Protein tyrosine kinases in human brain and gliomas

Randomized clinical trial to compare the effects of preoperative oral carbohydrate versus placebo on insulin resistance after colorectal surgery

Background

Preoperative oral carbohydrate (OCH) reduces postoperative insulin resistance (PIR). This randomized trial investigated whether this effect is related to insulin-induced activation of the phosphatidylinositol 3-kinase (PI3K)/protein kinase B (PKB) signalling pathway.

Methods

Patients with colorectal cancer scheduled for elective open resection were randomly assigned to preoperative OCH, fasting or placebo. Preoperative general well-being, insulin resistance before and immediately after surgery, and postoperative expression of PI3K, PKB, protein tyrosine kinase (PTK) and glucose transporter 4 (GLUT4) in rectus abdominis muscle were evaluated.

Results

Patient and operative characteristics did not differ between groups. Subjective well-being was significantly better in OCH and placebo groups than in the fasting group, primarily because of reduced thirst (P = 0·005) and hunger (P = 0·041). PIR was significantly greater in fasting and placebo groups (P < 0·010). By the end of surgery, muscle PTK activity as well as PI3K and PKB levels were significantly increased in the OCH group compared with values in fasting and placebo groups (P < 0·050), but GLUT4 expression was unaffected.

Conclusion

PIR involves the PI3K/PKB signalling pathway. Preoperative OCH intake improves preoperative subjective feelings of hunger and thirst compared with fasting, while attenuating PIR by stimulation of the PI3K/PKB pathway. Registration number: NCT00755729 (http://www.clinicaltrials.gov).

Inhibitors of protein tyrosine phosphorylation reduce the proliferation of two human glioma cell lines

Epidermal growth factor (EGF) and platelet-derived growth (PDGF) are suggested to be involved in the proliferation of human gliomas. We examined the effects of these growth factors on two human malignant glioma cell lines. Treatment of the A172 glioblastoma and the Hs683 glioma cell line with EGF and PDGF resulted in the tyrosine autophosphorylation, and hence activation, of the respective growth factor receptors. In addition, both cell lines responded to EGF and PDGF with increased deoxyribonucleic acid (DNA) synthesis. Because the intrinsic protein tyrosine kinase activity of this class of growth factor receptors is indispensable for their functioning, we tested the effects of specific protein tyrosine kinase inhibitors on growth factor-induced DNA synthesis and glioma cell proliferation. Genistein inhibited both EGF- and PDGF-stimulated autophosphorylation of the receptors and induction of DNA synthesis. However, genistein seemed to be cytotoxic to the cells. The tyrphostins RG 50875 and RG 13022 dose-dependently inhibited DNA synthesis induced by EGF, PDGF, and serum. RG 13022 completely blocked the EGF- and PDGF-induced DNA synthesis at a concentration of 50 mumol/L. The tyrphostins showed no selectivity in blocking either EGF or PDGF signaling. With concentrations up to mumol/L, no cytotoxic side effects of the tyrphostins were observed. Both tyrphostins also inhibit serum-driven cell growth in a dose-dependent manner. These results support the hypothesis that activated protein tyrosine kinase receptors are involved in the proliferation of A172 and Hs683 glioma cells. Selective inhibitors of protein tyrosine kinases, therefore, might have the potential to contribute to the treatment of growth factor-dependent gliomas.

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.

Aberrant tyrosine phosphorylation in head and neck tumours and potentially premalignant tissues

Protein tyrosine kinases (PTK) and protein tyrosine phosphatases (PTPase) activity in tumor tissue, obtained from 107 patients with squamous cell carcinoma of the upper aerodigestive tract, was determined. In 79 patients samples were also taken from a histologically proven non-tumourous part of the mucosa. In this extensive study we confirmed our previous findings of increased enzyme activities (cytosol PTK, membranes PTK, cytosol PTPase) in non-tumour tissues compared with control tissues. These biochemical changes suggesting a premalignant mucosa could not be correlated to a higher probability of secondary tumours.

Examination of the natural protein substrates affected by staurosporine in the developing cerebral cortex

The protein substrates affected by staurosporine (SP), the most potent inhibitor of protein kinases yet described, are unknown. In order to approach this problem we incubated cerebral cortex tissue with 0, 20, 50 and 100 nM of SP using [32P]orthophosphate as radioactive precursor. The analysis of the phosphoproteins were made with a modified high resolution two dimensional gel electrophoresis, followed by autoradiography. We detected several proteins affected by SP. Specially noticeable was an approximately 55 kDa protein which strikingly diminished the intensity of phosphorylation. However, the reverse phenomenon was also observed. To the best of our knowledge this is the first examination of protein substrates affected by SP in intact tissue.