Biomedical subjects

A Wells

Publications and source records attributed to A Wells.

At least 127 records · Page 7Linked to original sources

PubMed1996

Sickle cell acute chest syndrome associated with parvovirus B19 infection: case series and review.

Acute Chest Syndrome (ACS) continues to be a major source of morbidity and mortality among patients with sickle cell disease. It is characterized by the presence of pleuritic chest pain, fever, raises on lung auscultation, and pulmonary infiltrates on chest x-ray [Castro et all: Blood 84:643-649]. The pathophysiology of this disorder remains poorly understood leading to the descriptive term "Acute Chest Syndrome" designated by Charache et al. [Arch Intern Med 139:67-69, 1979]. Typical bacterial pathogens are seldom isolated in adults, although they play a significant role in the pathogenesis of this entity in children. Until recently, the technology to accurately study viral infection as a precipitating cause of ACS has been unavailable. Parvovirus B19 is being increasingly recognized as an important human pathogen, and has been established as the cause of transient "aplastic crisis" in patients with sickle cell diseases [Saarien et al: Blood 67:-11411-11417, 1986; Young: Sem Hematol 25:159-172, 1988]. We present three patients with hemoglobin SC variant of sickle cell disease who developed ACS in association with acute parvovirus B19 infection, one of which died of respiratory failure. Parvovirus B19 infection was established by polymerase chain reaction for parvovirus B19 DNA, and the presence of parvovirus B19 specific IgM antibodies. These cases suggest that parvovirus B19 may be associated with more than self-limited illness in patients with sickle cell disease, and that this ubiquitous virus may merit further study as a precipitating cause of ACS.

Acute Disease↗

PubMed1996

Receptor-mediated effects on ligand availability influence relative mitogenic potencies of epidermal growth factor and transforming growth factor alpha.

Epidermal growth factor (EGF) and transforming growth factor alpha (TGF alpha) elicit quantitatively different cell proliferation responses even though they act via a common receptor, the epidermal growth factor receptor (EGFR). We hypothesized that differential cellular trafficking of available ligand is responsible for the different mitogenic responses elicited by EGF and TGF alpha. Mitogenesis and ligand depletion were determined simultaneously in NR6 mouse fibroblasts expressing either wild-type (WT) or internalization-deficient cytoplasmic domain-truncated (c'973) EGFR. Thus we could determine the effects of both ligand-induced and low level constitutive ligand/receptor processing. For a given initial amount of growth factor, TGF alpha is a weaker stimulus than EGF in cells expressing either form of the EGFR. This difference in the mitogenic potencies correlates with increased depletion of TGF alpha observed during the growth assays. When this difference in ligand depletion is accounted for, or minimized, EGF and TGF alpha elicit quantitatively similar growth responses. Therefore, the relative mitogenic potencies of EGF and TGF alpha depend on ligand availability, as determined by the cellular trafficking of these ligands in conjunction with environmental circumstances. Interestingly, our data demonstrate that TGF alpha can be a less potent mitogenic stimulus than EGF under conditions where ligand availability is limited. Further, in our assays, differences in ligand processing are sufficient to explain the different mitogenic potencies of these growth factors in either of the receptor trafficking scenarios. Our results suggest a model of regulation of hormone responsiveness which favors dissociative ligands (such as TGF alpha) in receptor-limited situations and non-dissociative ligands (such as EGF) in the face of high receptor levels.

Animals↗

PubMed1996

Epidermal growth factor modulates cell attachment to hyaluronic acid by the cell surface glycoprotein CD44.

Cell adhesion to and migration through extracellular matrices (ECM) are critical events in tumor invasion and metastasis. Previous work by us had demonstrated that signaling of epidermal growth factor receptor (EGFR) confers an oncogenic phenotype on NR6 cells and that these cells when transfected with holo EGFR demonstrate greater motility and invasiveness than cells carrying a carboxy-terminal truncated EGFR. Recently, a cell surface glycoprotein, CD44, has been implicated in cell-ECM adhesion involved in tumor cell migration, signal transduction, and metastasis. We investigated whether EGF regulates cellular interactions with ECM components, and in particular, hyaluronate, by modulating CD44 expression. In vitro cell attachment assays on hyaluronate-coated plates demonstrated similar basal level of binding (approximately 33%) for murine NR6 parental cells devoid of endogenous EGFR (P) or expressing wild-type EGFR (WT), while a time-dependent increase in binding was observed in WT cells stimulated with EGF. Additionally, utilizing monoclonal antibody blocking assays, CD44, but not EGFR, was shown to be directly involved in this attachment. Both WT and P cells possessed equivalent 95 kDa bands on immunoblots, corresponding to CD44. The existence of CD44 mRNA was verified by RT-PCR using synthetic oligonucleotides in which a 1.1 kb cDNA was detected in both cell lines and confirmed by DNA sequencing. After 24-h exposure to exogenous EGF, an increase in CD44 protein and mRNA expression was found in WT cells, but not in P cells, supporting the contention that a functional EGFR signaling pathway is required for CD44 regulation. Thus, EGF stimulates cell binding to hyaluronate in vitro by regulating CD44 expression.

Animals↗

PubMed1996

EGF receptor signaling enhances in vivo invasiveness of DU-145 human prostate carcinoma cells.

Carcinomas of the prostate and other lineages often present an autocrine stimulatory loop acting via the EGF receptor (EGFR). We have recently shown that EGFR-mediated signals enhance DU-145 prostate carcinoma cell transmigration of an extracellular matrix in vitro, and that this increased invasiveness was independent of proteolytic degradation of the matrix (Xie et al., 1995, Clin Exp Metastasis, 13, 407). To determine whether up-regulated EGFR signaling promotes tumor progression in vivo and to define the EGFR-induced cell property responsible, we inoculated athymic mice with genetically-engineered DU-145 cells. Parental DU-145 cells and those transduced to overexpress a full-length wild type (WT) EGFR formed tumors and metastasized to the lung when inoculated in the prostate and peritoneal cavity. The WT DU-145 tumors were more invasive. DU-145 cells expressing a mitogenically-active, but motility-deficient (c'973) EGFR formed small, non-invasive tumors without evidence of metastasis. All three sublines demonstrated identical, EGFR-dependent rates of cell growth in vitro, suggesting that the differential invasiveness was not due to altered growth rates. To determine whether cell motility may be, in part, responsible for tumor invasiveness, we treated WT DU-145 intraperitoneal tumors with a pharmacologic agent (U73122) which blocks EGFR-mediated cell motility but not mitogenesis. Under this treatment regimen, the WT DU-145 cells formed tumors of similar numbers and size to those formed without treatment; however, these tumors were much less invasive. These data suggest that EGFR-mediated cell motility is an important mechanism involved in tumor progression, and that this cell property may represent a novel target to limit the spread of tumors.

Animals↗

PubMed1996

Levels of substance P and IgE decapeptide in nasal polyp fluid and matching sera: a preliminary study.

Sixteen unselected patients with nasal polyps had the levels of substance P and IgE decapeptide measured by ELISA in the oedema fluids and their matched sera. All 16 samples had low levels of substance P in their sera and had high level of substance P in eight samples of nasal polyp oedema. There was a considerable variation in the values of IgE decapeptide found in the sera but 14 polyp oedema fluids had high levels of IgE decapeptide. This study supports the idea that there is a linkage between the cellular and neurovascular responses. High levels of IgE decapeptide suggest that mast cell reactions occur in the majority of cases and that IgE may be implicated in the process of mast cell degranulation.

Enzyme-Linked Immunosorbent Assay↗

PubMed1996

Engineering epidermal growth factor for enhanced mitogenic potency.

Successful use of growth factors in therapeutic and bioprocessing applications requires overcoming two attenuation mechanisms: growth factor depletion and receptor down-regulation. Current ameliorative strategies use physiologically inappropriate high growth-factor concentrations, along with periodic media refeeding in vitro and reinjection or controlled-release devices in vivo. We demonstrate a new approach derived from understanding how these attenuation mechanisms arise from ligand/receptor trafficking processes. Specifically, a recombinant epidermal growth factor (EGF) mutant with reduced receptor binding affinity is a more potent mitogenic stimulus for fibroblasts than natural EGF or transforming growth factor alpha because of its altered trafficking properties.

3T3 Cells↗

PubMed1996

A role for gelsolin in actuating epidermal growth factor receptor-mediated cell motility.

Phospholipase C-gamma (PLC gamma) is required for EGF-induced motility (Chen, P., H. Xie, M.C. Sekar, K.B. Gupta, and A. Wells. J. Cell Biol. 1994. 127:847-857); however, the molecular basis of how PLC gamma modulates the actin filament network underlying cell motility remains undetermined. We propose that one connection to the actin cytoskeleton is direct hydrolysis of PIP2 with subsequent mobilization of membrane-associated actin modifying proteins. We used signaling-restricted EGFR mutants expressed in receptor-devoid NR6 fibroblast cells to investigate whether EGFR activation of PLC causes gelsolin mobilization from the cell membrane in vivo and whether this translocation facilitates cell movement. Gelsolin anti-sense oligonucleotide (20 microM) treatment of NR6 cells expressing the motogenic full-length (WT) and truncated c'1000 EGFR decreased endogenous gelsolin by 30-60%; this resulted in preferential reduction of EGF (25 nM)-induced cell movement by > 50% with little effect on the basal motility. As 14 h of EGF stimulation of cells did not increase total cell gelsolin content, we determined whether EGF induced redistribution of gelsolin from the membrane fraction. EGF treatment decreased the gelsolin mass associated with the membrane fraction in motogenic WT and c'1000 EGFR NR6 cells but not in cells expressing the fully mitogenic, but nonmotogenic c'973 EGFR. Blocking PLC activity with the pharmacologic agent U73122 (1 microM) diminished both this mobilization of gelsolin and EGF-induced motility, suggesting that gelsolin mobilization is downstream of PLC. Concomitantly observed was reorganization of submembranous actin filaments correlating directly with PLC activation and gelsolin mobilization. In vivo expression of a peptide that is reported to compete in vitro with gelsolin in binding to PIP2 dramatically increased basal cell motility in NR6 cells expressing either motogenic (WT and c'1000) or nonmotogenic (c'973) EGFR; EGF did not further augment cell motility and gelsolin mobilization. Cells expressing this peptide demonstrated actin reorganization similar to that observed in EGF-treated control cells; the peptide-induced changes were unaffected by U73122. These data suggest that much of the EGF-induced motility and cytoskeletal alterations can be reproduced by displacement of select actin-modifying proteins from a PIP2-bound state. This provides a signaling mechanism for translating cell surface receptor-mediated biochemical reactions to the cell movement machinery.

3T3 Cells↗

PubMed1996

Mitogenic signaling from the egf receptor is attenuated by a phospholipase C-gamma/protein kinase C feedback mechanism.

We recently demonstrated that epidermal growth factor receptor (EGFR)-mediated signaling of cell motility and mitogenesis diverge at the immediate post-receptor level. How these two mutually exclusive cell responses cross-communicate is not known. We investigated a possible role for a phospholipase C (PLC)-dependent feedback mechanism that attenuates EGF-induced mitogenesis. Inhibition of PLC gamma activation by U73122 (1 microM) augmented the EGF-induced [3H]thymidine incorporation by 23-55% in two transduced NR6 fibroblast lines expressing motility-responsive EGFR; increased cell division and mitosis was observed in parallel. The time dependence of this increase revealed that it was due to an increase in maximal incorporation and not a foreshortened cell cycle. Motility-responsive cell lines expressing a dominant-negative PLC gamma fragment (PLCz) also demonstrated augmented mitogenic responses by 25-68% when compared with control cells. PLCz- or U73122-augmented mitogenesis was not observed in three non-PLC gamma activating, nonmotility-responsive EGFR-expressing cell lines. Protein kinase C (PKC), which may be activated by PLC-generated second messengers, has been proposed as mediating feedback attenuation due to its capacity to phosphorylate EGFR and inhibit the receptor's tyrosine kinase activity. Inhibition of PKC by Calphostin C (0.05 microM) resulted in a 57% augmentation in the fold of EGF-induced thymidine incorporation. To further establish PKC's role in this feedback attenuation mechanism, an EGFR point mutation, in which the PKC target threonine654 was replaced by alanine, was expressed. Cells expressing these PKC-resistant EGFR constructs demonstrated EGF-induced motility comparable to cells expressing the threonine-containing EGFR. However, when these cells were treated with U73122 or Calphostin C, the mitogenic responses are not enhanced. These findings suggest a model in which PKC activation subsequent to triggering of motility-associated PLC gamma activity attenuates the EGFR mitogenic response.

Animals↗

PubMed1996

Role of cholecystokinin as a regulator of solid and liquid gastric emptying in humans.

The role of endogenous cholecystokinin (CCK) in the regulation of gastric emptying remains controversial. We therefore studied the effect of the CCK-A receptor antagonist loxiglumide on gastric emptying of a high-caloric solid-liquid meal in humans. Gastric emptying was assessed in eight volunteers using intravenous loxiglumide or placebo in a randomized double-blind order. Subjects were studied by a dual-headed gamma camera after ingestion of a pancake (570 kcal) labeled with 99mTc-sulfur colloid and 500 ml 10% glucose containing 111In-diethylenetriamine pentaacetic acid. Plasma CCK was measured by a specific radioimmunoassay. Loxiglumide markedly accelerated gastric emptying of both phases of the meal. The lag period was shortened by 26% (P < 0.03); the area under the emptying curve and half-emptying time of solid emptying were lowered by 19 and 24% (P < 0.02) and of liquid emptying by 18 and 24% (P < 0.04), respectively. Plasma CCK levels were higher during infusion of loxiglumide compared with placebo (P < 0.02). These data demonstrate that post-prandially released CCK is a major regulator of gastric emptying of physiological meals containing both solid and liquid components.

Adult↗

PubMed1996

Epidermal growth factor induces glucose storage in transgenic 3T3-L1 adipocytes overexpressing epidermal growth factor receptors.

3T3-L1 adipocytes represent an established physiological model for studying glucose uptake and storage. Overexpression of epidermal growth factor (EGF) receptors in these cells (200,000-250,000 receptors per cell) confers EGF-inducible GLUT4-mediated glucose uptake (17). We now report that EGF receptor (EGFR)-mediated signals can induce incorporation of glucose into glycogen and lipids in these cells. Incorporation into lipids was stimulated to similar levels by insulin or EGF in adipocytes expressing full-length (wild type) EGFR (2.05 +/- 0.26-fold for insulin vs. 2.28 +/- 0.15-fold for EGF). EGF induced incorporation into glycogen at roughly 60% of the level of insulin (4.53 +/- 0.57-fold for insulin vs. 2.76 +/- 0.25-fold for EGF); this corresponded with similarly lower levels of glycogen synthase activation by EGF relative to insulin stimulation. EGFR kinase activity was required for induced storage because a kinase-inactive (M721) EGFR failed to stimulate glucose incorporation into glycogen or lipids. EGFRs that lack all or part of the unique EGFR COOH-terminal tail induced glucose incorporation at levels similar to that stimulated by full-length (wild type) EGFR. Thus, domains in the COOH-terminal tail of the EGFR, which are necessary for stimulating glucose transport, are not required for signaling EGF-induced glucose storage. EGF-induced glucose storage did not require de novo protein synthesis, suggesting that EGFR signaling uses existing pathways in the adipocytes. These data demonstrate that signaling pathways for EGFR-mediated glucose storage and GLUT4-mediated glucose transport diverge at the receptor level. Thus, EGF-induced glucose storage can be achieved in the absence of induced GLUT4-mediated glucose transport.

3T3 Cells↗

PubMed1995

Depressed and anxious moods mediate relations among perceived socialization, self-focused attention, and dysfunctional attitudes.

This study examined three factors that may influence cognitive vulnerability to depression and anxiety: (1) subjects' perceptions of their relationships with their parents and the climate in their family of origin (socialization); (2) self-focused attention (focusing attention inwardly, on the self); and (3) current symptoms of depression and anxiety. Subjects were 173 university undergraduates. Perceptions of unfavorable socialization and public self-consciousness were related to dysfunctional attitudes. However, nearly all these relations disappeared when depression and anxiety were controlled statistically. These results suggest that memories of negative experiences in one's family of origin, self-focused attention, depression and anxiety, and dysfunctional attitudes all may be indicators of latent negative schemas that have been activated, perhaps by recent stress.

Adolescent↗

PubMed1995

In vitro invasiveness of DU-145 human prostate carcinoma cells is modulated by EGF receptor-mediated signals.

Prostate carcinomas often present an autocrine stimulatory loop in which the transformed cells both express the EGF receptor (EGFR) and produce activating ligands (TGF alpha and EGF forms). Up-regulated EGFR signalling has been correlated with tumor progression in other human neoplasia; however, the cell behaviour which is promoted remains undefined. To determine whether an EGFR-induced response contributes to cell invasiveness, we transduced DU-145 human prostate carcinoma cells with either a full-length (WT) or a mitogenically-active but motility-deficient truncated (c'973) EGFR. The DU-145 Parental and two transgene sublines all produced EGFR and TGF alpha, but the transduced WT and c'973 EGFR underwent autocrine downregulation to a lesser degree, with more receptor remaining intact. DU-145 cells transduced with WT EGFR transmigrated a human amniotic basement membrane matrix (Amgel) to a greater extent than did Parental DU-145 cells (175 +/- 22%). Cells expressing the c'973 EGFR invaded through the Amgel only to about two thirds the extent of the Parental cells (62 +/- 23%). A monoclonal antibody which prevents ligand-induced activation of EGFR decreased the invasiveness of WT-expressing cells by half and Parental cells by a fifth, but had little effect on the invasiveness of c'973-expressing cells; with the result that in the presence of antibody, all three cell lines transmigrated the Amgel to the same extent. The different levels of invasiveness between the three sublines were independent of cell proliferation. These findings demonstrated that EGFR-mediated signals increase tumor cell invasiveness and suggested that domains in the carboxy-terminus are required to signal invasiveness. As an initial investigation into the mechanisms underlying the EGFR-mediated enhanced invasiveness, we determined whether these cells presented different collagenolytic activity, as the major constituents of Amgel are collagen types I and IV. All three sublines secreted easily detectable levels of gelatin-directed proteases and TIMP-1, with WT cells secreting equivalent or lower levels of proteases. The proteolytic balance in these cells did not correlate with invasiveness. These data suggest that the TGF alpha-EGFR autocrine loop promotes invasiveness and that this is accomplished by signalling cell properties other than differential secretion of collagenolytic activity.

Carcinoma↗

PubMed1995

Worry and the incubation of intrusive images following stress.

This study investigated the effects of post-event processing on intrusive images following exposure to stress. It was hypothesized that ruminative activity, especially verbal worry about a stressor leads to an incubation of intrusions. Five groups which differed in the use of post-event processing strategies were used to test for a hypothesized co-joint mechanism underlying the effect. Worrying about a stressor for a period of 4 min after exposure led to significantly more intrusions in the next 3 days than a settle-down control condition. The strategies of imaging about the stressor, distraction, and worrying about usual concerns, produced a significant incremental linear pattern of intrusions across these groups. The pattern of results was as predicted by a co-joint model in which incubation results from 'tagging' of memories and blocked emotional processing. The clinical implications of these findings are briefly discussed.

Adolescent↗

PubMed1995

The effect of acute (60 minute) insulin stimulation upon human skeletal muscle glycogen synthase and protein phosphatase-1 in non-insulin-dependent diabetic patients and control subjects.

Previous studies have established that activation of muscle glycogen synthase (GS) is abnormal in non-insulin-dependent diabetes mellitus (NIDDM). Insulin-mediated activation of GS depends upon protein phosphatase-1 (PP1), which dephosphorylates the relevant sites of GS. In order to determine whether defects in PP1 activation cause subnormal activation of GS or whether PP1 activation itself is normal, we administered a short insulin infusion to 8 NIDDM subjects and 8 healthy controls matched for gender, age, and body mass index (BMI). GS fractional activity and PP1 activity were determined in biopsies taken from the gastrocnemius muscle before and after 60 min insulin infusion (0.1 U kg h-1). In the NIDDM group, muscle GS fractional activity was 6.8 +/- 1.6 and 10.0 +/- 1.5% (mean +/- SEM) (p = 0.11) before and after insulin infusion. In the control group, muscle GS fractional activity increased from 7.3 +/- 2.0 to 13.3 +/- 2.7% (p < 0.02). PP1 activity had returned towards basal levels after insulin infusion; NIDDM group 156 +/- 24.7 to 184.1 +/- 28.1 U mg-1; control group 220.8 +/- 30.1 to 233.8 +/- 29.8 U mg-1. In the NIDDM group there was a positive correlation between the increases in GS fractional activity and PP1 activity following insulin stimulation r = 0.77; p < 0.025). These data indicate that in vivo insulin-dependent activation of muscle PP1 is transient in normal subjects but is delayed in NIDDM. The defect in GS activation in NIDDM is likely to be proximal to PP1 in the pathway of transmission of the insulin signal.

Biopsy↗

PubMed1995

Epidermal growth factor (EGF) receptor carboxy-terminal domains are required for EGF-induced glucose transport in transgenic 3T3-L1 adipocytes.

Insulin-stimulated glucose transport in adipocytes is mediated by the insulin receptor. To ascertain whether a related receptor could also trigger this response, the epidermal growth factor (EGF) receptor (EGFR) was introduced into adipocytes. 3T3-L1 fibroblasts were infected by a retroviral construct encoding either the full-length (WT) or a carboxy-terminal truncated (c'973) human EGFR; truncation of the amino acids distal to 973 removes all autophosphorylation motifs. After selection and conversion to adipocytes, the level of EGFR expression was retained in infectant adipocytes (150,000 and 250,000/cell, respectively), but not in the parental 3T3-L1 adipocytes (< 5000/cell). WT and c'973 EGFR exhibited ligand-dependent tyrosine kinase activity and stimulated mitogen-activated protein kinase activity equivalently; neither phosphorylated insulin receptor substrate-1. WT EGFR, but not c'973 EGFR, underwent ligand-induced autophosphorylation. EGF did not stimulate tyrosine phosphorylation of the insulin receptor or insulin receptor substrate-1. EGF had a minimal effect on glucose transport by parental 3T3-L1 adipocytes. Glucose transport in the WT EGFR adipocytes was stimulated equivalently by insulin and EGF; exposure to insulin and EGF in combination did not result in augmented transport. Glucose transport in the c'973 EGFR adipocytes was stimulated by insulin, but not by EGF. GLUT4 was translocated to the plasma membrane to a similar extent in response to insulin or EGF in the WT EGFR adipocytes; only insulin caused a significant GLUT4 translocation in the parental or c'973 EGFR adipocytes. These data suggest that the insulin and EGF signaling pathways that lead to glucose transport converge in these adipocytes down-stream of the insulin receptor, and that activation of this pathway requires signaling motifs in the carboxy-terminus of the EGFR. This model system represents a novel approach with which to dissect signal transduction pathways in terminally differentiated adipocytes.

3T3 Cells↗

PubMed1994

Qualitative dimensions of normal worry and normal obsessions: a comparative study.

Despite the crucial role typically given to negative thoughts in cognitive conceptualizations of emotional problems, few studies have compared the characteristics of varieties of such thoughts. The present study compared the process features of naturally occurring worries and obsessions in a non-patient group. Analyses of variance revealed several significant differences between these types of thought. The relationship between worries and obsessions, and the clinical and conceptual importance of the observed differences is briefly discussed.

Adult↗

PubMed1994

The Thought Control Questionnaire: a measure of individual differences in the control of unwanted thoughts.

Previous research has suggested that unpleasant and unwanted thoughts are a frequent experience in both normal and clinical populations. This paper describes the development and validation of a questionnaire that assesses strategies for controlling such thoughts. Analyses of the Thought Control Questionnaire (TCQ) demonstrated five replicable factors: Distraction; Social Control; Worry; Punishment and Reappraisal. Significant associations were found between the punishment and worry subscales of the TCQ and various measures of emotional vulnerability and perceptions of impaired control over cognition. The implications of these findings are discussed in relation to the literature on thought suppression, worry and mental self-regulation.

Adaptation, Psychological↗

PubMed1994

Cell movement elicited by epidermal growth factor receptor requires kinase and autophosphorylation but is separable from mitogenesis.

The EGF receptor (EGFR) upon activation signals increased cell movement. However, the domains within the receptor, and the pathway which trigger movement are undefined. We expressed EGFR mutants at physiologic levels in receptor-devoid NR6 cells to investigate this biologic response. The receptors possessed kinase activity and underwent autophosphorylation as predicted by primary amino acid sequence. EGF-induced cell motility was assessed in vitro by excess migration into an acellular area and colony scatter in the presence of saturating concentrations of EGF. Wild-type (WT)-EGFR signaled increased motility. However, replacing the conserved lysine721 with methionine resulted in a kinase-inactive receptor which did not elicit movement. Removal of the entire terminus by truncation (c'973) also abrogated ligand-induced motility. Thus, we concentrated on the carboxy-terminal domains. EGF-induced movement was seen with a less-truncated mutant (c'1000) that contained a single autophosphorylated tyrosine (tyrosine992). Other mutants, c'991 and c'1000F992, in which this tyrosine was removed did not signal motility. Fusion mutants which presented other autophosphorylated tyrosine domains also exhibited EGF-induced movement. These findings suggested that the presence of both an autophosphorylated tyrosine signaling domain and the kinase activity are necessary for this biologic response. All kinase-positive mutants signaled cell proliferation but only those that contained autophosphorylatable tyrosines induced movement. The motility responses mediated by these EGFR were identical in the presence or absence of mitomycin-C, at a dose (0.5 micrograms/ml) which completely inhibited cell proliferation. On the other side, D-actinomycin (50 ng/ml) blocked EGF-induced motility but did not affect thymidine incorporation. Thus, EGF-induced mitogenesis and cell motility are mediated through different pathways.

Amino Acid Sequence↗