New variation on the translocation of proteins during early biogenesis of apolipoprotein B

Apolipoprotein B (apo B) is crucial for the transport of cholesterol in humans. It is a large secretory protein that mediates the uptake of low-density lipoproteins and renders several forms of lipid droplets soluble in the blood. The binding of lipid by apo B also prevents this hydrophobic protein from precipitating in aqueous solution. In the endoplasmic reticulum, nascent secretory proteins must be translocated through an aqueous channel in the membrane into the aqueous lumen, so some novel form of processing may be necessary to maintain the solubility of apo B during its translocation. We have discovered that the biogenesis of apo B in cell-free systems does indeed involve a new variation on protein translocation: unlike typical secretory proteins, apo B is synthesized as a series of transmembrane chains with large cytoplasmic domains and progressively longer amino-terminal regions that are protected against added proteases during the translocation process. In contrast to typical transmembrane proteins, these transmembrane chains are not integrated into the bilayer. Moreover, the transmembrane chains with the shortest protected domains are precursors of forms whose protection is progressively extended to cover the length of the protein. This stepwise conversion occurs post-translationally for the most part. We propose a model on the basis of these findings for the biogenesis of apo B.

Experimental study and clinical application of a single-row suturing esophagogastrostomy

A single-row suturing anastomosis (SRA) for an esophagogastrostomy was experimentally investigated in dogs. SRA not only shortened operating time, but also led to better pathological results when compared with double-row suturing anastomosis. Wide-brim suturing and equal distance between the sutures, providing increased and well-distributed blood circulation, are the key points for success of SRA. Its simplicity and safety are advantages of SRA as has been shown in 90 cases in clinical application.

[Effects of oxygenated volume expander on hemorrhagic shock]

36 dogs were divided into 3 groups: group A were administered with non-oxygenated crystalloid solution as a control; group B, with oxygenated crystalloid solution; group C, with oxygenated no 3 perfluorocarbon emulsion (PFC-O2) as volume expander. Result of measurements of serum CPK, LDH, lactic acid, gas analysis, MAP, and dynamic heart function (including pulmonary water index, LVET, LVEF, SV, CO and HR) and ultrastructural observation on lung tissue and skeletal muscles showed that oxygenated crystalloid solution can more quickly revert the hemodynamic changes after hemorrhagic shock, improves oxygen-utilizing ability of the tissue, and therefore possesses a good protective effect of the organ cells.

[Epidermal growth factor receptor of human liver cancer cells and its modulation by phorbol ester]

Using radioligand binding assay, the presence of epidermal growth factor (EGF) receptors in cells of two human liver cancer cell lines, BEL-7402 and SMMC-7721, was demonstrated. The ligand binding data were analyzed by a computer program. The dissociation constants (KD) of the ligand-receptor binding complex at equilibrium for 7402 and 7721 cells were 1.2 nM and 0.8 nM respectively, and their number of EGF receptors per cell were 6.2 x 10(4) and 2.5 x 10(4) respectively. After the treatment of cells with phorbol 12-myristate 13-acetate (PMA), no change either in the affinity or in the number of EGF receptors was found in 7721 cells. However, in the case of 7402 cells, while the number of receptors, like 7721 cells, remained unchanged, the affinity of EGF receptors displayed a time dependent modulation after PMA treatment. It dropped within the first hour to a KD value of 3.0 nM and then gradually returned to the normal control value at 48 hours or even slightly higher than normal (0.95 nM) at 96 hours of treatment. The modulation or down-regulation of EGF receptors by PMA in 7402 cells was paralleled by the simultaneous inhibition of DNA synthesis in these cells as evidenced from their reduction of 3H-TdR uptake. It is not clear what is the basis for the differences found between 7402 cells and 7721 cells in their number of EGF receptors per cell and their responsiveness to PMA treatment. It might be related to their difference in autocrine secretion of alpha-transforming growth factors.(ABSTRACT TRUNCATED AT 250 WORDS)

[A transforming growth factor-beta like growth factor in mouse embryonal carcinoma cells]

Our previous study indicated that polypeptides isolated from acid/ethanol extracts of solid tumors of a cloned F9-3 embryonal carcinoma cells by Bio-Gel P60 column chromatography were found to be able to stimulate anchorage independent growth of either NIH 3T3 cells or NRK 49 F cells in soft agar. The major peak of active elute had a molecular weight of about 15 kDa as determined by SDS-polyacrylamide gel electrophoresis. In the present report we further isolated and purified the active compound corresponding to molecular weight of 15 kDa by gel filteration on Bio-Gel P10 column (Fig. 1) and then by high pressure liquid chromatography (Fig. 2). It was found that the purified 15 kDa molecules showed some properties similar to transforming growth factor-beta (TGF-beta): 1. Colony-stimulating activity in soft agar can be induced in NRK 49 F cells only in the presence of mouse epidermal growth factor (EGF) (Plate I); 2. Increase in relative uptake of 3H-thymidine in NRK 49 F cells occurred in the presence of EGF, but with the same amount of EGF, not much change in 3H-thymidine incorporation could be found with further increasing amounts of purified 15 kDa molecules (Fig. 3); 3. Like human blood platelets derived TGF-beta, inhibition effect on the growth of mink lung epithelial cells (CCL/64) can also be exhibited by purified 15 kDa molecules (Fig. 4). In addition, using ELISA procedure, we have also demonstrated that the 15 kDa molecules had immunological reactivity with the antibody raised against a synthetic oligopeptide identical to the N-terminal residues 1-29 of TGF-beta 1 from human blood platelets (Fig.5). Thus, the 15 kDa molecules isolated from mouse F9-3 embryonal carcinoma cells appeared to share some common antigenic determinants with human TGF-beta 1 molecule. These results taken together provide strong support for the existence of TGF-beta like growth factor in mouse embryonal carcinoma cells.

Phosphatidylethanolamine levels and regulation of phosphatidylethanolamine N-methyltransferase

The activity of phosphatidylethanolamine (PE) N-methyltransferase in liver microsomes, measured using endogenous microsomal PE as a substrate, was elevated 2-fold in the choline-deficient state. However, methyltransferase activity assayed in the presence of a saturating concentration of phosphatidyl-N-mono-methylethanolamine or microsomal PE was unchanged by choline deficiency. Accompanying the increase in methyltransferase activity in liver homogenates and microsomes were increased PE concentrations and an increased PE to phosphatidylcholine ratio. The concentration of other phospholipids was unchanged. Immunoblot analysis of choline-deficient and choline-supplemented rat liver microsomes using a rabbit polyclonal anti-PE N-methyltransferase antibody revealed that the amount of enzyme protein was unaltered. The regulation of methyltransferase by PE levels was also investigated in cultured hepatocytes obtained from choline-deficient rat livers. Supplementation of deficient hepatocytes with 200 microM methionine resulted in a 50% reduction in cellular PE levels over a 12-h period. PE N-methyltransferase activity assayed with endogenous PE was also reduced by 50%, but phosphatidyl-N-monomethylethanolamine-dependent activity was unchanged. A 4-h supplementation with choline did not affect PE levels or methyltransferase activity. Either methionine or choline supplementation resulted in net synthesis of cellular phosphatidylcholine. Immunoblotting of membranes from methionine-supplemented hepatocytes revealed no change in enzyme protein, a further indication that enzyme mass was constitutive, and activity was regulated by the concentration of PE.

Antigenic determinant of trichosanthin peptide fragments

Purified plant protein, Trichosanthin (TCS), was partially digested with chymotrypsin to produce peptide fragments. Two large fragments, I and II, have been isolated and identified as C-terminal peptides located at sequence positions between 79-234 and 107-234. Their molecular weights determined by electrophoretic mobility on SDS gel were 16,000 and 14,000 daltons. Studies using fluorescence quenching measurements by titrating anti-TCS Fab with TCS and fragment I and II showed that four epitopes were present in intact TCS and one each epitope in fragment I and II. One of the epitopes is therefore located between sequence positions 107 and 234.