Purification of two forms of colony-stimulating factor from mouse L-cell-conditioned medium

A modified procedure for the purification of the colony-stimulating factors (CSFs) in mouse L-cell-conditioned medium is used to isolate two forms of CSF, which are separable by reversed-phase high performance liquid chromatography with 300-A pore size supports. The specific biological activity of these CSFs (2 X 10(9) colonies/mg) was considerably higher than has been achieved by other methods. Even at high concentration (200 pM) both molecules stimulated predominantly more macrophage than granulocyte colonies; however, the less hydrophobic form appeared to stimulate the formation of more pure granulocytic colonies. Almost twice as much of the less hydrophobic CSF was recovered from L-cell-conditioned medium. Analysis using sodium dodecyl sulfate-polyacrylamide gel electrophoresis indicated that both forms of L-cell CSF had apparent molecular masses of approximately 70,000 daltons. However, on reduction with 2-mercaptoethanol, while both forms generated a 39,000-dalton subunit, the less hydrophobic form also yielded a 32,000-dalton subunit. Storage of either form of L-cell CSF at pH 2.1, in the presence of acetonitrile or isopropanol, destroyed the biological activity. Electrophoretic analysis of the L-cell CSFs stored under these conditions indicated that this was associated with a spontaneous dissociation of the CSF dimer into the inactive subunits. There was some charge heterogeneity (pI 3.5-4.7) indicating different degrees of glycosylation. The unique N-terminal amino acid sequences of both forms of CSF were the same: (Lys-Glu-Val-Ser-Glu-His-X-Ser-His-Met-Ile-Gly-Asn). Thus, the polypeptide chains appear to be identical for the subunits of both forms of L-cell CSF.     

Strategies for the identification and purification of ligands for orphan biomolecules

Summary The isolation of related genes with evolutionary conserved motifs by the application of polymerase chain reaction-based molecular biology techniques, or from database searching strategies, has facilitated the identification of new members of protein families. Many of these protein molecules will be involved in protein-protein interactions (e.g. growth factors, receptors, adhesion molecules), since such interactions are intrinsic to virtually every cellular process. However, the precise biological function and specific binding partners of these novel proteins are frequently unknown, hence they are known as ‘orphan’ molecules. Complementary technologies are required for the identification of the specific ligands or receptors for these and other orphan proteins (e.g., antibodies raised against crude biological extracts or whole cells). We describe herein several alternative strategies for the identification, purification and characterisation of orphan peptide and protein molecules, specifically the synergistic use of micropreparative HPLC and biosensor techniques. These authors made equivalent contributions.     

In vitro actions on hemopoietic cells of recombinant murine GM-CSF purified after production in Escherichia coli: comparison with purified native GM-CSF

Recombinant murine GM-CSF produced in Escherichia coli was purified to homogeneity and tested in parallel with purified native GM-CSF. Both recombinant and native GM-CSF stimulated granulocyte and/or macrophage colony formation by adult and fetal mouse progenitor cells, and with adult marrow cells the specific activity of the recombinant GM-CSF (25 X 10(8) U/mg) was similar to that of the native form (15 X 10(8) U/mg). At high concentrations (greater than 200 U/ml), both forms of GM-CSF also stimulated eosinophil colony formation by adult marrow cells and, at very high concentrations (greater than 800 U/ml), megakaryocyte and some erythroid and mixed-erythroid colony formation. Recombinant GM-CSF was as effective in stimulating the proliferation of the GM-CSF-dependent cell line FD as the native molecule. Both recombinant and native GM-CSF were able to induce partial differentiation in colonies of WEHI-3B myeloid leukemic cells. Recombinant GM-CSF competed effectively for the binding of 125I-labeled native GM-CSF to hemopoietic cells, and antiserum to recombinant GM-CSF also neutralized the biological activity of native GM-CSF. The bacterially synthesized GM-CSF was a slightly more effective stimulus for megakaryocyte colony formation than the native molecule. The demonstration that purified bacterially synthesized GM-CSF is biologically active in vitro now permits studies to be undertaken on the in vivo effects of this material.     

Binding of fluoresceinated epidermal growth factor to A431 cell sub-populations studied using a model-independent analysis of flow cytometric fluorescence data.

A method is developed for determining ligand-cell association parameters from a model-free analysis of data obtained with a flow cytometer. The method requires measurement of the average fluorescence per cell as a function of ligand and cell concentration. The analysis is applied to data obtained for the binding of fluoresceinated epidermal growth factor to a human epidermoid carcinoma cell line, A431. The results indicate that the growth factor binds to two classes of sites on A431 cells: 4 X 10(4) sites with a dissociation constant (KD) of less than or equal to 20 pM, and 1.5 X 10(6) sites with a KD of 3.7 nM. A derived plot of the average fluorescence per cell versus the average number of bound ligands per cell is used to construct binding isotherms for four sub-populations of A431 cells fractionated on the basis of low-angle light scatter. The four sub-populations bind the ligand with equal affinity but differ substantially in terms of the number of binding sites per cell. We also use this new analysis to critically evaluate the use of 'Fluorotrol' as a calibration standard in flow cytometry.     

Granulocyte/macrophage colony-stimulating factor from mouse lung conditioned medium. Purification of multiple forms and radioiodination.

Four forms of mouse granulocyte/macrophage colony-stimulating factor (GM-CSF) were purified 100,000-fold from mouse lung conditioned medium. Each of the CSF species stimulated the formation of both granulocyte and macrophage colonies, and half-maximal stimulation in the semi-solid mouse bone-marrow colony assay occurred at 1 pm. The four GM-CSF species exhibited similar charge microheterogeneity, focusing between pH 4.2 and pH 5.2. On SDS/polyacrylamide gels two of the GM-CSF sub-species had apparent Mr values of 23,000, and the other two, 21, 000. Treatment with neuraminidase decreased the Mr values of these two sets to 21,000 and 19,000 respectively. Incubation with endoglucosidase F decreased the charge heterogeneity and the Mr of all species to 16,500. A gas-phase radioiodination procedure was used to incorporate 2-3 atoms of 125I/molecule into purified GM-CSF without any loss of biological activity. The 125I-labelled GM-CSF was analysed on a microbore reversed-phase h.p.l.c. column to determine its specific radioactivity directly. This 125I-labelled GM-CSF molecule is suitable for cell-surface receptor-binding studies.     

Regulation of rat ovarian cell growth and steroid secretion

A cultured rat ovarian cell line (31 A-F(2)) was used to study the effect of growth factors (epidermal growth factor [EGF] and fibroblast growth factor [FGF]), a survival factor (ovarian growth factor [OGF]), a hormone (insulin), and an iron-binding protein (transferring) on cell proliferation and steroid production under defined culture conditions. EGF and insulin were shown to be mitogenic (half-maximal response at 0.12 nM and 0.11 muM, respectively) for 31A-F(2) cells incubated in serum-free medium. EGF induced up to three doublings in the cell population, whereas insulin induced an average of one cell population doubling. FGF, OGF, and transferrin were found not to have any prominent effect on cell division when incubated individually with 31A-F(2) cells in serum-free medium. However, a combination of EGF, OGF, insulin, and transferrin stimulated cell division to the same approximate extent as cells incubated in the presence of 5 percent fetal calf serum. EGF or insulin did not significantly affect total cell cholesterol levels (relative to cells incubated in serum-free medium) when incubated individually with 31A-F(2) cells. However, cell cholesterol levels were increased by the addition of OGF (250 percent), FGF (370 percent), or a combination of insulin and EGF (320 percent). Progesterone secretion from 31A-F(2) cells was enhanced by EGF (25 percent), FGF (80 percent), and insulin (115 percent). However, the addition of a mitogenic mixture of EGF, OGF, insulin, and transferrin suppressed progesterone secretion 150 percent) below that of control cultures. These studies have permitted us to determine that EGF and insulin are mitogenic factors that are required for the growth of 31A-F(2) cells and that OGF and transferrin are positive cofactors that enhance growth. Also, additional data suggest that cholesterol and progesterone production in 31A-F(2) cells can be regulated by peptide growth factors and the hormone insulin.     

In situ cyanogen bromide cleavage of N-terminally blocked proteins in a gas-phase sequencer

Herein we describe a procedure for the in situ cyanogen bromide cleavage of N-terminally blocked proteins which have been immobilised onto the glass fiber sample disk of the gas-phase sequencer. In this manner, new amino terminii suitable for automated Edman degradation can be generated. Cytochrome C was cleaved using this method on the carboxyl side of methionine residues 65 and 80. This allowed sequence analysis to begin simultaneously at residues 66 and 81 (Table 1). This procedure offers an alternative sequencing tactic for methionine-containing proteins which are N-terminally blocked.     

Murine epidermal growth factor: structure and function

Murine epidermal growth factor (EGF), a 53 amino acid protein, has been modified by enzymic digestion, site-specific chemical reactions, and recombinant DNA technology. After trypsin digestion the EGF derivatives EGF1-48 (called EGF-T) and EGF1-45 (called EGF-T2) were separated from the residual EGF and the C-terminal pentapeptide by reversed-phase high-performance liquid chromatography. EGF-T competes for binding to EGF receptors with the same efficiency as EGF. The EGF-T2 derivative had no detectable receptor binding activity even at 100 nM. The in vitro mitogenic potencies of EGF and EGF-T for Balb/c 3T3 cells were indistinguishable. Treatment of EGF-T with carboxypeptidase Y yielded two derivatives, EGF-T-(des-Arg48) and EGF-T-des(Leu47-Arg48). There was only a 3-7-fold diminution in the binding efficiency and mitogenic potency for EGF-T-(des-Arg48). However, there was more than a 100-fold decrease in the binding efficiency and mitogenic activity of EGF-T-des (Leu47-Arg48). These results indicated that Leu47 is intimately involved in the formation of the ligand-receptor complex. Studies with a number of proteases indicated that the C-terminus of EGF was susceptible to enzymic digestion; however, the N-terminus appears to be folded into a conformation which prevents access to proteolytic digestion. Consequently, the N-terminus was modified by preparing an analogue with recombinant DNA technology. Oligonucleotides corresponding to EGF(3-48). Met3 Lys21 residues were ligated in frame to a beta-galactosidase expression vector. The beta-Gal-EGF fusion protein was cleaved with cyanogen bromide and EGF(4-48).Lys21 purified.(ABSTRACT TRUNCATED AT 250 WORDS)