Growth induction of hepatic stimulator substance in hepatocytes through its regulation on EGF receptors

The cytosolic liver-specific growth factor-hepatic stimulator substance (HSS) has been shown to be able to amplify the rat hepatocyte proliferation responded to EGF. In order to get more insight into the mechanism, the regulatory effect of HSS on EGF-receptor(EGF-R) and the receptor phosphorylation at molecular level was studied. HSS partially purified from weanling rat liver was given to cultured hepatocytes and its influence on EGF-R specific binding and internalization as well as mRNA expression were investigated. The results showed that preincubation of hepatocytes with HSS could lead to an increase in [125I]-EGF binding to its receptors and inhibit EGFinduced receptor down-regulation. Furthermore, the overexpression of EGF-R mRNA stimulated by HSS was seen during 2-12 h after the incubation. Additionally, it was demonstrated with human hepatoma sMMC-7721 cells in Western blot that the EGF-R expression and the receptor autophosphorylation were increased with dose/timedependency after HSS treatment. These results strongly suggest that the mechanism of HSS action on hepatocyte growth might be related to its modulation on EGF-R and receptor-mediated signaling transduction.

EGF receptor-mediated intracellular calcium increasein human hepatoma BEL-7404 cells

Epidermal growth factor （EGF） induced intracellular free calcium ([Ca2+]i) response was studied in fura-2- or fluo-3-loaded human hepatoma cells of BEL-7404 cell line. Single cell [Ca2+]i analysis and [Ca2+], measurement in cell populations revealed that EGF triggered a rapid [Ca2+]iincrease in the dose-dependent and time- dependent manner. Pretreatment of cells with an endoplasmic reticulum （ER） Ca2+-ATPase inhibitor, thapsigargin （TG） at 100 nM concentration for 20 min, completely abolished EGF-induced [Ca2+]i increase, and chelating extracellular calcium by excess EGTA partially inhibited the increase.Furthermore, the expression of antisense EGF receptor sequence in BEL-7404 cells suppressed the [Ca2+]i response to EGF. The results suggest that EGF receptor-mediated [Ca2+]i increase in the human hepatoma cells is essentially dependent on the Ca2+ storage in ER.

ANTIPROLIFERATIVE ACTIVITY OF HUMAN IFN-γ-EGF_3 FUSION PROTEIN ARE RELATED TO ITS EGF RECEPTOR COMPETITION

The relationship between antiproliferative effect of human IFN γ EGF 3 fusion protein and the influence of EGF receptor binding activity has been studied on A431 cell line. Antiproliferative activity of human IFN γ EGF 3 was higher than that of its parent IFN γ. In the 125 I EGF receptor competition experiment, the inhibition of EGF receptor binding capacity on the target cells was observed in the treatments of human IFN γ or IFN γ EGF 3, but the later was more significant. Our data suggests that the antiproliferative effects by IFN γ and its fusion protein are closely related to their EGF receptor competitions.

Effect of He-Ne Laser on the Expressions of EGF and EGFR in Gastric Mucosa of Chronic Atrophic Gastritis

To investigate the histological change and the expressions of epidermal growth factor (EGF) and epidermal growth factor receptor (EGFR) in atrophic gastric mucosa in rats so as to appraise the effect of these regulators on the formation of atrophic gastritis, to study the expressions of EGF and EGFR in rats with chronic atrophic gastritis (CAG) after the irradiation of He-Ne laser, and to investigate the relations of He-Ne laser and precancerous lesion or apoptosis. The rats were divided into normal group, model group and laser group. The models of CAG rats were established with enema which was the mixed liquor consisted of sodium salicylate and alcohol, combined with irregular fasting and compulsive sporting as pathogenic factors. He-Ne laser(3.36 J/cm2 ) was used to irradiate CAG rats, once a day for 7 min, 20 days as a course of treatment; the expressions of EGF and EGFR were detected with immunohistochemical method. During the process of antral atrophy, the expressions of EGF and EGFR increased, they were higher in model group than those in normal group (P<0.05). After the irradiation of He-Ne laser, the expressions of EGF and EGFR were obviously lower than those in model group (P<0.05). We draw the conclusion as follows: gastric mucosa of model rat is in a hyper-proliferation status, with high protein expressions of apoptosis suppressor EGF and EGFR. CAG has some correlation with the imbalance between cell proliferation and apoptosis. He-Ne laser (3.36 J/cm2 ) can reduce the expressions of EGF and EGFR, which is an effective physiostimulator to stimulate the gastric mucosa of rat. The appropriate secretions of EGF and EGFR are propitious to the repair and regeneration for the gastric mucosa tissues, thus preventing CAG to canceration.

Controlled and reversible induction of differentiation and activation of adult human hepatocytes by a biphasic culture technique

AIM:Clinical application of human hepatocytes (HC) is hampered by the progressive loss of growth and differentiation in vitro. The object of the study was to evaluate the effect of a biphasic culture technique on expression and activation of growth factor receptors and differentiation of human adult HC. METHODS: Isolated HC were sequentially cultured in a hormone enriched differentiation medium (DM) containing nicotinamide, insulin, transferrin, selenium, and dexame-thasone or activation medium (AM) containing hepatocyte growth factor (HGF), epidermal growth factor (EGF), and granulocyte-macrophage colony-stimulating factor (GMCSF). Expression, distribution and activation of the HC receptors (MET and EGFR) and the pattern of characteristic cytokeratin (CK) filaments were measured by fluorometry, confocal microscopy and Western blotting. RESULTS: In the biphasic culture system, HC underwent repeated cycles of activation (characterized by expression and activation of growth factor receptors) and re-differentiation (illustrated by distribution of typical filaments CK-18 but low or absent expression of CK-19). In AM increased expression of MET and EGFR was associated with receptor translocation into the cytoplasm and induction of atypical CK-19. In DM low expression of MET and EGFR was localized on the cell membrane and CK-19 was reduced. Receptor phosphorylation required embedding of HC in collagen type I gel. CONCLUSION: Control and reversible modulation of growth factor receptor activation of mature human HC can be accomplished in vitro, when defined signals from the extracellular matrix and sequential growth stimuli are provided. The biphasic technique helps overcome dedifferentiation, which occurs during continuous stimulation by means of growth factors.