Uptake of epidermal growth factor into a lysosomal enzyme-deficient organelle: correlation with cell's mitogenic response and evidence for ubiquitous existence in fibroblasts

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.

Inhibitors of vacuolar-type H(+)-ATPase suppresses proliferation of cultured cells

We investigated effects of bafilomycin A1, a specific inhibitor of vacuolar-type H(+)-ATPase (V-ATPase), and its analogues on proliferation of various cultured cells. The proliferation of the various cell lines was suppressed by adding bafilomycin A1 to the culture medium. This inhibitory effect appeared at a concentration of nanomolar order and was dose dependent. Although the suppression was reversible, the drug exerted not only suppression of the proliferation but also death to some cell lines. Drug concentration required for 50% inhibition of the cell proliferation during 48 h differed markedly depending on cell species and the sensitivity appears to increase by the transformation of the cells. Two derivatives of concanamycin A, an analogue of bafilomycin A1, also inhibited strongly V-ATPase in vitro and in vivo, and simultaneously cell proliferation. Two concanamycin A derivatives which have lost inhibitory effect on V-ATPase lost inhibitory effect on cell proliferation as well. These results suggest that V-ATPase is involved in the machinery maintaining the cell proliferation.

Ligand induced internalization of epidermal growth factor receptors by A431 cells decreases at high cell densities in culture

Internalization of epidermal growth factor (EGF) receptors by human A431 epidermoid carcinoma cells was studied at various culture densities. The extent of EGF receptor internalization was measured by quantitation of internalized 125I-EGF during incubation at 37 degrees C for 30 min. When cell culture density was below 1 x 10(5) cells/cm2 receptor internalization was active; 30-40% excess moles of ligand over the moles of surface EGF receptors were internalized during this period. However, when culture density increased to above 1.5 x 10(5) cells/cm2 receptor internalization became less extensive, as only 30-50% of ligand bound to the cell surface underwent internalization during 30 min incubation. In parallel with this reduction in receptor internalization, the degradation rate of 35S-methionine labeled EGF receptors was reduced at a high culture density. In contrast with this regulation of receptor internalization, the affinity of EGF receptors for the ligand increased as culture density increased. The extent of EGF-dependent receptor phosphorylation was found to be constant at all culture densities tested. Thus, the observed low level of receptor internalization at high culture densities was not attributable to lower responsiveness of receptors to EGF. These data suggest the presence of an as yet unidentified cell density-dependent mechanism for regulating receptor internalization in cultured A431 cells.

Modulation of tyrosine, serine, and threonine phosphorylation and intracellular processing of the epidermal growth factor receptor by antireceptor monoclonal antibody

To investigate the functional significance of epidermal growth factor (EGF) receptor phosphorylation, experimental systems were explored in which receptor phosphorylation on tyrosine and serine/threonine could be differentially stimulated. Exposure of A431 cells to 20 nM EGF at 37 degrees C results in phosphorylation of serine, threonine, and tyrosine sites on the receptor. Monoclonal antibody (mAb) 225 binds to the EGF receptor with affinity comparable to EGF and competes with the binding of EGF. Exposure of A431 cells to 20 nM EGF in the presence of 300 nM anti-EGF receptor mAb 225 (15-fold excess) selectively activated serine and threonine phosphorylation of the receptor, but not tyrosine phosphorylation. This observation indicates that EGF-mediated receptor phosphorylation on tyrosine and on serine/threonine residues is dissociable. The intracellular fate of the EGF receptor was examined under conditions that produce different phosphorylation states of receptor amino acids. Exposure of A431 cells to EGF decreased the half-life (T1/2) of the receptor from 17.8 h to 5.6 h, with activation of tyrosine, serine, and threonine phosphorylation. Incubation with mAb 225 augmented the degradation rate (T1/2 = 8.5 h) without activation of receptor phosphorylation. Concurrent exposure to EGF (20 nM) and mAb 225 (300 nM) resulted in comparable enhanced degradation (T1/2 = 9.5 h), with increased phosphorylation only on serine and threonine residues. These results suggest that serine/threonine phosphorylation is irrelevant to the augmentation of receptor degradation. Methylamine, an inhibitor of lysosomal function that did not affect phosphorylation of the EGF receptor, completely protected EGF receptors from rapid degradation induced by EGF, but it only slightly altered the rate of EGF receptor degradation elicited by mAb 225 or by EGF plus 15-fold excess mAb 225. In contrast, mAb 455, which binds to the receptor but does not inhibit EGF binding and EGF-induced activation of phosphorylation on tyrosine, serine, and threonine residues, did not influence EGF-induced rapid, methylamine sensitive degradation of EGF receptor. The results suggest that when EGF receptors are internalized under conditions that do not activate the receptor tyrosine kinase, they are sorted into a nonlysosomal pathway that differs from the methylamine-sensitive lysosomal pathway traversed following activation by EGF. The data indicate the possibility of a function for tyrosine kinase activation and tyrosine autophosphorylation in determining the lysosomal intracellular pathway of EGF receptor processing and degradation.

Expression of epidermal growth factor receptors in four histologic cell types of lung cancer

Lung cancer tissues from 68 patients were examined for epidermal growth factor (EGF) receptor levels and EGF receptor gene copy numbers. Histologic cell types of these lung cancer tissues included squamous-cell carcinoma (n = 30), adenocarcinoma (n = 28), large-cell carcinoma (n = 4), and small-cell carcinoma (n = 6). Tissues of squamous-cell carcinoma exhibited exceptionally high 125I-EGF binding activity, and those of small-cell carcinoma showed no EGF binding activity. Southern blot hybridization analysis revealed EGF receptor gene amplification in the squamous-cell carcinomas with high EGF binding activity. The EGF receptor levels in squamous-cell carcinomas and adenocarcinomas were compared with their pathological staging grouping and pathological findings, including degree of differentiation, diameter of tumor, and lymph node metastasis. However, unlike previous reports on breast and bladder cancers, there was no obvious correlation between these pathological characteristics and the EGF receptor levels of lung cancer.

The effects of bestatin, a microbial aminopeptidase inhibitor, on epidermal growth factor-induced DNA synthesis and cell division in primary cultured hepatocytes of rats

We investigated the effects of microbial protease inhibitors, in particular the aminopeptidase inhibitor bestatin, on DNA synthesis and cell division induced by epidermal growth factor (EGF) in hepatocytes. Although bestatin did not significantly affect binding of EGF to hepatocytes, it inhibited EGF-induced DNA synthesis and cell division. DNA synthesis in rat hepatocytes was maximal 24-26 h after EGF addition to the medium. The time required for maximal DNA synthesis was not affected if bestatin was removed less than 12 h after addition, but synthesis was partially inhibited if bestatin was added to the medium several hours after EGF addition, depending on the time of bestatin addition. Our results suggest that bestatin arrests the new cell cycle induced by EGF at about 12 h after the initiation. Considering also our results obtained by employing other protease inhibitors, we concluded that specific proteases play important roles in hepatocyte DNA synthesis and cell division induced by EGF.

Insulin-like growth factor I receptor analysis of satellite cell-derived myotube membranes established from two lines of Targhee rams selected for growth rate

Ovine-derived fibroblasts were used to validate an insulin-like growth factor I (IGF-I) membrane-receptor binding assay system. Competitive binding using fibroblasts revealed that half-maximal inhibition of 125I-IGF-I binding by IGF-I was 2.3 nM. SDS-polyacrylamide gel electrophoresis analysis of specific protein-associated 125I-IGF-I was consistent with the migration of 125I-IGF-I-labeled Type I IGF receptor alpha-subunits at Mr 133,000 daltons. Further, the efficiency of two cell solubilization methods was examined and time-dependent binding equilibrium was determined for the membrane assay system. Satellite cell-derived myotubes were subsequently isolated from primary satellite cell cultures established from the semimembranosus muscles of high and low efficiency-of-gain (EOG) Targhee rams, and IGF-I receptor dynamics were measured. A membrane competitive binding study revealed that half-maximal inhibition of 125I-IGF-I binding was achieved by 1-ng IGF-I for low, and 10-ng IGF-I for high, EOG myotube membrane preparations. Kd values were similar between the high EOG (4.78 nM) and low EOG (2.95 nM) groups; however, receptor concentrations (Bmax) appeared to differ between groups. High EOG membrane receptor Bmax was 3.88 pmole/micrograms protein (19.87 pmole/micrograms DNA), whereas low EOG membrane receptor Bmax was 1.22 pmole/micrograms protein (9.28 pmole/micrograms DNA). These preliminary findings support the hypothesis that genetic selection for EOG results in altered satellite cell responsiveness to IGF-I.

Prognostic significance of epidermal growth factor receptor in esophageal squamous cell carcinomas

The prognostic value of epidermal growth factor (EGF) receptor level was studied in 32 patients with esophageal squamous cell carcinoma. The EGF receptor levels of tumors were measured by iodine 125 (125I)-EGF binding assay, and the patients subsequently were divided into two groups: a group with high EGF binding capacities (greater than or equal to 2.5% of input), and a group with low EGF binding capacities (less than 2.5% of input). The cumulative survival rates for the two groups were calculated by the Kaplan-Meier method. The generalized Wilcoxon test indicated that the survival rate of the high EGF binding group was significantly lower than that of the low EGF binding group (P less than 0.05). In tumors from two patients with the highest EGF receptor levels, EGF receptor gene amplification was observed. These patients developed mediastinal lymph node metastasis and died 4 and 11 months after surgery, respectively. These results suggest that elevated EGF receptor level is a significant prognostic indicator for esophageal squamous cell carcinoma.

Stimulation of a MR 80,000 protein phosphorylation by EGF in EGF receptor-hyperproducing human tumor cells

NA and Ca9-22 cells derived from squamous cell carcinomas of the tongue possess a large number of epidermal growth factor (EGF) receptors (2.0 X 10(6) and 1.3 X 10(6) receptors/cell, respectively). In these cell lines, EGF stimulated receptor autophosphorylation and phosphatidylinositol (PI) turnover. Furthermore, EGF enhanced the phosphorylation of an acidic protein of Mr 80,000. Phosphorylation of this protein was also stimulated by 12-O-tetradecanoyl-phorbol-13-acetate (TPA), a phorbol ester tumor promoter, and was mainly at serine residues. Phosphopeptide mapping using protease V8 or trypsin indicated that Mr 80,000 proteins isolated from the EGF- and TPA-treated cells were identical. The Mr 80,000 protein was present mainly in the cytosol, but it became closely associated with the membrane as a phosphorylated form upon EGF or TPA stimulation. These results suggest that the EGF-stimulated phosphorylation of the Mr 80,000 acidic phosphoprotein in EGF receptor-hyperproducing tumor cells is mediated through the activation of PI turnover and protein kinase C.

Selective killing of squamous carcinoma cells by an immunotoxin that recognizes the EGF receptor

We have conjugated a murine monoclonal antibody (B4G7) against the human epidermal growth factor (EGF) receptor to gelonin, a 60S ribosome inactivating protein, via N-succinimidyl-3-(2-pyridyldithio)propionate (SPDP) and 2-iminothiolane. The B4G7-gelonin conjugate bound to the cell surface in proportion to the number of EGF receptors and competed with B4G7 antibody for binding to EGF receptors. The conjugate killed EGF receptor-hyperproducing squamous carcinoma cells (A431, NA, Ca9-22, TE5), and to some extent, human fibroblasts (HFO). It did not kill EGF receptor-deficient small-cell lung cancer cells (H69) and mouse fibroblasts (Swiss/3T3). Free B4G7, gelonin or a mixture of B4G7 and gelonin did not kill A431 cells. The number of EGF receptors was correlated to cytotoxicity at 10(-8) M of the conjugate, and the data were fitted to the regression equation: y = -35.83 log x +233.4 (correlation coefficient = -0.9995). These results suggest that the B4G7-gelonin conjugate may be a useful weapon for targeting therapy to squamous-cell carcinomas.

Epidermal growth factor receptors in cancer tissues of esophagus, lung, pancreas, colorectum, breast and stomach

The levels of epidermal growth factor (EGF) receptors were investigated in surgically resected tumors of various origins including esophagus (n = 33), lung (n = 14), pancreas (n = 9), colorectum (n = 10), breast (n = 23) and stomach (n = 8). The 125I-EGF binding capacities of squamous cell carcinomas of esophagus and lung were exceptionally higher than those of the other cancer tissues. Immunohistochemical staining with an anti-EGF receptor monoclonal antibody detected EGF receptors in the basal cells and parabasal cells of normal esophageal epithelium and in all the cancer cells of squamous cell carcinoma tissues of esophagus and lung. DNA replicating cells were examined by the bromodeoxyuridine staining method and it was found that the basal cells and parabasal cells of normal epithelium and peripheral cells of cancer pearls are proliferating. Contrary to this, a tumor antigen TA-4, known as a specific marker for squamous carcinoma, was detected in the differentiated cancer cells and in middle-layer squamous cells. These results strongly suggest that the increase in EGF receptor levels may be associated with the development of human squamous cell cancers of esophagus and lung. Thus, measurement of EGF receptor expression in tumor tissues has diagnostic value and should prove useful for the development of new therapies.

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

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

Stimulation by EGF of the growth of EGF receptor-hyperproducing tumor cells in athymic mice

EGF receptor-hyperproducing cells of squamous carcinoma origin were inoculated s.c. into the bilatero-abdominal regions of athymic mice and a mini-osmotic pump containing EGF was implanted on teh back. After 2 weeks the tumors formed from 5 different cell lines in the presence of EGF weighed 3 to 6 times more than those formed in the absence of EGF. The cells recovered from these tumors maintained their original characteristics such as the amplified EGF receptor gene, high numbers of EGF receptors and a sensitivity to EGF-mediated inhibition of growth in vitro. These results suggest that EGF plays an important role in promoting growth of squamous-cell carcinoma in vivo.

High incidence of EGF receptor hyperproduction in esophageal squamous-cell carcinomas

EGF receptor levels were investigated in esophageal squamous-cell carcinoma tissues from 31 patients. Twenty-two (71%) of these cancer tissues exhibited significantly higher 125I-EGF binding activity than normal mucosa in the adjacent non-cancerous tissues. These EGF receptor levels were then compared on the basis of pathological findings including lymph-node metastasis, depth of invasion, differentiation type, vascular invasion, infiltration and location of the lesion. Unlike previous reports on breast and bladder cancers, our study showed no obvious correlation between these pathological characteristics and the EGF receptor levels in esophageal carcinomas. Immunohistochemical staining with the anti-EGF receptor monoclonal antibody detected EGF receptors in squamous cells of the cancer tissues as well as in the basal cells of nearby normal epithelium. Since the basal cells have proliferative potential in the esophagus, the increase in EGF receptor levels in these cells may possibly be associated with the development of human esophageal squamous-cell cancer.

Growth inhibition of 3T3 fibroblasts by lysosomotropic amines: correlation with effects on intravesicular pH but not vacuolation

The effects of five lysosomotropic amines on the growth of Swiss 3T3 fibroblasts were measured and compared with effects on intravesicular pH. Tributylamine and benzylamine, amines that affect intravesicular pH without causing vacuolation, were found to inhibit cell growth to a similar extent as vacuologenic amines previously tested. Excellent correlation between the half-maximal concentrations for the growth and pH effects were found for tributylamine, benzylamine, chloroquine, and ammonium chloride. The results suggest that growth inhibition by these amines is a direct result of their effects on pH and not due to other effects (such as vacuolation). In contrast, a 100-fold difference in the half-maximal concentrations was found for methylamine, suggesting that methylamine inhibits growth by a mechanism unrelated to pH.

Perinuclear location and recycling of epidermal growth factor receptor kinase: immunofluorescent visualization using antibodies directed to kinase and extracellular domains

This paper describes studies on the migratory behavior of epidermal growth factor (EGF) receptor kinase using antibodies that are specific for either the kinase domain or the extracellular domain of the receptor. Antiserum was raised to a 42,000-D subfragment of EGF receptor, which was shown earlier to carry the kinase catalytic site but not the EGF-binding site. Another antiserum was raised to the pure intact 170,000-D EGF receptor. The specificities of these antibodies were established by immunoprecipitation and immunoblotting experiments. The domain specificity was examined by indirect immunofluorescent staining of fixed cells. The anti-42-kD peptide antibody could bind specifically to EGF receptors of both human and murine origin and was found to be directed to the cytoplasmic part of the molecule. It did not bind to EGF receptor-negative cells, which contained other types of tyrosine kinases. The antibodies raised against the intact receptor recognized only EGF receptor-specific epitopes and were directed to the extracellular part of the molecule. The anti-receptor antibodies described above were used to visualize the cyclic locomotory behavior of EGF receptor kinase under various conditions of EGF stimulation and withdrawal. The receptor was examined in fixed and permeabilized cells by indirect immunofluorescent staining. The results demonstrate the following: (a) the receptor kinase domain migrates to the perinuclear region upon challenge with EGF; (b) both extracellular and cytoplasmic domains of the receptor are involved in migration as a unit; (c) withdrawal of EGF results in rapid recycling of the perinuclear receptors to the plasma membrane; (d) this return to the cell surface is inhibited by methylamine, chloroquine, and monensin; and (e) neither the internal migration nor the recycling process is blocked by inhibitors of protein biosynthesis.