The anomalous behaviour of exogenous 25-hydroxyvitamin D in competitive binding assays

The Vitamin D International External Quality Assessment Scheme (DEQAS) was established in 1989 to monitor the performance of assays for 25-hydroxyvitamin D (25-OHD) and 1,25-dihydroxyvitamin D (I,25(OH)(2)D). This is achieved through the quarterly distribution of five samples of human serum. Results are used to calculate an All-Laboratory Trimmed Mean and a Method Mean for each of the methods used by participants. In July 2005, participants were asked to assay serum to which 50.9 nmol of either 25-OHD(3) or 25-OHD(2) had been added as ethanolic solutions. The final concentration of ethanol in the serum was 0.7%. The distribution also included a sample of the original serum (OS) containing 0.7% pure ethanol. The percentage recoveries of exogenous 25-OHD(3) (R1) and 25-OHD(2) (R2) were calculated for each method. Results (OS nM, R1 and R2) were as follows: DiaSorin RIA (n=53); 39.2, 82.1%, 83.3%, DiaSorin Liason (n=16); 36.8, 81.4%, 88.6%, IDS RIA (n=21); 36.4, 54.2%, 29.1%, IDS OCTEIA (n=16); 47.3, 78.8%, 56.4%, Nichols Advantage (n=21); 58.9, 46.4%, 43.2%, HPLC (n=9); 42.6, 112.2%, 97.1%, LC-MS (n=4); 34.0, 111.5%, 118.1%. The IDS RIA and Nichols assays gave unexpectedly low recoveries. This does not appear to be a calibration problem or the effect of ethanol.

The internal affairs of an integrin

Integrins are adhesion receptors that exchange signals between the extracellular and intracellular compartments. From their cell surface transmembrane location, they interact with extracellular matrix ligands or cellular counter-receptors, translating external cues into signals that affect cytoskeletal organization, cell shape and motility. Conversely, intracellular events may modify the affinities of integrins for external ligands. Inside the cell, integrins connect with cytoskeletal structures that, until recently, were thought to be exclusively actin microfilaments. We comment on the case of the epithelial integrin, alpha(6)beta(4), which may instead interact with intermediate filaments. This integrin was recently shown by several laboratories to be part of the hemidesmosome complex, an epithelial adhesive structure that is the plasma membrane anchoring site for keratin-containing intermediate filaments.

Interactions of a hemidesmosome component and actinin family members

Hemidesmosomes are multimeric protein complexes that attach epithelial cells to their underlying matrix and serve as cell surface anchorage sites for the keratin cytoskeleton. Two hemidesmosome components, the alpha6beta4 integrin heterodimer and a human autoantigen termed BP180, are transmembrane proteins that link the extracellular matrix to the keratin network in cells. Here, we report that actinin-4, an actin-bundling protein, is a potential binding partner for BP180. Using yeast two-hybrid, we have mapped the binding site for BP180 to the C-terminal region of actinin-4. This site contains two EF-hand, Ca2+ regulation domains and shares 87% sequence homology with the same region in actinin-1. Consistent with this, BP180 can bind actinin-1 in both the yeast two-hybrid assay and in immunoprecipitation assays. To determine whether the EF-hand domain is a consensus binding sequence for BP180, we tested whether other proteins with this domain bind BP180. None of the proteins tested including calmodulin, with 4 EF-hand domains, and myosin regulatory light chain, with 1 EF-hand domain, interacts with BP180 in yeast two-hybrid system and immunoprecipitation studies, suggesting that the interaction between BP180 and actinin family members is specific. We have compared the distribution of actinin-1 and actinin-4 with that of BP180 in MCF-10A and pp126 cells. Surprisingly, BP180 localizes not only to sites of cell-substratum interaction, but is also present at sites of cell-cell contacts where it co-distributes with both actinin-1 and actinin-4 as well as other adherens junction proteins. In oral tissues, BP180 is present along the basement membrane and at cell-cell contact sites in basal epithelial cells where it co-distributes with adherens junction proteins. Since BP180 antibodies inhibit association of junction proteins at sites of cell-cell contact in oral keratinocytes, these results suggest that BP180 may play a role in establishing cell-cell interactions. We discuss a role for BP180 in crosstalk between cell-matrix and cell-cell junctions.

Pemphigoid nodularis associated with autoantibodies to the NC16A domain of BP180 and a hyperproliferative integrin profile

Pemphigoid nodularis, a rare variant of bullous pemphigoid, has clinical features resembling prurigo nodularis, with blisters arising from normal-appearing or nodular skin. The fine antigenic epitope of the autoantibodies and the mechanism accounting for the nodular phenotype has not been delineated. We describe a patient with pemphigoid nodularis that fulfilled the criteria of bullous pemphigoid by histopathologic examination and direct and indirect immunofluorescence studies. Immunopathologic examination also revealed in situ deposition and circulating autoantibodies of all IgG subclasses, except IgG3, and both light chains to the patient's skin basement membrane. By immunoblotting, the patient's IgG autoantibodies labeled BP180, BP230, and an unidentified 150-kd epidermal protein and mapped the BP180 epitope to the MCW-1, region 2 of the NC16A domain. The nodular plaque skin showed expression of alpha-6 and beta-1 integrin subunits, mediators of matrix-cell signaling and proliferation, at the basal and the suprabasal epidermis, a pattern found in psoriasis, which is the prototype of hyperproliferative dermatoses.

Follicle-stimulating hormone stimulates protein kinase A-mediated histone H3 phosphorylation and acetylation leading to select gene activation in ovarian granulosa cells

We examined the phosphorylation and acetylation of histone H3 in ovarian granulosa cells stimulated to differentiate by follicle-stimulating hormone (FSH). We found that protein kinase A (PKA) mediates H3 phosphorylation on serine 10, based on inhibition exclusively by PKA inhibitors. FSH-stimulated H3 phosphorylation in granulosa cells is not downstream of mitogen-activated protein kinase/extracellular signal-regulated kinase, ribosomal S6 kinase-2, mitogen- and stress-activated protein kinase-1, p38 MAPK, phosphatidylinositol-3 kinase, or protein kinase C. Transcriptional activation-associated H3 phosphorylation on serine 10 and acetylation of lysine 14 leads to activation of serum glucocorticoid kinase, inhibin alpha, and c-fos genes. We propose that phosphorylation of histone H3 on serine 10 by PKA in coordination with acetylation of H3 on lysine 14 results in reorganization of the promoters of select FSH responsive genes into a more accessible configuration for activation. The unique role of PKA as the physiological histone H3 kinase is consistent with the central role of PKA in initiating granulosa cell differentiation.

Structure and function of a vimentin-associated matrix adhesion in endothelial cells

The alpha4 laminin subunit is a component of endothelial cell basement membranes. An antibody (2A3) against the alpha4 laminin G domain stains focal contact-like structures in transformed and primary microvascular endothelial cells (TrHBMECs and HMVECs, respectively), provided the latter cells are activated with growth factors. The 2A3 antibody staining colocalizes with that generated by alphav and beta3 integrin antibodies and, consistent with this localization, TrHBMECs and HMVECs adhere to the alpha4 laminin subunit G domain in an alphavbeta3-integrin-dependent manner. The alphavbeta3 integrin/2A3 antibody positively stained focal contacts are recognized by vinculin antibodies as well as by antibodies against plectin. Unusually, vimentin intermediate filaments, in addition to microfilament bundles, interact with many of the alphavbeta3 integrin-positive focal contacts. We have investigated the function of alpha4-laminin and alphavbeta3-integrin, which are at the core of these focal contacts, in cultured endothelial cells. Antibodies against these proteins inhibit branching morphogenesis of TrHBMECs and HMVECs in vitro, as well as their ability to repopulate in vitro wounds. Thus, we have characterized an endothelial cell matrix adhesion, which shows complex cytoskeletal interactions and whose assembly is regulated by growth factors. Our data indicate that this adhesion structure may play a role in angiogenesis.

Spatial regulation and activity modulation of plasmin by high affinity binding to the G domain of the alpha 3 subunit of laminin-5

Cells in complex tissues contact extracellular matrix that interacts with integrin receptors to influence gene expression, proliferation, apoptosis, adhesion, and motility. During development, tissue remodeling, and tumorigenesis, matrix components are modified by enzymatic digestion with subsequent effects on integrin binding and signaling. We are interested in understanding the mechanisms by which broad spectrum proteinases such as plasmin are targeted to their extracellular matrix protein substrates. We have utilized plasmin-mediated cleavage of the epithelial basement membrane glycoprotein laminin-5 as a model to evaluate molecular events that direct plasmin activity to specific structural domains. We report that plasminogen and tissue plasminogen activator (tPA) exhibit high affinity, specific binding to the G(1) subdomain of the N terminus of the laminin-5 alpha(3) subunit, with equilibrium dissociation constants of 50 nm for plasminogen and 80 nm for tPA. No high affinity binding to the G(2), G(3), and G(4) subdomains was observed. As a result of binding to the G(1) subdomain, the catalytic efficiency of tPA-catalyzed plasminogen activation is enhanced 32-fold, leading to increased matrix-associated plasmin that is positioned favorably for cleavage within the G(4) subdomain as we have reported previously (Goldfinger, L. E., Stack, M. S., and Jones, J. C. R. (1998) J. Cell Biol. 141, 255-265). Thus, physical constraints dictated by interaction of proteinase and matrix macromolecule control not only enzymatic activity but may regulate substrate targeting of proteinases.

Urinary-type plasminogen activator (uPA) expression and uPA receptor localization are regulated by alpha 3beta 1 integrin in oral keratinocytes

Expression of urinary-type plasminogen activator (uPA) and its receptor (uPAR) is correlated with matrix proteolysis, cell adhesion, motility, and invasion. To evaluate the functional link between adhesion and proteolysis in gingival keratinocytes (pp126), cells were treated with immobilized integrin antibodies to induce integrin clustering. Clustering of alpha(3) and beta(1) integrin subunits, but not alpha(2), alpha(5), alpha(6), or beta(4), enhanced uPA secretion. Bead-immobilized laminin-5 and collagen I, two major alpha(3)beta(1) ligands, also induced uPA expression. Coordinate regulation of the serpin plasminogen activator inhibitor 1 was also apparent; however, a net increase in uPA activity was predominant. alpha(3)beta(1) integrin clustering induced extracellular signal-regulated kinase 1/2 phosphorylation, and both uPA induction and extracellular signal-regulated kinase activation were blocked by the mitogen-activated protein kinase/extracellular signal-regulated kinase kinase inhibitor PD98059. Integrin aggregation also promoted a dramatic redistribution of uPAR on the cell surface to sites of clustered alpha(3)beta(1) integrins. Co-immunoprecipitation of beta(1) integrin with uPAR provided further evidence that protein-protein interactions between uPAR and beta(1) integrin control uPAR distribution. As a functional consequence of uPA up-regulation and uPA-mediated plasminogen activation, the globular domain of the laminin-5 alpha(3) subunit, a major pp126 matrix protein, was proteolytically processed from a 190-kDa form to a 160-kDa species. Laminin-5 containing the 160-kDa alpha(3) subunit efficiently nucleates hemidesmosome formation and reduces cell motility. Together, these data suggest that multivalent aggregation of the alpha(3)beta(1) integrin regulates proteinase expression, matrix proteolysis, and subsequent cellular behavior.

Antenatal dexamethasone and the growth hormone-insulin-like growth factor axis

Dexamethasone administration has marked effects on the growth hormone-insulin-like growth factor axis (GH-IGF) in animal and human studies. During pregnancy in the rat, it is associated with fetal growth restriction due to inhibition of IGF bioactivity. In the human only repeated dosages have been associated with fetal growth restriction. The aim of this study is to test the hypothesis that antenatal dexamethasone administration to pregnant women is associated with reduced activity of the GH-IGF axis. To achieve this blood samples were taken from 12 pregnant women pre- and at 24 h and 48 h after dexamethasone administration. In these samples GH, IGF-I, IGF bioactivity and IGF binding protein (IGFBP)-3 protease activity were measured. In view of the interaction between insulin and the GH-IGF axis, glucose and insulin concentrations were also measured. There were no significant differences between the concentrations of GH, IGF-I, IGF bioactivity and IGFBP-3 protease activity before and after dexamethasone. The concentrations of glucose and insulin were significantly higher at 24 h, but not 48 h post-dexamethasone. It is concluded that a single antenatal course of dexamethasone does not alter the GH-IGF-I axis in pregnant women at the time points studied.

Imidazoline receptor antisera-selected (IRAS) cDNA: cloning and characterization

The imidazoline-1 receptor (IR1) is considered a novel target for drug discovery. Toward cloning an IR1, a truncated cDNA clone was isolated from a human hippocampal lambda gt11 cDNA expression library by relying on the selectivity of two antisera directed against candidate IR proteins. Amplification reactions were performed to extend the 5' and 3' ends of this cDNA, followed by end-to-end PCR and conventional cloning. The resultant 5131-basepair molecule, designated imidazoline receptor-antisera-selected (IRAS) cDNA, was shown to encode a 1504-amino acid protein (IRAS-1). No relation exists between the amino acid sequence of IRAS-1 and proteins known to bind imidazolines (e.g., it is not an alpha2-adrenoceptor or monoamine oxidase subtype). However, certain sequences within IRAS-1 are consistent with signaling motifs found in cytokine receptors, as previously suggested for an IR1. An acidic region in IRAS-1 having an amino acid sequence nearly identical to that of ryanodine receptors led to the demonstration that ruthenium red, a dye that binds the acidic region in ryanodine receptors, also stained IRAS-1 as a 167-kD band on SDS gels and inhibited radioligand binding of native I1 sites in untransfected PC-12 cells (a source of authentic I1 binding sites). Two epitope-selective antisera were also generated against IRAS-1, and both reacted with the same 167-kD band on Western blots. In a host-cell-specific manner, transfection of IRAS cDNA into Chinese hamster ovary cells led to high-affinity I1 binding sites by criteria of nanomolar affinity for moxonidine and rilmenidine. Thus, IRAS-1 is the first protein discovered with characteristics of an IR1.

Association between postoperative outcome and results of magnetic resonance imaging and computed tomography in working dogs with degenerative lumbosacral stenosis

OBJECTIVE

To determine whether results of magnetic resonance imaging (MRI) and computed tomography (CT) are associated with postoperative outcome in working dogs with degenerative lumbosacral stenosis.

DESIGN

Prospective cohort study.

ANIMALS

12 dogs treated surgically for degenerative lumbosacral stenosis.

PROCEDURE

The lumbosacral vertebral column was examined before surgery by use of MRI and CT and after surgery by use of CT. Outcome, based on performance in standardized training exercises, was assessed 6 months after decompressive surgery. Associations between imaging results and postoperative outcome were determined by use of a Fisher exact test and logistic regression.

RESULTS

None of the dogs were able to perform their duties before surgery. By 6 months after surgery, 8 of 12 dogs had been returned to full active duty. Nerve tissue compression was effectively localized by use of CT and MRI. Significant associations between results of imaging studies and postoperative outcome were not identified.

CONCLUSIONS AND CLINICAL RELEVANCE

Surgical intervention is justified in high-performance working dogs with degenerative lumbosacral stenosis. However, results of imaging studies may be less important than clinical or surgical factors for predicting outcome in affected dogs.

The ADP ribosylation factor nucleotide exchange factor ARNO promotes beta-arrestin release necessary for luteinizing hormone/choriogonadotropin receptor desensitization

Desensitization of guanine nucleotide binding protein-coupled receptors is a ubiquitous phenomenon characterized by declining effector activity upon persistent agonist stimulation. The luteinizing hormone/choriogonadotropin receptor (LH/CGR) in ovarian follicles exhibits desensitization of effector adenylyl cyclase activity in response to the mid-cycle surge of LH. We have previously shown that uncoupling of the agonist-activated LH/CGR from the stimulatory G protein (G(s)) is dependent on GTP and attributable to binding of beta-arrestin present in adenylyl cyclase-rich follicular membrane fraction to the third intracellular (3i) loop of the receptor. Here, we report that LH/CGR-dependent desensitization is mimicked by ADP ribosylation factor nucleotide-binding site opener, a guanine nucleotide exchange factor of the small G proteins ADP ribosylation factors (Arfs) 1 and 6, and blocked by synthetic N-terminal Arf6 peptide, suggesting that the GTP-dependent step of LH/CGR desensitization is receptor-dependent Arf6 activation. Arf activation by GTP and ADP ribosylation factor nucelotide-binding site opener promotes the release of docked beta-arrestin from the membrane, making beta-arrestin available for LH/CGR; Arf6 but not Arf1 peptides block beta-arrestin release from the membrane. Thus, LH/CGR appears to activate two membrane delimited signaling cascades via two types of G proteins: heterotrimeric G(s) and small G protein Arf6. Arf6 activation releases docked beta-arrestin necessary for receptor desensitization, providing a feedback mechanism for receptor self-regulation.

Human bronchial epithelial cells secrete laminin 5, express hemidesmosomal proteins, and assemble hemidesmosomes

Epithelial cells attach to the basement membrane through adhesive contacts between the basal cells of the epithelium and the proteins of the extracellular matrix (ECM). The hemidesmosome (HD) is a specialized cell-ECM contact, that mediates the attachment of the epithelial cell basal surface to the ECM. In bronchial epithelial cells, the protein components that constitute the HD have not been demonstrated. Using immunohistochemical techniques, we determined that normal human bronchial epithelial (NHBE) cells express the HD cell surface integrin alpha6beta4 and produce laminin 5, the ECM protein associated with HDs. Furthermore, expression of the HD-associated structural proteins, bullous pemphigoid antigens 1 (BPAG 1) and 2 (BPAG 2), was demonstrated in NHBE cells by immunofluorescence microscopy and immunoblot analyses. In addition, we confirmed the presence of laminin 5 in the basement membrane (BM) of bronchial epithelial biopsy specimens and of BP230, BP180, and the alpha6beta4 integrin heterodimer at the site of bronchial epithelial cell-ECM interaction in vivo. Finally, using electron microscopy, we were able to demonstrate intact HDs in a glutaraldehyde-fixed NHBE cell monolayer. These findings suggest that bronchial epithelium forms HDs and that the laminin 5-alpha6beta4 integrin interaction may be important in stabilizing epithelial cell adhesion to the BM in the lung.

Inhibition of laminin-5 production in breast epithelial cells by overexpression of p300

The transcriptional coactivator p300 is essential for normal embryonic development and cellular differentiation. We have been studying the role of p300 in the transcription of a variety of genes, and we became interested in the role of this coactivator in the transcription of genes important in breast epithelial cell biology. From MCF-10A cells (spontaneously immortalized, nontransformed human breast epithelial cells), we developed cell lines that stably overexpress p300. These p300-overexpressing cells displayed reduced adhesion to culture dishes and were found to secrete an extracellular matrix deficient in laminin-5. Laminin-5 is the major extracellular matrix component produced by breast epithelium. Immunofluorescence studies, as well as experiments using normal matrix, confirmed that the decreased adhesion of p300-overexpressing cells is due to laminin-5-deficient extracellular matrix and not due to loss of laminin-5 receptors. Northern blots revealed markedly decreased levels of expression of two of the genes (designated LAMA3 and LAMC2) encoding the alpha3 and gamma2 chains of the laminin-5 heterotrimer in the cells that overexpress p300, whereas LAMB3 mRNA, encoding the third or beta3 chain of laminin-5, was not markedly reduced. Transient transfection experiments with a vector containing a murine LAMA3 promoter demonstrate that overexpressing p300 down-regulates the LAMA3 promoter. In summary, overexpression of p300 leads to down-regulation of laminin-5 production in breast epithelial cells, resulting in decreased adhesion.

Preoperative FDG-PET temporal lobe hypometabolism and verbal memory after temporal lobectomy

OBJECTIVE

To examine the relationship of preoperative fluorodeoxyglucose (FDG)-PET asymmetry in temporal lobe metabolism and memory outcome after anterior temporal lobectomy (ATL).

METHODS

In a university-based epilepsy surgery center, 60 ATL patients (27 left, 33 right) were divided into two groups: no/mild (n = 21) or moderate/ severe (n = 39) asymmetry in temporal lobe hypometabolism as determined by FDG-PET. All patients were nonretarded, at least 18 years of age, left-hemisphere speech dominant, without MRI abnormalities other than hippocampal atrophy, and with unilateral temporal lobe origin of intractable complex partial seizures. Neuropsychological measures of intelligence and verbal and visual memory function were assessed preoperatively and 6 months postoperatively.

RESULTS

Left ATL patients with no/mild asymmetry in FDG-PET temporal lobe metabolism exhibited significantly greater verbal memory decline compared with left ATL patients with moderate/severe hypometabolism. There was no significant relationship between PET asymmetry and pre- to postsurgical IQ change. No significant relationship was observed between extent of PET hypometabolism and memory outcome for right ATL patients.

CONCLUSIONS

FDG-PET asymmetry can be added to the preoperative clinical markers that appear useful in predicting verbal memory decline after left ATL.

The N terminus of the transmembrane protein BP180 interacts with the N-terminal domain of BP230, thereby mediating keratin cytoskeleton anchorage to the cell surface at the site of the hemidesmosome

In epidermal cells, the keratin cytoskeleton interacts with the elements in the basement membrane via a multimolecular junction called the hemidesmosome. A major component of the hemidesmosome plaque is the 230-kDa bullous pemphigoid autoantigen (BP230/BPAG1), which connects directly to the keratin-containing intermediate filaments of the cytoskeleton via its C terminus. A second bullous pemphigoid antigen of 180 kDa (BP180/BPAG2) is a type II transmembrane component of the hemidesmosome. Using yeast two-hybrid technology and recombinant proteins, we show that an N-terminal fragment of BP230 can bind directly to an N-terminal fragment of BP180. We have also explored the consequences of expression of the BP230 N terminus in 804G cells that assemble hemidesmosomes in vitro. Unexpectedly, this fragment disrupts the distribution of BP180 in transfected cells but has no apparent impact on the organization of endogenous BP230 and alpha6beta4 integrin. We propose that the BP230 N terminus competes with endogenous BP230 protein for BP180 binding and inhibits incorporation of BP180 into the cell surface at the site of the hemidesmosome. These data provide new insight into those interactions of the molecules of the hemidesmosome that are necessary for its function in integrating epithelial and connective tissue types.

Subclinical CT abnormalities in the lumbosacral spine of older large-breed dogs

Computed tomography (CT) of the L5-S3 vertebral levels was performed in six, large-breed dogs presented for problems unrelated to the lumbosacral spine. All dogs were asymptomatic for lumbosacral stenosis on neurologic examination. Breeds included German Shepherd, Golden Retriever, Boxermix and Belgian Malinois. Ages ranged from 5-12 years. Five out of six dogs exhibited CT abnormalities. Among the 18 disc levels examined, the most common findings were idiopathic stenosis, loss of vertebral canal epidural fat, and nerve tissue displacement. Less common abnormalities were vertebral canal or foraminal bone proliferation, loss of intervertebral foramen fat, vertebral canal disc bulging, degenerative articular process joint disease, transitional vertebra, dural ossification, foraminal disc bulging, Schmorl's nodes, calcified extruded disc fragment, and sacroiliac joint osteophytes. Vertebral subluxation was absent in all dogs. Findings indicate that some lumbosacral CT abnormalities may be clinically insignificant, especially in older dogs.