Induction of interferon regulatory factors 2'-5' oligoadenylate synthetase, P68 kinase and RNase L in chronic myelogenous leukaemia cells and its relationship to clinical responsiveness

Expression microarray identifies the unliganded glucocorticoid receptor as a regulator of gene expression in mammary epithelial cells

Background

While glucocorticoids and the liganded glucocorticoid receptor (GR) have a well-established role in the maintenance of differentiation and suppression of apoptosis in breast tissue, the involvement of unliganded GR in cellular processes is less clear. Our previous studies implicated unliganded GR as a positive regulator of the BRCA1 tumour suppressor gene in the absence of glucocorticoid hormone, which suggested it could play a similar role in the regulation of other genes.

Methods

An shRNA vector directed against GR was used to create mouse mammary cell lines with depleted endogenous levels of this receptor in order to further characterize the role of GR in breast cells. An expression microarray screen for targets of unliganded GR was performed using our GR-depleted cell lines maintained in the absence of glucocorticoids. Candidate genes positively regulated by unliganded GR were identified, classified by Gene Ontology and Ingenuity Pathway Analysis, and validated using quantitative real-time reverse transcriptase PCR. Chromatin immunoprecipitation and dual luciferase expression assays were conducted to further investigate the mechanism through which unliganded GR regulates these genes.

Results

Expression microarray analysis revealed 260 targets negatively regulated and 343 targets positively regulated by unliganded GR. A number of the positively regulated targets were involved in pro-apoptotic networks, possibly opposing the activity of liganded GR targets. Validation and further analysis of five candidates from the microarray indicated that two of these, Hsd11b1 and Ch25h, were regulated by unliganded GR in a manner similar to Brca1 during glucocorticoid treatment. Furthermore, GR was shown to interact directly with and upregulate the Ch25h promoter in the absence, but not the presence, of hydrocortisone (HC), confirming our previously described model of gene regulation by unliganded GR.

Conclusion

This work presents the first identification of targets of unliganded GR. We propose that the balance between targets of liganded and unliganded GR signaling is responsible for controlling differentiation and apoptosis, respectively, and suggest that gene regulation by unliganded GR may represent a mechanism for reducing the risk of breast tumourigenesis by the elimination of abnormal cells.

hsp70 and a novel axis of type I interferon-dependent antiviral immunity in the measles virus-infected brain

The major inducible 70-kDa heat shock protein (hsp70) is host protective in a mouse model of measles virus (MeV) brain infection. Transgenic constitutive expression of hsp70 in neurons, the primary target of MeV infection, abrogates neurovirulence in neonatal H-2(d) congenic C57BL/6 mice. A significant level of protection is retained after depletion of T lymphocytes, implicating innate immune mechanisms. The focus of the present work was to elucidate the basis for hsp70-dependent innate immunity using this model. Transcriptome analysis of brains from transgenic (TG) and nontransgenic (NT) mice 5 days after infection identified type I interferon (IFN) signaling, macrophage activation, and antigen presentation as the main differences linked to survival. The pivotal role of type I IFN in hsp70-mediated protection was demonstrated in mice with a genetically disrupted type I IFN receptor (IFNAR(-/-)), where IFNAR(-/-) eliminated the difference in survival between TG and NT mice. Brain macrophages, not neurons, are the predominant source of type I IFN in the virus-infected brain, and in vitro studies provided a mechanistic basis by which MeV-infected neurons can induce IFN-β in uninfected microglia in an hsp70-dependent manner. MeV infection induced extracellular release of hsp70 from mouse neuronal cells that constitutively express hsp70, and extracellular hsp70 induced IFN-β transcription in mouse microglial cells through Toll-like receptors 2 and 4. Collectively, our results support a novel axis of type I IFN-dependent antiviral immunity in the virus-infected brain that is driven by hsp70.

The role of interferon regulatory factor-1 and interferon regulatory factor-2 in IFN-gamma growth inhibition of human breast carcinoma cell lines

Interferon (IFN) regulatory factor-1 (IRF-1) and IRF-2 play opposing roles in the regulation of many IFN-gamma-inducible genes. To investigate the signal transduction pathway in response to IFN-gamma in light of differences in growth effects, we selected four human breast carcinoma cell lines based on a spectrum of growth inhibition by IFN-gamma. MDA468 growth was markedly inhibited by IFN-gamma, and it showed substantial induction of IRF-1 mRNA but little IRF-2 induction. SKBR3 showed little growth inhibition and little induction of IRF-1 mRNA but significant induction of IRF-2 mRNA. HS578T and MDA436 growth inhibition and IRF-1/IRF-2 induction were intermediate. All four cell lines showed intact receptor at the cell surface and Stat1 translocation to the nucleus by immunostaining. By EMSA, there were marked differences in the induced ratio of IRF-1 and IRF-2 binding activity between the cell lines that correlated with growth inhibition. Finally, antisense oligonucleotides specific for IRF-1 attenuated IFN-gamma growth inhibition in MDA436 and MDA468, confirming the direct role of IRF-1 in IFN-gamma growth inhibition. Induction of IRF-1 causes growth inhibition in human breast cancer cell lines, and induction of IRF-2 can oppose this. The relative induction of IRF-1 to IRF-2 is a critical control point in IFN-gamma response.

Interferons and apoptosis

The interferons (IFNs), in addition to their well-known antiviral activities, have important roles in the control of cell proliferation and are effective agents for the treatment of a limited number of malignant diseases. IFNs not only regulate cell growth and division but also influence cell survival through their effects on apoptosis. This review describes the current state of knowledge about the mechanisms of action of these cytokines on the apoptotic machinery, with particular emphasis on the synergism that exists between the IFNs and other proapoptotic agents, such as members of the tumor necrosis factor (TNF) family. The review also discusses the physiologic and clinical implications of the effects of the IFNs on apoptosis for regulation of viral infection and tumor growth.

Pharmacokinetic and pharmacodynamic studies of a human serum albumin-interferon-alpha fusion protein in cynomolgus monkeys

Interferon-alpha (IFN-alpha) is indicated for the treatment of certain viral infections including hepatitis B and C, and cancers such as melanoma. The short circulating half-life of unmodified IFN-alpha makes frequent dosing (daily or three times weekly) over an extended period (6-12 months or more) necessary. To improve the pharmacokinetics of IFN-alpha and decrease dosing frequency, IFN-alpha was fused to human serum albumin producing a new protein, Albuferon. In vitro comparisons of Albuferon and IFN-alpha showed similar antiviral and antiproliferative activities, although Albuferon was less potent on a molar basis than IFN-alpha. Pharmacokinetic and pharmacodynamic properties of the fusion protein were enhanced in monkeys. After a single intravenous injection (30 microg/kg,) clearance was 0.9 ml/h/kg, and the terminal half-life was 68 h. After 30 microg/kg subcutaneous injection, apparent clearance (clearance divided by bioavailability) was 1.4 ml/h/kg, the terminal half-life was 93 h, and bioavailability was 64%. The rate of clearance of Albuferon was approximately 140-fold slower, and the half-life 18-fold longer, than for IFN-alpha given by the subcutaneous route in other monkey studies. Sera from Albuferon-treated monkeys demonstrated dose-related antiviral activity for > or =8 days based on an in vitro bioassay, whereas antiviral activity from IFN-alpha-treated animals was only slightly elevated relative to vehicle on day 0. Significant increases in 2',5'-oligoadenylate synthetase mRNA relative to IFN-alpha- or vehicle-treated animals were maintained for > or =10 days after subcutaneous dosing. The improved pharmacokinetics of Albuferon are accompanied by an improved pharmacodynamic response suggesting that Albuferon may offer the benefits of less frequent dosing and a potentially improved efficacy profile compared with IFN-alpha.

Low expression of interferon regulatory factor-1 and identification of novel exons skipping in patients with chronic myeloid leukaemia

Chronic myeloid leukaemia (CML) is a malignant clonal disorder of the haematopoietic stem cell. Treatment of CML patients with interferon alpha (IFN-alpha) has induced haematological and cytogenetic remission. Interferons transcriptionally activate target genes through the JAK-STAT and interferon regulated factors (IRFs) family pathways. Interferon regulated factor-1 (IRF-1) is a transcriptional activator of genes critical for cell growth, differentiation and apoptosis. The skipping of exons 2 or 2 and 3 of IRF-1 in patients with myelodysplastic syndromes and acute myelogenous leukaemia suggests that this factor may have a critical role in leukaemogenesis. The role of IRF-1 in CML is currently unknown. Therefore, mutational analysis of IRF-1 was performed and its expression pattern was also studied in CML patients. We studied IRF-1 in peripheral blood mononuclear cells of 21 patients in chronic phase CML. No point mutations were identified at the cDNA level. Surprisingly, fourfold reduction of full-length IRF-1 mRNA expression was established in 17/21 patients compared with normal individuals. Low expression of full-length IRF-1 was observed in conjunction with high levels of aberrantly spliced mRNAs, reported for the first time. In three patients who were also analysed during blastic transformation, further reduction of full-length IRF-1 mRNA was observed. These findings demonstrate that, in CML patients, IRF-1 can produce high levels of aberrant spliced mRNAs with subsequent reduction in the levels of full-length IRF-1 mRNA. This observation is consistent with the notion that exon skipping may constitute another mechanism of tumour suppressor gene inactivation in this disease.

13cis- and all-trans retinoic acid have antiproliferative effects on CML cells and render IFN alpha antiproliferative potency after combined treatment in vitro

The treatment of CML with IFN alpha is limited due to resistance against this substance. Recent studies with different cells than chronic myelogenous leukemic cells revealed a synergistic effect of a combined use of Retinoids (RA) and IFN alpha. The purpose of the study was to detect possible interactions of IFN alpha and RA in CML considering also the effect of the BCR-ABL gene-product. Therefore, we investigated three CML cell lines in their proliferation after incubation with IFN alpha and Retinoids alone and in combination. We measured low susceptibility to IFN alpha but a marked influence of the Retinoids. In combination, the growth inhibition was enhanced potentially in response to an increased efficacy of IFN alpha. Even solely, ineffective concentrations of both substances lead to decreased proliferation.

Philadelphia-positive chronic myelogenous leukemia with a 5q-- abnormality in a patient following interferon-alpha therapy

In this report, we describe a rare 5q--/CML association in a patient with Ph-positive chronic myelogenous leukemia (CML) who achieved complete cytogenetic response on interferon-alpha (IFN-alpha) treatment, but who developed a new clone in the blastic crisis. The patient was treated with interferon-alpha beginning in 1996 and a serial chromosome and molecular study was performed over the clinical course of the disease. The patient remained in complete hematologic and cytogenetic remission until November 1998, when a reverse transcriptase PCR study performed on the bone marrow and peripheral blood cells was negative for chimeric BCR/ABL mRNA. The treatment was discontinued until April 1999, when the patient developed acute transformation of the disease. In June 1999, cytogenetic examination showed the development of a new clone, consisting of the deletion of the long arm of chromosome 5 in addition to the standard Ph translocation. The unusual association of a Ph with an abnormality usually observed in a secondary myeloproliferative disease raises the question of whether the new finding is treatment-induced or part of the disease process and casually related to the acute transformation.

Interferon-alpha combined with cytarabine in chronic myelogenous leukemia - clinical benefits

During the last decade, several studies have evaluated the treatment of chronic phase chronic myeloid leukemia (CML) with a combination of interferon (IFN)-alpha and low- dose cytarabine (Ara-C). This combination therapy has been shown to be superior compared to monotherapy with IFN-alpha in randomized studies with regard to hematologic and cytogenetic remissions. However, the survival benefit is small, and the toxicity of the combination therapy is high. This paper reviews the published studies on IFN-alpha/low-dose Ara-C for the treatment of chronic phase CML and discusses the value of the combination therapy.

Lack of Interferon Consensus Sequence Binding Protein (ICSBP) Transcripts in Human Myeloid Leukemias

Interferon consensus sequence binding protein (ICSBP) was first identified as a transcription factor of the interferon (IFN) regulatory factor family (IRF) which regulates expression of IFN-dependent genes by binding to DNA at specific sites, IFN-stimulated responsive elements. Analysis of ICSBP-deficient mice showed hematologic alterations similar to chronic myelogenous leukemia (CML) in humans and suggested a novel role for ICSBP in regulating proliferation and differentiation of hematopoietic progenitor cells. Here we show that ICSBP-mRNA expression is impaired in human myeloid leukemias: 27 of 34 CML patients (79%) and 21 of 32 patients with acute myeloid leukemia (AML) (66%) showed very low or absent transcript numbers of ICSBP. In contrast, only 2 of 33 normal volunteers (6%) showed low transcription of ICSBP(P < .0001 both for CML and AML values). The lack of expression was not associated with lack of lymphatic cells, which normally have been shown to express ICSBP at the highest level. More detailed analysis showed an absence of ICSBP-mRNA also in sorted B cells derived from CML patients. To analyze whetherICSBP may be induced in leukemic cells, ex vivoexperiments using a known inducer of ICSBP, IFN-γ, were performed. Ex vivo treatment of primary CML cells using IFN-γ resulted in induction of ICSBP transcripts. Furthermore, samples of CML patients during IFN-α treatment were analyzed. In 11 of 12 CML patients ICSBP-mRNA was inducible upon in vivo treatment with IFN-α, but decreased with progression of CML. Stable transfection of K-562 cell line with ICSBP led to no difference in bcr-abl expression in vitro, although two patients showed an inverse correlation between bcr-abl andICSBP in vivo. These data suggest that lack of ICSBPmay have an important role also in human myeloid leukemogenesis.

Lack of Interferon Consensus Sequence Binding Protein (ICSBP) Transcripts in Human Myeloid Leukemias

Interferon consensus sequence binding protein (ICSBP) was first identified as a transcription factor of the interferon (IFN) regulatory factor family (IRF) which regulates expression of IFN-dependent genes by binding to DNA at specific sites, IFN-stimulated responsive elements. Analysis of ICSBP-deficient mice showed hematologic alterations similar to chronic myelogenous leukemia (CML) in humans and suggested a novel role for ICSBP in regulating proliferation and differentiation of hematopoietic progenitor cells. Here we show that ICSBP-mRNA expression is impaired in human myeloid leukemias: 27 of 34 CML patients (79%) and 21 of 32 patients with acute myeloid leukemia (AML) (66%) showed very low or absent transcript numbers of ICSBP. In contrast, only 2 of 33 normal volunteers (6%) showed low transcription of ICSBP(P < .0001 both for CML and AML values). The lack of expression was not associated with lack of lymphatic cells, which normally have been shown to express ICSBP at the highest level. More detailed analysis showed an absence of ICSBP-mRNA also in sorted B cells derived from CML patients. To analyze whetherICSBP may be induced in leukemic cells, ex vivoexperiments using a known inducer of ICSBP, IFN-γ, were performed. Ex vivo treatment of primary CML cells using IFN-γ resulted in induction of ICSBP transcripts. Furthermore, samples of CML patients during IFN-α treatment were analyzed. In 11 of 12 CML patients ICSBP-mRNA was inducible upon in vivo treatment with IFN-α, but decreased with progression of CML. Stable transfection of K-562 cell line with ICSBP led to no difference in bcr-abl expression in vitro, although two patients showed an inverse correlation between bcr-abl andICSBP in vivo. These data suggest that lack of ICSBPmay have an important role also in human myeloid leukemogenesis.

Natural history and staging of chronic myelogenous leukaemia

The natural history of chronic myelogenous leukaemia has changed in recent years, partly as a result of earlier diagnosis but mostly as a consequence of the availability of effective therapies that have the potential to eradicate the Philadelphia-positive clone. The prognostic models designed in the pre-interferon-alpha (IFN-alpha) era based on clinical characteristics of the disease are still useful in identifying different risk groups after treatment with IFN-alpha, but achieving a cytogenetic response with IFN-alpha is now the most important prognostic factor for survival. The significance of other molecular and biological variables remains to be determined.

Involvement of Fas-Mediated Apoptosis in the Inhibitory Effects of Interferon-α in Chronic Myelogenous Leukemia

Interferon-α (IFN-α) is an established treatment for chronic myelogenous leukemia (CML) in chronic phase, but the mechanism of its antileukemic activity is not clear. One possible mechanism of action might include the induction of apoptosis, and especially Fas-mediated cell killing may play an important role in the elimination of malignant cells. We investigated Fas receptor (Fas-R) expression and the consequences of Fas-R triggering in CML patients. Using two-color flow cytometry, we found a significantly higher number of Fas-R–expressing CD34+ cells in the bone marrow (BM) of CML patients compared with normal subjects. We have previously shown that IFN-γ induces Fas-R expression on CD34+ cells; in this study, we investigated whether IFN-α induces Fas-R expression on CML progenitor cells. Dose-dependent induction of Fas-R expression was observed after IFN-α stimulation of CD34+ cells from CML BM. In methylcellulose culture, IFN-α alone at a therapeutic concentration showed only marginal antiproliferative effects on both normal and CML BM progenitors. In contrast, a Fas-R agonist, the anti-CD95 monoclonal antibody CH11, inhibited colony formation from normal progenitors, and the inhibition was even stronger on CML progenitors. When CML BM cells were cultured in the presence of IFN-α, Fas-R–mediated inhibition of colony growth was potentiated in a dose-dependent fashion, consistent with IFN-α induction of Fas-R expression. This functional effect did not require the presence of accessory cells, since similar results were obtained with purified CD34+ cells. In suspension cultures, we demonstrated that suppression of CML hematopoiesis by IFN-α and Fas-R agonist was exerted through Fas-R–mediated induction of apoptosis. Our findings suggest that the Fas-R/Fas-ligand system might be involved in the immunologic regulation of CML progenitor growth and that its effect can be amplified by IFN-α.