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Query: EC:2.7.10.1 (ERK)
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Chronic myelogenous leukemia is typically characterized by the presence of the Philadelphia chromosome (Ph) in which 5' portions of the BCR gene are fused to a large portion of the ABL gene. Our studies and those of others indicate that Bcr sequences within the Bcr-Abl oncoprotein are critically involved in activating the Abl tyrosine kinase and actively participate in the oncogenic response, which is generated by the Bcr-Abl oncoprotein. We investigated the role of the Bcr protein in the oncogenic effects of Bcr-Abl. Reduction of the level of the Bcr protein by incubating cells with a 3' BCR anti-sense oligodeoxynucleotide increased the growth rate and survival of hematopoietic cell lines expressing Bcr-Abl. Also, enforced expression of Bcr in Bcr-Abl cell lines strongly reduced transformation efficiency. Induction of Bcr expression drastically reduced the phosphotyrosine content of Bcr-Abl in Rat-1 fibroblasts transformed by P185 BCR-ABL and in hematopoietic cells expressing P210 Bcr-Abl within days following induction of Bcr. Rat-1/P185 cells maintained for three weeks after Bcr induction had dramatically reduced amounts of phosphotyrosine proteins compared to cells in which Bcr expression was repressed by the addition of Tet. In contrast Bcr expression did not decrease the phosphotyrosine content of either v-Src or activated Neu tyrosine kinase. Importantly, the phosphotyrosine content of total P160 BCR (induced plus endogenous) was strongly reduced by inducing expression of Bcr, indicating that the induced Bcr protein was not a target of the tyrosine kinase activity of Bcr-Abl but instead functioned as an inhibitor of Bcr-Abl. These results show that the Bcr protein can function as a negative regulator of Bcr-Abl, but that the inhibitory effects of Bcr are dependent on achieving an elevated level of Bcr expression relative to Bcr-Abl.
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PMID:Bcr: a negative regulator of the Bcr-Abl oncoprotein. 1044 32

Bispecific antibody (bsAb)-based clinical trials of cancer have been conducted primarily using intact murine monoclonal antibody (mAb)-derived molecules. In some of these trials, toxicity resulting from the interactions of antibody Fc domains with cellular Fc receptors has limited the doses of antibody (Ab) that can be employed. Furthermore, human anti-mouse Ab responses prohibit multiple therapy courses. These factors have decreased the efficacy of the bsAb 2B1, which targets the extracellular domains (ECD) of the HER2/neu protooncogene product and the human FcgammaRIII (CD16). To address these obstacles, we have constructed and characterized a fully human gene-fused bsAb from single-chain Fv (scFv) molecules specific for HER2/neu and CD16. The human anti-CD16 scFv component, NM3E2, was isolated from a human scFv phage display library. As binding of NM3E2 to human neutrophil-associated CD16 decreased in the presence of plasma IgG, we have concluded that NM3E2 recognizes an epitope in the vicinity of the Fc binding pocket. Furthermore, the NM3E2 scFv was found by surface plasmon resonance-based epitope mapping to share an overlapping epitope with the Leu-11c mAb. The human anti-HER2/neu scFv component, C6.5, which was previously isolated from a human scFv phage display library, was employed as fusion partner for the creation of a bispecific scFv (bs-scFv). In the presence of the C6.5 x NM3E2 bs-scFv, peripheral blood lymphocytes promoted significant lysis of human SK-OV-3 ovarian cancer cells overexpressing HER2/neu. Biodistribution studies performed in SK-OV-3 tumor-bearing scid mice revealed that 1% ID/g of 125I-labeled C6.5 x NM3E2 bs-scFv was specifically retained in tumor at 23 h following injection. These results indicated that both scFv components of the bs-scFv retained their function in the fusion protein. This bsAb should overcome some of the problems associated with the 2B1 bsAb. C6.5 x NM3E2 bs-scFv offers promise as a platform for multifunctional binding proteins with potential clinical applications as a result of its human origin, lack of an Fc domain, ease of production, high level of in vitro tumor cell cytotoxicity and highly selective tumor targeting.
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PMID:Isolation and characterization of an anti-CD16 single-chain Fv fragment and construction of an anti-HER2/neu/anti-CD16 bispecific scFv that triggers CD16-dependent tumor cytolysis. 1044 96

In response to extracellular stimuli, mitogen-activated protein kinase (MAPK, also known as ERK) translocates from the cytoplasm to the nucleus. MAP kinase kinase (MAPKK, also know as MEK), which possesses a nuclear export signal (NES), acts as a cytoplasmic anchor of MAPK. Here we show evidence that tyrosine (Tyr190 in Xenopus MPK1/ERK2) phosphorylation of MAPK by MAPKK is necessary and sufficient for the dissociation of the MAPKK-MAPK complex, and that the dissociation of the complex is required for the nuclear translocation of MAPK. We then show that nuclear entry of MAPK through a nuclear pore occurs via two distinct mechanisms. Nuclear import of wild-type MAPK (mol. wt 42 kDa) was induced by activation of the MAPK pathway even in the presence of wheat germ agglutinin or dominant-negative Ran, whereas nuclear import of beta-galactosidase (beta-gal)-fused MAPK (mol. wt 160 kDa), which occurred in response to stimuli, was completely blocked by these inhibitors. Moreover, while a dimerization-deficient mutant of MAPK was able to translocate to the nucleus upon stimulation, this mutant MAPK, when fused to beta-gal, became unable to enter the nucleus. These results suggest that monomeric and dimeric forms of MAPK enter the nucleus by passive diffusion and active transport mechanisms, respectively.
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PMID:Two co-existing mechanisms for nuclear import of MAP kinase: passive diffusion of a monomer and active transport of a dimer. 1050 67

The Eph receptors are the largest known family of receptor protein tyrosine kinases, which play important roles with their ligands called ephrin in the neural development, angiogenesis, and vascular network assembly. It was previously shown that ephrin-A2, -A3 and -A5 bind to, and activate the EphA8 receptor tyrosine kinase, respectively. In this study, we have examined if there are other additional ephrin ligands interacting with the EphA8 receptor tyrosine kinase expressed in NIH3T3 fibroblasts. For this purpose, we have constructed chimeric ephrin-A1, -A4, -B1, -B2 or -B3 ligands consisting of the Fc portion of human IgG fused to their carboxyl-terminus. Both ephrin-A1 and ephrin-A4 chimeric ligands efficiently bound to the EphA8 receptor expressed in NIH3T3 fibroblasts, whereas the transmembrane ligands including ephrin-B1, -B2 and -B3 did not. Additionally we have demonstrated that both the EphA8-TrkB chimeric receptor and the EphA8 receptor expressed in NIH3T3 fibroblasts are efficiently tyrosine-phosphorylated upon stimulating with epthin-A1 or -A4 but none of transmembrane ephrin-B proteins. These results strongly indicate that the EphA8 receptor functions exclusively as an glycosyl phosphatidylinositol (GPI)-linked ephrin ligand-dependent receptor protein tyrosine kinase.
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PMID:Characterization of ephrin-A1 and ephrin-A4 as ligands for the EphA8 receptor protein tyrosine kinase. 1051 10

Anaplastic large cell lymphoma (ALCL) is associated with the t(2;5)(p23;q35), which generates the NPM-ALK fusion gene encoding an 80-kD protein. Several studies have suggested that genes other than NPM may be fused to the ALK gene. Here we have identified TRK-fused gene (TFG) as a new ALK partner in 2 ALCL, 1 of which exhibited a t(2;3)(p23;q21). In these cases, TFG was involved in 2 different fusion genes, TFG-ALK(S) and TFG-ALK(L), coding respectively 85-kD and 97-kD chimeric proteins. The ALK breakpoint in these translocations was the same as in the classic t(2;5) translocation. These 2 proteins were both active in an in vitro tyrosine kinase assay showing that the new cloned cDNA sequences are translated into chimeric proteins with functional activity. These findings indicate that TFG can provide an alternative to NPM as a fusion partner responsible for activation of the ALK and the pathogenesis of ALCL.
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PMID:TRK-fused gene (TFG) is a new partner of ALK in anaplastic large cell lymphoma producing two structurally different TFG-ALK translocations. 1055 17

The RET finger protein (RFP), which belongs to the B box zinc finger protein family, has a tripartite motif consisting of a Ring finger, a B box finger and a coiled-coil domain. The RET finger protein becomes oncogenic when its tripartite motif is fused with the tyrosine kinase domain of the RET protein. This study examined the RFP expression in normal and tumor tissues by immunohistochemistry. RFP was detected in the nuclei of various cells, including peripheral and central neurones, hepatocytes, adrenal chromaffin cells and male germ cells. Among them, RFP was expressed at high levels in male germ cells such as primary spermatocytes and round spermatids, and formed a perinuclear cap structure in primary spermatocytes. On the other hand, high levels of cytoplasmic expression of RFP were observed in some plasma cells as well as solitary plasmacytoma and multiple myeloma. These results suggested that different nuclear/cytoplasmic distributions of RFP might play a role in the regulation of growth or differentiation of different cell types.
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PMID:Different nuclear/cytoplasmic distributions of RET finger protein in different cell types. 1057 21

Rearrangements of NTRK1 proto-oncogene were detected in 'spontaneous' papillary thyroid carcinomas with a frequency varying from 5 to 25% in different studies. These rearrangements result in the formation of chimaeric genes composed of the tyrosine kinase domain of NTRK1 fused to 5' sequences of different genes. To investigate if the NTRK1 gene plays a role in radiation-induced thyroid carcinogenesis, we looked for the presence of NTRK1-activating rearrangements in 32 human thyroid tumours (16 follicular adenomas, 14 papillary carcinomas and two lymph-node metastases of papillary thyroid carcinomas) from patients who had received external radiation, using the reverse transcription polymerase chain reaction, Southern blot and direct sequencing techniques. These data were compared with those obtained in a series of 28 'spontaneous' benign and malignant thyroid tumours, collected from patients without a history of radiation exposure and four in vitro culture cell lines derived from 'spontaneous' thyroid cancers. Our results concerning the radiation-associated tumours showed that only rearrangements between NTRK1 and TPM3 genes (TRK oncogene) were detected in 2/14 papillary carcinomas and in one lymph-node metastasis of one of these papillary thyroid carcinomas. All the radiation-associated adenomas were negative. In the 'spontaneous' tumours, only one of the 14 papillary carcinomas and one of the four in vitro culture cell lines, derived from a papillary carcinoma, presented a NTRK1 rearrangement also with the TPM3 gene. Twenty-five of this series of radiation-associated tumours were previously studied for the ras and RET/PTC oncogenes. In conclusion, our data: (a) show that the overall frequency of NTRK1 rearrangements is similar between radiation-associated (2/31: 6%) and 'spontaneous' epithelial thyroid tumours (2/32: 6%). The frequency, if we consider exclusively the papillary carcinomas, is in both cases 12%; (b) show that the TRK oncogene plays a role in the development of a minority of radiation-associated papillary thyroid carcinomas but not in adenomas; and (c) confirm that RET/PTC rearrangements are the major genetic alteration associated with ionizing radiation-induced thyroid tumorigenesis.
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PMID:Search for NTRK1 proto-oncogene rearrangements in human thyroid tumours originated after therapeutic radiation. 1064 82

Induction of cfos expression is a definite end point of signal transduction by receptor tyrosine kinases via MAPK cascades. We have examined signal transduction to transcription factor cFos in isolated fibroblasts of a patient with an inherited syndrome of insulin resistance. MAPK phosphorylation and activity were unaltered, but inducibility of cfos transcription was strongly impaired by insulin and reduced by PDGF. Induction of the cfos promoter via MAPK is mediated by activation of the ternary complex. Abundance of SRF or Elk-1 was unaltered, but Elk-1 phosphorylation following stimulation was reduced. Transient transfections with reporter genes under control of the Elk-1 binding ets/sre cis element or expression plasmids coding for the regulatory domain of Elk-1 fused to heterologous DNA binding domains revealed a defect of Elk-1 activation in the patient cells. These data identify a novel postreceptor defect of insulin and growth factors involving activation of transcription.
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PMID:Characterization of a postreceptor signaling defect that impairs cfos expression in cultured fibroblasts of a patient with insulin resistance. 1067 46

The hallmark of the 8p12 stem cell myeloproliferative disorder (MPD) is the disruption of the FGFR1 gene, which encodes a tyrosine kinase receptor for members of the fibroblast growth factor family. FGFR1 can be fused to at least 3 partner genes at chromosomal regions 6q27, 9q33, or 13q12. We report here the cloning of the t(8;9)(p12;q33) and the detection of a novel fusion betweenFGFR1 and the CEP110 gene, which codes for a novel centrosome-associated protein with a unique cell-cycle distribution. CEP110 is widely expressed at various levels in different tissues and is predicted to encode a 994-amino acid coiled-coil protein with 4 consensus leucine zippers [L-X(6)-L-X(6)-L-X(6)-L]. Both reciprocal fusion transcripts are expressed in the patient's cells. The CEP110-FGFR1 fusion protein encodes an aberrant tyrosine kinase of circa 150-kd, which retains most of CEP110 with the leucine zipper motifs and the catalytic domain of FGFR1. Transient expression studies show that the CEP110-FGFR1 protein has a constitutive kinase activity and is located within the cell cytoplasm. (Blood. 2000;95:1788-1796)
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PMID:FGFR1 is fused to the centrosome-associated protein CEP110 in the 8p12 stem cell myeloproliferative disorder with t(8;9)(p12;q33). 1068 39

We recently isolated a novel cDNA, designated ELKS, that was fused to RET cDNA in a papillary thyroid carcinoma. Its encoded polypeptide sequence was rich in glutamic acid (E), leucine (L), lysine (K), and serine (S), and was characterized by the presence of nine alpha-helical coiled-coil domains consisting of periodic heptad repeats. We have now cloned the entire structure of the human ELKS gene from within a 700-kb genomic region represented by overlapping bacteriophage P1-derived artificial chromosome (PAC) and bacterial artificial chromosome (BAC) clones, and localized it to chromosomal band 12p13.3 by fluorescence in situ hybridization. The gene is approximately 500 kb long, with 19 exons and 18 introns; the transcription initiation site within exon 1 is separate from the initiation codon (in exon 2). Analysis of the exon/intron structure revealed that introns interrupt the coding sequence in such a way that many functional segments of the protein are encoded by distinct exons. Exon 1 encodes the 5' non-coding region; exons 2, 3, 6, 7, 8, 9, 11, 14, and 15 encode the nine coiled-coil domains. Exons 17-19 constitute the 3' non-coding region. Analysis of the region immediately upstream of exon 1 showed that it was extremely rich in G/C nucleotides and contained multiple Sp-1 and AP2 binding sequences. The ELKS-RET gene fusion rearrangement we had observed in a papillary thyroid carcinoma occurred between intron 10 of the ELKS gene and intron 11 of RET.
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PMID:Genomic organization and chromosomal mapping of ELKS, a gene rearranged in a papillary thyroid carcinoma. 1069 56


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