Interaction of epidermal growth factor with adult rat liver parenchymal cells in primary culture

Monoclonal antibody to human epidermal growth factor

A monoclonal antibody directed to a species-specific determinant of human epidermal growth factor (h-EGF) was obtained by fusing murine myeloma cells with BALB/c mouse splenocytes sensitized to h-EGF. This antibody, referred to as 863.D4, did not react with either rat or mouse epidermal growth factor or with 11 other polypeptide hormones tested as shown by solid-phase radioimmunoassay (SPRIA), and immunoprecipitation followed by sodium dodecylsulfate polyacrylamide gel electrophoresis (SDS-PAGE). Scatchard analysis of the antibody binding to purified h-EGF revealed an apparent equilibrium dissociation constant of 1 X 10(-8) M. The antibody blocked both the binding of h-EGF and h-EGF stimulation of 3H-thymidine incorporation into DNA by greater than 90% in confluent cultures of human foreskin fibroblasts.

An electrophoretic characterization of the glucocorticoid response of the Fu5-5 rat hepatoma cell line

In this study we have further characterized the response of liver-derived cells to glucocorticoid treatment using the rat hepatoma, Fu5-5. Using two-dimensional electrophoresis we have examined changes in the synthetic rates of cytosol proteins following glucocorticoid administration by using [35S]methionine. We have also demonstrated changes in the incorporation of 32P by several cytosol proteins after hormone treatment. One of these changes occurs within 1 h of hormone treatment. We were unable to detect any changes in the nuclear protein content of Fu5-5 cells after glucocorticoid treatment. We then compared the glucocorticoid-regulated changes in cytosol protein synthesis in Fu5-5 cells with those of the H35 rat hepatoma, monolayer cultures of rat hepatocytes and the response of rat liver in vivo. This examination revealed that although nearly all of the eighteen hormonally responsive proteins appeared to be present in all of the cells types, only three were responsive to glucocorticoid in more than one system. Moreover, the response patterns were often reversed in different cell types, the same protein being induced in one cell type and repressed in another.

Killing of cultured hepatocytes by conjugates of asialofetuin and EGF linked to the A chains of ricin or diphtheria toxin

A disulfide-linked conjugate between asialofetuin (ASF) and the toxic A chain (RTA) of ricin is as potent a toxin for cultured rat hepatocytes as our previously described conjugate between ASF and fragment A of diphtheria toxin (DTA). An RTA conjugate of epidermal growth factor (EGF) was a potent toxin for 3T3 cells. In contrast, EGF-DTA was essentially nontoxic for 3T3 cells. We have now examined the toxicity of EGF-RTA and EGF-DTA on cultured hepatocytes. The EGF-DTA conjugate, nontoxic to 3T3 cells, is also a potent toxin for hepatocytes. We also observed a decrease with time of culture in the sensitivity of hepatocytes to the ASF and EGF conjugates. This decrease is not a result of a decrease in EGF or asialoglycoprotein receptors.

Toxic ligand conjugates as tools in the study of receptor-ligand interactions

We have constructed hybrid proteins in which the toxic A chains of ricin or diptheria toxin have been linked to either asialofetuin, fetuin, or epidermal growth factor (EGF). Both ASF-RTA and ASF-DTA are potent toxins on cultured rat hepatocytes, cells that display the asialoglycoprotein receptor. Toxicity of these two compounds is restricted to hepatocytes and can be blocked by asialoglycoproteins but not the native glycoproteins or asialoagalactoglycoprotein derivatives, indicating that the toxicity of the conjugates is mediated by the hepatic asialoglycoprotein receptor. The EGF-RTA conjugate is an extremely potent toxin on cells that can bind the hormone, but is only poorly effective on cells that are unable to bind EGF. The EGF-DTA conjugate, in contrast, is unable to kill 3T3 cells and is at least two orders of magnitude less effective than EGF-RTA on A431 cells, a cell line with 1-2 X 10(6) EGF receptors per cell. However, when EGF-RTA and EGF-DTA were tested on primary liver hepatocyte cultures, which were susceptible to both ASF-RTA and ASF-DTA, both EGF conjugates were potent toxins. Sensitivity of the hepatocyte cultures to ricin toxicity increases slightly during a 52-hr culture period. In contrast, sensitivity to EGF-RTA and ASF-RTA decline dramatically during this period. Receptors for both ligands remain plentiful on the cell surface during this time.

Inhibition of thymidine incorporation into the DNA of normal and neoplastic cells by a factor from bovine maternal placenta: interaction of the inhibitor with cell membranes

An inhibitor was isolated from the maternal part of bovine placentas which inhibits the incorporation of [3H]thymidine into the DNA of a variety of tumor cells to a significantly higher degree as compared to normal cells. This protein-type component was labeled by reaction with N-succinimidyl[2,3-3H]propionate, and interactions with receptors on cell membranes were investigated. Results indicated that receptors on tumor cell surfaces have higher binding capacities versus the inhibitor than those of normal cells. Moreover, an additional type of receptor was detected on tumor membranes. Obviously one of the reasons for the higher inhibitory capacity of the factor in tumor cells is the better internalization of this component.

Epidermal growth factor stimulation of ornithine decarboxylase activity in a human hepatoma cell line

Epidermal growth factor (EGF) bound specifically to the human hepatoma cell line PLC/PRF/5. Treatment of these cells with nanomolar concentrations of EGF for 4-6 hr resulted in a 2- to 6-fold increase in ornithine decarboxylase (L-ornithine carboxy-lyase, EC 4.1.1.17) activity. 12-O-Tetradecanoylphorbol 13-acetate also produced an increase in enzyme activity in these cells and exhibited an additive effect with EGF. It did not inhibit the binding of 125I-labeled EGF to these cells. The stimulation of enzyme activity by EGF was not inhibited by cycloheximide or actinomycin D, although these agents did cause a significant decrease in enzyme levels when added without EGF. Also, colchicine, chloroquine, ammonium chloride, and methylamine, compounds that inhibit EGF degradation in various cells types, did not interfere with the ability of EGF to elevate enzyme levels in the human hepatoma cells.