Expression of human preproendothelin-1 cDNA in COS cells results in the production of mature vasoactive endothelin-1.

Transient transfection of simian kidney (COS) cells with a recombinant plasmid encoding human preproendothelin-1 resulted in the production of biologically active endothelin-1. Conditioned medium from human preproendothelin-1 transfected cells demonstrated a significant increase in immunoreactive endothelin and big endothelin which co-eluted, when analyzed by reverse phase HPLC, with synthetic endothelin-1 and big endothelin-1, respectively. In addition, biological activity was confirmed by both inhibition of [125I]endothelin-1 binding to rat cerebellar and renal medullary membrane endothelin receptors and in vitro vasoconstriction of rabbit aorta. This is the first demonstration that human preproendothelin-1 is capable of being processed to a vasoactive form in a heterologous system and suggests that human preproendothelin-1 transfected COS cells may provide a useful model system for the study of endothelin biosynthesis.

Identification and characterization of two distinct alpha-(1-3)-L-fucosyltransferase activities in human colon carcinoma.

Two distinct alpha-(1-3)-fucosyltransferase activities have been identified in the colon carcinoma cell lines HT-29 and COLO-205. While both enzymatic activities exhibit similar affinities for a synthetic alpha-(1-3) acceptor and GDP-fucose, they differ with respect to divalent cation requirements, N-ethylmaleimide inhibition, and glycoprotein substrate specificity. The COLO-205 alpha-(1-3) activity exhibits maximal enzymatic activity in the presence of 20 mM Mn2+ but retains less than 10% activity in the absence of divalent cations. In contrast, the optimal Mn2+ concentration for the HT-29 enzyme is 1 mM, although this activity is relatively insensitive to divalent cation stimulation. In addition, the HT-29 alpha-(1-3)-fucosyltransferase activity is resistant to inhibition by 30 mM N-ethylmaleimide and relatively inactive toward the glycoprotein substrate fetuin as compared to its desialylated derivative, asialofetuin. The COLO-205 activity is inhibited approximately 90% by N-ethylmaleimide and is equally active with either glycoprotein acceptor. Although the alpha-(1-3) specific activities are similar in both cell lines, N-ethylmaleimide-sensitive alpha-(1-4) fucosyltransferase activity is 40-fold higher in COLO-205 as compared to HT-29, suggesting that the COLO-205 fucosyltransferase activity may be an alpha-(1-3/4) enzyme, while the HT-29 activity appears to be an alpha-(1-3) specific form. Further examination of a panel of cell lines, tumor biopsies, and xenografts, based on the effect of metal ions and N-ethylmaleimide, indicated that both enzyme activities are similarly expressed in human colon carcinoma tissue.

Biosynthesis and modulation of endothelin from bovine pulmonary arterial endothelial cells.

The biosynthesis and modulation of the vasoconstrictor peptide endothelin was studied in the conditioned medium from cultured bovine pulmonary artery endothelial (BPAE) cells. Conditioned medium from cultured BPAE cells produced contraction of isolated rabbit aortic rings. Incubation of BPAE cells with the protease inhibitors TPCK or isatoic anhydride attenuated the extent of conditioned medium-induced contractions. Incubation of BPAE cells with thrombin produced an enhancement of conditioned medium-induced contraction by approximately 25%. Endothelin levels in conditioned medium were measured by RIA and incubation of BPAE cells with TPCK or isatoic anhydride significantly reduced endothelin levels, whereas incubation with thrombin or transforming growth factor beta-1 stimulated the levels of endothelin in the conditioned medium. These data indicate that endothelin may be modulated by certain protease inhibitors and by platelet and immune cell mediators and suggest a potential new mode of vascular tone regulation.

Transient production and secretion of human transforming growth factor TGF-beta 2.

Transient transfection of simian COS cells with a recombinant plasmid encoding the human transforming growth factor TGF-beta 2 precursor protein results in the production of a latent, biologically inactive protein. Upon acidification, recombinant TGF-beta 2 exhibits full biological activity, including inhibition of mink lung epithelial cell growth, stimulation of anchorage-independent growth of murine embryonic fibroblasts, and competition for TGF-beta receptor binding. Further analysis of conditioned media with antiserum to either a pro- [amino acid (aa) residues 1-220] or mature [aa 297-414] peptide of the TGF-beta 2 precursor suggests that TGF-beta 2, similar to TGF-beta 1 production in Chinese hamster ovary cells [Gentry et al., Mol. Cell. Biol. 7 (1987) 3418-3427], is initially synthesized as a larger precursor protein which is proteolytically cleaved to yield the mature 112-aa transforming growth factor.

Induction of the 32-kD human stress protein by auranofin and related triethylphosphine gold analogs.

Challenge of human cells with auranofin, 2,3,4,6-tetra-O-acetyl-1-thio-beta-D-glucopyranosato-S-triethylpho sphine gold(I) (Ridaura), a gold-containing compound approved by the FDA for the treatment of rheumatoid arthritis, induces the specific synthesis of a 32-kD stress protein (p32) [Caltabiano et al., Biochem. biophys. Res. Commun. 138, 1074 (1986)]. To establish a structure-activity relationship for this effect, a series of auranofin ligands, gold analogs, and other anti-arthritic agents were examined for their abilities to stimulate p32 synthesis. The results indicate that the gold atom is necessary for enhanced expression of p32. However, the structure of co-ordinated ligands also affected potency, and gold complexes bearing several phosphine or thiosugar groups exhibited the greatest activity. These data indicate that the distinct potencies of auranofin analogs probably reflect their membrane permeability and subsequent delivery of pharmacologically active concentrations of gold to the cytoplasmic compartment.

Isolation and immunological characterization of the mammalian 32-/34-kDa stress protein.

Challenge of mammalian cells with heavy metals or sulfhydryl-reactive agents including sodium arsenite induces the de novo synthesis of a 32-/34-kDa stress protein (p32) (M. M. Caltabiano, T. P. Koestler, G. Poste, and R. G. Greig (1986) J. Biol. Chem. 261, 13,381). Here we report that antibody prepared against p32/p34 purified from human A375 melanoma cells immunoprecipitated an antigen of similar molecular mass from a panel of human, rat, and murine cells following challenge with sodium arsenite. No reactivity was observed in lysates from control, uninsulted cultures. The precise molecular mass of the arsenite-induced antigen was species-specific: 32 kDa (human and rat) and 34 kDa (murine). Indirect immunofluorescence analysis using affinity-purified monospecific IgG demonstrated that p32/p34 was localized to the cytoplasm and displayed a perinuclear distribution.

Alterations in lipid-linked oligosaccharide metabolism in human melanoma cells concomitant with induction of stress proteins.

Challenge of human A375 melanoma cells with sodium arsenite induced the synthesis of stress proteins and stimulated [3H]mannose incorporation into a novel component migrating on sodium dodecyl sulfate-polyacrylamide gel electrophoresis with an apparent molecular mass of 14 kDa (designated M14). Enhanced M14 expression was elicited by heavy metals (zinc, copper, cadmium, and nickel), thiol-reactive agents (iodoacetamide and auranofin), and hyperthermia. The kinetics of M14 induction and recovery from stress were similar to those of the stress proteins, but M14 half-life was only 15 min. Incorporation of [3H]mannose into M14 was inhibited by tunicamycin but not by cycloheximide or actinomycin D. M14 was metabolically labeled with [32P]orthophosphate but not by [35S] methionine or [3H]asparagine. Further studies revealed that M14 was selectively soluble in chloroform/methanol/water (10:10:3) and sensitive to both endo-beta-N-acetylglucosaminidase H digestion and mild acid hydrolysis. The latter released a water-soluble mannose-labeled moiety which eluted from Bio-Gel P-6 in a manner similar to Glc3Man9GlcNAc2. Together, these data suggest that M14 is a lipid-oligosaccharide intermediate of N-linked protein glycosylation and that enhanced expression of this class of molecule in response to chemical insults and hyperthermia is a newly described cellular reaction to stress.

Induction of 32- and 34-kDa stress proteins by sodium arsenite, heavy metals, and thiol-reactive agents.

Challenge of human or murine melanoma cells with sodium arsenite, heavy metals (Zn2+, Cu2+ and Cd2+), or thiol-reactive agents (p-chloromercuribenzoate and iodoacetamide) induced the synthesis of four stress proteins with molecular masses of 100, 90, 72 (a doublet), and 32 (human) or 34 (murine) kDa. Enhanced expression of the 32- and 34-kDa polypeptides (p32 and p34) preceded or paralleled the synthesis of the other stress proteins. Hyperthermia, the calcium ionophore A23187, and amino acid analogs (L-azetidine-2-carboxylic acid and L-canavanine) induced the formation of the major stress proteins, but failed to increase synthesis of p32 and p34. Characterization of the dose and time dependence of p32 and p34 synthesis in human (A375) and murine (B16-F10) melanoma cells, respectively, indicated that these proteins were subject to similar regulatory mechanisms. Electrophoretic analysis of stressed cells pulsed with different metabolic precursors revealed that p32 and p34 were radiolabeled with [35S]methionine or 3H-amino acids but not by [3H]mannose or [35S]cysteine. Polyclonal antibodies raised against human p32 cross-reacted with murine p34. These data suggest that p32 and p34 are closely regulated human and murine gene products, respectively, whose synthesis can be modulated by thiol-reactive reagents. Induction of p32 and p34 by these agents, but not by heat shock, suggests that these proteins are a subset of stress-inducible gene products.

Induction of mammalian stress proteins by a triethylphosphine gold compound used in the therapy of rheumatoid arthritis.

In vitro exposure of cultured human, murine and rat cells to pharmacologic concentrations (10(-8) to 10(-6) M) of auranofin, 2,3,4,6,-tetra-O-acetyl-1-thio-beta-D-glucopyranosato-S- triethylphosphine gold(I) (Ridaura), a gold containing compound approved for the treatment of rheumatoid arthritis, results in the induction of several stress proteins. The enhanced synthesis of two polypeptides, p32 and p34, was particularly prominent. A similar response was observed in freshly collected human monocytes challenged with auranofin. In addition, oral administration of auranofin to rats induced enhanced synthesis of a 32-kDa protein in peritoneal exudate cells analyzed ex vivo at various times following drug treatment. These data suggest that increased synthesis of p32 and p34 might participate in mediating certain aspects of auranofin pharmacology.