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

Epidermal growth factor regulates the expression of its own receptor

The epidermal growth factor (EGF) receptor gene is the cellular homolog of the avian erythroblastosis virus erbB oncogene. Control of EGF receptor expression determines cellular responsiveness to EGF and might play an important role in neoplastic development. Using RNA blot hybridization, we have found that exposure of human KB carcinoma cells to EGF results in elevated levels of EGF receptor mRNA. The phorbol ester 4 beta-phorbol 12-myristate 13-acetate also stimulates EGF receptor RNA accumulation. Immunoprecipitation of metabolically labeled (30 min) EGF receptor protein revealed that synthesis of new EGF receptor follows the increase in receptor RNA. Addition of cycloheximide together with EGF further enhances EGF receptor RNA accumulation. Results of nuclear runoff-transcription experiments suggest that the stimulatory effects of EGF and cycloheximide are most likely due to a posttranscriptional control mechanism.

The action of oncogenes in the cytoplasm and nucleus

As many as 40 distinct oncogenes of viral and cellular origin have been identified to date. Many of these genes can be grouped into functional classes on the basis of their effects on cellular phenotype. These groupings suggest a small number of mechanisms of action of the oncogene-encoded proteins. Some data suggest that, in the cytoplasm, these proteins may regulate levels of critical second messenger molecules; in the nucleus, these proteins may modulate the activity of the cell's transcriptional machinery. Many of the gene products can also be related to a signaling pathway that determines the cell's response to growth-stimulating factors. Because some of these genes are expressed in nongrowing, differentiated cells, the encoded proteins may in certain tissues mediate functions that are unrelated to cellular growth control.

Association of multiple copies of the N-myc oncogene with rapid progression of neuroblastomas

Eighty-nine patients with untreated primary neuroblastomas were studied to determine the relation between the number of copies of the N-myc oncogene and survival without disease progression. Genomic amplification (3 to 300 copies) of N-myc was detected in 2 of 16 tumors in Stage II, 13 of 20 in Stage III, and 19 of 40 in Stage IV; in contrast, 8 Stage I and 5 Stage IV-S tumors all had 1 copy of the gene (P less than 0.01). Analysis of progression-free survival in all patients revealed that amplification of N-myc was associated with the worst prognosis (P less than 0.0001); the estimated progression-free survival at 18 months was 70 per cent, 30 per cent, and 5 per cent for patients whose tumors had 1, 3 to 10, or more than 10 N-myc copies, respectively. Of 16 Stage II tumors, 2 with amplification metastasized, whereas only 1 of 14 without amplification did so (P = 0.03). Stage IV tumors with amplification progressed most rapidly: nine months after diagnosis the estimated progression-free survival was 61 per cent, 47 per cent, and 0 per cent in patients whose tumors had 1, 3 to 10, or more than 10 copies, respectively (P less than 0.0001). These results suggest that genomic amplification of N-myc may have a key role in determining the aggressiveness of neuroblastomas.

Amplification of a novel v-erbB-related gene in a human mammary carcinoma

The cellular gene encoding the receptor for epidermal growth factor (EGF) has considerable homology to the oncogene of avian erythroblastosis virus. In a human mammary carcinoma, a DNA sequence was identified that is related to v-erbB but amplified in a manner that appeared to distinguish it from the gene for the EGF receptor. Molecular cloning of this DNA segment and nucleotide sequence analysis revealed the presence of two putative exons in a DNA segment whose predicted amino acid sequence was closely related to, but different from, the corresponding sequence of the erbB/EGF receptor. Moreover, this DNA segment identified a 5-kilobase transcript distinct from the transcripts of the EGF receptor gene. Thus, a new member of the tyrosine kinase proto-oncogene family has been identified on the basis of its amplification in a human mammary carcinoma.

The neu gene: an erbB-homologous gene distinct from and unlinked to the gene encoding the EGF receptor

The neu oncogene, identified in ethylnitrosourea-induced rat neuroglioblastomas, had strong homology with the erbB gene that encodes the epidermal growth factor receptor. This homology was limited to the region of erbB encoding the tyrosine kinase domain. It was concluded that the neu gene is a distinct novel gene, as it is not coamplified with sequences encoding the EGF receptor in the genome of the A431 tumor line and it maps to human chromosome 17.

Structure and localization of genes encoding aberrant and normal epidermal growth factor receptor RNAs from A431 human carcinoma cells

A431 cells have an amplification of the epidermal growth factor (EGF) receptor gene, the cellular homolog of the v-erb B oncogene, and overproduce an aberrant 2.9-kilobase RNA that encodes a portion of the EGF receptor. A cDNA (pE15) for the aberrant RNA was cloned, sequenced, and used to analyze genomic DNA blots from A431 and normal cells. These data indicate that the aberrant RNA is created by a gene rearrangement within chromosome 7, resulting in a fusion of the 5' portion of the EGF receptor gene to an unidentified region of genomic DNA. The unidentified sequences are amplified to about the same degree (20- to 30-fold) as the EGF receptor sequences. In situ hybridization to chromosomes from normal cells and A431 cells show that both the EGF receptor gene and the unidentified DNA are localized to the p14-p12 region of chromosome 7. By using cDNA fragments to probe DNA blots from mouse-A431 somatic cell hybrids, the rearranged receptor gene was shown to be associated with translocation chromosome M4.

Differences in human skin between the epidermal growth factor receptor distribution detected by EGF binding and monoclonal antibody recognition

Two methods have been used to examine epidermal growth factor (EGF) receptor distribution in human scalp and foreskin. The first employed [125I]EGF viable explants and autoradiography to determine the EGF binding pattern while the second used a monoclonal antibody to the human EGF receptor to map the distribution on frozen skin sections of an extracellular epitope on the EGF receptor. The [125I]EGF binding experiments showed accessible, unoccupied EGF receptors to be present on the epidermal basal cells (with reduced binding to spinous cells), the basal cells of the hair shaft and sebaceous gland, the eccrine sweat glands, capillary system, and the hair follicle outer root sheath, generally similar in pattern to that previously reported for full-thickness rat skin and human epidermis. The same areas also bound EGF-R1 but in addition the monoclonal antibody recognized a cone of melanin containing presumptive cortex cells, excluding the medulla, lying around and above the upper dermal papilla of anagen hair follicles, epithelial cells around the lower dermal papilla region, and in some tissue samples the cell margins of the viable differentiating layers of the epidermis. In a control study, to clarify whether EGF-R1 could recognize molecules unrelated to the EGF receptor, the EGF binding and EGF-R1 recognition profiles were compared on cultures of SVK14 cells, a SV40 transformed human keratinocyte cell line. EGF binding and EGF-R1 monoclonal antibody distribution on these cells was found to be similar, indicating that, at least for SVK14 cells, EGF-R1 binding provides a reliable marker for EGF binding. Explanations for the discrepancies between these two methods for determining EGF receptor distribution in human skin are discussed, including the possibility that latent EGF receptors, unable to bind [125I]EGF, may be present in some differentiating epithelial compartments.

Translocation chromosome 7 of A431 cells contains amplification and rearrangement of EGF receptor gene responsible for production of variant mRNA

The epidermal growth factor (EGF) receptor, along with several oncogene protein products, possesses tyrosine-specific protein kinase activity. Furthermore, the EGF receptor has structural similarity to the putitive v-erb-B transforming protein. Because of these closely shared characteristics, it is important to elucidate the possible involvement of the EGF receptor in malignant transformation. The epidermal carcinoma cell line A431 exhibits an abnormally high number of EGF receptors, which is associated with the presence of translocation chromosome M4. Recently, A431 cells have been shown to contain amplified sequences for the EGF receptor gene(s) and also to produce a variant mRNA which diverges from the normal EGF receptor mRNA at the 3' end. Here we report, using the human EGF receptor cDNA probe pE7, that the chromosome M4 has a six- to sevenfold amplification of the EGF receptor gene. Furthermore, the presence of M4 in somatic cell hybrids correlates with the production of the variant 2.9-kb mRNA. This aberrant mRNA is apparently generated by an intrachromosomal rearrangement which was detected using as a probe a fragment of the pE15cDNA encoding the variant mRNA.

Amplified, overexpressed and rearranged epidermal growth factor receptor gene in a human astrocytoma cell line

We report here that SK-MG-3, a human astrocytoma cell line with a high number of epidermal growth factor (EGF) receptors, has an amplified and overexpressed EGF receptor gene. Northern blot analysis did not show any abnormal EGF receptor gene-related mRNA species. No amplification or rearrangement was noted in 21 other astrocytoma cell lines. In contrast to other cell lines that have EGF receptor gene amplifications, we have not detected inhibition of in vitro proliferation of the SK-MG-3 line by EGF.

Developmental changes in expression of the Drosophila melanogaster epidermal growth factor receptor gene

A Drosophila gene homologous to the human EGF receptor gene has recently been isolated and sequenced. Two transcripts, 7.6- and 7.1-kb long, encoded by this gene were identified in Drosophila melanogaster. The transcripts are present at low abundance in the maternal RNA stored in unfertilized eggs and in 2-hr-old embryos. The abundance of both transcripts increases sharply between 2 and 5 hr after egg deposition, it remains high throughout embryogenesis, and decreases again in the larval and pupal stages. In adult flies the two transcripts are expressed differentially. The 7.1-kb transcript is present during adulthood at the same level detected previously in pupal stage, but the abundance of the 7.6-kb transcript decreases substantially and it remains low during adulthood.

Characterization and sequence of the promoter region of the human epidermal growth factor receptor gene

The promoter region of the epidermal growth factor (EGF) receptor has been identified by in vitro transcription using EGF receptor genomic DNA fragments as template and by primer extension and nuclease S1 mapping using EGF receptor mRNA. Six transcriptional start sites were identified. DNA sequence analysis shows that the promoter region contains neither a "TATA box" nor a "CAAT box," has an extremely high G+C content (88%), and contains five CCGCCC repeats and four (TCC)TCCTCCTCC repeats. This promoter region is situated close to or within a DNase I-hypersensitive site in A431 human epidermoid carcinoma cells, which overproduce the EGF receptor. The EGF receptor gene promoter has some resemblance to the promoter of the hydroxymethylglutaryl-CoA reductase gene and the early promoter of simian virus 40. This similarity may offer a clue to the mechanism by which the receptor gene is regulated.

Cell-type-specific pattern of myc protooncogene expression in developing human embryos

The expression of viral oncogenes in cells transformed by acutely transforming retroviruses profoundly alters proliferation and differentiation in the target cell, suggesting that the cellular homologues of the viral oncogenes, the protooncogenes, have a role in normal cell proliferation and differentiation. To investigate the possible developmental role of protooncogenes in human embryogenesis, we have determined the spatial distribution of myc gene transcripts in early human embryos by using in situ hybridization of a labeled myc exon to thin sections. The results indicate a stage- and cell-type-specific regulation of c-myc gene expression in primarily epithelial cells of late first trimester embryos. Furthermore, the data suggest that the linkage between c-myc gene expression and cellular proliferation holds for only a restricted set of embryonic cells.

c-erbB activation in ALV-induced erythroblastosis: novel RNA processing and promoter insertion result in expression of an amino-truncated EGF receptor

ALV-induced erythroblastosis results from the specific interruption of the host oncogene, c-erbB, by the insertion of an intact provirus. Integrated proviruses are oriented in the same transcriptional direction as c-erbB, and expression of truncated c-erbB transcripts is observed. Evidence, including sequence analysis of cDNA clones, indicates that transcription of truncated c-erbB mRNA is initiated in the 5' LTR of the integrated provirus. This transcript is processed through a series of remarkable splicing reactions to yield viral gag and env sequences fused to erbB sequences. These results establish a novel pathway of promoter insertion oncogenesis that stands in contrast to the pathways used in the activation of c-myc in B lymphomas.

Structure and localization of genes encoding aberrant and normal epidermal growth factor receptor RNAs from A431 human carcinoma cells

A431 cells have an amplification of the epidermal growth factor (EGF) receptor gene, the cellular homolog of the v-erb B oncogene, and overproduce an aberrant 2.9-kilobase RNA that encodes a portion of the EGF receptor. A cDNA (pE15) for the aberrant RNA was cloned, sequenced, and used to analyze genomic DNA blots from A431 and normal cells. These data indicate that the aberrant RNA is created by a gene rearrangement within chromosome 7, resulting in a fusion of the 5' portion of the EGF receptor gene to an unidentified region of genomic DNA. The unidentified sequences are amplified to about the same degree (20- to 30-fold) as the EGF receptor sequences. In situ hybridization to chromosomes from normal cells and A431 cells show that both the EGF receptor gene and the unidentified DNA are localized to the p14-p12 region of chromosome 7. By using cDNA fragments to probe DNA blots from mouse-A431 somatic cell hybrids, the rearranged receptor gene was shown to be associated with translocation chromosome M4.

The c-fms proto-oncogene product is related to the receptor for the mononuclear phagocyte growth factor, CSF-1

The feline c-fms proto-oncogene product is a 170 kd glycoprotein with associated tyrosine kinase activity. This glycoprotein was expressed on mature cat macrophages from peritoneal inflammatory exudates and spleen. Similarly, the receptor for the murine colony-stimulating factor, CSF-1, is restricted to cells of the mononuclear phagocytic lineage and is a 165 kd glycoprotein with an associated tyrosine kinase. Rabbit antisera to a recombinant v-fms-coded polypeptide precipitated the feline c-fms product and specifically cross-reacted with a 165 kd glycoprotein from mouse macrophages. This putative product of the murine c-fms gene exhibited an associated tyrosine kinase activity in immune complexes, specifically bound murine CSF-1, and, in the presence of the growth factor, was phosphorylated on tyrosine in membrane preparations. The murine c-fms proto-oncogene product and the CSF-1 receptor are therefore related, and possibly identical, molecules.

Relationship between production of epidermal growth factor receptors, gene amplification, and chromosome 7 translocation in variant A431 cells

Synthesis of the epidermal growth factor (EGF) receptor has been analyzed in a series of variant A431 human epidermoid carcinoma cell clones reported to contain different amounts of EGF binding sites. The amount of EGF receptor protein, quantitated by immunoaffinity chromatography, and EGF receptor mRNA, quantitated by cDNA hybridization, were closely correlated to the extent of EGF receptor gene amplification. This correlation existed in variants selected for reduced EGF receptors and in revertants from those variants with increased EGF receptors. There was also a correlation between the frequency of translocation of chromosome 7, containing the EGF receptor gene, and EGF receptor protein. These results support gene amplification as the mechanism enhancing A431 cell EGF receptor protein and determining growth responses.

Dominant and recessive mitogen-nonproliferative variants of 3T3 cells

We have previously isolated 3T3 cell variants unable to respond to specific mitogens. In this report we analyze the dominant and/or recessive nature of these variants. Two independently isolated EGF nonproliferative variants are unable to bind EGF. Hybrids between 3T3R5 cells (thymidine kinase deficient, ouabain-resistant) and these variants express EGF receptors; the "EGF receptorless" phenotype of these variants is recessive. Hybrids between these two variants do not bind EGF; they are defective in a common, non-complementing function. A TPA nonproliferative 3T3 variant is also recessive; hybrids with 3T3R5 mount a mitogenic response to TPA. In contrast a fourth variant, which can neither bind labeled EGF nor respond to TPA, is dominant for both characteristics. Hybrids between this latter variant and 3T3R5 can neither bind EGF nor mount a mitogenic response to TPA.

Binding and processing of epidermal growth factor in Panc-I human pancreatic carcinoma cells

The binding of 125I-labeled epidermal growth factor (EGF) was studied in Panc-I human pancreatic carcinoma cells. At 37 degrees C, binding was rapid and associated with marked endocytosis of the ligand. Bound EGF was sequentially converted to a number of more acidic species as follows: pI 4.55 to pI 4.2, to pI 4.35, to pI 4.0. EGF internalization and processing were blocked at 4 degrees C. EGF did not alter cell growth when Panc-I cells were incubated in the presence of 2 to 10% serum. In contrast, when the serum concentration was lowered to 0.1%, EGF significantly enhanced cell replication after 6 days of culture.

High-frequency transduction of c-erbB in avian leukosis virus-induced erythroblastosis

Twenty-one cases of Rous-associated virus type 1-induced erythroblastosis have been analyzed for novel restriction endonuclease fragments of c-erbB. Twenty of the erythroleukemias contained novel c-erbB fragments; 10 of these were found to contain a proviral insertion in c-erbB, and 10 were found to have a new transduction of c-erbB. Each of the proviral insertions was in the same transcriptional orientation as c-erbB, and most appeared to have retained both long terminal repeats as well as 5' viral sequences that signal packaging of RNA into virions. Each of the new c-erbB transducing viruses had a characteristic EcoRI fragment that contained a spliced form of c-erbB sequences. When inoculated into 1-week-old chickens, the new transducing viruses caused rapid-onset erythroblastosis.

Expression of the receptor for epidermal growth factor correlates with increased dosage of chromosome 7 in malignant melanoma

Epidermal growth factor (EGF) receptor is expressed selectively by human melanoma cells which show the presence of an extra copy of chromosome 7. None of the cells of benign pigmented lesions (nevi) or radial growth phase (nonmetastatic) primary melanoma expressed EGF receptor and none of these cells showed an extra copy of chromosome 7. The results indicate that a single extra dose of a gene (for EGF receptor) may provide a selective advantage to cells in the late stages of tumorigenesis.

Coexpression of the sis and myc proto-oncogenes in developing human placenta suggests autocrine control of trophoblast growth

First trimester human placentas actively express the sis proto-oncogene, the structural gene for the B chain of platelet-derived growth factor (PDGF). Using the in situ hybridization technique, the 4.2 kb c-sis transcript has been localized to the cytotrophoblastic component, especially the highly proliferative and invasive cytotrophoblastic shell, paralleling the distribution of c-myc transcripts in early placenta. Explants of first trimester placenta release significant levels of PDGF-like activity into the medium under apparent developmental control. Moreover, cultured trophoblasts display abundant high-affinity PDGF receptors and respond to exogenous authentic PDGF by an activation of the c-myc gene and DNA synthesis. The developing human placenta may therefore represent a case of autocrine growth regulation in a normal tissue, in which cells bearing receptors for a growth factor can also synthesize and respond to that factor.

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 by EGF

Epidermal growth factor (EGF) has been noted to stimulate proliferation of a variety of normal and malignant cells including those of human breast epithelium. We report here that MDA-468, a human breast cancer cell line with a very high number of EGF receptors, is growth-inhibited at EGF concentrations that stimulate most other cells. The basis for the elevated receptor level is EGF receptor gene amplification and over-expression. An MDA-468 clone selected for resistance to EGF-induced growth inhibition shows a number of receptors within the normal range. The results are discussed in relation to a threshold model for EGF-induced growth inhibition.

Crystallization studies of cAMP-dependent protein kinase. Crystals of catalytic subunit diffract to 3.5 A resolution

The catalytic subunit of cAMP-dependent protein kinase from porcine heart has been crystallized in several different crystal forms. One of these forms diffracts to 3.5 A resolution. It is in monoclinic space group P2(1) with a = 64.24 A, b = 143.58 A, c = 48.40 A, alpha = gamma = 90 degrees and beta = 106.9 degrees.

Transmembrane orientation of glycoproteins encoded by the v-fms oncogene

The retroviral oncogene v-fms encodes a glycoprotein whose transport to the plasma membrane is required for transformation. Tryptic digestion of microsomes from transformed cells yielded membrane-protected amino-terminal fragments 40 kd smaller than intact molecules. These fragments were glycosylated, and they included v-fms-coded epitopes expressed at the cell surface. Deletion of the predicted membrane-spanning peptide generated polypeptides that were completely sequestered within microsomes. The mutant glycoproteins acquired more asparagine-linked oligosaccharide chains than did wild-type molecules, lacked kinase activity in vitro, were not transported to the cell surface, and had no transforming activity. Thus, the membrane-spanning segment in the middle of the glycoprotein interrupts translocation of nascent chains into the endoplasmic reticulum, ultimately orienting the amino-terminal domain outside the cell and the carboxy-terminal kinase domain in the cytoplasm. These topological features are similar to those of several growth factor receptors, suggesting that v-fms transforms cells through modified receptor-mediated signals.

c-erbB activation in avian leukosis virus-induced erythroblastosis: clustered integration sites and the arrangement of provirus in the c-erbB alleles

There is considerable evidence that links the activation of cellular genes to oncogenesis. We previously reported that structural rearrangements in the cellular oncogene c-erbB correlate with the development of erythroblastosis induced by avian leukosis virus (ALV). c-erbB recently has been shown to be related to the gene encoding epidermal growth factor receptor. We now have characterized the detailed mechanisms of c-erbB activation by ALV proviruses. We report here that the ALV proviral integration sites are clustered 5' to the region where homology to v-erbB starts, suggesting that interruption in this region of c-erbB is important for its activation. The proviruses are oriented in the same transcriptional direction as c-erbB and usually are full-size. The latter finding is in contrast to the frequent deletions observed within the c-myc-linked proviruses in B-cell lymphomas. We have also identified a second c-erbB allele, which differs from the previously known allele primarily by a deletion in an intron region. This allele is also oncogenic upon mutation by an ALV provirus.

Amplification, enhanced expression and possible rearrangement of EGF receptor gene in primary human brain tumours of glial origin

Epidermal growth factor (EGF), through interaction with specific cell surface receptors, generates a pleiotropic response that, by a poorly defined mechanism, can induce proliferation of target cells. Subversion of the EGF mitogenic signal through expression of a truncated receptor may be involved in transformation by the avian erythroblastosis virus (AEV) oncogene v-erb-B, suggesting that similar EGF receptor defects may be found in human neoplasias. Overexpression of EGF receptors has been reported on the epidermoid carcinoma cell line A431, in various primary brain tumours and in squamous carcinomas. In A431 cells the receptor gene is amplified. Here we show that 4 of 10 primary brain tumours of glial origin which express levels of EGF receptors that are higher than normal also have amplified EGF receptor genes. Amplified receptor genes were not detected in the other brain tumours examined. Further analysis of EGF receptor defects may show that such altered expression and amplification is a particular feature of certain human tumours.

Regulation of the epidermal growth factor receptor by phosphorylation

The receptor for epidermal growth factor (EGF) is a glycosylated transmembrane phosphoprotein that exhibits EGF-stimulable protein tyrosine kinase activity. On EGF stimulation, the receptor undergoes a self-phosphorylation reaction at tyrosine residues located primarily in the extreme carboxyl-terminal region of the protein. Using enzymatically active EGF receptor purified by immunoaffinity chromatography from A431 human epidermoid carcinoma cells, the self-phosphorylation reaction has been characterized as a rapid, intramolecular process which is maximal at 30-37 degrees C and exhibits a very low Km for ATP (0.2 microM). When phosphorylation of exogenous peptide substrates was measured as a function of receptor self-phosphorylation, tyrosine kinase activity was found to be enhanced two to threefold at 1-2 mol of phosphate per mol of receptor. Analysis of the dependence of the tyrosine kinase activity on ATP concentration yielded hyperbolic kinetics when plotted in double-reciprocal fashion, indicating that ATP can serve as an activator of the enzyme. Higher concentrations of peptide substrates were found to inhibit both the self- and peptide phosphorylation, but this inhibition could be overcome by first self-phosphorylating the enzyme. These results suggest that self-phosphorylation can remove a competitive/inhibitory constraint so that certain exogenous substrates can have greater access to the enzyme active site. In addition to self-phosphorylation, the EGF receptor can be phosphorylated on threonine residues by the calcium- and phospholipid-dependent protein kinase C. The sites on the EGF receptor phosphorylated in vitro by protein kinase C are identical to the sites phosphorylated on the receptor isolated from A431 cells exposed to the tumor promoters 12-O-tetradecanoylphorbol 13-acetate or teleocidin. This phosphorylation of the EGF receptor results in a suppression of its tyrosine kinase and EGF binding activities both in vivo and in vitro. The EGF receptor can thus be variably regulated by phosphorylation: self-phosphorylation can enhance tyrosine kinase activity whereas protein kinase C-catalyzed phosphorylation can depress enzyme activity. Because these two phosphorylations account for only a fraction of the phosphate present in the EGF receptor in vivo, other protein kinases can apparently phosphorylate the receptor and these may exert additional controls on EGF receptor/kinase function.

Characterization of epidermal growth factor receptor gene expression in malignant and normal human cell lines

To investigate the possibility that the epidermal growth factor (EGF) receptor functions as an oncogene product, we have determined the levels of EGF receptor protein and RNA in a variety of malignant and normal human cells, using a specific polyclonal antibody to the EGF receptor and a cDNA clone (plasmid pE7) that encodes the EGF receptor, respectively. Besides A431 epidermoid carcinoma cells, which are known to make large amounts of EGF receptor, cell lines from two ovarian cancers, two cervical cancers, and one kidney cancer were found to contain substantial amounts of receptor protein (11-22% of A431). Normal human fibroblasts (Detroit 551), a human lymphocyte line (IM-9), and a leukemic lymphocyte line (CEM) contained low or undetectable levels of EGF receptor. RNA blot analysis showed that among the human cell lines examined the levels of a 10- and a 5.6-kilobase species of pE7-specific RNA generally correlated with the amount of the EGF receptor protein. Genomic DNA blot analysis revealed that except for A431 none of these cell lines expressing high levels of EGF receptor protein possessed amplified receptor gene sequences. A431 cells are known to secrete a truncated form of the EGF receptor. An abundant 2.9-kilobase RNA is found only in A431 cells; it could encode the truncated form of the EGF receptor.

Expression of the c-fos gene and of an fos-related gene is stimulated by platelet-derived growth factor

Complementary DNA clones of genes induced by platelet-derived growth factor (PDGF) in BALB/c-3T3 cells were isolated; one such clone contains a domain having nucleotide sequence homology with the third exon of c-fos. This nucleotide sequence homology is reflected in the predicted amino acid sequences of the gene products. Under low stringency conditions, the mouse v-fos gene cross-hybridizes with the PDGF-inducible complementary DNA clone. However, the messenger RNA transcripts of mouse c-fos and the new fos-related gene can be distinguished by gel electrophoresis and by S1 nuclease analysis. Expression of the authentic c-fos gene is induced by PDGF and superinduced by the combination of PDGF and cycloheximide.

Translation in Xenopus oocytes of messenger RNA from A431 cells for human epidermal growth factor receptor proteins

Translation of messenger RNAs (mRNAs) for human epidermal growth factor receptor (EGF-R) proteins was accomplished in a Xenopus oocyte translation system. Translation of these mRNAs in rabbit reticulocyte lysates and wheat germ extracts were unsuccessful, in accordance with the general difficulty in translating mRNAs for membrane-bound glycoproteins in conventional heterologous cell-free systems. Total poly(A)+RNA from a human epidermoid carcinoma cell line A431 was injected into oocytes from Xenopus laevis. After incubation in the presence of [35S]methionine, the oocytes were homogenized and the supernatant incubated with several different polyclonal antibodies (IgGs) against the human EGF-R. Immunocomplexes were bound to protein A-Sepharose, washed extensively, and electrophoresed in sodium dodecyl sulfate-polyacrylamide gels. A protein of Mr = 160,000, corresponding to the EGF-R glycoprotein, was specifically precipitated from RNA-injected oocytes by each of the anti-EGF-R IgGs. This protein was not detectable in the immunoprecipitates from uninjected oocytes nor was it precipitated from RNA-injected oocytes by IgG from normal rabbit serum or IgG to an unrelated protein. A second protein of Mr = 100,000 was also immunoprecipitated from the homogenates of RNA-injected oocytes. This product corresponds to the EGF-R-related protein, present in A431 cells, which is structurally similar to the EGF-R (Weber et al., 1984). Thus, frog oocytes provide an efficient and generally applicable heterologous system for translation of mRNAs for large glycoproteins such as growth factor receptors. In addition, successful immunoprecipitation of translated products in this system provides a method for assay of mRNAs where biological activity of the proteins cannot be monitored.

Human epidermal growth factor receptor cDNA is homologous to a variety of RNAs overproduced in A431 carcinoma cells

The recently discovered similarity between the human epidermal growth factor (EGF) receptor and the avian erythroblastosis virus v-erb-B protein supports the hypothesis that viral oncogenes share a common evolutionary origin with genes encoding growth-regulating cell-surface receptors. To elucidate the relationship between receptors and malignant transformation, we have now used a fragment of v-erb-B as a probe to screen a cDNA library of mRNA from A431 human carcinoma cells, which possess a large number of EGF receptors. Of the six clones isolated, the largest (pE7) contains an insert of 2.4 kilobase pairs (kbp) whose deduced amino acid sequence is homologous to the v-erb-B protein and identical to reported EGF receptor peptide sequences. This pE7 cDNA hybridized to three prominent RNAs of approximately 10, 5.6 and 2.9 kilobases (kb), and to three minor species of 6.3, 4.6 and 3.3 kb. All were present in elevated levels in A431 cells. The prominent 2.9-kb RNA was homologous only to the 5' portion of the pE7 insert. This result raises the possibility that differential RNA processing is used by A431 cells to generate a variety of RNAs.