Epidermal growth factor precursor is related to the translation product of the Moloney sarcoma virus oncogene mos

A 34-kd protein with strong homology to ras-like proteins inhibits epidermal growth factor activity

Epidermal growth factor (EGF) and its analog, transforming growth factor-alpha, are felt to be important in oncogenesis. When malignant rabbit fibroma virus infects RK-13 rabbit kidney cells, a 34-kd protein that inhibits the effects of EGF on certain target cell lines is produced. We have purified this protein using high-pressure liquid chromatography and gel electrophoresis. This purified protein abolishes EGF-induced cellular proliferation. It also causes the EGF receptor-bearing A431 carcinoma cell line to stop proliferating in vitro. This purified 34-kd EGF inhibitor (EGFI) redirects cellular protein phosphorylation in the presence or absence of EGF. Whereas EGF increases phosphorylation of cellular proteins in normal rat kidney cells, clone 49F, and A431 EGFI generally decreases it. Both EGF and EGFI cause increased protein production in A431 and normal rat kidney cells. The major species of protein synthesized by cells seem invariant to EGFI, with or without EGF. The partial protein sequence of two fragments of EGFI shows striking similarity to two ras like proteins. Possible means by which such a ras-like protein might inhibit EGF-induced cellular proliferation are discussed. Therefore, a purified 34-kd ras-like protein inhibits EGF-induced cellular proliferation and changes the targets for cellular protein phosphorylation. Studies are in progress to characterize this protein further, both structurally and functionally.

Specific mRNAs accumulate in long-wavelength UV-irradiated mouse epidermis

Total RNA from hairless mice epidermis was analysed by RNA-DNA hybridization on slot blots at various times following irradiation with long-wavelength UV light (UV-B or UV-B plus UV-A). Densitometric scanning of the autoradiographies indicates that the amount of RNA which hybridizes with an Ha-ras DNA probe remains constant for up to 72 h after irradiation. The amount of the transcript which hybridizes to a c-fos DNA probe increases dose dependently from 15 min to 2 h after irradiation. RNA which hybridizes to a tubulin DNA probe accumulates in parallel with the increase in mitotic index associated with the radiation-induced hyperplasia.

Genetic recombination in human melanoma and astrocytoma cell lines involves oncogenes and growth factor genes

We describe here the chromosomal distribution of sister chromatid exchanges (SCEs) in four human tumor cell lines (two melanomas and two astrocytomas), and have mapped the sister chromatid recombination (SCR) sites. A higher incidence of SCR sites than expected on the basis of chromosome length occurred in chromosomes 2, 4, 5 and 15 in both the RPMI 5966 and MEL57 melanoma cell lines, and in chromosomes 1, 5, 13 and 15 of the IJKt and GUVW astrocytoma cell lines. A majority of the recombination sites occurred close to chromosomal fragile sites. A third of these occurred at the same bands as fragile sites. The recombination sites involved the N-ras and the epidermal growth factor gene in the melanomas. In the astrocytomas, the N-ras, Rb and c-mos genes appeared to be involved in the recombination events. The beta 2-microglobulin gene was involved in both astrocytomas and one melanoma. The erbB2 was involved in SCR only in the RPMI melanoma.

Regulation of collagen metabolism and cell growth by epidermal growth factor and ascorbate in cultured human skin fibroblasts

Epidermal growth factor (2-50 ng/ml), prepared from mouse submaxillary glands, stimulated growth and the synthesis of non-collagenous proteins and hyaluronic acid, but inhibited collagen synthesis in cultured human skin fibroblasts, both stimulation and inhibition being dose-dependent. All these effects may be intrinsic functions of the epidermal growth factor molecule, because these effects were cancelled by the co-presence of antiserum specific for epidermal growth factor and because they were also observed following the addition of human epidermal growth factor produced urogastrone cDNA. On the other hand, L-ascorbate (vitamin C) stimulated growth and collagen synthesis, as well as synthesis of non-collagenous proteins, with no significant effect on hyaluronic acid synthesis. Co-presence of epidermal growth factor and ascorbate gave additive effects on growth and protein synthesis of the cells. These results suggest that the two growth-promoting factors, epidermal growth factor and L-ascorbate, modulate metabolism of extracellular matrix components as well as cell growth in a quite different manner in human skin fibroblasts.

Interaction between epidermal growth factor and its receptor in progression of human gastric carcinoma

The expressions of epidermal growth factor (EGF) and its receptor were studied immunohistochemically in a total of 156 gastric carcinomas; 26 early and 130 advanced. No EGF immunoreactivity was found in early carcinomas, while EGF-positive tumor cells were detected in 38 (29.2%) of the 130 advanced carcinomas. EGF receptor immunoreactivity was detected in one (3.8%) of the 26 early carcinomas and in 44 (33.8%) of the 130 advanced carcinomas, the incidence being significantly different (p less than 0.01). Out of the 130 advanced carcinomas, 17 (13.1%) had synchronous expression of EGF and its receptor and most of the tumors with strong expression of EGF were positive to EGF receptor. A significant correlation was observed between the depth of tumor invasion and EGF or its receptor immunoreactivity in tumor cells (p less than 0.05). Furthermore, a good correlation was demonstrated between the synchronous expression of EGF and its receptor and the depth of tumor invasion or the tumor staging. The incidence of cases with EGF in metastatic tumors was significantly higher than that in primary tumors (p less than 0.05). Patients with synchronous expression of EGF and its receptor had a far poorer prognosis than those without EGF and receptor.

Cellular oncogenes in neoplasia

In recent years cellular homologues of many viral oncogenes have been identified. As these genes are partially homologous to viral oncogenes and are activated in some tumour cell lines they are termed "proto-oncogenes". In tumour cell lines proto-oncogenes are activated by either quantitative or qualitative changes in gene structure: activation of these genes was originally thought to be a necessary primary event in carcinogenesis, but activated cellular oncogenes, unlike viral oncogenes, do not transform normal cells in culture. In experimental models cooperation between two oncogenes can induce transformation of early passage cells, and this has become the basis of an hypothesis for multistep carcinogenesis. Proto-oncogene products also show sequence homology to various components in the mitogenic pathway (growth factors, growth factor receptors, signal transducing proteins and nuclear proteins), and it has been postulated that they may cause deregulation of the various components of this pathway. In human tumours single or multiple oncogene activation occurs. The pattern of oncogene activation in common solid malignancies is not consistent within any one class of tumour, nor is it uniform between classes, with three exceptions. In neuroblastoma, breast cancer, and perhaps in lung cancer there is relatively consistent activation of N-myc, neu, and c-myc/N-myc, respectively. Amplification of these genes generally correlates with poor prognosis. The introduction of methods for the direct study of oncogene transcription and their products will undoubtedly broaden our vision of cancer biology in man and, hopefully, add diagnostic and prognostic precision to tumour typing.

Human epidermal growth factor precursor: cDNA sequence, expression in vitro and gene organization

Complementary DNA clones encoding the human kidney epidermal growth factor (EGF) precursor have been isolated and sequenced. They predict the sequence of a 1,207 amino acid protein which contains EGF flanked by polypeptide segments of 970 and 184 residues at its NH2- and COOH-termini, respectively. The structural organization of the human EGF precursor is similar to that previously described for the mouse protein and there is 66% identity between the two sequences. Transfection of COS-7 cells with the human EGF precursor cDNA linked to the SV40 early promoter indicate that it can be synthesized as a membrane protein with its NH2-terminus external to the cell surface. The human EGF precursor gene is approximately 110 kilobase pairs and has 24 exons. Its exon-intron organization revealed that various domains of the EGF precursor are encoded by individual exons. Moreover, 15 of the 24 exons encode protein segments that are homologous to sequences in other proteins. Exon duplication and shuffling appear to have played an important role in determining the present structure of this protein.

Functional and structural characteristics of EGF and its receptor and their relationship to transforming proteins

Epidermal growth factor (EGF) is a peptide which effects the growth and/or differentiated functions of many cell types. Several pieces of evidence indicate that EGF and its receptor may play a role in carcinogenesis. Functional and structural characteristics of EGF and its receptor and their relationship to transforming proteins are discussed. EGF has extensive homology with alpha-transforming growth factor (alpha-TGF), which may actually be an embryonic form of EGF. Nevertheless, both EGF and alpha-TGF elicit transformation-associated phenotypes in target cells under certain conditions. EGF effects are mediated by a receptor present on the plasma membrane. The EGF receptor is a highly complex protein having several functions in addition to binding EGF in a highly specific manner. One of these functions is to phosphorylate tyrosyl residues on certain proteins. This activity is similar to that expressed by the src family of oncogene-encoded proteins. Besides sharing functional homology the EGF receptor also exhibits structural homology to several oncogene-encoded proteins. The v-erb-B-transforming protein has a striking extent of homology (95%) to the cytoplasmic portion of the EGF receptor. These data support the concept that some aspect of EGF-stimulated metabolism is involved in cellular transformation.

The versatility of proteolytic enzymes

The growing realization of their physiological importance has generated renewed interest in the study of proteolytic enzymes. Modern methods of protein chemistry and molecular biology have revealed new insights into the protein and gene structure of a variety of protein precursors and their processing by limited proteolysis. Examples are given in this review for transmembrane processes and the role of signal peptidases of both eukaryotic and prokaryotic origin, the processing of prohormones and precursors of growth factors, protein components of blood coagulation, fibrinolysis, and of the complement system, and a group of granulocyte proteases, including the mast cell serine proteases. The relationship of homologous domains found in many of these proteases and their zymogens to protein evolution is a recurrent theme of this discussion.

The molecular biology of chromosome alterations in myelogenous leukemia

In the past few years, new developments have rapidly emerged that promise to unravel the pathogenesis of malignant transformation. By understanding the molecular events in neoplastic transformation, such as in myelogenous leukemia, we should be able to devise specific and effective therapies and to intervene in the development of these diseases. Furthermore, the study of cancer genes is likely to have far-reaching effects with regard to our understanding of normal development and other nonneoplastic conditions.

Retroviral gag and DNA endonuclease coding sequences in IgE-binding factor gene

Immunoglobulin-binding factors are known to regulate the synthesis of B-cell-derived immunoglobulin heavy-chain isotypes. Cloning and nucleotide sequence determination of complementary DNA encoding rodent IgE-binding factors (IgE-BF) revealed that messenger RNA encodes a glycoprotein of 557 amino acids which is expressed as a precursor of relative molecular mass (Mr) 60,000 (60K) in COS7 monkey cells. We report here that the 3' two-thirds of the IgE-BF coding sequence shows a surprising homology (72%) at the DNA level with coding sequences of the gag and pol (DNA endonuclease) genes of the Syrian hamster intracisternal A particle (IAP H18), an endogenous retrovirus. This marked homology demonstrates that the rodent gene encoding IgE-BF is a hybrid gene which evolved very recently by integrating genes of viral origin, and that the encoded polypeptide comprises three separate domains: an IgE-BF domain and retrovirus-derived gag and DNA endonuclease-like domains. This may represent the first report of a cellular gene containing a virus-derived coding sequence.