[Dependence of epidermal growth factor activation on its affinity and oligomerization]. / Zavisimost' aktivatsii retseptora épidermal'nogo faktora rosta ot ego affinnosti i oligomerizatsii.

Epidermal growth factor receptor (EGF-R) oligomerization has been followed on A-431 cells using covalent labeling by 125I-EGF and EGF-dependent autophosphorylation of receptor-kinase. High molecular weight complexes corresponding to monomeric, dimeric, and trimeric forms of EGF-R are detected. The process of oligomerization occurs effectively at 37 degrees C while at 4 degrees C no oligomer formation is detected. PMA or ATP treatment reduces the number of high-affinity EGF-binding sites but has no influence on dimer formation. Dimerisation of the EGF-R in the absence of the ligand has been established on formalin-fixed A-431 cells.

[The effect of epidermal growth factor on protein phosphorylation in normal and transformed hepatocytes]. / Vliianie épidermal'nogo faktora rosta na fosforilirovanie belkov v normal'nykh i transformirovannykh gepatotsitakh.

Qualitative differences in the content of tyrosine-phosphorylated proteins in normal and transformed hepatocytes have been found using the method of two-dimensional electrophoresis. Epidermal growth factor (EGF) has induced quantitative changes in the spectra of phosphotyrosine-containing proteins in normal cells and qualitative changes in the transformed ones. Results of immunoprecipitation with antibodies against phosphotyrosine permit revealing a protein with Mm 50 kDa which is subjected to EGF-dependent tyrosine-phosphorylation in normal hepatocytes. The intensity of protein phosphorylation is 10 times higher in the transformed cells but the dependence of this process on the EGF is not exhibited. The role of protein-tyrosine-kinases in the transmission of a mitogenic signal and in liver carcinogenesis is discussed.

[Changes in the epidermal growth factor receptors in the liver cells of rats in N-nitrosodiethylamine-induced hepatic carcinogenesis]. / Izmenenie retseptorov épidermal'nogo faktora rosta v kletkakh pecheni krys pri gepatokantserogeneze, indutsirovannom N-nitrozodiétilaminom.

A sharp decrease in the number of epidermal growth factor receptors (EGF-R) in the rat liver plasma membranes had been found at different stages of diethylnitrosamine-induced carcinogenesis. The complete loss of high-affinity binding sites for EGF did not prevent EGF-dependent autophosphorylation of EGF-R. Hepatocytes from the rat liver tumors in the primary culture had two classes of EGF-R: high and low affinity ones, though their number had been twice less than in the normal hepatocytes. The dynamics of internalization and down-regulation of EGF-R was very similar in the primary culture of transformed and normal hepatocytes. It testifies that there are some factors of microenvironment in the liver during carcinogenesis which cause the loss of EGF-R (down-regulation) and a decrease of their affinity (activation of protein kinase C). A possible autocrine or paracrine nature of these factors is discussed.

[Increase in the level of polypeptide growth factors and their receptors in induced carcinogenesis and regeneration of the intestinal mucosa in rats]. / Povyshenie urovnia nekotorykh polipeptidnyk faktorov rosta i ikh retseptorov pri indutsirovannom kantserogeneze i regeneratsii slizistoi obolochki kishechnika krys.

It has been established for the first time that in extracts of the regenerating and preneoplastic (4 months after the beginning of carcinogen introduction) intestine as well as in the peritumor tissue the content of EPR-similar polypeptides and insulin raises, whereas in tumours it remains not high. Proteins with molecular weight greater than 120 kD able to compete with 125I-EPR for the binding with the receptors of EPR and being, evidently, the precursors of EPP are found in case of carcinogenesis. Besides, the content of insulin receptors rises, this process being most typical of the large intestine.

[Changes in the contents of epidermal growth factor and EGF-like polypeptides in the liver tissue of rats in N-nitrosodiethylamine-induced hepatocarcinogenesis]. / Izmenenie soderzhaniia épidermal'nogo faktora rosta i podobnykh emu polipeptidov v tkani pecheni krys pri gepatokantserogeneze, indutsirovannom N-nitrozodiétilaminom.

It has been determined that concentration of EGF-like substances in the liver of rats with N-diethylnitrosamine-induced hepatocarcinogenesis increases and reaches its maximum in tumours (50-150 ng/mg protein). In the regenerating liver the amount of these peptides does not exceed 10 ng/mg protein. High pressure gel-filtration of appropriate extracts has revealed EGF-competing substances with m. w. about 20-30 kD in the liver carcinomas. The presented data confirm that registered EGF-like substances belong to TGF-alpha peptides.

[Change in the number of epidermal growth factor receptors of hepatocytes during liver regeneration in rats]. / Izmenenie kolichestva retseptorov épidermal'nogo faktora rosta gepatotsitov pri regeneratsii pecheni u krys.

The number of epidermal growth factor (EGF) receptors was determined for rat's hepatocytes under condition of their regeneratory proliferation, following a partial hepatectomy. In the normal hepatocytes two classes of EGF-receptors are distinguished, with high and low affinity, respectively. As early as 2 hours after the partial hepatectomy the total number of EGF-receptors sharply decreases, those with high affinity being not determined at all. The patterns of autophosphorylation of EGF-receptors with low affinity, examined in regenerating liver hepatocytes, remained the same as in the intact liver: their kinase activity was EGF-dependent, tyrosine residues of receptor molecules, with molecular mass equal to 150-170 kDa, underwent phosphorylation.

[The production of epidermal growth factor and polypeptides similar to it in the intestinal mucosa of rats in 1,2-dimethylhydrazine-induced carcinogenesis and compensatory regeneration]. / Produktsiia épidermal'nogo faktora rosta i podobnykh emu polipeptidov slizistoi obolochke kishechnika krys pri indutsirovannom 1,2-dimetilgidrazinom kantserogeneze i kompensatornoi regeneratsii.

The production of EGF and EGF-like polypeptides in the normal intestinal mucosa and during 1,2-dimethylhydrazine (DMH)-induced carcinogenesis and postresection regeneration was studied in albino rats using chromatographic separation of acid-ethanol extracts. Fractions after gel filtration on Biogel P-60 with subsequent reverse-phase high performance liquid chromatography in acetonitrile gradient were tested in radioreceptor assay for competition with EGF. It has been established that intestinal tumours induced by DMH and regenerating intestinal mucosa have amplified production of EGF--alpha-TGF and related proteins of high molecular weight (approx. 30; 45-55; 120 kD) with the EGF-competitive activity. It is supposed that the high molecular weight EGF-competitive material represents nonprocessed forms of EGF and/or alpha-TGF which are accumulated in rapidly proliferating low-differentiated cells due to the intensified expression of their genes.

[Effect of the epidermal growth factor on 1,2-dimethylhydrazine-induced carcinogenesis in the rat intestinal mucosa]. / Vliianie épidermal'nogo faktora rosta na kantserogenez, indutsirovannyi 1,2-dimetilgidrazinom v slizistoi obolochke kishechnika krys.

The radioimmunological and radioreceptor methods have been used to show that sialadenectomy leads to the stable decrease of the epidermal growth factor (EGF) concentration in saliva and blood serum. The mean number of colon tumours per rat was significantly lower among the rats which had been sialadenectomized before injections of the carcinogen, than in the control. But a sharp stimulation of carcinogenesis in the duodenal mucosa was observed after sialadenectomy. The production of the alpha-transforming growth factor with the EGF-competing activity for the EGF-receptors was found in the chemically-induced rat colon tumours.

[Proliferation of the intestinal epithelium and of the regenerating liver with a deficiency of the epidermal growth factor]. / Proliferatsiia épiteliia kishechnika i regeneriruiushchei pecheni krys pri nedostatke épidermal'nogo faktora rosta.

To determine the role of the epidermal growth factor (EGF) in the regenerative stimulation of intestinal epithelium and hepatocyte proliferation after partial resection of these organs the labeling index of the intestine and liver in sialadenectomized rats was studied. EGF concentration in the saliva and serum was determined using radioimmunoassay. The decrease in EGF concentration after the removal of submandibular salivary glands was shown to slower hepatocytes entering the mitotic cycle and to inhibit the activity of enterocyte proliferation in the small intestine. The data show pronounced in vivo mitogenic effect of EGF on the liver and intestinal epithelium.

[Characteristics of the epidermal growth factor receptors in the epithelium of the gastrointestinal tract of rats and in intestinal tumors induced by 1,2-dimethylhydrazine]. / Kharakteristika retseptorov épidermal'nogo faktora rosta v épitelii zheludochno-kishechnogo trakta krys i v opukholiakh kishechnika, indutsirovannykh 1,2-dimetilgidrazinom.

Using the Scatchard analysis of 125J-EGF binding it was shown that plasma membranes of gastric and small intestinal epithelial cells contain approximately 20 times less EGF-receptors (EGF-R) than liver cells. Investigation of the phosphorylation activity of EGF-R-kinase was performed in vitro on plasma membranes from intestine, intestinal tumours and liver cells. The main protein phosphorylated at tyrosine in the tumours was p34 but the intensity of EGF-R autophosphorylation and its total protein-tyrosine kinase activity were reduced (as compared with small-intestinal and liver cell membranes). In the tumours of the colon induced by DMH an increased binding of 125J-EGF has been observed as compared with normal colonic enterocytes and increased number of EGF-R was clearly demonstrated. Phosphorylation of p34 in the intestinal membranes proceeds much more intensively than that of EGF-R.

[Interaction of growth factors and oncogenes in the tumorous transformation of cells]. / Vzaimodeistvie faktorov rosta i inkogenov pri opukholevoi transformatsii kletok.

Different aspects of the interaction of polypeptide growth factors with their receptors are reviewed. The problem of structural and functional interactions of the normal and transforming growth factors as well as the protein products of oncogenes during transmittance of a mitogenic signal and the proliferation regulation of normal and tumour cells is discussed.

[Rapid isolation of highly purified epidermal growth factor by reverse-phase liquid chromatography]. / Uskorennoe poluchenie vysokoochishchennogo épidermal'nogo faktora rosta s pomoshch'iu zhidkostnoi khromatografii v obrashchennoi faze.

The first step in the isolation of murine epidermal growth factor (EGF) from submaxillary glands was the trace enrichment of the acid-ethanol extract on Sep-pak C18 cartridges using the step elution with ethanol. The fraction eluted by 60% ethanol contained above 75% of EGF. The final purification of EGF was achieved by reverse-phase liquid chromatography on Novapak C18 column in the gradient of acetonitrile. A comparison of the effectiveness of gel filtration (on Bio-gel P-60 column) and trace enrichment (on Sep-pak C18 cartridges) of the appropriate fractions were analyzed by the reverse-phase high-pressure liquid chromatography, which had demonstrated that hydrophobic separation of EGF had a number of advantages. The homogeneous character of EGF was confirmed by the silver staining of gels after disc-electrophoresis and isoelectric focusing (pI 4.8). The pronounced mitogenic effect of EGF on the primary culture of the rat hepatocytes is described.

[Synchronization of proliferating cells in the liver, gastric glands and duodenum]. / Sinkhronizatsii proliferiruiushchikh kletok pecheni, zhelez zheludka i dvenadtsatiperstnoi kishki.

Multiple injections (5-6 times) of hydroxyurea to hepatectomized rats lead to synchronization of 78% of proliferating cells in the regenerating liver. The amount of DNA-synthesizing cells of the foveolar epithelium of the pyloric glands of the gastric mucosa increases 2.7-fold, the proliferation in slowly renewing Brunner glands of the duodenum is dramatically activated.