The mannose/N-acetylgalactosamine-4-SO4 receptor displays greater specificity for multivalent than monovalent ligands.

Recognition of carbohydrates on glycosylated molecules typically requires multivalent interactions with receptors. Monovalent forms of terminal saccharides engaged by the receptor binding sites typically display weak affinities in the mm range and poor specificity. In contrast, multivalent forms of the same saccharides are bound with strong affinity (10(-7)-10(-9) m) and significantly greater specificity. Although multivalency can readily account for increased affinity, the molecular basis for enhanced specificity is not well understood. We have examined the specificity of the cysteine-rich domain of the mannose/GalNAc-4-SO4 receptor using monovalent and multivalent forms of the trisaccharide GalNAcbeta1,4GlcNAcbeta1,2Manalpha (GGnM) sulfated at either the C4 (S4GGnM) or C3 (S3GGnM) hydroxyl of the terminal GalNAc. Monovalent S4GGnM and S3GGnM have K(i) values of 25.8 and 16.2 microm, respectively. Multivalent conjugates of the same GalNAc-4-SO4- and GalNAc-3-SO4-bearing trisaccharides (6.7 mol of trisaccharide/mol of bovine serum albumin) have K(i) values of 0.013 and 0.170 microm, respectively. The 2000-fold versus 95-fold change in affinity seen for the multivalent forms of these 4-sulfated and 3-sulfated trisaccharides reflects a difference in the impact of conformational entropy. A large fraction of the SO4-3-GalNAc structures exists in a form that is not favorable for binding to the Cys-rich domain. This reduces the effective concentration of SO4-3-GalNAc as compared with SO4-4-GalNAc under the same conditions and results in a markedly lower association rate. This difference in association rate accounts for the 12-fold difference in the rate of clearance from the blood seen with S4GGnM-BSA and S3GGnM-BSA in vivo.

Molecular basis of lutropin recognition by the mannose/GalNAc-4-SO4 receptor.

The circulatory half-life of the glycoprotein hormone lutropin (LH) is precisely regulated by the mannose (Man)/GalNAc-4-SO(4) receptor expressed in hepatic endothelial cells. Rapid clearance from the circulation contributes to the episodic rise and fall of LH levels that is essential for maximal stimulation of the G protein-coupled LH receptor. We have defined two molecular forms of the Man/GalNAc-4-SO(4) receptor that differ in ligand specificity, cell and tissue expression, and function. The form expressed by hepatic endothelial cells binds GalNAc-4-SO(4)-bearing ligands and regulates hormone circulatory half-life, whereas the form expressed by macrophages binds Man-bearing ligands and may play a role in innate immunity. We demonstrate that the GalNAc-4-SO(4)-specific form in hepatic endothelial cells is dimeric whereas the Man-specific form in lung macrophages is monomeric, accounting for the different ligand specificities of the receptor expressed in these tissues. Two cysteine-rich domains, each of which binds a single GalNAc-4-SO(4), are required to form stable complexes with LH. The kinetics of LH binding by the GalNAc-4-SO(4)-specific form of the receptor in conjunction with its rate of internalization from the cell surface make it likely that only two of the four terminal GalNAc-4-SO(4) moieties present on native LH are engaged before receptor internalization. As a result, the rate of hormone clearance will remain constant over a wide range of LH concentrations and will not be sensitive to variations in the number of terminal GalNAc-4-SO(4) moieties as long as two or more are present on multiple oligosaccharides.

Regulation of 3-hydroxy-3-methylglutaryl-coenzyme A reductase degradation by the nonsterol mevalonate metabolite farnesol in vivo.

We have previously reported that degradation of 3-hydroxy-3-methylglutaryl-coenzyme A reductase, the rate-limiting enzyme in the isoprenoid pathway leading to cholesterol production, can be accelerated in cultured cells by the addition of farnesyl compounds, which are thought to mimic a natural, nonsterol mevalonate metabolite(s). In this paper we report accelerated reductase degradation by the addition of farnesol, a natural product of mevalonate metabolism, to intact cells. We demonstrate that this regulation is physiologically meaningful, shown by its blockage by several inhibitory conditions that are known to block the degradation induced by mevalonate addition. We further show that intracellular farnesol levels increase significantly after mevalonate addition. Based on these results, we conclude that farnesol is a nonsterol, mevalonate-derived product that plays a role in accelerated reductase degradation. Our conclusion is in agreement with a previous report (Correll, C. C., Ng, L., and Edwards, P. A. (1994) J. Biol. Chem. 269, 17390-17393), in which an in vitro system was used to study the effect of farnesol on reductase degradation. However, the apparent stimulation of degradation in vitro appears to be due to nonphysiological processes. Our findings demonstrate that in vitro, farnesol causes reductase to become detergent insoluble and thus lost from immunoprecipitation experiments, yielding apparent degradation. We further show that another resident endoplasmic reticulum protein, calnexin, similarly gives the appearance of protein degradation after farnesol addition in vitro. However, after the addition of farnesol to cells in vivo, calnexin remains stable, whereas reductase is degraded, providing further evidence that the in vivo effects of farnesol are physiologically meaningful and specific for reductase, whereas the in vitro effects are not.

Comparison of control subjects recruited by random digit dialing and area survey.

Although random digit dialing (RDD) is an accepted and commonly used method of sampling populations for controls in case-control studies, there have been surprisingly few attempts to compare the accuracy of RDD with that of the best traditional alternative, i.e., household area surveys. The aim of the present study was to compare a variety of characteristics of control subjects selected by RDD and area survey methods. All data were gathered through in-person interviews of both types of control subjects. The area survey identified a population-based sample of 20- to 79-year-old residents of two Washington State counties in 1978 and 1979. Control groups for three case-control studies of bladder cancer, gynecologic cancers, and multiple myeloma were drawn from this area sample, for a total of 240 control subjects. Controls aged 21-64 years from the same counties were identified for the National Bladder Cancer Study using RDD telephone sampling during the same time period. There were 134 respondents in the RDD control group. Overall, the two control groups selected by these two different methods yielded similar estimated frequencies of various population characteristics. The small differences observed in some age/sex subgroups and the statistical significance of the overall measure of association for occupational exposure to organic substances may be attributed to multiple comparisons.

Sexually transmitted diseases and carcinogenesis.

Issues related to the development of cancer of the urogenital system in men and women and the possible role played by agents of sexually transmitted diseases are discussed. Research evidence supporting the role of specific viral agents in the etiology of cancer of the uterine cervix, penis, testis, prostate, and urinary bladder is presented. Also included is a discussion of the current speculations about the role played by agents of sexually transmitted diseases in acquired immune deficiency syndrome (AIDS).