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

Innovative design for a phase 1 trial with intra-patient dose escalation: The Crotoxin study

Introduction

Crotoxin has a broad antitumor activity but has shown frequent neurotoxic toxicity. To induce tolerance and limit this toxicity, we propose a new design with intra-patient dose escalation.

Methods

A new Dose Limiting Toxicity definition was used. The concept of Target Ceiling Dose was introduced.

Results

Dose Limiting Toxicity was the inability to dose escalate twice. Target Ceiling Dose was the highest planned dose to be administered to a patient and could change for patients along time. Recommended Dose was defined similarly as in a (3 + 3) conventional design.

Conclusion

This innovant design was used and the clinical trial is now closed for inclusions. Results will be presented later.

Cell culture of human gingival fibroblasts, oral cancer cells and mesothelioma cells with serum-free media, STK1 and STK2

The majority of cells are cultured with Dulbecco's modified Eagle's medium (DMEM) or RPMI supplemented with fetal bovine serum (FBS), which contains numerous factors, including cytokines, nutrients and unknown growth factors. These factors may affect cell growth, apoptosis and differentiation. The serum-free medium, STK2, has been previously reported as suitable for the cell culture of human mesenchymal stem cells. However, how STK1 or STK2 affect the cell proliferation of normal and cancer cells remains unknown. The present study examined the growth of the human gingival fibroblast (HGF-1) cell-line and the HSC-3, CA9-22 and MSTO cancer cell-lines, cultured with STK1 and STK2. STK1 increased the cell proliferation of HGF-1 compared to DMEM by assessment with the 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)- 2H-tetrazolium (MTS) assay, whereas STK1 and STK2 markedly inhibited the cell proliferation of HSC-3 and MSTO. The cell proliferation rate of CA9-22 cultured with STK1 or STK2 for 96 h was ~2-fold higher than the rate for 24 h culture. The shape of the HSC-3 cells was also found to have changed to round when cultured with STK2. These results indicate that STK1 increased the cell proliferation of HGF-1 compared to DMEM, whereas the proliferation of HSC-3 and MSTO was inhibited by STK1 and STK2. Thus, STK1 and STK2 had different affects on the cell growth of HGF-1, CA9-22, HSC-3 and MSTO.

BHLH transcription factor DEC2 regulates pro-apoptotic factor Bim in human oral cancer HSC-3 cells

DEC1 (BHLHE40/Stra13/Sharp2) and DEC2 (BHLHE41/Sharp1) are basic helix-loop-helix (bHLH) transcription factors that are involved in the regulation of apoptosis, cell proliferation, circadian rhythms and the response to hypoxia. We previously showed the functional effects of DEC1 and DEC2 on apoptosis in human breast cancer MCF-7 cells. However, the roles of DEC1 and DEC2 in oral cancer are poorly understood. We examined whether DEC1 and DEC2 are involved in the regulation of apoptosis in human oral cancer HSC-3 and CA9-22 cells. The expression of DEC2 was upregulated by cis-diamminedichloroplatinum (II) (cisplatin: CDDP) treatment in HSC-3 cells, whereas CDDP treatment had little effects on the expression of DEC2 in CA9-22 cells. We showed that DEC2 overexpression inhibits pro-apoptotic factor Bim and inhibits apoptosis induced by CDDP in HSC-3 cells, whereas it had little effects on apoptosis in CA9-22 cells. DEC1 overexpression had little effects on apoptosis induced by CDDP in these cells. We also found that CDDP upregulated the amounts of DEC2 in the nucleus in HSC-3 cells. These results suggest that DEC2 has anti-apoptotic effects on apoptosis induced by CDDP in HSC-3 cells.

Highly sensitive proximity mediated immunoassay reveals HER2 status conversion in the circulating tumor cells of metastatic breast cancer patients

Background

The clinical benefits associated with targeted oncology agents are generally limited to subsets of patients. Even with favorable biomarker profiles, many patients do not respond or acquire resistance. Existing technologies are ineffective for treatment monitoring as they provide only static and limited information and require substantial amounts of tissue. Therefore, there is an urgent need to develop methods that can profile potential therapeutic targets with limited clinical specimens during the course of treatment.

Methods

We have developed a novel proteomics-based assay, Collaborative Enzyme Enhanced Reactive-immunoassay (CEER) that can be used for analyzing clinical samples. CEER utilizes the formation of unique immuno-complex between capture-antibodies and two additional detector-Abs on a microarray surface. One of the detector-Abs is conjugated to glucose oxidase (GO), and the other is conjugated to Horse Radish Peroxidase (HRP). Target detection requires the presence of both detector-Abs because the enzyme channeling event between GO and HRP will not occur unless both Abs are in close proximity.

Results

CEER was able to detect single-cell level expression and phosphorylation of human epidermal growth factor receptor 2 (HER2) and human epidermal growth factor receptor 1 (HER1) in breast cancer (BCa) systems. The shift in phosphorylation profiles of receptor tyrosine kinases (RTKs) and other signal transduction proteins upon differential ligand stimulation further demonstrated extreme assay specificity in a multiplexed array format. HER2 analysis by CEER in 227 BCa tissues showed superior accuracy when compared to the outcome from immunohistochemistry (IHC) (83% vs. 96%). A significant incidence of HER2 status alteration with recurrent disease was observed via circulating tumor cell (CTC) analysis, suggesting an evolving and dynamic disease progression. HER2-positive CTCs were found in 41% (7/17) while CTCs with significant HER2-activation without apparent over-expression were found in 18% (3/17) of relapsed BCa patients with HER2-negative primary tumors. The apparent 'HER2 status conversion' observed in recurrent BCa may have significant implications on understanding breast cancer metastasis and associated therapeutic development.

Conclusion

CEER can be multiplexed to analyze pathway proteins in a comprehensive manner with extreme specificity and sensitivity. This format is ideal for analyzing clinical samples with limited availability.

Laminin- and fibronectin-like molecules produced by periodontal ligament fibroblasts under serum-free culture are potent chemoattractants for gingival epithelial cells

Previously, we revealed that hepatocyte growth factor (HGF) or an HGF-like factor secreted by periodontal ligament fibroblasts (PLF) and gingival fibroblasts cultured in the presence of serum was a major chemoattractant for gingival epithelial cells, and suggested that it might play a role in epithelial invasion. However, our recent study showed that serum-free culture of PLF and gingival fibroblasts produced potent chemoattractants other than HGF for gingival epithelial cells. To identify these chemoattractants, PLF-conditioned medium (PLF-CM) from serum-free cultures was obtained, concentrated, and separated by gel filtration column chromatography, and the chemotactic activity for gingival epithelial cells of each eluted fraction was monitored by a modified Boyden chamber assay. The chemoattractant activity was eluted at a molecular mass of around 600 kDa, which would include laminin and fibronectin, but not HGF, determined by ELISA. The chemotactic activity was reduced by treatment with antilaminin and/or antifibronectin polyclonal antibodies. Western blots using both antibodies revealed that the PLF-CM contained laminin- and fibronectin-like molecules. Along with HGF, these large glycoprotein molecules produced by PLF may be involved in the pathogenesis and progression of periodontitis by inducing the apical migration of epithelial cells.

Effects of serum on hepatocyte growth factor secretion and activation by periodontal ligament and gingival fibroblasts

BACKGROUND

Hepatocyte growth factor (HGF)/scatter factor is a paracrine growth factor secreted by mesenchymal cells, which exerts an effect on a variety of epithelial cell types. Our recent study revealed that periodontal ligament fibroblasts (PLF) and gingival fibroblasts (GF) cultured in the presence of serum which contains various stimulants produced HGF or HGF-like factor, a predominant chemoattractant for gingival epithelial cells, and suggested that it could be involved in epithelial down-growth in periodontitis.

METHODS

To clarify whether serum in medium stimulates PLF and GF to synthesize or activate HGF, the effect of fetal bovine serum (FBS) on HGF production was determined by enzyme-linked immunoabsorbent assay (ELISA), and its chemotactic activity for gingival epithelial cells was examined by modified Boyden chamber assay.

RESULTS

One to 10% FBS in the culture medium stimulated HGF secretion in a dose-dependent manner and the chemotactic activity was decreased by treatment with anti-hHGF neutralizing antibody. Furthermore, fibroblast-conditioned medium incubated with FBS and aprotinin reduced its chemotactic activity. Interestingly, serum-free culture of PLF and GF produced potent chemoattractants for gingival epithelial cells other than HGF.

CONCLUSIONS

These results show that FBS stimulates both HGF secretion and activation by PLF and GF.

Ionizing radiation stimulates existing signal transduction pathways involving the activation of epidermal growth factor receptor and ERBB-3, and changes of intracellular calcium in A431 human squamous carcinoma cells

Previous studies demonstrated that ionizing radiation activates the epidermal growth factor receptor (EGFR), as measured by Tyr autophosphorylation, and induces transient increases in cytosolic free [Ca2+], [Ca2+]f. The mechanistic linkage between these events has been investigated in A431 squamous carcinoma cells with the EGFR Tyr kinase inhibitor, AG1478. EGFR autophosphorylation induced by radiation at doses of 0.5-5 Gy or EGF concentrations of 1-10 ng/ml is inhibited by >75% at 100 nM AG1478. Activation of EGFR enhances IP3 production as a result of phospholipase C (PLC) activation. At the doses used, radiation stimulates Tyr phosphorylation of both, PLCgamma and erbB-3, and also mediates the association between erbB-3 and PLCgamma not previously described. The increased erbB-3 Tyr phosphorylation is to a significant extent due to transactivation by EGFR as >70% of radiation- and EGF-induced erbB-3 Tyr phosphorylation is inhibited by AG 1478. The radiation-induced changes in [Ca2+]f are dependent upon EGFR, erbB-3 and PLCgamma activation since radiation stimulated IP3 formation and Ca2+ oscillations are inhibited by AG1478, the PLCgamma inhibitor U73122 or neutralizing antibody against an extracellular epitope of erbB-3. These results demonstrate that radiation induces qualitatively and quantitatively similar responses to EGF in stimulation of the plasma membrane-associated receptor Tyr kinases and immediate downstream effectors, such as PLCgamma and Ca2+.

Influence of epidermal growth factor on photodynamic therapy of glioblastoma cells in vitro

Photodynamic therapy (PDT) could be a useful adjuvant in glioblastoma treatment. The fact that epidermal growth factor (EGF) and its receptor are involved in glioblastoma growth control led us to investigate the relationships between EGF and PDT with respect to three different glioma cell lines (C6, T98 G, U87 MG) responsive to growth stimulation by EGF. Flow cytometric analysis revealed that each cell line expressed EGF receptors. PDT was then applied to the cells using haematoporphyrin derivative (HPD) as photosensitizer and argon laser irradiation. When cells were incubated for 2 h with HPD (0.1-10 micrograms/ml) and then laser-irradiated (lambda = 514 nm; energy density 25 J/cm2), all three cell lines showed photosensitivity. The median lethal dose was respectively 3, 4.5 and 2.7 micrograms/ml for C6, T98 G and U87 MG. EGF (2-50 ng/ml) had no effect on HPD- and laser-induced toxicity when added to cells before PDT, whereas toxicity decreased for all three cell lines when EGF was added after PDT. HPD (1-2 micrograms/ml, incubation times 30-180 min) also induced an increase in EGF receptor expression for the C6 line.

Regulation of epidermal growth factor receptor activity by crotoxin, a snake venom phospholipase A2 toxin. A novel growth inhibitory mechanism

Crotoxin (CT), a phospholipase A2 (PLA2) derived from the venom of Crotalus durissus terrificus, is a heterodimeric protein composed of subunit B with enzymatic activity and a binding regulatory subunit (A) without enzyme activity. Although the PLA2 activity of CT may be important in its anti-proliferative activity, its cytostatic mechanism is unknown. In this study, we examined the cytostatic effect of PLA2-associated CT activity on squamous carcinoma cells expressing distinct levels of epidermal growth factor receptor (EGFr). CT was most effective in suppressing growth on cells expressing high intrinsic levels of EGFr. Cardiotoxin, another membrane active toxin with no intrinsic PLA2 activity, had no differential anti-proliferative activity on cells expressing high EGFr levels, suggesting a correlation between EGFr expression and CT-directed anti-proliferative activity. Both chemically modified CT (MCT) devoid of PLA2 activity and covalently cross-linked CT (CCT), which is functionally unable to utilize cellular membranes as PLA2 substrate, were also without growth inhibitory activity. No evidence for direct binding of CT to EGFr was found, although pretreatment with EGF was able to partially suppress the anti-proliferative activity of CT. Tyrosine phosphorylation of EGFr, however, was stimulated by CT in intact A431 cells. Tyrosine phosphorylation of EGFr was concentration-dependently stimulated (3- to 8-fold) in cellular membranes of A431 cells treated in vitro with CT but not with anti-proliferatively inactive MCT or CCT. The data provide evidence for transmembrane receptors involved in growth signaling (namely EGFr) as cellular targets and potential effectors of PLA2-mediated anti-proliferative activity of snake venom.

Two chimeric receptors of epidermal growth factor receptor and c-Ros that differ in their transmembrane domains have opposite effects on cell growth

Two chimeric receptors, ER1 and ER2, were constructed. ER1 contains the extracellular and transmembrane (TM) domains derived from epidermal growth factor receptor and the cytoplasmic domain from c-Ros; ER2 is identical to ER1 except that its TM domain is derived from c-Ros. Both chimeras can be activated by epidermal growth factor and are capable of activating or phosphorylating an array of cellular signaling proteins. Both chimeras promote colony formation in soft agar with about equal efficiency. Surprisingly, ER1 inhibits while ER2 stimulates cell growth on monolayer culture. Cell cycle analysis revealed that all phases, in particular the S and G2/M phases, of the cell cycle in ER1 cells were elongated whereas G1 phase of ER2 cells was shortened threefold. Comparison of signaling pathways mediated by the two chimeras revealed several differences. Several early signaling proteins are activated or phosphorylated to a higher extent in ER1 than in ER2 cells in response to epidermal growth factor. ER1 is less efficiently internalized and remains tyrosine phosphorylated for a longer time than ER2. However, phosphorylation of the 66-kDa She protein, activation of mitogen activated protein kinase, and induction of c-fos and c-jun occur either to a lesser extent or for a shorter time in ER1 cells. Cellular protein phosphorylation patterns are also different in ER1 and ER2 cells. In particular, a 190-kDa Shc-associated protein is tyrosine phosphorylated in ER2 but not in ER1 cells. Our results indicate that the TM domains have a profound effect on the signal transduction and biological activity of those chimeric receptors. The results also imply that sustained stimulation of ER1 due to its retarded internalization apparently triggers an inhibitory response that dominantly counteracts the receptor-mediated mitogenic signals. These two chimeras, expressed at similar levels in the same cell type but having opposite effects on cell growth, provide an ideal system to study the mechanism by which a protein tyrosine kinase inhibits cell growth.

Loss of cytotoxic effect of epidermal growth factor (EGF) on EGF receptor overexpressing cells is associated with attenuation of EGF receptor tyrosine kinase activity

The biological activity of epidermal growth factor (EGF) is mediated through the intrinsic tyrosine kinase activity of the EGF receptor (EGFR). In numerous cell types, binding of EGF to the EGFR stimulates the tyrosine kinase activity of the receptor eventually leading to cell proliferation. In tumor-derived cell lines, which overexpress the EGFR, however, growth inhibition is often seen in response to EGF. The mechanism for growth inhibition is unclear. To study the relationship between growth inhibition and EGFR kinase activity, we have used a cell line (PC-10) derived from a human squamous cell carcinoma that overexpresses EGFR. When exposed to 25 ng/ml EGF at low cell densities (1,300 cells/cm2), PC-10 cells exhibit cell death. In contrast, if EGF is added to high density cultures, no EGF mediated cell death is seen. When PC-10 cells were maintained at confluency in the presence of 25 ng/ml EGF for a period of 1 month, they were subsequently found competent to proliferate at low density in the presence of EGF. We designate these cells APC-10. The APC-10 cells exhibited a unique response to EGF, and no concentration of EGF tested could produce cell death. By 125I-EGF binding analysis and [35S]methionine labeling of EGFR, it was found that the total number of EGFR on the cell surface of APC-10 was not decreased relative to PC-10. No difference between PC-10 and APC-10 was seen in EGF binding affinity to the EGFR. Significantly, EGF stimulated autophosphorylation of the EGFR of APC-10 was 8-10-fold lower than that of PC-10. This reduced kinase activity was also seen in vitro in membrane preparations for EGFR autophosphorylation as well as phosphorylation of an exogenously added substrate. No difference between PC-10 and APC-10 in the overall pattern of EGFR phosphorylation in the presence or absence of EGF was detectable. However, the serine and threonine phosphorylation of the EGFR of APC-10 cells was consistently 2-3-fold lower than that seen in PC-10 cells. These results suggest a novel mechanism for EGFR overexpressing cells to survive EGF exposure, one that involves an attenuation of the tyrosine kinase activity of the EGFR in the absence of a change in receptor levels or receptor affinity.

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.

Heterogeneity in epidermal growth factor responsiveness and tumor growth of human maxillary cancer cell lines

We have established three cell lines (IMC-2, IMC-3, and IMC-4) from a human maxillary tumor, which exhibited different sensitivities to epidermal growth factor (EGF). It was inhibitory to colony-forming abilities of IMC-3 and IMC-4 cells in culture, while it affected that of IMC-2 cells slightly if at all. The differential sensitivities to EGF among the three cell lines were reproducibly observed when several cell sublines were further established from tumors appearing in nude mice. Saturation-binding kinetics with 125I-EGF showed similar levels of EGF-binding activities among the three cell lines. However, IMC-2, IMC-3, and IMC-4 showed almost similar sensitivities to cisplatin. Autophosphorylation of EGF receptor in the presence of EGF proceeded at similar levels among the three cell lines. Tumor growth was followed in nude mice when IMC-2, IMC-3, and IMC-4 at 1 x 10(7) cells were inoculated. The IMC-2 tumors enlarged at much faster rates than the other two cell lines. The IMC-4 tumors showed very slow growth rates, and IMC-3 tumors enlarged at an intermediate rate. These data suggest that the maxillary tumor used comprised cell populations that differed in their growth behaviors in response to EGF.

Variation in EGF-induced EGF receptor downregulation in human hepatoma-derived cell lines expressing different amounts of EGF receptor

The effect of epidermal growth factor (EGF) receptor overexpression on ligand-induced EGF receptor downregulation was examined using a hepatoma-derived cell line, PLC/PRF/5, which expresses normal amounts of the EGF receptor, and a subline, NPLC/PRF/5, which expresses 10-fold more receptors at its cell surface. PLC/PRF/5 cells efficiently downregulated surface receptor levels upon exposure to saturating and subsaturating concentrations of EGF; the rate of receptor downregulation corresponded to that of ligand-receptor internalization. Upon internalization, EGF receptors were degraded and receptor biosynthesis remained at basal levels. EGF surface receptor remained downregulated for as long as cells were exposed to EGF. By contrast, surface EGF receptor abundance in NPLC/PRF/5 cells decreased by only 5-15% after 1-4 h incubation with subsaturating doses of EGF and actually increased by 67% within 20 h. Exposure of these cells to saturating concentrations of EGF induced modest decreases in surface receptor abundance during the initial 12 h incubation, followed by a progressive decline to 30% of initial values by 24 h. Relative ligand-receptor internalization rates in NPLC/PRF/5 cells were lower than those in PLC/PRF/5, although their surface receptor population was even higher than that predicted by the decreased internalization rates. EGF receptor degradation in NPLC/PRF/5 cells was also inhibited; exposure to saturating levels of EGF for more than 16 h was necessary before significant degradation occurred. Receptor protein and mRNA biosynthesis in NPLC/PRF/5 were stimulated by 8 h exposure to EGF but when saturating concentrations of EGF were present for 16 h, receptor biosynthesis was inhibited. EGF receptor overexpression circumvents the downregulatory effect of EGF by decreasing the rate of receptor internalization, inhibiting degradation of the internalized receptor pool, and stimulating EGF receptor biosynthesis. Conversely, receptor downregulation becomes pronounced at late times when receptor degradation is high and biosynthesis is inhibited.

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.

Kinetics of tyrosine phosphorylation and internalization of human EGF receptors overexpressed in NIH 3T3 fibroblasts

Binding of epidermal growth factor (EGF) to cells rapidly induces tyrosine phosphorylation of its receptor which is followed by its internalization and dephosphorylation. The kinetics of these processes differs widely in time from minutes to hours according to cell types. In this paper we analyzed EGF receptor phosphorylation and down-regulation in NIH 3T3 cells transfected with the recombinant hEGF-R cDNA which express 4 X 10(5) receptors/cell. In the presence of EGF receptor phosphorylation reached a maximum after 1 min and was then maintained for about 1 h, while during this time the number of EGF-binding sites was reduced to 40% of the initial number. Detailed analysis of the fate of a population of receptors previously activated and autophosphorylated at 4 degrees C, after warming to 37 degrees C in the absence of the ligand, showed that internalization of the cell surface-associated EGF and dephosphorylation of the receptor were rapid (t1/2 15 min) and followed a similar kinetics. Our data indicate that at any given time only a fraction of the total cell surface receptors is phosphorylated on tyrosine and that dephosphorylation occurs at the cell surface or very rapidly after internalization. In addition the data also suggest that a certain recycling of previously internalized receptors may occur in these cells during EGF treatment.

Purification of two distinct proteins of approximate Mr 80,000 from human epithelial cells and identification as proper substrates for protein kinase C

A Mr-80,000 acidic phosphoprotein ('80K protein') is a specific substrate for protein kinase C. We attempted to purify the 80K protein from a human squamous-cell carcinoma cell line, Ca9-22, by the sequential use of heat treatment, (NH4)2SO4 precipitation, Mono Q column chromatography, proRPC column chromatography and gel filtration. The 80K protein was assayed by phosphorylation in vitro by using partially purified human type III protein kinase C, and was fractionated into two distinct molecular species with slightly different Mr values, designated 80K-L and 80K-H proteins. Phosphorylation occurred mainly at serine residues of these proteins. Two-dimensional phosphopeptide maps after trypsin digestion and kinetic profiles of phosphorylation were different from each other. Ca2(+)- and phospholipid-dependency of the phosphorylation in vitro confirmed that both 80K-L and 80K-H proteins are true substrates for three subtypes of protein kinase C. The 80K-L protein was a preferential substrate for type III protein kinase C, and the 80K-H protein was phosphorylated more effectively by type I and type II protein kinase C. The possible roles of these two distinct 80K proteins in signal transduction are discussed.

EGF receptor down-regulation attenuates ligand-induced second messenger formation

Epidermal growth factor (EGF)-induced increases in cytosolic Ca2+ and inositol polyphosphate production were compared in a human hepatocellular carcinoma-derived cell line, PLC/PRF/5, and in an EGF receptor-overexpressing subline, NPLC/PRF/5. Formation of these second messengers was correlated to EGF receptor display at the cell surface by monitoring ligand-induced EGF receptor down-regulation. Both cell lines exhibited a strikingly similar cytosolic Ca2+ increase upon exposure to EGF. The initial inositol phosphate responses were also similar in the two cell lines; inositol 1,4,5-trisphosphate increased within 10-15 s and returned to prestimulatory values after 2 min in both cell lines, while inositol tetrakisphosphate and inositol 1,3,4-trisphosphate were elevated after a 2-min exposure to EGF. At later times the responses were markedly different; NPLC/PRF/5 cells exhibited prolonged production of inositol 1,3,4-trisphosphate and inositol tetrakisphosphate (maximum at 1-3 h) but PLC/PRF/5 cells showed decreased levels of these isomers after 10 min and a return to basal values by 1 h. Exposure of PLC/PRF/5 cells to EGF caused a progressive decrease in the amount of EGF receptor at the cell surface whereas such treatment did not change the surface receptor levels in NPLC/PRF/5 cells. Kinetic analysis of EGF receptor down-regulation showed that receptor internalization was rapid enough to account for the transient nature of the inositol phosphate response in PLC/PRF/5 cells. Thus, the divergent patterns of signaling exhibited by the two cell lines may reflect differences in the efficiency of EGF-induced down-regulation of surface receptors.

Reduced tyrosine phosphorylation and nonresponsiveness to EGF-mediated cytotoxicity in EGF receptor-hyperproducing UCVA-1 cells

UCVA-1 cells, derived from human pancreas adenocarcinoma, have a high number of epidermal growth factor (EGF) receptors (1.0 x 10(6) per cell) but their growth is not inhibited by EGF, unlike other EGF receptor-hyperproducing tumour cells. In UCVA-1 cells EGF activates neither the phosphatidylinositol turnover nor protein kinase C. EGF, however, enhances the phosphorylation of EGF receptors at specific tyrosine residues, indicating that the EGF receptor kinase is active and subject to autophosphorylation. Downmodulation of EGF receptors by 12-O-tetradecanoylphorbol 13-acetate (TPA) is also observed. Using an anti-phosphotyrosine antibody several phosphoproteins, including EGF receptors, were immunoprecipitated from UCVA-1 cell lysates, whereas more than 20 phosphoproteins were detected in other EGF receptor-hyperproducing tumour cells (NA), indicating that tyrosine-phosphorylation of endogenous substrates by EGF receptor kinase is significantly reduced in UCVA-1 cells. Thus, non-responsiveness of UCVA-1 cells to EGF is correlated with the reduced tyrosine phosphorylation.

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.

Lung cancer cells often express high levels of protein kinase C activity

We analyzed protein kinase C (PKC) activity in twenty-two tumor cell lines derived from lung, pancreas, stomach, tongue and vulva, and found that lung cancer cells often (9 out of 13) exhibit significantly higher PKC activity than other types of cancer cells. The PKC in these lung cancer cells was separated into one major and one minor peaks by a Mono Q column chromatography. The PKC in the major peak had an absolute requirement for Ca2+, phosphatidylserine and 12-O-tetradecanoylphorbol-13-acetate (TPA), as expected. However, the PKC in the minor peak did not require TPA for its activation. Hydroxyapatite column chromatography revealed that the PKC in the major peak is type III. These results indicate that in lung cancer cells type III PKC activity is often elevated compared to other types of cancer cells. The growth of many lung cancer cell lines was inhibited by TPA.

Unique chromosomal location of amplified EGF receptor genes in EGF receptor-hyperproducing tumor cell line NA

The epidermal growth factor receptor (EGFR) gene was analyzed by in situ hybridization using a squamous cell carcinoma line NA, which has high numbers of EGF receptors and carries a 20-fold amplification of EGFR genes. NA cells are pseudotriploid (mode of chromosome number is 69) and have three copies of an apparently normal chromosome 7 together with several aberrant chromosomes. Strong hybridization signals were observed in the abnormal banding region of one of the aberrant chromosome, MH1, which has no structural homology to chromosome 7. This MH1 chromosome was lost in NA-derived variant lines that possess reduced numbers of EGF receptors. These results are in contrast to previous findings that EGFR gene amplification is associated with structural alterations of the short arm of chromosome 7 and provide new evidence in regard to the location of the amplified EGFR gene in tumor cells.