Human alpha 2-HS-glycoprotein: the A and B chains with a connecting sequence are encoded by a single mRNA transcript

Urinary Fetuin-A Fragments Predict Progressive Estimated Glomerular Filtration Rate Decline in Two Independent Type 2 Diabetes Cohorts of Different Ethnicities

INTRODUCTION

There is a great clinical need for novel markers to predict kidney function decline in patients with type 2 diabetes. We explored the potential of posttranslationally modified fetuin-A fragments in urine (uPTM-FetA) as such a marker.

METHODS

We included patients with type 2 diabetes from two independent, nonoverlapping prospective cohort studies. A cut-off for uPTM-FetA, measured via ELISA method, was determined using the Youden index in the primary cohort of patients with type 2 diabetes from Taiwan. Kidney endpoint was defined as an estimated glomerular filtration rate (eGFR) decline ≥30% from baseline, reaching of an eGFR <15 mL/min/1.73 m2, or a need of renal replacement therapy. Prospective associations were assessed in Cox regression models. All analyses were replicated in a cohort of patients with type 2 diabetes from the Netherlands.

RESULTS

In total, 294 patients with type 2 diabetes (age 61 ± 10 years, 55% male, eGFR 88 ± 16 mL/min/1.73 m2) were included in the primary cohort. During a follow-up of median 4.6 years, 42 participants (14%) experienced the kidney endpoint. Using the defined cut-off, a high uPTM-FetA was associated with a higher risk of renal function decline (Plog-rank < 0.0001). This association was similar in subgroups depending on albuminuria. This association remained, independent of age, sex, baseline eGFR, albuminuria, HbA1c, and other potential confounders (HR: 9.94; 95% CI: 2.96-33.40; p < 0.001 in the final model). Analyses in the validation cohort (376 patients with type 2 diabetes, age 64 ± 11 years, 66% male, eGFR 76 ± 24 mL/min/1.73 m2) using the same cut-off yielded similar results.

CONCLUSION

uPTM-FetA was independently associated with kidney function decline in patients with type 2 diabetes validated in a 2-cohort study. The significant additive predictive power of this biomarker from conventional risk factors suggests its clinical use for renal function progression in patients with type 2 diabetes.

Transcriptome analysis revealed the existence of family-specific regulation of growth traits in grass carp

The grass carp (Ctenopharyngodon idella) is the world's most prolific freshwater fish. Little is known, however, about the functional genes and genetic regulatory networks that govern its growth traits. We created three grass carp families in this study by using two grass carp parents with fast-growing offspring and two grass carp parents with slow-growing offspring, namely the fast-growing × fast-growing family (FF), the slow-growing × slow-growing family (SS), and the fast-growing × slow-growing family (FS). Under the satiation and starvation feeding modes, the average body weight of these families' offspring exhibited a consistent ordering (FF > FS > SS). The transcriptomes of grass carp whole brain and hepatopancreas were then acquired for each family, and it was discovered that the number of differentially expressed genes (DEGs) in the different organs demonstrated family specificity. DEGs were mostly identified in the hepatopancreas of FF and the whole brain of SS, but they were more evenly distributed in FS. There were 14 DEGs that were found in all three families, including three that were negatively correlated in hepatopancreas (ahsg2, lect2) or in brain (drd5), and 11 that were positively connected in hepatopancreas (sycn, pabpc4, zgc:112294, cel, endou, ela2, prss3, zbtb41, ela3) or in brain (fabp7, endod1). The deletion of ahsg2 boosted the growth rate only in certain zebrafish, suggesting that the growth-promoting effects of ahsg2 varies among individuals. Furthermore, we examined the SNP in each family and conducted preliminary research on the probable genetic pathways of family-specific control of growth traits. The family specificity of the growth regulation mechanism of grass carp at the transcriptional level was revealed for the first time in this study, and it was discovered that growth differences among individuals in the FF family were primarily due to differences in nutrient metabolism, whereas growth differences among individuals in the SS family may be primarily due to differences in foraging ability caused by differences in brain development. This research adds to our understanding of the genetic regulatory mechanism of grass carp growth.

The structure, biosynthesis, and biological roles of fetuin-A: A review

Fetuin-A is a heterodimeric plasma glycoprotein containing an A-chain of 282 amino acids and a B-chain of 27 amino acid residues linked by a single inter-disulfide bond. It is predominantly expressed in embryonic cells and adult hepatocytes, and to a lesser extent in adipocytes and monocytes. Fetuin-A binds with a plethora of receptors and exhibits multifaceted physiological and pathological functions. It is involved in the regulation of calcium metabolism, osteogenesis, and the insulin signaling pathway. It also acts as an ectopic calcification inhibitor, protease inhibitor, inflammatory mediator, anti-inflammatory partner, atherogenic factor, and adipogenic factor, among other several moonlighting functions. Fetuin-A has also been demonstrated to play a crucial role in the pathogenesis of several disorders. This review mainly focuses on the structure, synthesis, and biological roles of fetuin-A. Information was gathered manually from various journals via electronic searches using PubMed, Google Scholar, HINARI, and Cochrane Library from inception to 2022. Studies written in English and cohort, case-control, cross-sectional, or experimental studies were considered in the review, otherwise excluded.

Proteomic Analysis of Aqueous Humor Proteins in Association with Cataract Risks: Diabetes and Smoking

Cataracts are one of the most common eye diseases that can cause blindness. Discovering susceptibility factors in the proteome that contribute to cataract development would be helpful in gaining new insights in the molecular mechanisms of the cataract process. We used label-free nanoflow ultra-high-performance liquid chromatography–tandem mass spectrometry to compare aqueous humor protein expressions in cataract patients with different cataract risk factors such as diabetes mellitus (DM) and smoking and in controls (with cataract) without risk exposure. Eight patients with diabetes and who smoked (with double risk factors), five patients with diabetes and five patients who smoked (both with a single risk factor), and nine aged-matched cataract controls patients (non-risk exposure) were enrolled. In total, 136 aqueous humor proteins were identified, of which only alpha-2-Heremans–Schmid (HS)-glycoprotein was considered to be significantly risk-associated because it was differentially expressed in these three groups and exhibited increased expression with increasing risk factors. Significant changes in the aqueous humor level of alpha-2-HS-glycoprotein between DM and control samples and between smoking and control samples were confirmed using ELISA. The alpha-2-HS-glycoprotein, called fetuin-a, could be a potential aqueous biomarker associated with DM and smoking, which were cataract risk factors.

Urinary fetuin-A peptides as a new marker for impaired kidney function in patients with type 2 diabetes

Background

The hepatokine fetuin-A, released by the human liver, promotes pro-inflammatory effects of perivascular fat. The involvement of inflammation in type 2 diabetes mellitus (T2DM) can affect the kidney and contribute to the development of diabetic kidney disease. Therefore we examined the association of urinary fetuin-A protein fragments with renal damage in T2DM patients.

Methods

Urinary peptides of 1491 individuals using proteome data available from the human urine proteome database were analysed. Prediction of proteases involved in urinary peptide generation was performed using the Proteasix tool.

Results

We identified 14 different urinary protein fragments that belong to the region of the connecting peptide (amino acid 301–339) of the total fetuin-A protein. Calpains (CAPN1 and CAPN2), matrix metalloproteinase and pepsin A-3 were identified as potential proteases that were partially confirmed by previous in vitro studies. Combined fetuin-A peptides (mean of amplitudes) were significantly increased in T2DM patients with kidney disease and to a lesser extent with cardiovascular risk. Furthermore, fetuin-A peptide levels displayed a significant negative correlation with baseline estimated glomerular filtration rate (eGFR) values (r = −0.316, P < 0.0001) and with the slope (%) of eGFR per year (r = −0.096, P = 0.023). A multiple regression model including fetuin-A peptide and albuminuria resulted in a significantly improved correlation with eGFR (r = −0.354, P < 0.0001) compared with albuminuria, indicating an added value of this novel biomarker.

Conclusions

The urinary proteome analysis demonstrated the association of fetuin-A peptides with impaired kidney function in T2DM patients. Furthermore, fetuin-A peptides displayed early signs of kidney damage before albuminuria appeared and therefore can be used as markers for kidney disease detection.

Pathophysiological Implication of Fetuin-A Glycoprotein in the Development of Metabolic Disorders: A Concise Review

Alpha 2-Heremans-Schmid glycoprotein, also known as fetuin-A (Fet-A), is a multifunctional plasma glycoprotein that has been identified in both animal and human beings. The protein is a hepatokine predominantly synthesized in the liver, which is considered as an important component of diverse normal and pathological processes, including bone metabolism regulation, vascular calcification, insulin resistance, and protease activity control. Epidemiological studies have already consistently demonstrated significant elevated circulating Fet-A in the course of obesity and related complications, such as type 2 diabetes mellitus, metabolic syndrome, and nonalcoholic fatty liver disorder (NAFLD). Moreover, Fet-A has been strongly correlated with many parameters related to metabolic homeostasis dysregulation, such as insulin sensitivity, glucose tolerance, circulating lipid levels (non-esterified free fatty acids and triglycerides), and circulating levels of both pro- and anti-inflammatory factors (C-reactive protein, tumor necrosis factor-α (TNF-α), and interleukin (IL)-6). Metabolic-interfering effects of Fet-A have thus been shown to highly exacerbate insulin resistance (IR) through blocking insulin-stimulated glucose transporter 4 (GLUT-4) translocation and protein kinase B (Akt) activation. Furthermore, the protein appeared to interfere with downstream phosphorylation events in insulin receptor and insulin receptor substrate signaling. The emerging importance of Fet-A for both diagnosis and therapeutics has therefore come to the attention of researchers and the pharmaceutical industry, in the prospect of developing new therapeutic strategies and diagnosis methods for metabolic disorders.

Clinical implications of fetuin-A

Fetuin-A, also termed alpha2-Heremans-Schmid glycoprotein, is a 46kDa hepatocyte derived protein (hepatokine) and serves multifaceted functions.

Hyaluronic Acid Coated Chitosan Nanoparticles Reduced the Immunogenicity of the Formed Protein Corona

Studying the interactions of nanoparticles (NPs) with serum proteins is necessary for the rational development of nanocarriers. Optimum surface chemistry is a key consideration to modulate the formation of the serum protein corona (PC) and the resultant immune response. We investigated the constituent of the PC formed by hyaluronic acid-coated chitosan NPs (HA-CS NPs). Non-decorated chitosan NPs (CS NPs) and alginate-coated chitosan NPs (Alg-CS NPs) were utilized as controls. Results show that HA surface modifications significantly reduced protein adsorption relative to controls. Gene Ontology analysis demonstrates that HA-CS NPs were the least immunogenic nanocarriers. Indeed, less inflammatory proteins were adsorbed onto HA-CS NPs as opposed to CS and Alg-CS NPs. Interestingly, HA-CS NPs differentially adsorbed two unique anti-inflammatory proteins (ITIH4 and AGP), which were absent from the PC of both controls. On the other hand, CS and Alg-CS NPs selectively adsorbed a proinflammatory protein (Clusterin) that was not found on the surfaces of HA-CS NPs. While further studies are needed to investigate abilities of the PCs of only ITIH4 and AGP to modulate the interaction of NPs with the host immune system, our results suggest that this proof-of-concept could potentially be utilized to reduce the immunogenicity of a wide range of nanomaterials.

Visceral and subcutaneous adipose tissue express and secrete functional alpha2hsglycoprotein (fetuin a) especially in obesity

The secretion of the hepatokine alpha-2-Heremans-Schmid glycoprotein/Fetuin A, implicated in pathological processes including systemic insulin resistance, by adipose tissue has been recently described. Thus, we have recently identified its presence in white adipose tissue secretomes by mass spectrometry. However, the secretion pattern and function of adipose-derived alpha-2-Heremans-Schmid glycoprotein are poorly understood. The aim of this study is to evaluate the expression and secretion of total and active phosphorylated alpha-2-Heremans-Schmid glycoprotein by adipose tissue from visceral and subcutaneous localizations in animals at different physiological and nutritional status including anorexia and obesity. Alpha-2-Heremans-Schmid glycoprotein expression and secretion in visceral adipose tissue and subcutaneous adipose tissue explants from animals under fasting and exercise training, at pathological situations such as anorexia and obesity, and from human obese individuals were assayed by immunoblotting, quantitative real-time polymerase chain reaction and enzyme-linked immunosorbent assay. We reveal that visceral adipose tissue expresses and secretes more alpha-2-Heremans-Schmid glycoprotein than subcutaneous adipose tissue, and that this secretion is diminished after fasting and exercise training. Visceral adipose tissue from anorectic animals showed reduced alpha-2-Heremans-Schmid glycoprotein secretion; on the contrary, alpha-2-Heremans-Schmid glycoprotein is over-secreted by visceral adipose tissue in the occurrence of obesity. While secretion of active-PhophoSer321α2HSG by visceral adipose tissue is independent of body mass index, we found that the fraction of active-alpha-2-Heremans-Schmid glycoprotein secreted by subcutaneous adipose tissue increments significantly in situations of obesity. Functional studies show that the inhibition of adipose-derived alpha-2-Heremans-Schmid glycoprotein increases insulin sensitivity in differentiated adipocytes. In conclusion, visceral adipose tissue secretes more alpha-2-Heremans-Schmid glycoprotein than subcutaneous adipose tissue and this secretion is more sensitive to nutritional and physiological changes. The over-secretion of alpha-2-Heremans-Schmid glycoprotein by visceral adipose tissue, the increased secretion of the active phosphorylated form by subcutaneous adipose tissuein obese animals, and the adipose-derived alpha-2-Heremans-Schmid glycoprotein capacity to inhibit the insulin pathway suggest the participation of adipose-derived alpha-2-Heremans-Schmid glycoprotein in the deleterious effects of obesity.

Adipokines in psoriasis: An important link between skin inflammation and metabolic alterations

Psoriasis is a chronic inflammatory skin disease most common in Europe, North America, and Australia. The etiology and pathomechanisms underlying the evolution and persistence of the skin alterations are increasingly being understood and have led to the development of effective anti-psoriatic therapies. Apart from the skin manifestations, psoriasis is associated with the metabolic syndrome (MetS), known to increase the risk of type 2 diabetes mellitus and cardiovascular disorders. Research of the last years demonstrated a dysregulated adipokine balance as an important link between inflammation, MetS, and consequential disorders. This article describes selected adipokines and their potential role in both metabolic comorbidity and skin inflammation in psoriasis.

Allelic Imbalance of mRNA Associated with α2-HS Glycoprotein (Fetuin-A) Polymorphism

Alpha 2-HS glycoprotein (AHSG), also designated as fetuin-A, exhibits polymorphism in population genetics consisting of two major alleles of AHSG^∗1 and AHSG^∗2. The serum level in the AHSG^∗1 homozygote is significantly higher than that of the AHSG^∗2 homozygote. This study examined the molecular mechanism for the cis-regulatory expression. To quantitate allele-specific mRNA in intra-assays of the heterozygote, RT-PCR method employing primers that were incorporated to the two closely located SNPs was developed. The respective magnitudes of AHSG^∗1 to AHSG^∗2 in the liver tissues and hepatic culture cells of PLC/PRF/5 were determined quantitatively as 2.5-fold and 6.2-fold. The mRNA expressional difference of two major alleles was observed, which is consistent with that in the serum level. The culture cells carried heterozygous genotypes in rs4917 and rs4918, but homozygous one in rs2248690. It was unlikely that the imbalance was derived from the SNP located in the promotor site. Furthermore, to investigate the effect of mRNA degradation, RNA synthesis in the cell culture was inhibited potently by the addition of actinomycin-D. No marked change was apparent between the two alleles. The results indicated that the cis-regulatory expressional difference is expected to occur at the level of transcription or splicing of mRNA.

Fetuin-A 742 (C/T) and 766 (C/G) polymorphic sites are associated with increased risk of myocardial infarction in older patients (≥ 40 years of age)

Inflammation and genetics have key roles in the pathogenesis of atherosclerosis, and the etiology of myocardial infarction (MI). Recent studies have indicated that lower serum levels of fetuin-A may accelerate the vascular mineralization process, which leads to pathophysiological conditions, such as coronary heart disease and chronic renal failure. The aim of the present study was to evaluate the association between specific fetuin-A polymorphisms (742 and 766) that are associated with circulating serum levels, and MI cases. The study consisted of 292 participants; 146 healthy control subjects and 146 patients with MI. The patient group was divided into two subgroups: 56 MI ≤ 40 years and 90 MI ≥ 40 years. The genotype distribution of fetuin 742 (C/T) and fetuin 766 (C/G) were determined by restriction enzyme digestion of polymerase chain reaction products. A significant difference was determined between the patients with MI and the control subjects with regards to fetuin-A 742 C/T gene polymorphism (P=0.028), regardless of age. Genotype distributions of fetuin-A 742 (C/G, P=0.004) and 766 (C/T, P=0.017) were statistically different in the older patients with MI (MI ≥ 40 years old), as compared with the healthy controls; however, there were no significant differences between the younger patients with MI and the controls, with regards to fetuin-A 742 C/T (P=0.519) and 766 C/G (P=0.653) gene polymorphisms. In addition, an association was observed between the presence of fetuin-A 742 T and 766 G alleles, and MI cases. The present study demonstrates that fetuin-A 742 (C/T) and 766 (C/G) genotypes may be risk factors for MI in patients older than 40 years of age.

Cell surface serine protease matriptase-2 suppresses fetuin-A/AHSG-mediated induction of hepcidin

Matriptase-2 is a type II transmembrane serine protease controlling the expression of hepcidin, the key regulator of iron homeostasis. By cleaving hemojuvelin, matriptase-2 suppresses bone morphogenetic protein/sons of mothers against decapentaplegic signaling. So far, the only known putative substrates of matriptase-2 are hemojuvelin and matriptase-2 itself. In this study, fetuin-A (α2-Heremans-Schmid glycoprotein) was identified in vitro as a substrate of matriptase-2. The protease–substrate interaction was validated by isolating matriptase-2 via the affinity to fetuin-A. Fetuin-A is a liver-derived plasma protein with multiple functions, which is proteolytically processed to yield a disulfide-linked two-chain form. In co-transfected cells, a matriptase-2-dependent conversion of unprocessed fetuin-A into a two-chain form was detected. Conversely, downregulation of endogenously expressed matriptase-2 stabilized fetuin-A. Arg and Lys residues located within the 40 residue spanning connecting peptide of fetuin-A were identified as cleavage sites for matriptase-2. Analysis of hepcidin expression revealed an inductive effect of fetuin-A, which was abolished by matriptase-2. Fetuin-A deficiency in mice resulted in decreased hepcidin mRNA levels. These findings implicate a role of fetuin-A in iron homeostasis and provide new insights into the mechanism of how matriptase-2 might modulate hepcidin expression.

HSP70, Peroxiredoxin-3 and -6 are upregulated during renal warm ischaemia in a donation after circulatory death model

BACKGROUND

The use of donation after circulatory death (DCD) kidneys for transplantation is increasing. Subsequent delayed graft function is related to ischaemia/reperfusion injury (I/R), warm ischaemia (WI) being one of the main contributing factors. This proteomics study aimed to identify candidate biomarkers of WI.

METHODS

Termination biopsies were obtained over 180min in 6 pigs. Proteins were subjected to differential in-gel electrophoresis (DIGE) and identified using LC MS/MS.

RESULTS

Thirty nine protein spots showed significant changes in expression (ANOVA, p<0.05). Peroxiredoxin-3 and -6 (PRX3 and PRX6) were expressed with a fold change (FD) of +1.8 (p=0.03 and 0.02 respectively). A significant upregulation of Alpha-2-HS-glycoprotein (A2HSG, FD+1.9, p=0.047) and heat-shock protein 70-1b (HSP70-1b, FD+2.1 p=0.002) was recorded.

CONCLUSIONS

The expression of PRX3, PRX6 and HSP70-1b during the first 30min of WI may be critical in measuring cellular responses. This is the first large animal model to describe the novel candidate biomarker, structural protein A2HSG. A2HSG upregulation during WI alone in this study is encouraging and further assessment in a DCD auto-transplant model is warranted.

BIOLOGICAL SIGNIFICANCE

Warm ischaemia (WI) during donation after circulatory death (DCD) organ retrieval is associated with higher rates of post transplant organ dysfunction. The cellular and molecular mechanism of this paradigm is poorly reported. The work carried out in this large animal study has been performed to enable better understanding of protein expression during DCD WI at the time of retrieval. We have identified differential increased expression of PRX3, PRX6 and HSP70 during the first 30min of WI. Observation of this behaviour has not been reported before. Application of these results in a reperfusion model or autograft animal study would further help study of the named proteins as clinical biomarkers of WI. Alpha 2-HS Glycoprotein (A2HSG) species were also differentially expressed during the WI period. This remains a novel finding. Assessment of A2HSG is also recommended for further study in a reperfusion context. Previous reports of A2HSG have suggested an association in chronic kidney disease and diabetes, but no association with WI has previously been noted in either small or large animals.

Fetuin A concentration in the second trimester amniotic fluid of fetuses with trisomy 21 appears to be lower: phenotypic considerations

OBJECTIVE

We investigated whether the concentration of the glycoprotein fetuin A is altered in the second trimester amniotic fluid of trisomy 21 pregnancies compared with euploid pregnancies.

METHODS

25 pregnancies with an extra chromosome 21 were matched for maternal and gestational age with 25 pregnancies with normal karyotype. Levels of fetuin A in amniotic fluid were measured by a commercially available enzyme-linked immunosorbent assay (ELISA) kit.

RESULTS

The median concentration of fetuin A in amniotic fluid of trisomy 21 pregnancies (5.3 ng/ml) was statistically significantly lower (P value = 0.008) compared with that in euploid pregnancies (6.8 ng/mL).

CONCLUSION

Lower levels of fetuin A in trisomy 21 may indicate an association with altered metabolic pathways in this early stage that could potentially be associated with features of the syndrome, such as growth restriction or impaired osteogenesis.

The "thrifty" gene encoding Ahsg/Fetuin-A meets the insulin receptor: Insights into the mechanism of insulin resistance

Ahsg (fetuin-A) is a 55-59kDa phosphorylated glycoprotein synthesized in the adult predominantly by hepatocytes, from which it enters the circulation. When dysregulated, this glycoprotein operates to influence the clinical sequelae of insulin resistance-type 2 diabetes and cardiovascular disease. The pathological sequelae likely arise from two separable molecular "faces" of Ahsg-one acting at the level of the insulin receptor and a second face influencing ectopic biomineralization in the intima. A detailed understanding of these two functional faces of Ahsg is not yet clear for lack of structural studies. Ahsg has a physiological role in the biomineralization of bone, which when dysregulated can lead to ectopic calcification of soft tissues in the vasculature. Ahsg has a second physiological function in regulating how insulin signals through its receptor, a transmembrane tyrosine kinase. Dysregulation of this "face" of Ahsg results in morbid sequelae such as impaired glucose disposal and fatty liver. Ahsg binds to tandem fibronectin type 3 (Fn3) domains present in the 194 amino acid residue extracellular portion of the β-subunit of the insulin receptor, distant from the high-affinity pocket formed by two complementing α-subunits where insulin binds. Only two proteins are known to bind directly to the insulin receptor ectodomain - insulin and Ahsg - the former turns on the receptor's intrinsic tyrosine kinase (TK) activity, and the latter shuts it down. Recent X-ray crystallographic studies of the ectodomain of the insulin receptor now sharpen our understanding of the receptor's extracellular α-subunit and linked β-subunit. Ahsg genotype and its circulating level have been correlated with body morphometrics (obese versus lean and visceral adiposity) in epidemiological studies enrolling thousands of patients. Epidemiological studies from the clinic reveal high levels of circulating Ahsg in insulin resistance and diabetes. This review endeavors to explain how one protein can mediate diverse pathologies, but specifically addresses its metabolic "face" blunting insulin receptor activity, an action leading to insulin resistance.

Non-collagen proteins in bone

The non-collagen proteins of bone are a complex set of molecules that arise from local or exogenous sources. Because bone mineral is an excellent adsorbent, many circulatory and/or cell surface proteins bind to bone, where they may have immediate or subsequent effects. These include the alpha 2-HS-glycoprotein from blood and the potent growth factors TGF-beta, PDGF, IGF-1, FGF-a and -b, and IL-1, derived from both bone and non-bone cells. Furthermore, bone cell membrane proteins such as alkaline phosphatase may be cleaved from the cell surface and entrapped in the bone matrix. Bone is enriched in a variety of enzymes and their inhibitors by similar adsorption processes. Even osteocalcin, a bone cell product, is adsorbed to bone via mineral-binding (Gla) groups. The bone sialoproteins (BSP-I or osteopontin and BSP-II) also bind to the mineral via acidic groups. Because of this phenomenon it is difficult to distinguish whether a given protein's presence in bone is advantageous or merely fortuitous. The bone matrix proper consists of type I collagen and other osteoblast products such as osteonectin (a phosphorylated glycoprotein) and small proteoglycans (PG-I and/or PG-II) which are incorporated into bone collagen fibrils. These proteins may have additional roles in tissue morphogenesis and/or differentiation.

Cell-specific pituitary gene expression profiles after treatment with leukemia inhibitory factor reveal novel modulators for proopiomelanocortin expression

Leukemia inhibitory factor (LIF) mediates the hypothalamo-pituitary-adrenal stress response. Transgenic mice overexpressing LIF in the developing pituitary have altered pituitary differentiation with expansion of corticotropes, maintenance of Rathke's cleft cysts, and suppression of all other pituitary cell types. Affymetrix GeneChips were used to identify modulators of LIF effects in corticotrope (AtT-20) and somatolactotrope (GH(3)) cells. In addition to genes known to respond to LIF in corticotrope cells [e.g. suppressor of cytokine signaling-3 (SOCS-3), signal transducer and activator of transcription-3, SH2 domain-containing tyrosine phosphatase-1, and proopiomelanocortin (POMC)], corticotrope-specific changes were also observed for genes involved in glycolysis and gluconeogenesis, transcription factors, signaling molecules, and expressed sequence tags. Two transcription factors identified, CCAAT/enhancer-binding protein beta (C/EBPbeta) and glial cell-derived neurotrophic factor (GDNF)-inducible factor (GIF), dose-dependently induced expression of the rat POMC promoter when overexpressed in AtT-20 cells. LIF further induced POMC transcription with C/EBPbeta, but not with GIF. C/EBPbeta also induced expression of the SOCS-3 promoter that was further enhanced by cotreatment with LIF. However, GIF did not affect SOCS-3 expression. These results indicate that C/EBPbeta and GIF are downstream effectors of LIF corticotrope action. LIF also stimulates the expression of inhibitors of its actions, such as SOCS-3 and SH2 domain-containing tyrosine phosphatase-1. alpha(2)-HS-glycoprotein (AHSG)/fetuin, a secreted protein that antagonizes bone TGFbeta/bone morphogenic protein signaling, was induced by LIF in a signal transducer and activator of transcription-3-dependent fashion. Pretreatment with AHSG/fetuin blocked LIF-induced expression of the POMC promoter independently of SOCS-3. Thus, using GeneChips, C/EBPbeta and GIF have been identified as novel mediators and AHSG/fetuin as an inhibitor of LIF action in corticotropes.

Stable isotope phospho-profiling of fibrinogen and fetuin subunits by element mass spectrometry coupled to capillary liquid chromatography

We have used one-dimensional polyacrylamide gel electrophoresis, tryptic digestion, and capillary liquid chromatography-mass spectrometry with inductively coupled plasma ionization and phosphorus-31 detection or electrospray ionization for the analysis of protein phosphorylation. We have analyzed human fibrinogen with two well-characterized phosphorylation sites and bovine fetuin with unknown phosphorylation status. Both serine-3 and serine-345 (both in Aalpha) of fibrinogen were clearly recognized. In bovine fetuin, four phosphorylated sites were newly characterized (serine-138, serine-320, serine-323, and serine-324). The novel strategy provides a fast and quantitative overview of the presence of protein phosphorylation sites.

Alpha2-HS glycoprotein: a protein in search of a function

In this issue (pp. 305-310) Jun Ren and Amy J. Davidoff author an article entitled 'Alpha2-HS glycoprotein, a putative inhibitor of tyrosine kinase, prevents glucose toxicity associated with cardiomyocyte dysfunction'. The protein responsible for this biological activity has recently come to the forefront of research on the biological activity of plasma proteins.

Phosphorylation of human plasma alpha2-Heremans-Schmid glycoprotein (human fetuin) in vivo

A fraction of alpha2-Heremans-Schmid (alpha2-HS) glycoprotein (human fetuin) isolated from plasma was phosphorylated at serine-120 and serine-312 as shown by MS and peptide fragment sequencing after tryptic digestion. Serine-312-containing peptides were phosphorylated to 77% as determined from relative peak heights in the mass spectrum, which together with the phosphorylation of serine-120 implies a molar degree of phosphorylation of at least 1. Approximately 20% of the circulating fetuin plasma pool was phosphorylated to approx. 1 mol of phosphate/mol of protein. The remainder did not contain phosphate, resulting in an average phosphorylation degree for the protein in plasma of approx. 0.2 mol/mol. The isolated alpha2-HS glycoprotein was a heterodimer in which the entire C-terminal part of the connecting peptide including threonine-321 was present, but traces of C-terminally trimmed connecting peptide fragments were also found. The short B-chain was O-glycosylated to approx. 40%, whereas the N-glycosylation of asparagine-138 and asparagine-158 seemed to be 100%. This finding, for the first time, that circulating human plasma fetuin is partly phosphorylated, implies that the effects of phosphorylated alpha2-HS glycoprotein on insulin signal transduction seen in different cell systems could be relevant to its physiological function in vivo.

Molecular evolution in the hypervariable regions of fetuin: comparison between human and African green monkey fetuin

Sequences of fetuin cDNA and its deduced amino acid residues from the African green monkey cell line Vero were found to differ by 7.3% and 12.9%, respectively, from the corresponding human sequences. Most amino acid substitutions were clustered within a small segment of the third domain (D3). Calculations of nonsynonymous and synonymous nucleotide substitution rates suggest that this small segment was mutated under positive selection. cDNAs encoding alpha1-antitrypsin, beta-actin and the sequences of intron 4 of alpha1-antitrypsin gene in human liver and Vero cells were also investigated. The results substantiated the positive selection imposed on the D3 segment.

Positive and negative elements modulate the promoter of the human liver-specific alpha2-HS-glycoprotein gene

The human alpha2-HS-glycoprotein (AHSG) and the 63-kDa rat phosphoprotein (pp63) are homologous plasma proteins that belong to the fetuin family. AHSG and pp63 are involved in important functions such as inhibition of insulin receptor tyrosine kinase activity, inhibition of protease activities, and regulation of calcium metabolism and osteogenesis. Studies of the AHSG proximal promoter performed in vitro in rat and human cells indicate that several NF-1 and C/EBP binding sites exert a positive effect on its transcriptional activity. However, until now, no distal elements have been examined in this gene, in either species. We report that the human AHSG gene promoter acts in a liver-specific manner and is further controlled by three distal, 5'-flanking elements. The negative elements III and I are, respectively, located 5' and 3' of the positive element II. All three elements require the natural context of the human AHSG gene to fully exert their negative or positive effect. Element I harbours a single binding site for NF-1. This nuclear factor thus appears to be able to up- or downregulate the AHSG gene depending on the site it binds to. Elements I, II and possibly III are absent in the rodent Ahsg gene encoding pp63.

cDNA sequencing of guinea pig alpha 2-HS glycoprotein, its expression in various tissues and acute phase expression

cDNA encoding alpha 2-HS glycoprotein was amplified from guinea pig liver mRNA by reverse-transcription polymerase chain reaction (RT-PCR) and rapid amplification of cDNA ends, cloned and sequenced. By RT-PCR and nested PCR, alpha 2-HS glycoprotein mRNA was detected not only in liver tissue but also in pancreas, stomach, small intestine, colon, spleen, kidney, testis, skeletal muscle, brain, heart and leukocytes, but not in the lung. The alpha 2-HS glycoprotein mRNA levels in the liver were reduced to half at 48 h after subcutaneous injection of turpentine oil.

Structural and functional analysis of the 5'-transcription control region for the human alpha2-HS glycoprotein gene

The human alpha2-HS glycoprotein (A2HS) and rat phosphoprotein of Mr 63000 (pp63) are homologous plasma proteins and members of the fetuin superfamily. A2HS is involved in important functions such as inhibition of the tyrosine kinase activity of the insulin receptor, regulation of calcium metabolism and osteogenesis as well as protease inhibitory activity. We report an analysis of the 5' transcription control region (4 kb) of the A2HS gene. Its most proximal 300 nt display a very potent transcriptional activity. The latter is likely accounted for by C/EBP and NF1 binding sites that are conserved from the human A2HS gene to the rat pp63 gene. In contrast, these human and rat genes appear to largely diverge beyond their proximal promoter.

Structure of the gene encoding human alpha 2-HS glycoprotein (AHSG)

Alpha 2-HS glycoprotein (AHSG) is a human plasma glycoprotein and fetuin is the homologue in the calf. In this report, we present the structure and organization of the AHSG gene. Introns and the 5' and 3'-flanking regions were obtained by polymerase chain reaction (PCR) and the inverted PCR, respectively, from genomic DNA using AHSG cDNA-specific oligonucleotide primers. The sequence of the PCR products shows that the coding region spans approximately 8.2 kb and is composed of seven exons interrupted by six introns. The exon-intron splice junctions agree with the consensus sequence, and the positions interrupted by introns are precisely identical to those of the rat insulin receptor tyrosine kinase inhibitor (fetuin) gene. The 5'-promoter region contains several characteristic sequences such as an A + T-rich sequence of TAAATAA, C/EBP-binding site, and hepatocyte nuclear factor-5 (HNF-5) and serum response factor (SRF) sites.

Friends and relations of the cystatin superfamily--new members and their evolution

The cystatin "superfamily" encompasses proteins that contain multiple cystatin-like sequences. Some of the members are active cysteine protease inhibitors, while others have lost or perhaps never acquired this inhibitory activity. In recent years, several new members of the superfamily have characterized, including proteins from insects and plants. Based on partial amino acid homology, new members, such as the invariant chain (Ii), and the transforming growth factor-beta receptor type II (TGF-beta receptor II) may, in fact, represent members of an emerging family within the superfamily that may have used some common building blocks to form functionally diverse proteins. Cystatin super-family members have been found throughout evolution and members of each family of the superfamily are present in mammals today. In this review, the new and older, established members of the family are arranged into a possible evolutionary order, based on sequence homology and functional similarities.

Limited proteolysis of human alpha2-HS glycoprotein/fetuin. Evidence that a chymotryptic activity can release the connecting peptide

alpha2-HS glycoprotein is a major protein of human plasma whose function is still obscure. A proteolytically processed form of alpha2-HS glycoprotein lacking a segment of 40 amino acid residues bridging its heavy and light chain portions ("connecting peptide") has been described suggesting that this peptide is released by post-translational processing to fulfill biological role(s) of alpha2-HS glycoprotein. To test this hypothesis we investigated how the connecting peptide is released from the parental molecule by limited proteolysis. We developed monoclonal antibodies to various portions of the connecting peptide and its NH2-terminal flanking region which cross-react with the native alpha2-HS glycoprotein. Purified alpha2-HS glycoprotein from human plasma was subjected to limited proteolysis by proteinases including trypsin, chymotrypsin, elastase plasmin, kallikrein, thrombin, and renin. Immunoprint analysis of the proteolytic digests indicated that alpha2-HS glycoprotein is readily cleaved in its connecting peptide region. NH2-terminal amino sequence analysis of the generated fragments demonstrated that a single proteinase, chymotrypsin, cleaves the critical Leu-Leu bond flanking the NH2-terminal portion of the connecting peptide region. Most but not all of the other proteinase cleavage sites map to a short stretch of 9 residues located in the center portion of the connecting peptide region. Immunoprint analysis of plasma samples from patients with sepsis demonstrate that the connecting peptide region is cleaved under pathological conditions. Our results indicate that the connecting peptide and/or fragments thereof are readily releasable from alpha2-HS glycoprotein in vitro and in vivo.

The serum protein alpha2-HS glycoprotein/fetuin inhibits apatite formation in vitro and in mineralizing calvaria cells. A possible role in mineralization and calcium homeostasis

We present data suggesting a function of alpha2-HS glycoproteins/fetuins in serum and in mineralization, namely interference with calcium salt precipitation. Fetuins occur in high serum concentration during fetal life. They accumulate in bones and teeth as a major fraction of noncollagenous bone proteins. The expression pattern in fetal mice confirms that fetuin is predominantly made in the liver and is accumulated in the mineralized matrix of bones. We arrived at a hypothesis on the molecular basis of fetuin function in bones using primary rat calvaria osteoblast cultures and salt precipitation assays. Our results indicate that fetuins inhibit apatite formation both in cell culture and in the test tube. This inhibitory effect is mediated by acidic amino acids clustering in cystatin-like domain D1. Fetuins account for roughly half of the capacity of serum to inhibit salt precipitation. We propose that fetuins inhibit phase separation in serum and modulate apatite formation during mineralization.

Fetuin/alpha2-HS glycoprotein is a transforming growth factor-beta type II receptor mimic and cytokine antagonist

The serum glycoprotein fetuin is expressed during embryogenesis in multiple tissues including limb buds and has been shown to promote bone remodeling and stimulate cell proliferation in vitro. In this report, we demonstrate that fetuin antagonizes the antiproliferative action of transforming growth factor-beta1 (TGF-beta1) in cell cultures. Surface plasmon resonance measurements show that fetuin binds directly to TGF-beta1 and TGF-beta2 and with greater affinity to the TGF-beta-related bone morphogenetic proteins (BMP-2, BMP-4, and BMP-6). In a competitive enzyme-linked immunosorbent assay, fetuin blocked binding of TGF-beta1 to the extracellular domain of TGF-beta receptor type II (TbetaRII), one of the primary TGF-beta-binding receptors. A comparison of fetuin and TbetaRII shows homology in an 18-19-amino acid sequence, which we have designated TGF-beta receptor II homology 1 domain (TRH1). Since the TRH1 sequence is known to form a disulfide loop in fetuin, cyclized TRH1 peptides from both fetuin and TbetaRII were chemically synthesized and tested for cytokine binding activity. Cyclized TRH1 peptide from TbetaRII bound to TGF-beta1 with greater affinity than to BMP-2, while the cyclized TRH1 peptide from fetuin bound preferentially to BMP-2. Finally, fetuin or neutralizing anti-TGF-beta antibodies blocked osteogenesis and deposition of calcium-containing matrix in cultures of dexamethasone-treated rat bone marrow cells. In summary, these experiments define the TRH1 peptide loop as a cytokine-binding domain in both TbetaRII and fetuin and suggest that fetuin is a natural antagonist of TGF-beta and BMP activities.

Electrophoretic and isoelectric focusing analysis of human recombinant alpha 2-HS glycoprotein produced in insect cells: analysis of the post-translational events

Alpha 2-HS glycoprotein (AHSG) is a human serum glycoprotein synthesized by liver cells. It is a natural inhibitor of the insulin receptor tyrosine kinase activity. We produced this protein in insect cells by using a recombinant baculovirus expressing the whole coding sequence of the protein. By analyzing AHSG on isoelectric focusing and on sodium dodecyl sulfate (SDS) gels, followed by immunoblot, AHSG produced in insect cells was found to be phosphorylated and to possess the connecting peptide between the A and the B chains. The same features were found in the protein produced by Hep3B, a human liver cell line that synthesizes AHSG. By contrast, no phosphorylation could be detected in AHSG present in normal human plasma, and the connecting peptide was clipped. As the protein produced in insect cells is active on insulin receptors, in contrast to the plasma protein, our results suggest that the biological activity of the protein may be associated with its single chain form together with its phosphorylation.

Isolation, characterization, and primary structure of a calcium-binding 63-kDa bone protein

A novel noncollagenous protein of the mineralized matrix of bovine bone was isolated by ion exchange and gel permeation chromatography. The apparent M(r) of the protein is 63,000 as determined by SDS-polyacrylamide gel electrophoresis. The protein is a rather minor constituent in bone and could not be detected in other connective tissues by enzyme-linked immunosorbent assay of guanidine HCl extracts. The 63-kDa protein was detected in the osteoid and around the osteocytes upon immuno-histochemical staining of bovine compact bone. The sequence of the 63-kDa protein was deduced from cDNA clones isolated from a rat calvaria lambda gt11 expression library. The protein contains two centrally located EF-hand Ca(2+)-binding domains. Seven heptad repeats are present indicating the ability of the protein for coiled-coil interactions. Ability to bind calcium was confirmed by 45Ca2+ binding to protein blotted onto nitrocellulose membrane. The protein was synthesized in calvaria explants as detected by immunoprecipitation of radiolabeled protein from the culture medium. Although the protein can be detected in biochemical amounts in bone only, varying amounts of mRNA for this protein were detected in several rat tissues by RNase protection assay with highest levels in rat calvaria. This extracellular protein corresponds to a mouse protein called nucleobindin.

Isolation and molecular cloning of a novel bone phosphoprotein related in sequence to the cystatin family of thiol protease inhibitors

We describe here the isolation of a novel non-collagenous protein from the acid demineralization extract of bovine cortical bone. This 24-kDa protein is multiply phosphorylated at serine residues in Ser-X-Glu/Ser(P) sequences, a recognition motif for phosphorylation by the secretory pathway protein kinase, and we have termed this protein secreted phosphoprotein 24 (spp24). The cDNA structure of spp24 was determined by sequencing cDNA fragments obtained by reverse transcription-polymerase chain reaction, 3'-rapid amplification of cDNA ends, and screening a lambda gt11 cDNA library. This cDNA sequence predicts a 200-residue initial translation product which consists of a 20-residue signal sequence and the 180-residue mature spp24. Northern blot analysis using the spp24 cDNA showed that spp24 mRNA is in liver and bone but not in heart, lung, kidney, or spleen. A search of existing protein sequences revealed that the N-terminal 107 residues of mature spp24 are related in sequence to the cystatin family of thiol protease inhibitors, which suggests that spp24 could function to modulate the thiol protease activities that are known to be involved in bone turnover. Several of the proteins in the cystatin family that are most closely related to spp24 are not only thiol protease inhibitors but are also precursors to peptides with potent biological activity, peptides such as bradykinin and the neutrophil antibiotic peptides. It is therefore possible that the intact form of spp24 found in bone could also be a precursor to a biologically active peptide, a peptide which could coordinate an aspect of bone turnover.

Calcium-binding properties of fetuin in fetal bovine serum

Fetuin, an abundant protein in fetal bovine plasma, is the bovine homolog of human alpha 2HS glycoprotein (alpha 2HS). In spite of numerous studies, the biological functions of both proteins remain elusive. We now report the remarkable 45Ca-binding activity of fetuin in fetal bovine serum that has been blotted on a membrane after electrophoresis. The Ca-binding ability of the purified protein was analyzed by equilibrium dialysis, which revealed that bovine fetuin had multiple Ca-binding sites, one of which had a Kd of 0.95 x 10(-4) M. It was also shown that the Ca-binding activity of fetuin was greater than that of albumin in serum of the bovine fetus at the late gestational stage. Since fetal bovine serum contains not only a high concentration of fetuin but also a high concentration of Ca, it is possible that fetuin functions to maintain high levels of Ca in fetal serum via normalization of the concentration of Ca2+ ions.

Posttranslational processing of human alpha 2-HS glycoprotein (human fetuin). Evidence for the production of a phosphorylated single-chain form by hepatoma cells

alpha 2-HS glycoprotein (alpha 2-HS) is a major protein occurring in human blood and calciferous tissues. Due to extensive sequence identity, alpha 2-HS has been grouped with the fetuins, a family of proteins that occur in fetal plasma in high concentrations. Native alpha 2-HS undergoes a series of posttranslational modifications including proteolytic processing, multiple N-glycosylations and O-glycosylations, and sulfation of the carbohydrate side chains. Various two-chain forms of alpha 2-HS have been prepared from human plasma, however, the single-chain precursor has not yet been isolated. Here, we have studied the biosynthesis of alpha 2-HS by a human hepatoma cell line, HepG2. We demonstrate that a single-chain form and the two-chain form of alpha 2-HS are secreted by this cell line. The alpha 2-HS forms are further modified by phosphorylation on multiple serine residues. Mapping studies indicate that the connecting peptide region releasable from the heavy chain of alpha 2-HS contains at least one such phosphorylation site. Our results identify proteolytic trimming and/or phosphorylation as modifications possibly regulating the biological effects of alpha 2-HS and the homologous fetuins.

Human inter-alpha-inhibitor family in inflammation: simultaneous synthesis of positive and negative acute-phase proteins

The inter-alpha-inhibitor (I alpha I) family encompasses four plasma proteins, namely free bikunin as well as I alpha I, pre-alpha-inhibitor (P alpha I) and inter-alpha-like inhibitor (I alpha LI). Each of the last three proteins is a distinct assembly of one bikunin chain with one or more unique heavy (H) chains designated H1, H2 and H3. The three H chains and the bikunin chain are encoded by four distinct mRNAs. These molecules and chains, as well as the corresponding mRNAs, were quantified in sera and liver biopsies from a series of patients with or without mild or severe acute infection. The decrease or increase observed for a given molecule or chain in the serum was in agreement with a similar change in the corresponding liver mRNA. In acute inflammation the H2 and bikunin chains are down-regulated and the relevant molecules (I alpha I, I alpha LI) behave as negative acute-phase proteins, whereas the H3 chain is up-regulated and the corresponding P alpha I molecule is a positive acute-phase protein. Also, P alpha I displays a higher-than-usual M(r); this is probably due to ligand binding. The H1 gene does not seem to be affected by the inflammatory condition. The quantitative changes in RNA levels seen in vivo were confirmed in vitro in the human hepatoma Hep3B cell line prior to or after induction with the acute-phase mediators interleukin-1 and/or -6. These results provide the first example in humans of positive and negative acute-phase proteins that are encoded by evolutionary related genes.

Haemonectin, a granulocytic-cell-binding protein, is related to the plasma glycoprotein fetuin

Haemonectin, a protein present in rabbit bone marrow extracellular matrix extracts, has been reported to bind granulocytes in a developmentally regulated manner. We have purified haemonectin from such extracts and determined the partial amino-acid sequence. The sequence obtained shows 60-70% similarity with the sequence of the plasma glycoprotein fetuin from other mammal species. This difference is consistent with the difference between fetuins from different species. We conclude that the rabbit haemonectin molecule is related to fetuin. The similarity between haemonectin and fetuin is reinforced by analysis with Western blots of one- and two-dimensional gels. These show that haemonectin, like fetuin, is present in serum and that migration of haemonectin from serum and extracellular matrix extracts, on two-dimensional gels, co-incides with that of human fetuin (alpha 2HS-glycoprotein) from serum, extracellular matrix extracts and in purified form. Also, antihaemonectin antibodies cross react with human fetuin. These data imply that the rabbit haemonectin molecule is closely related to fetuin, but do not rule out the possibility that these molecules are functionally distinct.

Molecular cloning and sequence analysis of cDNA for a 59 kD bone sialoprotein of the rat: demonstration that it is a counterpart of human alpha 2-HS glycoprotein and bovine fetuin

A complementary DNA (cDNA) for the 59 kD bone sialoprotein, which is supposed to be the rat counterpart of human alpha 2-HS glycoprotein (alpha 2-HSG) and is synthesized by both hepatocytes and osteoblasts, has been cloned from a rat liver cDNA library. Polyclonal rabbit antibodies to rat 59 kD bone sialoprotein were used to identify and isolate the cDNA. The amino acid sequence of 59 kD bone sialoprotein deduced from the cDNA revealed that the entire protein consisted of 352 amino acid residues, including a signal peptide of 18 amino acid residues, and contained three possible N-glycosylation sites. On Northern blot analysis of rat liver, an mRNA of about 1.5 kilobases was detected. An mRNA of 59 kD bone sialoprotein was also detectable in rat bone but not in other tissues, such as kidney, brain, and lung. A computer search of protein and nucleic acid data bases revealed that 68.2, 63.2, and 97.4% amino acid residues of 59 kD bone sialoprotein were identical with those of human alpha 2-HSG, bovine fetuin, and rat phosphorylated N-glycoprotein (pp63), respectively. The positions of cysteine residues in 59 kD bone sialoprotein also completely matched those in human alpha 2-HSG and bovine fetuin, indicating that the sialoprotein is the rat counterpart of human alpha 2-HSG and bovine fetuin. In addition, comparison of the nucleotide sequence of cDNA for rat fetuin/alpha 2-HSG with that for pp63 recently corrected showed only two differences in nucleotides in the entire protein coding regions of the two proteins, and immunoreactive rat fetuin/alpha 2-HSG in the conditioned medium of adult rat hepatocytes in primary culture was found to be phosphorylated. Thus, because rat fetuin/alpha 2-HSG isolated from bone and synthesized by osteoblasts in culture does not contain phosphorus, it seems to be pp63 dephosphorylated during circulation or in the bone matrix.

Human fetuin/alpha 2 HS glycoprotein in colloid and parenchymal cells in human fetal pituitary gland

An immunohistochemical study was undertaken, in an attempt to identify the acidic glycoprotein(s) present in colloid and in parenchymal cells in human fetal pituitary gland. As the colloid has been proposed to represent disintegrating cells, a series of antibodies against plasma glycoproteins and plasma proteins was applied; their presence intracellularly would generally be an indicator of plasma membrane leakage in dying parenchymal cells. In tissue sections from 9- to 20-week-old fetuses, the colloid showed prominent staining with an antibody to human fetuin/alpha 2 HS glycoprotein. Anti-alpha 2-HS glycoprotein labelled parenchymal cells in pars anterior and intermedia. Apart from a minor immunoreactivity for alpha 1 beta glycoprotein, no other plasma glycoprotein was seen in colloid or parenchymal cells. An antibody against bovine fetuin showed staining of the colloid and of some parenchymal cells in pars distalis and intermedia; the plasma and stroma of the pituitary gland were unstained. In contrast, the anti-human plasma protein antibodies all stained the stroma. The presence of alpha 2 HS glycoprotein in parenchymal cells and absence of other plasma glycoproteins imply integrity of the parenchymal cell plasma membrane. Thus, alpha 2 HS glycoprotein is either synthesized locally or taken up specifically in the parenchymal cells, which are proposed to participate in the formation of colloid. It is suggested that alpha 2 HS glycoprotein is part of a homeostatic system, which controls remodelling and physiological cell death during development.

Structure of the N- and O-glycans of the A-chain of human plasma alpha 2HS-glycoprotein as deduced from the chemical compositions of the derivatives prepared by stepwise degradation with exoglycosidases

The structure of the glycans of the A-chain of human plasma alpha 2HS-glycoprotein was established from the chemical compositions of its derivatives prepared by sequential enzymatic degradation of the carbohydrate moiety, from the determination of the kind and amount of the monosaccharides liberated after each step of the enzymatic digestion, and from the distinct specificity of the highly purified exoglycosidases. The exoglycosidases were three sialidases (Vibrio cholerae, fowl plague virus, and Arthrobacter ureafaciens), two beta-galactosidases (Streptococcus pneumoniae and bovine testis), one alpha-N-acetylgalactosaminidase, one beta-N-acetylglucosaminidase, and one alpha-mannosidase. Utilizing sialidases with different cleavage specificities, the number of alpha 2-3- and alpha 2-6-linked sialic acid residues could be separately determined. As to the beta-galactosidases, the enzyme isolated from S. pneumoniae cleaves only beta 1-4-linked galactose residues, whereas the bovine testes enzyme acts on both the beta 1-4- and beta 1-3-linked galactose residues. Jack bean beta-N-acetylglucosaminidase cleaves beta 1-2, beta 1-4, and beta 1-6 GlcNAc with higher activity for the beta 1-2. Jack bean alpha-mannosidase cleaves alpha 1-2, alpha 1-6, and alpha 1-3 Man with greater activity for alpha 1-2 and alpha 1-6. Bovine liver alpha-N-acetylgalactosaminidase cleaves O-linked GalNAc. On the basis of these results, the A-chain of alpha 2 HS-glycoprotein was found to possess two biantennary N-glycans and two O-linked trisaccharides.

Fetuin--an old friend revisited

Bovine fetuin, the first fetal protein to be described, has recently been shown to be a species homologue of a well known human plasma protein--alpha 2HS glycoprotein (alpha 2HS). The fetuins are now known to be members of the cystatin superfamily. The structural properties of the six fetuins that have been fully sequenced are compared. Despite the structural homology of these proteins, their described properties in the literature make them appear to be quite different. The diverse in vitro properties claimed for fetuin/alpha 2HS are reviewed. In vivo, fetuins are involved in the acute phase response. In development, in all species studied so far, fetuins are present in a specific cell population that forms the developing neocortex. The possible functional significance of this distribution is discussed.

Origin and fate of fetuin-containing neurons in the developing neocortex of the fetal sheep

The development of the neocortex has previously been extensively studied in carnivores (cat and ferret), rodents (rat and mouse) and primates (monkey and human). In these species, it has been shown that the initial population of cells migrating from the ventricular zone forms the primordial plexiform layer. This is subsequently split into marginal zone and subplate zone by the insertion of later-migrating cells into the primordial plexiform layer, to form the cortical plate proper. Many of the cells derived from the split primordial plexiform layer are transient. The neurons of the subplate zone are found in the deeper part of layer VI, and white matter deep to layer VI in the more mature cortex; most of these neurons disappear by adulthood. [3H]-thymidine labelling in the present study has shown a similar pattern of neocortical development in Artiodactyla (sheep). In addition it has been shown that the previously described staining of subplate and cortical plate cells for the fetal protein fetuin indicates that fetuin is a useful marker for a proportion of this transient population of neurons and defines its extent in neocortical development more clearly. Dividing cells were labelled by a single intra-amniotic injection of [3H]-thymidine at E26 to E35 (birth is at E150). The brains were subsequently examined at E40 or E80 for [3H]-thymidine labelling and fetuin staining by a combination of autoradiography and immunocytochemistry. The earliest generated neocortical cells detected in this study (E26) were found in two layers by E40, the outer marginal zone and inner subplate zone. Neurons of the marginal zone were generated up to E28; those of the early subplate zone were generated up to E31. The cortical plate proper was generated by cells "born" on E32 and later. This sequence is similar to that described in other species, especially the cat. A proportion of the early-generated neurons in the marginal zone, subplate zone and early cortical plate stained for fetuin. By E80 these earliest-generated, fetuin-positive cells were found in the white matter deep to the forming neocortical layers and in layer VI. In adult brains no fetuin-positive neurons could be identified in the neocortex, and neurons had almost entirely disappeared from the white matter. The fetal glycoprotein fetuin seems to be specifically associated with a population of cells that has the same developmental history as the transient marginal zone and subplate neurons described in other species.(ABSTRACT TRUNCATED AT 400 WORDS)

Cystatins--inhibitors of cysteine proteinases

The cystatin superfamily of proteins, derived from a common ancestor, is comprised of a diverse group of potent cysteine proteinase inhibitors and antibacterial/viral agents grouped into several families. This review concentrates on family 2 cystatins, namely, the human salivary cystatins and cystatin C. Emphasis is given to their physicochemical and functional properties at both the protein and the molecular level. The role of cystatins in disease processes, including those in the oral cavity, is also discussed. Finally, future directions for cystatin research in oral biology are presented.

Comparison of N-glycosides of fetuins from different species and human alpha 2-HS-glycoprotein

Complex type N-glycosides of commercial bovine fetuin preparations from pooled fetal calf serum have been shown to contain comparable amounts of Gal4,4,4TRI (see structure A below) and Gal4,4,3TRI (structure B) as major asialo-structures. To investigate whether there is a clear genetic specificity for synthesis of these oligosaccharides, N-glycosides from two preparations of bovine fetuin, each from a single calf, were examined. Both of these structures were present in each calf, and there was only a subtle quantitative difference in the ratio of these two structures between the calves. Thus, a specific galactosyltransferase, presumably required for the biosynthesis of the Gal4,4,3TRI structure, may exist in both of these individual calves. Comparison of fetuin N-glycosides was also extended to sheep, pig, and human alpha 2-HS-glycoprotein, the human counterpart of bovine fetuin, using high-pH anion-exchange chromatography of the reducing oligosaccharides as well as HPLC of their pyridinylamino derivatives. The N-glycosides of ovine fetuin also have both Gal4,4,4TRI and Gal4,4,3TRI structures in a ratio similar to that of bovine fetuin. However, the major N-glycoside of porcine fetuin is of a fucosyl biantennary complex type structure (structure C below) and human alpha 2-HS-glycoprotein has an N-glycoside which is almost exclusively a nonfucosylated biantennary structure (structure D). This species-specific presence of N-glycosides of fetuins and comparison with N-glycosides of other glycoproteins suggest that the polypeptide sequence of a glycoprotein may affect its N-glycan structure by regulating the activity of specific glycosyltransferases. [formula: see text]

Functional characterization of the promoter of pp63, a gene encoding a natural inhibitor of the insulin receptor tyrosine kinase

PP63 is a liver specific phosphorylated glycoprotein encoded by a single copy gene, which has the property of inhibiting both autophosphorylation and tyrosine kinase activity of the insulin receptor. In this study, we have analyzed the structure activity relationship of the pp63 gene promoter. Five protein binding sites were found in the proximal 5' flanking region of the gene (-223 to +4). Using oligonucleotides as competitors and purified recombinant C/EBP in footprinting and gel retardation assays, we identified two typical C/EBP sites (X1 and X3) plus a heterogenous, C/EBP-NF1 like site (X5), separated by two classical NF1 binding sites (X2 and X4). C/EBP or the related proteins were predominantly involved in supporting cell-free transcription. Occupancy of the first high affinity C/EBP site conferred almost maximal promoter efficiency, in vitro. However, this pp63 promoter activity remained very low as compared to that in intact hepatocytes. In these cells, occupancy of the first C/EBP (X1) and NF1 (X2) sites was already required for achieving a weak transcriptional activity. The use of the second C/EBP site (X3) strongly enhanced transcription, up to 60-70% of the maximum, whereas occupancy of the two more distal sites (X4 and X5) was necessary to fully activate the promoter. Thus, the strength of the promoter as well as the liver specific expression of pp63 gene appear to result from the interplay of several DNA-protein complexes involving mainly C/EBP and/or related proteins as well as the ubiquitous NF1 factor(s), rather than from the interaction of a more liver specific trans-acting factor with the promoter.