A divergence in the MAP kinase regulatory network defined by MEK kinase and Raf

Mitogen-activated protein kinases (MAPKs) are rapidly phosphorylated and activated in response to various extracellular stimuli in many different cell types. Such regulation of MAPK results from sequential activation of a series of protein kinases. The kinases that phosphorylate MAPKs, the MAP kinase kinases (MEKs) are also activated by phosphorylation. MEKs are related in sequence to the yeast protein kinases Byr1 (from Schizosaccharomyces pombe) and Ste7 (from Saccharomyces cerevisiae), which function in the pheromone-induced signaling pathway that results in mating. Byr1 and Ste7 are in turn regulated by the protein kinases Byr2 and Ste11. The amino acid sequence of the mouse homolog of Byr2 and Ste11, denoted MEKK (MEK kinase), was elucidated from a complementary DNA sequence encoding a protein of 672 amino acid residues (73 kilodaltons). MEKK was expressed in all mouse tissues tested, and it phosphorylated and activated MEK. Phosphorylation and activation of MEK by MEKK was independent of Raf, a growth factor-regulated protein kinase that also phosphorylates MEK. Thus, MEKK and Raf converge at MEK in the protein kinase network mediating the activation of MAPKs by hormones, growth factors, and neurotransmitters.

Social semantics: altruism, cooperation, mutualism, strong reciprocity and group selection

From an evolutionary perspective, social behaviours are those which have fitness consequences for both the individual that performs the behaviour, and another individual. Over the last 43 years, a huge theoretical and empirical literature has developed on this topic. However, progress is often hindered by poor communication between scientists, with different people using the same term to mean different things, or different terms to mean the same thing. This can obscure what is biologically important, and what is not. The potential for such semantic confusion is greatest with interdisciplinary research. Our aim here is to address issues of semantic confusion that have arisen with research on the problem of cooperation. In particular, we: (i) discuss confusion over the terms kin selection, mutualism, mutual benefit, cooperation, altruism, reciprocal altruism, weak altruism, altruistic punishment, strong reciprocity, group selection and direct fitness; (ii) emphasize the need to distinguish between proximate (mechanism) and ultimate (survival value) explanations of behaviours. We draw examples from all areas, but especially recent work on humans and microbes.

Nitric oxide dioxygenase: an enzymic function for flavohemoglobin

Nitric oxide (NO*) is a toxin, and various life forms appear to have evolved strategies for its detoxification. NO*-resistant mutants of Escherichia coli were isolated that rapidly consumed NO*. An NO*-converting activity was reconstituted in extracts that required NADPH, FAD, and O2, was cyanide-sensitive, and produced NO3-. This nitric oxide dioxygenase (NOD) contained 19 of 20 N-terminal amino acids identical to those of the E. coli flavohemoglobin. Furthermore, NOD activity was produced by the flavohemoglobin gene and was inducible by NO*. Flavohemoglobin/NOD-deficient mutants were also sensitive to growth inhibition by gaseous NO*. The results identify a function for the evolutionarily conserved flavohemoglobins and, moreover, suggest that NO* detoxification may be a more ancient function for the widely distributed hemoglobins, and associated methemoglobin reductases, than dioxygen transport and storage.

Signal transduction pathways regulated by mitogen-activated/extracellular response kinase kinase kinase induce cell death

Mitogen-activated/extracellular response kinase kinase (MEK) kinase (MEKK) is a serine-threonine kinase that regulates sequential protein phosphorylation pathways, leading to the activation of mitogen-activated protein kinases (MAPK), including members of the Jun kinase (JNK)/stress-activated protein kinase (SAPK) family. In Swiss 3T3 and REF52 fibroblasts, activated MEKK induces cell death involving cytoplasmic shrinkage, nuclear condensation, and DNA fragmentation characteristic of apoptosis. Expression of activated MEKK enhanced the apoptotic response to ultraviolet irradiation, indicating that MEKK-regulated pathways sensitize cells to apoptotic stimuli. Inducible expression of activated MEKK stimulated the transactivation of c-Myc and Elk-1. Activated Raf, the serine-threonine protein kinase that activates the ERK members of the MAPK family, stimulated Elk-1 transactivation but not c-Myc; expression of activated Raf does not induce any of the cellular changes associated with MEKK-mediated cell death. Thus, MEKK selectively regulates signal transduction pathways that contribute to the apoptotic response.

Apoptotic vs. nonapoptotic cytotoxicity induced by hydrogen peroxide

The regulation of cellular cytotoxicity induced by hydrogen peroxide (H2O2) over a wide concentration range was assessed. Three distinct patterns were detected: the highest concentrations (> 10 mM) rapidly induced a necrotic form of death characterized by smeared patterns of DNA digestion and morphological evidence of primary cytoplasm and plasma membrane damage; In contrast, 10 and 5 mM H2O2 induced endonucleosomal DNA digestion concurrently with cytotoxicity and target cell death was associated with morphologic evidence of apoptosis. Apoptosis was inhibited by cycloheximide, emetine, aminobenzamide (ABA), aurintricarboxylic acid, and calcium depletion. The lowest concentrations of H2O2 (0.5 and 0.1 mM)-induced delayed cytotoxicity (at 24 or 48 hr), which was not associated with DNA ladder formation or morphologic evidence of apoptosis, but was inhibited by ABA. Enforced expression of BCL-2 induced resistance to 0.5 and 0.1 mM H2O2 but had no effect on cytotoxicity induced by 5 and 10 mM. Exposure of isolated nuclei to H2O2 in the absence of calcium or magnesium failed to induce endonucleosomal fragmentation. These data indicate that distinct pathways of H2O2-induced cytotoxicity can be distinguished by their different concentration dependences, and that BCL-2 can protect against some forms of H2O2-induced cytotoxicity.

The prevention of hepatitis B with vaccine. Report of the centers for disease control multi-center efficacy trial among homosexual men

A randomized, double-blind, vaccine/placebo trial of the Merck 20-micrograms hepatitis B virus (HBV) vaccine was done among 1402 homosexual men attending venereal disease clinics in five American cities. Vaccination was followed by only minimal side effects. Two doses of vaccine induced antibody in 80% of vaccine recipients. A booster dose 6 months after the first dose induced antibody in 85% of recipients and markedly increased the proportion of recipients who produced high antibody titers. The incidence of HBV events was markedly less in the vaccine recipients compared to that in the placebo recipients (p = 0.0004). Between month 3 and 15 after the first dose, 56 more significant HBV events (hepatitis, or hepatitis B surface antigen positive, or both) occurred in the placebo group while only 11 occurred in the vaccine group. Ten of the 11 HBV events in the vaccine recipients occurred in hypo- or nonresponders to the vaccine. This vaccine appears to be safe, immunogenic, and efficacious in preventing infection with hepatitis B virus.

Neuronal sodium-channel alpha1-subunit mutations in generalized epilepsy with febrile seizures plus

Generalized epilepsy with febrile seizures plus (GEFS+) is a familial epilepsy syndrome characterized by the presence of febrile and afebrile seizures. The first gene, GEFS1, was mapped to chromosome 19q and was identified as the sodium-channel beta1-subunit, SCN1B. A second locus on chromosome 2q, GEFS2, was recently identified as the sodium-channel alpha1-subunit, SCN1A. Single-stranded conformation analysis (SSCA) of SCN1A was performed in 53 unrelated index cases to estimate the frequency of mutations in patients with GEFS+. No mutations were found in 17 isolated cases of GEFS+. Three novel SCN1A mutations-D188V, V1353L, and I1656M-were found in 36 familial cases; of the remaining 33 families, 3 had mutations in SCN1B. On the basis of SSCA, the combined frequency of SCN1A and SCN1B mutations in familial cases of GEFS+ was found to be 17%.

X-exome sequencing of 405 unresolved families identifies seven novel intellectual disability genes

X-linked intellectual disability (XLID) is a clinically and genetically heterogeneous disorder. During the past two decades in excess of 100 X-chromosome ID genes have been identified. Yet, a large number of families mapping to the X-chromosome remained unresolved suggesting that more XLID genes or loci are yet to be identified. Here, we have investigated 405 unresolved families with XLID. We employed massively parallel sequencing of all X-chromosome exons in the index males. The majority of these males were previously tested negative for copy number variations and for mutations in a subset of known XLID genes by Sanger sequencing. In total, 745 X-chromosomal genes were screened. After stringent filtering, a total of 1297 non-recurrent exonic variants remained for prioritization. Co-segregation analysis of potential clinically relevant changes revealed that 80 families (20%) carried pathogenic variants in established XLID genes. In 19 families, we detected likely causative protein truncating and missense variants in 7 novel and validated XLID genes (CLCN4, CNKSR2, FRMPD4, KLHL15, LAS1L, RLIM and USP27X) and potentially deleterious variants in 2 novel candidate XLID genes (CDK16 and TAF1). We show that the CLCN4 and CNKSR2 variants impair protein functions as indicated by electrophysiological studies and altered differentiation of cultured primary neurons from Clcn4(-/-) mice or after mRNA knock-down. The newly identified and candidate XLID proteins belong to pathways and networks with established roles in cognitive function and intellectual disability in particular. We suggest that systematic sequencing of all X-chromosomal genes in a cohort of patients with genetic evidence for X-chromosome locus involvement may resolve up to 58% of Fragile X-negative cases.

Common chromosomal fragile site FRA16D sequence: identification of the FOR gene spanning FRA16D and homozygous deletions and translocation breakpoints in cancer cells

Fluorescence in situ hybridization of a tile path of DNA subclones has previously enabled the cyto-genetic definition of the minimal DNA sequence which spans the FRA16D common chromosomal fragile site, located at 16q23.2. Homozygous deletion of the FRA16D locus has been reported in adenocarcinomas of stomach, colon, lung and ovary. We have sequenced the 270 kb containing the FRA16D fragile site and the minimal homozygously deleted region in tumour cells. This sequence enabled localization of some of the tumour cell breakpoints to regions which contain AT-rich secondary structures similar to those associated with the FRA10B and FRA16B rare fragile sites. The FRA16D DNA sequence also led to the identification of an alternatively spliced gene, named FOR (fragile site FRA16D oxidoreductase), exons of which span both the fragile site and the minimal region of homozygous deletion. In addition, the complete DNA sequence of the FRA16D-containing FOR intron reveals no evidence of additional authentic transcripts. Alternatively spliced FOR transcripts (FOR I, FOR II and FOR III) encode proteins which share N-terminal WW domains and differ at their C-terminus, with FOR III having a truncated oxidoreductase domain. FRA16D-associated deletions selectively affect the FOR gene transcripts. Three out of five previously mapped translocation breakpoints in multiple myeloma are also located within the FOR gene. FOR is therefore the principle genetic target for DNA instability at 16q23.2 and perturbation of FOR function is likely to contribute to the biological consequences of DNA instability at FRA16D in cancer cells.

Inversin, a novel gene in the vertebrate left-right axis pathway, is partially deleted in the inv mouse

Visceral left-right asymmetry occurs in all vertebrates, but the inversion of embryo turning (inv) mouse, which resulted following a random transgene insertion, is the only model in which these asymmetries are consistently reversed. We report positional cloning of the gene underlying this recessive phenotype. Although transgene insertion was accompanied by neighbouring deletion and duplication events, our YAC phenotype rescue studies indicate that the mutant phenotype results from the deletion. After extensively characterizing the 47-kb deleted region and flanking sequences from the wild-type mouse genome, we found evidence for only one gene sequence in the deleted region. We determined the full-length 5.5-kb cDNA sequence and identified 16 exons, of which exons 3-11 were eliminated by the deletion, causing a frameshift. The novel gene specifies a 1062-aa product with tandem ankyrin-like repeat sequences. Characterization of complementing and non-complementing YAC transgenic families revealed that correction of the inv mutant phenotype was concordant with integration and intact expression of this novel gene, which we have named inversin (Invs).

Fibroblast growth factor-2 suppression of tumor necrosis factor alpha-mediated apoptosis requires Ras and the activation of mitogen-activated protein kinase

Treatment of L929 cells with tumor necrosis factor alpha (TNFalpha) activates a programmed cell death pathway resulting in apoptosis. We investigated the intracellular signaling pathways activated in L929 cells by TNFalpha. TNFalpha robustly activates Jun kinase (JNK), a member of the mitogen-activated protein kinase (MAPK) family. In addition, p42(MAPK) is activated, but a 10-fold greater concentration of TNFalpha was required for substantial MAPK activation than was needed for maximal JNK stimulation. Simultaneous treatment of L929 cells with fibroblast growth factor (FGF-2) significantly reduced the apoptotic response to TNFalpha. FGF-2 substantially activated the Raf/MEK/MAPK (where MEK is mitogen-activated protein kinase kinase) pathway but did not affect TNFalpha activation of JNK. These results indicate that although JNK may play an important role in transmitting the TNFalpha signal from the cell surface to the nucleus, activation of the JNK pathway is not sufficient to induce apoptosis. Expression of dominant-negative Asn-17 Ras in L929 cells diminished the FGF-2 stimulation of p42(MAPK) and eliminated the protective effect of FGF-2. Asn-17 Ras expression did not affect JNK activity and had no effect on TNFalpha activation of JNK. Pharmacological inhibition of MEK-1 activity by incubation of cells with the compound PD 098059 blocked p42(MAPK) activation and FGF-2 protection against apoptosis. Interestingly, activated Val-12 Ras expression substantially enhanced TNFalpha-mediated apoptosis in L929 cells, but Val-12 Ras did not constitutively activate MAPK in L929 cells and FGF-2 partially protected Val-12 Ras-expressing cells from TNFalpha-mediated apoptosis. Our data indicate that activation of the MAPK pathway mediates an FGF-2 protective effect against apoptosis and highlights the important role that integration of multiple intracellular signaling pathways plays in the regulation of cell growth and death.

In vitro cytoreductive effects on multiple myeloma cells induced by bisphosphonates

In a double blind randomized study, the bisphosphonate drug Pamidronate (Aredia) significantly protected Durie-Salmon stage III multiple myeloma patients from osteolytic bone disease. In the patient sub-group on salvage chemotherapy. Pamidronate treatment was also significantly associated with prolonged survival. To test if this drug could induce direct antitumor effects, we exposed myeloma cells to increasing concentrations of Pamidronate or a more potent bisphosphonate, Zoledronate. A concentration- and time-dependent cytotoxic effect was detected on four of five myeloma cell lines as well as three specimens obtained directly from myeloma patients. Zoledronate-induced cytotoxicity was significantly greater than that of Pamidronate. Cytotoxicity could not be explained by bisphosphonate-induced chelation of extracellular calcium or secondary decrease in production of the myeloma growth factor interleukin-6. Morphological examination, DNA electrophoresis and cell cycle analysis indicated that the bisphosphonate-induced cytotoxic effect consisted of a combination of cytostasis and apoptotic myeloma cell death. Enforced expression of BCL-2 protected against the apoptotic death but not against cytostasis. Most cytotoxic effects were seen between 10 and 100 microM of drug. The results suggest a possible direct anti-tumor effect in myeloma patients treated with bisphosphonates which may participate in their significantly increased survival. This hypothesis should now be further tested in clinical trials.

Capturing the superorganism: a formal theory of group adaptation

Adaptation is conventionally regarded as occurring at the level of the individual organism. However, in recent years there has been a revival of interest in the possibility for group adaptations and superorganisms. Here, we provide the first formal theory of group adaptation. In particular: (1) we clarify the distinction between group selection and group adaptation, framing the former in terms of gene frequency change and the latter in terms of optimization; (2) we capture the superorganism in the form of a 'group as maximizing agent' analogy that links an optimization program to a model of a group-structured population; (3) we demonstrate that between-group selection can lead to group adaptation, but only in rather special circumstances; (4) we provide formal support for the view that between-group selection is the best definition for 'group selection'; and (5) we reveal that mechanisms of conflict resolution such as policing cannot be regarded as group adaptations.

Whole-exome sequencing points to considerable genetic heterogeneity of cerebral palsy

Cerebral palsy (CP) is a common, clinically heterogeneous group of disorders affecting movement and posture. Its prevalence has changed little in 50 years and the causes remain largely unknown. The genetic contribution to CP causation has been predicted to be ~2%. We performed whole-exome sequencing of 183 cases with CP including both parents (98 cases) or one parent (67 cases) and 18 singleton cases (no parental DNA). We identified and validated 61 de novo protein-altering variants in 43 out of 98 (44%) case-parent trios. Initial prioritization of variants for causality was by mutation type, whether they were known or predicted to be deleterious and whether they occurred in known disease genes whose clinical spectrum overlaps CP. Further, prioritization used two multidimensional frameworks-the Residual Variation Intolerance Score and the Combined Annotation-dependent Depletion score. Ten de novo mutations in three previously identified disease genes (TUBA1A (n=2), SCN8A (n=1) and KDM5C (n=1)) and in six novel candidate CP genes (AGAP1, JHDM1D, MAST1, NAA35, RFX2 and WIPI2) were predicted to be potentially pathogenic for CP. In addition, we identified four predicted pathogenic, hemizygous variants on chromosome X in two known disease genes, L1CAM and PAK3, and in two novel candidate CP genes, CD99L2 and TENM1. In total, 14% of CP cases, by strict criteria, had a potentially disease-causing gene variant. Half were in novel genes. The genetic heterogeneity highlights the complexity of the genetic contribution to CP. Function and pathway studies are required to establish the causative role of these putative pathogenic CP genes.

Spite and the scale of competition

In recent years there has been a large body of theoretical work examining how local competition can reduce and even remove selection for altruism between relatives. However, it is less well appreciated that local competition favours selection for spite, the relatively neglected ugly sister of altruism. Here, we use extensions of social evolution theory that were formulated to deal with the consequences for altruism of competition between social partners, to illustrate several points on the evolution of spite. Specifically, we show that: (i) the conditions for the evolution of spite are less restrictive than previously assumed; (ii) previous models which have demonstrated selection for spite often implicitly assumed local competition; (iii) the scale of competition must be allowed for when distinguishing different forms of spite (Hamiltonian vs. Wilsonian); (iv) local competition can enhance the spread of spiteful greenbeards; and (v) the theory makes testable predictions for how the extent of spite should vary dependent upon population structure and average relatedness.

Demography, altruism, and the benefits of budding

It is now widely appreciated that competition between kin inhibits the evolution of altruism. In standard population genetics models, it is difficult for indiscriminate altruism towards social partners to be favoured at all. The reason is that while limited dispersal increases the kinship of social partners it also intensifies local competition. One solution that has received very little attention is if individuals disperse as groups (budding dispersal), as this relaxes local competition without reducing kinship. Budding behaviour is widespread through all levels of biological organization, from early protocellular life to cooperatively breeding vertebrates. We model the effects of individual dispersal, budding dispersal, soft selection and hard selection to examine the conditions under which altruism is favoured. More generally, we examine how these various demographic details feed into relatedness and scale of competition parameters that can be included into Hamilton's rule.

Fluconazole versus amphotericin B in the treatment of hematogenous candidiasis: a matched cohort study

PURPOSE

To compare the efficacy and toxicity of fluconazole and amphotericin B in the treatment of hematogenous candidiasis in cancer patients.

PATIENTS AND METHODS

A matched cohort study of cancer patients with hematogenous candidiasis was conducted. Forty-five patients with hematogenous candidiasis who received fluconazole (200 to 600 mg/day) in an open-label trial at the University of Texas M. D. Anderson Cancer Center, Houston, Texas, between February 1990 and June 1992 were matched to 45 patients treated with amphotericin B (0.3 to 1.2 mg/kg/day) for the same diagnosis. Criteria for matching included the following prognostic variables at the initiation of therapy: pneumonia, neutropenia (< 1,000 cells/mm3), number of positive blood cultures before therapy, infecting Candida species, underlying disease, and the simplified acute physiology score. Response and survival at 48 hours, after 5 days of therapy, and at the end of therapy, as well as toxicity rates were obtained. Other post hoc analyses were performed. Differences in outcomes were assessed by the McNemar, the sign, and the log rank tests.

RESULTS

Patients were similar with respect to the matching criteria, age, sex, status of underlying disease, use of antibiotics and growth factors, duration of treatment, presence and removal of central venous catheters, disseminated disease, and concomitant infections. Response rates at 48 hours and 5 days were similar between the two study groups. Overall response rates at the end of therapy were 73% for patients treated with fluconazole and 71% for patients treated with amphotericin B (P = 0.78). There were no differences in survival rates or causes of death. Toxicity was observed in 9% of patients treated with fluconazole and in 67% of patients treated with amphotericin B (P < 0.0001). Toxic effects of amphotericin B included nephrotoxicity, hypokaliemia, and fever and chills.

CONCLUSION

Fluconazole is effective and better tolerated than amphotericin B for the treatment of hematogenous candidiasis in cancer patients.

Multistage scoring system for identifying infants at risk of unexpected death

Obstetric and perinatal records have been assembled on 250 infant deaths and an equal number of live controls including 55 deaths associated with congenital anomalies. The information was used to construct a scoring system to identify high-risk infants at birth. Parents of 115 of the cases and their controls were also interviewed and all hospital, general practitioner, and health service records abstracted. Cases and controls were compared item by item in respect of all information available up to the age of one month and a scoring system constructed for use at one month. The 'at birth' and combined scoring systems are presented. The chance of death by age attained is presented for various risk groups. In a small prospective test, the multistage scoring system was nearly 50% more effective than the birth score alone.

Steady-state and transient kinetics of Escherichia coli nitric-oxide dioxygenase (flavohemoglobin). The B10 tyrosine hydroxyl is essential for dioxygen binding and catalysis

Escherichia coli expresses an inducible flavohemoglobin possessing robust NO dioxygenase activity. At 37 degrees C, the enzyme shows a maximal turnover number (V(max)) of 670 s(-1) and K(m) values for NADH, NO, and O(2) equal to 4.8, 0.28, and approximately 100 microM, respectively. Individual reduction, ligand binding, and NO dioxygenation reactions were examined at 20 degrees C, where V(max) is approximately 94 s(-1). Reduction by NADH occurs in two steps. NADH reduces bound FAD with a rate constant of approximately 15 microM(-1) s(-1), and heme iron is reduced by FADH(2) with a rate constant of 150 s(-1). Dioxygen binds tightly to reduced flavohemoglobin, with association and dissociation rate constants equal to 38 microM(-1) s(-1) and 0.44 s(-1), respectively, and the oxygenated flavohemoglobin dioxygenates NO to form nitrate. NO also binds reversibly to reduced flavohemoglobin in competition with O(2), dissociates slowly, and inhibits NO dioxygenase activity at [NO]/[O(2)] ratios of 1:100. Replacement of the heme pocket B10 tyrosine with phenylalanine increases the O(2) dissociation rate constant approximately 80-fold and reduces NO dioxygenase activity approximately 30-fold, demonstrating the importance of the tyrosine hydroxyl for O(2) affinity and NO scavenging activity. At 37 degrees C, V(max)/K(m)(NO) is 2,400 microM(-1) s(-1), demonstrating that the enzyme is extremely efficient at converting toxic NO into nitrate under physiological conditions.

Monoclonal antibodies raised against a subsequence of senile plaque core protein react with plaque cores, plaque periphery and cerebrovascular amyloid in Alzheimer's disease

Four monoclonal antibodies (1D2/1/2, 1G10/2/3, 3B6/1/1, 4D12/2/6) were raised against a synthetic peptide consisting of residues 8-17 of a protein reported to be common to senile plaque cores, cerebrovascular amyloid and neurofibrillary tangles in Alzheimer's disease. In an immunoperoxidase study of Alzheimer brain tissue, these antibodies stained plaque and vascular amyloid but not tangles, suggesting that the polypeptide chain in the region of residues 8-17 is exposed in the former two but, if present, inaccessible in the latter. In addition, staining of granular material in the plaque periphery was observed. These antibodies will be useful tools for future work on the origin of this protein.

Sporadic imprinting defects in Prader-Willi syndrome and Angelman syndrome: implications for imprint-switch models, genetic counseling, and prenatal diagnosis

The Prader-Willi syndrome (PWS) and the Angelman syndrome (AS) are caused by the loss of function of imprinted genes in proximal 15q. In approximately 2%-4% of patients, this loss of function is due to an imprinting defect. In some cases, the imprinting defect is the result of a parental imprint-switch failure caused by a microdeletion of the imprinting center (IC). Here we describe the molecular analysis of 13 PWS patients and 17 AS patients who have an imprinting defect but no IC deletion. Heteroduplex and partial sequence analysis did not reveal any point mutations of the known IC elements, either. Interestingly, all of these patients represent sporadic cases, and some share the paternal (PWS) or the maternal (AS) 15q11-q13 haplotype with an unaffected sib. In each of five PWS patients informative for the grandparental origin of the incorrectly imprinted chromosome region and four cases described elsewhere, the maternally imprinted paternal chromosome region was inherited from the paternal grandmother. This suggests that the grandmaternal imprint was not erased in the father's germ line. In seven informative AS patients reported here and in three previously reported patients, the paternally imprinted maternal chromosome region was inherited from either the maternal grandfather or the maternal grandmother. The latter finding is not compatible with an imprint-switch failure, but it suggests that a paternal imprint developed either in the maternal germ line or postzygotically. We conclude (1) that the incorrect imprint in non-IC-deletion cases is the result of a spontaneous prezygotic or postzygotic error, (2) that these cases have a low recurrence risk, and (3) that the paternal imprint may be the default imprint.

Nitric-oxide dioxygenase activity and function of flavohemoglobins. sensitivity to nitric oxide and carbon monoxide inhibition

Widely distributed flavohemoglobins (flavoHbs) function as NO dioxygenases and confer upon cells a resistance to NO toxicity. FlavoHbs from Saccharomyces cerevisiae, Alcaligenes eutrophus, and Escherichia coli share similar spectra, O(2), NO, and CO binding kinetics, and steady-state NO dioxygenation kinetics. Turnover numbers (V(max)) for S. cerevisiae, A. eutrophus, and E. coli flavoHbs are 112, 290, and 365 NO heme(-1) s(-1), respectively, at 37 degrees C with 200 microm O(2). The K(M) values for NO are low and range from 0.1 to 0.25 microm. V(max)/K(M)(NO) ratios of 900-2900 microm(-1) s(-1) indicate an extremely efficient dioxygenation mechanism. Approximate K(M) values for O(2) range from 60 to 90 microm. NO inhibits the dioxygenases at NO:O(2) ratios of > or =1:100 and makes true K(M)(O(2)) values difficult to determine. High and roughly equal second order rate constants for O(2) and NO association with the reduced flavoHbs (17-50 microm(-1) s(-1)) and small NO dissociation rate constants suggest that NO inhibits the dioxygenase reaction by forming inactive flavoHbNO complexes. Carbon monoxide also binds reduced flavoHbs with high affinity and competitively inhibits NO dioxygenases with respect to O(2) (K(I)(CO) = approximately 1 microm). These results suggest that flavoHbs and related hemoglobins evolved as NO detoxifying components of nitrogen metabolism capable of discriminating O(2) from inhibitory NO and CO.

Tumor necrosis factor alpha rapidly activates the mitogen-activated protein kinase (MAPK) cascade in a MAPK kinase kinase-dependent, c-Raf-1-independent fashion in mouse macrophages

Tumor necrosis factor alpha (TNF alpha) is bound by two cell surface receptors, CD120a (p55) and CD120b (p75), that belong to the TNF/nerve growth factor receptor family and whose signaling is initiated by receptor multimerization in the plane of the plasma membrane. The initial signaling events activated by receptor crosslinking are unknown, although activation of the mitogen-activated protein kinase (MAPK) cascade occurs shortly after ligand binding to CD120a. In this study, we investigated the upstream kinases that mediate the activation of the 42-kDa MAPK p42mapk/erk2 following crosslinking of CD120a in mouse macrophages. Exposure of mouse macrophages to TNF alpha stimulated a time-dependent increase in the activity of MAPK/ERK kinase (MEK) that temporally preceded peak activation of p42mapk/erk2. MEKs, dual-specificity threonine/tyrosine kinases, act as a convergence point for several signaling pathways including Ras/Raf, MEK kinase (MEKK), and Mos. Incubation of macrophages with TNF alpha was found to transiently stimulate a MEKK that peaked in activity within 30 sec of exposure and progressively declined toward basal levels by 5 min. By contrast, under these conditions, activation of either c-Raf-1 or Raf-B was not detected. These data suggest that the activation of the MAPK cascade in response to TNF alpha is mediated by the sequential activation of a MEKK and a MEK in a c-Raf-1- and Raf-B-independent fashion.