they were differentiated. As a result, E2F-6 enhanced the clonogenic growth of colony-forming unit-granulocyte, erythroid, macrophage, and megakaryocyte. These results suggest that E2F-6 provides a failsafe mechanism against loss of hematopoietic progenitor cells during proliferation. Disclosure of potential conflicts of interest is found at the end of this article.

DNA damage signaling and p53-dependent senescence after prolonged beta-interferon stimulation

Interferons are cytokines with potent antiviral and antiproliferative activities. We report that although a transient exposure to beta-interferon induces a reversible cell cycle arrest, a sustained treatment triggers a p53-dependent senescence program. Beta-interferon switched on p53 in two steps. First, it induced the acetylation of p53 at lysine 320 and its dephosphorylation at serine 392 but not p53 activity. Later on, it triggered a DNA signaling pathway, the phosphorylation of p53 at serine 15 and its transcriptional activity. In agreement, beta-interferon-treated cells accumulated gamma-H2AX foci and phosphorylated forms of ATM and CHK2. The DNA damage signaling pathway was activated by an increase in reactive oxygen species (ROS) induced by interferon and was inhibited by the antioxidant N-acetyl cysteine. More important, RNA interference against ATM inhibited p53 phosphorylation at serine 15, p53 activity and senescence in response to beta-interferon. Beta-interferon-induced senescence was more efficient in cells expressing either, p53, or constitutive allele of ERK2 or RasV12. Hence, beta-interferon-induced senescence targets preferentially cells with premalignant changes.

Stat1 and Stat2 but not Stat3 arbitrate contradictory growth signals elicited by alpha/beta interferon in T lymphocytes

Alpha/beta interferon (IFN-alpha/beta) triggers antiviral and antiproliferative responses in target cells through modulation of gene expression. The JAK-STAT pathway is the major mediator of these biological effects through the activation of the transcription factors STAT1 and STAT2, and gene ablation studies have demonstrated that both STAT1 and STAT2 are required for most antiviral responses induced by IFN-alpha/beta. However, additional signaling pathways are also activated by IFN. Here, we show that these additional pathways provoke a proliferative response in activated T lymphocytes. While activation of IFN-stimulated gene factor 3 produces a dominant inhibitory signal capable of overriding the mitogenic response, absence of either STAT1 or STAT2 leads to a proliferative response to IFN. Growth stimulation by IFN-alpha/beta is independent of other STAT proteins, particularly of STAT3, since T lymphocytes from STAT1-STAT3 double-knockout mice are growth stimulated by IFN-alpha/beta treatment. IFN-alpha/beta can cooperate with numerous T-cell mitogens, including interleukin-2 (IL-2), IL-4, IL-7, and IL-12, and can contribute to the rapid restoration of the thymus following glucocorticoid-mediated ablation. These results underscore the complexity of the cellular response to IFN and suggest that the ultimate outcome of IFN action results from a balance between growth-inhibitory and -stimulatory effects.

Viral hepatitis and hepatocellular carcinoma

BACKGROUND

Hepatocellular carcinoma (HCC) is one of the most common malignant tumors in the world. The incidence of HCC varies considerably with the geographic area because of differences in the major causative factors. Chronic hepatitis B and C, mostly in the cirrhotic stage, are responsible for the great majority of cases of HCC worldwide. The geographic areas at the highest risk are South-East Asia and sub-Saharan Africa, here hepatitis B is highly endemic and is the main cause of HCC. In areas with an intermediate rate of HCC such as Southern Europe and Japan, hepatitis C is the predominant cause, whereas in low rate areas such as Northern Europe and the USA, HCC is often related to other factors as alcoholic liver disease. There is a rising incidence in HCC in developed countries during the last two decades, due to the increasing rate of hepatitis C infection and improvement of the clinical management of cirrhosis.

METHODS

This article reviews the literature on hepatitis and hepatocellular carcinoma. The Medline search was carried out using these key words and articles were selected on epidemiology, risk factors, screening, and prevention of hepatocellular carcinoma.

RESULTS

Screening of patients with advanced chronic hepatitis B and C with hepatic ultrasound and determination of serum alfa-fetoprotein may improve the detection of HCC, but further studies are needed whether screening improves clinical outcome. Hepatitis B and C viruses (HBV/HCV) can be implicated in the development of HCC in an indirect way, through induction of chronic inflammation, or directly by means of viral proteins or, in the case of HBV, by creation of mutations by integration into the genome of the hepatocyte.

CONCLUSION

The most effective tool to prevent HCC is avoidance of the risk factors such as viral infection. For HBV, a very effective vaccine is available. Preliminary data from Taiwan indicate a protective effect of universal vaccination on the development of HCC. Vaccination against HBV should therefore be a health priority. In patients with chronic hepatitis B or C, interferon-alfa treatment in a noncirrhotic stage is protective for HCC development in responders, probably by prevention of cirrhosis development. When cirrhosis is already present, the protective effect is less clear. For cirrhosis due to hepatitis B, a protective effect was demonstrated in Oriental, but not in European patients. For cirrhosis due to hepatitis C, interferon-alfa treatment showed to be protective in some studies, especially in Japan with a high incidence of HCC in untreated patients. Virological, but also merely biochemical response, seems to be associated with a lower risk of development of HCC. As most studies are not randomized controlled trials, no definitive conclusions on the long-term effects of interferon-alfa in HBV or HCV cirrhosis can be established. Especially in hepatitis C, prospective studies should be performed using the more potent reference treatments for cirrhotics, namely the combination of peginterferon and ribavirin.

Inactivation of TGF-beta signaling in hepatocytes results in an increased proliferative response after partial hepatectomy

The transforming growth factor beta (TGF-beta) signaling pathway, which is activated by the TGF-beta receptor complex consisting of type I and type II TGF-beta receptors (TGFBR1 and TGFBR2), regulates cell growth and death. TGF-beta and components of its signaling pathway, particularly TGFBR2, have been implicated as tumor suppressor genes and important antimitogenic factors in the gastrointestinal tract and liver. An in vivo approach to study these effects has been hindered by the embryonic lethality of Tgfbr2(-/-) mice and poor viability of the Tgfb1(-/-) mice. Consequently, we have developed a hepatocyte-specific Tgfbr2 knockout mouse, the Alb-cre Tgfbr2(flx/flx) mouse, to study the physiologically relevant effects of TGF-beta signaling on epithelial cell proliferation in vivo. After 70% hepatectomy, we observed increased proliferation and an increased liver mass : body weight ratio in the Alb-cre Tgfbr2(flx/flx) mice compared to Tgfbr2(flx/flx) mice. We also observed decreased expression and increased phosphorylation of p130 in the livers from the Alb-cre Tgfbr2(flx/flx) mice as well as increased expression of cyclin E, which is transcriptionally regulated, in part, by p130:E2F4. Consistent with these results, in a hepatocyte cell line derived from the Tgfbr2(flx/flx) mice, we found that TGF-beta increases the nuclear localization of E2F4, and presumably the transcriptional repression of the p130:E2F4 complex. Thus, we have demonstrated that TGF-beta signaling in vivo regulates the mitogenic response in the regenerating liver, affecting the liver mass : body weight ratio after partial hepatectomy, and that these mitogenic responses are accompanied by alterations in p130 expression and phosphorylation, implicating p130 as one of the proteins regulated in vivo by TGF-beta during liver regeneration.

IFN-gamma inhibits human airway smooth muscle cell proliferation by modulating the E2F-1/Rb pathway

Elucidating the factors that inhibit the increase in airway smooth muscle (ASM) mass may be of therapeutic benefit in asthma. Here, we investigated whether interferon-gamma (IFN-gamma), a potent inducer of growth arrest in various cell types, regulates mitogen-induced ASM cell proliferation. IFN-gamma (1-100 U/ml) was found to markedly decrease both DNA synthesis and ASM cell number induced by the mitogens epidermal growth factor (EGF) and thrombin. Interestingly, IFN-gamma had no effect on mitogen-induced activation of three major mitogenic signaling pathways, phosphatidylinositol 3-kinase, p70(S6k), or mitogen-activated protein kinases. Mitogen-induced expression of cell cycle regulator cyclin D1 was increased by IFN-gamma, whereas no effect was observed on degradation of p27(Kip1). Expression array analysis of 23 cell cycle-related genes showed that IFN-gamma inhibited EGF-induced increases in E2F-1 expression, whereas induction of c-myc, cyclin D2, Egr-1, and mdm2 were unaffected. Induction of E2F-1 protein and Rb hyperphosphorylation after mitogen stimulation was also suppressed by IFN-gamma. In addition, IFN-gamma decreased activation of cdk2 and expression of cyclin E, upstream signaling molecules responsible for Rb hyperphosphorylation in the late G1 phase. IFN-gamma also increased levels of IFI 16 protein, whose mouse homolog p202 has been associated with growth inhibition. Together, our data indicate that IFN-gamma is an effective inhibitor of ASM cell proliferation by blocking transition from G1-to-S phase by acting at two different levels: modulation of cdk2/cyclin E activation and inhibition of E2F-1 gene expression.

Interferon-alpha inhibits cell cycle progression by Ba/F3 cells through the antagonisation of interleukin-3 effects on key regulators of G(1)/S transition

The molecular mechanisms of interferon-alpha (IFN-alpha)-mediated cell growth inhibition are incompletely understood. Here, we have analysed how IFN-alpha interferes with the interleukin-3 (IL-3)-stimulated cell cycle progression by Ba/F3 cells. The antiproliferative cytokine caused a delay in cell cycle progression, which correlated with a diminished activation of the cyclin-dependent kinases 2 and 4 in IL-3-stimulated cells. While IFN-alpha did not affect the expression of p27(Kip1) and p21(Waf1), it efficiently inhibited the IL-3-induced expression of D-type cyclin and cyclin E proteins. No IL-3-antagonistic effects of the IFN, however, were observed at the mRNA level of cyclin expression. Furthermore, IFN-alpha suppressed the IL-3-induced release of E2F transcription factors from the retinoblastoma protein (pRb) and enhanced pRb-mediated transcriptional repression. The growth factor-antagonistic action of IFN-alpha correlated with a strong stimulation of protein kinase R expression, suggesting that inhibition of protein synthesis plays a pivotal role in IFN-alpha-mediated inhibition of cell cycle progression.

Review: IFN-alpha/beta receptor interactions to biologic outcomes: understanding the circuitry

Type I interferons (IFNs), which include the IFN-alphas, IFN-beta, IFN-omega, IFN-kappa, and IFN-tau, are an evolutionarily conserved group of secreted cytokines that serve as potent extracellular mediators of host defense and homeostasis. Binding of IFNs to specific cell surface receptors results in the activation of multiple intracellular signaling cascades, leadingto the synthesis of proteins that mediate antiviral, growth inhibitory and immunomodulatory responses. In the past decade, considerable information has accumulated pertaining to the different signalingpathways that are activated by the type I IFNs. Although many of the literature findings are specific to defined cell systems or are tissue restricted, the intent of this review is to place these signaling cascades and their effectors in the context of distinct biologic outcomes.

Differences in E2F subunit expression in quiescent and proliferating vascular smooth muscle cells

E2F is a family of transcriptional factors that control G(1)/S transition. We investigated how the E2F family participates in the biological responses of vascular smooth muscle cells (VSMC) to vasoconstrictive hormones compared with fetal bovine serum (FBS). FBS induced upregulation of E2F-1 and E2F-5 at both mRNA and protein levels and slightly reduced E2F-3 protein. Angiotensin II (ANG II) and arginine vasopressin increased E2F-3 protein, but not E2F-1 and E2F-5, without upregulating its mRNA level. FBS transactivated the E2F-1 gene through the induction of free E2F-1 binding onto its promoter, whereas ANG II-induced binding of E2F-3 did not result in activation of the E2F-1 promoter. These changes are responsible for hypertrophic or hyperplastic response of VSMC to different growth factors or stimulants. In contrast, both FBS and vasoconstrictive hormones drove transcription of the cdc6 gene by downregulating p130 and recruiting free E2F-3 in the latter, which underlies the progression of VSMC into S phase.

Hyperglycemia enhances VSMC proliferation with NF-kappaB activation by angiotensin II and E2F-1 augmentation by growth factors

To clarify the mechanisms of hyperglycemia-induced proliferation of vascular smooth muscle cells (VSMC), we examined the effects of high glucose (HG) on nuclear factor (NF)-kappaB and E2F-1. Angiotensin II (Ang II) significantly enhanced DNA binding activity of NF-kappaB under HG (25.6 mM) conditions with an increase in p65 subunit of NF-kappaB, and did it slightly under normal glucose (NG; 5.6 mM) conditions. Ang II failed to induce E2F-1 expression, or its binding to the cdc2 promoter, even under HG conditions. HG greatly augmented the cdc2 inducibility of fetal calf serum (FCS), through the increase in E2F-1 activity. These data indicate that hyperglycemia contributes to abnormal proliferation of VSMC by two mechanisms; the induction of NF-kappaB activation by Ang II, which facilitates transcription of certain growth factors, and the augmentation of E2F-1 in response to growth factors.

Prolonging the half-life of human interferon-alpha 2 in circulation: Design, preparation, and analysis of (2-sulfo-9-fluorenylmethoxycarbonyl)7- interferon-alpha 2

Polypeptide drugs are generally short-lived species in circulation. In this study, we have covalently linked seven moieties of 2-sulfo-9-fluorenylmethoxycarbonyl (FMS) to the amino groups of human interferon-alpha2. The derivative thus obtained (FMS(7)-IFN-alpha2) has approximately 4% the biological potency and 33 +/- 4% the receptor binding capacity of the native cytokine. Upon incubation, FMS(7)-IFN-alpha2 undergoes time-dependent spontaneous hydrolysis, generating active interferon with t(1/2) values of 24 +/- 2 h at pH 8.5 and 98 +/- 10 h at pH 7.4. When native IFN-alpha2 is intravenously administered to mice, circulating antiviral activity is maintained for a short duration and then declines with t(1/2) = 4 +/- 0.5 h, reaching undetectable values at approximately 18 h after administration. With intravenously administered FMS(7)-IFN-alpha2, there is a lag period of 2 h, followed by a progressive elevation in circulating antiviral-active protein, which peaked at 20 h and declined with t(1/2) = 35 +/- 4 h. FMS(7)-IFN-alpha2 is resistant to alpha-chymotrypsin digest and to proteolytic inactivation by human serum proteases in vitro. We have thus introduced here an inactive IFN-alpha2 derivative, which is resistant to in situ inactivation and has the capability of slowly reverting to the native active protein at physiological conditions in vivo and in vitro. Having these attributes, FMS(7)-IFN-alpha2 maintains prolonged circulating antiviral activity in mice, exceeding 7-8 times the activity of intravenously administered native cytokine.

Interferon-beta induces S phase slowing via up-regulated expression of PML in squamous carcinoma cells

Type I Interferon (IFN) and all-trans retinoic acid (RA) inhibit cell proliferation of squamous carcinoma cell lines (SCC). Examinations of growth-affected cell populations show that SCC lines ME-180 and SiHa treated with IFN-beta undergo a specific slower progression through the S phase that seems to trigger cellular death. In combination treatment RA potentiates IFN-beta effect in SCC ME-180 but not in SiHa cell line, partially resistant to RA antiproliferative action. RA added as single agent affects cell proliferation differently by inducing a slight G1 accumulation. The IFN-beta-induced S phase lengthening parallels the increased expression of PML, a nuclear phosphoprotein specifically up-regulated at transcriptional level by IFN, whose overexpression induces cell growth inhibition and tumor suppression. We report that PML up-regulation may account for the alteration of cell cycle progression induced by IFN-beta in SCC by infecting cells with PML-PINCO recombinant retrovirus carrying the PML-3 cDNA under the control of the 5' LTR. In fact PML overexpression reproduces the IFN-beta-induced S phase lengthening. These findings provide important insight into the mechanism of tumor suppressing function of PML and could allow PML to be included in the pathways responsible for IFN-induced cell growth suppression.

How Stat1 mediates constitutive gene expression: a complex of unphosphorylated Stat1 and IRF1 supports transcription of the LMP2 gene

Analysis of mRNA levels in cells that express or lack signal transducers and activators of transcription 1 (Stat1) reveals that Stat1 mediates the constitutive transcription of many genes. Expression of the low molecular mass polypeptide 2 (LMP2), which requires Stat1, has been studied in detail. The overlapping interferon consensus sequence 2/gamma-interferon-activated sequence (ICS-2/GAS) elements in the LMP2 promoter bind to interferon regulatory factor 1 (IRF1) and Stat1 and are occupied constitutively in vivo. The point mutant of Stat1, Y701F, which does not form dimers involving SH2-phosphotyrosine interactions, binds to the GAS element and supports LMP2 expression. Unphosphorylated Stat1 binds to IRF1 directly and we conclude that this complex uses the ICS-2/GAS element to mediate constitutive LMP2 transcription in vivo. The promoter of the IRF1 gene, which also contains a GAS site but not an adjacent ICS-2 site, is not activated by Stat1 Y701F. The promoters of other genes whose constitutive expression requires Stat1 may also utilize complexes of unphosphorylated Stat1 with IRF1 or other transcription factors.

Ectopic expression of c-myc fails to overcome downregulation of telomerase activity induced by herbimycin A, but ectopic hTERT expression overcomes it

Telomerase plays a key role in the maintenance of chromosomal stability in tumors, but the mechanism regulating telomerase activity is still unclear. Recent studies have suggested that c-myc may be vital for regulation of hTERT mRNA expression and telomerase activity. In this study, we investigated the changes of telomerase activity and telomerase-related genes induced by herbimycin A in K562 human chronic myelogeous leukemic cells. Telomerase activity showed a biphasic pattern in herbimycin A-treated K562 cells. Initially, the telomerase activity decreased along with the decline of cells in S and G2/M phases, but it recovered slightly at the end of treatment. Expression of mRNA for the telomerase catalytic subunit (hTERT) was decreased before the decline of telomerase activity, and increased slightly before the reactivation of telomerase activity. During herbimycin A treatment, both c-myc and cyclin D1 mRNA showed transient downregulation before the increase of G1 cells. Herbimycin A treatment caused the downregulation of both telomerase activity and hTERT mRNA in cyclin D1-transfected K562 cells, while telomerase activity was partially restored in c-Myc-transfected cells. In contrast, hTERT-transfected K562 cells maintained a high level of telomerase activity during herbimycin A treatment. Neither the template RNA component of telomerase (hTERC) nor telomerase-associated protein (TEP-1) were altered in any of the transfected K562 cells. These results indicate that telomerase activity is mainly regulated by hTERT, and that c-Myc protein is one of the positive regulators of hTERT in leukemic cells but is not enough to counteract the downregulation of telomerase activity by herbimycin A completely.

Molecular mechanism of interferon alfa-mediated growth inhibition in human neuroendocrine tumor cells

BACKGROUND & AIMS

Although human neuroendocrine tumors respond to interferon (IFN)-alpha treatment in vivo, the underlying mechanisms of growth inhibition are poorly understood. To characterize the antiproliferative effects at a molecular level, we explored the growth-regulatory action of IFN-alpha in the human neuroendocrine tumor cell lines BON and QGP1.

METHODS

IFN-alpha receptor expression and signal transduction were examined by reverse-transcription polymerase chain reaction, immunoblotting, subcellular fractionation, and transactivation assays. Growth regulation was evaluated by cell numbers, soft agar assays, and cell cycle analysis using flow cytometry. Expression and activity of cell cycle-regulatory molecules were determined by immunoblotting and histone H1-kinase assays.

RESULTS

Both cell lines expressed IFN-alpha receptor mRNA transcripts. Ligand binding initiated phosphorylation of Jak kinases and Stat transcription factors, resulting in Stat activation, nuclear translocation, and transcription from an ISRE-reporter construct. Prolonged IFN-alpha treatment dose-dependently inhibited both anchorage-dependent and -independent growth. Cell cycle analysis of IFN-alpha-treated, unsynchronized cultures revealed an increased S-phase population, which was further substantiated in G(1) synchronized QGP1 cells. IFN-alpha-treated cells entered S phase in parallel to control cultures, but their progress into G(2)/M phase was delayed. Both cellular cyclin B levels and CDC 2 activity were substantially reduced. The extent and time course of this reduction corresponded to the observed S-phase accumulation.

CONCLUSIONS

IFN-alpha directly inhibits growth of human neuroendocrine tumor cells by specifically delaying progression through S phase and into G(2)/M. These cell cycle changes are associated with inhibition of cyclin B expression, resulting in reduced CDC2 activity.

Three-dimensional matrix suppresses E2F-controlled gene expression in glomerular mesangial cells

BACKGROUND

Extracellular matrix (ECM) regulates mitogenesis of glomerular mesangial cells. Currently, however, the molecular mechanisms that mediate the control of cell growth by ECM are not fully elucidated.

METHODS

The effects of structurally distinct forms of type I collagen matrix on mesangial cell proliferation and cell cycle distribution were examined. Expressions of the cell cycle-regulatory transcription factor E2F and retinoblastoma susceptibility gene family proteins were also investigated.

RESULTS

Mesangial cells cultured on monomeric collagen matrix showed a substantial growth response to serum. In contrast, mesangial cells cultured on polymerized collagen matrix exhibited arrest of the cell cycle in the G0/G1 phase. The induction of the quiescent phenotype was correlated with down-regulation of E2F-1, the prototypal transcription factor that controls cell cycle progression. The suppression of E2F-1 was associated with (1) dephosphorylation of retinoblastoma susceptibility gene proteins, pRB and p130, and (2) accumulation of E2F-pRB and E2F-p130 DNA binding complexes that bind to the E2F consensus sequence located in the E2F-1 promoter. Other E2F regulatory genes, including c-myc, cyclin A, and cdc 2, were also down-regulated in mesangial cells cultured on polymerized collagen matrix.

CONCLUSION

These results suggest that a three-dimensional collagen induces cell cycle arrest via suppression of E2F-controlled gene expression in mesangial cells. Dephosphorylation of pRB and p130 and subsequent generation of transrepressor complexes, E2F-pRB and E2F-p130, may be involved in this process.

Failure of cdc2 promoter activation and G(2)/M transition by ANG II and AVP in vascular smooth muscle cells

The physiological role of the vasoconstrictive hormones arginine vasopressin (AVP) and angiotensin II (ANG II) in the development of vascular hyperplasia is still unclear. We examined the effects of these hormones on cell cycle regulation of cultured rat vascular smooth muscle cells (VSMC). AVP and ANG II were able to induce G(1)/S transition and DNA synthesis in serum-starved quiescent VSMC but failed to promote further progression into G(2)/M phases. AVP and ANG II enhanced the expression and activity of cdk2, cyclin E, and proliferating cell nuclear antigen but did not induce expression of cdc2/cyclin B complex, a critical regulator of G(2)/M transition. The failure of cdc2 mRNA induction was found to be caused by a defect in cdc2 promoter activation. Binding of free E2F-1 to the cdc2 promoter did not occur in hormone-treated VSMC, which may account for the defective induction of cdc2. The absence of cdc2 promoter activation and G(2)/M transition may be important for the prevention of hyperplasia under physiological conditions but underlies the hypertrophy of VSMC.

Interferon-alpha repressed telomerase along with G1-accumulation of Daudi cells

The implications of telomerase on senescence and human carcinogenesis are widely accepted, but the changes of telomerase activity along with cell cycle modulation by anticancer treatment still remain obscure. In this paper, we issued whether the telomerase activity fluctuated along with cell cycle of cultured cancer cells using the antiproliferative effect of interferon-alpha (IFN-alpha). Daudi Burkitt lymphoma cells, treated with IFN-alpha, showed proliferation inhibition and cell cycle arrest at G1. The telomerase activity at 72 h was repressed to about 20% of control cells. Furthermore, after 72 h IFN-alpha treatment, the cells in G1 phase showed the marked decrease of telomerase activity, while cells in S and G2/M still possessed it. Among expressions of telomerase-related genes, only the catalytic subunit of telomerase (hTERT) decreased from 48 h, while the template RNA component (hTERC) and telomerase-associated protein 1 (TEP-1) were not affected. The downregulation of c-Myc preceded the change of hTERT. Moreover, the analysis of cells treated with IFN-alpha for 24 h revealed that cells in G1-to-S transition mainly expressed high hTERT, while S and G2/M cells had higher level of telomerase activity than that of G1 cells. These results indicate that (i) the expression of hTERT precedes the telomerase activity which is higher in S and G2/M phases than G1 phase, (ii) IFN-alpha repressed the telomerase activity in a cell cycle-dependent manner with the downregulation of hTERT.

Defective binding of IRFs to the initiator element of interleukin-1beta-converting enzyme (ICE) promoter in an interferon-resistant Daudi subline

To investigate mechanisms of interferon (IFN) resistance, we have established an IFN-resistant Daudi subline (Daudi(res)), which is 1 X 10(4) times more resistant to IFN-alpha than parental cells. Among the IFN-inducible genes examined, only ICE mRNA expression was deficient in Daudi(res) cells. We then analyzed the regulatory mechanisms of ICE transcription, and found that IFN-induced activation of the ICE promoter was dependent on the binding of IRFs to its initiator (Inr) element. Inr binding of IRFs was markedly diminished in Daudi(res) cells, and forced expression of IRF-1 was able to activate the ICE promoter to the level of parental cells. These results suggest that IRFs and their target genes, as represented by ICE in this study, are involved in IFN resistance.

Transcriptional repression of the E2F-1 gene by interferon-alpha is mediated through induction of E2F-4/pRB and E2F-4/p130 complexes

E2F is a heterodimeric transcription factor composed of one of five E2F subunits (E2F-1 to E2F-5) and a DP subunit. E2F regulates the expression of several growth-promoting genes, and thus, can be a target of antiproliferative action of interferons (IFNs). In this study, we investigated the mechanisms whereby IFN-alpha suppresses transcription of the E2F-1 gene. Transfection studies revealed that E2F-1 promoter was functionally divided into two parts: upstream activation sequences (UAS) and a downstream negative-regulatory element (E2F-binding sites). When cells were proliferating, transcription of the E2F-1 gene was primarily driven by the UAS, while E2F sites were not involved in activation. IFN-alpha markedly reduced E2F-1 promoter activity, but introduction of non-binding mutation at the E2F sites completely abrogated the inhibition. Free E2F4 was found to be the predominant species bound to the E2F sites in proliferating cells. IFN-alpha induced upregulation of E2F-4 along with dephosphorylation of pRB and p130, which resulted in the formation of E2F-4/pRB and E2F-4/p130 complexes on the E2F-1 promoter. These complexes function as transcriptional repressors to inhibit E2F-1 mRNA expression. Our findings indicate that E2F-4 is a critical regulator of E2F-1, which offer an excellent paradigm for understanding functional diversity within the E2F family.

Cell cycle regulation of the double stranded RNA activated protein kinase, PKR

The interferon (IFN)-induced, double stranded RNA (dsRNA)-activated serine/threonine kinase, PKR, is a potent negative regulator of cell growth when overexpressed in yeast or mammalian cells. To determine whether endogenous PKR plays a role in cell growth control, we have investigated the regulation of PKR levels and activity during the cell cycle in human glioblastoma T98G cells. The steady-state level of PKR mRNA in T98G cells was highest in growth arrested cells, dropped sharply within 3 h of serum stimulation then gradually increased as cells progressed through G1, reaching a plateau in early S phase. PKR protein level increased following serum stimulation reaching a peak at the G2+M boundary and declining thereafter. In contrast, PKR kinase activity exhibited two peaks, in early G1 and at the G1/S boundary, declining sharply in early S phase. Thus, the activity profile did not follow the protein profile indicating a tight regulation of PKR at the level of activity. In T98G cells expressing the catalytically inactive PKRK296R the dsRNA-induced activation of NF-kappaB and IRF-1 was suppressed and the mutant cells exhibited resistance to stress induced apoptosis. Cell cycle distribution analysis showed that the mutant expressing cells exhibited longer G1 phase and fewer cells engaged in S phase. Furthermore, early passage mouse embryo fibroblasts derived from PKR knockout mice grew more slowly compared with the control cells. Taken together these results suggest that PKR may play a role in cell cycle progression.

Participation of Bax-alpha in IFN-alpha-mediated apoptosis in Daudi B lymphoma cells

Although interferon-alpha (IFN-alpha) has proved beneficial in the treatment of some tumors, the basis for this is still uncertain. In this study, we examined the effects of IFN-alpha on the growth of tumor cells in vitro, using the Daudi line of B lymphoma cells as a model. There was a dose-dependent accumulation of these cells in the G1 phase of the cell cycle 24-48 h from the time of exposure to IFN-alpha. This was followed between 48 h and 96 h by an increasing degree of apoptosis, as assessed by cell survival, propidium iodine staining, and transmission electron microscopy. Concomitantly with the apoptosis, there was the appearance of pl8 Bax-alpha, an apparently novel variant low molecular weight form of the p21 Bax-alpha found in normal cells. There was also a slight diminution in Bcl-xL, with a resultant drop in the Bcl-xL:Bax-alpha ratio. Treatment of cells with CD40-L partially inhibited the development of apoptosis in response to IFN-alpha. At the same time, generation of p18 Bax-alpha was reduced, which suggests that this plays a part in the apoptotic process. These findings may throw light on the development of lymphomas and perhaps point to future ways of improving therapy with IFN-alpha.

p130, p107, and pRb are differentially regulated in proliferating cells and during cell cycle arrest by alpha-interferon

We have determined how the phosphorylation of the retinoblastoma family (pRb, p107, and p130) is governed in individual cell cycle phases of Daudi B-cells during cell cycle exit triggered by alpha-interferon (alpha-IFN). alpha-IFN causes dephosphorylation of pRb and loss of p130 phosphorylated Form 3. However, the change in p130 phosphorylation in response to alpha-IFN occurs before dephosphorylation of pRb is complete because loss of p130 Form 3 occurs throughout the cell cycle prior to complete arrest in G1, whereas pRb is dephosphorylated only in G1. In contrast, p107 is dephosphorylated and is then depleted from cells as they exit the cell cycle. p130, predominantly in Form 1, and hypophosphorylated pRb bind an E2F DNA binding site; p130 complexes E2F-4, whereas pRb binds both E2F-4 and E2F-1. The phosphorylated forms of E2F-4 that bind to the E2F DNA site are different from hyperphosphorylated E2F-4, which predominates in primary hemopoietic cells in G0. We conclude that although cell cycle arrest induced by alpha-IFN may be mediated in part by formation of a complex containing p130 and E2F-4, alpha-IFN does not induce hyperphosphorylation of E2F-4, which characterizes primary hemopoietic cells in G0.