Genetics of cell surface receptors for bioactive polypeptides: binding of epidermal growth factor is associated with the presence of human chromosome 7 in human-mouse cell hybrids

Epidermal growth factor receptor (EGFR) gene alteration and protein overexpression in Malaysian triple-negative breast cancer (TNBC) cohort

Background

Epidermal growth factor receptor (EGFR) is a member of the ErbB family of tyrosine kinase receptor proteins that plays important roles in tumour cell survival and proliferation. EGFR has been reported to be overexpressed in up to 78% of triple-negative breast cancer (TNBC) cases suggesting it as a potential therapeutic target. The clinical trials of anti-EGFR agents in breast cancer showed low response rates. However, a subgroup of patients demonstrated response to EGFR inhibitors highlighting the necessity to stratify patients, who might benefit from effective combination therapy that could include anti EGFR-agents. Population variability in EGFR expression warrants systematic evaluation in specific populations.

Purpose

To study EGFR alterations and expressions in a multi ethnic Malaysian TNBC patient cohort to determine the possibility of using anti-EGFR combinatorial therapy for this population.

Patients and methods

In this study, we evaluated 58 cases of Malaysian TNBC patient samples for EGFR gene copy number alteration and EGFR protein overexpression using fluorescence in-situ hybridization (FISH) and immunohistochemistry (IHC) methods, respectively.

Results

EGFR protein overexpression was observed in about 30% while 15.5% displayed high EGFR copy number including 5.17% gene amplification and over 10% high polysomy. There is a positive correlation between EGFR protein overexpression and gene copy number and over expression of EGFR is observed in ten out of the 48 low copy number cases (20.9%) without gene amplification.

Conclusion

This study provides the first glimpse of EGFR alterations and expressions in a multi ethnic Malaysian TNBC patient cohort emphasising the need for the nationwide large scale EGFR expression evaluation in Malaysia.

Drug delivery approaches for breast cancer

Breast cancer is one of the most common cancers affecting women worldwide. The controlled release of drugs to the precise site of the disease using a nanocarrier vehicle increases the therapeutic efficiency of the drugs. Nanotechnology-based approaches used to endorse clinical improvement from a disease also help to understand the interaction of malignant cells with their microenvironment. Receptor-based targeting is another approach for drug delivery which is undergoing clinical trials. Nanoparticles (NPs) delivery has been proven to promise high loading capacity, less toxicity, and stability of the drugs or biomolecules compared to traditional chemotherapeutic drugs. The goal of this review is to present the current problems of breast cancer therapy and discuss the NP-based targeting to overcome the hurdles of conventional drug therapy approach.

Multicolor FISHs for simultaneous detection of genes and DNA segments on human chromosomes

We have developed a convenient multicolor fluorescent in situ hybridization (FISH) (five-, four-, three-, and two-color FISHs) for detecting specific genes/DNA segments on the human chromosomes. As a foundation of multicolor FISH, we first isolated 80 bacterial artificial chromosome (BAC) probes that specifically detect the peri-centromeres (peri-CEN) and subtelomeres (subTEL) of 24 different human chromosomes (nos. 1~22, X, and Y) by screening our homemade BAC library (Keio BAC library) consisting of 200,000 clones. Five-color FISH was performed using human DNA segments specific for peri-CEN or subTEL, which were labeled with five different fluorescent dyes [7-diethylaminocoumarin (DEAC): blue, fluorescein isothiocyanate (FITC): green, rhodamine 6G (R6G): yellow, TexRed: red, and cyanine5 (Cy5): purple]. To observe FISH signals under a fluorescence microscope, five optic filters were carefully chosen to avoid overlapping fluorescence emission. Five-color FISH and four-color FISH enabled us to accurately examine the numerical anomaly of human chromosomes. Three-color FISH using two specific BAC clones, that distinguish 5' half of oncogene epidermal growth factor receptor (EGFR) from its 3' half, revealed the amplification and truncation of EGFR in EGFR-overproducing cancer cells. Moreover, two-color FISH readily detected a fusion gene in leukemia cells such as breakpoint cluster region (BCR)/Abelson murine leukemia viral oncogene homologue (ABL) on the Philadelphia (Ph') chromosome with interchromosomal translocation. Some other successful cases such as trisomy 21 of Down syndrome are presented. Potential applications of multicolor FISH will be discussed.

In silico identification of EGFR-T790M inhibitors with novel scaffolds: start with extraction of common features

Background

Epidermal growth factor receptor (EGFR) is an attractive therapeutic target for a number of human tumors including non-small cell lung cancer (NSCLC). Most patients with NSCLC and somatic mutations have shown a dramatic initial clinical response to reversible EGFR inhibitors. The clinical efficacy of reversible inhibitors is, however, ultimately limited due to the emergence of drug resistance, which is usually conferred by the EGFR T790M mutation. Importantly, irreversible, synthetic small molecule inhibitors are currently evaluated and some of them have been shown to overcome the acquired resistance that is oftentimes observed in these patients. Thus far, irreversible EGFR inhibitors as a drug class have not received regulatory approval due in part to their poor effectiveness at clinically achievable concentrations. Therefore, there is an urgent need to discover and develop novel, potent irreversible inhibitors against the EGFR T790M mutation.

Material and methods

In the following study, we report a novel “hybrid strategy” to identify irreversible EGFR inhibitors with active scaffolds starting with the identification and extraction of a common chemical reactive feature and a pharmacophore feature. The chemical reactive feature was elucidated by investigating 138 currently known irreversible inhibitors at B3LYP/6-31G(d) level using the density function theory method. The pharmacophore feature was extracted from the same inhibitors using pharmacophore modeling. Based on these unique features, two constraints were set while calibrating the protocols of in silico screening. Compounds bearing these specific features were obtained from the National Cancer Institute diversity database to form our subsequent library. Finally, a structure based virtual screening against the library was conducted using standard protocols validated in our lab.

Results

Twenty-eight candidate compounds that demonstrated antitumor activity and that had novel scaffolds different from commonly known quinazoline/quinoline analogs were obtained. The interaction modes between three representative candidates and our model system are similar to that between the model system and the reference compound T-001, which has previously been reported to be one of the most potent of the 138 irreversible inhibitors.

Conclusion

The hybrid strategy starting with the extraction of common features is an effective approach to design potential irreversible inhibitors with novel scaffolds and therefore to obtain lead molecules in the selection process. These candidates possessing unique scaffolds have a strong likelihood to act as further starting points in the preclinical development of potent irreversible T790M EGFR inhibitors.

Recombinant human IgG antibodies recognizing distinct extracellular domains of EGF receptor exhibit different degrees of growth inhibitory effects on human A431 cancer cells

Recently, we isolated 4 distinct kinds of single chain antibody against human EGF receptor (EGFR) after screening the Keio phage display scFv library by using two methods of target-guided proximity labeling. In the current study, these monovalent scFv antibodies were converted to bivalent IgGs of humanized forms (hIgGs) by recombinant technology using the specially designed expression vectors followed by protein production in CHO cells. The resulting recombinant hIgGs were examined for their binding specificity using several different transformed human BJ cell lines that express deletion mutants of EGFR, each lacking one of 4 distinct extracellular domains (L1, L2, C1 and C2). Immuno-fluorescent microscopy and immuno-precipitation assay on these cells indicated that 4 distinct kinds of hIgGs bind to one of 3 different domains (L1, C1 and C2). Then, these hIgGs were further examined for biological effects on human A431 cancer cells, which overexpress EGFR. The results indicated that hIgG38 binding to L1 and hIgG45 binding to C2 substantially suppressed the EGF-induced phosphorylation of EGFR, resulting in the growth inhibition of A431 cancer cells. On the contrary, hIgG40 binding to C1 and hIgG42 binding to another site (epitope) of C2 exhibited no such inhibitory effects. Thus, the newly produced four recombinant hIgG antibodies recognize 4 different sites (epitopes) in 3 different extracellular domains of EGFR and exhibit different biological effects on cancer cells. These characteristics are somewhat different from the currently utilized therapeutic anti-EGFR antibodies. Hence, these hIgG antibodies will be invaluable as a research tool for the detailed molecular analysis of the EGFR-mediated signal transduction mechanism and more importantly a possible application as new therapeutic agents to treat certain types of cancers.

Screening of scFv-displaying phages recognizing distinct extracellular domains of EGF receptor by target-guided proximity labeling method

We recently constructed the scFv-displaying phage library with extremely high repertoire and have successfully utilized for screening scFv antibodies against various proteins, polysaccharides and glyco-lipids. Here, we developed a new screening strategy to isolate scFv antibodies against cell surface EGF receptor (EGFR). For this, we applied two slightly different methods of "target-guided proximity labeling," such as Proximity selection (ProxiMol) method and a new sulfo-SBED labeling method with the aide of monoclonal anti-human EGFR antibody B4G7 as a guide molecule. ProxiMol method relies on the Biotin-labeling of scFv-displaying phages that bound to the target in a vicinity of 100Å from the guide molecule, whereas sulfo-SBED method transfers Biotin to scFv-displaying phages, which bound to the target in a distance of 20 Å. After two rounds of panning on the EGFR-overexpressing A431 cells starting from approx. 1 × 10¹² pfu, 47 each of Biotin-labeled scFv-displaying phages were recovered using Streptoavidin-coated magnetic beads, and among them total 11 scFv-phages were found to be definitely positive for binding to A431 cell surface by ELISA assay. Restriction mapping and sequencing analysis of these scFv-phage DNAs revealed that they encode 4 different scFv-nucleotide sequences in total. Immuno-fluorescent microscopy provided evidence that these 4 scFv antibodies bind specifically to EGFR on the A431 cells, showing slightly different staining patterns. Thus, "target-guided proximity labeling" methods were powerful for isolating scFv-displaying phages that recognize distinct extracellular domains of the target receptor. This novel screening strategy could be applicable to many other cell surface antigens and receptors.

Epidermal growth factor variations in amniotic membrane used for ex vivo tissue constructs

INTRODUCTION

The amniotic membrane (AM) is used for engineering ex vivo tissue constructs used in ocular surface reconstruction. Epidermal growth factor (EGF) content of the AM is believed to play a key role in supporting corneal epithelial cell expansion on AM. This study investigated EGF content in AM in relation to intra- and inter-donor variations and the effect of processing and preservation (handling).

METHODS

Fifteen human AM, both fresh and handled, were analyzed for EGF gene and protein expression by real-time polymerase chain reaction and ELISA, respectively.

RESULTS

EGF gene expression was predominantly seen in the AM epithelium (p<0.01). Similarly, EGF protein too was predominantly seen in the epithelial layer (p<0.01) for fresh and handled samples. EGF protein content varied between membranes (inter-donor) and at different sites within the same membrane (intra-donor). The highest EGF protein concentration was noted in the AM apical and mid-region epithelium. Significant EGF protein loss (p<0.01) was observed after handling.

CONCLUSION

There is a considerable variation in EGF content between and within donors. This is further affected by handling of the AM. Such variations could affect the clinical efficacy of tissue constructs. Current use of AM for ex vivo expansion of epithelial cells is not standardized and remains an area of concern.

Somatic mutations of the epidermal growth factor receptor and non-small-cell lung cancer

Frequent overexpression of epidermal growth factor receptor (EGFR) in non-small-cell lung cancer (NSCLC) makes EGFR a new therapeutic target. Two specific EGFR tyrosine kinase inhibitors, gefitinib (ZD1839, Iressa) and erlotinib (OSI-774, Tarceva), have been developed and approved by the US Food and Drug Administration for second-line and third-line treatment of advanced NSCLC. Clinical trials have shown considerable variability in the response rate between different patients with NSCLC, which led to the discovery of somatic EGFR-activating mutations. This brief review summarises the discovery and functional consequences of the mutations, their clinicopathological features and significant implications in the treatment and prognosis of NSCLC.

EGFR gene amplification in breast cancer: correlation with epidermal growth factor receptor mRNA and protein expression and HER-2 status and absence of EGFR-activating mutations

The human epidermal growth factor receptor (HER) family of receptor tyrosine kinase has been extensively studied in breast cancer; however, systematic studies of EGFR gene amplification and protein overexpression in breast carcinoma are lacking. We studied EGFR gene amplification by chromogenic in situ hybridization (CISH) and protein expression by immunohistochemistry in 175 breast carcinomas, using tissue microarrays. Tumors with >5 EGFR gene copies per nucleus were interpreted as positive for gene amplification. Protein overexpression was scored according to standardized criteria originally developed for HER-2. EGFR mRNA levels, as measured by Affymetrix U133 Gene Chip microarray hybridization, were available in 63 of these tumors. HER-2 gene amplification by fluorescence in situ hybridization (FISH) and protein overexpression by immunohistochemistry were also studied. EGFR gene amplification (copy number range: 7-18; median: 12) was detected in 11/175 (6%) tumors, and protein overexpression was found in 13/175 (7%) tumors. Of the 11 tumors, 10 (91%) with gene amplification also showed EGFR protein overexpression (2+ or 3+ by immunohistochemistry). The EGFR mRNA level, based on Affymetrix U133 chip hybridization data, was increased relative to other breast cancer samples in three of the five tumors showing gene amplification. Exons 19 and 21 of EGFR, the sites of hotspot mutations in lung adenocarcinomas, were screened in the 11 EGFR-amplified tumors but no mutations were found. Three of these 11 tumors also showed HER-2 overexpression and gene amplification. Approximately 6% of breast carcinomas show EGFR amplification with EGFR protein overexpression and may be candidates for trials of EGFR-targeted antibodies or small inhibitory molecules.

Mapping of the human HPC-1/syntaxin 1A gene (STX1A) to chromosome 7 band q11.2

We previously described the cDNA sequence of HPC-1/syntaxin 1A (HGMW-approved symbol STX1A) from rat and bovine brains. HPC-1/syntaxin 1A belongs to the syntaxin family and is apparently involved in intracellular membrane transport and the exocytosis of neurotransmitters. In this study, we isolated the cDNA and the genomic DNA clone for human HPC-1/syntaxin 1A and carried out gene mapping. Polymerase chain reaction analysis of human/rodent somatic cell hybrid panels and fluorescence in situ hybridization analysis using a genomic DNA clone provided evidence that the gene for human HPC-1/syntaxin 1A maps to chromosome region 7q11.2.

Detection of epidermal growth factor receptor gene amplification in human squamous cell carcinomas using fluorescence in situ hybridization

The gene for epidermal growth factor receptor (EGFR) is associated with development of certain human cancers. In this study, we employed the improved fluorescence in situ hybridization technique to detect EGFR gene amplification in cell lines and tissue sections from human squamous cell carcinomas. We detected multiple distinct signals as arrayed amplicons on metaphase chromosomes and interphase nuclei of tumor cells. Our results provide a basis for rapid and quantitative DNA diagnosis of the EGFR gene amplification in individual cells of tumor specimens.

Coamplification on chromosomes 7p12-13 and 9q12-13 identified by reverse chromosome painting in a glioblastoma multiforme

DNA amplification is known to occur in approximately 50% of glioblastomas, with the epidermal growth factor receptor (EGFR) gene being the most frequently amplified. Whereas previous amplification studies have largely been limited to the analysis of known tumor-related genes, reverse chromosome painting allows us to search for as yet unidentified amplified domains. Here, we report the analysis of a glioblastoma multiforme by reverse chromosome painting. Hybridization signals were found on chromosome 7p12-13 and chromosome 9q12-13. Standard Southern blot analysis revealed amplification of the EGFR gene, which is localized on band 7p13. These findings corroborate previous reports on coamplification of sequences on different chromosomes in glioblastoma.

A novel gene delivery system using EGF receptor-mediated endocytosis

A monoclonal antibody to the human epidermal growth factor (EGF) receptor was conjugated with polylysine and the resulting conjugate was affinity-linked with DNA (gene). This novel gene delivery system utilizes receptor-mediated endocytosis and would be especially suitable for gene therapy for EGF receptor-overproducing squamous cell carcinomas.

Precise mapping of the EGF receptor gene on the human chromosome 7p12 using an improved fish technique

The gene for epidermal growth factor receptor (EGFR) has been localized to the p14-p12 region of human chromosome 7 by somatic cell hybridization and radioisotope in situ hybridization techniques. In this paper, we report the precise mapping of the EGFR gene to the band p12 of chromosome 7 using a novel method in which fluorescence images from in situ hybridization and Q-banding are computer graphically merged. The novel procedure is described in detail.

Epidermal growth factor receptor expression in squamous cell lung carcinomas: an immunohistochemical and gene analysis in formalin-fixed, paraffin-embedded material

Epidermal growth factor (EGF) and its receptor (EGFr) constitute an important and well-characterized mitogenic system in various ectodermal tissues. We evaluated the expression of EGFr and examined possible EGFr gene alterations in 18 formalin-fixed, paraffin-embedded squamous cell lung carcinomas (SCLC) by an immunohistochemical assay, Southern blotting and differential polymerase chain reaction (DPCR). The immunohistochemical study employing the F4 and EGF-R1 monoclonal antibodies, directed against the intra- and extra-cellular portion of the receptor respectively, showed EGFr over-expression in 89% of the SCLC cases examined. All cases showed positive immunostaining for both antibodies, thus excluding the possibility of truncated receptors. In addition, analysis of the EGFr gene was carried out by Southern blotting and DPCR on paraffin extracted DNA from the same carcinoma cases. We found amplification of the EGFr gene in 5/18 (27%) SCLCs. All 5 positive cases showed EGFr over-expression, suggesting a possible correlation between the presence of EGFr gene amplification and over-expression of receptor protein. No correlation was observed among EGFr staining, EGFr gene amplification and differentiation of carcinomas. In addition, Southern blot analysis with HER-A2, a probe which hybridizes a sequence of the receptor's intracellular domain, revealed three novel EcoRI restriction fragment patterns. We suggest that these patterns correspond to EcoRI polymorphic sites of the receptor's tyrosine kinase domain.

Evidence for intracellular down-regulation of the epidermal growth factor (EGF) receptor during adenovirus infection by an EGF-independent mechanism

We have reported previously that human group C adenoviruses down-regulate the epidermal growth factor (EGF) receptor (EGF-R) (C. R. Carlin, A. E. Tollefson, H. A. Brady, B. L. Hoffman, and W. S. M. Wold, Cell 57:135-144, 1989). Expression of a 13.7-kDa protein encoded by a gene in the E3 transcription unit is necessary and sufficient for this effect (Carlin et al., Cell, 1989; B. L. Hoffman, A. Ullrich, W. S. M. Wold, and C. R. Carlin, Mol. Cell. Biol. 10:5521-5524, 1990). We show here that EGF-R down-regulation is accelerated in cells which overexpress the receptor when these cells are infected with virus mutants that overproduce the 13.7-kDa protein compared with wild-type virus. This is in contrast to EGF stimulation, for which others have shown that high concentrations of ligand are associated with low rates of receptor internalization in EGF-R-overexpressing cells (D. Kuppuswamy and L. J. Pike, J. Biol. Chem. 264:3357-3363, 1989; H. S. Wiley, J. Cell Biol. 107:801-810, 1988). We also show that the E3 protein is not present in media conditioned by infected cells and that it does not induce secretion of an EGF-like autocrine factor. Moreover, while mature membrane-bound EGF-R is down-regulated, the precursor of the membrane-bound form is not. Adenovirus infection also does not affect receptor-related molecules expressed in the secretory pathway. Interestingly, adenovirus-induced down-regulation is not regulated by concentrations of EGF associated with a slow rate of internalization in A431 cells. This suggests that 13.7-kDa protein expression triggers receptor entry by a novel ligand-independent pathway or, alternatively, that it compensates for a cellular factor that may be rate limiting during EGF-mediated endocytosis.

Flow cytometric analysis of the expression of 9A3 antigen, E-cadherin and EGF receptor in TMK-1 stomach cancer cells

We have previously produced a monoclonal antibody (MAb) against TMK-1 cells, a poorly differentiated stomach-cancer cell line, and designated the antigen as 9A3. Immunohistochemical analysis of various tumor tissues revealed that the expression of 9A3 antigen is specific for human adenocarcinoma. In the present study, we analyzed the expression patterns of 9A3 antigen on TMK-1 cells and compared them with the expression patterns of E-cadherin and epidermal-growth-factor (EGF) receptors, using immunofluorescent microscopy and flow cytometry. The flow cytometric analysis revealed that the TMK-1 cell population consists of 9A3-positive cells and 9A3-negative cells. The isolated 9A3-negative cell population generates 9A3-positive cells as they divide, whereas the isolated 9A3-positive cell population does not generate 9A3-negative cells. The 9A3-positive cells grow as tight colonies, whereas the 9A3-negative cell form loose colonies in soft agar culture. E-cadherin was expressed only in the 9A3-positive TMK-1 cells and not in the 9A3-negative cells. In contrast, EGF receptor was expressed in both cell populations. The 9A3 antigen was localized mainly at the cell-cell adhesion sites where E-cadherin was apparently condensed.

Extrachromosomal amplification of the epidermal growth factor receptor gene in a human colon carcinoma cell line

In situ hybridization, using a biotinylated cDNA probe for the epidermal growth factor receptor (EGFR) gene, indicates that the amplified EGFR genes in the colon tumor cell line, DiFi, are localized in many small double minute chromosomes (dmin) of varying size and visibility. Analysis of the electrophoretic mobility of gamma-irradiated DNA from DiFi by pulsed-field gel electrophoresis and Southern blot hybridization using EGFR probe, indicates that the amplified EGFR in DiFi exists in extrachromosomal, covalently closed circular episomes, presumably equivalent to dmin. Two major and one minor species were observed which had estimated sizes of 650, 1,300, and 2,000 kb, respectively. The DiFi cell line appears to represent a unique case of extrachromosomal EGFR gene amplification in human cells.

Altered expression of epidermal growth factor receptor gene in a classical multidrug-resistant variant of a human cancer cell line, KB

A variant clone resistant to high doses of colchicine (KB-C1) derived from human cancer KB cell line is resistant to various anticancer agents. The KB-C1 cells were much more resistant to epidermal growth factor and a chimeric toxin, EGF-Pseudomonas exotoxin (PE), than the parental KB cells. KB-C1 cells have decreased numbers of EGF-receptors, though the affinity of the receptors is similar to that in the parental KB cells. A drug-sensitive revertant (C1-R2) partially recovered its EGF-receptor activity. Northern blot analysis showed a decreased level of EGF-receptor mRNA in KB-C1 cells, while the multidrug-resistance gene, mdr-1, was expressed at very high levels in KB-C1 cells, but not in KB or C1-R2 cells. The drug-resistant cells were less tumorigenic than the parental cells when injected into nude mice. A decreased expression of EGF-receptor in these cells may be one of the pleiotropic properties of multidrug-resistant cells and may perhaps represent the basis for their reduced tumorigenicity.

Localization of human phosphoribosylpyrophosphate synthetase subunit I and II genes (PRPS1 and PRPS2) to different regions of the X chromosome and assignment of two PRPS1-related genes to autosomes

Complementary DNA clones for phosphoribosylpyrophosphate synthetase subunits I and II (PRS I and PRS II) were used to determine the chromosomal localization of the corresponding human genes. Southern blot analysis of genomic DNAs isolated from human placenta and a panel of human-mouse somatic cell hybrids revealed that the rat PRS I cDNA probe detected at least five human specific DNA segments (23, 20, 14.5, 6.7, and 4.3 kb) in BamHI digests. The 23-, 14.5-, and 6.7-kb DNA segments were detected only if the hybrids contained human chromosome X or translocation chromosome 7p+ (7qter greater than 7p22::Xq21 greater than Xqter), indicating the location of these segments to Xq21-qter (PRPS1). The 20- and 4.3-kb DNA segments did not cosegregate with the other three segments, and spot blot hybridization analysis using flow-sorted human chromosomes indicated that these are the PRPS1-related genes (PRPS1L1 and PRPS1L2) and could be assigned to chromosomes 7 and 9, respectively. The human-specific PRS II cDNA probe revealed a BamHI DNA segment (17 kb), which segregated condordantly with the X chromosome but not with the PRPS1 gene. We surmise that the gene for PRS II (PRPS2) is located at a different region of the X chromosome, namely Xpter-a21.

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.

In vivo selection of tumorigenic subline from non-tumorigenic human gastric carcinoma cells: in relation to proliferative properties in vivo and in nude mice

Human gastric carcinoma cells from one of three long-term cultured cell lines (HPE-GAC-T) were injected into peritoneal cavities of BALB/c mice. The surviving celss in vivo were collected 3 days later. Following brief cultivation in vitro, those cells were reinjected into mice by the same route. This procedure was repeated 3 times. The cultured cancer cells recovered from the mice on the 3rd passage, at a 92.5% recovery rate, showed xenotransplantability in BALB/C nu/nu mice by subcutaneous injection. This subline (GAC-T.M-2) can be maintained in vitro but not in vivo while maintaining heterotransplantability. Three original cancer cell lines did not show tumorigenicity in nude mice. Animal passages by the same protocol failed to select tumorigenic sublines from the other cell lines (HPE-GAC-2 and -3). Factors affecting tumorigenic capacity of cancer cells in nude mice were studied in vivo and in vitro by comparing the properties of GAC-T.M-2 and parental cancer cells (GAC-T.O). Treatment of the hosts by injection of anti-asialoGM1 antibody or cyclophosphamide, adult thymectomy of BALB/c mice, and 400 rads whole body irradiation did not enhance the growth of either GAC-T.M-2 or -T.O cells. There was no detectable difference between in vitro growth properties of the original and variant cells at a rather high cell density. However, at a low cell density GAC-T.M-2 cells showed a higher cell growth rate and increased [3H] thymidine incorporation and possessed higher colony forming activity in the liquid medium than their parental cells. High dense expression of epidermal growth factor (EGF) receptors was evident equally in both GAC-T cells, however, GAC-T.M-2 cells were more sensitive to down-regulation by EGF in culture. Tumor cells of HPE-GAC-2 and -3 lines expressed minimum amount of EGF receptors on their cell surfaces and were refractory to additional EGF in culture. The results indicate that growth factors and their receptors are responsible for tumorigenicity in nude mice.

Growth characteristics of human epidermal melanocytes in pure culture with special reference to genetic differences

Human melanocyte cultures were established using disaggregated epidermal cell suspensions derived from foreskins and plated onto culture dishes in medium containing 2% fetal bovine serum, growth factors, hormones, and melanocyte growth factor (MGF) extracted from bovine hypothalamus (Wilkins et al., J.Cell. Physiol., 122:350, 1985). After 2 days in culture the cells were transferred to serum-free medium to eliminate keratinocyte and fibroblast growth. Melanocytes grew preferentially and pure melanocyte populations could be harvested after 12-16 days in vitro. Melanocytes were later subcultured in the presence of 1% FBS. Pure melanocyte cultures were characterized by light and electron microscopic criteria, as well as by cytochemical demonstration of the melanocyte-specific enzyme, tyrosinase. At the ultrastructural level, cultured melanocytes derived from black (negroid) neonatal skin (B-M) had numerous mature rod-shaped stage IV melanosomes, while white (caucasoid) skin-derived melanocytes (W-M) in culture contained no mature melanosomes. Growth rate, cell yield, and in vitro lifespan for B-M were more than twice that for W-M in pure melanocyte cultures in the presence of MGF. Our results suggest that MGF-dependent growth of B-M differs from that of W-M.

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.

Human erythropoietin gene: high level expression in stably transfected mammalian cells and chromosome localization

The glycoprotein hormone erythropoietin plays a major role in regulating erythropoiesis and deficiencies of erythropoietin result in anemia. Detailed studies of the hormone and attempts at replacement therapy have been difficult due to the scarcity of purified material. We used a cloned human erythropoietin gene to develop stably transfected mammalian cell lines that secrete large amounts of the hormone with potent biological activity. These cell lines were produced by cotransfection of mammalian cells with a plasmid containing a selectable marker and plasmid constructions containing a cloned human erythropoietin gene inserted next to a strong promoter. The protein secreted by these cells stimulated the proliferation and differentiation of erythroid progenitor cells and, with increased selection, several of these cell lines secrete up to 80 mg of the protein per liter of supernatant. Hybridization analysis of DNA from human chromosomes isolated by high resolution dual laser sorting provides evidence that the gene for human erythropoietin is located on human chromosome 7.

Molecular cloning of an oncogene from a human hepatocellular carcinoma

A transforming DNA, named lca (for liver cancer), was obtained from a primary human hepatocellular carcinoma (HCC) in transformation assays using NIH 3T3 cells and a calcium phosphate coprecipitation method. High molecular weight DNA obtained from the HCC tissue was employed for this purpose. This transforming DNA had a linkage to the Alu sequence and was cloned in lambda phage for further studies. Restriction enzyme analyses showed that the minimal size of the lca transforming DNA is about 10 kilobase pairs and that its cleavage profiles are different from those of any one of the previously reported human transforming genes or retroviral oncogenes. No cross-hybridization was observed between these genes and the lca DNA. Southern blot analyses of DNAs from flow-sorted human chromosomes and human-mouse somatic cell hybrids indicated that the lca DNA is located on human chromosome 2. An independently obtained transforming DNA from another HCC exhibited identical restriction enzyme cleavage profiles. Thus, lca DNA is likely to represent a commonly encountered transforming DNA in HCC.

Monosomy 7 and multipotential stem cell transformation

Monosomy 7 was the sole karyotypic abnormality seen in a case of biphenotypic leukaemia involving both the myeloid and lymphoid lineages and in a case of de novo ALL undergoing a phenotypic shift to acute myeloid leukaemia at relapse. These observations suggest that monosomy 7 can be associated with transformation of a common lymphoid-myeloid progenitor cell.

Variant of A431 cells isolated by ricin A-conjugated monoclonal antibody directed to EGF receptor: phosphorylation of EGF receptor and phosphatidylinositol

A monoclonal antibody specific for human EGF receptors was cross-linked to subunit A of toxic ricin. Using this conjugate, we isolated a variant of A431 cells, designated C1-B7, with approximately 40 times less EGF binding capacity. Unlike the parental cells, the C1-B7 variant was resistant to EGF-induced suppression of cell growth. The EGF receptors retained in this variant were of high-affinity type and susceptible to EGF-induced autophosphorylation. Membrane prepared from C1-B7 cells was highly phosphorylated in the presence of 2 microM [gamma-32P]-ATP, primarily on the lipid components shown as phosphatidylinositol 4-phosphate and phosphatidylinositol 4,5-bisphosphate. This same level of lipid phosphorylation was observed on A431 membrane only in the presence of higher ATP concentrations. After addition of EGF to A431 membrane, phosphatidylinositol phosphorylation was significantly decreased with a concomitant increase in EGF-dependent protein phosphorylation. Thus, the EGF-dependent receptor-mediated protein phosphorylation precedes phosphatidylinositol phosphorylation. These observations support the idea that the growth inhibitory effect of EGF on A431 cells is caused by high ATP consumption due to the EGF-induced protein phosphorylation and reduction of phosphatidylinositol turnover.

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.

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.

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.

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.

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.

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.

Human chromosomal mapping of genes for insulin-like growth factors I and II and epidermal growth factor

Many of the actions previously attributed to pituitary-derived growth hormone are mediated by polypeptide growth factors. These include the insulin-like growth factors I and II (IGF-I and IGF-II), which are members of the insulin family of proteins. We report here the chromosomal mapping of the human genes for IGF-I and IGF-II. IGF-II maps to the short arm of chromosome 11, which also contains the gene for insulin and the proto-oncogene c-Ha-ras1 (ref. 9). IGF-I maps to chromosome 12, which is evolutionarily related to chromosome 11 and carries the gene for the proto-oncogene c-Ki-ras2 (refs 10,44). We have also localized the human gene for an unrelated polypeptide hormone, epidermal growth factor, to chromosome 4q, in the same region as another specialized growth factor, T-cell growth factor. We speculate that these map assignments reflect the existence of gene families involved in growth control.

Human epidermal growth factor receptor cDNA sequence and aberrant expression of the amplified gene in A431 epidermoid carcinoma cells

The complete 1,210-amino acid sequence of the human epidermal growth factor (EGF) receptor precursor, deduced from cDNA clones derived from placental and A431 carcinoma cells, reveals close similarity between the entire predicted v-erb-B mRNA oncogene product and the receptor transmembrane and cytoplasmic domains. A single transmembrane region of 23 amino acids separates the extracellular EGF binding and cytoplasmic domains. The receptor gene is amplified and apparently rearranged in A431 cells, generating a truncated 2.8-kilobase mRNA which encodes only the extracellular EGF binding domain.

Assignment of the human gene for the low density lipoprotein receptor to chromosome 19: synteny of a receptor, a ligand, and a genetic disease

The availability of a species-specific monoclonal antibody that recognizes the low density lipoprotein (LDL) receptor of human but not hamster origin permitted assignment of the structural gene for the human receptor to chromosome 19. The antibody was used to detect the human LDL receptor in a series of hamster-human somatic cell hybrids by two assays: (i) a structural assay that measured cellular incorporation of [35S]methionine into immunoprecipitable receptor and (ii) a functional assay that measured the rate of receptor-dependent uptake and degradation of the 125I-labeled anti-receptor monoclonal antibody. Both assays showed that the human LDL receptor was expressed in 15 out of 20 hybrid cell lines. Expression of the human LDL receptor was 100% concordant with the presence of human chromosome 19; all other human chromosomes showed at least 25% discordance. As expected, the gene for the LDL receptor (LDLR) is located on the same chromosome as the gene for the disease familial hypercholesterolemia, which has been previously mapped to chromosome 19 by pedigree studies and is caused by allelic mutations at the LDL receptor locus. The gene for apolipoprotein E, a ligand for the LDL receptor, is also known to be located on chromosome 19, raising the possibility of an evolutionary link between a protein ligand and its receptor.

Close similarity of epidermal growth factor receptor and v-erb-B oncogene protein sequences

Each of six peptides derived from the human epidermal growth factor (EGF) receptor very closely matches a part of the deduced sequence of the v-erb-B transforming protein of avian erythroblastosis virus (AEV). In all, the peptides contain 83 amino acid residues, 74 of which are shared with v-erb-B. The AEV progenitor may have acquired the cellular gene sequences of a truncated EGF receptor (or closely related protein) lacking the external EGF-binding domain but retaining the transmembrane domain and a domain involved in stimulating cell proliferation. Transformation of cells by AEV may result, in part, from the inappropriate acquisition of a truncated EGF receptor from the c-erb-B gene.

Genetic analysis of hyperproduction of epidermal growth factor receptors in human epidermoid carcinoma A431 cells

Human epidermoid carcinoma A431 cells, possessing an extraordinarily high number of epidermal growth factor (EGF) receptors (1), were found to be hypotetraploid in their chromosome constitution and to contain two copies of intact chromosome 7 and two types of the translocation chromosomes involving chromosome 7 (M4 and M14) as well as several other rearranged chromosomes. The A431 cells were fused with mouse A9 cells, which lack EGF receptors (2) and are deficient in hypoxanthine phosphoribosyltransferase (3), and the human-mouse cell hybrid (AA series) were selected in HAT/ouabain medium (3, 4). The expression of high EGF binding ability was correlated with the presence of human translocation chromosome M4. AA hybrid clones that contained intact human chromosome 7 but not the marker chromosome M4 expressed only ordinary levels of EGF receptors. The EGF receptors expressed in the AA hybrids were proven to be of human nature by immunoprecipitation of the receptors cross-linked with [125I]EGF. These observations and our previous gene assignment of the EGF receptor to human chromosome 7 (2, 5) suggest that the marker chromosome M4 may carry an alteration(s) in the gene(s) involved in EGF receptor biosynthesis.