OmoMYC blunts promoter invasion by oncogenic MYC to inhibit gene expression characteristic of MYC-dependent tumors.

MYC genes have both essential roles during normal development and exert oncogenic functions during tumorigenesis. Expression of a dominant-negative allele of MYC, termed OmoMYC, can induce rapid tumor regression in mouse models with little toxicity for normal tissues. How OmoMYC discriminates between physiological and oncogenic functions of MYC is unclear. We have solved the crystal structure of OmoMYC and show that it forms a stable homodimer and as such recognizes DNA in the same manner as the MYC/MAX heterodimer. OmoMYC attenuates both MYC-dependent activation and repression by competing with MYC/MAX for binding to chromatin, effectively lowering MYC/MAX occupancy at its cognate binding sites. OmoMYC causes the largest decreases in promoter occupancy and changes in expression on genes that are invaded by oncogenic MYC levels. A signature of OmoMYC-regulated genes defines subgroups with high MYC levels in multiple tumor entities and identifies novel targets for the eradication of MYC-driven tumors.

The nucleotide excision repair protein UvrB, a helicase-like enzyme with a catch.

Nucleotide excision repair (NER) is a universal DNA repair mechanism found in all three kingdoms of life. Its ability to repair a broad range of DNA lesions sets NER apart from other repair mechanisms. NER systems recognize the damaged DNA strand and cleave it 3', then 5' to the lesion. After the oligonucleotide containing the lesion is removed, repair synthesis fills the resulting gap. UvrB is the central component of bacterial NER. It is directly involved in distinguishing damaged from undamaged DNA and guides the DNA from recognition to repair synthesis. Recently solved structures of UvrB from different organisms represent the first high-resolution view into bacterial NER. The structures provide detailed insight into the domain architecture of UvrB and, through comparison, suggest possible domain movements. The structure of UvrB consists of five domains. Domains 1a and 3 bind ATP at the inter-domain interface and share high structural similarity to helicases of superfamilies I and II. Not related to helicase structures, domains 2 and 4 are involved in interactions with either UvrA or UvrC, whereas domain 1b was implicated for DNA binding. The structures indicate that ATP binding and hydrolysis is associated with domain motions. UvrB's ATPase activity, however, is not coupled to the separation of long DNA duplexes as in helicases, but rather leads to the formation of the preincision complex with the damaged DNA substrate. The location of conserved residues and structural comparisons with helicase-DNA structures suggest how UvrB might bind to DNA. A model of the UvrB-DNA interaction in which a beta-hairpin of UvrB inserts between the DNA double strand has been proposed recently. This padlock model is developed further to suggest two distinct consequences of domain motion: in the UvrA(2)B-DNA complex, domain motions lead to translocation along the DNA, whereas in the tight UvrB-DNA pre-incision complex, they lead to distortion of the 3' incision site.

Crystal structure of UvrB, a DNA helicase adapted for nucleotide excision repair.

Nucleotide excision repair (NER) is a highly conserved DNA repair mechanism. NER systems recognize the damaged DNA strand, cleave it on both sides of the lesion, remove and newly synthesize the fragment. UvrB is a central component of the bacterial NER system participating in damage recognition, strand excision and repair synthesis. We have solved the crystal structure of UvrB in the apo and the ATP-bound forms. UvrB contains two domains related in structure to helicases, and two additional domains unique to repair proteins. The structure contains all elements of an intact helicase, and is evidence that UvrB utilizes ATP hydrolysis to move along the DNA to probe for damage. The location of conserved residues and structural comparisons allow us to predict the path of the DNA and suggest that the tight pre-incision complex of UvrB and the damaged DNA is formed by insertion of a flexible beta-hairpin between the two DNA strands.

Shared management of children with cancer.

OBJECTIVE: To determine the risks and benefits of university-based pediatric oncologists and community-based primary care physicians sharing the management of children with cancer. DESIGN: Physicians participating in shared management of children with cancer were surveyed, and the outcomes of the children were measured. SETTING AND PARTICIPANTS: One hundred thirty-seven community-based primary care physicians participated in the management of the 226 children with cancer in Iowa and western Illinois during the past 15 years. The survival of the 226 children was compared with that of 240 randomly selected children treated using the identical treatment protocols but treated only by pediatric oncologists. INTERVENTION: A 7-point Likert scale questionnaire was completed by 97 (71%) of the participating primary care physicians. RESULTS AND OUTCOME MEASURES: There were no differences in the survival of children using shared management compared with those treated only by pediatric oncologists. Primary care physicians believed that shared management is of economic and psychosocial benefit to patients, improves the treatment choices available to patients, does not require excessive time, and does not result in loss of practice income. The system strengthens the primary care physicians' relationships with oncologists and results in additional referrals to the university-based pediatric oncologists. It is of educational value, is personally satisfying, and provides relief from the stress associated with caring for these families. Primary care physicians would like to see this system expanded to include other children with special health care needs. CONCLUSION: The shared-management approach to care is a viable attractive option of health care provision for children.

Structure of ADP x AIF4(-)-stabilized nitrogenase complex and its implications for signal transduction.

The coupling of ATP hydrolysis to electron transfer by the enzyme nitrogenase during biological nitrogen fixation is an important example of a nucleotide-dependent transduction mechanism. The crystal structure has been determined for the complex between the Fe-protein and MoFe-protein components of nitrogenase stabilized by ADP x AIF4-, previously used as a nucleoside triphosphate analogue in nucleotide-switch proteins. The structure reveals that the dimeric Fe-protein has undergone substantial conformational changes. The beta-phosphate and AIF4- groups are stabilized through intersubunit contacts that are critical for catalysis and the redox centre is repositioned to facilitate electron transfer. Interactions in the nitrogenase complex have broad implications for signal and energy transduction mechanisms in multiprotein complexes.

Treatment of nonmetastatic osteosarcoma of the extremity with preoperative and postoperative chemotherapy: a report from the Children's Cancer Group.

PURPOSE: The specific aims of this study were to improve event-free survival (EFS) in patients with newly diagnosed nonmetastatic osteosarcoma of an extremity using the histologic response to neoadjuvant chemotherapy to determine postoperative chemotherapy; to evaluate a uniform histologic grading system that measures tumor response; and to identify patient characteristics that might influence EFS and survival. PATIENTS AND METHODS: Two hundred sixty-eight patients with nonmetastatic osteosarcoma of the extremity were entered between August 1983 and October 1986. Preoperative chemotherapy consisted of four courses of high-dose methotrexate (MTX) and one course of bleomycin, cyclophosphamide, and dactinomycin (BCD). Histologic response to preoperative chemotherapy was determined by morphometric analysis. Good histologic responders (< 5% residual viable tumor) were treated postoperatively with MTX, BCD, and doxorubicin (DOX); poor histologic responders were treated with BCD, DOX, and cisplatin (CDDP). RESULTS: The 8-year EFS and survival rates were 53% and 60%, respectively. Two hundred six patients had their tumors assessed for histologic response: 28% displayed a good histologic response to preoperative chemotherapy. Good histologic responders had an 8-year postoperative EFS rate of 81% and survival rate of 87%; those with a poor histologic response had an 8-year postoperative EFS rate of 46% and survival rate of 52%. A primary tumor site in the proximal humerus or proximal femur and an elevated serum alkaline phosphatase level were associated with an increased risk of an adverse event, whereas the type of surgical procedure was not. CONCLUSION: EFS and survival appear to be directly related to histologic response to neoadjuvant chemotherapy.

Molecular basis of sulfite oxidase deficiency from the structure of sulfite oxidase.

The molybdenum-containing enzyme sulfite oxidase catalyzes the conversion of sulfite to sulfate, the terminal step in the oxidative degradation of cysteine and methionine. Deficiency of this enzyme in humans usually leads to major neurological abnormalities and early death. The crystal structure of chicken liver sulfite oxidase at 1.9 A resolution reveals that each monomer of the dimeric enzyme consists of three domains. At the active site, the Mo is penta-coordinated by three sulfur ligands, one oxo group, and one water/hydroxo. A sulfate molecule adjacent to the Mo identifies the substrate binding pocket. Four variants associated with sulfite oxidase deficiency have been identified: two mutations are near the sulfate binding site, while the other mutations occur within the domain mediating dimerization.

AIDS-associated non-Hodgkin's lymphomas as primary and secondary AIDS diagnoses in hemophiliacs. Hemophilia Malignancy Study Group.

We studied the characteristics and temporal trends of AIDS- associated non-Hodgkin's lymphoma (AIDS-NHL) in individuals with hemophilia. Prospective data were collected on 33 HIV-positive hemophiliacs with AIDS-NHL enrolled in the Hemophilia Malignancy Study (HMS), of whom 21 had primary and 12 had secondary or subsequent AIDS-defining illnesses, and analyzed for frequency and temporal trends. As compared with primary AIDS- NHL, secondary AIDS-NHL occurred at an older mean age, 37 versus 29 years (p = 0.12); at a lower mean CD4 count, 46 versus 154 (p = 0.07); after a longer period of immunosuppression (CD4 < 200/microl), 41 versus 16 months (p = 0.03); and with shorter median survival, 2 versus 7 months (p = 0.09). The presence of EBV in tumor tissue was associated with shorter survival, 1 versus 7 months (p = 0.17). Between 1981 and 1988 and 1989 and 1994, the proportion of primary AIDS diagnoses that were AIDS-NHL changed minimally, 4.6 versus 6.1%, whereas there were significant decreases in Pneumocystis carinii pneumonia (PCP, p = 0.02) and wasting (p = 0.07), and an increase in Candida (p = 0.004). These findings confirm that an increasing proportion of AIDS-NHL in hemophiliacs are occurring as secondary or later AIDS diagnoses, and they are associated with prolonged duration of immunosuppression.

Crystal structure of DMSO reductase: redox-linked changes in molybdopterin coordination.

The molybdoenzyme dimethylsulfoxide (DMSO) reductase contributes to the release of dimethylsulfide, a compound that has been implicated in cloud nucleation and global climate regulation. The crystal structure of DMSO reductase from Rhodobacter sphaeroides reveals a monooxo molybdenum cofactor containing two molybdopterin guanine dinucleotides that asymmetrically coordinate the molybdenum through their dithiolene groups. One of the pterins exhibits different coordination modes to the molybdenum between the oxidized and reduced states, whereas the side chain oxygen of Ser147 coordinates the metal in both states. The change in pterin coordination between the Mo(VI) and Mo(IV) forms suggests a mechanism for substrate binding and reduction by this enzyme. Sequence comparisons of DMSO reductase with a family of bacterial oxotransferases containing molybdopterin guanine dinucleotide indicate a similar polypeptide fold and active site with two molybdopterins within this family.

The complex formed between Tet repressor and tetracycline-Mg2+ reveals mechanism of antibiotic resistance.

In recent years Gram-negative bacteria have developed several resistance mechanisms against the broad-spectrum antibiotic tetracycline (Tc). The most abundant mechanism involves a membrane-associated protein (TetA) that exports the antibiotic out of the bacterial cell before it can attach to the ribosomes and inhibit polypeptide elongation. The expression of the TetA protein is regulated by the Tet repressor (TetR). It occurs as a homodimer and binds with two alpha-helix-turn-alpha-helix motifs (HTH) to two tandemly orientated DNA operators, thereby blocking the expression of the associated genes, one encoding for TetA and the other for TetR. If Tc in complex with a divalent cation binds to TetR, a conformational change occurs and the induced TetR is then unable to bind to DNA. TetR of class D, TEtRD, was cocrystallized with tetracycline (7HTc) and Mg2+ in space group I4(1)22 and studied by X-ray diffraction. One TetRD monomer occupies the crystal asymmetric unit, and the dimer is formed by a crystallographic 2-fold rotation. The crystal structure was determined by multiple isomorphous replacement at 2.5 A resolution, and on this basis the structure of the nearly isomorphous complex with 7-chlorotetracycline, TetRD/(Mg 7CITc)+, has been refined to an R-factor of 18.3% using all reflections to 2.1 A resolution. TetRD folds into ten alpha-helices with connecting turns and loops. The N-terminal three alpha-helices of the repressor form the DNA-binding domain, including the HTH with an inverse orientation compared with HTH in other DNA-binding proteins. The distance of 39 A between the two recognition helices explains the inability of the induced TetR to bind to B-form DNA. The core of the protein is formed by helices alpha 5 to alpha 10. It is responsible for dimerization and contains, for each monomer, a binding pocket that accommodates Tc in the presence of a divalent cation. The structure of the TetRD/(Mg 7CITc)+ complex reveals the octahedral coordination of Mg2+ by Tc (chelating O-11, and O-12), His100 N epsilon and by three water molecules; in addition there is an extended network of hydrogen bonding and van der Waals interactions formed between 7CITc and TetR. The detailed view of the Tc-binding pocket and the interactions between the antibiotic and the repressor offers the first solid basis for rational tetracycline design, with the aim of circumventing resistance.

Acquired immunodeficiency syndrome-associated non-Hodgkin's lymphomas and other malignancies in patients with hemophilia.

Non-Hodgkin's lymphoma (NHL) is the most common human immunodeficiency virus (HIV)-associated malignancy in hemophiliacs. We studied the incidence and clinicopathologic features of NHL in 3,041 hemophiliacs followed at 18 US Hemophilia Centers between 1978 and 1989. Of the 1,295 (56.6%) who were HIV(+), 253 (19.5%) developed acquired immunodeficiency syndrome (AIDS), of whom 14 (5.5%) developed NHL. Three NHL occurred in HIV(-) hemophiliacs, for a 36.5-fold greater risk in HIV(+) than HIV(-) hemophiliacs (P < .001). The NHL incidence rate was 29-fold greater than in the US population by Surveillance, Epidemiology, and End Results (SEER) estimates (P < .001). Between 0 and 4 lymphomas have been observed per year between 1978 and 1989. At presentation 13 (92.9%) of the HIV(+) NHL were extranodal. Ten were stage IV, 1 stage II, and 3 stage IE. Ten (71.4%) were high-grade, 3 (21.4%) intermediate-grade, and 1 (7.1%) was a low-grade B-cell lymphoma. Epstein-Barr virus (EBV) DNA was detected in 36% by in situ hybridization, including one central nervous system (CNS) lymphoma. The mean CD4 cell count at NHL diagnosis was 64/mm3, the mean latency from initial HIV infection was estimated to be 59 months, and the median survival was 7 months. The incidence of basal cell carcinoma in HIV(+) hemophiliacs was 18.3-fold greater than in HIV(-) hemophiliacs (P < .001) and 11.4-fold greater than in the US population (P < .001). In conclusion, incidence rates of NHL and basal cell carcinoma in HIV(+) hemophiliacs are significantly increased over rates in HIV(-) hemophiliacs and over rates in the US population. Clinicopathologic presentation of NHL in HIV(+) hemophiliacs is similar to that in HIV(+) homosexual men.

Embolization therapy in the management of infantile hemangioma with Kasabach Merritt syndrome.

A case is presented in which a giant infantile hemangioma with thrombocytopenia is managed successfully by serial transcatheter embolization.

Hepatic imaging in stage IV-S neuroblastoma.

Stage IV-S neuroblastoma describes a group of infants with tumor spread limited to liver, skin, or bone marrow. Such patients, who constitute about 25% of affected infants with neuroblastoma, may expect spontaneous tumor remission. We report 18 infants with Stage IV-S neuroblastoma, 83% of whom had liver involvement. Imaging investigations included Technetium 99m sulfur colloid scan, ultrasound, and CT. Two patterns of liver metastasis were noted: ill-defined nodules or diffuse tumor throughout the liver. Distinction of normal and abnormal liver with diffuse type metastasis could be quite difficult, particularly with liver scans. We conclude that patients with Stage IV-S neuroblastoma have ultrasound or CT examination as an initial workup, with nuclear medicine scans reserved for followup studies.

Intelligence and achievement testing in childhood cancer: three years postdiagnosis.

Intellectual and educational testing, employing primarily the Wechsler Intelligence Scale for Children-Revised (WISC-R) and the Wide Range Achievement Test (WRAT), was administered to two groups of children, one with acute lymphoblastic leukemia (ALL), the other with a solid tumor (ST) which did not invade or involve the central nervous system (CNS). Initial testing was completed within 30 days following diagnosis and repeated one year and three years later. Separate ANOVA procedures on the ALL and ST patients were completed, with followup ANOVA procedures for two age groups. The ALL patients declined significantly on WISC-R vocabulary (p less than 0.05) and Full Scale IQ (p less than 0.05), but no significant changes were obtained from the ST patients. Separation of the ALL group into two age groups, less than 8 years and greater than or equal to 8 years revealed significant declines in the younger group on Verbal IQ, Performance IQ, Full Scale IQ, and WRAT arithmetic. However, no significant declines were observed in the older ALL group. The results suggest that declines in ability and achievement are limited to those ALL patients treated with CNS prophylaxis at relatively young ages.

Physician incentives for shared management of childhood cancer patients.

Four years' experiences of 69 primary care physicians who delivered more than 70% of the chemotherapy to 174 children with cancer were assessed. Five academic pediatric oncologists were responsible for diagnosis, assignment to a clinical trial protocol, and overall management. The academicians saw the patients at diagnosis and at regularly scheduled intervals but provided care for less than 30% of the outpatient visits. Factors examined included: (1) why the primary care physicians agreed to participate in the care of these patients, (2) how they thought their participation affected the patient and the patient's family, (3) how participation affected their personal and professional development, (4) how participation affected their practice, (5) what their perceptions were concerning the merits of traditional specialist management, and (6) their overall evaluation of the Iowa shared-management program. The initial agreement by primary care physicians to participate in shared management was related to their perception that it would improve the overall care of their patients. The physicians agreed that the program saved the family time and money, was of educational value, personally satisfying, and not economically detrimental to their practice. They did not identify areas where specialist management had clear advantages over shared management and none reported dissatisfaction with this management program.

Diagnosis and treatment of coagulopathy in the newborn.

Appropriate management of the bleeding newborn is easily accomplished by first assessing the clinical circumstances under which the bleeding occurs. Having determined the clinical circumstances, knowledge of the pathophysiology of disseminated intravascular coagulation, liver failure, vitamin K deficiency, and hemophilia coupled with knowledge of the normal levels of coagulation factor activities at birth leads to selection of appropriate laboratory tests to confirm the etiology of the bleeding. Once the etiology is confirmed, treatment requires management of associated clinical conditions and replacement of vitamin K and/or deficient coagulation factors.

Health outcomes of a community-based therapy program for children with cancer--a shared-management approach.

Critical to providing cancer therapy to children in rural areas is finding dependable sources of therapy near the patients' homes. In this study, comparison was made of 668 visits by 24 patients to nearby private practitioners, who carried out 70% of the therapy, with 712 visits by 22 other patients for whom all care was managed by pediatric hematologist-oncologists. There was no significant difference by Wilcoxon rank sum test between the two groups in the accuracy with which protocol rules were followed, in the incidence of neutropenia, infection, fever, thrombocytopenia, drug toxicity, or the proportion of days hospitalized. The findings indicate that the private practitioners participating in a shared-management system were a dependable resource for providing 70% of the total cancer therapy to these patients.

Cost-effectiveness of a shared-management delivery system for the care of children with cancer.

Costs of two alternative methods for obtaining comparable quality outpatient care for pediatric cancer patients were examined. Costs incurred in obtaining care from specialists, "specialist-management," were compared to costs incurred in obtaining "shared-management," care provided by specialists and primary physicians combined. Shared-management medical costs for outpatient care were 10% less than they would have been had the care been obtained from specialists. The nonmedical costs of transportation, parking, food away from home, and lost productivity or income were all less under the shared-management medical care delivery system than they would have been had specialist management been utilized. The total estimated cost differences between the alternative systems for the delivery of outpatient care ($2,191.34) represents for shared management a mean saving per patient of approximately 29% in direct out-of-pocket expenses and a 59% savings in the indirect costs of lost income or productivity. A total theoretical mean 41% saving per patient was shown to accrue through the use of shared management.