Variations in the rate of secretion of different glycosylated forms of rat alpha 1-acid glycoprotein

Male-specific protein (MSP): a new gene linked to sexual behavior and aggressiveness of tilapia males

MSP is a male-specific protein initially identified in the serum of sexually active Sarotherodon galilaeus males, and is shown herein to be present in the serum of sexually mature males, but not females, of three other tilapia species. Cloning of the MSP cDNA and analysis of its predicted amino-acid sequence revealed that it is an outlier lipocalin that contains a signal peptide in its N-terminal region. The abundance of highly homologous sequences found in fish and the monophyletic relationship to tetrapod Alpha-1-acid glycoprotein (AGP) places it as a clade XII lipocalin. MSP was shown to undergo major N-glycosylation, characteristic of many lipocalins. The expression pattern of MSP, as determined at both the RNA and protein levels, points to the liver, head kidney and testis as production tissues, and resembles a pattern typical of some hormones. We found that MSP is secreted in urine and seminal fluids, and is present in the skin mucus of socially dominant males. Moreover, we discovered a positive correlation between MSP levels in the serum and the dominance and aggressive behavior displayed by socially dominant males. Based on these data, we suggest that MSP is a novel male-specific lipocalin that may function in intra and inter-sex communication.

Alpha 1-acid glycoprotein (orosomucoid): pathophysiological changes in glycosylation in relation to its function

The aim of this review is to summarize the research efforts of the last two decades with respect to (i) the determination and characterization of the changes in glycosylation of AGP under various physiological and pathological states; and (ii) the effects of such changes on its possible anti-inflammatory functions. It will become clear that the heterogeneity observed in the glycosylation of AGP in serum, represents various so-called glycoforms of AGP, of which the relative amounts are strictly determined by the (patho) physiological conditions.

Differential secretion of alpha 1-acid glycoprotein occurs in the Golgi complex of isolated rat hepatocytes. Evidence of partial retention in the Golgi

Using weakly basic amines, we investigated the step at which the secretion kinetics of concanavalin-A-retained and nonretained alpha 1-acid glycoprotein glycoforms diverge in isolated rat hepatocytes. Both chloroquine and primaquine, whose action on protein secretion is targeted to terminal domains of the Golgi apparatus, cancelled the kinetic difference without influencing carbohydrate chain sialylation. To test for a possible interaction of alpha 1-acid glycoprotein with Golgi membranes, we also permeabilized control and primaquine-treated hepatocytes, as well as purified Golgi preparations, with saponin. In each case, we found that alpha 1-acid glycoprotein was associated with Golgi membranes, the association being more marked in primaquine-treated cells than in control cells. Membrane-bound alpha 1-acid glycoprotein appeared to be preferentially retained on concanavalin A. Such retention could account for the divergent secretion kinetics of alpha 1-acid glycoprotein glycoforms.

Elimination of non-reactive and weakly reactive human alpha 1-acid glycoprotein after induction of the acute phase response in rats

The disposition of concanavalin A (Con A)-non-reactive and Con A-reactive human alpha 1-acid glycoprotein (AAG) was studied in normal male rats and in acute phase response-activated male rats. Activation of the acute phase response was made using a subcutaneous administration of ethynyloestradiol in sesame oil. This technique increased the endogenous AAG concentration 7-fold. In control rats the two forms of human AAG showed identical kinetics with an average clearance of 5.4 mL h-1 kg-1, terminal half-life of 13.5 h and a volume of distribution (steady state) of 91 mL kg-1. In the acute phase response-activated animals, both the clearance and volume of distribution were larger: the average clearance of the Con A-non-reactive AAG was 10.2 mL h-1 kg-1, the volume of distribution (steady state) 152 mL kg-1 and the terminal half-life 11.7 h. The Con A-reactive AAG had a clearance of 14.7 mL h-1 kg-1, a volume of distribution (steady state) of 262 mL kg-1 and a half-life of 15.8 h. The results indicate that not only does activation of the acute phase response alter the kinetics of AAG but that the change is different for the different types of AAG.

Changes in serum glycoprotein glycosylation during experimental inflammation in mice are general, unrelated to protein type, and opposite changes in man and rat: studies on mouse serum alpha 1-acid glycoprotein, alpha 1-esterase, and alpha 1-protease inhibitor

Using the method of crossed affinity immunoelectrophoresis with concanavalin A in combination with digital image processing, unrelated serum glycoproteins from normal mice and from mice undergoing an experimentally induced inflammation were analyzed for their carbohydrate-derived microheterogeneity profile. This profile changed in a generalized way in mouse serum samples taken at various time intervals after the initial induction of inflammation. The changes are not related to the acute-phase behavior of the protein itself (be it positive, negative, or nonreacting), and they are opposite to the changes in microheterogeneity profiles reported previously for glycoproteins during the acute phase in human and rat sera. These findings are discussed in the context of the biosynthetic control of glycoprotein glycosylation during the acute-phase response.

Differential rates of glycoprotein secretion by isolated rat hepatocytes studied in terms of concanavalin A binding

Using a concanavalin-A-based method which respects cell function, we have shown that the kinetics of glycoprotein secretion appear to depend on the nature of the oligosaccharide moiety. In 37 degrees C pulse/chase experiments using freshly isolated normal rat hepatocytes, we found that except for transferrin, whose rate of secretion was independent of its concanavalin A reactivity, the secretion of the concanavalin-A-retained forms of alpha 1 acid glycoprotein, T-kininogen, alpha 1 protease inhibitor and alpha 1 inhibitor III was slower than that of the concanavalin-A-non-retained forms. When hepatocytes were incubated at 20 degrees C, secretion was blocked with the accumulation of mainly endoglycosidase-H-sensitive forms. The secretion kinetics of the concanavalin-A-differentiated forms were still different when the temperature was shifted back to 37 degrees C. The divergence between the secretion rates of the concanavalin-A-differentiated forms would appear to be due to a late event in intracellular protein trafficking, which may depend on the sugar content and/or the number of carbohydrate chains of the glycoproteins.