[Electrical Burn with an Extensive Deep Defect of the Fronto-Orbital Region]

A 34-year-old worker suffered electrical burns on his head and right hand caused by the contact with a 380 V power source. He was unconscious, intubated, hospitalised at the ICU, and later he woke up. The entry wound was on the right hand and the exit wound on the head. These factors resulted in an extensive deep mutilating defect of the right fronto-orbital region. This article describes the management and surgical treatment of this interesting case of burn injury. Key words:electrical injury, surgical treatment.

Toxic epidermal necrolysis data from the CELESTE multinational registry. Part I: Epidemiology and general microbiological characteristics

INTRODUCTION

Toxic epidermal necrolysis (TEN) is a rare, life-threatening autoimmune disease predominantly manifested in the skin and mucous membranes. Today, infectious complications have the dominant share in mortality of TEN patients. Due to the nature of the therapy and administration of immunosuppressive medications, a wide range of potentially pathogenic microorganisms, which cause infectious complications in different compartments in these patients, is not surprising.

MATERIAL AND METHODOLOGY

This is a multicentric study, which included all patients with TEN hospitalized between 2000-2015 in specialized centres in the Czech Republic and Slovakia. The total catchment area was over 12.5 million inhabitants. The actual implementation of the project was carried out using data obtained from the registry CELESTE (Central European LyEll Syndrome: Therapeutic Evaluation), when specific parameters relating to epidemiological indicators and infectious complications in patients with TEN were evaluated in the form of a retrospective analysis.

RESULTS

In total, 39 patients with TEN were included in the study (12 patients died, mortality was 31%), who were hospitalized in the monitored period. The median age of patients in the group was 63 years (the range was 4-83 years, the mean was 51 years), the median of the exfoliated area was 70% TBSA (total body surface area) (range 30-100%, mean 67%). SCORTEN was calculated for 38 patients on the day of admission. Its median in all patients was 3 (range 1-6; mean 3). Any kind of infectious complication in the study group was recorded in 33 patients in total (85%). In total, 30 patients (77%) were infected with gram-positive cocci, 27 patients (69%) with gram-negative rods, and yeast cells or fibrous sponge were cultivated in 12 patients (31%). A total of 32 patients (82%) were found to have infectious complications in the exfoliated area, 15 patients (39%) had lower respiratory tract infections, 18 patients (46%) urinary tract infections and 15 patients (39%) an infection in the bloodstream. The most common potentially pathogenic microorganism isolated in our study group was coagulase neg. Staphylococcus, which caused infectious complications in 24 patients. Enterococcus faecalis/faecium (19 patients), Pseudomonas aeruginosa (17 patients), Staphylococcus aureus (11 patients) and Escherichia coli (11 patients) were other most frequently isolated micro-organisms.

CONCLUSION

The published data were obtained from the unique registry of TEN patients in Central Europe. In the first part, we have succeeded in defining the basic epidemiological indicators in the group of patients anonymously included in this registry. The study clearly confirms that infectious complications currently play an essential role in TEN patients, often limiting the chances of survival. The study also shows a high prevalence of these complications in the period after 15days from the start of hospitalization, when most patients already have completely regenerated skin cover.

Anti-Atherogenic Properties of Allium ursinum Liophylisate: Impact on Lipoprotein Homeostasis and Cardiac Biomarkers in Hypercholesterolemic Rabbits

The present investigation evaluates the capacity of Allium ursinum (wild garlic) leaf lyophilisate (WGLL; alliin content: 0.261%) to mitigate cardiovascular damage in hypercholesterolemic rabbits. New Zealand rabbits were divided into three groups: (i) cholesterol-free rabbit chow (control); (ii) rabbit chow containing 2% cholesterol (hypercholesterolemic, HC); (iii) rabbit chow containing 2% cholesterol + 2% WGLL (hypercholesterolemic treated, HCT); for eight weeks. At the zero- and eight-week time points, echocardiographic measurements were made, along with the determination of basic serum parameters. Following the treatment period, after ischemia-reperfusion injury, hemodynamic parameters were measured using an isolated working heart model. Western blot analyses of heart tissue followed for evaluating protein expression and histochemical study for the atheroma status determination. WGLL treatment mediated increases in fractional shortening; right ventricular function; peak systolic velocity; tricuspidal annular systolic velocity in live animals; along with improved aortic and coronary flow. Western blot analysis revealed WGLL-associated increases in HO-1 protein and decreases in SOD-1 protein production. WGLL-associated decreases were observed in aortic atherosclerotic plaque coverage, plasma ApoB and the activity of LDH and CK (creatine kinase) in plasma. Plasma LDL was also significantly reduced. The results clearly demonstrate that WGLL has complex cardioprotective effects, suggesting future strategies for its use in prevention and therapy for atherosclerotic disorders.

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.

Electrical burns in our workplace

BACKGROUND

There were totally 2320 patients during the period 2004-2013 hospitalised in our workplace with thermal injury, 87 of which were electric burns (3.75%).

RESULTS

The majority of electric burns occurred to men 67 cases (76.74%), then to children - 18 cases (20.94%) and the rest to women - 2 cases (2.32%). The mechanism of injury to the group of men was direct contact with the source of current (54.5%), electric arc injury (37.9%), ignition of clothes and subsequently flame (6.1%), and lightning injury (1.5%). The cause of injury to the group of children was contact injury (83.4%), electric arc injury (16.6%); no ignition or lightning injury occurred. The cause of injury in the group of women (2 cases) was contact injury for both; no arc, ignition or lighting injury occurred. The average extent of burn wounds was 11.7% in the group of men, 5.83% in the group of children and 2% in the group of women. Surgical treatment (necrectomy, skin grafting, flap, and amputation) was necessary in 41 cases in the group of men, in 15 cases in the group of children and in 2 cases in the group of women.

DISCUSSION AND CONCLUSION

Electric injury is a common problem in modern world. Some authors reported a 16.9% contribution of electric injuries of all hospitalised burn patients. There were 3.75% electric injury cases of all hospitalised burn patients in our department in the last nine years. The occurrence varies from year to year.

Memories of a senior scientist: on passing the fiftieth anniversary of the beginning of deciphering the genetic code

2011 marked the fiftieth anniversary of breaking the genetic code in 1961. Marshall Nirenberg, the National Institutes of Health (NIH) scientist who was awarded the Nobel Prize in Physiology or Medicine in 1968 for his role in deciphering the code, wrote in 2004 a personal account of his research. The race for the code was a competition between the NIH group and Severo Ochoa's laboratory at New York University (NYU) School of Medicine, where I was a graduate student and conducted many of the experiments. I am now 83 years old. These facts prompt me to recall how I, together with Joe Speyer, an instructor in the Department of Biochemistry at NYU, unexpectedly became involved in deciphering the code, which also became the basis of my PhD thesis. Ochoa won the Nobel Prize in Physiology or Medicine in 1959 for discovering polynucleotide phosphorylase (PNP), the first enzyme found to synthesize RNA in the test tube. The story of how PNP made the deciphering of the code feasible is recalled here.

The p200 family protein p204 as a modulator of cell proliferation and differentiation: a brief survey

The expression of the murine p200 family protein p204 in numerous tissues can be activated by a variety of distinct, tissue-specific transcription factors. p204 modulates cell proliferation, cell cycling, and the differentiation of various tissues, including skeletal muscle myotubes, beating cardiac myocytes, osteoblasts, chondrocytes, and macrophages. This protein modulates these processes in various ways, such as by (1) blocking ribosomal RNA synthesis in the nucleolus, (2) inhibiting Ras signaling in the cytoplasm, (3) promoting the activity of particular transcription factors in the nucleus by forming complexes with them, and (4) overcoming the block of the activity of other transcription factors by inhibitor of differentiation (Id) proteins. Much remains to be learned about p204, particularly with respect to its expected involvement in the differentiation of several as yet unexplored tissues.

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.

Multiple splicing results in at least two p203 proteins that are expressed in the liver and down-regulated during liver regeneration

The interferon inducible p200 family proteins are expressed in a variety of cells and tissues. Intensive studies showed that they were involved in the regulation of cell proliferation and differentiation based on their ability to bind and modulate the activities of multiple transcription activators and inhibitors. Among p200 proteins, p203 has received the least attention and its function is unknown. In the present study, four multiple splicing isoforms of Ifi203, named temporally as Ifi203a/b-1, Ifi203a/b-2, Ifi203 a/b-3, and Ifi203a/b-4, were cloned from the interferon induced 10T1/2 cells. Anti-p203 antiserum was prepared and it could immunodetect a 46 kD and a 51 kD p203 proteins in a variety of cell lines. Unlike other p200 proteins, p203 was exclusively expressed in the liver in the adult C129/SvJ and C57BL/6 inbred strain mice. During the liver regeneration following a standard partial hepatectomy in C57BL/6 mice, the level of p203 decreased significantly in 6-24 h post-operation prior to the cell cycle progression through the G1/S transition.

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.

Comparison of postsurgical and community acquired bacterial meningitis--analysis of 372 cases within a nationwide survey

The aim of this study was to assess if differences in etiology and risk factors among 372 cases of bacterial meningitis acquired after surgery (PM) or in community (CBM) have impact on outcome of infected patients. Among 372 cases of bacterial meningitis within last 17 years from 10 major Slovak hospitals, 171 were PM and 201 CBM. Etiology, risk factors such as underlying disease, cancer, diabetes alcoholism, surgery, VLBW, ENT infections, trauma, sepsis were recorded and mortality, survival with sequellae, therapy failure were compared in both groups. Significant differences in etiology and risk factors between both groups were reported. Those after neurosurgery had more frequently Coagulase negative staphylococci (p<0.001), Enterobacteriaceae (p=0.01) and Acinetobacter baumannii (p=0.0008) isolated from CSF and vice versa Streptococcus pneumoniae (p<0.001), Neisseria meningitis (p<0.001) and Haemophillus influenza (p=0.0009) were more commonly isolated from CSF in CBM. Neurosurgery (p<0.001), sepsis (p=0.006), VLBW neonates (p=0.00002) and cancer (p=0.0007) were more common in PM and alcohol abuse (p<0.001) as well as otitis/sinusitis (p<0.001) and Roma ethnic group (p=0.001) in CAM. Initial treatment success was significantly more frequently observed among CAM (p<0.001) but cure after modification was more common in PM (p=0.002). Therefore outcome in both groups was similar (14.6% vs. 12.4%, p=NS).

Bacterial meningitis after sinusitis and otitis media: ear, nose, throat infections are still the commonest risk factors for the community acquired meningitis

We investigated how many cases of bacterial meningitis in our national survey were associated with sinusitis or otitis media. Among 372 cases of bacterial meningitis within our nationwide 17 years survey, 201 cases were community acquired (CBM) and in 40 (20%) otitis media or sinusitis acuta/chronica were reported 1-5 weeks before onset of CBM. Diabetes mellitus (20% vs. 7.5%, p=0.01), alcohol abuse (35% vs. 15.4%, p=0.003) and trauma (30% vs. 14.9%, p=0.02) were significantly associated with CBM after ENT infections. Concerning etiology, CBM after sinusitis/otitis was insignificantly associated with pneumococcal etiology (50% vs. 33.8 %, NS) and significantly associated with other (L. monocytogenes, Str. agalactiae) bacterial agents (9.9 % vs. 25 %, p=0.008) . However those significant differences for new ENT related CBM had no impact on mortality (12.4 % vs. 5%, NS), failure after initial antibiotics (10 % vs. 9.5%, NS) and neurologic sequellae (12.5 % vs. 15.4 %, NS).

Bacterial meningitis after craniocerebral trauma in the community

Craniocerebral trauma is one of major risk factors for development of meningitis. We reviewed 30 cases of bacterial meningitis occurring in community after craniocerebral trauma. Alcohol abuse was significant risk factor occurring in trauma patients with meningitis present in 50% in our cohort (p=0.0001). The most common pathogen in posttraumatic meningitis was Str. pneumoniae (90% vs. 33.8%, p=0.0001). However mortality was very low, only 5% probably because of early diagnosis and treatment of patients at risk for bacterial meningitis but neurologic sequellea were significantly more common (p=0.00001) in patients after craniocerebral trauma.

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.

Increased expression of Ifi202, an IFN-activatable gene, in B6.Nba2 lupus susceptible mice inhibits p53-mediated apoptosis

Increased expression of p202 protein (encoded by the Ifi202 gene) in splenocytes derived from B6.Nba2 mice (congenic for the Nba2 interval derived from the New Zealand Black mice) was correlated with defects in apoptosis of splenic B cells and increased susceptibility to develop systemic lupus erythematosus. We have now investigated the molecular mechanisms by which increased expression of p202 in B6.Nba2 cells contributes to defects in apoptosis. In this study, we report that increased expression of p202 in the B6.Nba2 splenocytes, as compared with cells derived from the parental C57BL/6 (B6) mice, was correlated with increased levels of p53 protein and inhibition of p53-mediated transcription of target genes that encode proapoptotic proteins. Conversely, knockdown of p202 expression in B6.Nba2 cells resulted in stimulation of p53-mediated transcription. We found that p202 bound to p53 in the N-terminal region (aa 44-83) comprising the proline-rich region that is important for p53-mediated apoptosis. Consistent with the binding of p202 to p53, increased expression of p202 in B6.Nba2 mouse embryonic fibroblasts inhibited UV-induced apoptosis. Taken together, our observations support the idea that increased expression of p202 in B6.Nba2 mice increases the susceptibility to develop lupus, in part, by inhibiting p53-mediated apoptosis.

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.

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.

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.

The increase in levels of interferon-inducible proteins p202a and p202b and RNA-dependent protein kinase (PKR) during myoblast differentiation is due to transactivation by MyoD: their tissue distribution in uninfected mice does not depend on interferons

The murine 200 family proteins p202a, p202b, and p204, and also RNA-dependent protein kinase (PKR) are inducible by interferons (IFNs). p202a, p202b, and p204 modulate the activity of a large variety of transcription factors and also are involved in muscle differentiation. PKR is a multifunctional serine/threonine kinase, which is involved in antiviral defense and cell growth control and in the response to various stress signals. We reported earlier that the level of p204 increases during cultured C2C12 myoblast differentiation to myotubes in consequence of transactivation by the skeletal muscle-specific MyoD protein. The levels of p202a, p202b, and PKR also increase during the differentiation. We report here that these increased protein levels also are due to the transactivation of their genes by MyoD. This is made possible by the occurrence in each of these genes of at least six E boxes, which are recognition sites for MyoD. We also show that the distribution of the p204, p202a, p202b, and PKR proteins in five tissues of adult C129 mice is the same in wild-type mice and mice lacking the IFN-alpha, IFN-beta, and IFN-gamma receptors. This indicates that the synthesis and distribution of these proteins in uninfected adult mice are not affected by endogenous IFNs.

The MyoD-inducible p204 protein overcomes the inhibition of myoblast differentiation by Id proteins

The murine p204 protein level is highest in heart and skeletal muscle. During the fusion of cultured myoblasts to myotubes, the p204 level increases due to transcription dependent on the muscle-specific MyoD protein, and p204 is phosphorylated and translocated from the nucleus to the cytoplasm. p204 overexpression accelerates myoblast fusion in differentiation medium and triggers this process even in growth medium. Here we report that p204 is required for the differentiation of C2C12 myoblasts. We propose that it enables the differentiation, at least in part, by overcoming the inhibition of the activities of the MyoD and E47 proteins by the Id proteins: Id1, Id2, and Id3. These are known to inhibit skeletal muscle differentiation by binding and blocking the activity of MyoD, E12/E47, and other myogenic basic helix-loop-helix (bHLH) proteins. Our hypothesis is based on the following findings. (i) A decrease in the p204 level in C2C12 myoblasts by antisense RNA (a) increased the level of the Id2; (b) inhibited the MyoD-, E12/E47-, and other bHLH protein-dependent accumulation of the muscle-specific myosin heavy-chain protein; and (c) inhibited the fusion of myoblasts to myotubes in differentiation medium. (ii) p204 bound to the Id proteins in vitro and in vivo. (iii) In the binding of p204 to Id2, the b segment of p204 and the HLH segment of Id2 were involved. (iv) Addition of p204 overcame the inhibition by the Id proteins of the binding of MyoD and E47 to DNA in vitro. (v) Overexpression of p204 in myoblasts (a) decreased the level of the Id proteins, even in a culture in growth medium, and (b) overcame the inhibition by the Id proteins of MyoD- and E47 dependent transcription and also overcame the inhibition by Id2 of the fusion of myoblasts to myotubes.

p202, an interferon-inducible negative regulator of cell growth, is a target of the adenovirus E1A protein

Studies have revealed that human adenovirus-encoded E1A protein promotes cell proliferation through the targeted interaction with cellular proteins that act as key negative regulators of cell growth. The targets of E1A protein include the retinoblastoma tumor suppressor protein (pRb). Because p202, an interferon (IFN)-inducible murine protein (52-kDa), negatively regulates cell growth in part through the pRb/E2F pathway, we tested whether the p202 is a target of the adenovirus-encoded E1A protein for functional inactivation. Here we report that the expression of E1A protein overcame p202-mediated inhibition of cell growth and this correlated with an alleviation of p202-mediated inhibition of the transcriptional activity of E2F. Furthermore, E1A protein relieved p202-mediated inhibition of the specific DNA-binding activity of E2F complexes, including those containing the pocket proteins. Additionally, the E1A protein bound to p202 both in vitro and in vivo and a deletion of four amino acids in the conserved region 2 (CR2) of E1A protein significantly reduced the binding of E1A to p202. Interestingly, ectopic expression of p202 under reduced serum conditions significantly reduced E1A-mediated apoptosis. Taken together, our observations provide support to the idea that the p202 and adenovirus E1A protein functionally counteract each other and E1A protein targets p202 to promote cell proliferation.

The interferon- and differentiation-inducible p202a protein inhibits the transcriptional activity of c-Myc by blocking its association with Max

p202a is a murine protein that is induced during the fusion of myoblasts to myotubes and can also be induced by interferon. Even 2-3-fold overexpression of p202a in cells retards proliferation. p202a was shown to modulate transcription by binding, and inhibiting the activity of several transcription factors including c-Fos, c-Jun, AP-2, E2F1, E2F4, NF-kappaB, MyoD, and myogenin. Here we report that p202a also bound the c-Myc protein in vitro and in vivo; the C-terminal p202a b segment bound the C-terminal basic region helix-loop-helix-leucine zipper (bHLHLZ) region of c-Myc. The transfection of a p202a expression plasmid inhibited the c-Myc-dependent expression of reporter plasmids in transient assays; moreover, overexpression of p202a in stable cell lines decreased the endogenous levels of mRNAs whose expression is driven by c-Myc. These effects of p202a are consistent with our finding that the binding of p202a to c-Myc inhibited the binding of c-Myc to Max in vitro and in vivo. p202a also inhibited the c-Myc-induced anchorage-independent growth and apoptosis of Rat-1 cells. The inhibition of c-Myc-dependent transcription, proliferation, and apoptosis by p202a is in line with the involvement of p202a in differentiation.

MyoD-dependent induction during myoblast differentiation of p204, a protein also inducible by interferon

p204, an interferon-inducible p200 family protein, inhibits rRNA synthesis in fibroblasts by blocking the binding of the upstream binding factor transcription factor to DNA. Here we report that among 10 adult mouse tissues tested, the level of p204 was highest in heart and skeletal muscles. In cultured C2C12 skeletal muscle myoblasts, p204 was nucleoplasmic and its level was low. During myoblast fusion this level strongly increased, p204 became phosphorylated, and the bulk of p204 appeared in the cytoplasm of the myotubes. Leptomycin B, an inhibitor of nuclear export that blocked myoblast fusion, inhibited the nuclear export signal-dependent translocation of p204 to the cytoplasm. The increase in the p204 level during myoblast fusion was a consequence of MyoD transcription factor binding to several MyoD-specific sequences in the gene encoding p204, followed by transcription. Overexpression of p204 (in C2C12 myoblasts carrying an inducible p204 expression plasmid) accelerated the fusion of myoblasts to myotubes in differentiation medium and induced the fusion even in growth medium. The level of p204 in mouse heart muscle strongly increased during differentiation; it was barely detectable in 10. 5-day-old embryos, reached the peak level in 16.5-day-old embryos, and remained high thereafter. p204 is the second p200 family protein (after p202a) found to be involved in muscle differentiation. (p202a was formerly designated p202. The new designation is due to the identification of a highly similar protein-p202b [H. Wang, G. Chatterjee, J. J. Meyer, C. J. Liu, N. A. Manjunath, P. Bray-Ward, and P. Lengyel, Genomics 60:281-294, 1999].) These results reveal that p204 and p202a function in both muscle differentiation and interferon action.

Characteristics of three homologous 202 genes (Ifi202a, Ifi202b, and Ifi202c) from the murine interferon-activatable gene 200 cluster

The Ifi202 gene is part of the interferon-activatable murine gene 200 cluster on chromosome 1. Ifi202 encodes the p202 protein whose overexpression is growth inhibitory and which can bind and inhibit the activity of numerous transcription factors including c-Jun, c-Fos, NF-kappaB, E2F-1, E2F-4, MyoD, and myogenin. We report here the exon-intron structure of Ifi202 and the discovery of Ifi202b and Ifi202c, close homologs of Ifi202 (whose designation we now change to Ifi202a). Ifi202a, b, and c were colocalized to chromosome 1 bands H4-H5 by fluorescence in situ hybridization. Ifi202b encodes p202b, which is interferon-inducible and differs from p202a in only 7 of 445 amino acids. 202b mRNA is constitutively expressed in tissues in which 202a mRNA is expressed. Ifi202c is apparently an unexpressed pseudogene. In murine embryonic fibroblasts (MEFs) from 129 mice, the level of 202b mRNA is approximately half that of 202a mRNA. We knocked out the Ifi202a gene from 129 mice. The expression of 202b mRNA, but not 202a mRNA, persisted in the knockout mice and their MEFs at the same level as in wildtype mice. However, in MEFs from the knockout mice, the constitutive and interferon-induced levels of p202b were approximately as high as the constitutive and the interferon-induced levels of p202a plus p202b, respectively, in MEFs from wildtype mice. These findings suggest dosage compensation at the posttranscriptional level. This might account for the apparent lack of phenotype of the knockout mice.

The interferon-inducible nucleolar p204 protein binds the ribosomal RNA-specific UBF1 transcription factor and inhibits ribosomal RNA transcription

p204, a member of the interferon-inducible p200 family of murine proteins, is primarily nucleolar. We generated cell lines in which p204 was inducible by muristerone. This induction resulted in retardation of cell proliferation and inhibition of rRNA transcription in vivo. Interferon treatment, resulting in p204 induction and retardation of proliferation, also caused inhibition of rRNA transcription in vivo. p204 also inhibited rRNA transcription in vitro. This inhibition was overcome by addition of UBF1, the rRNA-specific transcription factor. A direct interaction between p204 and UBF1 was revealed in vitro in pull-down assays, and in vivo by co-immunoprecipitation from cell extracts. UBF1 bound strongly to at least two regions of p204: the N-terminal segment linked to the conserved 200 amino acid a segment, and the conserved 200 amino acid b segment. Cleavage of the a or b segments into two segments (encoded by single exons) resulted in a strong decrease or loss of binding. The inhibition of rRNA transcription by p204 may be due to the inhibition by p204 of the specific DNA binding of UBF1. This was revealed in electrophoretic mobility shift, magnetic bead and footprinting assays. Thus, p204 serves as a mediator of the inhibition of rRNA transcription by interferon.

Increase in p202 expression during skeletal muscle differentiation: inhibition of MyoD protein expression and activity by p202

p202 is a primarily nuclear, interferon-inducible murine protein that is encoded by the Ifi 202 gene. Overexpression of p202 in transfected cells retards cell proliferation. p202 modulates the pattern of gene expression by inhibiting the activity of various transcription factors including NF-kappaB, c-Fos, c-Jun, E2F-1, and p53. Here we report that p202 was constitutively expressed in mouse skeletal muscle and that the levels of 202 RNA and p202 greatly increased during the differentiation of cultured C2C12 myoblasts to myotubes. When overexpressed in transfected myoblasts, p202 inhibited the expression of one muscle protein (MyoD) without affecting the expression of a second one (myogenin). Thus, the decrease in the level of MyoD (but not of myogenin) during muscle differentiation may be the consequence of the increase in p202 level. Overexpressed p202 also inhibited the transcriptional activity of both MyoD and myogenin. This inhibition was correlated with an interaction of p202 with both proteins, as well as the inhibition by p202 of the sequence-specific binding of both proteins to DNA. This inhibition of the expression of MyoD and of the transcriptional activity of MyoD and myogenin may account for the inhibition of the induction of myoblast differentiation by premature overexpression of p202.

p202, an interferon-inducible modulator of transcription, inhibits transcriptional activation by the p53 tumor suppressor protein, and a segment from the p53-binding protein 1 that binds to p202 overcomes this inhibition

p202, an interferon-inducible murine protein, is a member of the "200 family" of proteins and is primarily nuclear. p202 is a modulator of transcription; it binds several transcription factors, including NF-kappaB p50 and p65, AP-1 c-Fos and c-Jun, and E2F1, and inhibits their transcriptional activity. p202 also binds pRb, the retinoblastoma protein, and if overexpressed it retards cell proliferation. Here we report that using the yeast two-hybrid assay we found that p202 bound the murine homolog of the human p53-binding protein 1 (53BP1), a protein shown to interact with the DNA binding domain of the p53 tumor suppressor protein. p202 bound a 98amino acid segment from 53BP1. This binding was inhibited by the replacement in p202 of a histidine (from the M(F/L)HATVA(T/S) sequence that is conserved among all of the 200 family proteins) by phenylalanine. We also report that overexpression of p202 inhibited the p53-dependent expression of reporter genes containing p53-activable segments from the mdm2 and p21 genes, whereas a decrease in the p202 level (in consequence of the expression of 202 antisense RNA) resulted in an increase in the p53-dependent expression of these reporters. Expression of the 53BP1 segment binding to p202 overcame the inhibition by overexpressed p202 of the transcription of reporters mediated by the p53 or the AP-1 transcription factors and of the proliferation of yeast.

Inhibition of E2F-mediated transcription by p202

Many of the antimicrobial, immunomodulatory and cell growth inhibitory activities of the interferons are mediated by interferon-inducible proteins. Earlier we characterized an interferon-inducible murine protein, p202, whose expression in transfected cells inhibits cell proliferation and which can form a complex with retinoblastoma protein (pRb). Here we report that in transfected cells expression of p202 inhibits E2F-stimulated transcription of a reporter gene and of endogenous genes. Inhibition of the transcriptional activity of E2F by p202 does not depend on fully functional pRb and is correlated with inhibition of the sequence-specific DNA binding of E2F. p202 interacts with the transcription factor E2F (E2F-1/DP-1) in vitro and in vivo. Inhibition of E2F activity by p202 may contribute to growth inhibition by the interferons.

The interferon-inducible p202 protein as a modulator of transcription: inhibition of NF-kappa B, c-Fos, and c-Jun activities

The antimicrobial, immunomodulatory, and cell growth-regulatory activities of the interferons are mediated by interferon-inducible proteins. One of these is p202, a nuclear protein that is encoded by the Ifi 202 gene from the interferon-activatable gene 200 cluster. Overexpression of p202 in transfected cells slows down cell proliferation. As shown earlier, p202 binds to the hypophosphorylated form of the retinoblastoma susceptibility protein. Here we report that p202 inhibits the activities of the NF-kappa B and the AP-1 enhancers both in transiently transfected cells and in transfected stable cell lines overexpressing p202. Furthermore, p202 binds the NF-kappa B p50 and p65 and the AP-1 c-Fos and c-Jun transcription factors in vitro and in vivo. NF-kappa B, c-Fos, and c-Jun participate in the transcription of various cellular and viral genes, and thus p202 can modulate the expression of these genes in response to interferons.

Binding of an interferon-inducible protein (p202) to the retinoblastoma protein

Many of the antimicrobial, immunomodulatory, and cell growth regulatory activities of the interferons are mediated by interferon-inducible proteins. One family of such murine proteins is encoded by six or more adjacent and structurally related genes (gene 200 cluster). Two homologous human genes have also been reported. p202, encoded by the Ifi202 gene in the gene 200 cluster, is a 52-kDa nuclear phosphoprotein. Constitutive overexpression of p202 in transfected cells is growth-inhibitory. We report here that p202 binds the cell growth regulatory retinoblastoma protein (pRb) in vitro and in vivo. The binding is due to direct interaction between the two proteins. p202 has two nonoverlapping segments for binding pRb, and pRb has two nonoverlapping segments (one of them including the pocket region) for binding p202. The hypophosphorylated form of pRb binds to p202, p202 is the first interferon-inducible protein found to bind pRb.

Tumor-suppressor genes: news about the interferon connection

The interferons are a family of secreted, multifunctional proteins which are components of the defenses of vertebrates against viral, bacterial, and parasitic infections and certain tumors. They exert their various activities by inducing the synthesis of a large variety of proteins. There are direct and indirect indications that several of these proteins may have tumor-suppressor activities. The interferon-inducible proteins implicated include: (i) a double-stranded RNA-activatable protein kinase that can phosphorylate and thereby inactivate the eukaryotic peptide chain initiation factor eIF-2; (ii) the interferon regulatory factors IRF-1 and IRF-2, which can modulate the expression of the interferons and of some interferon-inducible proteins; and (iii) RNase L, a latent endoribonuclease which can be activated by (2'-5')oligoadenylates, the products of a family of enzymes which are also interferon-inducible. It is note-worthy that some of the proteins encoded by tumor virus oncogenes (e.g., E1A from adenovirus, EBNA-2 from Epstein-Barr virus, and terminal protein from hepatitis B virus) impair the induction of at least some proteins by interferons.

Interferon action: cytoplasmic and nuclear localization of the interferon-inducible 52-kD protein that is encoded by the Ifi 200 gene from the gene 200 cluster

Recently, we reported that an interferon (IFN)-inducible, murine 72-kD phosphoprotein (the 204 protein) that is encoded by the Ifi 204 gene from the gene 200 cluster is localized in the nucleolus and the nucleoplasm. We have now raised a polyclonal antiserum against the 202 protein that is encoded by the Ifi 202 gene from the same gene cluster and regions of which are homologous to those from the 204 protein. Using the antiserum, we established that the 202 protein is a 52-kD phosphoprotein whose level in cells from various murine lines can be increased up to 16-fold upon treatment with IFN-alpha. Experiments involving fractionation of cell lysates and indirect immunofluorescence microscopy of cultured cells revealed that the 202 protein was localized in the cytoplasm and the nucleus. Upon treatment of cells with IFN, the 202 protein first accumulated on the surface of a cytoplasmic, membranous fraction and after prolonged treatment with IFN it was localized mainly in the nucleus. In IFN-treated mitotic AKR cells, the 202 protein was colocalized with chromosomes. 202 protein extracted from IFN-treated AKR cells bound double-stranded DNA in vitro. Studies on 202 protein function should be facilitated by the availability of complete cDNA clones and the finding of cell lines and an inbred strain of mice in which the expression of this protein was impaired.

Interferon action: nucleolar and nucleoplasmic localization of the interferon-inducible 72-kD protein that is encoded by the Ifi 204 gene from the gene 200 cluster

The interferons are cytokines with antiviral, cell growth regulatory, and immunomodulatory activities. These activities are mediated by the proteins induced by the interferons. Earlier we described a gene cluster (the 200 cluster) consisting of at least six adjacent, interferon-activatable genes located next to the erythroid alpha-spectrin locus on murine chromosome 1. The genes of the cluster arose by repeated gene duplication and they specify proteins with pronounced sequence similarity. We have now raised polyclonal antibodies against a segment from one of these proteins (the 204 protein of 72 kD). Using these, we established that the 204 protein is a phosphoprotein whose level in cells from various murine lines can be increased up to 75-fold upon treatment with alpha interferon. Experiments involving fractionation of cell lysates and indirect immunofluorescence microscopy of control and interferon-treated cells revealed that the 204 protein is nucleolar and nucleoplasmic. This conclusion was confirmed by co-localization with B23, a known nucleolar protein. The 204 protein is the first interferon-induced protein found to be located in the nucleoli, the subcellular organelles of ribosomal RNA production and ribosome assembly. It remains to be seen whether the 204 protein affects any of these processes. Studies on 204 protein function should be facilitated by the availability of complete cDNA clones and the finding of cell lines in which the expression of this protein is impaired.

Impaired transcription of the poly rI:rC- and interferon-activatable 202 gene in mice and cell lines from the C57BL/6 strain

Activation of 202 and (2'-5')(A)n synthetase genes after injection of interferon (IFN)-inducing, double-stranded, poly rI:rC was compared in various mouse strains. The 202 mRNA level increased 4.5- to 10-fold in DBA/2, BALB/c, and C3H/HeJ mice, whereas in C57BL/6 mice it rose only to about that in untreated DBA/2, BALB/c, and C3H/HeJ mice. To determine whether this low level was due to a reduced transcription rate, a nuclear "run-on" assay was performed with NIH 3T3 cells or BLK cells derived from C57BL/6 mice. IFN-alpha increased the 202 mRNA transcription severalfold in NIH 3T3 cells only, and that of a (2'-5')(A)n synthetase gene in both cell lines. The possibility that an alteration in transacting factors could be responsible for this difference was examined. For this purpose the 5' terminal flanking region (called the b segment, about 0.8 kb) of the 202 gene was linked to a heterologous reporter gene--chloramphenicolacetyl-transferase (CAT) and transfected into normal or transformed NIH 3T3 cells and into various C57BL/6-derived cell lines. IFN-alpha induced strong CAT activity in transfected normal or transformed NIH 3T3 cells, but a much lower activity in those from C57BL/6 mice. The b segment contains an IFN-responsive element (ISRE) (35 bp) homologous to that present in several other IFN-inducible genes. Three tandem copies of the 202 ISRE were linked to an enhancerless SV40 early promoter driving an influenza virus hemagglutinin (HA) cDNA segment. No increase in HA mRNA expression was detected in the transfected BLK cell line derived from C57BL/6 mice following IFN treatment, whereas in the NIH 3T3 cell line, the IFN treatment resulted in a 2.5-fold increase. These and other results suggest that C57BL/6 mice and cell lines derived from them might carry defective transacting factors impairing the ability of IFN-alpha to activate the 202 gene without impairing its ability to activate a (2'-5')(A)n synthetase gene.

Recessive (mediator-) revertants from c-H-ras oncogene-transformed NIH 3T3 cells: tumorigenicity in nude mice and transient anchorage and serum independence of the recovered tumor cells in culture

We have reported earlier the isolation of two recessive, serum- and anchorage-dependent revertants (R116 and R260) from a c-H-ras oncogene-transformed NIH 3T3 line. In both revertants, the oncogene was fully expressed and fusion of either revertant with (untransformed) NIH 3T3 cells, or of the two revertants with one another, resulted in transformed progeny. These, and other data, indicated that the transforming activity of the oncogene was impaired in the two revertants in consequence of defects in distinct genes needed to mediate this activity. We report here that neither revertant could be re-transformed by the K-ras or N-ras oncogene (though they could be re-transformed by several other oncogenes). The two revertants turned out to be tumorigenic in nude mice (though less so than the parental transformed cells). The tumor cells, as recovered, formed foci and had a transformed morphology and a greatly diminished serum and anchorage dependence. Growth of the cells in culture (for 20 passages) resulted in their regaining the characteristics (i.e., anchorage and serum dependence) of cultured R116 and R260 cells. Proliferation of the cells in nude mice was not accompanied by a change in the level of ras oncogene expression or in gene amplification, at least as manifested in the lack of appearance of double-minute chromosomes. The addition of the growth factors TGF alpha and beta to the medium of either revertant did not support anchorage-independent growth.

Interferon action: binding of viral RNA to the 40-kilodalton 2'-5'-oligoadenylate synthetase in interferon-treated HeLa cells infected with encephalomyocarditis virus

The 40-kDa 2'-5'-oligoadenylate [(2'-5') (A)n] synthetase isoenzyme was proven to be a mediator of the inhibition of encephalomyocarditis virus (EMCV) replication by interferon (IFN). When activated by double-stranded RNA, this enzyme converts ATP into 2'-5'-oligoadenylate [(2'-5') (A)n], and (2'-5') (A)n was found to accumulate in IFN-treated, EMCV-infected cells. The only known function of (2'-5') (A)n is the activation of RNase L, a latent RNase, and this was also implicated in the inhibition of EMCV replication. Intermediates or side products in EMCV RNA replication, presumed to be partially double stranded, were shown to activate (2'-5') (A)n synthetase in vitro. These findings served as the basis of the long-standing hypothesis that the activator of (2'-5') (A)n synthetase in IFN-treated, EMCV-infected cells is the viral RNA. To test this hypothesis, we have generated a polyclonal rabbit antiserum to the human 40-kDa (2'-5') (A)n synthetase. The antiserum immunoprecipitated, from IFN-treated HeLa cells that had been infected with EMCV, the 40-kDa (2'-5') (A)n synthetase protein in complex with both strands of EMCV RNA. The immunoprecipitate was active in (2'-5') (A)n synthesis even without addition of double-stranded RNA, whereas the immunoprecipitate from IFN-treated, uninfected cells was not. These and other results demonstrate that in IFN-treated, EMCV-infected cells, viral RNA is bound to the (2'-5') (A)n synthetase and suggest that the agent activating the (2'-5') (A)n synthetase is the bound viral RNA.

Characterization of recessive (mediator-) revertants from NIH 3T3 cells transformed with a c-H-ras oncogene

We have reported earlier the isolation of two recessive, serum- and anchorage-dependent revertants from an NIH 3T3 line which had been transformed with multiple copies of a c-H-ras oncogene. In both revertants the oncogene was fully expressed and fusion of either revertant with normal (untransformed) cells or of the two revertants with one another resulted in transformed progeny. These, and other data indicate that the transforming activity of the c-H-ras oncogene is impaired in the two revertants, in consequence of defects in distinct genes needed to mediate this activity. Here, we describe some of the biochemical features of the revertants. In both of these (as in the transformed line) the bulk of the ras-p21 protein was found in the membrane fraction. This suggests proper posttranslational processing. Furthermore, no difference was detected either in the ras-p21 protein GTPase stimulating activity of GAP or in the extent of GAP-tyrosine phosphorylation among growing cultures of the two revertants, the transformed line and the parental NIH 3T3 line. The level of glucose transporter mRNA was severalfold higher in the transformed line than in the NIH 3T3 line. In the two revertants, however, the level was as low as that in the NIH 3T3 line. This indicates that the reversion impaired the effect of the c-H-ras oncogene on transcription. The raf oncogene (proposed to increase transcription factor activity) could retransform both revertants. Moreover, as revealed in experiments with growing cultures, neither transformation by the c-H-ras oncogene nor reversion from the transformed state altered the electrophoretic mobility of the raf protein or the level of its actin kinase activity. These results suggest that transformation by the c-H-ras oncogene is not mediated by the activation of raf protein kinase. The tyrosine phosphorylation of the p34cdc2 protein kinase (a cell cycle regulatory enzyme) was severalfold higher in the transformed line than in the NIH 3T3 line. The level of p34cdc2 protein kinase phosphorylation was as high in the R260 revertant as in the transformed line and as low in the R116 revertant as in the NIH 3T3 line. We are attempting to identify the defective mediator genes impairing the transforming activity of the c-H-ras oncogene in the two revertants.