Ligand activation of overexpressed epidermal growth factor receptors transforms NIH 3T3 mouse fibroblasts

The cell surface receptor for the mitogenic peptide epidermal growth factor (EGF) is involved in control of normal cell growth and may play a role in the genesis of human neoplasia such as squamous carcinoma and glioblastoma. Soft-agar growth and focus-formation experiments with NIH 3T3 mouse fibroblasts transfected with an expression plasmid demonstrated the ligand-dependent transforming potential of the human EGF receptor without structural alterations. Activation of overexpressed normal receptor alone appears to be sufficient for transformation of NIH 3T3 cells in vitro.

A point mutation at the ATP-binding site of the EGF-receptor abolishes signal transduction

The EGF-receptor (EGF-R) is a transmembrane glycoprotein with intrinsic protein tyrosine kinase (TK) activity. To explore the importance of the receptor TK in the action of EGF, we have used transfected NIH-3T3 cells expressing either the normal human EGF-R or a receptor mutated at Lys721, a key residue in the presumed ATP-binding region. The wild-type receptor responds to EGF by causing inositol phosphate formation, Ca2+ influx, activation of Na+/H+ exchange and DNA synthesis. In contrast, the TK-deficient mutant receptor fails to evoke any of these responses. It is concluded that activation of the receptor TK is a crucial signal that initiates the multiple post-receptor effects of EGF leading to DNA synthesis. Furthermore, the results suggest that tyrosine phosphorylation plays a role in the activation of the phosphoinositide signalling system.

Defects in human insulin receptor gene expression

The insulin receptor plays a central role in mediating the biological actions of insulin. We have used Epstein-Barr virus-transformed lymphocytes (EBV-lymphocytes) to investigate the receptor defects in patients with genetic forms of insulin resistance. Within the normal population, we found a close correlation between the number of insulin receptors on the surface of EBV-lymphocytes and the cellular content of insulin receptor mRNA. In addition, we have used the cloned human insulin receptor cDNA to investigate the nature of the mutations causing the reduction in the number of insulin receptors in EBV-lymphocytes from three insulin resistant patients. One patient with leprechaunism has a marked reduction in the level of receptor mRNA, which probably accounts for the extremely slow rate of receptor biosynthesis measured in this patient's cells. The remaining two patients with type A extreme insulin resistance are sisters, the products of a consanguineous marriage, who have normal levels of insulin receptor mRNA. We have previously shown that the insulin receptor precursor is synthesized at a normal rate in these patients' cells, thus suggesting a defect in the posttranslational processing of the receptor or in its translocation to the plasma membrane.

Overexpression of the human EGF receptor confers an EGF-dependent transformed phenotype to NIH 3T3 cells

The epidermal growth factor receptor (EGFR) gene is frequently amplified and/or overexpressed in human malignancies. To investigate the biological effects of its overexpression, we constructed a eukaryotic vector containing human EGFR cDNA. Introduction of this construct led to reconstitution of functional EGF receptors in NR6 mutant cells, which are normally devoid of this receptor. Transfection of NIH 3T3 resulted in no significant alterations in growth properties. However, EGF addition led to the formation of densely growing transformed foci in liquid culture and colonies in semisolid medium. NIH 3T3-EGFR clonal lines, which expressed the EGF at 500- to 1000-fold levels over control NIH 3T3 cells, demonstrated a marked increase in DNA synthesis in response to EGF. Thus EGF receptor overexpression appears to amplify normal EGF signal transduction. Finally, high levels of EGFR expression, which conferred a transformed phenotype to NIH 3T3 cells in the presence of ligand, were demonstrated in representative human tumor cell lines that contained amplified copies of the EGFR gene.

Primary structure and mRNA localization of protein F1, a growth-related protein kinase C substrate associated with synaptic plasticity

Protein F1 is a neuron-specific, synaptic-enriched, membrane-bound substrate of protein kinase C (PKC) whose phosphorylation is related to synaptic plasticity in the adult. The sequence of 26 N-terminal amino acids was determined from purified rat protein F1. A 78-mer synthetic oligonucleotide designed from the partial N-terminal sequence enabled identification of protein F1 cDNA clones in a rat brain library. F1 protein is a 226 amino acid protein encoded by a 1.5 kb brain-specific, developmentally-regulated mRNA. Transcripts for protein F1 can be detected at birth, and their level declines after maturation. A full-length cDNA clone was transcribed and translated in vitro. Translation products could be immunoprecipitated with anti-F1 antibodies. In situ hybridization analysis revealed protein F1 transcripts in hippocampal pyramidal cells, but not in granule cells. In cerebellum, granule cells contained protein F1 mRNA, while Purkinje cells did not. Co-localization of protein F1 with protein kinase C-II [PKC-II (beta)], rather than PKC-I (gamma) suggests that PKC-II may phosphorylate protein F1.

[Early prognostic assessment using evoked potentials in severe craniocerebral trauma]

103 patients in acute posttraumatic coma were assessed during 72 hours following severe head injury by clinical examinations (documented with a modified Glasgow-Coma-Score and a brain-stem-score and brainstem auditory evoked potentials (BAEP) as well as short latency somatosensory evoked potentials (SEP). Patient outcomes were classified at 6 months or more, according to the following categories: good recovery, severely disabled or vegetative, and brain dead. Patients who had died by systemic complications were excluded from the study. The Glasgow-Coma-Score was reliable in forecasting a favorable outcome, but tended to produce false-pessimistic predictions. The brainstemscore and the BAEPs were reliable predictors of an unfavorable but not a favorable outcome. SEP data however, performed well as a prognostic indicant in predicting an unfavorable as well as a favorable outcome. Using the BAEP, the amplitude ratio Wave V/Wave I is more sensitive to detect a lesion than the interpeak-latency Wave I-Wave V, and--using the SEP--the amplitude ratio N20/N13b (over C2) is more sensitive than the central conduction time (N13a (over C7)--N20).

A mutant epidermal growth factor receptor with defective protein tyrosine kinase is unable to stimulate proto-oncogene expression and DNA synthesis

Cultured NIH-3T3 cells devoid of endogenous epidermal growth factor (EGF) receptors were transfected with cDNA expression constructs encoding either normal human EGF receptor or a receptor mutated in vitro at Lys-721, a residue that is thought to function as part of the ATP-binding site of the kinase domain. Unlike the wild-type EGF-receptor expressed in these cells, which exhibited EGF-dependent protein tyrosine kinase activity, the mutant receptor lacked protein tyrosine kinase activity and was unable to undergo autophosphorylation and to phosphorylate exogenous substrates. Despite this deficiency, the mutant receptor was normally expressed on the cell surface, and it exhibited both high- and low-affinity binding sites. The addition of EGF to cells expressing wild-type receptors caused the stimulation of various responses, including enhanced expression of proto-oncogenes c-fos and c-myc, morphological changes, and stimulation of DNA synthesis. However, in cells expressing mutant receptors, EGF was unable to stimulate these responses, suggesting that the tyrosine kinase activity is essential for EGF receptor signal transduction.

Human proto-oncogene c-kit: a new cell surface receptor tyrosine kinase for an unidentified ligand

Structural features of v-kit, the oncogene of HZ4 feline sarcoma virus, suggested that this gene arose by transduction and truncation of cellular sequences. Complementary DNA cloning of the human proto-oncogene coding for a receptor tyrosine kinase confirmed this possibility: c-kit encodes a transmembrane glycoprotein that is structurally related to the receptor for macrophage growth factor (CSF-1) and the receptor for platelet-derived growth factor. The c-kit gene is widely expressed as a single, 5-kb transcript, and it is localized to human chromosome 4 and to mouse chromosome 5. A c-kit peptide antibody permitted the identification of a 145,000 dalton c-kit gene product that is inserted in the cellular plasma membrane and is capable of self-phosphorylation on tyrosine residues in both human glioblastoma cells and transfected mouse fibroblasts. Our results suggest that p145c-kit functions as a cell surface receptor for an as yet unidentified ligand. Furthermore, carboxy- and amino-terminal truncations that occurred during the viral transduction process are likely to have generated the transformation potential of v-kit.

Point mutation at the ATP binding site of EGF receptor abolishes protein-tyrosine kinase activity and alters cellular routing

Cultured NIH 3T3 cells devoid of endogenous EGF receptors were transfected with cDNA constructs encoding either the human EGF receptor or an EGF receptor mutant in which Lys721, a key residue in the ATP binding site, was replaced with an alanine residue. The mutant receptor was properly processed, and it displayed both high- and low-affinity surface binding sites. Unlike the wild-type receptor, the mutant receptor did not possess intrinsic protein-tyrosine kinase activity. The initial rate of EGF internalization was similar for wild-type and mutant EGF receptors. Surprisingly, the mutant receptors were not down regulated, but appeared to recycle in transfected cells. These data suggest that degradation of normal EGF receptors after endocytosis is due to the kinase activity endogenous to this receptor. A single amino acid substitution rendered a "down-regulated" receptor into a receptor that can recycle from cytoplasmic compartment back to the cell surface.

Alternative splicing increases the diversity of the human protein kinase C family

Isolation of two protein kinase C (PKC) cDNA clones containing divergent carboxy-terminal sequences suggested a common genetic origin for these cDNAs. Partial characterization of the hPKC beta chromosomal gene provided direct evidence for the existence of two adjacent carboxy-terminal exons (beta 1 and beta 2) that are alternatively spliced to generate two types of hPKC beta sequences. PKC beta 1 and beta 2 mRNAs are expressed in a selective manner in both human hematopoietic cells and bovine brain tissues.

Increased expression of the putative growth factor receptor p185HER2 causes transformation and tumorigenesis of NIH 3T3 cells

The HER2 gene encodes a cell-surface glycoprotein with extensive homology to the epidermal growth factor receptor. Recently it was found to be amplified in about 30% of primary human breast malignancies. In experiments designed to assess the role of the HER2 gene in oncogenesis, we found that overexpression of unaltered HER2 coding sequences in NIH 3T3 cells resulted in cellular transformation and tumorigenesis.

An insertional mutant of epidermal growth factor receptor allows dissection of diverse receptor functions

Cultured NIH-3T3 cells devoid of endogenous EGF-receptors were transfected with cDNA constructs encoding normal human EGF-receptor and with a construct encoding an insertional mutant of the EGF-receptor containing four additional amino acids in the kinase domain after residue 708. Unlike the wild-type receptor expressed in these cells which exhibits EGF-stimulatable protein tyrosine kinase activity, the mutant receptor lacks protein tyrosine kinase activity both in vitro and in vivo. Despite this deficiency the mutant receptor is properly processed, it binds EGF and it exhibits both high and low affinity binding sites. Moreover, it undergoes efficient EGF-mediated endocytosis. However, EGF fails to stimulate DNA synthesis and is unable to stimulate the phosphorylation of S6 ribosomal protein in cells expressing this receptor mutant. Hence, it is proposed that the protein tyrosine kinase activity of EGF-receptor is essential for the initiation of S6 phosphorylation and for DNA synthesis induced by EGF. However, EGF-receptor processing, the expression of high and low affinity surface receptors and receptor internalization, require neither kinase activity nor receptor autophosphorylation. Interestingly, phorbol ester (TPA) fails to abolish the high affinity state and is also unable to stimulate the phosphorylation of this receptor mutant. This result is consistent with the notion that kinase-C phosphorylation of EGF-receptor is essential for the loss of high affinity EGF-receptors caused by TPA.

Tissue-specific and developmentally regulated transcription of the insulin-like growth factor 2 gene

Transcription of the rat and human IGF-2 gene loci is unusually complex. The pattern of expression of these genes varies both between tissues and within a given tissue during different stages of development. Alternative splicing or possibly transcriptional initiation events generate variant IGF-2 mRNAs that contain different 5'-untranslated leader sequences. These leader exon sequences are shared with non-IGF-2 mRNAs. Certain noncoding IGF-2 gene sequence elements are transcribed extensively and are found in multiple copies elsewhere in the human genome. Furthermore, IGF-2 mRNA levels are particularly high in a variety of human malignancies.

Characterization of an endogenous substrate of the insulin receptor in cultured cells

Using antiphosphotyrosine antibodies, we have characterized the tyrosine phosphorylation of an endogenous substrate of the insulin receptor in Fao hepatoma cells and in Chinese hamster ovary cells transfected with a eukaryotic expression vector containing the human insulin receptor cDNA. In Fao cells, besides the beta-subunit of the insulin receptor, a protein with a molecular mass between 170 and 210 kDa designated pp185, undergoes tyrosine phosphorylation immediately after insulin stimulation reaching a maximum level within 30 s. After 4 h of continuous insulin stimulation, the labeling of pp185 decreased to less than half of its original intensity, whereas the insulin receptor was unchanged. After 24 h of insulin stimulation, the phosphotyrosine-containing insulin receptor decreased by 75% owing to down-regulation, whereas the pp185 was completely undetectable. By several biochemical and physiological criteria, the pp185 is distinct from the insulin receptor. The pp185 and the beta-subunit of the insulin receptor were strongly labeled with [32P]orthophosphate, but in contrast to the insulin receptor, the pp185 was not labeled by cross-linking with 125I-insulin or surface 125I iodination. Unlike the insulin receptor, the pp185 was extracted from Fao cells without detergent, and tryptic phosphopeptide mapping of the pp185 and the insulin receptor yielded distinct patterns. Thus, the pp185 is not located at the external face of the plasma membrane and does not bind insulin. Treatment of Fao cells with the phorbol ester, phorbol 12-myristate 13-acetate, stimulated the phosphorylation of two proteins with molecular weights of 170 and 210 kDa which were immunoprecipitated with the anti-phosphotyrosine antibody. Subsequent insulin stimulation increased the phosphorylation of the 210 kDa protein, but the pp185 was not detected. Increasing the concentration of the human insulin receptor in the Chinese hamster ovary cells by transfection with a plasmid containing the human insulin receptor cDNA caused a higher level of tyrosine phosphorylation of the beta-subunit and the pp185. These data support the notion that the insulin signal may be transmitted to a cellular substrate (pp185) which may initiate insulin action at intracellular sites.

Human HER2 (neu) promoter: evidence for multiple mechanisms for transcriptional initiation

We localized the 5' region of the human gene HER2 in a cloned fragment of genomic DNA. This clone contained exons 1 to 4 of HER2, spanning the coding sequence for the first 191 amino acids. The promoter region of HER2 was identified upstream to exon 1 by nuclease S1 mapping and by a functional assay in which the promoter region drives the expression of a chloramphenicol acetyltransferase gene. The HER2 promoter is different from the promoter of the epidermal growth factor receptor gene (HER1), and the GC boxes which are typical of the promoter of the epidermal growth factor receptor gene are absent from the HER2 promoter. One major and two minor RNA start sites located at nucleotides 178, 244, and 257 upstream to the initiator ATG were identified. The first one is 21 and 70 base pairs downstream from typical TATAA and CAAT boxes, respectively. This indicates that transcription of HER2/neu can be regulated by a mechanism involving a TATA box, as well as by other unidentified regulatory elements.

Down-regulation of protein kinase C is due to an increased rate of degradation

The phorbol-ester-induced loss of protein kinase C that has been documented in many cell types appears to be a critical event in the generation of a cellular refractory state. We have investigated here the synthesis and degradation of the protein kinase C polypeptide in order to determine why its steady-state amounts are depleted in response to phorbol esters. These results indicate that depletion is due to an increased rate of degradation, with no change either in mRNA amounts or in rates of polypeptide synthesis.

Short-latency somatosensory evoked potentials in brain death

Simultaneous recording of somatosensory evoked potentials to median nerve stimulation above the upper and lower neck in brain-dead patients revealed that all cervical responses were preserved in 10%, whereas a marked reduction in amplitude or even loss of N 13b at the level of the C2 spinous process was observed in 90%. Of the patients, 55% revealed an additional loss of N 13a, recorded at the level of the C7 spinous process; in 15% all cortical and spinal evoked potentials were missing, but Erb's point waves were still normal. These results suggest two different origins of the main negative waves (N 13a and N 13b), recorded above the upper and lower cervical spinal cord. N 13a (C7) is supposed to arise in the dorsal horn at the C6/7 level, N 13b (C2) in the cervicomedullary junction.

A chimeric, ligand-binding v-erbB/EGF receptor retains transforming potential

Comparison of amino acid sequences from human epidermal growth factor (EGF) receptor and avian erythroblastosis virus erbB oncogene product suggests that v-erbB represents a truncated avian EGF receptor gene product. Although both proteins are transmembrane tyrosine kinases, the v-erbB protein lacks most of the extracellular ligand-binding domain and a 32-amino acid cytoplasmic sequence present in the human EGF receptor. To test the validity of the proposed origin of v-erbB and to investigate the functional significance of the deleted extracellular sequences, a chimeric gene encoding the extracellular and the transmembrane domain of the human EGF receptor joined to sequences coding for the cytoplasmic domain of the avian erbB oncogene product was constructed. When expressed in Rat1 fibroblasts, this reconstituted gene product (HER-erbB) was transported to the cell surface and bound EGF. Its autophosphorylation activity was stimulated by interaction with the ligand. Expression of the HER-erbB chimera led to anchorage-independent cell growth in soft agar and EGF-induced focus formation in Rat1 monolayers. Thus, it appears that v-erbB protein sequences in the chimeric receptor retain their transforming activity under the influence of the human extracellular EGF-binding domain.

High-affinity interleukin 2 binding by an oncogenic hybrid interleukin 2-epidermal growth factor receptor molecule

Both interleukin 2 (IL-2) and epidermal growth factor (EGF) receptors exist in two forms that differ with respect to affinity for their ligand. Only the high-affinity receptors appear to be responsible for the proliferation signal delivered upon binding of the growth factor. Fibroblasts transfected with IL-2 receptor cDNA generate only low-affinity receptors for IL-2, but fusion of membranes from these fibroblasts with T-cell membranes converts some receptors to high affinity, indicating the involvement of a T cell-specific factor in the generation of high-affinity receptors. We have constructed a chimeric cDNA molecule containing the extracellular IL-2-binding domain of the IL-2 receptor cDNA and the transmembrane and intracellular tyrosine kinase domains of the EGF receptor cDNA. When transfected into fibroblasts, this IL-2-EGF receptor cDNA generated high-affinity receptors for IL-2. Moreover, fibroblasts transfected with the chimeric molecule were morphologically transformed and produced rapidly growing tumors in nude mice.

Transforming potential of the c-fms proto-oncogene (CSF-1 receptor)

The c-fms proto-oncogene encodes a transmembrane glycoprotein that is probably identical to the receptor for the macrophage colony stimulating factor, CSF-1. Forty C-terminal amino acids of the normal receptor are replaced by 11 unrelated residues in the feline v-fms oncogene product, deleting a C-terminal tyrosine residue (Tyr969) whose phosphorylation might negatively regulate the receptor kinase activity. We show that the human c-fms gene stimulates growth of mouse NIH 3T3 cells in agar in response to human recombinant CSF-1, indicating that receptor transduction is sufficient to induce a CSF-1 responsive phenotype. Although cells transfected with c-fms genes containing either Tyr969 or Phe969 were not transformed, cotransfection of these genes with CSF-1 complementary DNA induced transformation, with c-fms(Phe969) showing significantly more activity than c-fms(Tyr969). In the absence of CSF-1, chimaeric v-fms/c-fms genes encoding the wild-type c-fms C terminus were poorly transforming, whereas chimaeras bearing Phe969 were as transforming as v-fms. Thus, the Phe969 mutation, although not in itself sufficient to induce transformation, activates the oncogenic potential of c-fms in association with an endogenous ligand or in conjunction with mutations elsewhere in the c-fms gene that confer ligand-independent signals for growth.

Human insulin receptors mutated at the ATP-binding site lack protein tyrosine kinase activity and fail to mediate postreceptor effects of insulin

Transfected Chinese hamster ovary cell lines were developed that expressed equivalent numbers of either normal human receptor or receptor that had alanine substituted for Lys-1018 in the ATP-binding domain of the beta subunit. The mutated receptor was processed into subunits and bound insulin but lacked protein tyrosine kinase activity. Five effects of insulin were assayed: deoxyglucose uptake, S6 kinase activity, endogenous protein-tyrosine phosphorylation, glycogen synthesis, and thymidine uptake. In each case, cells bearing normal human receptors were 10-100-fold more sensitive to insulin than the parental cells. Cells with the mutant receptor behaved like the parental cells with respect to S6 kinase activation, endogenous substrate phosphorylation, glycogen synthesis, and thymidine uptake, but their deoxyglucose uptake was significantly depressed and relatively insensitive to insulin. The analyses led to the following conclusions: substitution of alanine for lysine at amino acid 1018 inactivates the kinase activity of the receptor; a kinase-negative receptor can be properly processed and bind insulin; insulin-dependent deoxyglucose uptake, S6 kinase activation, endogenous substrate phosphorylation, glycogen synthesis, and thymidine incorporation into DNA are mediated by the normal but not by the kinase-deficient human receptor.

Structure and nucleotide sequence of a Drosophila melanogaster protein kinase C gene

Genomic and cDNA clones encoding a Drosophila melanogaster protein kinase C (PKC) homologue were identified using a bovine PKC cDNA probe. The cDNA clones contain a single open reading frame that encodes a 639 amino acid, 75-kd protein having extensive homology with bovine, human and rat PKC and homology with the kinase domains of other serine, threonine and tyrosine kinases. The Drosophila PKC gene is localized to region 53E of chromosome 2. The gene spans approximately 20 kb and contains at least 14 exons. Messenger RNA for PKC could not be detected in 0-3 h Drosophila embryos. Adult flies contain three PKC transcripts of 4.3, 4.0 and 2.4 kb.