The retinoblastoma protein is an essential mediator that links the interferon-inducible 204 gene to cell-cycle regulation

PYHIN protein IFI207 regulates cytokine transcription and IRF7 and contributes to the establishment of K. pneumoniae infection

PYHIN proteins AIM2 and IFI204 sense pathogen DNA, while other PYHINs have been shown to regulate host gene expression through as-yet unclear mechanisms. We characterize mouse PYHIN IFI207, which we find is not involved in DNA sensing but rather is required for cytokine promoter induction in macrophages. IFI207 co-localizes with both active RNA polymerase II (RNA Pol II) and IRF7 in the nucleus and enhances IRF7-dependent gene promoter induction. Generation of Ifi207-/- mice shows no role for IFI207 in autoimmunity. Rather, IFI207 is required for the establishment of a Klebsiella pneumoniae lung infection and for Klebsiella macrophage phagocytosis. These insights into IFI207 function illustrate that PYHINs can have distinct roles in innate immunity independent of DNA sensing and highlight the need to better characterize the whole mouse locus, one gene at a time.

PRMT5 control of cGAS/STING and NLRC5 pathways defines melanoma response to antitumor immunity

Protein arginine methyltransferase 5 (PRMT5) controls diverse cellular processes and is implicated in cancer development and progression. Here, we report an inverse correlation between PRMT5 function and antitumor immunity. PRMT5 expression was associated with an antitumor immune gene signature in human melanoma tissue. Reducing PRMT5 activity antagonized melanoma growth in immunocompetent but not immunocompromised mice. PRMT5 methylation of IFI16 [interferon-γ (IFN-γ)-inducible protein 16] or its murine homolog IFI204, which are components of the cGAS/STING (stimulator of IFN genes) pathway, attenuated cytosolic DNA-induced IFN and chemokine expression in melanoma cells. PRMT5 also inhibited transcription of the gene encoding NLRC5 (nucleotide-binding oligomerization domain-like receptor family caspase recruitment domain containing 5), a protein that promotes the expression of genes implicated in major histocompatibility complex class I (MHCI) antigen presentation. PRMT5 knockdown augmented IFN and chemokine production and increased MHCI abundance in melanoma. Increased expression of IFI204 and NLRC5 was associated with decreased melanoma growth in murine models, and increased expression of IFI16 and NLRC5 correlated with prolonged survival of patients with melanoma. Combination of pharmacological (GSK3326595) or genetic (shRNA) inhibition of PRMT5 with immune checkpoint therapy limited growth of murine melanoma tumors (B16F10 and YUMM1.7) and enhanced therapeutic efficacy, compared with the effect of either treatment alone. Overall, our findings provide a rationale to test PRMT5 inhibitors in immunotherapy-based clinical trials as a means to enhance an antitumor immune response.

RNA-Seq analysis of interferon inducible p204-mediated network in anti-tumor immunity

p204, a murine member of the interferon-inducible p200 protein family, and its human analogue, IFI16, have been shown to function as tumor suppressors in vitro, but the molecular events involved, in particular in vivo, remain unclear. Herein we induced the Lewis Lung carcinoma (LLC) murine model of human lung cancer in p204 null mice (KO) and their control littermates (WT). We compared the transcriptome in spleen from WT and p204 KO mice using a high-throughput RNA-sequencing array. A total 30.02 Gb of clean data were obtained, and overall Q30% was greater than 90.54%. More than 75% of clean data from 12 transcriptome samples were mapped to exons. The results showed that only 11 genes exhibited altered expression in untreated p204 KO mice relative to untreated WT mice, while 393 altered genes were identified in tumor-bearing p204 KO mice when compared with tumor-bearing WT mice. Further differentially expressed gene cluster and gene ontology consortium classification revealed that numerous cytokines and their receptors, chemoattractant molecules, and adhesion molecules were significantly induced in p204 KO mice. This study provides novel insights to the p204 network in anti-tumor immune response and also presents a foundation for future work concerning p204-mediated gene expressions and pathways.

Impaired STING Pathway in Human Osteosarcoma U2OS Cells Contributes to the Growth of ICP0-Null Mutant Herpes Simplex Virus

Human herpes simplex virus 1 (HSV-1) is a widespread pathogen, with 80% of the population being latently infected. To successfully evade the host, the virus has evolved strategies to counteract antiviral responses, including the gene-silencing and innate immunity machineries. The immediately early protein of the virus, infected cell protein 0 (ICP0), plays a central role in these processes. ICP0 blocks innate immunity, and one mechanism is by degrading hostile factors with its intrinsic E3 ligase activity. ICP0 also functions as a promiscuous transactivator, and it blocks repressor complexes to enable viral gene transcription. For these reasons, the growth of a ΔICP0 virus is impaired in most cells, except cells of the human osteosarcoma cell line U2OS, and it is only partially impaired in cells of the human osteosarcoma cell line Saos-2. We found that the two human osteosarcoma cell lines that supported the growth of the ΔICP0 virus failed to activate innate immune responses upon treatment with 2'3'-cyclic GAMP (2'3'-cGAMP), the natural agonist of STING (i.e., stimulator of interferon genes) or after infection with the ΔICP0 mutant virus. Innate immune responses were restored in these cells by transient expression of the STING protein but not after overexpression of interferon-inducible protein 16 (IFI16). Restoration of STING expression resulted in suppression of ΔICP0 virus gene expression and a decrease in viral yields. Overexpression of IFI16 also suppressed ΔICP0 virus gene expression, albeit to a lesser extent than STING. These data suggest that the susceptibility of U2OS and Saos-2 cells to the ΔICP0 HSV-1 is in part due to an impaired STING pathway.IMPORTANCE The DNA sensor STING plays pivotal role in controlling HSV-1 infection both in cell culture and in mice. The HSV-1 genome encodes numerous proteins that are dedicated to combat host antiviral responses. The immediate early protein of the virus ICP0 plays major role in this process as it targets hostile host proteins for degradation with its E3 ligase activity, and it disrupts repressor complexes via protein-protein interaction to enable viral gene transcription. Therefore, the ΔICP0 HSV-1 virus is defective for growth in most cells, except the human osteosarcoma cell lines U2OS and Saos-2. We found that both cell lines that support ΔICP0 virus infection have defects in the STING DNA-sensing pathway, which partially accounts for the rescue of the ΔICP0 virus growth. Restoration of STING expression in these cells rescued innate immunity and suppressed ΔICP0 virus infection. This study underscores the importance of STING in the control of HSV-1.

E2F/Rb Family Proteins Mediate Interferon Induced Repression of Adenovirus Immediate Early Transcription to Promote Persistent Viral Infection

Interferons (IFNs) are cytokines that have pleiotropic effects and play important roles in innate and adaptive immunity. IFNs have broad antiviral properties and function by different mechanisms. IFNs fail to inhibit wild-type Adenovirus (Ad) replication in established cancer cell lines. In this study, we analyzed the effects of IFNs on Ad replication in normal human cells. Our data demonstrate that both IFNα and IFNγ blocked wild-type Ad5 replication in primary human bronchial epithelial cells (NHBEC) and TERT-immortalized normal human diploid fibroblasts (HDF-TERT). IFNs inhibited the replication of divergent adenoviruses. The inhibition of Ad5 replication by IFNα and IFNγ is the consequence of repression of transcription of the E1A immediate early gene product. Both IFNα and IFNγ impede the association of the transactivator GABP with the E1A enhancer region during the early phase of infection. The repression of E1A expression by IFNs requires a conserved E2F binding site in the E1A enhancer, and IFNs increased the enrichment of the E2F-associated pocket proteins, Rb and p107, at the E1A enhancer in vivo. PD0332991 (Pabociclib), a specific CDK4/6 inhibitor, dephosphoryles pocket proteins to promote their interaction with E2Fs and inhibited wild-type Ad5 replication dependent on the conserved E2F binding site. Consistent with this result, expression of the small E1A oncoprotein, which abrogates E2F/pocket protein interactions, rescued Ad replication in the presence of IFNα or IFNγ. Finally, we established a persistent Ad infection model in vitro and demonstrated that IFNγ suppresses productive Ad replication in a manner dependent on the E2F binding site in the E1A enhancer. This is the first study that probes the molecular basis of persistent adenovirus infection and reveals a novel mechanism by which adenoviruses utilize IFN signaling to suppress lytic virus replication and to promote persistent infection.

Interferons play important roles in both innate and adaptive immunity, and have broad antiviral properties. We demonstrate that type I (IFNα) and type II (IFNγ) IFNs inhibit the replication of divergent adenoviruses via an evolutionally conserved E2F binding site. IFNs augment the association of the tumor suppressors Rb and p107 with the E1A enhancer region in vivo to repress viral immediate early transcription. By comparing the properties of wild type and E2F site mutant viruses, we show that the IFN–E2F/Rb axis is critical for restriction of adenovirus replication to promote persistent viral infection. Relief of E2F/Rb repression counteracts IFN signaling whereas enforcement of E2F/Rb interaction mimics IFN signaling. These results reveal a novel mechanism by which adenoviruses utilize IFN signaling to suppress lytic virus replication and promote persistent infection.

The DNA damage response and immune signaling alliance: Is it good or bad? Nature decides when and where

The characteristic feature of healthy living organisms is the preservation of homeostasis. Compelling evidence highlight that the DNA damage response and repair (DDR/R) and immune response (ImmR) signaling networks work together favoring the harmonized function of (multi)cellular organisms. DNA and RNA viruses activate the DDR/R machinery in the host cells both directly and indirectly. Activation of DDR/R in turn favors the immunogenicity of the incipient cell. Hence, stimulation of DDR/R by exogenous or endogenous insults triggers innate and adaptive ImmR. The immunogenic properties of ionizing radiation, a prototypic DDR/R inducer, serve as suitable examples of how DDR/R stimulation alerts host immunity. Thus, critical cellular danger signals stimulate defense at the systemic level and vice versa. Disruption of DDR/R-ImmR cross talk compromises (multi)cellular integrity, leading to cell-cycle-related and immune defects. The emerging DDR/R-ImmR concept opens up a new avenue of therapeutic options, recalling the Hippocrates quote "everything in excess is opposed by nature."

The roles of interferon-inducible p200 family members IFI16 and p204 in innate immune responses, cell differentiation and proliferation

p204 is a member of the interferon-inducible p200 family proteins in mice. The p200 family has been reported to be multifunctional regulators of cell proliferation, differentiation, apoptosis and senescence. Interferon-inducible protein 16 (IFI16) is regarded as the human ortholog of p204 in several studies. This is possibly due to the similarity of their structures. However the consistency of their functions is still elusive. Currently, an emerging focus has been placed upon the role of the p200 proteins as sensors for microbial DNA in innate immune responses and provides new insights into infections as well as autoimmune diseases. This review specially focuses on IFI16 and p204, the member of p200 family in human and murine respectively, and their pathophysiological roles in innate immune responses, cell differentiation and proliferation.

A novel CDK7 inhibitor of the Pyrazolotriazine class exerts broad-spectrum antiviral activity at nanomolar concentrations

Protein kinases represent central and multifunctional regulators of a balanced virus-host interaction. Cyclin-dependent protein kinase 7 (CDK7) plays crucial regulatory roles in cell cycle and transcription, both connected with the replication of many viruses. Previously, we developed a CDK7 inhibitor, LDC4297, that inhibits CDK7 in vitro in the nano-picomolar range. Novel data from a kinome-wide evaluation (>330 kinases profiled in vitro) demonstrate a kinase selectivity. Importantly, we provide first evidence for the antiviral potential of the CDK7 inhibitor LDC4297, i.e., in exerting a block of the replication of human cytomegalovirus (HCMV) in primary human fibroblasts at nanomolar concentrations (50% effective concentration, 24.5 ± 1.3 nM). As a unique feature compared to approved antiherpesviral drugs, inhibition occurred already at the immediate-early level of HCMV gene expression. The mode of antiviral action was considered multifaceted since CDK7-regulated cellular factors that are supportive of HCMV replication were substantially affected by the inhibitors. An effect of LDC4297 was identified in the interference with HCMV-driven inactivation of retinoblastoma protein (Rb), a regulatory step generally considered a hallmark of herpesviral replication. In line with this finding, a broad inhibitory activity of the drug could be demonstrated against a selection of human and animal herpesviruses and adenoviruses, whereas other viruses only showed intermediate drug sensitivity. Summarized, the CDK7 inhibitor LDC4297 is a promising candidate for further antiviral drug development, possibly offering new options for a comprehensive approach to antiviral therapy.

Wanderings in biochemistry

My Ph.D. thesis in the laboratory of Severo Ochoa at New York University School of Medicine in 1962 included the determination of the nucleotide compositions of codons specifying amino acids. The experiments were based on the use of random copolyribonucleotides (synthesized by polynucleotide phosphorylase) as messenger RNA in a cell-free protein-synthesizing system. At Yale University, where I joined the faculty, my co-workers and I first studied the mechanisms of protein synthesis. Thereafter, we explored the interferons (IFNs), which were discovered as antiviral defense agents but were revealed to be components of a highly complex multifunctional system. We isolated pure IFNs and characterized IFN-activated genes, the proteins they encode, and their functions. We concentrated on a cluster of IFN-activated genes, the p200 cluster, which arose by repeated gene duplications and which encodes a large family of highly multifunctional proteins. For example, the murine protein p204 can be activated in numerous tissues by distinct transcription factors. It modulates cell proliferation and the differentiation of a variety of tissues by binding to many proteins. p204 also inhibits the activities of wild-type Ras proteins and Ras oncoproteins.

IFI16: At the interphase between innate DNA sensing and genome regulation

DNA carries the genetic code, and is also a potent stimulator of innate immune responses. IFI16 is a member of the family of PYHIN proteins and is composed of a PYRIN domain involved in homotypic protein-protein interactions and two HIN domains mediating DNA binding. PYHIN proteins have been described to possess functions as innate pattern recognition receptors or transcriptional regulators. Interestingly, it is now emerging that IFI16, which exhibits both nuclear and cytosolic location, possesses both of these functions. In this review we discuss the current literature on IFI16 and propose key questions now facing this field of research. We propose that IFI16 plays a central role in the close interaction between the innate immune system and cellular regulation of the genome.

The mammalian PYHIN gene family: phylogeny, evolution and expression

Background

Proteins of the mammalian PYHIN (IFI200/HIN-200) family are involved in defence against infection through recognition of foreign DNA. The family member absent in melanoma 2 (AIM2) binds cytosolic DNA via its HIN domain and initiates inflammasome formation via its pyrin domain. AIM2 lies within a cluster of related genes, many of which are uncharacterised in mouse. To better understand the evolution, orthology and function of these genes, we have documented the range of PYHIN genes present in representative mammalian species, and undertaken phylogenetic and expression analyses.

Results

No PYHIN genes are evident in non-mammals or monotremes, with a single member found in each of three marsupial genomes. Placental mammals show variable family expansions, from one gene in cow to four in human and 14 in mouse. A single HIN domain appears to have evolved in the common ancestor of marsupials and placental mammals, and duplicated to give rise to three distinct forms (HIN-A, -B and -C) in the placental mammal ancestor. Phylogenetic analyses showed that AIM2 HIN-C and pyrin domains clearly diverge from the rest of the family, and it is the only PYHIN protein with orthology across many species. Interestingly, although AIM2 is important in defence against some bacteria and viruses in mice, AIM2 is a pseudogene in cow, sheep, llama, dolphin, dog and elephant. The other 13 mouse genes have arisen by duplication and rearrangement within the lineage, which has allowed some diversification in expression patterns.

Conclusions

The role of AIM2 in forming the inflammasome is relatively well understood, but molecular interactions of other PYHIN proteins involved in defence against foreign DNA remain to be defined. The non-AIM2 PYHIN protein sequences are very distinct from AIM2, suggesting they vary in effector mechanism in response to foreign DNA, and may bind different DNA structures. The PYHIN family has highly varied gene composition between mammalian species due to lineage-specific duplication and loss, which probably indicates different adaptations for fighting infectious disease. Non-genomic DNA can indicate infection, or a mutagenic threat. We hypothesise that defence of the genome against endogenous retroelements has been an additional evolutionary driver for PYHIN proteins.

The multifaceted interferon-inducible p200 family proteins: from cell biology to human pathology

The interferon-inducible p200 family proteins consist of a group of homologous human and mouse proteins that have an N-terminal Pyrin domain and 1 or 2 partially conserved 200 amino acid long C-terminal domains (designated the HIN domain or p200 X domain). These proteins display multifaceted activity due to their ability to bind to various target proteins (eg, transcription factors, signaling proteins, and tumor suppressor proteins) and modulate different cell functions. In addition to a role in interferon biology, increasing evidence supports a role for these proteins as regulators of various cell functions, including proliferation, differentiation, apoptosis, senescence, inflammasome assembly, and control of organ transplants. As a consequence, alterations in their expression and function may be of relevance in the pathogenesis of human diseases, such as systemic autoimmune syndromes, tumors, and degenerative diseases. This review summarizes the literature describing these data, highlights some of the important findings derived from recent studies, and speculates about future perspectives.

Transient expression of interferon-inducible p204 in the early stage is required for adipogenesis in 3T3-L1 cells

A member of the interferon-inducible p200 family of proteins, p204, has recently been reported to function in the development of many mesoderm-derived tissues, such as bone, muscle, and cartilage. However, no published study has yet investigated the role of p204 in adipogenesis. Our preliminary experiments showed that p204 can be found in 3T3-L1 preadipocytes, and its expression was up-regulated in a differentiation-dependent manner. As such, we hypothesized that p204 is associated with adipogenesis and focused on the influence of p204 on adipogenesis. In the present study, we investigated the transient elevated expression and cytoplasm-to-nucleus translocation of p204 in the early stage of adipogenesis. To determine the effect of p204 on adipogenesis, p204-siRNA and expression vector were produced for p204 suppression and overexpression, respectively. The knockdown of p204 resulted in a significantly depressed adipocyte differentiation, whereas p204 overexpression promoted adipocyte differentiation. The mRNA expression of adipogenic markers, such as peroxisome-proliferator-activated receptor (PPAR)gamma, CCAAT/enhancer-binding-protein (C/EBP)alpha, lipoprotein lipase, and adipsin, was decreased by p204 suppression and increased by p204 overexpression. A coimmunoprecipitation assay coupled with an indirect immunofluorescence assay also indicated that p204 interacted and colocalized with C/EBPdelta in the nucleus. Furthermore, the knockdown of p204 disrupted the interaction between p204 and C/EBPdelta and partially suppressed the PPARgamma transcriptional activity by dissociating C/EBPdelta with the PPARgamma promoter element. Collectively, our data indicate that the transient expression of p204 in the early stage is indispensable for adipocyte differentiation. Disruption of p204 expression patterns at this stage leads to irreversible damage in fat formation.

Inducible activation of IFI 16 results in suppression of telomerase activity, growth suppression and induction of cellular senescence

Expression of the human HIN-200 family member IFI 16 has been reported to suppress cell growth and contribute to the onset of cellular senescence. However the molecular events involved in this process have not been fully characterised. We fused IFI 16 to the estrogen receptor ligand-binding domain to establish an inducible model for studying the molecular events that cause these phenomena. In cells induced to express the ER-IFI 16 within the nucleus there was a decrease in cellular proliferation and concomitant growth arrest in the G1 phase of the cell cycle. Unlike previous reports, this did not appear to involve the p53-p21(WAF1/CIP1)-cdk2-pRb pathway. Following nuclear expression of ER-IFI 16 we noted senescence-like morphological changes and expression of senescence-associated beta-galactosidase in growth arrested cells. Importantly, we also found a marked reduction in telomerase activity in arrested cells compared to controls. Moreover, IFI 16 and hTERT co-localised within the nucleus and these two proteins physically interacted in vivo and in vitro. Together, these data suggest that IFI 16 may act as an endogenous regulator of telomerase activity and, through its interaction with hTERT, contributes to the inhibition of proliferation and induces a senescence-like state.

p204, a p200 family protein, as a multifunctional regulator of cell proliferation and differentiation

The interferon-inducible p200 family comprises a group of homologous mouse and human proteins. Most of these have an N-terminal DAPIN domain and one or two partially conserved, 200 amino acid long C-terminal domains (designated as 200X domain). These proteins play important roles in the regulation of cell proliferation, tissue differentiation, apoptosis and senescence. p200 family proteins are involved also in autoimmunity and the control of tumor growth. These proteins function by binding to various target proteins (e.g. transcription factors, signaling proteins, oncoproteins and tumor suppressor proteins) and modulating target activity. This review concentrates on p204, a murine member of the family and its roles in regulating cell proliferation, cell and tissue differentiation (e.g. of skeletal muscle myotubes, beating cardiac myocytes, osteoblasts, chondrocytes and macrophages) and signaling by Ras proteins. The expression of p204 in various tissues as promoted by tissue-specific transcription factors, its distribution among subcellular compartments, and the controls of these features are also discussed.

Cloning and characterisation of Ifi206: a new murine HIN-200 family member

HIN-200 proteins are interferon-inducible proteins capable of regulating cell growth, senescence, differentiation and death. Using a combination of in silico analysis of NCBI EST databases and screening of murine C57BL/6 cDNA libraries we isolated novel murine HIN-200 cDNAs designated Ifi206S and Ifi206L encoding two putative mRNA splice variants. The p206S and p206L protein isoforms have a modular domain structure consisting of an N-terminal PAAD/DAPIN/Pyrin domain, a region rich in serine, threonine and proline residues and a C-terminal 200 B domain characteristic of other HIN-200 proteins. Ifi206 mRNA was detected only in the spleen and lung of BALB/c and C57BL/6 mice and expression was up-regulated by both types I and II IFN subtypes. p206 protein was predominantly expressed in the cytoplasm and addition of LMB, a CRM1 dependent nuclear export inhibitor, caused p206 to accumulate in the nucleus. Unlike other human and mouse HIN-200 proteins that contain only a single 200 amino acid domain, overexpression of p206 impaired the clonogenic growth of tumour cell lines. Thus, p206 represents the newest HIN-200 family member discovered. It has distinct and restricted pattern of expression however maintains many of the hallmarks of HIN-200 proteins including the presence of a characteristic 200 X domain, induction by interferon and an ability to suppress tumour cell growth.

p204 protein overcomes the inhibition of core binding factor alpha-1-mediated osteogenic differentiation by Id helix-loop-helix proteins

Id proteins play important roles in osteogenic differentiation; however, the molecular mechanism remains unknown. In this study, we established that inhibitor of differentiation (Id) proteins, including Id1, Id2, and Id3, associate with core binding factor alpha-1 (Cbfa1) to cause diminished transcription of the alkaline phosphatase (ALP) and osteocalcin (OCL) gene, leading to less ALP activity and osteocalcin (OCL) production. Id acts by inhibiting the sequence-specific binding of Cbfa1 to DNA and by decreasing the expression of Cbfa1 in cells undergoing osteogenic differentiation. p204, an interferon-inducible protein that interacts with both Cbfa1 and Id2, overcame the Id2-mediated inhibition of Cbfa1-induced ALP activity and OCL production. We show that 1) p204 disturbed the binding of Id2 to Cbfa1 and enabled Cbfa1 to bind to the promoters of its target genes and 2) that p204 promoted the translocation from nucleus to the cytoplasm and accelerated the degradation of Id2 by ubiquitin-proteasome pathway during osteogenesis. Nucleus export signal (NES) of p204 is required for the p204-enhanced cytoplasmic translocation and degradation of Id2, because a p204 mutant lacking NES lost these activities. Together, Cbfa1, p204, and Id proteins form a regulatory circuit and act in concert to regulate osteoblast differentiation.

p204 protein is a novel modulator of ras activity

The murine p200 family protein, p204, modulates cell proliferation and tissue differentiation. Many of its activities are exerted in the nucleus. However, in cardiac myocytes, p204 accumulated in the cytoplasm. A yeast two-hybrid assay revealed a p204-cytoplasmic Ras protein interaction. This was confirmed (i) by coimmunoprecipitation of p204 with Ras in mouse heart extract and with endogenous or ectopic H-Ras and K-Ras in cell lysates as well as (ii) by binding of purified H-Ras-GTP to purified p204 in vitro. p204 inhibited (i) the cleavage of RasGTP to RasGDP by RasGAP; (ii) the binding to RasGTP of Raf-1, phosphatidylinositol 3-kinase, and Ral-GDS, effectors of Ras signaling; and (iii) activation by the Ras pathway of the phosphorylation and thus activation of downstream targets (e.g. MEK, Akt, and p38 MAPK). Oncogenic Ras expression triggered the phosphorylation and translocation of p204 from the nucleus to the cytoplasm. This is expected to increase the interaction between the two proteins. Translocation triggered by Ras oncoprotein was blocked by the LY294002 inhibitor of phosphatidylinositol 3-kinase. Ras did not promote phosphorylation or translocation to the cytoplasm of mutated p204 in which serine 179 was replaced by alanine. p204 overexpression inhibited the anchorage-independent proliferation of cells expressing Ras(Q61L) oncoprotein. Ras oncoprotein triggered in MEF3T3 cells the rearrangement of the actin cytoskeleton and the enhancement of cell migration through a membrane. Overexpression of p204 inhibited both. Ras oncoprotein or activated, wild-type Ras was described to increase Egr-1 transcription factor expression. We report that a sequence in the gene encoding p204 bound Egr-1, and Egr-1 activated p204 expression. Ras oncoprotein or activated wild-type Ras increased the expression in 3T3 cells of p204 together with that of Egr-1. Furthermore, the activation of expression of a single copy of K-ras oncogene in cultured murine embryonic cells induced the expression of a high level of p204 as well as its distribution between the nuclei and the cytoplasm. Thus, p204 may serve as a negative feedback inhibitor of Ras activity.

Structure-function analysis of the retinoblastoma tumor suppressor protein - is the whole a sum of its parts?

Biochemical analysis of the retinoblastoma protein's function has received considerable attention since it was cloned just over 20 years ago. During this time pRB has emerged as a key regulator of the cell division cycle and its ability to block proliferation is disrupted in the vast majority of human cancers. Much has been learned about the regulation of E2F transcription factors by pRB in the cell cycle. However, many questions remain unresolved and researchers continue to explore this multifunctional protein. In particular, understanding how its biochemical functions contribute to its role as a tumor suppressor remains to be determined. Since pRB has been shown to function as an adaptor molecule that links different proteins together, or to particular promoters, analyzing pRB by disrupting individual protein interactions holds tremendous promise in unraveling the intricacies of its function. Recently, crystal structures have reported how pRB interacts with some of its molecular partners. This information has created the possibility of rationally separating pRB functions by studying mutants that disrupt individual binding sites. This review will focus on literature that investigates pRB by isolating functions based on binding sites within the pocket domain. This article will also discuss the prospects for using this approach to further explore the unknown functions of pRB.

Effects of IFI16 overexpression on the growth and doxorubicin sensitivity of head and neck squamous cell carcinoma–derived cell lines

BACKGROUND

In a previous analysis of head and neck squamous cell carcinomas (HNSCCs), we showed that the levels of the interferon-inducible protein IFI16 inversely correlate with cancer grade. In this study, we further evaluate the molecular role of IFI16 in the development of HNSCCs.

METHODS

The effect of IFI16 expression was evaluated by its retroviral restoration in an IFI16-negative HNSCC-derived cell line, HNO136. Growth rate and soft agar colony formation were evaluated. The effect of IFI16 restoration in cells exposed to doxorubicin was also analyzed.

RESULTS

IFI16 restoration resulted in the inhibition of both cell growth and in vitro transforming activity and increased doxorubicin-induced cell death by accumulating the cells at the G2/M phase.

CONCLUSION

In agreement with our previous in vivo data, IFI16 appears to be involved in maintaining the normal growth of epithelial cells, whereas its downregulation may contribute to uncontrolled cell proliferation and tumorigenesis.

The retinoblastoma protein is an essential mediator of osteogenesis that links the p204 protein to the Cbfa1 transcription factor thereby increasing its activity

Bone formation requires the coordinated activity of numerous proteins including the transcription factor core-binding factor alpha1 (Cbfa1). Deregulation of Cbfa1 results in metabolic bone diseases including osteoporosis and osteopetrosis. The retinoblastoma protein (pRb) that is required for osteogenesis binds Cbfa1. We reported earlier that the p200 family protein p204, which is known to be involved in the differentiation of skeletal muscle myotubes, cardiac myocytes, and macrophages, also serves as a cofactor of Cbfa1 and promotes osteogenesis. In this study we established that suppression of p204 expression by an adenovirus construct encoding p204 antisense RNA inhibited osteoblast-specific gene activation by Cbfa1 in an osteogenesis assay involving the pluripotent C2C12 mesenchymal cell line. Using protein-protein interaction assays we established that Cbfa1, pRb, and p204 form a ternary complex in which pRb serves as a linker connecting p204 and Cbfa1. Chromatin immunoprecipitation assays revealed the binding of such a p204-pRb-Cbfa1 transcription factor complex to the promoter of the osteocalcin gene. The pRb requirement of the stimulation of Cbfa1 activity by p204 was established in experiments involving p204 mutants lacking one or two pRb binding (LXCXE) motifs. Such mutants failed to enhance the Cbfa1-dependent transactivation of gene expression as well as osteogenesis. Furthermore, as revealed in reporter gene and in vitro osteogenesis assays p204 synergized with pRb in the stimulation of Cbfa1-dependent gene activation and osteoblast differentiation.

p204 Is Required for the Differentiation of P19 Murine Embryonal Carcinoma Cells to Beating Cardiac Myocytes

Among 10 adult mouse tissues tested, the p204 protein levels were highest in heart and skeletal muscle. We described previously that the MyoD-inducible p204 protein is required for the differentiation of cultured murine C2C12 skeletal muscle myoblasts to myotubes. Here we report that p204 was also required for the differentiation of cultured P19 murine embryonal carcinoma stem cells to beating cardiac myocytes. As shown by others, this process can be triggered by dimethyl sulfoxide (DMSO). We established that DMSO induced the formation of 204RNA and p204. Ectopic p204 could partially substitute for DMSO in inducing differentiation, whereas ectopic 204 antisense RNA inhibited the differentiation. Experiments with reporter constructs, including regulatory regions from the Ifi204 gene (encoding p204) in P19 cells and in cultured newborn rat cardiac myocytes, as well as chromatin coimmunoprecipitations with transcription factors, revealed that p204 expression was synergistically transactivated by the cardiac Gata4, Nkx2.5, and Tbx5 transcription factors. Furthermore, ectopic p204 triggered the expression of Gata4 and Nkx2.5 in P19 cells. p204 contains a nuclear export signal and was partially translocated to the cytoplasm during the differentiation. p204 from which the nuclear export signal was deleted was not translocated, and it did not induce differentiation. The various mechanisms by which p204 promoted the differentiation are reported in the accompanying article (Ding, B., Liu, C., Huang, Y., Yu, J., Kong, W., and Lengyel, P. (2006) J. Biol. Chem. 281, 14893-14906).

p204 protein overcomes the inhibition of the differentiation of P19 murine embryonal carcinoma cells to beating cardiac myocytes by Id proteins

We reported in the accompanying article (Ding, B., Liu, C., Huang, Y., Hickey, R. P., Yu, J., Kong, W., and Lengyel, P. (2006) J. Biol. Chem. 281, 14882-14892) that (i) the p204 protein is required for the differentiation of murine P19 embryonal carcinoma stem cells to beating cardiac myocytes, and (ii) the expression of p204 in the differentiating P19 cells is synergistically transactivated by the cardiac transcription factors Gata4, Nkx2.5, and Tbx5. Here we report that endogenous or ectopic inhibitor of differentiation (Id) proteins inhibited the differentiation of P19 cells to myocytes. This was in consequence of the binding of Id1, Id2, or Id3 protein to the Gata4 and Nkx2.5 proteins and the resulting inhibitions (i) of the binding of these transcription factors to each other and to DNA and (ii) of their synergistic transactivation of the expression of various genes, including atrial natriuretic factor and Ifi204 (encoding p204). p204 overcame this inhibition by Id proteins in consequence of (i) binding and sequestering Id proteins, (ii) accelerating their ubiquitination and degradation by proteasomes, and (iii) decreasing the level of Id proteins in the nucleus by increasing their translocation from the nucleus to the cytoplasm. Points (ii) and (iii) depended on the presence of the nuclear export signal in p204. In the course of the differentiation, Gata4, Nkx2.5, and p204 were components of a positive feedback loop. This loop arose in consequence of it that p204 overcame the inhibition of the synergistic activity of Gata4 and Nkx2.5 by the Id proteins.

p205, a potential tumor suppressor, inhibits cell proliferation via multiple pathways of cell cycle regulation

p205 is a member of the interferon-inducible p200 family of proteins that regulate cell proliferation. Over-expression of p205 inhibits cell growth, although its mechanism of action is currently unknown. Therefore, we evaluated the effect of p205 on the p53 and Rb-dependent pathways of cell cycle regulation. p205 expression results in elevated levels of p21, and activates the p21 promoter in vitro in a p53-dependent manner. In addition, p205 induces increased expression of Rb, and binds directly to Rb and p53. Interestingly, p205 also induces growth inhibition independent of p53 and Rb by delaying G2/M progression in proliferating cells, and is a substrate for Cdk2 kinase activity. Finally, we have identified other binding partners of p205 by a yeast two-hybrid screen, including the paired homeodomain protein HoxB2. Taken together, our results indicate that p205 induces growth arrest by interaction with multiple transcription factors that regulate the cell cycle, including but not entirely dependent on the Rb- and p53-mediated pathways of growth inhibition.

The interferon-inducible gene, Ifi204, is transcriptionally activated in response to M-CSF, and its expression favors macrophage differentiation in myeloid progenitor cells

The interferon-inducible (Ifi)204 gene was isolated as a macrophage-colony stimulating factor (M-CSF)-responsive gene using a gene trap approach in the myeloid interleukin-3 (IL-3)-dependent FD-Fms cell line, which differentiates in macrophages in response to M-CSF. Here, we show that Ifi204 was transcriptionally activated in response to M-CSF, and FD-Fms cells decreased their growth and committed toward a macrophage morphology; this induction was abrogated when the differentiation signal of the M-CSF receptor was blocked; the Ifi204 gene was also induced during macrophage differentiation controlled by leukemia inhibitory factor; and the Ifi204 gene is expressed in different mature monocyte/macrophage cells. Finally, we showed that enforced expression of Ifi204 strongly decreased IL-3- and M-CSF-dependent proliferation and conversely, favored macrophage differentiation of FD-Fms cells in response to M-CSF. Altogether, these results demonstrate that the Ifi204 gene is activated during macrophage development and suggest that the Ifi204 protein may act as a regulator of the balance between proliferation and differentiation. Moreover, this study suggests that other members of the Ifi family might act as regulators of hematopoiesis under the control of hemopoietic cytokines.

Bladder cancer outcome and subtype classification by gene expression

Models of bladder tumor progression have suggested that genetic alterations may determine both phenotype and clinical course. We have applied expression microarray analysis to a divergent set of bladder tumors to further elucidate the course of disease progression and to classify tumors into more homogeneous and clinically relevant subgroups. cDNA microarrays containing 10,368 human gene elements were used to characterize the global gene expression patterns in 80 bladder tumors, 9 bladder cancer cell lines, and 3 normal bladder samples. Robust statistical approaches accounting for the multiple testing problem were used to identify differentially expressed genes. Unsupervised hierarchical clustering successfully separated the samples into two subgroups containing superficial (pT(a) and pT(1)) versus muscle-invasive (pT(2)-pT(4)) tumors. Supervised classification had a 90.5% success rate separating superficial from muscle-invasive tumors based on a limited subset of genes. Tumors could also be classified into transitional versus squamous subtypes (89% success rate) and good versus bad prognosis (78% success rate). The performance of our stage classifiers was confirmed in silico using data from an independent tumor set. Validation of differential expression was done using immunohistochemistry on tissue microarrays for cathepsin E, cyclin A2, and parathyroid hormone-related protein. Genes driving the separation between tumor subsets may prove to be important biomarkers for bladder cancer development and progression and eventually candidates for therapeutic targeting.

Altered patterns of the interferon-inducible gene IFI16 expression in head and neck squamous cell carcinoma: immunohistochemical study including correlation with retinoblastoma protein, human papillomavirus infection and proliferation index

AIMS

To investigate whether the expression of interferon (IFN)-inducible gene IFI16 is inversely related to proliferative activity in vivo, we compared immunohistochemical reactivity of IFI16 in a series of head and neck squamous cell carcinomas (HNSCCs) with their proliferation index and the cell cycle regulator pRb. As human papillomavirus (HPV) infection is manifested by changes in the function or expression level of host genes such as IFN-inducible genes, we also investigated the presence of HPV DNA to determine whether head and neck cancers associated with HPV DNA can be distinguished from tumours that are presumably transformed by other mechanisms.

METHODS

Thirty-six HNSCCs were evaluated for IFI16, pRb and Ki67 expression by immunohistochemistry. The presence of HPV was also detected by polymerase chain reaction. Nine tumours were located in the oropharynx (tonsillar area) and 27 in the larynx.

RESULTS

HPV DNA was found in 14 of 25 (56%) laryngeal SCCs and in five of nine (56%) tonsillar SCC specimens examined; 17 out of the 19 HPV-DNA-positive cases showed high-grade IFI16 expression. Overall, proliferative activity was significantly related to tumour differentiation and histological grading. IFI16 protein expression was significantly inversely correlated with Ki67 (P = 0.039). Low-proliferating tumours positive for IFI16 staining showed a marked expression of pRb and a better prognosis than those whose tumours had low IFI16, pRb levels and a high proliferation index.

CONCLUSIONS

To our knowledge, this is the first expression analysis of the IFN-inducible IFI16 gene in HNSCC. Low-proliferating tumours positive for IFI16 staining showed a marked expression of pRb and a better prognosis than those whose tumours had low IFI16, pRb levels and a high proliferation index.

The HIN domain of IFI-200 proteins consists of two OB folds

The interferon-inducible p200 (IFI-200/HIN-200) family of proteins regulates cell growth and differentiation, and confers resistance to the development of tumors and virus infections. IFI-200 family members are thought to exert their biological effects by modulation of the transcriptional activities of numerous factors and interaction with other proteins through the C-terminal HIN domains. However, the HIN domain structure and function have remained obscure. Therefore, we performed a comprehensive bioinformatics analysis and assembled a structure-based multiple sequence alignment of IFI-200 proteins. The application of fold recognition methods revealed that the HIN domain consists of two consecutive OB domains. Our structural models of DNA-binding HIN domains afford the long-sought interpretations for many previous experimental observations. Our results also raise the possibility of as yet unexplored functional roles of IFI-200 proteins as transcriptional regulators and as interaction partners of proteins involved in immunomodulatory and apoptotic processes.

Up-regulation of the interferon-inducible IFI16 gene by oxidative stress triggers p53 transcriptional activity in endothelial cells

Reactive oxygen species (ROS), including hydrogen peroxide (H2O2), induces injury of endothelium in a variety of pathophysiological conditions, such as inflammation, aging, and cancer. In our study, we characterized the signaling pathway linking oxidative stress induced by sublethal concentrations of H2O2 to p53 in primary human endothelial cells through the interferon (IFN)-inducible gene IFI16. Induction of IFI16 by H2O2 was concentration- and time-dependent (maximum at 50 microM, 6 h after treatment) and down-regulated by pretreatment with N-acetyl-L-cysteine, which acts as an antioxidant. This pathway is a general response to ROS and not specific to H2O2 treatment, as two other ROS-generating compounds, i.e., S-nitroso-N-acetylpenicillamine and tert-butyl hydroperoxide, were equally capable to induce IFI16. Moreover, IFI16 up-regulation is a result of protein accumulation, as expression of corresponding mRNA, assessed by real-time polymerase chain reaction, was not affected. To investigate the mechanism of IFI16 accumulation, cells were incubated for 6 h in the presence of H2O2 or IFN-beta, and then cycloheximide was added to inhibit further protein synthesis. The half-life of IFI16 protein was found to be significantly increased in H2O2-treated cells compared with IFN-beta-treated cells (t1/2 = 120 min vs. > 30 min in H2O2- vs. IFN-beta-treated cells, respectively). An increase of IFI16 was accompanied by interaction with p53 phosphorylated at its N terminus, as shown by immunoprecipitation experiments. Moreover, binding to IFI16 resulted in its transcriptional activation as shown by an increase in the activity of a reporter gene driven by p53-responsive sequences derived from the p21(WAF1) promoter, along with an increase in the p21 mRNA and protein levels. Altogether, these results demonstrate a novel role of IFI16 in the signal transduction pathway that leads to p53 activation by oxidative stress in endothelial cells.

Biochemical and growth regulatory activities of the HIN-200 family member and putative tumor suppressor protein, AIM2

The human HIN-200 family member AIM2 was originally identified in a screen for suppressors of melanoma tumorigenicity following introduction of chromosome 6 into the UACC903 human melanoma cell line. Although the AIM2 protein contained many of the conserved structural motifs common to other HIN-200 proteins, the biochemical characteristics of AIM2 and the ability of overexpressed AIM2 to phenocopy the effect of introduction of chromosome 6 in the UACC903 cells had not been assessed. Herein we demonstrated that AIM2 was localised within the nucleus of transfected or interferon-treated human cells. In addition, AIM2 could homodimerise via the amino-terminal (PAAD/DAPIN) region and heterodimerise with the related IFI 16 protein. However, overexpressed AIM2 did not significantly affect the growth or survival of UACC903 cells or another human melanoma cell line. These data indicate that AIM2 has many of the biochemical and structural characteristics of HIN-200 proteins, however, its expression is not sufficient to induce a tumor-suppressor-like phenotype.

The Interferon-inducible p204 Protein Acts as a Transcriptional Coactivator of Cbfa1 and Enhances Osteoblast Differentiation

The differentiation of uncommitted mesenchymal cells into osteoblasts is a fundamental molecular event governing both embryonic development and bone repair. The bone morphogenetic proteins (BMPs) are important regulators of this process; they function by binding to cell surface receptors and signaling by means of Smad proteins. Core binding factor alpha-1 (Cbfa1), a member of the runt family of transcription factors, is an essential transcriptional regulator of osteoblast differentiation and bone formation, and this process is positively or negatively regulated by a variety of coactivators and corepressors. We report that p204, an interferon-inducible protein that was previously shown to inhibit cell proliferation and promote the differentiation of myoblasts to myotubes, is a novel regulator in the course of osteogenesis. p204 is expressed in embryonic osteoblasts and hypertrophic chondrocytes in the growth plate as well as in the calvaria osteoblasts of neonatal mice. Its level is increased in the course of the BMP-2-triggered osteoblast differentiation of pluripotent C2C12 cells. This increase is probably due to the activation of the gene encoding 204 (Ifi204) by Smad transcription factor, including Smad1, -4, and -5. Overexpression of p204 enhances the BMP-2-induced osteoblast differentiation in vitro, as revealed by elevated alkaline phosphatase activity and osteocalcin production. p204 acts as a cofactor of Cbfa1: 1) high levels of p204 augment, whereas the lowering of p204 level decreases, the Cbfa1-dependent transcription, and 2) p204 associates with Cbfa1 both in vitro and in vivo. Two nonoverlapping segments in p204 bind to Cbfa1, and the N-terminal 88-amino acid segment of Cbfa1 is required for binding to p204. p204, which is the first interferon-inducible protein found to associate with Cbfa1, functions as a novel regulator of osteoblast differentiation.

Time- and dose-dependent analysis of gene expression using microarrays in sulfur mustard-exposed mice

The chemical warfare agent sulfur mustard (SM) produces blister formation with a severe inflammatory reaction in skin of exposed individuals. The development of efficacious countermeasures against SM vesication requires an understanding of the cellular and molecular mechanism of SM-induced tissue injury. This study examined SM-induced alterations in gene expression using Atlas Mouse 5K DNA microarrays (5002 genes) to identify transcriptional events associated with SM skin injury. Mice (N=3) were exposed topically to SM (0.04, 0.08, and 0.16 mg; 48.8, 97.5, and 195 mM) on the inner surface of the right ear and skin tissues were harvested at 1.5, 3, 6, and 12 h. Genes were selected based on the three mice in the same dose group demonstrating a > or =2-fold increase or decrease in gene expression for the SM-exposed tissue when compared to the dichloromethane vehicle control ear at all three doses and four time points. At the 0.04 mg SM dose, the genes observed were primarily involved in inflammation, apoptosis, and cell cycle regulation. Exposure to 0.08 mg SM increased the expression of genes related to inflammation and cell cycle regulation. Exposure to 0.16 mg SM led to a total of six genes that were changed at all observed time periods; however, these genes do not appear to be directly influential in biological mechanisms such as inflammation, apoptosis, and cell cycle regulation as was observed at the lower SM doses of 0.04 and 0.08 mg. These functional categories have been observed in previous studies utilizing both in vivo and in vitro model systems of SM-induced dermal injury, suggesting that molecular mechanisms associated with inflammation, apoptosis, and cell cycle regulation may be appropriate targets for developing prophylactic/therapeutic treatments for SM skin injury.

Inhibition of Growth by p205: A Nuclear Protein and Putative Tumor Suppressor Expressed during Myeloid Cell Differentiation

p205 belongs to a family of interferon-inducible proteins called the IFI-200 family, which have been implicated in the regulation of cell growth and differentiation. While p205 is induced in hematopoietic stem cells during myeloid cell differentiation, its function is not known. Therefore, the aim of this study was to determine the role of p205 in regulating proliferation in hematopoietic progenitor cells and in nonhematopoietic cell lines. We found that p205 localizes to the nucleus in hematopoietic and nonhematopoietic cell lines. Transient expression of p205 in murine IL-3-dependent BaF3 and 32D-C123 progenitor cell lines inhibited IL-3-induced growth and proliferation. The closely related IFI-200 family members, p204 and p202, similarly inhibited IL-3-dependent progenitor cell proliferation. p205 also inhibited the proliferation and growth of normal hematopoietic progenitor cells. In nonhematopoietic cell lines, p205 and p204 expression inhibited NIH3T3 cell colony formation in vitro, and microinjection of p205 expression vectors into NIH3T3 fibroblasts inhibited serum-induced proliferation. We have determined the functional domains of p205 necessary for activity, which were identified as the N-terminal domain in apoptosis and interferon response (DAPIN)/PYRIN domain, and the C-terminal retinoblastoma protein (Rb)-binding motif. In addition, we have demonstrated that a putative ataxia telangiectasia, mutated (ATM) kinase phosphorylation site specifically regulates the activity of p205. Taken together, these data suggest that p205 is a potent cell growth regulator whose activity is mediated by its protein-binding domains. We propose that during myelomonocytic cell differentiation, induction of p205 expression contributes to cell growth arrest, thus allowing progenitor cells to differentiate.

The interferon-inducible IFI16 gene inhibits tube morphogenesis and proliferation of primary, but not HPV16 E6/E7-immortalized human endothelial cells

Immunohistochemical analysis has demonstrated that the human IFI16 gene, in addition to the hematopoietic tissues, is highly expressed in endothelial cells and squamous stratified epithelia. In this study, we have developed a reliable HSV-derived replication-defective vector (TO-IFI16) to efficiently transduce IFI16 into primary human umbilical vein endothelial cells (HUVEC), which are usually poorly transfectable. HUVEC infection with TO-IFI16 virus suppressed endothelial migration, invasion and formation of capillary-like structures in vitro. In parallel, sustained IFI16 expression inhibited HUVEC cell cycle progression, accompanied by significant induction of p53, p21, and hypophosphorylated pRb. Further support for the involvement of these pathways in IFI16 activity came from the finding that infection with TO-IFI16 virus does not impair the in vitro angiogenic activity and cell cycle progression of HUVEC immortalized by HPV16 E6/E7 oncogenes, which are known to inactivate both p53 and pRb systems. This use of a reliable viral system for gene delivery into primary human endothelial cells assigns a potent angiostatic activity to an IFN-inducible gene, namely IFI16, and thus throws further light on antiangiogenic therapy employing IFNs.

IFI16 as a negative regulator in the regulation of p53 and p21(Waf1)

IFI16 is a member of the HIN-200 family (hematopoietic interferon-inducible nuclear antigens with 200 amino acid repeats) that contains a DNA binding domain, a transcriptional regulatory domain, and DAPIN/PAAD, a protein domain associated with interferon response. It can function as a transcription repressor and directly binds p53. Although the structural and biochemical properties of IFI16 are known, the physiological relevance of these properties in the cellular context is still elusive. Here we report that the inhibition of endogenous IFI16 expression by small interfering RNA (siRNA) induces p21Waf1 mRNA and protein expression through p53 but does not induce pro-apoptotic p53 target genes. This rapid induction of p21 was wild-type p53-dependent and resulted in cell cycle arrest along with a marked reduction of phosphorylated Rb in normally growing cells. We also showed that the repression of IFI16 affects p53 transcriptional activity at the p21 promoter as well as the protein stability of p53 and p21. Our findings identified a new role for IFI16 in modulating p53 function and its target gene regulation in the control of cell cycle regulation.

Reduced folate carrier and dihydrofolate reductase expression in acute lymphocytic leukemia may predict outcome: a Children's Cancer Group Study

PURPOSE

Methotrexate is a major component of current treatment regimens for children with acute lymphocytic leukemia (ALL). Potential mechanisms of methotrexate resistance include impaired drug uptake, decreased drug retention, and dihydrofolate reductase (DHFR) amplification. The purpose of this study was to assess whether reduced folate carrier (RFC) and DHFR expression in untreated leukemic blasts correlated with outcome.

METHODS

Quantitative real-time RT-PCR was used to measure RFC and DHFR mRNA expression in leukemic blasts from 40 newly diagnosed patients with ALL obtained in a blinded fashion from Children's Cancer Group studies.

RESULTS

Low RFC expression at diagnosis correlated significantly with an unfavorable event free survival. Surprisingly, low, not high, DHFR expression correlated significantly with an unfavorable event-free survival. Proliferative cell nuclear antigen (PCNA) expression demonstrated a weak inverse relationship between sample PCNA and DHFR or RFC expression, suggesting that DHFR and RFC expression may be markers for factors other than drug resistance.

CONCLUSIONS

These results suggest that impaired transport may be an important mechanism of intrinsic methotrexate resistance in ALL, and DHFR expression also may be an important prognostic factor in ALL. Additional studies are necessary to clarify the mechanism for the correlation of low DHFR expression with poor outcome.

Role of IFI 16, a member of the interferon-inducible p200-protein family, in prostate epithelial cellular senescence

Recent studies have implicated interferon signaling in the regulation of cellular senescence. However, the role of specific interferon-inducible proteins in cellular senescence remains to be defined. Here we report that IFI 16, an interferon-inducible transcriptional modulator from the p200-protein family, contributes to cellular senescence of prostate epithelial cells. Normal human prostate epithelial cells (PrEC) in culture expressed detectable levels of IFI 16, and the levels increased more than fourfold when cells approached cellular senescence. Consistent with a role of IFI 16 in cellular senescence, human prostate cancer cell lines either did not express IFI 16 or expressed a variant form, which was primarily detected in the cytoplasm of prostate cancer cells and not in the nucleus. Moreover, overexpression of functional IFI 16 in human prostate cancer cell lines inhibited colony formation. Additionally, ectopic expression of IFI 16 in clonal prostate cancer cell lines was associated with a senescence-like phenotype, production of senescence-associated beta-galactosidase (a biochemical marker for cellular senescence), and reduction of S-phase cells in culture. Importantly, upregulation of p21WAF1 and inhibition of E2F-stimulated transcription accompanied inhibition of cell growth by IFI 16 in prostate cancer cell lines. Collectively, our observations support the idea that increased levels of IFI 16 in PrECs contribute to senescence-associated irreversible cell growth arrest.

Retinoblastoma (Rb) protein upregulates expression of the Ifi202 gene encoding an interferon-inducible negative regulator of cell growth

Studies have indicated that ectopic expression of p202, an interferon (IFN)-inducible retinoblastoma (Rb)-binding protein, in cultured cells retards cell proliferation and modulates cell survival. Consistent with a role of p202 in cell cycle regulation, levels of p202 increase in cells arrested in the G0/G1 phase of cell cycle after withdrawal of serum growth factors. However, a role for p202 in cell growth arrest remains to be defined. Moreover, it remains unclear how levels of p202 are upregulated during the cell growth arrest. Here, we report that Rb upregulates expression of Ifi202 gene. We found that basal as well as IFN-induced levels of p202 were significantly higher in wild-type (Rb(+/+)) mouse embryonic fibroblasts (MEFs) than isogenic Rb(-/-) MEFs. Consistent with the regulation of Ifi202 gene by Rb, expression of functional Rb, but not a pocket mutant of it, stimulated the activity of a reporter whose expression was driven by the 5'-regulatory region of Ifi202 gene. Importantly, the stimulation by Rb was dependent, in part, on a JunD/AP-1 DNA-binding site present in the 5'-regulatory region of the Ifi202 gene. Moreover, basal levels of p202 were significantly higher in wild-type (JunD(+/+)) than isogenic JunD(-/-) MEFs. Additionally, we found that increased expression of p202 potentiated the Rb-mediated inhibition of cell growth and mutations in the Rb-binding motif (LxCxE) of p202 significantly reduced cell survival. Together, our observations support the idea that the transcriptional activation of Ifi202 gene by Rb/JunD may be important for the regulation of cell growth and survival.

The mouse Ifi200 gene cluster: genomic sequence, analysis, and comparison with the human HIN-200 gene cluster

The interferon-activatable Ifi200 gene cluster is located on mouse Chromosome 1q21-q23. We report here our analysis of two genomic regions encoding at least 10 closely related 200 family genes (Ifi201, Ifi202a, Ifi202b, Ifi202c, Ifi203a, Ifi203b, Ifi203c, Ifi203', Ifi204, and Ifi204') in 129/SvJ mice. Through a BAC-based sequencing approach, the exact structure and organization of these highly similar Ifi200 genes were obtained. A high degree of conservation (99% identity) was observed between Ifi202a and b and between Ifi203a and b. The presence of an additional transcribed region in intron 4 of Ifi203a and b suggests the possibility of alternative splicing, and a spliced variant of the Ifi204' mRNA exhibits 91% sequence identity with a related but unmapped D3 mRNA. Comparative analysis of the mouse and human clusters indicates an absence of significant sequence conservation in noncoding sequences, suggesting that the 200 family emerged prior to human-mouse speciation and subsequently diverged after gene duplication.

The interferon-inducible p202a protein modulates NF-kappaB activity by inhibiting the binding to DNA of p50/p65 heterodimers and p65 homodimers while enhancing the binding of p50 homodimers

p202a is a member of the interferon-inducible murine p200 family of proteins. These proteins share 1 or 2 partially conserved 200 amino acid segments of the a or the b type. The known biological activities of p202a include among others the regulation of muscle differentiation, cell proliferation, and apoptosis. These biological activities of p202a can be correlated with the inhibition of the activity of several transcription factors. Thus, the binding of p202a results in the inhibition of the sequence-specific binding to DNA of the c-Fos, c-Jun, E2F1, E2F4, MyoD, myogenin, and c-Myc transcription factors. This study concerns the mechanisms by which p202a inhibits the activity of NF-kappaB, a transcription factor involved among others in host defense, inflammation, immunity, and the apoptotic response. NF-kappaB consists of p50 and p65 subunits. We demonstrate that p202a can inhibit in vitro and in vivo the binding to DNA of p65 homodimers and p50/65 heterodimers, whereas it increases the binding of p50 homodimers. Thus p202a can impair NF-kappaB activity both by inhibiting the binding to DNA of the transcriptionally active p65 homodimers and p50/p65 heterodimers and by boosting the binding of the repressive p50 homodimers. p202a can bind p50 and p65 in vitro and in vivo, and p202a can be part of the p50 homodimer complex bound to DNA. p50 binds in p202a to the a type segment, whereas p65 binds to the b type segment. Transfected ectopic p202a increases the apoptotic effect of tumor necrosis factor (at least in part) by inhibiting NF-kappaB and its antiapoptotic activity.

Induction of p202, a modulator of apoptosis, during oncogenic transformation of NIH 3T3 cells by activated H-Ras (Q61L) contributes to cell survival

Previous studies have revealed that p202 (52 kDa), an interferon (IFN) and differentiation-inducible protein, negatively regulates cell proliferation and modulates cell survival. However, the role of p202 in transformed cells remains to be investigated. Here we report that constitutive expression of oncogenic H-Ras (Q61L) in NIH 3T3 cells, which resulted in cell transformation, was associated with increases in the steady-state levels of 202 RNA and protein. Interestingly, the increase in p202 levels in transformed cells correlated with increases in the activity of the transcription factor c-Jun/AP-1, which bound to the two potential AP-1 DNA binding sites (the AP-1CS1 and AP-1CS2) in the 5'-regulatory region of the 202 gene in gel mobility shift assays. Furthermore, the site-directed mutagenesis, coupled with promoter-reporter analyses, revealed that these two AP-1 DNA binding sites contribute to the regulation of the 202 gene in Ras transformed cells. Because treatment of transformed cells with a specific inhibitor of MEK (PD 98059) resulted in significant decreases in the levels of p202, these observations raise the possibility that in transformed cells Ras/Raf/MEK pathway regulates the transcriptional activation of the 202 gene. Significantly, decreases in the levels of p202 in Ras transformed NIH 3T3 cells under reduced serum conditions increased the susceptibility to apoptosis. Collectively, our observations support the idea that the transcriptional increases in the levels of p202 by oncogenic H-Ras in NIH 3T3 cells are needed for cell survival.

Retroviral mediated expression of the human myeloid nuclear antigen in a null cell line upregulates Dlk1 expression

The human myeloid nuclear differentiation antigen (MNDA) is a hematopoietic cell specific nuclear protein. MNDA and other related gene products interact with and alter the activity of a large number of proteins involved in regulating specific gene transcription. MNDA and related genes exhibit expression characteristics, which suggest functions unique to specific lineages of cells, in addition to mediating the effects of interferons. Cells of the human K562 myeloid line do not express MNDA and are relatively immature compared to lines that express MNDA (HL-60, U937, and THP1). The hypothesis that MNDA influences the expression of specific genes was tested by creating MNDA expressing K562 cells using stable retroviral mediated gene transfer followed by evaluation of transcription profiles. Two macroarrays containing a total of 2,350 cDNAs of known genes showed a specific up-regulation of Dlk1 expression in MNDA expressing K562 cell clones. Real time quantitative RT-PCR analysis confirmed an average of over 3- and 7-fold upregulation of Dlk1 in two clones of MNDA expressing K562 cells. The effects on Dlk1 were also confirmed by Northern blotting. Dlk1 is essential for normal hematopoiesis and abnormal expression is a proposed marker of myelodysplastic syndrome. Additional screening of transcription profiles after induced erythroid and megakaryoblastic differentiation showed no additional gene transcripts altered by the presence of MNDA. These results indicate that MNDA alters expression of a gene essential for normal hematopoiesis.

The mouse interferon-inducible gene Ifi204 product interacts with the Tpr protein, a component of the nuclear pore complex

We have used yeast two-hybrid screening to isolate cDNA-encoding proteins interacting with the protein encoded by the interferon (IFN)-inducible gene Ifi204. Four independent overlapping clones were isolated from an NIH3T3 cDNA library. The largest clone encoded a protein (1203 amino acids in length) sharing 94% identity with the C-terminal portion of the human translocated promoter region (Tpr) protein. Northern blot analysis revealed a 7.5-kilobase mRNA present in both mouse and human cell lines. In addition, in vivo interaction was demonstrated by coimmunoprecipitation experiments. Anti-Tpr polyclonal monospecific antibodies (Ab) used for immunofluorescence staining labeled the nuclear envelope (NE) in a punctate pattern characteristic of nucleoporins and also yielded staining throughout the nuclear interior. The intranuclear Tpr occurred in apparently discrete foci. When superimposed on optical sections obtained with anti-p204 Abs, these colocalized, with the sole exception of the nucleolar compartment stained by the anti-p204 Abs only. Although the specific function of Tpr is not defined, it appears to mediate p204 translocation from the cytoplasmic to the nuclear compartment following IFN treatment.

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.

Immunohistochemical expression analysis of the human interferon-inducible gene IFI16, a member of the HIN200 family, not restricted to hematopoietic cells

This is the first description of an extensive immunohistochemical analysis of interferon (IFN)-inducible gene IFI16 expression in normal tissues. Immunohistochemical detection of IFI16 in paraffin-embedded tissues is achieved by using a polyclonal antibody raised against its C-terminal fragment that recognizes its three closely migrating isoforms in Western blotting. The results clearly indicate that IFI16 expression is not restricted to the hematopoietic compartment. In normal adult human tissues, it is prominent in stratified squamous epithelia and particularly intense in parabasal cells in the proliferating compartments, but it gradually decreases in the more differentiated suprabasal layers. Understanding of IFI16 expression in vivo is essential for interpretation of the results obtained from in vitro studies and elucidation of its physiologic role. The constitutive expression and wider distribution of IFI16 in normal human tissues, not restricted to the hematopoietic compartment, strongly support the possibility of an important role in cell differentiation that can be further modulated by other stimuli, such as IFN.