Sequence and analysis of the murine Hmgiy (Hmga1) gene locus

The HMGIY non-histone proteins play important roles as architectural transcription factors that regulate gene transcription in mammalian cells and also act as host-supplied cofactors necessary for retroviral integration. The genes coding for the HMGIY proteins are proto-oncogenes, and their aberrant or over-expression is correlated with both neoplastic transformation and metastatic progression in a wide variety of tumors. Here, we report the first complete sequence of the murine Hmgiy (a.k.a. Hmga1) gene and provide a detailed comparison of this with the sequence and organization of the human HMGIY gene, including an analysis of its promoter region with the previously unreported 5' upstream region of the human gene. These analyses reveal a remarkable degree of overall sequence conservation in both the protein coding and promoter regions of the murine and human genes, including conservation of the c-Myc binding site that has been demonstrated to regulate murine Hmgiy transcription (Wood et al., 2000. Mol. Cell. Biol. 20, 5490-5502). The promoters of both genes contain other conserved transcription factor binding sites that may also represent important cis-regulatory elements. Two exons present in the 5' untranslated region of the human gene, however, are missing from the murine gene, suggesting that these two closely related mammalian species regulate transcription of their Hmgiy genes in an individualistic manner.

HMG-I/Y, a new c-Myc target gene and potential oncogene

The HMG-I/Y gene encodes the HMG-I and HMG-Y proteins, which function as architectural chromatin binding proteins important in the transcriptional regulation of several genes. Although increased expression of the HMG-I/Y proteins is associated with cellular proliferation, neoplastic transformation, and several human cancers, the role of these proteins in the pathogenesis of malignancy remains unclear. To better understand the role of these proteins in cell growth and transformation, we have been studying the regulation and function of HMG-I/Y. The HMG-I/Y promoter was cloned, sequenced, and subjected to mutagenesis analysis. A c-Myc-Max consensus DNA binding site was identified as an element important in the serum stimulation of HMG-I/Y. The oncoprotein c-Myc and its protein partner Max bind to this site in vitro and activate transcription in transfection experiments. HMG-I/Y expression is stimulated by c-Myc in a Myc-estradiol receptor cell line in the presence of the protein synthesis inhibitor cycloheximide, indicating that HMG-I/Y is a direct c-Myc target gene. HMG-I/Y induction is decreased in Myc-deficient fibroblasts. HMG-I/Y protein expression is also increased in Burkitt's lymphoma cell lines, which are known to have increased c-Myc protein. Like Myc, increased expression of HMG-I protein leads to the neoplastic transformation of both Rat 1a fibroblasts and CB33 cells. In addition, Rat 1a cells overexpressing HMG-I protein form tumors in nude mice. Decreasing HMG-I/Y proteins using an antisense construct abrogates transformation in Burkitt's lymphoma cells. These findings indicate that HMG-I/Y is a c-Myc target gene involved in neoplastic transformation and a member of a new class of potential oncogenes.

The oncogenic properties of the HMG-I gene family

The HMG-I gene family encodes high mobility group proteins originally identified as nonhistone chromosomal binding proteins. HMG-I and -Y proteins are alternatively spliced products of the same mRNA; HMG-C is encoded by a separate gene. The HMG-I proteins function as architectural chromatin-binding proteins that bind to the narrow groove of AT-rich regions in double-stranded DNA. Recent studies indicate an important role for HMG-I proteins in regulating gene expression. Moreover, increased expression of the HMG-I, -Y, and -C proteins correlates with cellular proliferation and neoplastic transformation in several cell types and human cancers. Previous work from our laboratory has shown that HMG-I is a direct c-Myc target gene that is involved in Myc-mediated neoplastic transformation. In this report, we show that increased expression of HMG-Y or -C leads to transformation with anchorage-independent cell growth in two experimental cell lines in a manner similar to that of HMG-I or c-Myc. Moreover, Rat la cells overexpressing HMG-Y or -C form tumors in nude mice analogous to Rat 1a cells overexpressing HMG-I or c-Myc. Distant metastases developed in animals injected with cells overexpressing HMG-I or -C. Our findings suggest that the HMG-I gene family is involved in neoplastic transformation and may represent a new family of oncogenes important in the pathogenesis of several human cancers.

Function of the c-Myc oncogenic transcription factor

The c-myc gene and the expression of the c-Myc protein are frequently altered in human cancers. The c-myc gene encodes the transcription factor c-Myc, which heterodimerizes with a partner protein, termed Max, to regulate gene expression. Max also heterodimerizes with the Mad family of proteins to repress transcription, antagonize c-Myc, and promote cellular differentiation. The constitutive activation of c-myc expression is key to the genesis of many cancers, and hence the understanding of c-Myc function depends on our understanding of its target genes. In this review, we attempt to place the putative target genes of c-Myc in the context of c-Myc-mediated phenotypes. From this perspective, c-Myc emerges as an oncogenic transcription factor that integrates the cell cycle machinery with cell adhesion, cellular metabolism, and the apoptotic pathways.

Hematologic abnormalities associated with influenza A infection: a report of 3 cases

Influenza A is associated with leukopenia, although it is not reported to cause isolated thrombocytopenia, anemia, or pancytopenia. The authors report three pediatric patients with transient cytopenias associated with influenza A infection, all of whom had evidence for influenza A infection by direct immunofluorescence from nasopharyngeal aspirates. In all patients, cytopenias were transient and improved as their viral symptoms resolved. All patients improved spontaneously. This is the first report of transient pancytopenia, anemia, or thrombocytopenia associated with influenza A infection. Given the high frequency of influenza A infections during the winter months, it is important to recognize the associated hematologic findings.

Fatal autoimmune hemolytic anemia in a child due to warm-reactive immunoglobulin M antibody

PURPOSE

Autoimmune hemolytic anemia (AIHA) due to warm-reactive immunoglobulin M (IgM) antibodies is rare in adults and has never been described in children. This report describes a pediatric patient with warm AIHA due to high-titer complete IgM antibody.

PATIENTS AND METHODS

A 9-year-old girl with a history of Evan's syndrome had severe anemia, fatigue, and skin mottling.

RESULTS

Serologic evaluation revealed a high-titer, high thermal amplitude (37 degrees C) complete IgM autoantibody. Despite aggressive management (including high dose corticosteroids, intravenous immune globulin, cyclophosphamide, mycophenolate mofetil, whole blood exchange transfusions, and cyclosporine A), the patient remained markedly anemic and developed multiorgan system failure related to diffuse in vivo hemagglutination. Her clinical course included cardiovascular collapse caused by agglutinated red blood cells in the right ventricle with outflow obstruction, cerebrovascular infarcts, hepatic failure, and infarction of her extremities. She ultimately died from disseminated Aspergillosis infection.

CONCLUSION

This rare form of AIHA is associated with a dismal prognosis. Early, aggressive treatment is advocated, although it remains to be seen whether the clinical course can be reversed and the outcome improved.

Recurrent seizures in a neonate after lidocaine administration

OBJECTIVE

We report recurrent seizures in a neonate after intravenous lidocaine administration at the recommended dose for intubation and supplementation of general anesthesia.

STUDY DESIGN

Further evaluation of this case included determination of serum lidocaine level, serum electrolyte levels, and arterial blood gas values; cerebral spinal fluid analysis; an electroencephalogram; head ultrasonography; brain stem auditory evoked response testing; and a complete developmental evaluation. Previously published literature discussing lidocaine toxicity and pharmacokinetics is reviewed.

RESULTS

The lidocaine level in the patient was 0.3 mg/L 2 hours after the last dose was administered. Results of the remaining studies were within normal limits, and the patient had no additional seizures several months after birth.

CONCLUSION

We caution that lidocaine administration to newborn infants at previously accepted doses may result in life-threatening side effects, including prolonged seizures.

Successful treatment of life-threatening acute chest syndrome of sickle cell disease with venovenous extracorporeal membrane oxygenation

PURPOSE

We describe a pediatric patient with sickle cell disease and life-threatening acute chest syndrome who was successfully treated with venovenous extracorporeal membrane oxygenation (ECMO).

PATIENT AND METHODS

An 8-year-old boy with sickle cell disease presented with vaso-occlusive crisis, which progressed to fulminant acute chest syndrome requiring a partial exchange transfusion and mechanical ventilation. Despite very high ventilator settings and significant barotrauma, hypoxia persisted and circulatory failure occurred. He was then successfully treated with venovenous ECMO for 11 days. One month after decannulation he had a seizure associated with abnormalities on magnetic resonance images (MRIs). His disease has been managed with a chronic transfusion program since then. Follow-up after 5 years reveals normal pulmonary function tests, a normal magnetic resonance angiogram (MRA), and above-average cognitive skills.

CONCLUSION

This is the first report of a pediatric patient with acute chest syndrome successfully managed with venovenous ECMO. His course was complicated by a seizure associated with MRI abnormalities, although the outcome has been excellent. This case suggests that treatment with venovenous ECMO should be strongly considered for sickle cell patients with life-threatening acute chest syndrome, despite maximal conventional support.

Skull infarction and epidural hematomas in a patient with sickle cell anemia

PURPOSE

Epidural hematomas are unusual manifestations of sickling disorders. We report a patient with sickle cell anemia and multiple skull infarctions associated with epidural hematomas. The association of skull infarctions and epidural hematomas in sickling hemoglobinopathies is reviewed.

PATIENTS AND METHODS

A 14-year-old boy with hemoglobin SS presented with lower back pain, left hip pain, headache, and fever. A bone scan was used to evaluate the patient for possible osteomyelitis. Head computed tomography (CT) and magnetic resonance imaging (MRI) were employed to delineate intracranial pathology.

RESULTS

The bone scan showed multiple areas of decreased uptake in the skull consistent with acute infarction before abnormalities were present on physical examination. CT scan showed a bony contour deformity of the right frontal bone, suggestive of infarction. A right frontal extra-axial collection of blood was also observed below the bony abnormality. MRI further delineated bilateral frontal and left parietal collections adjacent to the bony abnormalities consistent with subacute epidural hematomas.

CONCLUSIONS

This case emphasizes the need to recognize skull infarctions and epidural hematomas as rare but potential complications of sickle cell disease. The diagnosis was facilitated by MRI, which has not been used in previous cases of skull infarctions. Moreover, our patient was successfully managed without surgical intervention.

Cell density and paradoxical transcriptional properties of c-Myc and Max in cultured mouse fibroblasts

Deregulated expression of the c-Myc oncoprotein occurs in several human malignancies. The c-Myc protein behaves as a transcription factor, and undoubtedly its role in carcinogenesis involves its ability to affect the expression of genes involved in cell growth. c-Myc has been reported to both activate and repress transcription in transient transfection experiments using reporter constructs bearing multiple copies of the c-Myc binding site, CAC (G/A) TG. We investigated these apparently paradoxical effects of c-Myc by determining if they arose from differences in the cell proliferation states of transfected cells. We found that endogenous c-Myc protein levels vary inversely with the degree of cell confluency, such that at low cell confluency, where endogenous levels of c-Myc are high and presumably endogenous levels of Max are limiting, exogenous c-Myc fails to affect basal transcription. In cells at high cell confluency, in which endogenous c-Myc levels are low, exogenous c-Myc augments transactivation by titrating the relative excess endogenous Max. These observations suggest that the apparently paradoxical behavior of c-Myc in transfection experiments is partially dependent on ambient cellular levels of c-Myc.

B-myc inhibits neoplastic transformation and transcriptional activation by c-myc

B-myc is a recently described myc gene whose product has not been functionally characterized. The predicted product of B-myc is a 168-amino-acid protein with extensive homology to the c-Myc amino-terminal region, previously shown to contain a transcriptional activation domain. We hypothesized that B-Myc might also function in transcriptional regulation, although its role in regulating gene expression is predicted to be unique, because B-Myc lacks the specific DNA-binding motif found in other Myc proteins. To determine whether B-Myc could interact with the transcriptional machinery, we studied the transcriptional activation properties of a chimeric protein containing B-Myc sequences fused to the DNA-binding domain of the yeast transcriptional activator GAL4 (GAL4-B-Myc). We found that GAL4-B-Myc strongly activated expression of a GAL4-regulated reporter gene in mammalian cells. In addition, full-length B-Myc was able to inhibit or squelch reporter gene activation by a GAL4 chimeric protein containing the c-Myc transcriptional activation domain. We also observed that B-Myc dramatically inhibited the neoplastic cotransforming activity of c-Myc and activated Ras in rat embryo cells. Because B-Myc inhibits both neoplastic transformation and transcriptional activation by c-Myc, we suggest that the transforming activity of c-Myc is related to its ability to regulate transcription. Whether B-Myc functions biologically to squelch transcription and/or to regulate transcription through a specific DNA-binding protein remains unestablished.

Acute neurotoxicity after intrathecal cytosine arabinoside in two adolescents with acute lymphoblastic leukemia of B-cell type

BACKGROUND

Two adolescents with acute B-cell leukemia (Burkitt leukemia) had acute severe neurotoxicity after treatment with intrathecal (IT) cytosine arabinoside (AraC) at a dose of 50 mg/day for three consecutive days.

RESULTS

A 16-year-old boy had a rapidly ascending myelopathy and encephalopathy 20 hours after receiving the third dose of IT AraC. He remained quadriplegic and required ventilatory assistance for 10 months until his death from progressive tumor. A 12-year-old girl had acute encephalopathy, seizures, and focal neuroimaging abnormalities in the cerebellum and brain stem within 32 hours of the third AraC dose and 8 hours after IT methotrexate (MTX, 12 mg). Her clinical neurologic deficits resolved during the ensuing month. Patient 1 represents the first report to the authors' knowledge of acute severe neurotoxicity after AraC administered as the only IT drug. In Patient 2, IT AraC neurotoxicity may have been potentiated by the single dose of MTX.

CONCLUSION

IT AraC administered for 3 or more consecutive days may lead to profound neurologic dysfunction and require discontinuation of therapy.

The upstream stimulatory factor binds to and activates the promoter of the rat class I alcohol dehydrogenase gene

The gene encoding rat class I alcohol dehydrogenase (ADH) is expressed primarily in the liver. Recent studies in our laboratories indicate that multiple cellular factors present in the rat liver interact with various regions of the promoter of this gene. One of the regions contains the sequence 5'-CACATG-3' that has an "E box" homology to which a number of transcription factors containing the basic helix-loop-helix motif bind. We now demonstrate that the human transcription factor, upstream stimulatory factor (USF), a basic helix-loop-helix-containing protein, binds to and activates the promoter of the rat class I ADH gene. Electrophoretic mobility shift assays of labeled oligonucleotide containing the 5'-CACATG-3' sequence within the ADH promoter revealed the formation of multiple DNA-protein complexes when nuclear extracts obtained from adult rat liver were used. The binding of proteins to the DNA could be competed away with an oligonucleotide specifying a sequence within the adenovirus major late promoter (MLP) that had previously been shown to bind USF. Similar complexes were observed when electrophoretic mobility shift assays of labeled MLP oligonucleotide were performed with rat liver nuclear extracts. Conversely, nuclear extracts isolated from HeLa cells, cells known to have abundant USF, contain factors that interact with the sequence present in the ADH promoter. This interaction could be competed efficiently by the MLP oligonucleotide. USF synthesized in an in vitro transcription and translation system also binds to the ADH promoter as well as to the MLP. In addition, antiserum directed against USF recognizes factors present in the rat liver nuclear extracts that interact with the ADH promoter. Furthermore, transcription directed from both the ADH and the adenovirus major late promoters was inhibited by an oligonucleotide representing the USF-binding site within the ADH promoter in a cell-free in vitro transcription system. Lastly, an ADH promoter-reporter gene construct was transactivated by an eukaryotic expression vector containing USF in HepG2 cells co-transfected with the two constructs. These experiments demonstrate that USF is present in the rat liver and that it binds to and activates the promoter of the rat class I ADH gene in a sequence-specific manner.