Heritable severe combined anemia and thrombocytopenia in the mouse: description of the disease and successful therapy

A new autosomal recessive mouse mutation, scat (severe combined anemia and thrombocytopenia), causes intermittent episodes of severe bleeding in the homozygote. At birth, affected mice are pale with intradermal petechiae and bruises on exposed surfaces. Central nervous system (CNS) bleeding occurs in 22% of the mice. Gastrointestinal (GI) hemorrhaging and splenomegaly are noted in moribund mice at autopsy. Of the 291 mice studied, 113 mice survived the initial crisis and entered a spontaneous remission period lasting from day 16 to day 27. A second crisis period ensued, and all but 22 mice died by 45 days. Mice in crisis show significantly decreased platelets, erythrocytes, and leukocytes and increased reticulocytes when compared to normal littermates. During remission all parameters are significantly improved or revert to normal values. Neither splenomegaly nor internal bleeding are observed during remission. A platelet-specific antibody is present in the plasma of mutant mice during crisis. The symptoms (severe bleeding, anemia, low-platelet counts) and platelet-specific antibody production are transferred to lethally irradiated normal mice through spleen cell transplantation. Splenectomy of mice in remission significantly increases survival. Exploitation of the features common to both scat/scat mice and patients with some forms of autoimmune thrombocytopenic purpura will undoubtedly prove useful in defining common pathways of disease development and in testing potential therapeutic measures.     

Lymphatic abnormalities are associated with RASA1 gene mutations in mouse and man

Mutations in gene RASA1 have been historically associated with capillary malformation–arteriovenous malformation, but sporadic reports of lymphatic involvement have yet to be investigated in detail. To investigate the impact of RASA1 mutations in the lymphatic system, we performed investigational near-infrared fluorescence lymphatic imaging and confirmatory radiographic lymphangiography in a Parkes–Weber syndrome (PKWS) patient with suspected RASA1 mutations and correlated the lymphatic abnormalities against that imaged in an inducible Rasa1 knockout mouse. Whole-exome sequencing (WES) analysis and validation by Sanger sequencing of DNA from the patient and unaffected biological parents enabled us to identify an early-frameshift deletion in RASA1 that was shared with the father, who possessed a capillary stain but otherwise no overt disease phenotype. Abnormal lymphatic vasculature was imaged in both affected and unaffected legs of the PKWS subject that transported injected indocyanine green dye to the inguinal lymph node and drained atypically into the abdomen and into dermal lymphocele-like vesicles on the groin. Dermal lymphatic hyperplasia and dilated vessels were observed in Rasa1-deficient mice, with subsequent development of chylous ascites. WES analyses did not identify potential gene modifiers that could explain the variability of penetrance between father and son. Nonetheless, we conclude that the RASA1 mutation is responsible for the aberrant lymphatic architecture and functional abnormalities, as visualized in the PKWS subject and in the animal model. Our unique method to combine investigatory near-infrared fluorescence lymphatic imaging and WES for accurate phenoptyping and unbiased genotyping allows the study of molecular mechanisms of lymphatic involvement of hemovascular disorders.     

A new glucose-6-phosphate dehydrogenase variant G6PD Sugao (826C-->T) exhibiting chronic hemolytic anemia with episodes of hemolytic crisis immediately after birth

A case of glucose-6-phosphate dehydrogenase (G6PD) deficiency associated with chronic hemolysis with episodes of hemolytic crisis immediately after birth is reported. The propositus was a 1-month-old Japanese male infant. Molecular analysis of the G6PD gene revealed a novel missense mutation (826C-->4T) in exon 8 predicting a single amino acid substitution, Pro276Ser. The mother was confirmed to be heterozygous for this mutation. We designated this novel class 1 variant as G6PD Sugao. Pro276 is a phylogenetically conserved residue that may play a significant role in dimer formation.     

Diacylglycerol kinase iota regulates Ras guanyl-releasing protein 3 and inhibits Rap1 signaling

To study the physiological function of diacylglycerol (DAG) kinase iota (DGKiota), which converts DAG to phosphatidic acid, we deleted this gene in mice. In contrast to previous studies showing that DGK isoforms decrease Ras activity, signaling downstream of Ras in embryonic fibroblasts was significantly reduced in cells lacking DGKiota. DGKs regulate Ras signaling by attenuating the function of the DAG-dependent Ras guanyl nucleotide-releasing proteins (RasGRPs). We tested whether DGKiota inhibited the four known RasGRPs and found that it inhibited only RasGRP3. In addition to activating Ras, RasGRP3 also activates Rap1, which in some cases can antagonize the function of Ras. We demonstrate that DGKiota bound to RasGRP3 and inhibited its activation of Rap1 by metabolizing DAG. This inhibition consequently affected Ras signaling. We tested the physiological consequence of deleting DGKiota by crossing wild-type or DGKiota-deficient mice with mice carrying a v-Ha-Ras transgene, and then we assessed tumor formation. We observed significantly fewer tumors in DGKiota-deficient mice. Because Rap1 can antagonize the function of Ras, our data are consistent with a model in which DGKiota regulates RasGRP3 with a predominant effect on Rap1 activity. Additionally, we found that DGKzeta, which is structurally similar to DGKiota, inhibited RasGRPs 1, 3, and 4 and predominantly affected Ras signaling. Thus, type IV DGKs regulate RasGRPs, but the downstream effects differ depending on the DGK.     

Requirement for nitric oxide activation of p21(ras)/extracellular regulated kinase in neuronal ischemic preconditioning

The mechanisms underlying neuronal ischemic preconditioning, a phenomenon in which brief episodes of ischemia protect against the lethal effects of subsequent periods of prolonged ischemia, are poorly understood. Ischemia can be modeled in vitro by oxygen-glucose deprivation (OGD). We report here that OGD preconditioning induces p21(ras) (Ras) activation in an N-methyl-D-aspartate receptor- and NO-dependent, but cGMP-independent, manner. We demonstrate that Ras activity is necessary and sufficient for OGD tolerance in neurons. Pharmacological inhibition of Ras, as well as a dominant negative mutant Ras, block OGD preconditioning whereas a constitutively active form of Ras promotes neuroprotection against lethal OGD insults. In contrast, the activity of phosphatidyl inositol 3-kinase is not required for OGD preconditioning because inhibition of phosphatidyl inositol 3-kinase with a chemical inhibitor or with a dominant negative mutant does not have any effect on the development of OGD tolerance. Furthermore, using recombinant adenoviruses and pharmacological inhibitors, we show that downstream of Ras the extracellular regulated kinase cascade is required for OGD preconditioning. Our observations indicate that activation of the Ras/extracellular regulated kinase cascade by NO is a critical mechanism for the development of OGD tolerance in cortical neurons, which may also play an important role in ischemic preconditioning in vivo.     

Effect of farnesyl transferase inhibitor R115777 on the growth of fresh and cloned myeloma cells in vitro

Ras gene mutations occur in 30% to 40% of patients with multiple myeloma (MM), and farnesylation is the first and most important step in the posttranslational modification of Ras proteins. R115777 is a newly synthesized potent farnesyl transferase inhibitor (FTI) and has recently demonstrated significant antitumor activities in vitro and in vivo. Therefore, we examined the effect of R115777 on the growth of fresh and cloned myeloma cells in vitro. R115777 inhibited the growth of fresh and cloned myeloma cells dose dependently, and effects were not dependent on the status of N-Ras mutation in fresh myeloma cells. Flow cytometric analysis using annexin V and 7-aminoactinomycin D (7AAD) showed that R115777 induced apoptosis of 2 of 3 myeloma cell lines at a concentration of 1.0 x 10(-8) M. R115777 appears to be a potent inducer of apoptosis, and its effects depend on the status of Ras mutation in cloned myeloma cells but not on the status of N-Ras mutation in fresh myeloma cells. This is the first report that demonstrates the relationship between the N-Ras mutation in fresh myeloma cells and the effect of R115777. R115777 might have some benefit in the treatment of myeloma patients.     

Correlation between molecular and clinical events in the evolution of chronic myelocytic leukemia to blast crisis

A patient with typical Philadelphia chromosome (Ph1)-positive chronic myelocytic leukemia (CML) was studied during sequential phases of disease: (1) initial chronic phase; (2) myeloid blast crisis; (3) second chronic phase; and (4) accelerated disease. A point mutation in the coding sequence of the p53 gene first appeared concomitantly with the blast crisis and then disappeared with the re-establishment of a second chronic phase. The chromosomal concomitant of the molecular alteration was a deletion of 17p. These observations suggest that abnormalities of the p53 anti-oncogene are temporally related to the clinical progression of some cases of CML and are probably responsible for the development of blast crisis in these cases.     

Activation of the Raf-1/MAP kinase cascade is not sufficient for Ras transformation of RIE-1 epithelial cells.

The potent transforming activity of membrane-targeted Raf-1 (Raf-CAAX) suggests that Ras transformation is triggered primarily by a Ras-mediated translocation of Raf-1 to the plasma membrane. However, whereas constitutively activated mutants of Ras [H-Ras(61L) and K-Ras4B(12V)] and Raf-1 (DeltaRaf-22W and Raf-CAAX) caused indistinguishable morphologic and growth (in soft agar and nude mice) transformation of NIH 3T3 fibroblasts, only mutant Ras caused morphologic transformation of RIE-1 rat intestinal cells. Furthermore, only mutant Ras-expressing RIE-1 cells formed colonies in soft agar and developed rapid and progressive tumors in nude mice. We also observed that activated Ras, but not Raf-1, caused transformation of IEC-6 rat intestinal and MCF-10A human mammary epithelial cells. Although both Ras- and DeltaRaf-22W-expressing RIE-1 cells showed elevated Raf-1 and mitogen-activated protein (MAP) kinase activities, only Ras-transformed cells produced secreted factors that promoted RIE-1 transformation. Incubation of untransformed RIE-1 cells in the presence of conditioned medium from Ras-expressing, but not DeltaRaf-22W-expressing, cells caused a rapid and stable morphologic transformation that was indistinguishable from the morphology of Ras-transformed RIE-1 cells. Thus, induction of an autocrine growth mechanism may distinguish the transforming actions of Ras and Raf. In summary, our observations demonstrate that oncogenic Ras activation of the Raf/MAP kinase pathway alone is not sufficient for full tumorigenic transformation of RIE-1 epithelial cells. Thus, Raf-independent signaling events are essential for oncogenic Ras transformation of epithelial cells, but not fibroblasts.     

Requirement of Ras-dependent pathways for activation of the transforming growth factor beta3 promoter by estradiol

It has been previously observed that the transforming growth factor beta3 (TGFbeta3) gene can be activated by both estradiol (E(2)) and selective estrogen receptor modulators (SERMs) in vivo but that only SERMs have a potent stimulatory effect on the TGFbeta3 promoter in cultured cells. We demonstrate in this report that E(2) can act also as a potent inducer of the TGFbeta3 promoter via a novel and specific estrogen receptor (ER)alpha-mediated mechanism. Our results show that treatment with epidermal growth factor or transfection of a constitutively active Ras mutant allows E(2) to induce the TGFbeta3 promoter via ERalpha in cotransfected HeLa and osteosarcoma MG63 cells. Both protein kinase C (PKC) and mitogen-activated protein kinase (MAPK) inhibitors can block the combined stimulatory effect of E(2) and epidermal growth factor/Ras. However, E(2) induction of the TGFbeta3 promoter was found to be unaffected by mutation of ERalpha serine 118, a well-characterized target of MAPK. Progressive deletion analysis of the ERalpha amino-terminal region delineated three separate domains modulating the E(2)/activated Ras response, revealing a complex functional organization of the ERalpha A/B domain required for regulation of the TGFbeta3 promoter. In addition, PKC and MAPK inhibitors had no effect on the induction of TGFbeta3 promoter activity by the SERM EM-652. These results indicate that induction of the TGFbeta3 promoter by the E(2)/ERalpha complex requires the concomitant activation of PKC and MAPK signaling and provide a novel framework for the design of more effective estrogen-based therapeutic strategies.     

A splicing mutation accounts for the lack of p53 gene expression in a CML blast crisis cell line: a novel mechanism of p53 gene inactivation

Alterations of the p53 anti-oncogene have recently been found to occur frequently in the blast crisis of chronic myelocytic leukaemia. The p53 gene may be altered by gross structural alterations or by point mutations in the coding sequence. We now report a novel mechanism of gene inactivation in a blast crisis cell line where a mutation in a splice donor site at the 5' end of the fifth intron of the gene interrupts RNA processing and gene expression.     

Use of yeast artificial chromosomes (YACs) in studies of mammalian development: production of beta-globin locus YAC mice carrying human globin developmental mutants.

To test whether yeast artificial chromosomes (YACs) can be used in the investigation of mammalian development, we analyzed the phenotypes of transgenic mice carrying two types of beta-globin locus YAC developmental mutants: (i) mice carrying a G-->A transition at position -117 of the A gamma gene, which is responsible for the Greek A gamma form of hereditary persistence of fetal hemoglobin (HPFH), and (ii) beta-globin locus YAC transgenic lines carrying delta- and beta-globin gene deletions with 5' breakpoints similar to those of deletional HPFH and delta beta-thalassemia syndromes. The mice carrying the -117 A gamma G-->A mutation displayed a delayed gamma- to beta-globin gene switch and continued to express A gamma-globin chains in the adult stage of development as expected for carriers of Greek HPFH, indicating that the YAC/transgenic mouse system allows the analysis of the developmental role of cis-acting motifs. The analysis of mice carrying 3' deletions first provided evidence in support of the hypothesis that imported enhancers are responsible for the phenotypes of deletional HPFH and second indicated that autonomous silencing is the primary mechanism for turning off the gamma-globin genes in the adult. Collectively, our results suggest that transgenic mice carrying YAC mutations provide a useful model for the analysis of the control of gene expression during development.     

血液肿瘤患者FLT3/ITD基因突变的检测及临床意义

目的检测血液肿瘤患者FLT3/ITD基因突变,探讨其突变的临床意义。方法2001—2005年对南方医科大学南方医院血液科332例血液肿瘤患者,采用聚合酶链反应(PCR)方法检测FLT3/ITD基因突变。结果FLT3/ITD基因突变阳性率分别为急性髓性白血病(AML)22.3%(23/103)、慢性髓性白血病急变期(CML-BC)6.5%(2/31)、骨髓增生异常综合征(MDS)5.6%(2/36)和急性淋巴细胞白血病(ALL)2.6%(2/76)。而慢性髓性白血病慢性期(CML-CP)、慢性淋巴细胞白血病(CLL)、多发性骨髓瘤(MM)和非霍奇金淋巴瘤(NHL)均未发现FLT3/ITD基因突变。FLT3/ITD基因突变阳性AML患者外周血WBC计数及骨髓白血病细胞比例显著高于FLT3/ITD基因突变阴性AML患者(P<0.05),FLT3/ITD基因突变阳性AML患者完全缓解后18个月内累计复发率(63.6%)显著高于FLT3/ITD基因突变阴性AML组(27.7%)(P<0.05)。结论FLT3/ITD基因突变检测对血液肿瘤预后有一定意义;FLT3/ITD基因突变AML患者预后差。     

Activation of RasGRP3 by phosphorylation of Thr-133 is required for B cell receptor-mediated Ras activation

The Ras signaling pathway plays a critical role in B lymphocyte development and activation, but its activation mechanism has not been well understood. At least one mode of Ras regulation in B cells involves a Ras-guanyl nucleotide exchange factor, RasGRP3. We demonstrate here that RasGRP3 undergoes phosphorylation at Thr-133 upon B cell receptor cross-linking, thereby resulting in its activation. Deletion of phospholipase C-gamma2 or pharmacological interference with conventional PKCs resulted in marked reduction in both Thr-133 phosphorylation and Ras activation. Moreover, mutation of Thr-133 in RasGRP3 alone severely impaired its ability to activate Ras in B cell receptor signaling. Hence, our data suggest that PKC, after being activated by diacylglycerol, phosphorylates RasGRP3, thereby contributing to its full activation.     

Possible involvement of RasGRP4 in leukemogenesis

It is now conceivable that leukemogenesis requires two types of mutations, class I and class II mutations. We previously established a mouse bone marrow-derived HF6, an IL-3-dependent cell line, that was immortalized by a class II mutation MLL/SEPT6 and can be fully transformed by class I mutations such as FLT3 mutants. To understand the molecular mechanism of leukemogenesis, particularly progression of myelodysplastic syndrome (MDS) to acute leukemia, we made cDNA libraries from the samples of patients and screened them by expression-cloning to detect class I mutations that render HF6 cells factor-independent. We identified RasGRP4, an activator of Ras, as a candidate for class I mutation from three of six patients (MDS/MPD = 1, MDS-RA = 1, MDS/AML = 2, CMMoL/AML = 1 and AML-M2 = 1). To investigate the potential roles of RasGRP4 in leukemogenesis, we tested its in vivo effect in a mouse bone marrow transplantation (BMT) model. C57BL/6J mice transplanted with RasGRP4-transduced primary bone marrow cells died of T cell leukemia, myeloid leukemia, or myeloid leukemia with T cell leukemia. To further examine if the combination of class I and class II mutations accelerated leukemic transformation, we performed a mouse BMT model in which both AML1 mutant (S291fsX300) and RasGRP4 were transduced into bone marrow cells. The double transduction led to early onset of T cell leukemia but not of AML in the transplanted mice when compared to transduction of RasGRP4 alone. Thus, we have identified RasGRP4 as a gene potentially involved in leukemogenesis and suggest that RasGRP4 cooperates with AML1 mutations in T cell leukemogenesis as a class I mutation. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Sexual dimorphism of pancreatic beta-cell degeneration in transgenic mice expressing an insulin-ras hybrid gene

The human H-ras oncogene induces cell degeneration and diabetes when expressed in pancreatic beta-cells in transgenic mice. The disease develops predominantly in male mice between 5-8 months of age. Most transgenic female mice do not manifest this phenotype, even at much greater ages. However, ovariectomy induces female beta-cell degeneration similar to that in the males. In contrast, castration or the presence of the testicular feminization mutation do not alter the course of the disease in males. Treatment of males and ovariectomized females with estrogen prevents the development of diabetes. These results suggest that testicular androgens and a functional testosterone receptor are not required for the increased susceptibility of male beta-cells to the effects of the Ras oncoprotein, and that the relative resistance of female beta-cells is mediated by estrogen. In addition, a genetic component of female beta-cell resistance to Ras is revealed by crossing the transgenic mice with C3HeB/FeJ mice, which results in a pronounced increase in the incidence of female diabetes.