Expression cloning of human EGF receptor complementary DNA: gene amplification and three related messenger RNA products in A431 cells

Immunocytochemical and biochemical analysis of epidermal growth factor receptor expression in human breast cancer tissues: relationship to estrogen receptor and lymphatic invasion

Expression of epidermal growth factor receptor (EGFR) and estrogen receptor (ER) was examined by an immunocytochemical assay (ICA) using serial cross-sections of human breast cancer tissues. Immunocytochemical results were compared with those obtained by biochemical competitive binding assay and with histological lymphatic invasion. EGFR was evaluated as positive in 17 (34.0%) out of 50 primary tumors by ICA. A significant inverse relationship of the proportion of stained cells between EGFR and ER was demonstrated. In more than one-half of the tumors that were positive for both EGFR and ER, these 2 receptors were inversely stained in relation to the distribution. In ER-negative cells, EGFR expression was more marked than in ER-positive cells. Biochemical data confirmed the immunocytochemical results, pointing to an inverse relationship between EGFR and ER content. EGFR status correlated well with the degree of lymphatic invasion but not with the number of lymph nodes with metastases.

Structure and expression of c-erbB-2 and EGF receptor genes in inflammatory and non-inflammatory breast cancer: prognostic significance

C-erbB-2 and epidermal growth factor receptor (EGFR) genes were independently shown to be associated with breast cancer progression. In this report, we have analyzed the structure and expression of these 2 genes in the same tumor specimens of a large series of breast cancers. Two clinical types of tumor were studied: inflammatory (IBC) and non-inflammatory breast cancers (NBC) obtained from 221 untreated patients at different clinical stages. Amplification and over-expression of the c-erbB-2 proto-oncogene were observed in 27% and 47% of tumors, respectively, and were strongly associated with breast cancers of the most unfavorable prognosis, namely IBC and NBC with multiple positive axillary nodes. EGFR gene was neither amplified nor rearranged. A restriction fragment length polymorphism (RFLP) for HindIII endonuclease was observed. EGFR transcripts were detected in 46% of tumors and observed more frequently in IBC than in NBC (p less than 0.02). In NBC the presence of EGFR transcripts increased linearly with lymph-node involvement and was associated with estrogen-receptor-negative tumors (p = 0.01). Analysis of both genes from the same tumor samples indicated that genes are associated with cancer aggressiveness. Furthermore, in NBC these 2 genes were independently activated, in contrast to IBC in which activated genes were negatively correlated, suggesting that c-erbB-2 and EGFR genes play different roles in NBC and IBC.

Retroviruses expressing different levels of the normal epidermal growth factor receptor: biological properties and new bioassay

Two retroviral DNAs that encode the normal human epidermal growth factor (EGF) receptor hEGFR have been generated by inserting a hEGFR cDNA into two different retroviral vectors. One DNA (pCO11-EGFR-neo) also contained a linked selectable marker gene (neoR). The other (pCO12-EGFR) only expresses hEGFR. When introduced into NIH3T3 cells, the two DNAs and the viruses derived from them induced a fully transformed phenotype, including focal transformation and growth in agar or low serum, but transformation depended entirely upon EGF being present in the growth medium. Compared with pCO11-EGFR-neo, pCO12-EGFR induced EGF-dependent transformation 2-5 times more efficiently and expressed higher numbers of receptors (4 x 10(5) vs. 1 x 10(5) EGF receptors per cell). The results indicate that transforming potential is directly related to the number of EGF receptors. In defined, serum-free medium that contained only very low concentrations of insulin (0.6 microgram/ml) and transferrin (0.6 micrograms/ml), hEGFR-virus infected cells were able to grow with EGF as the only growth factor. Moreover, daily incubation of the cells with EGF for only 30 min was sufficient to induce growth. NR6 cells, which lack endogenous EGF receptors, were transformed as efficiently as NIH3T3 cells by the hEGFR virus. The dose-dependent growth response to EGF of infected NR6 cells grown in serum-free medium can be used as a highly sensitive bioassay for the quantitative assessment of EGF and transforming growth factor type alpha (TGF alpha). This bioassay is at least as sensitive as previously reported radioimmunoassays and can measure a much wider concentration range (10 pg-100 ng/ml). Uninfected NR6 cells or NR6 cells infected by helper virus alone can be used as controls for the EGF specificity of growth stimulation.

Inhibition of stimulus-dependent epidermal growth factor receptor and transforming growth factor-alpha mRNA accumulation by the protein kinase C inhibitor staurosporine

The ability of staurosporine, a potent inhibitor of protein kinase C, to block certain cellular events initiated by 12-O-tetradecanoylphorbol-13-acetate (TPA) and epidermal growth factor (EGF) was examined. Treatment of MDA468 breast cancer cells with TPA decreases EGF binding to the cell surface and this effect is blocked by pretreatment with staurosporine with an IC50 of 30 nM. Either 10(-9) M EGF or 100 ng/ml TPA stimulated the accumulation of both EGF receptor and TGF-alpha mRNA and staurosporine (50 nM) completely abolished these mRNA accumulations. Staurosporine did not block EGF-stimulated tyrosine phosphorylation of its receptor as measured by immunoblotting with anti-phosphotyrosine antibodies. The ability of staurosporine to block the mRNA responses of either EGF or TPA suggests that these two agents have common signaling pathways and it implies a role for protein kinase C in the control of EGF receptor and TGF-alpha expression.

Modulation of epidermal growth factor receptor proto-oncogene transcription by a promoter site sensitive to S1 nuclease

The epidermal growth factor (EGF) receptor is the functional target of the mitogen EGF and the cellular homolog of the avian erythroblastosis virus erbB oncogene product. Regulation of expression of the proto-oncogene encoding the EGF receptor can be elucidated by studying the structure and function of the gene promoter outside the confines of the cell. Previously, we reported the isolation of the human EGF receptor gene promoter. The promoter is highly GC rich, contains no TATA or CAAT box, and has multiple transcription start sites. An S1 nuclease-sensitive site has now been found 80 to 110 base pairs (bp) upstream from the major in vivo transcription initiation site. Two sets of direct repeat sequences were found in this area; both conform to the motif TCCTCCTCC. When deletion mutations were made in this region of the promoter by using either Bal 31 exonuclease or S1 nuclease, we found that in vivo activity dropped three- to fivefold, on the basis of transient-transfection analysis. Examination of nuclear protein binding to normal and mutated promoter DNAs by gel retardation analysis and DNase I footprinting revealed that two specific factors bind to the direct repeat region but cannot bind to the S1 nuclease-mutated promoter. One of the specific factors is the transcription factor Sp1. The results suggest that these nuclear trans-acting factors interact with the S1 nuclease-sensitive region of the EGF receptor gene promoter and either directly or indirectly stimulate transcription.

Mega base map of the epidermal growth factor (EGF) receptor gene flanking regions and structure of the amplification units in EGF receptor-hyperproducing squamous carcinoma cells

We have established a mega base scale physical map of the 5'- and 3'-flanking regions of the epidermal growth factor (EGF) receptor gene using CpG-recognition rare-cutting restriction enzymes and pulsed-field gel electrophoresis. In this map, a methylation-free CpG island (HTF island) is located within an 8-kilobase pair (kb) EcoRI fragment which includes exon 1 of the EGF receptor gene. From this HTF island, a 390-kb NotI fragment was identified as the longest 5'-flanking region and a 540-kb MluI fragment as the longest 3'-flanking region. Utilizing this map information, we have analyzed the structure of the flanking regions of amplified EGF receptor genes which are found in various squamous carcinoma cells. Among seven cell lines tested, four cell lines carrying EGF receptor genes in amounts more than 20 times that of normal cells showed amplification together with large 5'- and 3'-flanking regions. The amplified 5'-flanking regions were rearranged in different forms but were distinct in each cell line. The amplified 3'-flanking regions were at least 540 kb in size and common to all the cell lines, except that A431 had rearrangement points within 540 kb downstream of the HTF island. Thus, the size of amplification units appears to be large and different in each cell line.

Increased epidermal growth factor receptor in multidrug-resistant human neuroblastoma cells

Multidrug-resistant human neuroblastoma cell lines obtained by selection with vincristine or actinomycin D from two independent clonal lines, SH-SY5Y and MC-IXC, have 3- to 30-fold more cell surface epidermal growth factor (EGF) receptors than the drug-sensitive parental cells as indicated by EGF binding assays and immunoprecipitation, affinity-labeling, and phosphorylation studies. Reversion to drug sensitivity in one line was accompanied by a return to the parental level of EGF receptor. SH-EP cells, a clone derived from the same neuroblastoma cell line as SH-SY5Y but which displays melanocyte rather than neuronal lineage markers, also express significantly more EGF receptor than SH-SY5Y cells. By nucleic acid hybridization analysis with a molecularly cloned probe, increased receptor level in multidrug-resistant cells was shown to be the result of higher levels of EGF receptor mRNA in drug-resistant than in drug-sensitive cells. The increased steady state amount of specific RNA did not result from amplification of receptor-encoding genes. A small difference was observed in the electrophoretic mobility under denaturing conditions of EGF receptor immunoprecipitated from drug-resistant and drug-sensitive cells. Quantitative and qualitative modulation of the EGF receptor might reflect alterations in the transformation and/or differentiation phenotype of the resistant cells or might result from unknown selective pressures associated with the development of multidrug resistance.

Modulation of epidermal growth factor receptor proto-oncogene transcription by a promoter site sensitive to S1 nuclease

The epidermal growth factor (EGF) receptor is the functional target of the mitogen EGF and the cellular homolog of the avian erythroblastosis virus erbB oncogene product. Regulation of expression of the proto-oncogene encoding the EGF receptor can be elucidated by studying the structure and function of the gene promoter outside the confines of the cell. Previously, we reported the isolation of the human EGF receptor gene promoter. The promoter is highly GC rich, contains no TATA or CAAT box, and has multiple transcription start sites. An S1 nuclease-sensitive site has now been found 80 to 110 base pairs (bp) upstream from the major in vivo transcription initiation site. Two sets of direct repeat sequences were found in this area; both conform to the motif TCCTCCTCC. When deletion mutations were made in this region of the promoter by using either Bal 31 exonuclease or S1 nuclease, we found that in vivo activity dropped three- to fivefold, on the basis of transient-transfection analysis. Examination of nuclear protein binding to normal and mutated promoter DNAs by gel retardation analysis and DNase I footprinting revealed that two specific factors bind to the direct repeat region but cannot bind to the S1 nuclease-mutated promoter. One of the specific factors is the transcription factor Sp1. The results suggest that these nuclear trans-acting factors interact with the S1 nuclease-sensitive region of the EGF receptor gene promoter and either directly or indirectly stimulate transcription.

Similarities in glycosylation and transport between the secreted and plasma membrane forms of the epidermal growth factor receptor in A-431 cells

We have studied the synthesis and oligosaccharide processing of the 110,000 dalton form of the epidermal growth factor (EGF) receptor that is secreted into the medium of A-431 cells. Its 90,000 dalton precursor is soluble within the lumen of intracellular membrane vesicles shortly after synthesis, indicating that it lacks a membrane anchor. Analysis of labeled glycopeptides reveals that the glycosylation of the 110,000 dalton, secreted receptor is very similar to that of the 170,000 dalton, plasma membrane receptor. Based on Concanavalin A-Sepharose elution profiles of its glycopeptides, the secreted receptor has both complex and high-mannose N-linked oligosaccharides. Also, like the plasma membrane receptor, the secreted receptor contains N-acetylgalactosamine residues in its complex chains. Not only are major features of oligosaccharide processing of the soluble and membrane-bound forms of the receptor similar, but the kinetics of transport to the cell exterior is the same for each. These data indicate that the glycosylation pattern and kinetics of cellular transport of the EGF receptor are determined by factors other than the sequence of its cytoplasmic and transmembrane domains.

Proliferation and differentiation of human squamous carcinoma cell lines and normal keratinocytes: effects of epidermal growth factor, retinoids, and hydrocortisone

Exposure of squamous carcinoma cell (SCC) lines, exhibiting high levels of epidermal growth factor (EGF) receptors, to EGF for 6 d caused a dose-dependent inhibition of cell proliferation. This EGF-induced inhibition of cell proliferation occurred under both low (0.06 mM) and normal (1.6 mM) Ca2+ concentrations. Furthermore, the extent of EGF-induced inhibition of cell proliferation seemed to be independent of the number of EGF-receptors. This conclusion is based on the notion that the various SCC lines exhibited an increasing number of EGF receptors accompanied by a decreasing ability to differentiate, whereas no relationship was observed with the EGF-induced inhibition of cell proliferation in these cell lines. Retinoids caused also a dose-dependent inhibition of cell proliferation. The effects of EGF and retinoids were additive, indicating that different regulatory mechanisms are involved. On the other hand, hydrocortisone caused a stimulation of SCC-proliferation, also independent of EGF. In contrast to SCC cells, EGF did not affect significantly the rate of proliferation of normal keratinocytes. However, the simultaneous addition of EGF and hydrocortisone resulted in a significant increase in the rate of keratinocyte proliferation only in cells grown under normal calcium conditions. Differentiation capacity of normal keratinocytes and SCC lines was not affected by EGF. Furthermore, the retinoid-induced decrease and hydrocortisone-induced increase of competence of cells to form cornified envelopes was not affected by EGF. These observations suggest that the action of retinoids and hydrocortisone on both cell proliferation and cell differentiation occurs independently of EGF receptors.

Anomalous binding of epidermal growth factor to A431 cells is due to the effect of high receptor densities and a saturable endocytic system

This study was conducted to determine how extraordinarily high numbers of epidermal growth factor receptors (EGF-R) affected the binding and internalization of EGF in the transformed cell line A431. I found that at low EGF concentrations, the kinetics of binding behaved as a nonsaturable, first-order process showing no evidence of multiple-affinity classes of receptors. However, EGF dissociation rates were strongly dependent on the degree of receptor occupancy in both intact cells and isolated membranes. This occupancy-dependent dissociation appears to be due to diffusion-limited binding. EGF-induced receptor internalization was rapid and first order when the absolute number of occupied receptors was below 4 x 10(3) min-1. However, at higher occupancies the specific internalization rate progressively declined to a final limiting value of 20% normal. The saturation of EGF-R endocytosis was specific since internalization of transferrin receptors was not affected by high concentrations of either transferrin or EGF. Saturation of EGF-R endocytosis probably involves a specific component of the endocytic pathway since fluid phase endocytosis increased coordinately with EGF-R occupancy. I conclude that there are several aspects of EGF-R dynamics on A431 cells are neither similar to the behavior of EGF-R in other cell types nor similar to the reported behavior of other hormone receptors. Although A431 cells have an extraordinary number of EGF-R, they do not seem to have corresponding levels of at least two other crucial cell surface components: one that mediates EGF-induced rapid receptor internalization and one that attenuates EGF-induced membrane responses. These factors, in addition to the presence of diffusion-limited binding at low EGF concentrations, are probably responsible for the appearance of multiple-affinity classes of receptors in this cell type.

Abnormally banded region in a poorly differentiated sarcoma is not correlated with amplification of c-MYC or c-MOS protooncogenes

A poorly differentiated sarcoma in a 32-year-old female revealed a large, abnormally banded region in one chromosome #8 in all metaphases. The modal karyotype was 46,XX, -8, +mar. Southern blot hybridization was performed with probes for two protooncogenes located in chromosome 8q (c-MYC and c-MOS). No amplification or rearrangement was observed to account for the cytogenetic abnormality.

Two independent mechanisms for escaping epidermal growth factor-mediated growth inhibition in epidermal growth factor receptor-hyperproducing human tumor cells

Human squamous cell carcinoma cell lines often possess increased levels of epidermal growth factor (EGF) receptor. The growth of these EGF receptor-hyperproducing cells is usually inhibited by EGF. To investigate the mechanism of EGF-mediated inhibition of cell growth, variants displaying alternate responses to EGF were isolated from two squamous cell carcinoma lines, NA and Ca9-22; these cell lines possess high numbers of the EGF receptor and an amplified EGF receptor (EGFR) gene. The variants were isolated from NA cells after several cycles of EGF treatment and they have acquired EGF-dependent growth. Scatchard plot analysis revealed a decreased level of EGF receptor in these ER variants as compared with parental NA cells. Southern blot analysis and RNA dot blot analysis demonstrated that the ER variants had lost the amplified EGFR gene. One variant isolated from Ca9-22 cells, CER-1, grew without being affected by EGF. CER-1 cells had higher numbers of EGF receptor than parental Ca9-22 but similar EGFR gene copy number. Flow cytometric analysis indicated an increase in ploidy and cell volume which may give rise to the increase in receptor number per cell. The EGF receptors on both Ca9-22 and CER-1 cells were autophosphorylated upon EGF exposure in a similar manner suggesting no obvious alteration in receptor tyrosine kinase. However, very efficient down-regulation of the EGF receptor occurred in CER-1 cells. These data suggest two independent mechanisms by which EGF receptor-hyperproducing cells escape EGF-mediated growth inhibition: one mechanism is common and involves the loss of the amplified EGFR genes, and another is novel and involves the efficient down-regulation of the cell-surface receptor.

A transcription factor active on the epidermal growth factor receptor gene

We have developed an in vitro transcription system for the epidermal growth factor receptor (EGFR) oncogene by using nuclear extracts of A431 human epidermoid carcinoma cells, which overproduce EGFR. We found that a nuclear factor, termed EGFR-specific transcription factor (ETF), specifically stimulated EGFR transcription by 5- to 10-fold. In this report, ETF, purified by using sequence-specific oligonucleotide affinity chromatography, is shown by renaturing material eluted from a NaDodSO4/polyacrylamide gel to be a protein with a molecular mass of 120 kDa. ETF binds to the promoter region, as measured by DNase I "footprinting" and gel-mobility-shift assays, and specifically stimulates the transcription of the EGFR gene in a reconstituted in vitro transcription system. These results suggest that ETF could play a role in the overexpression of the cellular oncogene EGFR.

Temperature-sensitive Chinese hamster cell mutant with a defect in glycoprotein synthesis: accumulation of the EGF receptor in the endoplasmic reticulum and the role of the glucose-regulated protein GRP78

A temperature-sensitive mutant of Chinese hamster fibroblasts with a defect in glycoprotein synthesis is investigated after transfection and amplification of the gene for the human EGF receptor. We demonstrate that at the nonpermissive temperature a partially glycosylated species of the receptor accumulates in the endoplasmic reticulum. The oligosaccharides present are the high mannose types, since they can be removed completely by treatment with endoglycosidase H. Pulse-chase experiments show that the abnormal species of the receptor cannot be chased to a form that is either resistant to endoglycosidase H, or altered in its mobility on SDS polyacrylamide gels. The abnormal species of the receptor appears within the first hour of a shift to the nonpermissive temperature, and no further changes are observed upon prolonged incubation of cells at 40 degrees C. However, after 3-4 hours immunoprecipitations of the receptor yield another protein, which has properties very similar, if not identical, to the glucose-regulated protein GRP78. The induction of this protein at 40 degrees C can be suppressed completely with an inhibitor of RNA synthesis, without any effect on the glycosylation defect, or on the accumulation of the EGF receptor in the endoplasmic reticulum.

Primary structure of the human follistatin precursor and its genomic organization

Follistatin is a single-chain gonadal protein that specifically inhibits follicle-stimulating hormone release. By use of the recently characterized porcine follistatin cDNA as a probe to screen a human testis cDNA library and a genomic library, the structure of the complete human follistatin precursor as well as its genomic organization have been determined. Three of eight cDNA clones that were sequenced predicted a precursor with 344 amino acids, whereas the remaining five cDNA clones encoded a 317 amino acid precursor, resulting from alternative splicing of the precursor mRNA. Mature follistatins contain four contiguous domains that are encoded by precisely separated exons; three of the domains are highly similar to each other, as well as to human epidermal growth factor and human pancreatic secretory trypsin inhibitor. The genomic organization of the human follistatin is similar to that of the human epidermal growth factor gene and thus supports the notion of exon shuffling during evolution.

Transformation of diploid human fibroblasts by transfection with the v-sis, PDGF2/c-sis, or T24 H-ras genes

Gene transfection techniques have provided powerful methods to examine the roles of cellular and retroviral oncogenes in the transformation process in rodent fibroblasts. However, the use of such techniques with diploid human fibroblasts has been limited. We have developed transfection procedures to reproducibly transfect such cells with oncogenes, and methods for the biological characterization of the transformants. We have shown that the v-sis and T24 H-ras oncogenes, as well as the platelet-derived growth factor gene (PDGF2/c-sis), are capable of inducing a transformed phenotype in normal diploid human fibroblasts, but are not capable of conferring infinite lifespan or making such cells tumorigenic.

Genetic markers on chromosome 7

Chromosome 7 is frequently associated with chromosome aberrations, rearrangements, and deletions. It also contains many important genes, gene families, and disease loci. This brief review attempts to summarise these and other interesting aspects of chromosome 7. With the rapid accumulation of cloned genes and polymorphic DNA fragments, this chromosome has become an excellent substrate for molecular genetic studies.

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.

Urinary epidermal growth factor concentrations in various human malignancies

We determined the concentrations of immunoreactive epidermal growth factor in the urine (U-irEGF) of 97 adult patients with various malignancies, including carcinomas of the urinary bladder, kidney, stomach, colon, rectum, breast, endometrium, uterine cervix, ovary, vagina, prostate, pancreas and thyroid, liposarcoma and skin melanoma. The relative U-irEGF concentrations (ng m-1 creatinine) were higher (P = 0.002) for the whole series of female patients than for healthy controls matched for sex and age. Such difference did not appear for male patients. The only specific group with a statistically supranormal U-irEGF concentration (P = 0.0005) comprised women with endometrial carcinoma of the uterus.

Expression of epidermal growth factor receptor proto-oncogene mRNA in regenerating rat liver

The expression of EGF receptor mRNAs in regenerating rat liver was measured using two nonoverlapping cDNA probes for the human gene from a highly conserved region. These probes (pE7 and pE62) both hybridized to RNA species of 10 and 6 kb. The 10 and 6 kb RNA species were shown to decrease in the first 12 hours after partial hepatectomy. However, significant increases above control levels were noted at 24h and 72h. The level of alpha-actin mRNA increased as has been previously reported. These results suggest that a transcriptional and/or a posttranscriptional regulatory mechanism exists in regenerating rat liver with respect to EGF receptor gene expression.

Close association between interleukin 2 receptor mRNA expression and human T cell leukemia/lymphoma virus type I viral RNA expression in short-term cultured leukemic cells from adult T cell leukemia patients

Human T cell leukemia/lymphoma (T-lymphotropic) virus type I (HTLV-I) infection has been considered to be closely associated with the leukemogenesis of adult T cell leukemia (ATL), in which interleukin 2 (IL-2) receptors are abnormally expressed. In this study, however, Southern blot analysis revealed no gross rearrangement or obvious amplification of the IL-2 receptor gene in ATL leukemic cells, indicating that abnormal IL-2 receptor expression in ATL is not due to the structural change of its gene. Hence, we studied the expression of the IL-2 receptor and HTLV-I at the RNA level during short-term cultures of leukemic cells from 9 ATL patients. Cytoplasmic dot hybridization and Northern hybridization revealed that fresh leukemic cells from seven of nine patients expressed a small amount of IL-2 receptor mRNA but HTLV-I RNA was undetectable in all cases. After cultures for up to 7 d, both IL-2 receptor mRNA and HTLV-I RNA (including pX message) expression concomitantly increased, whereas the amounts of other cellular genes, except for beta-actin, did not. The increases in their RNA expression were inhibited by early addition (within 12 h after the beginning of the culture) of cycloheximide, indicating that these increases are mediated by newly synthesized protein(s). These results strongly suggested that IL-2 receptor expression is closely associated with HTLV-I expression in leukemic cells from ATL patients.

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.

Epidermal-growth-factor-dependent transformation by a human EGF receptor proto-oncogene

The epidermal growth factor (EGF) receptor gene EGFR has been placed in a retrovirus vector to examine the growth properties of cells that experimentally overproduce a full-length EGF receptor. NIH 3T3 cells transfected with the viral DNA or infected with the corresponding rescued retrovirus developed a fully transformed phenotype in vitro that required both functional EGFR expression and the presence of EGF in the growth medium. Cells expressing 4 x 10(5) EGF receptors formed tumors in nude mice, while control cells did not. Therefore, the EGFR retrovirus, which had a titer on NIH 3T3 cells that was greater than 10(7) focus-forming units per milliliter, can efficiently transfer and express this gene, and increased numbers of EGF receptors can contribute to the transformed phenotype.

Analysis of the protein glycosylation defect of a temperature-sensitive cell cycle mutant by the use of mutant cells overexpressing the human epidermal growth factor receptor after transfection of the gene

A temperature-sensitive mutant with a defect in glycoprotein synthesis and a cell cycle (G1)-specific arrest at the nonpermissive temperature (Tenner et al., J. Cell. Physiol., 90:145-160, 1977; Tenner and Scheffler, J. Cell. Physiol., 98:251-266, 1979) was investigated further after a human epidermal growth factor (EGF) receptor gene had been transfected and amplified in these cells. While a temperature shift-up lead to an immediate arrest in the biosynthesis of mature EGF receptor and its appearance on the plasma membrane, the observed turnover of the preexisting receptor was too slow to account for the arrest of DNA synthesis in these mutant cells. Tunicamycin could in fact mimic the effect of a temperature shift on the biosynthesis of EGF receptor, but it did not have the same rapid effect on DNA synthesis and cell cycle progression. These mutants have also been shown to induce a set of stress proteins or glucose-regulated proteins, GRPs (Lee et al., J. Cell. Physiol., 129:277-282, 1986). The question is addressed whether the defect in glycoprotein synthesis is the primary defect and a possible cause of the induction of the GRPs, or whether a more basic defect at the level of the endoplasmic reticulum (ER) is responsible for the complex phenotype of the mutant. Our results argue in favor of a primary defect which indirectly affects N-linked glycosylation of proteins, as well as several other functions associated with the ER. We hypothesize that the defect affects the calcium distribution between ER and cytosol, since the calcium ionophore A23187 has an effect similar to that of a temperature shift.

EGF-dependent phosphorylation of the EGF receptor in plasma membranes isolated from young and senescent WI-38 cells

Tyrosine-specific phosphorylation of the receptor for epidermal growth factor (EGF) in plasma membranes isolated from WI-38 cells is EGF-dependent and occurs to an equivalent extent and on identical tryptic peptides in preparations from cells of various in vitro ages. There is a marked reduction, however, in phosphorylation of receptor molecules from senescent as compared with young WI-38 cells, if enzyme activity is assayed in an immune complex following solubilization of plasma membranes with Nonidet P-40 (NP-40). Differences in the level of receptor phosphorylation in young vs. senescent NP-40 extracts are not resolved by changing the temperature at which the assay is performed, or the length of incubation. Moreover, addition of NP-40 or chloroform-methanol extracts of young cells to assays measuring receptor phosphorylation in senescent cell NP-40 preparations does not augment the senescent enzyme activity. The immunopurified senescent receptor is, however, capable of catalyzing phosphorylation of exogenous substrates. These results indicate that the loss of receptor autophosphorylation in solubilized preparations may result from a differential sensitivity of the senescent cell receptor to the detergent. This finding provides a marker for senescence and suggests subtle changes in protein structure, conformation, or regulation of the EGF receptor in senescent cells.

On the tertiary structure of the extracellular domains of the epidermal growth factor and insulin receptors

Alignment of the sequences, the identification of conserved residue patterns and secondary structure predictions indicate that the extra-cellular regions of the human and Drosophila epidermal growth factor (EGF), c-erb-B2 and human insulin receptors each contain two large, homologous domains (L) which are probably comprised of at least four short alpha-helices followed by turns of conserved length and beta-strands. In the human and Drosophila EGF and c-erb-B2 receptors these homologous domains are each followed by a series of smaller cystine-rich domains (S) to give a gene-duplicated structure of L1S11S12S13L2S21S22S23. In the human insulin receptor, the second series of cystine domains is replaced by a different sequence. These duplicated structures are probably organised as a pseudo-symmetrical dimer. There are two 'hyper-variable' regions, one at the end of the large domains and one in the cystine-rich sequences, which are candidates for hormone or growth-factor binding.

Increased expression of the epidermal growth factor receptor gene in malignant gliomas is invariably associated with gene amplification

Primary malignant gliomas from 63 patients were analyzed to determine the relationship between amplification of the gene encoding the epidermal growth factor receptor (EGFR) and expression of the corresponding mRNA. Twenty-four tumors were found to have amplified the EGFR gene and amplification of other genes occurred in three additional tumors. Hybridization with synthetic RNA probes was used to quantitate mRNA levels in situ. All 24 tumors with amplification of the EGFR gene had high levels of expression of this gene, while none of the 39 tumors without amplification had increased levels. This shows that, in human gliomas, large increases in the expression of the EGFR gene are invariably associated with alterations in gene structure.

Molecular cloning of a brain-specific calcium/calmodulin-dependent protein kinase

A calcium/calmodulin-dependent protein kinase type II (CaM-K) alpha-subunit cDNA has been cloned from rat brain. This enzyme is encoded by a 5.1-kilobase mRNA expressed exclusively in the brain. Hybridization histochemistry reveals that the CaM-K mRNA expression corresponds to the distribution of the immunoreactive alpha-subunit protein, suggesting that the high enzyme levels in specific brain areas reflect regional differences in gene expression. The sequence of CaM-K alpha-subunit cDNA indicates a 478-amino acid (54-kDa) protein with three functional domains. The domain organization suggests a structural model for calcium/calmodulin-dependent and independent states that might subserve short- and long-term responses to transient stimuli.

Epidermal growth factor and its receptor

Epidermal growth factor (EGF) binds with high affinity and specificity to a single site on the external domain of its transmembrane receptor to activate the tyrosine protein kinase activity of its cytoplasmic portion. The EGF receptor gene is amplified and over-expressed in several human tumors, suggesting that increased concentrations of the proto-oncogene leads to constitutive activity similar to that seen with oncogene erb B. Synthesis and degradation of the EGF receptor are regulated, in addition, covalent modification by phosphorylation regulates activity of the receptor protein. Intramolecular self-phosphorylation of Tyr1173 removes a competitive inhibitory constraint to enhance phosphorylation of substrates. Phosphorylation of Thr654 by protein kinase C decreases high affinity EGF binding and EGF-stimulated tyrosine protein kinase activity, providing a mechanism for heterologous regulation of the EGF receptor by tumor promoters and other ligand X receptor complexes. Extensive regulation contributes to normal growth control, abrogation of regulatory controls contributes to uncontrolled growth as seen with erb B transformation and EGF receptor gene amplification in human tumors.

Epidermal growth factor receptor gene-amplified MDA-468 breast cancer cell line and its nonamplified variants

We have recently reported (J. Filmus, M. N. Pollak, R. Cailleau, and R. N. Buick, Biochem. Biophys. Res. Commun. 128:898-905, 1985) that MDA-468, a human breast cancer cell line with a high number of epidermal growth factor (EGF) receptors, has an amplified EGF receptor gene and is growth inhibited in vitro pharmacological doses of EGF. We have derived several MDA-468 clonal variants which are resistant to EGF-induced growth inhibition. These clones had a number of EGF receptors, similar to normal human fibroblasts, and had lost the EGF receptor gene amplification. Karyotype analysis showed that MDA-468 cells had an abnormally banded region (ABR) in chromosome 7p which was not present in the variants. It was shown by in situ hybridization that the amplified EGF receptor sequences were located in that chromosome, 7pABR. Five of the six variants studied were able to generate tumors in nude mice, but their growth rate was significantly lower than that of tumors derived from the parental cell line. The variant that was unable to produce tumors was found to be uniquely dependent on EGF for growth in soft agar.

Regulation of transmembrane signaling by receptor phosphorylation

At least two major effects of receptor phosphorylation have been identified--regulation of receptor function, and regulation of receptor distribution. In many cases where phosphorylation directly alters the functions of receptors, this appears to be in a negative direction. Such decreases in receptor activity may reflect reduced ability to interact with biochemical effectors (e.g., the beta-adrenergic receptor, rhodopsin), reduced affinity for binding agonist ligands (EGF,IGF-I, insulin receptors) or reduced enzymatic activity (e.g., tyrosine kinase activity of the insulin or EGF receptor). In all instances, these negative modulations are associated with phosphorylation of serine and/or threonine residues of the receptor proteins. In contrast, the tyrosine kinase receptors also appear to be susceptible to positive modulation by phosphorylation. With these receptors, autophosphorylation of tyrosine residues may lead to enhanced protein-tyrosine kinase activity of the receptors and increased receptor function. In addition, the subcellular distribution of a receptor may be regulated by its phosphorylation status (e.g., the beta-adrenergic receptor, receptors for insulin, EGF, IGF-II, and transferrin). The emerging paradigm is that receptor phosphorylation may in some way promote receptor internalization into sequestered compartments where dephosphorylation occurs. The molecular and cellular mechanisms involved in translating changes in receptor phosphorylation into changes in receptor distribution remain to be elucidated. Moreover, the biological role of receptor internalization may be quite varied. Thus, in the case of the beta-adrenergic receptor, it may serve primarily as a mechanism for bringing the phosphorylated receptors into contact with intracellular phosphatases that dephosphorylate and resensitize it. By contrast, for the transferrin receptor and other receptors involved in receptor-mediated endocytosis, the internalization presumably functions to carry some specific ligand or metabolite into the cell. The role of phosphorylation in regulating receptor function dramatically extends the range of regulatory control of this important covalent modification.

Amplification of DNA sequences coding for the Na,K-ATPase alpha-subunit in ouabain-resistant C+ cells

We have studied the mechanism of cellular resistance to cardiac glycosides in C+ cells. C+ cells were resistant to ouabain and overproduced plasma membrane-bound Na,K-ATPase relative to parental HeLa cells. Overexpression of Na,K-ATPase in C+ cells correlated with increased ATPase mRNA levels and amplification (approximately 100 times) of the ATPase gene. Growth of C+ cells in ouabain-free medium resulted in a marked decline in ATPase mRNA and DNA levels. However, when cells were reexposed to ouabain, they proliferated and ATPase mRNA and DNA sequences were reamplified. Restriction analysis of C+ and other human DNA samples revealed the occurrence of rearrangements in the region of the Na,K-ATPase gene in C+ cells. Furthermore, C+ cells expressed an ATPase mRNA species not found in HeLa cells. These results suggest that amplification of the gene coding for Na,K-ATPase results in overproduction of Na,K-ATPase polypeptides. Amplification of the ATPase gene or the expression of new ATPase mRNA sequences or both may also be responsible for acquisition of the ouabain-resistant phenotype.