Influence of glycosylation on the clearance of recombinant human sex hormone-binding globulin from rabbit blood

Characterization and comparison of recombinant full-length ursine and human sex hormone-binding globulin

Sex hormone‐binding globulin (SHBG) regulates the bioavailability of sex steroid hormones in the blood. Levels of SHBG increase markedly in brown bears (Ursus arctos) during hibernation, suggesting that a key regulatory role of this protein is to quench sex steroid bioavailability in hibernation physiology. To enable characterization of ursine SHBG and a cross species comparison, we established an insect cell‐based expression system for recombinant full‐length ursine and human SHBG. Compared with human SHBG, we observed markedly lower secretion levels of ursine SHBG, resulting in a 10‐fold difference in purified protein yield. Both human and ursine recombinant SHBG appeared as dimeric proteins in solution, with a single unfolding temperature of ~ 58 °C. The thermal stability of ursine and human SHBG increased 5.4 and 9.5 °C, respectively, in the presence of dihydrotestosterone (DHT), suggesting a difference in affinity. The dissociation constants for [³H]DHT were determined to 0.21 ± 0.04 nm for human and 1.32 ± 0.10 nm for ursine SHBG, confirming a lower affinity of ursine SHBG. A similarly reduced affinity, determined from competitive steroid binding, was observed for most steroids. Overall, we found that ursine SHBG had similar characteristics to human SHBG, specifically, being a homodimeric glycoprotein capable of binding steroids with high affinity. Therefore, ursine SHBG likely has similar biological functions to those known for human SHBG. The determined properties of ursine SHBG will contribute to elucidating its potential regulatory role in hibernation physiology.

Effects of oral versus transdermal estradiol plus micronized progesterone on thyroid hormones, hepatic proteins, lipids, and quality of life in menopausal women with hypothyroidism: a clinical trial

OBJECTIVE

The aim of the study was to evaluate the effects of usual doses of oral estradiol with transdermal estradiol and the effects of these estrogens plus micronized progesterone (MP) in menopausal women with primary hypothyroidism.

METHODS

Twenty women were randomized to 12 weeks of treatment with estradiol 1 mg tablets or estradiol 1 mg gel. Then, women with a uterus received a 100 mg capsule of oral MP. Thyroid function, thyroxine-binding globulin (TBG), sex hormone-binding globulin (SHBG), insulin-like growth factor 1 (IGF-1), lipid profiles, and quality of life were measured at baseline and after 12 and 24 weeks.

RESULTS

Oral estradiol led to an increase in total T4 levels (5.84 ± 1.11 vs 8.41 ± 1.61 μg/dL; P < 0.001); changes in thyroid-stimulating hormone (TSH) levels were clinically important in 3 of 10 participants who needed to increase their dose of levothyroxine. Significant changes were detected in hepatic proteins with oral estradiol: TBG and SHBG levels increased (15.29 ± 3.87 vs 20.84 ± 5.49 μg/mL, P < 0.001; 61.85 ± 33.6 vs 121.4 ± 49.36 nmol/L, P < 0.001; respectively), whereas IGF-1 levels decreased (152 ± 38.91 vs 96 ± 17.59 ng/mL; P < 0.001). Transdermal estradiol alone did not significantly affect the thyroid function. Transdermal estradiol plus MP led to a decrease in TSH levels (1.79 ± 1.05 vs 1.09 ± 0.52 mIU/L; P = 0.04), while total T4 levels increased (7.54 ± 1.34 vs 9.95 ± 2.24 μg/dL; P = 0.01). Hormonal therapy had a greater impact on depressed mood and vasomotor symptoms.

CONCLUSIONS

Total T4 and TBG levels increase after oral estradiol in women with hypothyroidism and it may cause clinical changes in TSH levels. Conversely, transdermal estradiol alone or plus MP does not cause major changes in thyroid function in these women.

Molecular interactions between sex hormone-binding globulin and nonsteroidal ligands that enhance androgen activity

Sex hormone-binding globulin (SHBG) determines the equilibrium between free and protein-bound androgens and estrogens in the blood and regulates their access to target tissues. Using crystallographic approaches and radiolabeled competitive binding-capacity assays, we report here how two nonsteroidal compounds bind to human SHBG, and how they influence androgen activity in cell culture. We found that one of these compounds, (-)3,4-divanillyltetrahydrofuran (DVT), present in stinging nettle root extracts and used as a nutraceutical, binds SHBG with relatively low affinity. By contrast, a synthetic compound, 3-(1H-imidazol-1-ylmethyl)-2phenyl-1H-indole (IPI), bound SHBG with an affinity similar to that of testosterone and estradiol. Crystal structures of SHBG in complex with DVT or IPI at 1.71-1.80 Å resolutions revealed their unique orientations in the SHBG ligand-binding pocket and suggested opportunities for the design of other nonsteroidal ligands of SHBG. As observed for estradiol but not testosterone, IPI binding to SHBG was reduced by ∼20-fold in the presence of zinc, whereas DVT binding was almost completely lost. Estradiol-dependent fibulin-2 interactions with SHBG similarly occurred for IPI-bound SHBG, but not with DVT-bound SHBG. Both DVT and IPI increased the activity of testosterone in a cell culture androgen reporter system by competitively displacing testosterone from SHBG. These findings indicate how nonsteroidal ligands of SHBG maybe designed to modulate the bioavailability of sex steroids.

Loss and gain of N-linked glycosylation sequons due to single-nucleotide variation in cancer

Despite availability of sequence site-specific information resulting from years of sequencing and sequence feature curation, there have been few efforts to integrate and annotate this information. In this study, we update the number of human N-linked glycosylation sequons (NLGs), and we investigate cancer-relatedness of glycosylation-impacting somatic nonsynonymous single-nucleotide variation (nsSNV) by mapping human NLGs to cancer variation data and reporting the expected loss or gain of glycosylation sequon. We find 75.8% of all human proteins have at least one NLG for a total of 59,341 unique NLGs (includes predicted and experimentally validated). Only 27.4% of all NLGs are experimentally validated sites on 4,412 glycoproteins. With respect to cancer, 8,895 somatic-only nsSNVs abolish NLGs in 5,204 proteins and 12,939 somatic-only nsSNVs create NLGs in 7,356 proteins in cancer samples. nsSNVs causing loss of 24 NLGs on 23 glycoproteins and nsSNVs creating 41 NLGs on 40 glycoproteins are identified in three or more cancers. Of all identified cancer somatic variants causing potential loss or gain of glycosylation, only 36 have previously known disease associations. Although this work is computational, it builds on existing genomics and glycobiology research to promote identification and rank potential cancer nsSNV biomarkers for experimental validation.

Effect of placental sex hormone-binding globulin single nucleotide polymorphism rs6259 on protein and function in gestational diabetes mellitus

Sex hormone-binding globulin (SHBG) has a key role in the occurrence and development of the gestational diab-etes mellitus (GDM). Single nucleotide polymorphism (SNP) rs6259 is a functional site in SHBG gene, which is suspected to regulate the SHBG level. The present study explored the placental SHBG SNP rs6259 distribution in Chinese pregnant women and the influence on placental SHBG concentrations, to assess the relationship of SHBG rs6259 in the occurrence and development of GDM. We screened the SHBG rs6259 allele in 210 healthy and 180 GDM gravidas by PCR-RFLP and restriction enzyme and measured placental SHBG concentrations in each genotypic group with western blot analysis. The mechanisms of SHBG rs6259 function were analyzed by cell culture, recombinant lentivirus transfection, real-time PCR, and western blot analysis. We found the differences of SHBG Asn327 allele frequency and the genotype distribution in GDM and control groups were statistically significant (P<0.05). Western blot analysis results showed that the Asn327 allele group was associated with a higher placental SHBG level than the Asp327 allele homozygote group (P<0.05). In HTR8-SVneo cell transfection, the positive transfection groups (SHBG-rs6259 Asn) led to an obviously higher tendency of SHBG mRNA and protein expression than the negative control groups (SHBG-rs6259 Asp), the normal cell group, and the blank control group (blank lentivirus LV-5) (P<0.05). Our data, therefore, reflected that SHBG SNP rs6259 causes changes in placental SHBG concentration and may play a functional role in the molecular mechanisms of GDM etiology.

Sex hormone-binding globulin gene expression and insulin resistance

CONTEXT

The plasma level of sex hormone binding globulin (SHBG), a glycoprotein produced by hepatocytes, is subject to genetic, hormonal, metabolic, and nutritional regulation, and is a marker for the development of the metabolic syndrome and diabetes.

OBJECTIVE

Because the mechanism for these associations is unclear, and no studies of SHBG gene expression in humans have been published, SHBG mRNA was measured in human liver samples and related to anthropometric data.

SETTING

Inpatients at a private, nonprofit, university-associated hospital were studied.

PARTICIPANTS

Subjects were fifty five adult men and women undergoing hepatic resection as treatment for cancer.

MAIN OUTCOME MEASURES

Main outcome measures were SHBG mRNA and serum SHBG levels.

RESULTS

SHBG mRNA was a strong predictor of serum SHBG with higher levels of the mRNA and protein in women than in men. The relationship between SHBG mRNA and circulating SHBG differed in males and females consistent with a sex difference in post-transcriptional regulation. A strong positive correlation was found between the level of the mRNA for the transcription factor HNF4α and SHBG mRNA. Insulin resistance (IR), assessed by homeostatis model assessment, was related inversely to SHBG mRNA and to HNF4α mRNA as well as to circulating SHBG levels. These mRNAs, as well as serum SHBG, were higher when the hepatic triglyceride concentration was low, and decreased with increasing body mass index but were unrelated to age.

CONCLUSIONS

Fat accumulation in liver and IR are important determinants of SHBG gene expression and thereby circulating SHBG levels that are perhaps mediated through effects on the transcription factor HNF4α. These findings provide a potential mechanism to explain why low SHBG predicts the development of type 2 diabetes.

Naturally occurring mutants inform SHBG structure and function

SHBG transports and regulates the activities of androgens and estrogens. Several single nucleotide polymorphisms in the human SHBG gene have been linked to sex steroid-dependent diseases, including those associated with the metabolic syndrome. The N-terminal laminin G-like domain of SHBG includes binding sites for calcium, sex steroids, and fibulin family members, as well as a dimerization domain. We have found that 8 of 18 uncharacterized nonsynonymous single nucleotide polymorphisms within this domain alter the production or biochemical properties of SHBG in ways not previously recognized. O-Linked glycosylation at Thr7 is disrupted in SHBG T7N, whereas abnormal glycosylation of SHBG G195E limits its secretion. Three SHBG mutants (R135C, L165M, and E176K) bind estradiol with abnormally high affinity. SHBG R135C also has an increased interaction with fibulin-2. Two different substitutions within the dimer interface at R123 (R123H and R123C) reduce the affinity for 5α-dihydrotestosterone, while increasing the relative binding affinity for estradiol. SHBG T48I is defective in calcium binding, which leads to a defect in dimerization, reduced affinity for sex steroids, and an enhanced interaction with fibulin-2, which can all be restored by calcium supplementation. These naturally occurring mutants provide insight into SHBG structure and function, and defects in SHBG production or function need to be considered in the context of its utility as a biomarker of diseases.

Evolving utility of sex hormone-binding globulin measurements in clinical medicine

PURPOSE OF REVIEW

Sex hormone-binding globulin (SHBG) regulates the plasma levels and biological actions of the sex steroids: testosterone and estradiol. Advances in our understanding of how plasma SHBG levels are determined, and how SHBG functions, have provided insight into how SHBG should be used to assess the actions of its sex-steroid ligands, and as a biomarker of metabolic and endocrine abnormalities.

RECENT FINDINGS

Plasma SHBG levels fluctuate throughout life in response to the changes in metabolic and physiologic states, and are altered by natural hormones and synthetic steroids. Interindividual differences in plasma SHBG levels and activity are also influenced by polymorphisms within the structural and regulatory regions of the SHBG gene.

SUMMARY

Measurements of SHBG are widely used to predict plasma free testosterone levels in patients suffering from excess androgen exposures, but have broader utility in assessing the risk for endocrine diseases and clinical sequelae of the metabolic syndrome, namely, type 2 diabetes and cardiovascular disease. It is anticipated that new genetic and functional data regarding SHBG will reveal whether SHBG is simply a biomarker of these diseases or participants in their cause.

Glycosylation of therapeutic proteins: an effective strategy to optimize efficacy

During their development and administration, protein-based drugs routinely display suboptimal therapeutic efficacies due to their poor physicochemical and pharmacological properties. These innate liabilities have driven the development of molecular strategies to improve the therapeutic behavior of protein drugs. Among the currently developed approaches, glycoengineering is one of the most promising, because it has been shown to simultaneously afford improvements in most of the parameters necessary for optimization of in vivo efficacy while allowing for targeting to the desired site of action. These include increased in vitro and in vivo molecular stability (due to reduced oxidation, cross-linking, pH-, chemical-, heating-, and freezing-induced unfolding/denaturation, precipitation, kinetic inactivation, and aggregation), as well as modulated pharmacodynamic responses (due to altered potencies from diminished in vitro enzymatic activities and altered receptor binding affinities) and improved pharmacokinetic profiles (due to altered absorption and distribution behaviors, longer circulation lifetimes, and decreased clearance rates). This article provides an account of the effects that glycosylation has on the therapeutic efficacy of protein drugs and describes the current understanding of the mechanisms by which glycosylation leads to such effects.

Diversity and biological significance of sex hormone-binding globulin in fish, an evolutionary perspective

In fish, two different genes, shbga and shbgb, exist that encode for very different proteins. Shbga is the ortholog of mammalian Shbg and was found in all investigated teleosts. In contrast, Shbgb is highly divergent and appears to be a salmonid-specific protein. Here, we review existing data on fish Shbga and Shbgb that have been obtained in chondrichthyes and osteichtyes. Even though other significant expression sites exist, existing data indicate that Shbga is mainly expressed in liver and subsequently secreted into the blood as a homodimer. In contrast, Shbgb is mainly expressed in the ovary, probably secreted as a monomer, and could contribute to the regulation of local steroid action. Binding studies indicate a specialization of circulating Shbg during evolution towards the preferential binding of estradiol and testosterone in teleosts. In contrast, specific fish steroids such as 11-oxo-androgens and oocyte maturation-inducing steroids that are crucial for reproduction are poorly bound by either form of Shbg.

Structural analyses of sex hormone-binding globulin reveal novel ligands and function

Plasma sex hormone-binding globulin (SHBG) regulates the access of androgens and estrogens to their target tissues and cell types. An SHBG homologue, known as the androgen-binding protein, is expressed in Sertoli cells of many mammalians, but testicular expression of human SHBG is restricted to germ cells. The primary structure of SHBG comprises tandem laminin G-like (LG) domains. The amino-terminal LG-domain includes the steroid-binding site and dimerization interface, and its tertiary structure, resolved in complex with natural and synthetic sex steroids, has revealed unanticipated mechanisms of steroid binding at the atomic level. This LG-domain interacts with fibulin-1D and fibulin-2 in a ligand-specific manner, and this is attributed to the unique way estrogens reside within the steroid-binding site, and the ordering of an otherwise flexible loop structure covering the entrance of the steroid-binding pocket. This mechanism enables estradiol to enhance the sequestration of plasma SHBG by the stroma of some tissues through binding to these extra-cellular matrix-associated proteins. The human SHBG amino-terminal LG-domain also contains several cation-binding sites, and occupancy of a zinc-binding site influences its affinity for estradiol. The complete quaternary structure of SHBG remains unresolved but structural predictions suggest that the carboxy-terminal LG-domains extend laterally from the dimerized amino-terminal LG-domains. The carboxy-terminal LG-domain contains two N-glycosylation sites, but their biological significance remains obscure. Knowledge of the SHBG tertiary structure has helped develop computational techniques based on the use of a "bench-mark data set" of steroid ligands, and created novel drug discovery and toxicology risk assessment platforms.

Sex hormone-binding globulin gene expression in the liver: drugs and the metabolic syndrome

Sex hormone-binding globulin (SHBG) is the main transport binding protein for sex steroid hormones in plasma and regulates their accessibility to target cells. Plasma SHBG is secreted by the liver under the control of hormones and nutritional factors. In the human hepatoma cell line (HepG2), thyroid and estrogenic hormones, and a variety of drugs including the antioestrogen tamoxifen, the phytoestrogen, genistein and mitotane (Op'DDD) increase SHBG production and SHBG gene promoter activity. In contrast, monosaccharides (glucose or fructose) effectively decrease SHBG expression by inducing lipogenesis, which reduces hepatic HNF-4alpha levels, a transcription factor that play a critical role in controlling the SHBG promoter. Interestingly, diminishing hepatic lipogenesis and free fatty acid liver biosynthesis also appear to be associated with the positive effects of thyroid hormones and PPARgamma antagonists on SHBG expression. This mechanism provides a biological explanation for why SHBG is a sensitive biomarker of insulin resistance and the metabolic syndrome, and why low plasma SHBG levels are a risk factor for developing hyperglycemia and type 2 diabetes, especially in women. These important advances in our knowledge of the regulation of SHBG expression in the liver open new approaches for identifying and preventing metabolic disorder-associated diseases early in life.

Effects of polymorphisms of the sex hormone-binding globulin (SHBG) gene on free estradiol and bone mineral density

BACKGROUND

Polymorphisms of the sex hormone-binding globulin (SHBG) gene are associated with differences in SHBG levels, influencing the risk for breast cancer and polycystic ovarian syndrome, but no association has been reported for osteoporosis in postmenopausal women.

OBJECTIVE

To determine the effect of G to A substitution in the 5'UTR (rs1799941) and the Asp356Asn (rs6259) polymorphisms of the SHBG gene on bone mineral density (BMD).

METHODS

This is a cross-sectional study in a university-based research center from May, 2002 to December, 2007. A total of two hundred and thirteen healthy postmenopausal Caucasian women > or = 1 year from last menstrual period participated to this study. Serum estradiol by ultrasensitive radioimmnunoassay, serum sex hormone-binding globulin by immunoradiometric assay, and urinary NTx by enzyme-linked immunoassay were measured. BMD measurements were performed by dual energy X-ray absorptiometry and genotyping by Pyrosequencing.

RESULTS

There were no significant differences in SHBG levels associated with either rs1799941 or rs6259. Using a p value of <0.00625 for significance, we found that subjects with the A allele (GA+AA) for the rs1799941, had a trend for lower free estradiol index (FEI) compared to the GG genotype (p=0.04). They also had significantly lower BMD at the intertrochanter (p=0.003) and trend for lower BMD at the total hip (p=0.02). There was no significant difference in FEI levels between the genotypes for the rs6259 polymorphism, but women with the Asn allele (Asp/Asn+Asn/Asn), had significantly lower BMD in the total femur (p=0.004) and intertrochanter (0.002) compared to those with the Asp/Asp genotype.

CONCLUSIONS

Our data suggest that polymorphisms of the SHBG gene are associated with significant differences in BMD at the proximal femur sites. Thus, genetic variations in the SHBG gene may influence BMD at the hip in postmenopausal women.

Asp327Asn polymorphism of sex hormone-binding globulin gene is associated with systemic lupus erythematosus incidence

Endogenous sex hormones have been observed to have a role in systemic lupus erythematosus (SLE) predisposition. Sex hormone-binding globulin (SHBG) regulates the bioavailability of sex hormones to target tissues. Therefore, we examined the distribution of the SHBG functional polymorphism Asp327Asn (rs6259) in SLE patients (n = 150) and controls (n = 150) in a Polish population. We found a contribution of the SHBG327Asn variant to the development of SLE. Women with the Asp/Asn and Asn/Asn genotypes displayed a 2.630-fold increased risk of SLE (95% CI = 1.561-4.433, P = 0.0003). SHBG has a much higher affinity for testosterone than estradiol, and the SHBG327Asn variant displays a reduction of estradiol clearance. Therefore we suggest that the opposing effects of estrogens and testosterone on the immune system and imbalance in the levels of these hormones in SLE patients can be enhanced by the SHBG327Asn protein variant.

Identification of common variants in the SHBG gene affecting sex hormone-binding globulin levels and breast cancer risk in postmenopausal women

BACKGROUND

Circulating levels of sex hormone-binding globulin (SHBG) are inversely associated with breast cancer risk in postmenopausal women. Three polymorphisms within the SHBG gene have been reported to affect SHBG levels, but there has been no systematic attempt to identify other such variants.

METHODS

We looked for associations between SHBG levels in 1,134 healthy, postmenopausal women and 11 tagging single nucleotide polymorphisms (SNP) in or around the SHBG gene. Associations between SHBG SNPs and breast cancer were tested in up to 6,622 postmenopausal breast cancer cases and 6,784 controls.

RESULTS

Ten SNPs within or close to the SHBG gene were significantly associated with SHBG levels as was the (TAAAA)(n) polymorphism. The best-fitting combination of rs6259, rs858521, and rs727428 and body mass index, waist, hip, age, and smoking status accounted for 24% of the variance in SHBG levels (natural logarithm transformed). Haplotype analysis suggested that rs858518, rs727428, or a variant in linkage disequilibrium with them acts to decrease SHBG levels but that this effect is neutralized by rs6259 (D356N). rs1799941 increases SHBG levels, but the previously reported association with (TAAAA)(n) repeat length appears to be a consequence of linkage disequilibrium with these SNPs. One further SHBG SNP was significantly associated with breast cancer (rs6257, per-allele odds ratio, 0.88; 95% confidence interval, 0.82-0.95; P = 0.002).

CONCLUSION

At least 3 SNPs showed associations with SHBG levels that were highly significant but relatively small in magnitude. rs6257 is a potential breast cancer susceptibility variant, but relationships between the genetic determinants of SHBG levels and breast cancer are complex.

A comparison of the short-term effects of oral conjugated equine estrogens versus transdermal estradiol on C-reactive protein, other serum markers of inflammation, and other hepatic proteins in naturally menopausal women

OBJECTIVE

Our objective was to compare the effects of oral vs. transdermal estrogen therapy on C-reactive protein (CRP), IL-6, E- and P-selectin, intercellular adhesion molecule (ICAM)-1 and vascular cell adhesion molecule-1, serum amyloid A, transferrin, prealbumin, IGF-I, SHBG, thyroxine-binding globulin (TBG), and cortisol-binding globulin (CBG) in naturally menopausal women.

DESIGN

This was a randomized, open-label crossover clinical trial. A 6-wk withdrawal from prior hormone therapy (baseline) was followed in randomized order by 12-wk oral conjugated equine estrogens (CEEs) (0.625 mg/d) and 12-wk transdermal estradiol (E2) (0.05 mg/d), with oral micronized progesterone (100 mg/d) given continuously during both regimens.

RESULTS

A total of 27 women enrolled, and 25 completed both treatment periods. Nine parameters changed significantly during oral CEE (median percent change from baseline; P value): CRP (192%; P <0.001); E-selectin (-16.3%; P = 0.003); P-selectin (-15.3%; P = 0.012); ICAM-1 (-5%; P = 0.015); transferrin (5.3%; P = 0.024); IGF-I (-30.5%; P < 0.001); SHBG (113%; P < 0.001); TBG (38%; P < 0.001); and CBG (20%; P < 0.001). With transdermal E2, only three parameters changed significantly and to a lesser degree: ICAM-1 (-2.1%; P = 0.04); IGF-I (-12.5%; P < 0.001); and SHBG (2.6%; P = 0.042). During oral CEE the intrasubject changes in CRP correlated strongly with the changes in serum amyloid A (r = 0.805; P < 0.001), and were only weakly associated with the changes in SHBG (r = 0.248; nonsignificant), TBG (0.430; P = 0.031), and CBG (r = 0.072; nonsignificant). The log-log relationship between CRP and IL-6 observed at baseline showed a parallel shift during oral CEE, suggesting an amplified hepatic response or a greater sensitivity to IL-6 stimulation.

CONCLUSION

Compared with oral CEE, transdermal E2 exerts minimal effects on CRP and the other inflammation and hepatic parameters.

Adaptation of the "in-gel release method" to N-glycome analysis of low-milligram amounts of material

Protein N-glycosylation is a post-translational modification which plays numerous crucial physiological roles. The N-glycan pattern varies depending on the species organs, tissues and even cell types and their respective physiological states. Obtaining enough starting material from a particular cell type or tissue for N-glycan purification by conventional methods can, in certain cases, be very difficult. Previously, a sensitive technique, the "in-gel release method" that allows the determination of N-glycans attached to a protein isolated by SDS-PAGE, has been developed in this and other laboratories. Here, we describe the adaptation of this method to obtain information on the N-glycome from minute amounts of tissue. The starting material, ranging from less than a milligram to a few milligrams of fresh tissue, is directly ground in Laemmli sample buffer and subject briefly to discontinuous Tris-glycine-SDS-PAGE. The Coomassie-stained band containing the majority of the proteins is subject to the "in-gel release method". The developed technique was used to analyze N-glycan patterns of different samples from Caenorhabditis elegans, Drosophila melanogaster, Spodoptera frugiperda, Trichoplusia ni, Nicotiana benthamiana, Arabidopsis thaliana, and Mus musculus. Furthermore, the technique was used to determine the effects of transient small-scale RNAi-mediated knock-down of a glycosylation-related gene in Drosophila Schneider 2 cell line.

Association of breast cancer risk with a common functional polymorphism (Asp327Asn) in the sex hormone-binding globulin gene

Sex hormones play a central role in the development of breast cancer. Sex hormone-binding globulin (SHBG) modulates the bioavailability of circulating sex hormones and regulates their signaling system in the breast tissue. We evaluated the association of a common functional polymorphism (Asp327Asn) in the SHBG gene with breast cancer risk in a population-based case-control study (1,106 cases and 1,180 controls) conducted in Shanghai, China. The variant Asn allele was associated with a reduced breast cancer risk in postmenopausal women [odds ratio (OR), 0.73; 95% confidence interval (95% CI), 0.53-0.99], but not in premenopausal women (OR, 1.03; 95% CI, 0.82-1.27). The protective association was much stronger in postmenopausal women with a low body mass index (BMI; OR, 0.46; 95% CI, 0.29-0.75) or waist-to-hip ratio (OR, 0.51; 95% CI, 0.32-0.83) than those with a high BMI or waist-to-hip ratio (P for interaction < 0.05). Furthermore, the association was stronger for estrogen receptor-positive (OR, 0.64; 95% CI, 0.42-0.98) than for estrogen receptor-negative breast cancer (OR, 0.85; 95% CI, 0.50-1.45). Among postmenopausal controls, blood SHBG levels were 10% higher in carriers of the variant Asn allele than noncarriers (P = 0.06). Postmenopausal control women with the Asn allele and low BMI or waist-to-hip ratio had 20% higher SHBG levels (P < 0.05). This study suggests that the Asn allele in the SHBG gene may be related to a reduced risk of breast cancer among postmenopausal women by increasing their blood SHBG levels.

Pregnancy associated glycoprotein-1, -6, -7, and -17 are major products of bovine binucleate trophoblast giant cells at midpregnancy

Pregnancy associated glycoproteins (PAGs) are extensively glycosylated secretory proteins of ruminant trophoblast cells. In cattle placenta several PAG cDNAs are expressed, but the variety of correspondent proteins and their degree of glycosylation are not well characterized. Thus, we purified PAGs by using a protocol which included a lectin (Vicia villosa agglutinin) affinity chromatography. Due to their specific glycosylation pattern, PAGs derived from binucleate trophoblast giant cells were highly enriched by this protocol. PAGs were purified from cotyledons of 2 day 100 placentas and from a single placenta at day 155 and 180. In all samples three major bands (75; 66; 56 kDa) were detected by one-dimensional SDS-PAGE. Mass-spectrometric analysis identified the 75 kDa band as a mixture of PAG-7 and PAG-6, the 66 kDa band as PAG-1 and the 56 kDa band as PAG-17. N-terminal sequencing of the day 100 sample confirmed the mass spectrometric identifications. Enzymatic release of N-glycans with peptide-N-glycanase-F from PAGs reduced the molecular weight to approximately 37 kDa which corresponds to the theoretical molecular mass of PAGs. Limited peptide-N-glycanase-F treatment revealed that all four N-glycosylation sites are quantitatively occupied in PAG-1. Compared to PAG-1 the number of potential N-glycosylation sites is lower in PAG-17 (three sites) and higher in PAG-6 and -7 (five and six sites, respectively). This suggests that the number of attached N-glycans is the main determinant of molecular mass of bovine PAGs. The degree of glycosylation may be a major factor regulating the plasma half life of PAGs.

Racial difference in circulating sex hormone-binding globulin levels in prepubertal boys

Racial differences in disease risk (eg, osteoporosis, metabolic cardiovascular syndrome, and prostate cancer) may arise partly on a hormonal basis. While reports of racial differences in gonadal steroid hormone levels in middle-aged men have produced conflicting results, there is evidence that high sex hormone-binding globulin (SHBG) and estradiol levels are more common among young adult African American men than white men. To determine whether this difference relates to pituitary-testicular functioning or to other factors, we conducted a cross-sectional study of 47 healthy prepubertal African American and white boys aged 5 to 9 years at the time of their annual school physical examination. Height, weight, blood pressure, waist and hip circumference, and Tanner staging were determined, and a fasting blood sample was obtained. The African Americans studied were slightly older than the whites (mean +/- SD, 82.4 +/- 15.0 vs 70.5 +/- 10.3 months, P = .003). African Americans were also slightly taller and heavier and had a lower waist-to-hip ratio, but these differences could be explained by the difference in age. Mean SHBG levels were 25% higher (P = .15) in African Americans than in whites (197 +/- 104 vs 157 +/- 79 nmol/L), and when adjusted for age, values were 46 nmol/L higher among African Americans. The fifth quintile for SHBG (values > 245 nmol/L) included 1 (4.2%) of 24 whites and 8 (35%) of 23 African Americans studied (P = .003). There was no significant correlation between age, body mass index, waist circumference, or fasting insulin and SHBG. Total testosterone, the free androgen index, and dehydroepiandrosterone increased with age in both groups, but after adjusting for age, no racial differences were found. Estradiol, estrone, and inhibin B levels, as well as systolic and diastolic blood pressures, were also comparable in both groups. We conclude that high levels of SHBG are more common among African American than in white boys and hypothesize that this difference and its effect on the ratio between bound and free steroid hormones may contribute to racial differences in disease risk in adult men.

Efficient eukaryotic expression system for authentic human sex hormone-binding globulin

Sex hormone-binding globulin (SHBG) is the main carrier for androgens and oestrogens in humans. It mediates the transport of steroid hormones in the circulation and testicular fluid, and regulates their bioavailability to steroid-responsive tissues. In addition, the protein interacts with membrane receptors expressed in target tissues. Binding to the receptors is suspected to facilitate the uptake of steroid hormones and/or elicit cellular signal transduction. The identity of the SHBG receptor has not yet been resolved, in part due to a lack of sufficient quantities of authentic SHBG for receptor purification and molecular characterization. We have successfully addressed this problem by establishing an episomal expression system in human embryonic kidney cells that produces 5 mg of fully active human SHBG per litre. The recombinant protein resembles native SHBG in terms of structure, glycosylation pattern and steroid-binding activity. Moreover, the protein interacts with plasma membranes in steroid target tissues, an activity not observed with SHBG from other recombinant expression systems. Thus our studies have removed an important obstacle to the further elucidation of the role SHBG plays in steroid hormone action.