A novel germline mutation of PTEN associated with brain tumours of multiple lineages.

We have identified a novel germline mutation in the PTEN tumour suppressor gene. The mutation was identified in a patient with a glioma, and turned out to be a heterozygous germline mutation of PTEN (Arg234Gln), without loss of heterozygosity in tumour DNA. The biological consequences of this germline mutation were investigated by means of transfection studies of the mutant PTEN molecule compared to wild-type PTEN. In contrast to the wild-type molecule, the mutant PTEN protein is not capable of inducing apoptosis, induces increased cell proliferation and leads to high constitutive PKB/Akt activation, which cannot be increased anymore by stimulation with insulin. The reported patient, in addition to glioma, had suffered from benign meningioma in the past but did not show any clinical signs of Cowden disease or other hereditary diseases typically associated with PTEN germline mutations. The functional consequences of the mutation in transfection studies are consistent with high proliferative activity. Together, these findings suggest that the Arg234Gln missense mutation in PTEN has oncogenic properties and predisposes to brain tumours of multiple lineages.

An enzyme-linked immunosorbent assay for the determination of src-family tyrosine kinase activity in breast cancer.

An enzyme-linked immunosorbent assay is described for the determination of protein tyrosine kinase activity originating from the presence of src-like tyrosine kinases in biological samples. In this assay a peptide derived from p34cdc2, cdc2(6-20)NH2, is coupled to the wells of a maleic anhydride-activated microtiter plate. This particular peptide has been described as an efficient and specific substrate for protein tyrosine kinases belonging to the src family kinases (Cheng et al., J.Biol.Chem. 267 (1992) 9248-9256). After incubation of the coated substrate with sample and ATP, the amount of phosphorylated tyrosyl residues is determined with phosphotyrosine specific antibodies and a secondary peroxidase-labeled antibody. The assay appears to be very sensitive and is linear with sample protein concentration and phosphorylation time. Intra-assay variation is < 5%, whereas day-to-day variation is < 10%. The results of the assay have been compared with an ELISA in which the broad-specificity tyrosine kinase substrate poly(GluNa,Tyr)4:1 was coated. The results of both assays in 27 cytosolic breast cancer samples correlated very well (r = 0.94), in accordance with the predominant expression of src kinase activity in breast cancers (Ottenhoff-Kalff et al., Cancer Res. 52 (1992), 4773-4778). The present assay provides an easy, reproducible, and quick alternative for the usual radioactive methods used for the determination of src-kinase activities including immunecomplex kinase assay and TCA-precipitation assays. It allows the determination of src-like activities in human tumors for routine diagnostic purposes.

Clinical relevance of protein-tyrosine (de-)phosphorylation in head and neck cancer.

Previous studies have shown that protein tyrosine (de)phosphorylation plays an important role in head and neck cancer. Protein-tyrosine kinases (PTK) and protein-tyrosine phosphatases (PTPase) activities in the cytosol of tumor tissue were significantly increased compared to normal tissue of cancer patients as well as controls. Additionally, the enzyme activities in normal tissue of tumor patients were significantly higher than enzyme activities in normal tissue of the control group. In this paper, we have correlated the cytosolic and membranous PTK and PTPase activity of tumor and nontumor tissue with several clinical and histological parameters known to influence the clinical outcome. Furthermore, we have analyzed the value of the enzyme activities as an independent predictor of clinical behavior and occurrence of second primary tumors. We confirmed our earlier observations that cytosolic and membranous PTK activities and cytosolic PTPase activities in tumor tissues are increased compared to activities in nontumor tissues and controls. Moreover, we also confirmed the findings of increased enzyme activities in nontumor tissues compared to findings in control tissues. This finding in histologically proven healthy mucosa is highly interesting because it indicates that these biochemical changes are obviously not (yet) translated into morphological changes. Significant differences were found in membranous PTK activity when the patients were grouped by sex, tumor localization, lymph node metastasis, and previous radiotherapy. During the follow-up period, no relation could be found between enzyme activities in tumor and/or nontumor tissues and disease-free interval or occurrence of second primary tumors.

Protein tyrosine phosphatase activity as a diagnostic parameter in breast cancer.

Cellular phosphotyrosine levels are regulated by the balance between protein tyrosine kinases (PTKs) and protein tyrosine phosphatases (PTPs). It is supposed that this balance is disturbed in tumour cells, making the increased or altered activity of PTKs and PTPs likely hallmarks of tumour tissues. Indeed it could be shown that the PTK activity was increased in breast cancer in correlation with prognosis (Hennipman et al., Cancer Res. 49, 516-522, 1989). In the present report we measured the PTP activities in breast cancer and normal breast tissues. An increase of approximately three- to four-fold was measured in the cytosolic tumour fractions compared to normal, whereas the solubilized membrane fraction PTP activity showed an increase in tumours of approximately 1.5-fold. Remarkably, the membrane PTP activity correlated with the presence of tumour positive axillary lymph nodes (p = 0.004), whereas the cytosolic PTP activity correlated with the mitotic index, a higher PTP activity occurring when the mitotic index was higher than 10 (p = 0.0004). These results indicate the membrane PTP activity may be considered as an index of metastatic potential, whereas cytosolic PTP activity may be a measure of the growth capacity of the tumour. The increase of PTP activity in breast cancers was confirmed by enzyme-histochemical studies. In frozen sections of tumours a strong to moderate activity was found in both tumour cells and interstitial cells. In the interstitium membrane activity was most pronounced, whereas in the tumour cells diffuse staining of the cytoplasm together with a clear membrane staining was demonstrated. Immunoblotting with anti-phosphotyrosine antibodies also reveals differences between the tumours and normal tissues, confirming the disturbance of the balance between protein tyrosyl phosphorylation and dephosphorylation in the tumour cells.

Functional interaction between the epidermal growth factor receptor and c-Src kinase activity.

To study the relationship between the tyrosine kinase c-Src and the epidermal growth factor receptor (EGF-R), we used the breast cancer cell line ZR75-1, which was transfected with the EGF-R. The EGF-R transfected cell line expressed 60 times more EGF-R than a control cell line transfected with the empty vector. In the presence of EGF, the EGF-R over-expressing cell line grew much faster than the control cell line. Both cell lines expressed approximately equal amounts of c-Src. However, the cell line over-expressing the EGF-R showed a twofold enhancement of c-Src kinase activity after EGF stimulation. The activation of c-Src kinase by EGF was confirmed in other EGF-R expressing cell types.

Protein kinase C is not involved in the cytotoxic action of 1-octadecyl-2-O-methyl-sn-glycerol-3-phosphocholine in HL-60 and K562 cells.

We studied the effects of the alkyllysophospholipid 1-octadecyl-2-O-methyl-sn-glycerol-3-phosphocholine (ET-18-OCH3) on membrane associated protein kinase C (PK-C) activity in ET-18-OCH3 sensitive HL-60 cells and in two resistant cell types, Me2SO differentiated HL-60 cells and K562 cells. HL-60 cells expressed a lower PK-C activity level compared with both resistant cell types. However, membrane-bound PK-C activity in the sensitive HL-60 cells was approximately 3-fold increased in the presence of ET-18-OCH3, whereas in differentiated HL-60 cells and K562 cells PK-C was not influenced by ET-18-OCH3. The increase in PK-C activity in HL-60 cells was not due to translocation of cytosolic PK-C or synthesis de novo. The effect of ET-18-OCH3 on kinetic parameters of PK-C in all three cell types was investigated in order to elucidate the nature of the ET-18-OCH3 effects on PK-C activity in both sensitive and resistant cell types. A functional relationship between PK-C level and effect of ET-18-OCH3 on PK-C activity in the different cell types could not be found. Moreover, cells depleted of PK-C activity showed similar sensitivity or resistance to ET-18-OCH3 as cells expressing PK-C activity. These results suggest that a role of PK-C in the cytotoxic action of ET-18-OCH3 is very unlikely.

Redox regulation of signal transduction: tyrosine phosphorylation and calcium influx.

Studies presented here show that altering the intracellular redox balance by decreasing glutathione levels profoundly affects early signal transduction events in human T cells. In a T-cell receptor (TCR) signaling model, short-term pretreatment with buthionine sulfoximine, which specifically decreases intracellular glutathione, essentially abrogates the stimulation of calcium influx by anti-CD3 antibodies without significantly impairing other aspects of TCR-initiated signal transduction, such as overall levels of TCR-stimulated tyrosine phosphorylation. In an inflammatory-cytokine signaling model, the failure of tumor necrosis factor alpha to stimulate more than minimal tyrosine phosphorylation in lymphocytes is overcome by buthionine sulfoximine pretreatment--i.e., tumor necrosis factor alpha stimulates extensive tyrosine phosphorylation in glutathione-depleted lymphocytes. These redox-dependent changes in T-cell responsiveness suggest that the glutathione deficiency that we and others have demonstrated in human immunodeficiency virus-infected individuals may contribute significantly to the immunodeficiency and the increased inflammatory reactions in these individuals.

Protein tyrosine (de-)phosphorylation in head and neck squamous cell carcinoma.

Protein phosphorylation plays an important role in signal transduction of both normal and neoplastic cells. Since increased protein tyrosine phosphorylation may be associated with malignant transformation, we studied the activities of protein tyrosine kinases (PTK) and protein tyrosine phosphatases (PTPase) in patients with various head and neck tumors. Furthermore, we determined the patterns of tyrosine phosphorylated protein (P-tyr) in tissues by western blotting. Enzyme activities were studied in tumor and histologically normal, non-tumorous tissues of 54 patients and in 11 controls. P-tyr patterns were determined in 3 patients and 2 controls. PTK and PTPase activities were greater in tumor tissues than in normal tissue of the cancer patients as well as controls. P-tyr levels in tumors were also higher than in normal tissues. Additionally, PTK activity in normal tissue of tumor patients was significantly higher than in normal tissue of the control group. The same trend was observed for the PTPase activity and P-tyr levels.

Standardization of an enzyme-linked immunosorbent assay for the determination of protein tyrosine kinase activity.

A procedure for an enzyme-linked immunosorbent assay for the determination of protein tyrosine kinase (PTK) activity from cytosolic and solubilized membrane fractions from breast cancers, is described. The general PTK substrate poly(GluNa, Tyr) 4:1 is coated to the wells of a microtiter plate. After incubation with PTK sample and ATP the amount of phosphorylated tyrosyl residues is quantitated with phosphotyrosine specific antibodies and a secondary peroxidase-labeled antibody. The assay is optimized with respect to coating and phosphorylation conditions. The signal is linear with phosphorylation time and with sample protein concentrations in a sufficiently wide range. The assay is standardized by using both internal and external standards. A lyophilized rat spleen extract is used as an external standard. Its PTK activity, determined by established quantitative methods, can be used to calculate the activity of the breast cancer samples. To eliminate day-to-day variations an internal standard, consisting of BSA-coupled phosphotyrosine, is coated to some wells of the microtiter plate. Interassay variation can be minimized by determination of the ratio of optical densities from internal and external controls. Its variation appeared to be less than 18%. Intraassay variation appears to be < 6%. PTK activities measured with this assay correlated well with those of a nonradioactive dot-blot assay and with conventional radioactive assays in which [32P]ATP is used as the substrate. Compared to these assays it appeared to be more sensitive and far more easy to perform.

Adsorption and uptake of the alkyllysophospholipid ET-18-OCH3 by HL-60 cells during induction of differentiation by dimethylsulfoxide.

The human leukemic cell line HL-60 is highly sensitive to the antineoplastic agent alkyllysophospholipid, 1-octadecyl-2-methyl-sn-glycerol-3-phosphocholine (ET-18-OCH3). We investigated the adsorption and uptake of radiolabeled ET-18-OCH3 in undifferentiated HL-60 cells and during differentiation to granulocytes induced by dimethylsulfoxide. HL-60 cells become less sensitive to the cytotoxic action of ET-18-OCH3 during differentiation. The decrease in sensitivity is correlated with a decrease in both adsorption and uptake of [3H]ET-18-OCH3 during differentiation. Binding studies revealed that the binding of ET-18-OCH3 to both undifferentiated and differentiated HL-60 cells is non-saturable which renders the existence of a specific binding place highly unlikely.

Protein tyrosine kinase activity in laryngeal squamous cell carcinoma.

Oncogenes play an important role in the process of malignant transformation. Since many of the protein tyrosine kinases (PTK) are products of oncogenes, the aim of this study was to demonstrate whether an increased PTK activity could be found in head and neck tumors. By using a non-radioactive dot-blot assay, PTK activity was measured in tumor and normal tissues of 38 patients with laryngeal cancer. The control group consisted of 19 healthy persons. PTK activity in tumor cells was significantly higher (P < 0.001) than in normal cells of the tumor patients and normal controls. Additionally, the PTK activity in the normal mucosa of the tumor patients was significantly higher than in the normal mucosa of the control group.

Partial characterization of protein tyrosine kinases in human lymphoid cells.

We have examined several aspects of protein tyrosine kinase (PTK)-activity in the cytosolic and membrane fractions of both normal and malignant lymphoid cells. The expression of the PTK-encoding oncogenes fes, abl and src, was investigated with the use of antibodies generated to their respective gene products. These antibodies recognized proteins in all cell types examined, most frequently in both the cytosolic and the membrane fraction. PTKs were partially characterized by FPLC. PTK-activities of column fractions were assayed using a non-radioactive dot blot assay. Cytosolic and membrane fractions showed FPLC patterns with a constant as well as a variable part in both normal and malignant cells, suggestive of PTKs with specialized functions in normal cell growth and transformation. Lastly, using antibodies to phosphotyrosine, we found that cytosolic fractions contained the majority of proteins phosphorylated at tyrosine in all cell types. Normal peripheral blood lymphocytes and B-lymphoma cells showed a great similarity in tyrosine phosphorylation pattern, while in tonsillar lymphocytes a clearly different pattern was found. These methods further characterize PTK-activities in lymphoid cells, and the results give evidence that PTKs in normal and malignant cells have both similar and different aspects.

Characterization of protein tyrosine kinases from human breast cancer: involvement of the c-src oncogene product.

Tyrosine phosphorylation is an important regulatory mechanism in response to the action of growth factors and oncogenes. Since many oncogenes code for tyrosine kinases, increased or altered oncogene expression may be reflected in increased tyrosine kinase activity. In a recent study (Hennipman et al., Cancer Res., 49: 516-521, 1989), we found that the tyrosine kinase activity of the cytosolic and membrane fractions of malignant human breast tissue was significantly higher compared to the benign or the normal breast tissue. Moreover, the increase in the cytosolic fractions was found to be of prognostic value. In the present study we determined the protein tyrosine kinase (PTK) activity of another 72 breast cancer specimens, and it could be shown again that the PTK activity in all 72 of these tumors was elevated compared to normal controls. We characterized these cytosolic PTKs by anion exchange chromatography using fast protein liquid chromatography, and it could be shown that at least two different forms of PTK exist. Using antibodies against a number of known oncogene products, we could determine that at least 70% of the PTK activity in the cytosol originated from the presence of the c-src oncogene product. Both of the PTK activity peaks seen in the fast protein liquid chromatography patterns could be precipitated with the anti-Src antibody. Furthermore, using the MCF-7 breast cancer cell line, it could be shown that the antibody against c-src also precipitated a part of the cytosolic PTK activity. In normal human peripheral lymphocytes, no precipitation of the cytosolic and membrane PTK activity could be achieved using the anti-Src antibody. Inasmuch as the cytosolic PTK activity parallels the malignancy in breast tumors (Hennipman et al., Cancer Res., 49: 516-521, 1989), and the majority of this activity is precipitated by anti-Src antibodies, the c-src protooncogene may play a key role in the manifestation of breast cancer.

Phosphorylation of pyruvate kinase type K is restricted to the dimeric form.

In the absence of glycolytic intermediate, fructose-1,6-bisphosphate, pyruvate kinase type K exists in the dimeric form and is readily phosphorylated, whereas in the same sample and the same conditions pyruvate kinase type M is present as a tetramer and is not phosphorylated. Addition of fructose-1,6-bisphosphate results in the association of dimeric K2 molecules to a tetrameric K4 enzyme as determined by gel filtration and cellulose acetate electrophoresis, with concomitant loss of the capacity of the K isozyme to become phosphorylated. Phosphorylated K2 dimers can also tetramerize, but with a low recovery of the radiolabel, suggesting a fructose-1,6-bisphosphate induced dephosphorylation or selective degradation. The dimeric K isozyme is enzymatically active; inactive K-type monomers can be detected by immunoblot analysis in the absence of fructose-1,6-bisphosphate, but no phosphorylated pyruvate kinase is present in this fraction. The formation of K4 tetramers can not be accomplished by the substrate phosphoenolpyruvate. Fructose-1,6-bisphosphate is an allosteric activator of pyruvate kinase type K and induces hyperbolic saturation curves for phosphoenolpyruvate. In contrast, in the absence of effectors, pyruvate kinase type M exhibits Michaelis-Menten kinetics, but sigmoidal curves can be induced by the amino acid phenylalanine. However, even in the presence of phenylalanine, the M-type maintained its tetrameric configuration and did not serve as a substrate in the phosphorylation reaction. These findings argue for the importance of subunit interaction in the regulation of phosphorylation of pyruvate kinase.

The cytotoxicity of alkyl-lysophospholipid on clonogenic leukemia cells and on normal bone marrow progenitor cells is highly, but differentially, increased by cryopreservation.

We studied the cytotoxic effect of alkyl-lysophospholipid (ALP) in combination with cryopreservation on human clonogenic leukemia cells from 10 patients with acute leukemia and on normal bone marrow progenitors (committed stem cells) from 10 donors, in order to assess the applicability of ALP as a purging agent in autologous bone marrow transplantation (ABMT). The tumoricidal effect of ALP was greatly increased by the cryopreservation procedure, both on leukemic progenitors and to a lesser extent on normal bone marrow progenitors. The cytotoxic effects of ALP and of cryopreservation were synergistic. As a consequence, the ALP dose for ex vivo purging has to be adjusted. Furthermore, the cryopreservation procedure itself is more cytotoxic for leukemic progenitors than for normal marrow progenitors, indicating that cryopreservation has a purging effect in AMBT.

Protein tyrosine kinases in human brain and gliomas.

Tyrosine kinase activity was determined in neonatal and adult human brain, oligodendrogliomas, and astrocytomas. The astrocytomas were divided into low- (grade I and grade II) and high-grade (grade III and grade IV) tumors. We measured the tyrosine kinase activity in the cytosolic and membrane fraction using poly(glutamic acid:tyrosine, 4:1) as an artificial substrate. The cytosolic activity in oligodendrogliomas (n = 7), low-grade astrocytomas (n = 7), and neonatal brain (n = 1) was increased, on average, two- to fourfold compared with that in normal adult brain (n = 14). The cytosolic activities of high-grade astrocytomas (n = 11) were in approximately the same range as found in normal adult brain. The absence of an increase in cytosolic activity in high-grade astrocytomas compared with adult brain is likely due to the occurrence of necrosis in these tumors. In contrast to the cytosolic activity, no differences were found in the membrane-bound activity. By fast protein liquid chromatography, at least three forms of cytosolic protein tyrosine kinase could be separated, which eluted at 0, 115, and 210 mM NaCl. In most cases the highest amount of activity eluted at 210 mM NaCl. However, in oligodendrogliomas, high-grade astrocytomas, and neonatal brain, more activity eluted at 115 mM NaCl than in normal adult brain (p = 0.043). Nevertheless, protein tyrosine kinases from all three peaks contributed to the elevated levels of total cytosolic activity of oligodendrogliomas and low-grade astrocytomas.

Cellular expression of K-type pyruvate kinase in normal and neoplastic human tissues.

The cellular expression of K-type pyruvate kinase was studied immunohistochemically in several normal and neoplastic tissues of human origin. The authors used the monoclonal antibody, designated as ES1, which was raised against human K-type pyruvate kinase. In contrast to the normal counterparts, a strong immunoreactivity was found in a rhabdomyosarcoma (n = 1), in a carcinoma of the pancreas (n = 1), and in neurofibromas (n = 2). Furthermore, the staining in leiomyosarcomas (n = 2) was shown to be more intense when compared with both normal smooth muscle cells and leiomyomas (n = 2). These findings show that knowledge about the cellular expression of the K-type pyruvate kinase identifies cell types for which its expression serves as oncodevelopmental marker. In addition, these immunohistochemical studies give information whether shifts toward K-type containing isozymes of pyruvate kinase, which are determined by electrophoresis in whole cytosolic extracts of various tumors, are due to an altered gene expression or due to proliferation of cells which normally express already the K-type pyruvate kinase. The first possibility probably occurs in rhabdomyosarcomas. The latter possibility seems to be valid for astrocytomas because astrocytes express the K-type pyruvate kinase in normal brain.

Alkyllysophospholipid ET-18-OCH3 acts as an activator of protein kinase C in HL-60 cells.

HL-60 cells are very sensitive to the cytotoxic action of ether lipids. Several hypotheses have been proposed to explain this cytotoxicity. We investigated the influence of the alkylphospholipid ET-18-OCH3 on the activity of protein kinase C. HL-60 cells were incubated with ET-18-OCH3 at a concentration of 20 micrograms/ml for 4 h. After the incubation the membrane fraction of the HL-60 cells was isolated and the activity of protein kinase C was determined while it was still associated with the membrane, using the synthetic peptide substrate [Ser25]-protein kinase C (19-31) as a protein kinase C specific substrate. The activity of the membrane-bound protein kinase C was increased in HL-60 cells treated with ET-18-OCH3 compared to untreated HL-60 cells. The increase in protein kinase C activity was not a consequence of translocation and appeared to be additive to the effect of the phorbol ester 12-myristate 13-acetate. In contrast, solubilized protein kinase C from HL-60 cells could be inhibited or stimulated in vitro by ET-18-OCH3, dependent on the mode of addition of ET-18-OCH3 and phospholipids.

Pyruvate kinase activity and isozyme composition in normal fibrous tissue and fibroblastic proliferations.

Pyruvate kinase (PK) was studied in 57 fibroblastic and fibrohistiocytic proliferations and normal fibrous tissue (n = 10). The specific activity was significantly increased in malignant tumors (1.67 +/- 0.25) compared with normal tissue (0.26 +/- 0.04; P less than 0.001) and benign proliferations (0.52 +/- 0.05; P less than 0.005). Although an overlap exists between aggressive fibromatosis and the benign group, high values of PK activity are indicative of Grade 2 and 3 malignancy. Significant shifts in isozyme pattern, favoring the expression of K-type subunits were found in tumors with a metastasizing potential and aggressive fibromatosis. These changes in the isozyme pattern of PK in aggressive fibromatosis may act as another argument to place them in the category of malignant fibroblastic tumors.