Epidermal growth factor receptor metabolism and protein kinase activity in human A431 cells infected with Snyder-Theilen feline sarcoma virus or harvey or Kirsten murine sarcoma virus

Migration of growth factor-stimulated epithelial and endothelial cells depends on EGFR transactivation by ADAM17

The fibroblast growth factor receptor 2-IIIb (FGFR2b) and the vascular endothelial growth factor receptor 2 (VEGFR2) are tyrosine kinases that can promote cell migration and proliferation and have important roles in embryonic development and cancer. Here we show that FGF7/FGFR2b-dependent activation of epidermal growth factor receptor (EGFR)/ERK1/2 signalling and cell migration in epithelial cells require stimulation of the membrane-anchored metalloproteinase ADAM17 and release of heparin-binding epidermal growth factor (HB-EGF). Moreover, VEGF-A/VEGFR2-induced migration of human umbilical vein endothelial cells also depends on EGFR/ERK1/2 signalling and shedding of the ADAM17 substrate HB-EGF. The pathway used by the FGF7/FGFR2b signalling axis to stimulate shedding of substrates of ADAM17, including ligands of the EGFR, involves Src, p38 mitogen-activated protein-kinase and PI3K, but does not require the cytoplasmic domain of ADAM17. Based on these findings, ADAM17 emerges as a central component in a triple membrane-spanning pathway between FGFR2b or VEGFR2 and EGFR/ERK1/2 that is required for cell migration in keratinocytes and presumably also in endothelial cells.

A transforming Src mutant increases the bioavailability of EGFR ligands via stimulation of the cell-surface metalloproteinase ADAM17

ADAM17 (a disintegrin and metalloproteinase 17, also referred to as TNFα converting enzyme or TACE) is a cell-surface metalloproteinase that regulates signaling via the epidermal growth factor receptor (EGFR) and has important roles in diseases such as cancer and rheumatoid arthritis. ADAM17 can be activated by stimulation of several tyrosine kinase receptors, raising questions about whether oncogenic tyrosine kinases could also enhance EGFR signaling and activation of extracellular signal-regulated kinase (ERK) via stimulation of ADAM17. The main goal of this study was to evaluate the role of Src in activating ADAM17. We provide evidence that a constitutively active transforming form of Src, the E378G mutant, as well as v-Src enhance ADAM17-mediated shedding of the EGFR ligand TGFα. Moreover, we demonstrate that constitutive shedding of TGFα can be reduced by inhibition of Src in several cell lines, including COS7, MCF7 (the human breast cancer cell line), PAE (a pig aortic endothelial cell line) and HaCaT (the human keratinocyte cell line) cells. Src(E378G)-stimulated shedding of TGFα is abolished in Adam17(-/-) cells, but can be rescued by wild-type (wt) ADAM17 and a mutant ADAM17 lacking its cytoplasmic domain. These findings demonstrate that ADAM17 is the principal TGFα sheddase that is activated by Src in a manner that does not require the cytoplasmic domain of ADAM17. Finally, we show that stimulation of ADAM17 by Src(E378G) leads to enhanced paracrine signaling via release of EGFR ligands into the culture supernatant. These results raise the possibility that activation of ADAM17 by oncogenic forms of Src can aid in promoting tumorigenesis by enhancing signaling via the EGFR and ERK in an autocrine and paracrine manner. Enhanced autocrine signaling could further activate tumor cells expressing oncogenic mutants of Src, whereas paracrine signaling could stimulate EGFR and ERK signaling in surrounding non-transformed cells such as stromal cells, thereby contributing to crosstalk between tumor cells and stromal cells.

Different metastatic potentials of ras- and src-transformed BALB/c 3T3 A31 variant cells

The metastatic phenotype of tumor cells is thought to be induced by an aberrant signaling cascade or cascades that are different from those required for tumorigenicity. Oncogene-transfected cells with different tumorigenicities and metastatic potentials have been used to identify such pathways and responsible molecules. However, oncogenes that can induce tumorigenicity in recipient cells also frequently induce the metastatic phenotype at the same time. The difficulty in obtaining cell lines that are tumorigenic but not metastatic has hampered such studies. In this report, we transfected the activated c-Ha-ras oncogene into BALB/c 3T3 A31 variant cells and found that the transfectants were tumorigenic but they did not form metastatic lung modules in the experimental metastasis assay. The phenotype was very stable and was maintained during cultivation. On the other hand, the metastatic potentials of either the transfected cells or the original variant cells could be induced by transfection of the v-src oncogene. The src transfectants formed extensive nodules in lung when injected into the tail veins of congeneric mice. The cell motility of the metastatic src transfectants on Matrigel-coated dishes was greater than that of the ras transfectants. The src transfectants were also invasive in Matrigel when analyzed on a filter. These variant cells transformed by the ras and src oncogenes will be a useful system for identifying the signaling cascades responsible for the metastatic potential of tumors.

Transformation by Rous sarcoma virus induces clathrin heavy chain phosphorylation

We have shown that the heavy chain of clathrin is phosphorylated in chicken embryo fibroblast cells transformed by Rous sarcoma virus, but not in normal cells. Approximately 1 mol of phosphate is bound for every 5 mol of heavy chain in the maximally phosphorylated transformed cells. Two-thirds of the phosphate is on serine and one-third on tyrosine residues. Clathrin heavy chain is a substrate for pp60v-src in vitro. Cleveland analysis of the in vivo and in vitro clathrin heavy chain phosphopeptides, generated by protease V8 digestion, show labeled proteolytic fragments of similar molecular weight, suggesting that pp60v-src could be directly responsible for the in vivo phosphorylation of clathrin. Phosphate is equally incorporated into clathrin in both the unassembled and the assembled clathrin pools, whereas [35S]methionine is preferentially incorporated into the assembled pool. In normal cells, clathrin visualized by immunofluorescent staining appears in a punctate pattern along the membrane surface and concentrated around the nucleus; in transformed cells the perinuclear staining is completely absent. The phosphorylation of clathrin heavy chain in transformed cells may be linked to previously observed transformation-dependent alterations in receptor-mediated endocytosis of ligands such as EGF and thrombin.

Transformation by viral and cellular oncogenes of a mouse BALB/3T3 cell mutant resistant to transformation by chemical carcinogens

The mouse cell line MO-5 is resistant to transformation by various chemical carcinogens and also by UV irradiation (C. Yasutake, Y. Kuratomi, M. Ono, S. Masumi, and M. Kuwano, Cancer Res. 47:4894-4899, 1987). Northern (RNA) blot analysis showed active expression of ras and myc genes in MO-5 and BALB/3T3 cells. The effect of transfection of various oncogenes on transformation was compared in MO-5 cells and parental BALB/3T3 cells. Activated c-H-ras, c-N-ras, and v-mos gene induced transformation foci of MO-5 and BALB/3T3. Introduction of the polyomavirus middle T-antigen (mTag) or the Rous sarcoma virus-related oncogene v-src, however, efficiently transformed BALB/3T3 but not MO-5 cells. Expression and phosphorylation of mTag and the associated c-src proteins were observed in mTag-transfected clones of MO-5 as in BALB/3T3 and phosphorylation of the src protein was observed in v-src-transfected BALB/3T3 and MO-5 clones. Hybrids between mTag- or v-src-induced transformants of BALB/3T3 and untransformed MO-5 maintained the transformation phenotype, suggesting that no dominant suppressor of transformation exists in MO-5. A hybrid clone between BALB/3T3 and MO-5 induced efficient transformation foci after transfection with the mTag gene, suggesting that the deficient transformation phenotype of MO-5 was recessive. Instead, some other alteration of MO-5, plausibly membrane function, might lead to abortive transformation by chemical carcinogens and also by mTag and the v-src gene product.

Transformation by viral and cellular oncogenes of a mouse BALB/3T3 cell mutant resistant to transformation by chemical carcinogens

The mouse cell line MO-5 is resistant to transformation by various chemical carcinogens and also by UV irradiation (C. Yasutake, Y. Kuratomi, M. Ono, S. Masumi, and M. Kuwano, Cancer Res. 47:4894-4899, 1987). Northern (RNA) blot analysis showed active expression of ras and myc genes in MO-5 and BALB/3T3 cells. The effect of transfection of various oncogenes on transformation was compared in MO-5 cells and parental BALB/3T3 cells. Activated c-H-ras, c-N-ras, and v-mos gene induced transformation foci of MO-5 and BALB/3T3. Introduction of the polyomavirus middle T-antigen (mTag) or the Rous sarcoma virus-related oncogene v-src, however, efficiently transformed BALB/3T3 but not MO-5 cells. Expression and phosphorylation of mTag and the associated c-src proteins were observed in mTag-transfected clones of MO-5 as in BALB/3T3 and phosphorylation of the src protein was observed in v-src-transfected BALB/3T3 and MO-5 clones. Hybrids between mTag- or v-src-induced transformants of BALB/3T3 and untransformed MO-5 maintained the transformation phenotype, suggesting that no dominant suppressor of transformation exists in MO-5. A hybrid clone between BALB/3T3 and MO-5 induced efficient transformation foci after transfection with the mTag gene, suggesting that the deficient transformation phenotype of MO-5 was recessive. Instead, some other alteration of MO-5, plausibly membrane function, might lead to abortive transformation by chemical carcinogens and also by mTag and the v-src gene product.

Autogenous growth factor production by reticuloendotheliosis virus-transformed hematopoietic cells

Reticuloendotheliosis virus strain T (REV-T)-transformed cells gave rise spontaneously to variants which secrete a factor that forms a distinct visible ring of precipitation (halo) surrounding colonies grown in soft agar. An Mr 15,000 protein was produced at higher levels by halo variants than by nonhalo-producing cells. An assay designed to detect the formation of precipitates enabled purification of an Mr 15,000 protein, p15, from serum-free medium conditioned by the growth of REV-T-transformed hematopoietic cells. Fractions enriched in p15 permitted the growth of REV-T-transformed cells under conditions where they normally failed to proliferate.

Ligand-induced endocytosis of the EGF receptor is blocked by mutational inactivation and by microinjection of anti-phosphotyrosine antibodies

Early events in ligand-induced endocytosis of the EGF receptor have been examined. A mutant EGF receptor devoid of intrinsic protein-tyrosine kinase activity bound EGF and dimerized normally yet failed to undergo ligand-induced internalization. Immunofluorescence microscopy revealed that receptors lacking kinase activity failed to undergo the ligand-induced internalization characteristic of receptors with kinase activity. Monoclonal anti-phosphotyrosine antibodies effectively inhibited phosphorylation of exogenous substrates in vitro and, when microinjected into cells containing active EGF receptors, prevented internalization of the receptor when cells were subsequently challenged with EGF. These results point to a crucial role for the kinase activity of the EGF receptor in the process of ligand-induced endocytosis of receptors, and imply that a phosphorylated substrate(s) is required.

Loss of growth responsiveness to epidermal growth factor and enhanced production of alpha-transforming growth factors in ras-transformed mouse mammary epithelial cells

A mouse mammary epithelial cell line, NMuMG, exhibits a low capacity to grow in semisolid medium as colonies and it is not tumorigenic in nude mice. In contrast, NMuMG cells which have been transformed by an activated c-Harvey ras proto-oncogene, NMuMG/rasH, or by the polyoma middle T-transforming gene, NMuMG/pyt, are able to grow in soft agar and, when injected into nude mice, produce undifferentiated carcinomas. Human epidermal growth factor (EGF) or human alpha-transforming growth factor (alpha TGF) can stimulate, in a dose-dependent fashion, the anchorage-independent growth of NMuMG and NMuMG/pyt cells in soft agar but fail to enhance the anchorage-independent growth of the NMuMGrasH cells. Likewise, human EGF or human alpha TGF is also able to stimulate the anchorage-dependent growth of normal NMuMG cells and NMuMG/pyt cells in a serum-free medium supplemented with insulin, transferrin, fetuin, and laminin, or in medium containing low concentrations of serum, whereas these same growth factors under comparable culture conditions have little or no effect upon the anchorage-dependent growth of the ras-transformed NMuMG-rasH cells. The biological refractoriness of the NMuMG/rasH cells to human EGF or human alpha TGF is reflected by a reduction in the total number of cell surface receptors for EGF and by an absence of a high-affinity population of binding sites for mouse [125l]EGF on these cells as compared to the NMuMG or NMuMG/pyt cells. In addition, concentrated conditioned medium (CM) obtained from NMuMG/rasH and NMuMG/pyt cells contains a relatively higher amount of biologically active TGFs than CM obtained from comparably treated NMuMG cells as measured by the ability to induce the anchorage-independent growth of normal rat kidney cells in soft agar. The higher levels of biologically active TGFs found in the CM from the transformed cells relative to the NMuMG cells is paralleled by a corresponding increase in the CM from these cells in the amount of immunoreactive alpha TGF, by an increase in the amount of EGF receptor-competing activity, and by an increase in the levels of alpha TGF mRNA in the NMuMG/rasH cells. These results demonstrate that mammary epithelial cells which have been transformed by an activated ras proto-oncogene, but not by the polyoma middle T-transforming gene, become unresponsive to exogenous EGF or alpha TGF.(ABSTRACT TRUNCATED AT 400 WORDS)

Modulation of p36 phosphorylation in human cells: studies using anti-p36 monoclonal antibodies

We have characterized two monoclonal antibodies which recognize human p36. These have been used to examine the sites and extent of serine and tyrosine phosphorylation of p36 in human cells treated with epidermal growth factor and platelet-derived growth factor and in human cells transformed with viruses whose oncogenes encode protein-tyrosine kinases.

Direct identification of palmitic acid as the lipid attached to p21ras

p21v-H-ras, the transforming protein of Harvey murine sarcoma virus, contains a covalently attached lipid. Using thin-layer chromatography, we identified the acyl group as the 16-carbon saturated fatty acid palmitic acid. No myristic acid was detected in fatty acids released from in vivo-labeled p21v-H-ras. The p21v-K-ras protein encoded by Kirsten sarcoma virus was also palmitylated. The processing and acylation of p21v-K-ras however differed from that of p21v-H-ras. Three forms of [3H]palmitic acid-labeled p21ras proteins were detected in Kirsten sarcoma virus-transformed cells. This contrasted with Harvey sarcoma virus, in which two forms of p21v-H-ras contained palmitic acid. Analysis by partial proteolysis of p21v-H-ras labeled with [3H]palmitic acid suggested that all of the lipid found in intact p21v-H-ras was located in the C-terminal region. On sodium dodecyl sulfate-polyacrylamide gels, p21v-H-ras labeled with [3H]palmitic acid migrated slightly ahead of the majority of p21v-H-ras. Of the mature forms of p21v-H-ras, apparently only a subpopulation contains palmitic acid.

The cDNA sequence for the protein-tyrosine kinase substrate p36 (calpactin I heavy chain) reveals a multidomain protein with internal repeats

We have isolated and sequenced a full-length cDNA clone for the protein-tyrosine kinase substrate p36 (calpactin I heavy chain). This sequence predicts a 339 amino acid (Mr 38,493) protein containing an N-terminal region of 20 amino acids, known to interact with a 10 kd protein (light chain), and a C-terminal region, found to contain two Ca2+/phospholipid-binding sites, that can be aligned as four 70 amino acid repeats. A single p36 gene was detected in the mouse genome, and a major p36 mRNA of 1.6 kb was found to be expressed in different mouse tissues. Unexpectedly, p36 and the phospholipase A2 inhibitor lipocortin I were found to be 50% identical in sequence over the C-terminal 300 residues. The function of p36 and its relation to other proteins are discussed.

Antibodies to the ATP-binding site of the human epidermal growth factor (EGF) receptor as specific inhibitors of EGF-stimulated protein-tyrosine kinase activity

A region of the primary amino acid sequence of the epidermal growth factor receptor (EGF) protein-tyrosine kinase, which is involved in ATP binding, was identified using chemical modification and immunological techniques. EGF receptor was 14C-labelled with the ATP analogue 5'-p-fluorosulphonylbenzoyladenosine and from a tryptic digest a single radiolabelled peptide was isolated. The amino acid sequence was determined to be residues 716-724 and hence lysine residue 721 is located within the ATP-binding site. Antisera were elicited in rabbits to a synthetic peptide identical to residues 716-727 of the EGF receptor and the homologous sequence in v-erb B transforming protein from avian erythroblastosis virus. The affinity-purified antibodies precipitated human ECF receptor from A431 cells and placenta, and the v-erb B protein from erythroblasts. The antibodies inhibited EGF-stimulated receptor protein-tyrosine kinase autophosphorylation and phosphorylation of an exogenous peptide substrate containing tyrosine. The antibodies did not immunoprecipitate the transforming proteins pp60v-src or P120gag-abl or cAMP-dependent protein kinase, proteins which have homologous but not identical sequences surrounding the lysine residue within the ATP-binding site, nor did they react with the platelet-derived growth factor receptor. The antibodies had no effect on the kinase activity of purified v-abl protein in solution. The antibodies may therefore be a specific inhibitor of the tyrosine kinase of the EGF receptor.

Modulation of p36 phosphorylation in human cells: studies using anti-p36 monoclonal antibodies

We have characterized two monoclonal antibodies which recognize human p36. These have been used to examine the sites and extent of serine and tyrosine phosphorylation of p36 in human cells treated with epidermal growth factor and platelet-derived growth factor and in human cells transformed with viruses whose oncogenes encode protein-tyrosine kinases.

The protein-tyrosine kinase substrate, p81, is homologous to a chicken microvillar core protein

p81, a protein-tyrosine kinase substrate previously identified in epidermal growth factor-treated A431 cells, is demonstrated to be homologous to ezrin, an 80-kD component of microvillar core proteins. p81 has been characterized using antiserum raised against purified chicken intestinal ezrin. p81, located by indirect immunofluorescent staining, is concentrated in surface projections of A431 cells such as microvilli and retraction fibers. None of the conditions of biochemical cell fractionation tested completely solubilizes p81; the insoluble p81 partitions as if associated with the cytoskeleton. The soluble form of p81 behaves as a monomer in all extraction procedures studied. EGF-stimulated phosphorylation of p81 does not appear to change its intracellular location. p81 exhibits a wide tissue distribution with highest levels of expression in small intestine, kidney, thymus, and lung. Intermediate levels are found in spleen, thymus, lymph nodes, and bone marrow, with low levels in brain, heart, and testes. p81 is undetectable in muscle and liver. In A431 cells, p81 is phosphorylated on serine and threonine residues. Upon EGF treatment, approximately 10% of p81 becomes phosphorylated on tyrosine, and the phosphorylation of threonine residues increases.

Direct identification of palmitic acid as the lipid attached to p21ras

p21v-H-ras, the transforming protein of Harvey murine sarcoma virus, contains a covalently attached lipid. Using thin-layer chromatography, we identified the acyl group as the 16-carbon saturated fatty acid palmitic acid. No myristic acid was detected in fatty acids released from in vivo-labeled p21v-H-ras. The p21v-K-ras protein encoded by Kirsten sarcoma virus was also palmitylated. The processing and acylation of p21v-K-ras however differed from that of p21v-H-ras. Three forms of [3H]palmitic acid-labeled p21ras proteins were detected in Kirsten sarcoma virus-transformed cells. This contrasted with Harvey sarcoma virus, in which two forms of p21v-H-ras contained palmitic acid. Analysis by partial proteolysis of p21v-H-ras labeled with [3H]palmitic acid suggested that all of the lipid found in intact p21v-H-ras was located in the C-terminal region. On sodium dodecyl sulfate-polyacrylamide gels, p21v-H-ras labeled with [3H]palmitic acid migrated slightly ahead of the majority of p21v-H-ras. Of the mature forms of p21v-H-ras, apparently only a subpopulation contains palmitic acid.

Anti-O-phosphotyrosine antibodies in human sera

Antibodies reactive with O-phosphotyrosine (PTYR) were detected in 60 out of 621 inpatients, with high frequencies in hematologic and lung malignancies, hepatic diseases, cerebrovascular diseases, and autoimmune diseases. Affinity-purified antibodies proved capable of recognizing PTYR-containing proteins in a human carcinoma cell line, A431, both by immunofluorescent staining and by immunoaffinity chromatography, but had no detectable affinity for phosphorylated serine or threonine, or for the nucleotides tested. In these respects, the antibodies observed in human sera were indistinguishable from anti-PTYR antibodies raised experimentally in rabbits or mice.

Loss of epidermal growth factor receptors and release of transforming growth factors do not correlate with sarcoma virus-transformation in clonally-related NIH/3T3-derived cell lines

Transformation of NIH/3T3 cells by Kirsten murine sarcoma virus (MSV) caused a dramatic reduction in the number of cell-surface receptors for epidermal growth factor (EGF). However, the number of EGF receptors remained at a very low level in a non-tumourigenic revertant cell line isolated from the virus-transformed cells, indicating that an increase in EGF receptors is not a requirement for the phenotypic reversion of Kirsten MSV-transformed 3T3 cells. Serum-free conditioned medium from normal and virus-transformed cell lines contained similar amounts of cell growth-promoting activity as assayed by the ability to stimulate DNA synthesis in quiescent Swiss 3T3 cell cultures. However, the concentrated conditioned medium from these cell lines showed no evidence of beta-transforming growth factor (TGF) activity as assayed by promotion of anchorage-independent growth of untransformed normal rat kidney (NRK) fibroblasts in agarose. The cellular release of alpha-TGF activity was assayed by measuring the ability of concentrated conditioned medium to inhibit the binding of 125I-EGF to Swiss 3T3 cells. Conditioned medium protein from the virus-transformed cell line inhibited 125I-EGF binding but only to the same extent as conditioned medium protein prepared from the untransformed cell line. The alpha-TGF secretion by these cell lines was estimated to be 30-45-fold lower than the level of alpha-TGF released by a well-characterized alpha-TGF-producing cell line (3B11). These results suggest that the induction of TGF release is not a necessary event in the transformation of NIH/3T3 cells by Kirsten MSV.

Effects of epidermal growth factor and 12-O-tetradecanoylphorbol-13-acetate on metabolism of the epidermal growth factor receptor in normal human fibroblasts

The biosynthesis, phosphorylation, and degradation of the epidermal growth factor (EGF) receptor were examined in normal human fibroblasts. The receptor was initially synthesized as an Mr = 160,000 immature form which matured to an Mr = 170,000 form in a monensin-sensitive manner. Tunicamycin treatment led to the accumulation of an Mr = 130,000 protein. The receptor was phosphorylated on serine and threonine residues in normally growing and quiescent cells, and treatment with EGF or the tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA) resulted in a two- to threefold increase in receptor-bound phosphate. EGF increased the amount of phosphoserine and phosphothreonine and caused the appearance of a minor amount of phosphotyrosine. TPA increased the levels of phosphoserine and phosphothreonine exclusively. Prior treatment with TPA inhibited the EGF-dependent appearance of phosphotyrosine in the receptor. Analysis of tryptic phosphopeptides revealed that six of the seven major peptides were common to the receptor from cells treated with EGF or TPA. EGF strongly stimulated [3H]thymidine incorporation in confluent cells, increased final saturation density three to fourfold, and increased whole-cell levels of phosphotyrosine about threefold. Treatment of cells with TPA before addition of EGF inhibited all three of these EGF-dependent responses. EGF also decreased the receptor half-life from 15 h to 1 h, but this was not inhibited by TPA. TPA alone had no detectable effect on the receptor half-life.

Flat revertants derived from Kirsten murine sarcoma virus-transformed cells produce transforming growth factors

Two flat cellular revertant cell lines, F-2 and C-11, which were originally selected from the DT line of Kirsten murine sarcoma virus (Ki-MuSV)-transformed NIH/3T3 cells, were examined for the production of transforming growth factors (TGFs). The revertant cells fail to grow in semisolid medium as colonies and exhibit a markedly reduced level of tumorigenicity in nude mice, although they are known to express high levels of p21ras, the product of the Kirsten sarcoma virus oncogene, ras, and they contain a rescuable transforming virus. TGF activity associated with the transformed, revertant, and non-transformed cell lines was measured by the ability of concentrated conditioned medium (CM) from these cells to induce normal rat kidney (NRK) and NIH/3T3 cells to form colonies in semisolid agar suspension cultures and to inhibit the binding of 125I epidermal growth factor (EGF) to specific cell surface receptors. CM from the transformed DT cells and from both the F-2 and C-11 revertants contains TGF activity, in contrast to CM obtained from normal NIH/3T3 cells. Furthermore, unlike NIH/3T3 cells, neither the DT nor the revertant cells were able to bind 125I EGF. All four cell lines were able to proliferate in serum-free medium supplemented with transferrin, insulin, EGF, and Pedersen fetuin. However, in basal medium lacking these growth factors, only DT cells and, to a lesser extent, the revertant cells were able to grow. These results suggest that the F-2 and C-11 revertants fail to exhibit all of the properties associated with transformation because the series of events leading to the transformed phenotype is blocked at a point(s) distal both to the expression of the p21 ras gene product and also to the production of TGFs and that the production of TGFs may be necessary but not sufficient for maintaining the transformed state.

Effects of epidermal growth factor and 12-O-tetradecanoylphorbol-13-acetate on metabolism of the epidermal growth factor receptor in normal human fibroblasts

The biosynthesis, phosphorylation, and degradation of the epidermal growth factor (EGF) receptor were examined in normal human fibroblasts. The receptor was initially synthesized as an Mr = 160,000 immature form which matured to an Mr = 170,000 form in a monensin-sensitive manner. Tunicamycin treatment led to the accumulation of an Mr = 130,000 protein. The receptor was phosphorylated on serine and threonine residues in normally growing and quiescent cells, and treatment with EGF or the tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA) resulted in a two- to threefold increase in receptor-bound phosphate. EGF increased the amount of phosphoserine and phosphothreonine and caused the appearance of a minor amount of phosphotyrosine. TPA increased the levels of phosphoserine and phosphothreonine exclusively. Prior treatment with TPA inhibited the EGF-dependent appearance of phosphotyrosine in the receptor. Analysis of tryptic phosphopeptides revealed that six of the seven major peptides were common to the receptor from cells treated with EGF or TPA. EGF strongly stimulated [3H]thymidine incorporation in confluent cells, increased final saturation density three to fourfold, and increased whole-cell levels of phosphotyrosine about threefold. Treatment of cells with TPA before addition of EGF inhibited all three of these EGF-dependent responses. EGF also decreased the receptor half-life from 15 h to 1 h, but this was not inhibited by TPA. TPA alone had no detectable effect on the receptor half-life.

Human squamous cell lung cancers express increased epidermal growth factor receptors

Epidermal growth factor (EGF) promotes the growth of cultured benign and malignant cells. Recent studies have demonstrated that the amount of EGF receptor is elevated in squamous cell carcinoma cells in tissue culture when compared with normal epidermal cells. This study demonstrates that elevated levels of EGF receptor are detected in biopsy specimens of human squamous cell carcinomas of the lung with a murine monoclonal antibody, EGF-R1, which binds specifically to the receptor. The increased receptor ranged from 2.5- to 5-fold that of normal skin. These findings have been observed in 11 of 11 squamous carcinomas and two of two epidermoid head and neck cancers. Seven of eight adenocarcinomas, two of two small cell, and four of eight undifferentiated lung cancers had negligible amounts of EGF receptor. The EGF receptor antibody did not bind significantly to normal lung tissues and 35 nonepidermoid tumors. Therefore, EGF receptor may be an excellent marker for epidermoid malignancies.

Production of an epidermal growth factor receptor-related protein

Human epidermoid carcinoma A431 cells in culture produce a soluble 105-kilodalton protein which, by the criteria of epidermal growth factor (EGF) binding, recognition by monoclonal and polyclonal antibodies to the EGF receptor, amino-terminal sequence analysis and carbohydrate content, is related to the cell surface domain of the EGF receptor. The high rate of production and the finding that with biosynthetic labeling the specific activity of this 105-kilodalton protein exceeds that of the intact receptor indicate that it is not derived from membrane-bound mature receptor but is separately produced by the cell. These cells thus separately synthesize an EGF receptor that is inserted into the membrane and an EGF receptor-related protein that is secreted.

Nonfunctional epidermal growth factor receptor in cells transformed by Kirsten sarcoma virus

The cell membrane receptor for epidermal growth factor (EGF) appears to be a glycoprotein of Mr 170,000 and mediates the mitogenic and metabolic responses of cells with EGF receptors (EGF-R). Normal rat kidney (NRK) have about 3 X 10(5) EGF-R per cell. Upon transformation of NRK cells by Kirsten sarcoma virus, the transformed derivative (KNRK) loses the ability to bind 125I-EGF. Membranes from NRK and KNRK cells were included in EGF-dependent phosphorylation reactions to search for evidence of the EGF-R. A phosphorylated protein of Mr 170,000 was detected in both NRK and KNRK membranes. The Mr 170,000 protein was identified to be EGF-R by immunoprecipitation with monoclonal antibody to the receptor. Furthermore, two-dimensional peptide mapping using trypsin and chymotrypsin digestions of the iodinated receptors from both NRK and KNRK cells showed essentially identical patterns. These data indicate that the EGF-R is present in KNRK cells with apparently the same protein structure as the NRK counterpart.