Induction of alpha 1-acid glycoprotein by recombinant human interleukin-1 in rat hepatoma cells

The induction of alpha 1-acid glycoprotein mRNA by recombinant murine interleukin-1, recombinant human interleukin-1 alpha, and recombinant human interleukin-1 beta has been studied in the rat hepatoma cell line Fao. Whereas the stimulatory capacities of recombinant human interleukin-1 alpha and recombinant murine interleukin-1 were almost identical, the concentrations of recombinant human interleukin-1 beta needed for half-maximal induction of alpha 1-acid glycoprotein mRNA were lower by three orders of magnitude. A 60-fold increase in alpha 1-acid glycoprotein mRNA levels was observed 18 h after the addition of recombinant interleukin-1 beta. In parallel albumin mRNA levels decreased to about 30%. The alpha 1-acid glycoprotein mRNA induction was strictly dependent on the presence of dexamethasone. For a full stimulation dexamethasone concentrations of greater than 10(-7) M were needed, whereas concentrations of less than 10(-12) M were ineffective. The increase in alpha 1-acid glycoprotein mRNA after recombinant human interleukin-1 beta was followed by a 36-fold stimulation in alpha 1-acid glycoprotein synthesis and secretion. When protein synthesis was blocked by either cycloheximide, puromycin, or emetine, the induction of alpha 1-acid glycoprotein mRNA by recombinant human interleukin-1 beta was impaired suggesting the involvement of a short-lived protein in the induction of alpha 1-acid glycoprotein mRNA.     

Induction of several acute-phase protein genes by heavy metals: a new class of metal-responsive genes.

Acute-phase reactants, metallothioneins, and heat-shock proteins are the products of three families of genes that respond to glucocorticoids and cytokines. Metallothioneins and heat-shock proteins, however, are also stimulated by heavy metals, whereas very little is known about the effect of heavy metals on acute-phase-reactant genes. We have studied the effect of heavy metals (Hg, Cd, Pb, Cu, Ni, and Zn) and Mg on the acute-phase reactants alpha 1-acid glycoprotein, C-reactive protein, alpha 1-antitrypsin and alpha 1-antichymotrypsin. alpha 1-Acid glycoprotein and C-reactive protein mRNA levels were increased severalfold in livers of heavy-metal-treated Balb/c mice. The strongest induction was mediated by Hg, followed in order of response by Cd greater than Pb greater than Cu greater than Ni greater than Zn greater than Mg. None of the metals affected the mRNA levels of albumin, alpha 1-antitrypsin, and alpha 1-antichymotrypsin. Furthermore, failure to repress albumin, a negative acute-phase reactant, indicated that the induction of these genes was not due to a metal-mediated inflammatory response. The metals also induced alpha 1-acid glycoprotein and C-reactive protein in adrenalectomized animals, indicating that induction by the heavy metals is not mediated by the glucocorticoid induction pathway. Sequence analysis has revealed a region of homology to metal-responsive elements in the alpha 1-acid glycoprotein and C-reactive protein promoters. Additionally, an alpha 1-acid glycoprotein expression vector, pAGP(-595)CAT, responded to Hg and Cd when transfected into human HepG2 cells.(ABSTRACT TRUNCATED AT 250 WORDS)     

Protein glycosylation regulates the externalization of two distinct classes of glucocorticoid-induced glycoproteins in rat hepatoma cells

The relationship of protein glycosylation to the externalization of glucocorticoid inducible alpha1-acid glycoprotein and mouse mammary tumor virus glycoproteins was examined in M1.54, a clonal population of mouse mammary tumor virus-infected rat hepatoma cells. Multiple freeze-thaw of isolated microsomes revealed that while alpha 1-acid glycoprotein is carried through the cell as a soluble component of vesicles, extracellular viral glycoproteins are initially membrane-associated. At concentrations of tunicamycin that specifically inhibited N-linked protein glycosylation, alpha 1-acid glycoprotein fractionated between the cellular and extracellular compartments. Thus, approximately one half of the newly synthesized, nonglycosylated (22,000 Mr) alpha 1-acid glycoprotein was rapidly secreted with kinetics similar to its glycosylated counterpart (release half-time of 60 min), while the remaining species first localized in an undefined intracellular compartment prior to its slow secretion (release half-time of 24 h). The same distribution of nonglycosylated alpha 1-acid glycoprotein was observed at various absolute levels of polypeptide, suggesting that this was not due simply to the saturation of an efficient secretory pathway at high polypeptide levels. In contrast to alpha 1-acid glycoprotein, no labeled viral antigens were released by tunicamycin-treated M1.54, while a nonglycosylated viral precursor glycopolyprotein was expressed intracellularly. Taken together, these results suggest that carbohydrate attachment strongly regulates the externalization of both alpha 1-acid glycoprotein and mouse mammary tumor virus species, which represent two distinct classes of extracellular glycoproteins.     

Partial hepatectomy and mediators of inflammation decrease the expression of liver alpha 2-HS glycoprotein gene in rats

Liver mRNA levels of two acute phase reactant (APR) proteins, alpha 2-HS glycoprotein (a major negative APR) and alpha 1-acid glycoprotein (a major positive APR) were measured in male rats at different times after the administration of turpentine, of tumor necrosis factor, or following partial hepatectomy. In every case, a marked decrease in mRNA levels of alpha 2-HS glycoprotein was observed which reached a maximum at 24 h. A concomitant increase of alpha 1-acid glycoprotein mRNA levels was observed under the same conditions. These results indicate that the decreased levels of alpha 2-HS glycoprotein induced by the acute-phase response following inflammatory mediators and partial hepatectomy are due to a down-regulation of the gene expression of this protein in rat liver.     

Studies on incorporation of mannose into rat alpha 1-acid glycoprotein: evidence for precursor forms in rough membranes

Rats were given pulse injections of D-[14C]mannose and were killed at various times up to 60 min after injection. Rough, smooth, and Golgi fractions were prepared from liver, and alpha 1-acid glycoprotein was isolated from Lubrol extracts of the fractions. The kinetics of incorporation of D-[14C]mannose into total protein, Lubrol protein, and alpha 1-acid glycoprotein showed that proteins associated with rough fractions had particularly high specific radioactivities at early times of incorporation. One explanation for the kinetic data is that glycoproteins contain a high mannose content at early times of assembly of oligosaccharide chains. This idea was confirmed in the case of alpha 1-acid glycoprotein by isolation of a high mannose containing precursor species of alpha 1-acid glycoprotein from rough fractions of liver. This species contained 56 residues of hexose (mainly mannose) compared with 35 residues of hexose (roughly equal amounts of mannose and galactose) which are found in the native protein. It is proposed that the high mannose precursor is a form of alpha 1-acid glycoprotein that exists at an early stage in assembly of the glycoprotein and which contains largely unprocessed carbohydrate chains. In addition, evidence is presented from amino acid analyses and gel electrophoresis of the high mannose precursor and another fraction from which it is formed by limited tryptic treatment, that pro-forms of alpha 1-acid glycoprotein with extensions of the polypeptide chain may also exist.     

Induction of acute phase proteins by dexamethasone in rat hepatocyte primary cultures

The effect of dexamethasone on the synthesis of acute phase proteins has been studied in primary cultures of rat hepatocytes. In the absence of dexamethasone no detectable amounts of alpha 2-macroglobulin were synthesized by hepatocytes cultured for 1 day. alpha 2-Macroglobulin synthesis was induced by dexamethasone concentrations of 10(-8) M or higher with a maximum at a concentration of 10(-7) M. alpha 1-Acid glycoprotein was synthesized in the absence of dexamethasone; however, its synthesis was also greatly stimulated by dexamethasone concentrations of 10(-8)-10(-6) M. Synthesis of alpha 1-proteinase inhibitor was stimulated only 1.4-fold at a dexamethasone concentration of 10(-7) M. The kinetics of induction of alpha 2-macroglobulin and alpha 1-acid glycoprotein were studied at a dexamethasone concentration of 10(-7) M. After an initial lag phase of 3 h the synthesis of both proteins showed a steady increase during 2 days. Synthesis of albumin remained unchanged under these experimental conditions. Unlike alpha 2-macroglobulin and alpha 1-acid glycoprotein tyrosine aminotransferase activity increased already during the first 3 h of induction by dexamethasone with a maximum at 12 h followed by a slight decrease.     

The Trypanosoma brucei La protein is a candidate poly(U) shield that impacts spliced leader RNA maturation and tRNA intron removal

By virtue of its preferential binding to poly(U) tails on small RNA precursors and nuclear localisation motif, the La protein has been implicated for a role in the stabilisation and nuclear retention of processing intermediates for a variety of small RNAs in eukaryotic cells. As the universal substrate for trans-splicing, the spliced leader RNA is transcribed as a precursor with just such a tail. La protein was targeted for selective knockdown by inducible RNA interference in Trypanosoma brucei. Of three RNA interference strategies employed, a p2T7-177 vector was the most effective in reducing both the La mRNA as well as the protein itself from induced cells. In the relative absence of La protein T. brucei cells were not viable, in contrast to La gene knockouts in yeast. A variety of potential small RNA substrates were examined under induction, including spliced leader RNA, spliced leader associated RNA, the U1, U2, U4, and U6 small nuclear RNAs, 5S ribosomal RNA, U3 small nucleolar RNA, and tRNATyr. None of these molecules showed significant variance in size or abundance in their mature forms, although a discrete subset of intermediates appear for spliced leader RNA and tRNATyr intron splicing under La depletion conditions. 5'-end methylation in the spliced leader RNA and U1 small nuclear RNA was unaffected. The immediate cause of lethality in T. brucei was not apparent, but may represent a cumulative effect of multiple defects including processing of spliced leader RNA, tRNATyr and other unidentified RNA substrates. This study indicates that La protein binding is not essential for maturation of the spliced leader RNA, but does not rule out the presence of an alternative processing pathway that could compensate for the absence of normally-associated La protein.     

Identification and sequencing of cDNA clones for the rodent negative acute-phase protein alpha 1-inhibitor 3

Rat alpha 1-inhibitor 3 clones were isolated by immunological screening of a lambda gt11 cDNA library prepared from rat liver poly(A)-rich RNA. The recombinant cDNA clones were identified by the absence of their immunoprecipitable products following hybrid-arrested in vitro translation. The size of the cognate poly(A)-rich RNA was estimated to be roughly 5000 residues. Approximately 16 h after induction of inflammation the amount of alpha 1-inhibitor 3 poly(A)-rich RNA decreases as shown by dot-blot hybridization and Northern analyses. The response of this negative acute-phase plasma protein to inflammation may therefore be considered to be at the pretranslational level. The characterized DNA constitutes an open reading frame of 225 amino acids followed by a canonical eucaryotic polyadenylation signal and a poly(A) tail. Sequence microheterogeneity, particularly in the 3'-flanking region was observed. An amino acid homology of 70% for alpha 1-inhibitor 3 with human and rodent alpha 2-macroglobulin emphasizes the evolutionary relationship of the macroglobulins.     

Messenger RNA activities of four acute phase proteins during inflammation

Poly(A)+ RNA isolated from the livers of normal rats and of rats suffering from an acute inflammation was translated in a cell-free translation system from rabbit reticulocytes. The translation products were immunoprecipitated with specific antisera against alpha 1-acid glycoprotein, alpha 2-macroglobulin, transferrin, alpha 1-proteinase inhibitor and albumin. 15 to 21 h after intramuscular injection of turpentine 73-, 66-, 2.8-, and 2-fold increases in translatable mRNAs for alpha 1-acid glycoprotein, alpha 2-macroglobulin, transferrin and alpha 1-proteinase inhibitor, respectively, were observed. For albumin a decrease in translatable mRNA to about 30% of controls was measured.     

Secretion of high-mannose-type alpha 1-proteinase inhibitor and alpha 1-acid glycoprotein by primary cultures of rat hepatocytes in the presence of the mannosidase I inhibitor 1-deoxymannojirimycin

Two different forms of alpha 1-proteinase inhibitor and alpha 1-acid glycoprotein were found in primary cultures of rat hepatocytes. After a 2.5-h labeling period with [35S]methionine the high-mannose-type precursor of alpha 1-proteinase inhibitor (Mr 49000) and alpha 1-acid glycoprotein (Mr 39 000) and the mature-complex-type alpha 1-proteinase inhibitor (Mr 54 000) and alpha 1-acid glycoprotein (Mr 43 000-60 000) could be immunoprecipitated from the cells, but only the complex-type forms of the two glycoproteins were secreted into the hepatocyte media. When hepatocytes were incubated with the mannosidase I inhibitor 1-deoxymannojirimycin at a concentration of 4 mM, the 49 000-Mr form of alpha 1-proteinase inhibitor and the 39 000-Mr form of alpha 1-acid glycoprotein could be detected in the cells as well as in their media. Neither the secretion of alpha 1-proteinase inhibitor nor that of alpha 1-acid glycoprotein was impaired by 1-deoxymannojirimycin. While alpha 1-proteinase inhibitor and alpha 1-acid glycoprotein, secreted by control cells, were resistant to endoglucosaminidase H, alpha 1-proteinase inhibitor and alpha 1-acid glycoprotein, secreted by hepatocytes treated with 4 mM 1-deoxymannojirimycin, could be deglycosylated by endoglucosaminidase H. When the [3H]mannose-labeled oligosaccharides of alpha 1-proteinase inhibitor, secreted by 1-deoxymannojirimycin-treated hepatocytes, were cleaved off by endoglucosaminidase H and analyzed by Bio-Gel P-4 chromatography, they eluted at the position of Man9GlcNAc, indicating that mannosidase I had been efficiently inhibited. 1-Deoxymannojirimycin did not inhibit the synthesis or the cotranslational N-glycosylation of alpha 1-proteinase inhibitor or alpha 1-acid glycoprotein.     

Interaction between calcofluor white and carbohydrates of alpha 1-acid glycoprotein.

Interactions between the fluorescent probe, calcofluor white, and human serum albumin (HSA) and alpha 1-acid glycoprotein (orosomucoid) are compared. The two proteins have comparable isoelectric points, but alpha 1-acid glycoprotein is highly glycosylated (40% of glycans by weight), while the serum albumin is not. Binding of calcofluor to the proteins induces an increase in both the fluorescence anisotropy and the fluorescence intensity of the fluorophore. Also, we found that the calcofluor exhibits a fluorescence emission with a maximum located at 432, 415 or 445 nm, respectively, in the absence of proteins, in the presence of HSA, and in the presence of alpha 1-acid glycoprotein. The stoichiometries of the calcofluor-serum albumin and calcofluor-alpha 1-acid glycoprotein complexes are 2:1 and 1:1, respectively. The association constants are 0.04 and 0.15 microM-1, respectively. The calcofluor does not interact with Lens culinaris agglutinin (LCA), although the protein has a hydrophobic site. Nevertheless, one cannot exclude that the binding of the fluorophore to the HSA is nonspecific. Our results, when compared with those obtained with calcofluor dissolved in the hydrophobic solvent isobutanol, and with the fluorescent probe, potassium 6-(p-toluidino)-2-naphthalenesulfonate (TNS), bound to alpha 1-acid glycoprotein, indicate that the emission of calcofluor bound to HSA occurs from a hydrophobic state, while that of calcofluor bound to alpha 1-acid glycoprotein occurs from a hydrophilic state. The fluorescence intensity of calcofluor decreases in the presence of carbohydrates isolated from alpha 1-acid glycoprotein, while it increases in the presence of alpha 1-cellulose. Thus, calcofluor interacts mainly with the glycan moiety of alpha 1-acid glycoprotein, and its fluorescence is sensitive to the secondary structure of the glycans.