Kinase suppressor of Ras forms a multiprotein signaling complex and modulates MEK localization

Genetic screens for modifiers of activated Ras phenotypes have identified a novel protein, kinase suppressor of Ras (KSR), which shares significant sequence homology with Raf family protein kinases. Studies using Drosophila melanogaster and Caenorhabditis elegans predict that KSR positively regulates Ras signaling; however, the function of mammalian KSR is not well understood. We show here that two predicted kinase-dead mutants of KSR retain the ability to complement ksr-1 loss-of-function alleles in C. elegans, suggesting that KSR may have physiological, kinase-independent functions. Furthermore, we observe that murine KSR forms a multimolecular signaling complex in human embryonic kidney 293T cells composed of HSP90, HSP70, HSP68, p50(CDC37), MEK1, MEK2, 14-3-3, and several other, unidentified proteins. Treatment of cells with geldanamycin, an inhibitor of HSP90, decreases the half-life of KSR, suggesting that HSPs may serve to stabilize KSR. Both nematode and mammalian KSRs are capable of binding to MEKs, and three-point mutants of KSR, corresponding to C. elegans loss-of-function alleles, are specifically compromised in MEK binding. KSR did not alter MEK activity or activation. However, KSR-MEK binding shifts the apparent molecular mass of MEK from 44 to >700 kDa, and this results in the appearance of MEK in membrane-associated fractions. Together, these results suggest that KSR may act as a scaffolding protein for the Ras-mitogen-activated protein kinase pathway.

Polymorphism of human CD1 genes

Human CD1 genes have been reported to be invariant or to show limited polymorphism. Recently, certain functions of CD1 antigens have been described to include the presentation lipid and glycolipid antigens. These observations prompted a thorough survey of the genetic polymorphism in the five human CD1 genes (CD1a-CD1e). Using polymerase chain reaction-single stranded conformational polymorphism (PCR-SSCP) combined with sequence analyses, exons 2 and 3 from CD1a-CD1e were characterized from a total of 110 unrelated healthy donors. Results showed that all five genes (CD1a-CD1e) are polymorphic in exon 2. Substitutions in CD1b and CD1c are silent, whereas, substitutions in CD1a, CD1d and CD1e result in amino acid replacements in the deduced protein products. CD1a and CD1e polymorphisms are prevalent in the population. The substitutions in CD1a have characteristics that may influence interactions with beta2-microglobulin beta2-m) or accessory molecules. The substitution in CD1e is located in the region predicted to interact with ligands and may differentially impact the ability of CD1e alleles to bind antigen.

UNC-84 localizes to the nuclear envelope and is required for nuclear migration and anchoring during C. elegans development

Nuclear migrations are essential for metazoan development. Two nuclear migrations that occur during C. elegans development require the function of the unc-84 gene. unc-84 mutants are also defective in the anchoring of nuclei within the hypodermal syncytium and in the migrations of the two distal tip cells of the gonad. Complementation analyses of 17 unc-84 alleles defined two genetically separable functions. Both functions are required for nuclear and distal tip cell migrations, but only one is required for nuclear anchorage. The DNA lesions associated with these 17 mutations indicate that the two genetically defined functions correspond to two distinct regions of the UNC-84 protein. The UNC-84 protein has a predicted transmembrane domain and a C-terminal region with similarity to the S. pombe spindle pole body protein Sad1 and to two predicted mammalian proteins. Analysis of a green fluorescent protein reporter indicated that UNC-84 is widely expressed and localized to the nuclear envelope. We propose that UNC-84 functions to facilitate a nuclear-centrosomal interaction required for nuclear migration and anchorage.

Invariant or highly conserved TCR alpha are expressed on double-negative (CD3+CD4-CD8-) and CD8+ T cells

TCR alpha (TCRA) expression was examined in RNA samples from PBMC and isolated populations of CD4+, CD8+, and DN T cells from 15 healthy individuals. The expressed TCR repertoire was surveyed using spectratype analysis, a technique that displays the distribution of complementarity determining region 3 (CDR3) lengths for each TCRAV gene family. The results revealed the presence of unusual populations of double-negative (DN; CD4-CD8-CD3+) T cells that express invariant or conserved TCRAV4A, AV7, AV19, and AV24 chains. Each of the conserved TCRA families was over-represented in >70% of the individuals studied, and all individuals expressed at least one of the over-represented TCRAV families. Over-represented conserved AV4A or AV7 sequences were also present in CD8+ T cells from most donors. The extent of TCRA sequence conservation is unparalleled. TCRAV4A, AV19, and AV24 sequences were invariant, although AV4A and AV19 transcripts contained N region additions. TCRAV24 transcripts derived from the direct juxtaposition of V and J gene segments. TCRAV7 sequences showed some diversity in two amino acids encoded at junctions of V and J gene segments. Although derivation of DN T cells with conserved TCRA chains is puzzling, the wide-spread expression of these unusual cells suggests an important function.

[Pure red cell aplasia after allogeneic peripheral blood stem cell transplantation: a case report and literature review]

OBJECTIVE

To report a case of post-allogeneic peripheral blood stem cell transplantation (allo-PBSCT) pure red cell aplasia(PRCA) and the treatment outcome.

METHODS

A patient with acute non-lymphoblastic leukemia(M2a) was treated with allo-PBSCT. His post-PBSCT PRCA was treated with plasmapheresis(2-3 times weekly) and Epo(3,000 U/day, subcutaneously).

RESULTS

Reticulocyte count (Ret) recovered to 0.01 at day +131 and hemoglobin reached 110 g/L at day +154. Erythroid cells in the bone marrow recovered to 0.25, and BFU-E and CFU-E within normal range. This normalized hematopoiesis remained for over 5 months after the cessation of Epo.

CONCLUSION

Post allo-PBSCT PRCA can be successfully treated with plasma exchange and Epo.

Low-density lipoprotein apheresis retards the progression of hyperlipidemic overt diabetic nephropathy

BACKGROUND

Hyperlipidemia has recently received attention as being involved in the progression of diabetic nephropathy (DN). Low-density lipoprotein apheresis (LDL-A) can remove a large amount of plasma lipid directly from the patients in a short time.

METHODS

Fifteen type 2 diabetic patients with overt nephropathy received LDL-A in two different manners: short-term intensive therapy (SIT) for nine patients and long-term intermittent therapy (LIT) for six patients.

RESULTS

The changes in the monthly decline rates of reciprocal serum creatinine (1/Cr) were -0.035 +/- 0.020 in the three-month period before SIT, 0.047 +/- 0.041 during and until two weeks after SIT, and -0.035 +/- 0.015 after a period of two weeks from the therapy. The mean duration of LIT in six patients was 8.2 +/- 7.4 months, and the mean monthly decline rates of 1/Cr significantly decreased during the period of LIT as compared with the six-month period before the treatment.

CONCLUSION

LDL-A can retard the progression of overt DN, especially when it is performed repeatedly for a long period at two-week intervals.

[Evaluation of fat nutrition in the energy intake on low protein diets for patients with chronic renal failure]

Low protein diet has been proven to retard the progression of chronic renal failure. In this diet, the energy intake depends mainly on fats and carbohydrates instead of protein, and precautions should be taken against increasing risks of both lipid nephrotoxicity and atherosclerosis. In order to assess the adequacy of fat nutrition in a low protein diet for patients with chronic renal failure, we evaluated the total amounts of dietary fat intake, dietary individual fatty acid intake and serum individual fatty acid concentrations in 16 patients, whose mean creatinine clearance was 21.3 +/- 12.1 ml/m, serum creatinine 3.8 +/- 2.2 mg/dl and serum urea nitrogen 41.5 +/- 18.6 mg/dl. The percentage ratio of fat intake to total energy intake was 26.7 +/- 5.2%. The ratio of intake of saturated fatty acids, monounsaturated fatty acids and polyunsaturated fatty acids was 1:2:1.8, and n-6/n-3 was 8.5 +/- 9.3. These were significant correlations between dietary intake and the serum concentrations in both EPA and the ratio of EPA/AA. Consequently, it might be considered that polyunsaturated fatty acids intake should be lowered and patients with chronic renal failure on a low protein diet should be advised about the proper selection of foods containing animal protein and plant-derived oil. It may be beneficial to recommend the intake of more EPA and lowering the ratio of n-6/n-3 intake might be useful in improving the fat nutrition to adequate levels in these patients.

Clinical and genetic studies of an autosomal dominant cone-rod dystrophy with features of Stargardt disease

Cone-rod dystrophy (CORD) and Stargardt disease (STGD) are two hereditary retinal dystrophies with similarities to age-related macular degeneration. Cone-rod dystrophies are a group of degenerative disorders resulting in decreased visual acuity and color vision, attenuated electroretinographic (ERG) responses, and atrophic macular lesions. Autosomal dominant, autosomal recessive, and X-linked forms of cone-rod dystrophy have been reported. Stargardt disease is characterized by reduced visual acuity, atrophic macular changes, prominent 'flavimaculatus flecks' in the pigment epithelium of the posterior retina, and a virtually pathognomic 'dark choroid' pattern on fluorescein angiography. Stargardt disease is classically inherited as an autosomal recessive trait, although numerous families have been described in which features of Stargardt disease are transmitted in an autosomal dominant manner. We have identified a new kindred with autosomal dominant cone-rod dystrophy with features of Stargardt-like disease. Detailed clinical evaluation, genotype analysis, and linkage analysis were performed. Fluorescein angiography revealed a 'dark choroid' pattern in three affected subjects. Electroretinography disclosed markedly reduced scotopic and photopic responses in three affected individuals. Genetic analysis revealed linkage to known loci for cone-rod dystrophy (CORD7) and Stargardt-like disease (STGD3) on chromosome 6q14. A peak lod score of 3.3 was obtained with the marker D6S280 at straight theta =0.010. A physical map was constructed by screening a YAC library with short tandem repeat markers in the region. Screening of a candidate gene, the rho1 subunit of the GABA receptor, failed to reveal any mutations.

[Acute lymphoblastic leukemia complicated with tumor lysis syndrome--four cases report]

OBJECTIVE

To report four acute lymphoblastic leukemia(ALL) patients who developed tumor lysis syndrome(TLS) after initial chemotherapy.

METHODS

The clinical features and blood biochemical changes of four patients with TLS were analysed.

RESULTS

TLS was characterized by hyperuricemia, hyperkalemia, hyperphosphatemia and hypocalcemia. Three cases had renal dysfunction and the other died of acute renal failure. After allopurinol therapy and alkalinization of urine, the blood biochemical parameter became normalization in all the three cases.

CONCLUSIONS

TLS can be effectively controlled by early recognition and administration of allopurinol therapy and alkalinization of urine.

[Antagonism of folic acid on the toxicity of aspirin in yolk sac of rats]

The antagonistic effects of folic acid to aspirin on the development of rat yolk sac and embryos were studied during early organogenesis by using whole embryo culture technique and electron microscopy. The results showed that when treated with aspirin, the diameter of yolk sac and the body length of embryo were much shorter, the frequencies of abnormal embryos were significantly higher, and the yolk sac became thinner than those without treatment. The number of blood islands and capillaries decreased, the differentiation and development of blood vessel were retarded in the treated group. Ultrastructure observation also showed that the numbers of microvilli and capillaries were greatly decreased, and the structure and the numbers of lysosomes, endoplasmic reticula and ribosomes significantly changed in the treated group. When aspirin was added with high folic acid serum, the toxicity on yolk sac decreased or disappeared. The results suggested that the protection of yolk sac would be related to the antagonism of folic acid to aspirin.

A new locus for autosomal dominant stargardt-like disease maps to chromosome 4

Stargardt disease (STGD) is the most common hereditary macular dystrophy and is characterized by decreased central vision, atrophy of the macula and underlying retinal-pigment epithelium, and frequent presence of prominent flecks in the posterior pole of the retina. STGD is most commonly inherited as an autosomal recessive trait, but many families have been described in which features of the disease are transmitted in an autosomal dominant manner. A recessive locus has been identified on chromosome 1p (STGD1), and dominant loci have been mapped to both chromosome 13q (STGD2) and chromosome 6q (STGD3). In this study, we describe a kindred with an autosomal dominant Stargardt-like phenotype. A genomewide search demonstrated linkage to a locus on chromosome 4p, with a maximum LOD score of 5.12 at a recombination fraction of.00, for marker D4S403. Analysis of extended haplotypes localized the disease gene to an approximately 12-cM interval between loci D4S1582 and D4S2397. Therefore, this kindred establishes a new dominant Stargardt-like locus, STGD4.

Isolation and mapping of the rabbit DM genes

Proper peptide presentation by major histocompatibility complex (MHC)-encoded class II antigens is dependent on the products of the MHC DM loci. We identified the rabbit orthologues (RLA-DMA and -DMB) of human HLA-DMA and -DMB and found that they have 76.9% and 78.8% identity with HLA-DMA and -DMB, respectively. Like classical class II MHC genes, RLA-DM genes are more closely related to human HLA-DM genes than to mouse H2-DM. Among the DM family, there is a high degree of variability at the amino terminus of the DMa chains, and length variability in the cytoplasmic tails of both DMalpha and DMbeta. The rabbit DM genes are coexpressed with class II genes in lymphoid tissues, as are the DM genes of other mammals. The RLA-DM locus maps to the class II region of the rabbit MHC, and is flanked by the DP and DOB loci. Despite having some similarities to class II genes of bony fishes, the DM family represents a separate branch of the MHC class II family.

A gp330/megalin-related protein is required in the major epidermis of Caenorhabditis elegans for completion of molting

A genetic analysis of a gp330/megalin-related protein, LRP-1, has been undertaken in Caenorhabditis elegans. Consistent with megalin's being essential for development of mice, likely null mutations reveal that this large member of the low density lipoprotein receptor family is also essential for growth and development of this nematode. The mutations confer a striking defect, an inability to shed and degrade all of the old cuticle at each of the larval molts. The mutations also cause an arrest of growth usually at the molt from the third to the fourth larval stage. Genetic mosaic analysis suggests that the lrp-1 gene functions in the major epidermal syncytium hyp7, a polarized epithelium that secretes cuticle from its apical surface. Staining of whole mounts with specific monoclonal antibodies reveals that the protein is expressed on the apical surface of hyp7. Sterol starvation can phenocopy the lrp-1 mutations, suggesting that LRP-1 is a receptor for sterols that must be endocytosed by hyp7. These observations indicate that LRP-1 is related to megalin not only structurally but also functionally.

A Caenorhabditis elegans homologue of hunchback is required for late stages of development but not early embryonic patterning

We have cloned a Caenorhabditis elegans homologue of the Drosophila gap gene hunchback (hb) and have designated it hbl-1 (hunchback-like). hbl-1 encodes a predicted 982-amino-acid protein, containing two putative zinc-finger domains similar to those of Drosophila Hunchback. The gene is transcribed embryonically, but unlike the maternally expressed Drosophila hb, its mRNA is not detected in C. elegans oocytes. A hbl-1::gfp reporter is expressed primarily in ectodermal cells during embryonic and larval development. Double-stranded RNA-interference (RNAi) was used to indicate hbl-1 loss-of-function phenotypes. Progeny of hbl-1(RNAi) hermaphrodites exhibit a range of defects; the most severely affected progeny arrest as partially elongated embryos or as hatching, misshapen L1 larvae. Animals that survive to adulthood exhibit variably dumpy (Dpy), uncoordinated (Unc), and egg-laying defective (Egl) phenotypes, as well as defects in vulval morphology (Pvl). Abnormal organization of hypodermal cells and expression of a hypodermal marker in hbl-1(RNAi) animals suggests that most of the phenotypes observed could be due to improper specification of hypodermal cells. The pattern of hbl-1 expression is similar to that reported for the leech hunchback homologue Lzf-2, suggesting that these proteins may have similar biological functions in diverse species with cellular embryos.

Killing effect of interleukin-2 and interferon-alpha activated leukemic bone marrow in remission on K562 leukemic cells

OBJECTIVE

To evaluate the killing effect of interleukin-2 (IL-2) and interferon-alpha (IFN-alpha) activated bone marrow cells on K562 cells.

METHODS

Semi-solid colony and 3H-TdR incorporating method were used.

RESULTS

Bone marrow from leukemia patients in remission was activated in vitro with IL-2 for 3 days. The activated bone marrow (ABM) displayed killing effects of 0.31-2.30 logs on K562 cells. This killing effect was further increased to 0.30-3.15 logs when IFN-alpha added with IL-2 to the marrow for activation. IL-2 alone or in combination with IFN-alpha showed no inhibition of CFU-GM and K562 cells. Compared with IL-2 or IFN-alpha alone, the combination of the two cytokines could more effectively maintain the killing effect of ABM on leukemic cells.

CONCLUSIONS

IFN-alpha can augment the purging effect of IL-2 ABM and combination of the two cytokines can effectively maintain the cytotoxicity of ABM.

COG-2, a sox domain protein necessary for establishing a functional vulval-uterine connection in Caenorhabditis elegans

In screens for mutants defective in vulval morphogenesis, multiple mutants were isolated in which the uterus and the vulva fail to make a proper connection. We describe five alleles that define the gene cog-2, for connection of gonad defective. To form a functional connection between the vulva and the uterus, the anchor cell must fuse with the multinucleate uterine seam cell, derived from uterine cells that adopt a (pi) lineage. In cog-2 mutants, the anchor cell does not fuse to the uterine seam cell and, instead, remains at the apex of the vulva, blocking the connection between the vulval and uterine lumens, resulting in an egg-laying defective phenotype. According to lineage analysis and expression assays for two (pi)-cell-specific markers, induction of the (pi) fate occurs normally in cog-2 mutants. We have cloned cog-2 and shown that it encodes a Sox family transcription factor that is expressed in the (pi) lineage. Thus, it appears that COG-2 is a transcription factor that regulates a late-stage aspect of uterine seam cell differentiation that specifically affects anchor cell-uterine seam cell fusion.

Genetics of RAS signaling in C. elegans

Genetic analysis of the RAS function in Caenorhabditis elegans has not only clarified the functional relationship of signal transduction proteins, but also led to the discovery of new proteins involved positively or negatively in RAS signaling. The stereotyped development of C. elegans has allowed many of the functions of RAS to be elucidated at the level of fates of individual cells.

Enantioselective blockade of T-type Ca2+ current in adult rat sensory neurons by a steroid that lacks gamma-aminobutyric acid-modulatory activity

A number of steroids seem to have anesthetic effects resulting primarily from their ability to potentiate currents gated by gamma-aminobutyric acidA (GABAA) receptor activation. One such compound is (3alpha,5alpha, 17beta)-3-hydroxyandrostane-17-carbonitrile [(+)-ACN]. We were interested in whether carbonitrile substitution at other ring positions might result in other pharmacological consequences. Here we examine effects of (3beta,5alpha, 17beta)-17-hydroxyestrane-3-carbonitrile [(+)-ECN] on GABAA receptors and Ca2+ channels. In contrast to (+)-ACN, (+)-ECN does not potentiate GABAA-receptor activated currents, nor does it directly gate GABAA-receptor mediated currents. However, both steroids produce an enantioselective reduction of T-type current. (+)-ECN blocked T current with an IC50 value of 0.3 microM with a maximal block of 41%. (+)-ACN produced a partial block of T current (44% maximal block) with an IC50 value of 0.4 microM. Block of T current showed mild use- and voltage-dependence. The (-)-ECN enantiomer was about 33 times less potent than (+)-ECN, with an IC50 value of 10 microM and an amount of maximal block comparable to (+)-ECN. (+)-ECN was less effective at blocking high-voltage-activated Ca2+ current in DRG neurons (IC50 value of 9. 3 microM with maximal block of about 27%) and hippocampal neurons. (+)-ECN (10 microM) had minimal effects on voltage-gated sodium and potassium currents in rat chromaffin cells. The results identify a steroid with no effects on GABAA receptors that produces a partial inhibition of T-type Ca2+ current with reasonably high affinity and selectivity. Further study of steroid actions on T currents may lead to even more selective and potent agents.

Influence of erythropoietin treatment on hemoglobin A1c levels in patients with chronic renal failure on hemodialysis

We studied the influence of erythropoietin (EPO) treatment on hemoglobin A1c (HbA1c) levels under conditions which eliminate the effect of changes in the blood glucose concentration. HbA1c levels, blood glucose, hematocrit (Hct) and reticulocyte counts were serially measured every two weeks after starting or stopping EPO administration in 15 non-diabetic hemodialysis patients. EPO treatment significantly influenced HbA1c levels, and the more erythropoiesis fluctuated by changing the dose of EPO, the more HbA1c levels changed, though there were no significant changes in blood glucose levels during the study period. The changes in HbA1c during the 2-week period correlated inversely with both the changes in Hct during the same 2 weeks and the reticulocyte counts at that time. We concluded that the change in Hct should be kept in mind when the HbA1c level is evaluated in EPO-treated patients and a formula should be proposed to correct HbA1c levels based on the change in Hct or the reticulocyte count.

Renal denervation supersensitivity revisited

To determine whether the chronically denervated kidney is supersensitive to either physiological or pathophysiological plasma levels of norepinephrine (NE), studies were conducted in conscious dogs subjected to unilateral renal denervation and surgical division of the urinary bladder into hemibladders to allow separate 24-h urine collection from denervated and innervated kidneys. Plasma NE concentration was increased by chronic infusion of NE (4-5 days) at rates of 25, 100, and 200 ng . kg-1 . min-1. Twenty-four-hour control values for mean arterial pressure (MAP), plasma NE concentration, and ratios for urinary sodium and potassium excretion from denervated and innervated kidneys (Den/Inn) were 94 +/- 4 mmHg, 145 +/- 24 pg/ml, 1.05 +/- 0.05, and 0.97 +/- 0.07, respectively. With infusions of NE producing plasma levels of NE of up to approximately 3,000 pg/ml or plasma concentrations of NE at least threefold greater than present under most pathophysiological conditions and during acute activation of the sympathetic nervous system, there were no significant long-term changes in MAP or relative excretion rates of sodium and potassium from denervated and innervated kidneys. In marked contrast, pharmacological plasma levels of NE ( approximately 7,000 pg/ml) produced chronic increases in MAP (to 116 +/- 2% of control) and sustained reductions in Den/Inn for urinary sodium and potassium excretion to 57 +/- 4 and 68 +/- 5% of control, respectively, indicating a lower excretion rate of these electrolytes from denervated vs. innervated kidneys. We conclude that the chronically denervated kidney does not exhibit an exaggerated antinatriuretic response to either physiological or pathophysiological levels of circulating NE. It is therefore unlikely that renal denervation supersensitivity is a confounding issue in studies employing chronic renal denervation to elucidate the role of the renal nerves in the regulation of sodium excretion.

Antibody response in the intestinal tract of mice orally immunized with antigen associated with liposomes

In order to evaluate the usefulness of liposomes, which are stable in acidic solution, bile and pancreatin solution (stable liposomes), as vehicle for oral vaccines, the intestinal IgA antibody responses of mice to liposome-associated antigen after oral administration were examined. The intestinal IgA antibody responses against ganglioside GM1 were detected after the oral immunization of ganglioside GM1-containing stable liposomes. When monophosphoryl lipid A was incorporated into stable liposomes containing ganglioside GM1, further augmentation of IgA responses to ganglioside GM1 was observed. On the other hand, the oral administration with ganglioside GM1 alone was unable to induce any detectable intestinal anti-ganglioside GM1 IgA antibody response. These results suggest that liposomes which are stable in acidic solution, bile, and pancreatin solution would serve effectively as an oral delivery vehicle for inducing mucosal immune responses.

[Outcome of autologous bone marrow transplantation in 73 patients with acute leukemia]

OBJECTIVE

To evaluate the clinical outcome of autologous bone marrow transplantation(ABMT) in acute leukemias.

METHODS

Data of 73 acute leukemia patients performed ABMT in our hospital from October 1986 to December 1997 were retrospectively analyzed. The median age was 25.5(9-48) years. Forty-three of them were ANLL [CR1 35, CR2 or early relapse (ER)8], 30 were ALL (CR1 25, CR2 or ER 5). Conditioning regimens were CTX 120 mg/kg + STBI 9-10 Gy or Bu 16 mg/kg or Mel 160-180 mg/m2 + Ara-C 4 g/m2.

RESULTS

All patients engrafted successfully. The median follow-up duration was 806 (32-3400) days. The 3-year probabilities of disease-free survival (DFS) for ANLL and ALL in CR1 were 54.9 +/- 7.7% and 67.0% +/- 10.6%, respectively, and the probabilities of relapse were 39.3% +/- 9.3% and 23.7% +/- 10.6%, respectively.

CONCLUSION

To decrease relapse and increase DFS, patients with acute leukemia in CR1 who have no HLA-matched related donor are recommended for ABMT.

Caenorhabditis elegans SUR-5, a novel but conserved protein, negatively regulates LET-60 Ras activity during vulval induction

The let-60 ras gene acts in a signal transduction pathway to control vulval differentiation in Caenorhabditis elegans. By screening suppressors of a dominant negative let-60 ras allele, we isolated three loss-of-function mutations in the sur-5 gene which appear to act as negative regulators of let-60 ras during vulval induction. sur-5 mutations do not cause an obvious mutant phenotype of their own, and they appear to specifically suppress only one of the two groups of let-60 ras dominant negative mutations, suggesting that the gene may be involved in a specific aspect of Ras activation. Consistent with its negative function, overexpressing sur-5 from an extragenic array partially suppresses the Multivulva phenotype of an activated let-60 ras mutation and causes synergistic phenotypes with a lin-45 raf mutation. We have cloned sur-5 and shown that it encodes a novel protein. We have also identified a potential mammalian SUR-5 homolog that is about 35% identical to the worm protein. SUR-5 also has some sequence similarity to acetyl coenzyme A synthetases and is predicted to contain ATP/GTP and AMP binding sites. Our results suggest that sur-5 gene function may be conserved through evolution.

SUR-8, a conserved Ras-binding protein with leucine-rich repeats, positively regulates Ras-mediated signaling in C. elegans

We describe the identification and characterization of a novel gene, sur-8, that positively regulates Ras-mediated signal transduction during C. elegans vulval development. Reduction of sur-8 function suppresses an activated ras mutation and dramatically enhances phenotypes of mpk-1 MAP kinase and ksr-1 mutations, while increase of sur-8 dosage enhances an activated ras mutation. sur-8 appears to act downstream of or in parallel to ras but upstream of raf. sur-8 encodes a conserved protein that is composed predominantly of leucine-rich repeats. The SUR-8 protein interacts directly with Ras but not with the Ras(P34G) mutant protein, suggesting that SUR-8 may mediate its effects through Ras binding. A structural and functional SUR-8 homolog in humans specifically binds K-Ras and N-Ras but not H-Ras in vitro.