Metabolic/Proteomic Signature Defines Two Glioblastoma Subtypes With Different Clinical Outcome.

Glioblastoma (GBM) is one of the deadliest human cancers. Because of the extremely unfavorable prognosis of GBM, it is important to develop more effective diagnostic and therapeutic strategies based on biologically and clinically relevant subclassification systems. Analyzing a collection of seventeen patient-derived glioblastoma stem-like cells (GSCs) by gene expression profiling, NMR spectroscopy and signal transduction pathway activation, we identified two GSC clusters, one characterized by a pro-neural-like phenotype and the other showing a mesenchymal-like phenotype. Evaluating the levels of proteins differentially expressed by the two GSC clusters in the TCGA GBM sample collection, we found that SRC activation is associated with a GBM subgroup showing better prognosis whereas activation of RPS6, an effector of mTOR pathway, identifies a subgroup with a worse prognosis. The two clusters are also differentiated by NMR spectroscopy profiles suggesting a potential prognostic stratification based on metabolic evaluation. Our data show that the metabolic/proteomic profile of GSCs is informative of the genomic/proteomic GBM landscape, which differs among tumor subtypes and is associated with clinical outcome.

miRNA let-7c promotes granulocytic differentiation in acute myeloid leukemia.

MicroRNAs (miRNAs), small non-coding RNAs that regulate gene expression post-transcriptionally, are involved in many complex cellular processes. Several miRNAs are differentially expressed in hematopoietic tissues and play important roles in normal differentiation, but, when aberrantly regulated, contribute to the abnormal proliferation and differentiation of leukemic cells. Recently, we reported that a small subset of miRNAs is differentially expressed in acute promyelocytic leukemia (APL) blasts and is modulated by treatment with all-trans-retinoic acid (ATRA). In particular, PML/RARα-positive blasts from APL patients display lower levels of miRNA let-7c, a member of the let-7 family, than normal promyelocytes and its expression increases after ATRA treatment. In this study, we investigated the effects of let-7c in acute myeloid leukemia (AML) cells. We found that ectopic expression of let-7c promotes granulocytic differentiation of AML cell lines and primary blasts. Moreover, we identified PBX2, a well-known homeodomain protein whose aberrant expression enhances HoxA9-dependent leukemogenesis, as a novel let-7c target that may contribute to the AML phenotype. Together, these studies raise the possibility that perturbation of the let-7c-PBX2 pathway may have a therapeutic value in AML.

Overexpression of Ets-1 in human hematopoietic progenitor cells blocks erythroid and promotes megakaryocytic differentiation.

Ets-1 is a widely expressed transcription factor implicated in development, tumorigenesis and hematopoiesis. We analyzed Ets-1 gene expression during human erythroid and megakaryocytic (MK) differentiation in unilineage cultures of CD34+ progenitor cells. During erythroid maturation, Ets-1 is downmodulated and exported from the nucleus into the cytoplasm through an active mechanism mediated by a leucine-rich nuclear export signal. In contrast, during megakaryocytopoiesis Ets-1 increases and remains localized in the nucleus up to terminal maturation. Overexpression of Ets-1 in erythroid cells blocks maturation at the polychromatophilic stage, increases GATA-2 and decreases both GATA-1 and erythropoietin receptor expression. Conversely, Ets-1 overexpressing megakaryocytes are characterized by enhanced differentiation and maturation, coupled with upmodulation of GATA-2 and megakaryocyte-specific genes. We show that Ets-1 binds to and activates the GATA-2 promoter, in vitro and in vivo, indicating that one of the pathways through which Ets-1 blocks erythroid and promotes MK differentiation is via upmodulation of GATA-2 expression.

Ectopic expression of interferon regulatory factor-1 potentiates granulocytic differentiation.

Numerous transcription factors allow haematopoietic cells to respond to lineage- and stage-specific cytokines and to act as their effectors. It is increasingly evident that the interferon regulatory factor-1 (IRF-1) transcription factor can selectively regulate different sets of genes depending on the cell type and/or the nature of cellular stimuli, evoking distinct responses in each. In the present study, we investigated mechanisms underlying the differentiation-inducing properties of granulocytic colony-stimulating factor (G-CSF) and whether IRF transcription factors are functionally relevant in myeloid differentiation. Both normal human progenitors and murine 32Dcl3 myeloblasts induced to differentiate along the granulocytic pathway showed an up-regulation of IRF-1 expression. Ectopic expression of IRF-1 did not abrogate the growth factor requirement of 32Dcl3 cells, although a small percentage of cells that survived cytokine deprivation differentiated fully to neutrophils. Moreover, in the presence of G-CSF, granulocytic differentiation of IRF-1-expressing cells was accelerated, as assessed by morphology and expression of specific differentiation markers. Down-modulation of c-Myb protein and direct stimulation of lysozyme promoter activity by IRF-1 were also observed. Conversely, constitutive expression of IRF-2, a repressor of IRF-1 transcriptional activity, completely abrogated the G-CSF-induced neutrophilic maturation. We conclude that IRF-1 exerts a pivotal role in granulocytic differentiation and that its induction by G-CSF represents a limiting step in the early events of differentiation.

IFN-gamma and IL-4 differently regulate inducible NO synthase gene expression through IRF-1 modulation.

NO is a labile radical involved in several immunological, antimicrobial and inflammatory processes. In macrophages, NO formation is catalyzed by the cytokine-inducible enzyme inducible NO synthase (iNOS). The importance of IFN regulatory factor (IRF)-1 and of the signal transducers and activators of transcription (STAT)-1 for the induction of iNOS gene expression in response to IFN-gamma has been well defined. Here, we investigated the molecular events responsible for the inhibition of iNOS gene expression by IL-4 in the murine macrophage cell line RAW264.7. Unidirectional deletion analysis on iNOS promoter demonstrated that an IFN-stimulated responsive element (ISRE), contained in the -980 to -765 bp region of the iNOS promoter, may be involved in the IL-4-mediated inhibition of IFN-gamma-inducible iNOS transcription. Accordingly, the IFN-gamma-induced binding activity of IRF-1 to the ISRE sequence was reduced in cells pre-treated with IL-4, while the binding activity of STAT-1 to the STAT-binding element (SBE) within the same region of the iNOS promoter remained unaffected. Moreover, IL-4 even down-regulated IFN-gamma-inducible expression of IRF-1 mRNA. This could be related to a transcriptional mechanism by which IL-4 and IFN-gamma differentially influence the trans-acting activity of the STAT factors binding to SBE within the IRF-1 promoter. SBE is targeted by IFN-gamma-inducible STAT-1 and by IL-4-inducible STAT-6. Although STAT-6 has no trans-acting function on iNOS gene expression, it is able to inhibit the IFN-gamma-induced expression of IRF-1. Thus, IL-4 may down-regulate IFN-gamma-inducible iNOS transcription by activation of STAT-6 which in turn inhibits IRF-1 expression.

Expression of wild-type and V210I mutant prion protein in human neuroblastoma cells.

The conversion of the host-encoded prion protein (PrPc) into the insoluble, protease-resistant isoform (PrPsc) is the main pathogenic mechanism of transmissible spongiform encephalopathies. They are fatal neurodegenerative disorders, which in human occur as sporadic, inherited or familial forms. These last forms are linked to insert or point mutations of PrPc which may facilitate the spontaneous conversion into PrPsc. We have established stably transfected human neuroblastoma cells (SH-SY5Y) expressing mutant V210I, or wild-type PrPc. Both proteins were expressed and attached to the cell surface. The mutation in position 210 did not alter the biochemical properties of the protein in comparison with the wild-type protein nor induced any conformational changes similar to those observed in PrPsc.

STAT1 activation during monocyte to macrophage maturation: role of adhesion molecules.

Human monocytes isolated from peripheral blood of healthy donors show a time-dependent differentiation into macrophages upon in vitro cultivation, closely mimicking their in vivo migration and maturation into extravascular tissues. The mediator(s) of this maturation process has not been yet defined. We investigated the involvement of signal transducers and activators of transcription (STAT) factors in this phenomenon and reported the specific, time-dependent, activation of STAT1 protein starting at day 0/1 of cultivation and maximally expressed at day 5. STAT1 activity was evident on the STAT binding sequences (SBE) present in the promoters of genes which are up-regulated during monocyte to macrophage maturation such as FcgammaRI and ICAM-1, and in the promoter of the transcription factor IFN regulatory factor-1. Moreover, the effect of cell adhesion to fibronectin or laminin was studied to investigate mechanisms involved in STAT1 activation. Compared with monocytes adherent on plastic surfaces, freshly isolated cells allowed to adhere either to fibronectin- or laminin-coated flasks exhibited an increased STAT1 binding activity both in control and in IFN-gamma-treated cells. The molecular events leading to enhanced STAT1 activation and cytokine responsiveness concerned both Y701 and S727 STAT1 phosphorylation. Exogenous addition of transforming growth factor-beta, which exerts an inhibitory effect on some monocytic differentiation markers, inhibited macrophage maturation, integrin expression and STAT1 binding activity. Taken together these results indicate that STAT1 plays a pivotal role in the differentiation/maturation process of monocytes as an early transcription factor initially activated by adherence and then able to modulate the expression of functional genes, such as ICAM-1 and FcgammaRI.

Activation and repression of the 2-5A synthetase and p21 gene promoters by IRF-1 and IRF-2.

The Interferon Regulatory Factors-1 and -2 (IRF-1 and IRF-2) were originally identified as transcriptional regulators of the interferon (IFN) and IFN-stimulated genes. These factors also modulate immune response and play a role in cell growth regulation. In this study we analysed the effect of the ectopic expression of IRF-1 and IRF-2 on the regulation of two potential IRF target genes involved in cell growth regulation, 2-5A synthetase and p21 (WAF/CP1), both of which contain consensus binding sites for IRF family members within their promoters. Following ectopic expression, IRF-1 transactivated 2-5A synthetase and p21 genes, an effect that was counterbalanced by concomitant ectopic expression of IRF-2. These effects were mediated by direct binding of IRF to the gene promoters. A construct expressing an IRF-2 antisense (FRI-2) was able to revert the inhibitory effect of IRF-2 on the IRF-1 transactivation. IRF-1 also induced expression of its homologous repressor IRF-2 as indicated by EMSA analysis using an IRF-E probe from the IRF-2 promoter; and by cotransfection of IRF-1 together with an IRF-2 promoter CAT construct. Therefore, the induction of IRF-1 by IFNs or other stimuli acts as a transactivator of genes involved in cell growth regulation, as well as of its own repressor IRF-2, thus providing autoinhibitory regulation of IRF-1 activated genes.

The activity of the CCAAT-box binding factor NF-Y is modulated through the regulated expression of its A subunit during monocyte to macrophage differentiation: regulation of tissue-specific genes through a ubiquitous transcription factor.

In this study, we analyzed the regulation of NF-Y expression during human monocyte to macrophage maturation. NF-Y is a ubiquitous and evolutionarily conserved transcription factor that binds specifically to the CCAAT motif present in the 5' promoter region of a wide variety of genes. We show here that in circulating monocytes, NF-Y binding activity is not detected on the CCAAT motif present in the promoters of genes such as major histocompatibility complex (MHC) class II, gp91-phox, mig, and fibronectin, whereas during macrophage differentiation, a progressive increase in NF-Y binding activity is observed on these promoters. Analysis of NF-Y subunit expression indicates that the absence of NF-Y activity in circulating monocytes is caused by a lack of the A subunit. Furthermore, addition of the recombinant NF-YA subunit restores NF-Y binding. We show that the lack of NF-YA protein is due to posttranscriptional regulation and not to a specific proteolytic activity. In fact, NF-YA mRNA is present at the same level at all days of monocyte cultivation, whereas the protein is absent in freshly isolated monocytes but is progressively synthesized during the maturation process. We thus conclude that the NF-YA subunit plays a relevant role in activating transcription of genes highly expressed in mature monocytes. In line with this conclusion, we show that the cut/CDP protein, a transcriptional repressor that inhibits gpc91-phox gene expression by preventing NF-Y binding to the CAAT box, is absent in monocytes.

Synergistic stimulation of MHC class I and IRF-1 gene expression by IFN-gamma and TNF-alpha in oligodendrocytes.

In order to understand the molecular basis of the synergistic action of interferon gamma (IFN-gamma) and tumour necrosis factor alpha (TNF-alpha) on rat oligodendrocyte development, we studied some aspects of the signalling pathways involved in the regulation of the major histocompatibility complex (MHC) class I and the interferon regulatory factor 1 (IRF-1) gene expression. Two well-defined inducible enhancers of the MHC class I gene promoter, the MHC class I regulatory element (MHC-CRE) and the interferon consensus sequence (ICS), were analysed. Neither IFN-gamma nor TNF-alpha was capable of inducing MHC-CRE binding activity when administrated alone. Following the exposure of oligodendrocytes to IFN-gamma, TNF-R1 expression was transcriptionally induced by the binding of signal transducer and activator of transcription (STAT-1) homodimers to the IFN-gamma activated site (GAS) present in the gene promoter. The upregulation of TNF-R1 allowed TNF-alpha to induce the binding of nuclear factor-kappaB (NF-kappaB) to the MHC-CRE site. With respect to ICS element, IFN-gamma induced IRF-1 binding, that was further enhanced upon co-treatment with TNF-alpha. The existence of a synergism between IFN-gamma and TNF-alpha in stimulating IRF-1 expression at the transcriptional level was supported by IRF-1 promoter analysis: IFN-gamma directly induced the binding of STAT-1 homodimers to the GAS element, while NF-kappaB binding to the kappaB sequence was activated by TNF-alpha only after IFN-gamma treatment. This transcriptional regulation of IRF-1 gene by IFN-gamma and TNF-alpha was confirmed at the mRNA level. The synergism demonstrated in the present study highlights the importance of cytokine interactions in magnifying their biological effects during brain injury and inflammation.

Transcriptional regulation of the ferritin heavy-chain gene: the activity of the CCAAT binding factor NF-Y is modulated in heme-treated Friend leukemia cells and during monocyte-to-macrophage differentiation.

The ferritin H-chain gene promoter regulation was analyzed in heme-treated Friend leukemia cells (FLCs) and during monocyte-to-macrophage differentiation. In the majority of cell lines studied, the regulation of ferritin expression was exerted mostly at the translational level. However, in differentiating erythroid cells, which must incorporate high levels of iron to sustain hemoglobin synthesis, and in macrophages, which are involved in iron storage, transcriptional regulation seemed to be a relevant mechanism. We show here that the minimum region of the ferritin H-gene promoter that is able to confer transcriptional regulation by heme in FLCs to a reporter gene is 77 nucleotides upstream of the TATA box. This cis element binds a protein complex referred to as HRF (heme-responsive factor), which is greatly enhanced both in heme-treated FLCs and during monocyte-to-macrophage differentiation. The CCAAT element present in reverse orientation in this promoter region of the ferritin H-chain gene is necessary for binding and for gene activity, since a single point mutation is able to abolish the binding of HRF and the transcriptional activity in transfected cells. By competition experiments and supershift assays, we identified the induced HRF as containing at least the ubiquitous transcription factor NF-Y. NF-Y is formed by three subunits, A, B, and C, all of which are necessary for DNA binding. Cotransfection with a transdominant negative mutant of the NF-YA subunit abolishes the transcriptional activation by heme, indicating that NF-Y plays an essential role in this activation. We have also observed a differential expression of the NF-YA subunit in heme-treated and control FLCs and during monocyte-to-macrophage differentiation.

Regulation of expression of ferritin H-chain and transferrin receptor by protoporphyrin IX.

The effect of protoporphyrin IX (hemin without iron) on the expression of transferrin receptor and ferritin was investigated in Friend leukemia cells. Cells treated with protoporphyrin IX exhibit enhanced transferrin-receptor expression and markedly reduced ferritin synthesis. Stimulation of transferrin-receptor expression is observed at both the mRNA and protein level. The effect on ferritin synthesis is mediated by translational inhibition of the mRNA, which, in contrast, is transcriptionally stimulated by protoporphyrin IX treatment. The regulation of transferrin receptor and ferritin in response to iron perturbations has been studied extensively and is mediated by the binding of iron-regulatory proteins (IRP) to the iron-responsive elements (IRE) present in the 3' and 5' untranslated regions of the transferrin-receptor and ferritin mRNA, respectively. To elucidate the molecular mechanisms underlying the effects of protoporphyrin IX on ferritin and transferrin-receptor expression, the role of the IRE sequence was investigated both in vivo by transfection experiments, with a construct containing the coding region for the chloramphenicol acetyltransferase (CAT) reporter gene under the translational control of the ferritin IRE, and in vitro by RNA band-shift assays. Whereas, examination of IRP binding to the IRE by in vitro assays suggests an apparent inactivation of IRP by protoporphyrin IX treatment, CAT assays indicate that protoporphyrin IX is able to induce in vivo a translational inhibition similar to that obtained by treatment with the iron chelator Desferal. This observation raises the possibility of different effects on the IRP activity exerted by porphyrin treatment in intact tissue-culture cells and in vitro. We conclude that translation of ferritin mRNA and degradation of transferrin-receptor mRNA are inhibited in intact tissue-culture cells by protoporphyrin IX through a mechanism similar to that exerted by iron chelation, thus involving depletion of the intracellular iron pool. These results can improve the understanding of the regulation of ferritin gene expression in some pathological conditions associated with disturbed heme synthesis.

cDNA cloning reveals a tissue specific expression of alternatively spliced transcripts of the ryanodine receptor type 3 (RyR3) calcium release channel.

Ryanodine receptors (RyRs) are a family of intracellular calcium release channels. Three cDNAs encoding different isoforms of RyR have been identified and cloned. We report the complete sequence of the mink RyR3 cDNA and the characterization of three alternative spliced regions. The first two splicing sites are represented by insertions of five and six amino acids, respectively. The third site is represented by a mutually exclusive splicing. The tissue distribution of the alternatively spliced transcripts revealed a ubiquitous expression of splicing site I and a differential distribution of sites II and III, indicating that a further level of complexity in RyR3 expression may result from alternative splicings in this gene.

Alpha and beta isoforms of ryanodine receptor from chicken skeletal muscle are the homologues of mammalian RyR1 and RyR3.

To define the relationship between the two ryanodine receptor (RyR) isoforms present in chicken skeletal muscle, we cloned two groups of cDNAs encoding the chicken homologues of mammalian RyR1 and RyR3. Equivalent amounts of the two chicken isoform mRNAs were detected in thigh and pectoral skeletal muscles. RyR1 and RyR3 mRNAs were co-expressed in testis and cerebellum whereas RyR3 mRNA was expressed also in the cerebrum and heart. The full-length sequence of the chicken RyR3 cDNA was established. The RyR3 receptor from chicken had the same general structure as mammalian and amphibian RyRs. The 15089 nt cDNA encoded a 4869-amino-acid-long protein with a molecular mass of 552445. The predicted amino acid sequence of the chicken RyR3 showed 86.9% identity to mammalian RyR3 and 85.6% to frog RyR3. Antibodies specific for chicken RyR1 and RyR3 recognized two different proteins with an apparent molecular mass of about 500 kDa. The two proteins differ slightly in their apparent molecular mass on SDS/PAGE: the protein recognized by antibodies against RyR3 had a higher mobility than the protein recognized by the antiserum against RyR1. Antibodies against RyR1 detected a protein already present in chicken skeletal muscle from 12-day-old embryos and older, while antibodies against RyR3 isoform detected a protein in muscle from only 18-day-old embryos and older. The expression patterns of RyR1 and RyR3 superimpose with those previously reported for the alpha and beta isoforms respectively. We conclude that alpha and beta isoforms present in chicken skeletal muscle are the homologues of mammalian RyR1 and RyR3.

Cells resistant to interferon-beta respond to interferon-gamma via the Stat1-IRF-1 pathway.

The mechanism responsible for the induction of the 2-5A synthetase gene by Interferon-gamma (IFN-gamma) (type II) was studied in Friend leukemia cells. It was previously shown that activation of 2-5A synthetase gene expression by IFN-gamma in the 3Cl8 cell, a clone resistant to IFN-alpha,beta (type I), correlates with the formation of two major complexes, designated Fg and Fc, that bind to the interferon-stimulated responsive element of the gene. Conversely, in a clone resistant to both types of IFNs (3 gamma R8), no induction of DNA-protein complexes or of 2-5A synthetase gene expression was detected. In the present report the Fg complex has been characterized as including the interferon regulatory factor 1 (IRF-1), whereas the Fc factor, present also in control cells, has been characterized as composed of IRF-2. Incubation of cell extracts with antibodies to IRF-1 abolishes the formation of the Fg complex, and antibodies to IRF-2 abolish the formation of the Fc complex. Moreover, in the 3Cl8 cell, IFN-gamma is able to induce in few minutes the formation of a complex between a DNA element identified as the IFN-gamma activation site (GAS), present on the IRF-1 gene promoter, and the STAT1 protein. These findings suggest that in cells resistant to type I IFN, IFN-gamma is able, through the activation of the STAT1 protein, to induce the expression of the IRF-1 factor which in turn seems to be sufficient to transactivate the 2-5A synthetase gene.

Differential regulation of ferritin expression in Friend leukemia cells by iron compounds.

Ferritin is an ubiquitous iron storage protein that plays a key role in determining the intracellular fate of iron. Therefore, ferritin synthesis is highly regulated by the iron status of the cell through post-transcriptional mechanisms that involve a specific high-affinity interaction between an iron-responsive element (IRE) in the 5' untranslated region of ferritin mRNA and a 98 kDa cytoplasmic protein, the iron-regulatory factor (IRF). The mechanisms that regulate the expression of the iron storage protein ferritin were investigated in erythroid (Friend erythroleukemia cell, FLC) and fibroblastic (L929 and B6) cell lines after exposure to various iron compounds. Both hemin (ferric protoporphyrin IX) and iron (as ferric ammonium citrate, FAC) were used as inducers of ferritin synthesis. Administration of hemin increases ferritin synthesis 8-12 fold both in erythroid and in non-erythroid cell lines, whereas FAC is a weak inducer of ferritin in FLC (only 5-fold). These results correlate with ferritin mRNA expression in FLC observed after hemin treatment compared to the effect exerted by FAC administration. This differential effect suggests that heme is the physiological compound able to stimulate ferritin synthesis in erythroid cell lines and that it plays an important physiological role in regulating gene expression in developing erythroid cells.

Binding of germ cells to mutant Sld Sertoli cells is defective and is rescued by expression of the transmembrane form of the c-kit ligand.

Mutations in the steel (Sl) locus, encoding the c-kit ligand (KL), are associated with impaired germ cell development in mice. Two forms of KL exist: one more steadily associated with the plasma membrane and one more easily released as a soluble protein. We report here that the expression of the two mRNAs coding for the two different form of KL is developmentally regulated in mouse testis. At birth the two mRNAs are expressed at an equal ratio. Starting after 6 days of life, and in parallel to initiation of germ cell differentiation, the mRNA encoding the membrane-associated form of KL becomes more abundant. Germ cells, and especially spermatogonia, express c-kit; thus membrane-bound KL could mediate adhesion between Sertoli cells and germ cells. We find, in fact, that Sertoli cells from Sl/Sld mutant mice, which do not express the mRNA for the membrane-associated form of KL, are unable to bind germ cells. Introduction of a plasmid expressing the transmembrane form, but not the soluble form, of KL restores the ability of Sertoli cells from Sl/Sld mutant mice to bind germ cells. These data suggest that preferential expression of the membrane-anchored form of KL in Sertoli cells may have a role in mediating adhesion of c-kit-expressing germ cells to Sertoli cells.

Expression of a ryanodine receptor-Ca2+ channel that is regulated by TGF-beta.

Ryanodine receptors (RyRs) are intracellular channels that release calcium ions from the sarcoplasmic reticulum (SR) in response to either plasma membrane depolarization (in skeletal muscle) or increases in the concentration of intracellular free Ca2+ (in the heart). A gene (beta 4) encoding a ryanodine receptor (similar to, but distinct from, the muscle RyRs) was identified. The beta 4 gene was expressed in all tissues investigated, with the exception of heart. Treatment of mink lung epithelial cells (Mv1Lu) with transforming growth factor beta (TGF-beta) induced expression of the beta 4 gene together with the release of Ca2+ in response to ryanodine (but not in response to caffeine, the other drug active on muscle RyRs). This ryanodine receptor may be important in the regulation of intracellular Ca2+ homeostasis.

A novel c-kit transcript, potentially encoding a truncated receptor, originates within a kit gene intron in mouse spermatids.

We have cloned a novel c-kit mRNA of 3.2 kb expressed in postmeiotic male germ cells. This transcript initiates in the genomic region immediately upstream of the exon coding for the second box of the split c-kit tyrosine kinase domain. The open reading frame (ORF) contains 12 novel amino acids in frame with the C-terminal 190 amino acids of the c-kit protein. It lacks therefore the upstream region in the 5.5-kb c-kit mRNA encoding the extracellular and transmembrane domain, the ATP-binding site and the kinase insert domain present in the c-kit protein.

Transcriptional induction of H2 (class I) antigens and beta 2 microglobulin by interferon-gamma in interferon-sensitive and interferon-resistant Friend leukemia cells.

The effect of interferons (IFNs) type I (alpha/beta) and type II (gamma) on the stimulation of H2-Dd (class I) and beta 2 microglobulin genes transcription was analysed in IFN-sensitive (w.t.) and IFN-resistant Friend erythroleukemia cells (FLC). Type I IFN enhances the expression of H2-Dd and beta 2 microglobulin genes in w.t. FLC but does not modulate the expression of these genes in clones resistant to IFN-alpha/beta. IFN type II treatment of w.t. and IFN-alpha/beta resistant cell lines results in an increased expression of H2-Dd and beta 2 microglobulin genes, while being ineffective in the cell clone resistant to both types of IFNs. In this cell system the effect(s) of IFN type II is in part mediated by the induction of IFN-beta. The results reported in the present paper suggest that the IFN-gamma is able per se to increase the expression of H2-Dd and beta 2 microglobulin genes; since a reduced but clearly evident stimulation of the expression of these genes was observed in the FLC clone totally resistant to type I IFN.