A framework for diagnosing and identifying where technology-induced errors come from

Health information systems have the ability to reduce medical errors but they can also introduce new types of errors. In the cognitive and human factors literature there is a recognition that many of the high profile accidents that have occurred in other industries outside of healthcare have had their origins in the complexities of organizational work and how work is structured. The authors propose that in order to have a fully robust framework for diagnosing technology-induced errors one must understand the development and implementation of a technology and the influences of policy using a multi-organizational model. The authors propose that technology-induced errors may have their origins in up to four or more organizational structures that make up complex health care systems in addition to the health care provider: governments, model organizations, software development organizations, and local healthcare organizations. In this paper a framework for considering the origins of technology-induced error in healthcare is presented, along with our experiences to date in the application of the framework.

Management of hepatitis C in liver transplant recipients

Recurrent hepatitis C virus (HCV) disease is the leading cause of graft loss in liver transplant recipients with pre-transplant HCV infection. While natural history is variable, median time to recurrent cirrhosis is less than a decade. Factors contributing to risk of recurrence and rate of fibrosis progression are only partially known. Older donor age, treatment of acute rejection, cytomegalovirus infection and high pre-transplant viral load are most consistently linked with worse outcomes. Whether these factors can be modified to positively impact on HCV disease progression is unknown. The main therapeutic approach for patients with recurrent HCV disease has been the treatment with interferon and ribavirin (RBV) once recurrent disease is documented or progressive. Efficacy is lower than in nontransplant patients and tolerability, especially of RBV, is a major limitation. Stable or improved fibrosis scores are seen in the majority of sustained responders. Optimal dose, duration and timing of treatment have not been determined. Alternative strategies under study include pre-transplant treatment of decompensated cirrhotics, preemptive antiviral therapy started within weeks of transplantation and prophylactic therapy using HCV antibodies. Ongoing studies may establish a future role for alternative treatment approaches. Additionally, limited overall efficacy of interferon-based therapy in the transplant setting highlights the urgent need for new drug therapies.

Signals transduced by Ca(2+)/calcineurin and NFATc3/c4 pattern the developing vasculature

Vascular development requires an orderly exchange of signals between growing vessels and their supporting tissues, but little is known of the intracellular signaling pathways underlying this communication. We find that mice with disruptions of both NFATc4 and the related NFATc3 genes die around E11 with generalized defects in vessel assembly as well as excessive and disorganized growth of vessels into the neural tube and somites. Since calcineurin is thought to control nuclear localization of NFATc proteins, we introduced a mutation into the calcineurin B gene that prevents phosphatase activation by Ca(2+) signals. These CnB mutant mice exhibit vascular developmental abnormalities similar to the NFATc3/c4 null mice. We show that calcineurin function is transiently required between E7.5 and E8.5. Hence, early calcineurin/NFAT signaling initiates the later cross-talk between vessels and surrounding tissues that pattern the vasculature.

Identification of anaplastic lymphoma kinase as a receptor for the growth factor pleiotrophin

Pleiotrophin (PTN) is a secreted growth factor that induces neurite outgrowth and is mitogenic for fibroblasts, epithelial, and endothelial cells. During tumor growth PTN can serve as an angiogenic factor and drive tumor invasion and metastasis. To identify a receptor for PTN, we panned a phage display human cDNA library against immobilized PTN protein as a bait. From this we isolated a phage insert that was homologous to an amino acid sequence stretch in the extracellular domain (ECD) of the orphan receptor tyrosine kinase anaplastic lymphoma kinase (ALK). In parallel with PTN, ALK is highly expressed during perinatal development of the nervous system and down-modulated in the adult. Here we show in cell-free assays as well as in radioligand receptor binding studies in intact cells that PTN binds to the ALK ECD with an apparent Kd of 32 +/- 9 pm. This receptor binding is inhibited by an excess of PTN, by the ALK ECD, and by anti-PTN and anti-ECD antibodies. PTN added to ALK-expressing cells induces phosphorylation of both ALK and of the downstream effector molecules IRS-1, Shc, phospholipase C-gamma, and phosphatidylinositol 3-kinase. Furthermore, the growth stimulatory effect of PTN on different cell lines in culture coincides with the endogenous expression of ALK mRNA, and the effect of PTN is enhanced by ALK overexpression. From this we conclude that ALK is a receptor that transduces PTN-mediated signals and propose that the PTN-ALK axis can play a significant role during development and during disease processes.

A retrospective study of risk factors for repeated admissions for asthma in a rural/suburban university hospital

In the study reported, the authors examined risk factors for repeated hospital admissions for asthma in a rural/suburban setting. Charts of patients who were hospitalized two or more times with the diagnosis of asthma between June 1991 and January 1998 were reviewed. A questionnaire was completed for each admission for 65 patients. The results demonstrated an equal male-to-female ratio, with a mean age of 27 years. Hispanics represented 12% of the patients although they accounted for only 2.5% of the general population in the area under study. The mean number of hospital admissions was 3.2. A history of depression existed in 25% of the patients. Noncompliance was admitted in 38%. Twenty-five percent were active tobacco smokers. Acknowledged triggers of asthma included viral infections (74%), exercise (50%), weather conditions (43%), dust (38%), cats (36%), sinusitis (32%), pollen (32%), gastroesophageal reflux disease (31%), dogs (30%), smoke (28%), and emotional stress (15%). Medications at time of admission included albuterol (98%), salmeterol xinafoate (26%), theophylline (38%), ipratropium bromide (55%), nedocromil sodium (20%), cromolyn sodium (35%), prednisone (49%), and inhaled corticosteroids (69%). Ninety-five percent had access to a primary care physician. Fifty-seven percent had a pulmonary and 11% had an allergy consult. These data suggest that patients in rural/suburban areas with repeated hospitalizations for asthma have a high probability of noncompliance, depression, and allergenic triggers. Gastroesophageal reflux was a common recognized trigger. Inhaled steroids were underused, whereas ipratropium and theophylline were overused. Bilingual education on asthma and triggers and social support are necessary even in rural healthcare settings without a large minority population.

Inactivation of p53 tumor suppressor gene acts synergistically with c-neu oncogene in salivary gland tumorigenesis

Transgenic mice expressing specific oncogenes usually develop tumors in a stochastic fashion suggesting that tumor progression is a multi-step process. To gain further understanding of the interactions between oncogenes and tumor suppressor genes during tumorigenesis, we have crossed a transgenic strain (TG.NK) carrying an activated c-neu oncogene driven by the MMTV enhancer/promoter with p53-deficient mice. c-neu transgenic mice have stochastic breast tumor formation and normal appearing salivary glands. However, c-neu mice heterozygous for a p53 deletion develop parotid gland tumors and loose their wild type p53 allele. c-neu mice with a homozygous p53 deletion have increased rates of parotid tumor onset suggesting that inactivation of p53 is required and sufficient for parotid gland transformation in the presence of activated c-neu. In contrast to the dramatic effect of p53 in parotid gland transformation, p53 loss has little effect on the rate or stochastic appearance of mammary tumors. In addition, p53 loss was accompanied by the down regulation of p21 in parotid gland tumors but not breast tumors. The parotid gland tumors were aneuploid and demonstrated increased levels of Cyclin D1 expression. These observations suggest that in c-neu transgenic mice, p53 alterations have differential tissue effects and may be influenced by the tissue specific expression of genes influencing p53 activity.

Transmembrane transforming growth factor-alpha tethers to the PDZ domain-containing, Golgi membrane-associated protein p59/GRASP55

Transforming growth factor-alpha (TGF-alpha) and related proteins represent a family of transmembrane growth factors with representatives in flies and worms. Little is known about the transport of TGF-alpha and other transmembrane growth factors to the cell surface and its regulation. p59 was purified as a cytoplasmic protein, which at endogenous levels associates with transmembrane TGF-alpha. cDNA cloning of p59 revealed a 452 amino acid sequence with two PDZ domains. p59 is myristoylated and palmitoylated, and associates with the Golgi system, where it co-localizes with TGF-alpha. Its first PDZ domain interacts with the C-terminus of transmembrane TGF-alpha and select transmembrane proteins. p59 is the human homolog of GRASP55, which is structurally related to GRASP65. GRASP55 and GRASP65 have been shown to play a role in stacking of the Golgi cisternae in vitro. C-terminal mutations of transmembrane TGF-alpha, which decrease or abolish the interaction with p59, also strongly impair cell surface expression of TGF-alpha. Our observations suggest a role for membrane tethering of p59/GRASP55 to select transmembrane proteins, including TGF-alpha, in maturation and transport to the cell surface.

A region in domain II of the urokinase receptor required for urokinase binding

The urokinase receptor is composed of three homologous domains based on disulfide spacing. The contribution of each domain to the binding and activation of single chain urokinase (scuPA) remains poorly understood. In the present paper we examined the role of domain II (DII) in these processes. Repositioning DII to the amino or carboxyl terminus of the molecule abolished binding of scuPA as did deleting the domain entirely. By using alanine-scanning mutagenesis, we identified a 9-amino acid continuous sequence in DII (Arg(137)-Arg(145)) required for both activities. Competition-inhibition and surface plasmon resonance studies demonstrated that mutation of Lys(139) and His(143) to alanine in soluble receptor (suPAR) reduced the affinity for scuPA approximately 5-fold due to an increase in the "off rate." Mutation of Arg(137), Arg(142), and Arg(145), each to alanine, leads to an approximately 100-fold decrease in affinity attributable to a 10-fold decrease in the apparent "on rate" and a 6-fold increase in off rate. These differences were confirmed on cells expressing variant urokinase receptor. suPAR-K139A/H143A displayed a 50% reduction in scuPA-mediated plasminogen activation activity, whereas the 3-arginine variant was unable to stimulate scuPA activity at all. Mutation of the three arginines did not affect binding of a decamer peptide antagonist of scuPA known to interact with DI and DIII. However, this mutation abolished both the binding of soluble DI to DII-III in the presence of scuPA and the synergistic activation of scuPA mediated by DI and wild type DII-DIII. These data show that DII is required for high affinity binding of scuPA and its activation. DII does not serve merely as a spacer function but appears to be required for interdomain cooperativity.

Novel interactions between urokinase and its receptor

Urokinase-type plasminogen activator (uPA) binds to its receptor (uPAR) with a K(d) of about 1 nm. The catalytic activity of the complex is apparent at uPA concentrations close to K(d). Other functions of the complex, such as signal transduction, are apparent at much higher concentrations (35-60 nm). In the present study, we show that uPA and recombinant soluble uPAR (suPAR), at concentrations that exceed the K(d) and the theoretical saturation levels (10-80 nm), establish novel interactions that lead to a further increase in the activity of the single-chain uPA (scuPA)/suPAR and two-chain uPA (tcuPA)/suPAR complexes. Experiments performed using dynamic light scattering, gel filtration, and electron microscopy techniques indicate that suPAR forms dimers and oligomers. The three techniques provide evidence that the addition of an equimolar concentration of scuPA leads to the dissociation of these dimers and oligomers. Biacore data show that suPAR dimers and oligomers bind scuPA with decreased affinity when compared with monomers. We postulate that uPAR is present in equilibrium between oligomer/dimer/monomer forms. The binding of uPA to suPAR dimers and oligomers occurs with lower affinity than the binding to monomer. These novel interactions regulate the activity of the resultant complexes and may be involved in uPA/uPAR mediated signal transduction.

Urokinase-derived peptides regulate vascular smooth muscle contraction in vitro and in vivo

We examined the effect of urokinase (uPA) and its fragments on vascular smooth muscle cell contraction. Single-chain uPA inhibits phenylepherine (PE) -induced contraction of rat aortic rings, whereas two-chain uPA exerts the opposite effect. Two independent epitopes mediating these opposing activities were identified. A6, a capped peptide corresponding to amino acids 136-143 (KPSSPPEE) of uPA, increased the EC(50) of PE-induced vascular contraction sevenfold by inhibiting the release of calcium from intracellular stores. A6 activity was abolished by deleting the carboxyl-terminal Glu or by mutating the Ser corresponding to position 138 in uPA to Glu. A single-chain uPA variant lacking amino acids 136-143 did not induce vasorelaxation. A second epitope within the kringle of uPA potentiated PE-induced vasoconstriction. This epitope was exposed when single-chain uPA was converted to a two-chain molecule by plasmin. The isolated uPA kringle augmented vasoconstriction, whereas uPA variant lacking the kringle had no procontractile activity. These studies reveal previously undescribed vasoactive domains within urokinase and its naturally derived fragments.

Severe limb defects in Hypodactyly mice result from the expression of a novel, mutant HOXA13 protein

Hypodactyly (Hoxa13(Hd)) mice have a 50-bp deletion in the coding region of exon 1 of the Hoxa13 gene and have more severe limb defects than mice with an engineered deletion of the entire gene (Hoxa13(-/-)). Increased cell death is observed in the autopod of Hoxa13(Hd/Hd) but not Hoxa13(-/-) limb buds. In addition, compound heterozygotes for one Hd allele and a Hoxa13(-) allele have a more severe limb phenotype than mice homozygous for the engineered null allele, suggesting a dominant-negative effect of the Hd mutation. The Hoxa13(Hd) deletion does not interfere with steady-state mRNA levels; however, its consequences on translation are unknown. In this paper, we characterize the Hoxa13 transcription initiation site in limbs and determine the initiator methionine of HOXA13. We show that the Hoxa13(Hd) deletion results in a translational frame shift that leads to the loss of wild-type HOXA13 protein and the simultaneous production of a novel, stable protein in the limb buds of mutant mice. The mutant Hd protein (HOXA13(Hd)) consists of the first 25 amino acids of wild-type HOXA13 sequence, followed by 275 amino acids of arginine- and lysine-rich, novel sequence, and lacks the homeodomain. Like wild-type HOXA13, HOXA13(Hd) is localized to the nucleus in transfected COS-7 cells, perhaps mediated by the arginine- and lysine-rich peptide sequences created by the translational frame shift. To determine whether HOXA13(Hd) could alter limb morphogenesis, we misexpressed the mutant mRNA throughout the developing limb bud using a Prx-1 promoter-Hd gene construct in transgenic mice. Three of 15 transgenic founder animals displayed reduction or absence of proximal and distal limb structures. We propose that the expression of HOXA13(Hd) plays a role in the profound failure of digit formation in Hoxa13(Hd/Hd) mice and explains the morphologic differences between these two Hoxa13 alleles.

Defensin promotes the binding of lipoprotein(a) to vascular matrix

Retention of lipoproteins within the vasculature is a central event in the pathogenesis of atherosclerosis. However, the signals that mediate this process are only partially understood. Prompted by putative links between inflammation and atherosclerosis, we previously reported that alpha-defensins released by neutrophils are present in human atherosclerotic lesions and promote the binding of lipoprotein(a) [Lp(a)] to vascular cells without a concomitant increase in degradation. We have now tested the hypothesis that this accumulation results from the propensity of defensin to form stable complexes with Lp(a) that divert the lipoprotein from its normal cellular degradative pathways to the extracellular matrix (ECM). In accord with this hypothesis, defensin stimulated the binding of Lp(a) to vascular matrices approximately 40-fold and binding of the reactants to the matrix was essentially irreversible. Defensin formed stable, multivalent complexes with Lp(a) and with its components, apoprotein (a) and low-density lipoprotein (LDL), as assessed by optical biosensor analysis, gel filtration, and immunoelectron microscopy. Binding of defensin/Lp(a) complexes to matrix was inhibited (>90%) by heparin and by antibodies to fibronectin (>70%), but not by antibodies to vitronectin or thrombospondin. Defensin increased the binding of Lp(a) (10 nmol/L) to purified fibronectin more than 30-fold. Whereas defensin and Lp(a) readily traversed the endothelial cell membranes individually, defensin/Lp(a) complexes lodged on the cell surface. These studies demonstrate that alpha-defensins released from activated or senescent neutrophils stimulate the binding of an atherogenic lipoprotein to the ECM of endothelial cells, a process that may contribute to lipoprotein accumulation in atherosclerotic lesions.

Overexpression of urokinase receptor in mammalian cells following administration of the in vitro transcribed encoding mRNA

The ability to overexpress physiologically important proteins in cultured mammalian cells after delivering the encoding mRNAs could have important applications for analyzing their in vivo functions. To explore the potential of this approach, urokinase-type plasminogen activator receptor (uPAR), a membrane protein extensively modified post-translationally, was selected. The uPAR-encoding mRNAs, containing different 5' and 3' untranslated regions (UTR) were tested in cultured human osteosarcoma (HOS) cells following a cationic lipid-mediated delivery. The most effective structure was the capped and polyadenylated transcript containing Xenopus beta-globin 5' and 3' UTRs. Delivering this mRNA to HOS cells resulted in a significant increase of uPAR expression in 89% of the cells, measured by flow cytometry. Using a radioligand binding assay, the increase in functional uPAR levels was found to be up eight- to 11-fold between 8 and 48 h and up three-fold at 72 h after delivery. A similar increase in uPAR levels was achievable in a number of mammalian cell lines. Surprisingly, poly(A)-tailed mRNA leading to a uPAR production highest in magnitude and duration did not demonstrate increased intracellular stability compared with other tested mRNAs. Thus, the exceptional translational performance is not likely the result of an increased mRNA half-life. These results demonstrate that, after delivery of selected mRNAs into mammalian cells, immediate and significant overexpression of a post-translationally modified protein is achievable.

Urokinase receptor-dependent upregulation of smooth muscle cell adhesion to vitronectin by urokinase

The plasminogen activator system has been implicated in the modulation of the response to vascular injury. Although urokinase-type plasminogen activator (uPA) and its receptor (uPAR) may enhance matrix degradation as well as migration and invasion by smooth muscle cells (SMCs), their roles in cell adhesion are uncertain. Therefore, we examined the ability of uPA and uPAR to modulate adhesion of cultured human vascular SMCs to various matrices. We demonstrated a dose-dependent stimulation of adhesion by single-chain uPA (scuPA) to vitronectin (maximum 1.55-fold [+/-0. 04-fold] increase, 10 nmol/L, P<0.002) but not to laminin, collagen I, or collagen IV. Baseline adhesion to vitronectin was completely inhibited by both EDTA and RGD peptide but was restored to >40% of control in the presence of scuPA (P=0.001 and 0.046, respectively). Adhesion to vitronectin was also significantly enhanced by the amino-terminal fragment of uPA (P=0.007) and two-chain, high-molecular-weight uPA (P<0.01) but not by the low-molecular-weight fragment of uPA, which lacks the receptor-binding domain. Aprotinin, a plasmin inhibitor, had no effect on baseline or scuPA-stimulated adhesion, suggesting a plasmin-independent process. Preincubation of scuPA with soluble uPAR inhibited scuPA stimulation of adhesion by 88+/-14% (P=0.01), as did pretreatment of SMCs with phosphatidylinositol-specific phospholipase C, which removes glycophosphatidylinositol-anchored proteins, including uPAR. Antibodies to both alphavbeta3 and alphavbeta5 integrin inhibited baseline adhesion but not scuPA stimulation. Finally, coating plates with scuPA alone enabled cell adhesion, which could be inhibited by both soluble uPAR and anti-uPAR antibodies. These data suggest that uPA stimulates adhesion of SMCs specifically to vitronectin and that it is mediated by an interaction with uPAR. Upregulation of both proteins after vascular injury may facilitate migration through stimulation of both matrix degradation and cell adhesion.

Rapid and phosphoinositol-dependent binding of the SWI/SNF-like BAF complex to chromatin after T lymphocyte receptor signaling

Lymphocyte activation is accompanied by visible changes in chromatin structure. We find that antigen receptor signaling induces the rapid association of the BAF complex with chromatin. PIP2, which is regulated by activation stimuli, is sufficient in vitro to target the BAF complex to chromatin, but it has no effect on related chromatin remodeling complexes containing SNF2L or hISWI. Purification and peptide sequencing of the subunits of the complex revealed beta-actin as well as a novel actin-related protein, BAF53. beta-actin and BAF53 are required for maximal ATPase activity of BRG1 and are also required with BRG1 for association of the complex with chromatin/matrix. This work indicates that membrane signals control the activity of the mammalian SWI/SNF or BAF complex and demonstrates a direct interface between signaling and chromatin regulation.

ErbB tyrosine kinases and the two neuregulin families constitute a ligand-receptor network

The recently isolated second family of neuregulins, NRG2, shares its primary receptors, ErbB-3 and ErbB-4, and induction of mammary cell differentiation with NRG1 isoforms, suggesting functional redundancy of the two growth factor families. To address this possibility, we analyzed receptor specificity of NRGs by using an engineered cellular system. The activity of isoform-specific but partly overlapping patterns of specificities that collectively activate all eight ligand-stimulatable ErbB dimers was revealed. Specifically, NRG2-alpha [corrected], like NRG1-beta [corrected], emerges as a narrow-specificity ligand, whereas NRG2-beta [corrected] is a pan-ErbB ligand that binds with different affinities to all receptor combinations, including those containing ErbB-1, but excluding homodimers of ErbB-2. The latter protein, however, displayed cooperativity with the direct NRG receptors. Apparently, signaling by all NRGs is funneled through the mitogen-activated protein kinase (MAPK). However, the duration and potency of MAPK activation depend on the identity of the stimulatory ligand-receptor ternary complex. We conclude that the NRG-ErbB network represents a complex and nonredundant machinery developed for fine-tuning of signal transduction.

Lysis of plasma clots by urokinase-soluble urokinase receptor complexes

Single-chain urokinase plasminogen activator (scuPA), the unique form secreted by cells, expresses little intrinsic plasminogen activator activity. scuPA can be activated by proteolytic cleavage to form a two-chain enzyme (tcuPA), which is susceptible to inhibition by plasminogen activator inhibitor type I (PAI-1). scuPA is also activated when it binds to its cellular receptor (uPAR), in which case the protein remains as a single chain molecule with less susceptibility to PAIs. Fibrin clots are invested with PAI-1 derived from plasma and from activated platelets. Therefore, we compared the fibrinolytic activity of complexes between scuPA and recombinant soluble uPAR (suPAR) to that of scuPA, tcuPA, and tcuPA/suPAR complexes. scuPA/suPAR complexes mediated the lysis of plasma-derived fibrin clots 14-fold more extensively than did equimolar concentrations of scuPA and threefold more extensively than did tcuPA or tcuPA/suPAR, respectively. The enhanced catalytic activity of scuPA/suPAR required that all three domains of the receptor be present, correlated with its PAI-1 resistance, was not dependent on fibrin alone, and required a plasma cofactor that was identified as IgG. Human IgG bound specifically to suPAR and scuPA/suPAR as determined by using affinity chromatography and immunoprecipitation. Plasma depleted of IgG lost most of its capacity to promote the fibrinolytic activity of scuPA/suPAR, and the activity of the complex was restored by adding plasma concentrations of purified IgG. These studies indicate that scuPA/suPAR can function as a plasminogen activator in a physiological milieu.

The mouse formin (Fmn) gene: abundant circular RNA transcripts and gene-targeted deletion analysis

BACKGROUND

Mutations in the mouse formin (Fmn) gene result in limb deformities and incompletely penetrant renal aplasia. A molecular genetic approach was taken to characterize novel circular RNAs from the Fmn gene and to understand the developmental effects of gene-targeted mutations.

MATERIALS AND METHODS

RT-PCR and ribonuclease protection analyses were done to characterize the circular RNA transcripts arising from the Fmn gene. Two lines of mice with gene-targeted deletions of specific Fmn exons, namely exon 4 or exon 5, were generated and analyzed.

RESULTS

In our analysis of formin cDNAs, we discovered a class of transcripts in which the exon order is reversed such that downstream exons are joined to the acceptor end of a specific exon that lies 5' to them in the genome. RT-PCR and ribonuclease protection analyses indicate that these transcripts are circular and are the major transcripts arising from this locus in adult brain and kidney. To gain insight into the biological function of these transcripts, we have systematically deleted the relevant exons using gene-targeted homologous recombination. The resulting mice fail to produce circular transcripts, but appear to produce normal amounts of the linear RNA isoforms from this locus. While these deficient mice have normal limbs, they display variably penetrant renal aplasia characteristic of other mutant formin alleles.

CONCLUSIONS

Our results demonstrate novel circular transcripts arising from the Fmn gene. Moreover, their high levels of expression suggest that they are not products of aberrant splicing events, but instead, may play important biological roles. Mice with gene-targeted deletions of Fmn exons 4 or 5 lack these circular transcripts and have an incompletely penetrant renal agenesis phenotype. While the biologic function of circular Fmn RNA transcripts is not entirely known, our work suggests their possible involvement in kidney development.

Regulation of casein kinase 2 by direct interaction with cell surface receptor CD5

The transmembrane protein CD5, expressed on all T cells and the B1 subset of B cells, modulates antigen receptor-mediated activation. We used the yeast two-hybrid system to identify proteins that interact with its cytoplasmic domain and play a role in CD5 proximal signaling events. We found that the beta subunit of the serine/threonine kinase casein kinase 2 (CK2) interacts specifically with the cytoplasmic domain of CD5. Co-immunoprecipitation experiments showed activation-independent association of CK2 with CD5 in human and murine B and T cell lines and murine splenocytes. The interaction of CK2 holoenzyme with CD5 is mediated by the amino terminus of the regulatory subunit beta. CK2 binds and phosphorylates CD5 at the CK2 motifs flanked by Ser459 and Ser461. Cross-linking of CD5 leads to the activation of CD5-associated CK2 in a murine B-lymphoma cell line and a human T-leukemia cell line and is independent of net recruitment of CK2 to CD5. In contrast, CK2 is not activated following cross-linking of the B cell receptor complex or the T cell receptor complex. This direct regulation of CK2 by a cell surface receptor provides a novel pathway for control of cell activation that could play a significant role in regulation of CD5-dependent antigen receptor activation in T and B cells.

Native atherosclerosis and vein graft arterialization: association with increased urokinase receptor expression in vitro and in vivo

Interaction of proteases with cell surface receptors may modulate cell adhesion, migration, invasion, and matrix degradation. Since the plasminogen activator system has been hypothesized to play a role in intimal thickening after various types of vascular injury, we first studied the expression of urokinase receptor (u-PAR) protein and mRNA by smooth muscle cells (SMC) grown in explant cultures from normal and diseased vessels. Using equilibrium binding studies with radiolabeled 125I-labeled single chain urokinase-type plasminogen activator (scu-PA), we determined that SMC cultured from atherosclerotic arteries expressed a higher maximal number of binding sites/cell (3.6 +/- 0.4 x 10(5) sites/cell vs. 2.1 +/- 0.3 x 10(5), +/- SEM, p < 0.05) with a similar affinity (Kd = 1.5 +/- 0.1 vs. 1.2 +/- 0.2 nM, p = ns). However, SMC subcultured from diseased saphenous vein grafts expressed the highest levels of u-PAR compared to SMC from normal saphenous vein (4.8 +/- 0.6 x 10(5) sites/cell vs. 1.6 +/- 0.9 x 10(5), +/- SEM, p < 0.05). Using binding studies and Northern analysis, we demonstrated a dose and time dependent upregulation of u-PAR protein and mRNA expression respectively in human SMC in response to serum stimulation. Using a rabbit specific u-PAR cDNA probe, we demonstrated a similar upregulation of u-PAR mRNA both in rabbit aortic SMC in culture in response to serum stimulation and up to a 20 fold increase in u-PAR mRNA in rabbit jugular veins in response to implantation as arterial grafts in vivo. Finally, to confirm that u-PAR mRNA is upregulated in human vessels after injury, we performed immunohistochemistry and in situ hybridization studies on coronary arteries, normal saphenous veins and saphenous veins from 10 weeks to 13 years after implantation as grafts. u-PAR mRNA was found mainly in the periadventitial microcirculation in normal veins, but was found to be upregulated in the neointima and media of thickened veins in both macrophages and smooth muscle cells. SMC near the internal elastic laminae in diseased coronary arteries appeared to express increased u-PAR mRNA. These data suggest that this increased expression of u-PAR may contribute to early lesion development.

ErbB2 expression increases the spectrum and potency of ligand-mediated signal transduction through ErbB4

Interleukin 3-dependent murine 32D cells do not detectably express members of the ErbB receptor family and do not proliferate in response to known ligands for these receptors. 32D transfectants were generated expressing human ErbB4 alone (32D.E4) or with ErbB2 (32D.E2/E4). Epidermal growth factor (EGF), neuregulin 1-beta (NRG1-beta), betacellulin (BTC), transforming growth factor-alpha (TGF-alpha), heparin binding-EGF (HB-EGF), and amphiregulin were analyzed for their ability to mediate mitogenesis in these transfectants. 32D.E4 responded mitogenically to NRG1-beta and BTC. Surprisingly, EGF also induced significant DNA synthesis and TGF-alpha was negligibly mitogenic on 32D.E4 cells, whereas HB-EGF and amphiregulin were inactive. Although coexpression of ErbB2 with ErbB4 in 32D.E2/E4 cells did not significantly alter DNA synthesis in response to NRG1-beta or BTC, it greatly enhanced mitogenesis elicited by EGF and TGF-alpha and unmasked the ability of HB-EGF to induce proliferation. EGF-related ligands that exhibited potent mitogenic activity on 32D.E2/E4 cells at low concentrations induced adherence, morphological alterations, and up-regulation of the Mac-1 integrin and FcgammaRII/III at higher concentrations. While 125I-EGF could be specifically crosslinked to both 32D.E4 and 32D.E2/E4 cells, its crosslinking capacity was greatly enhanced in the cotransfected cells. The ability of the various ligands to mediate proliferation and/or adhesion in the two transfectants correlated with their capacity to induce substrate tyrosine phosphorylation and to initiate and sustain activation of mitogen-activated protein kinase. We conclude that the ability of ErbB4 to mediate signal transduction through EGF-like ligands is broader than previously assumed and can be profoundly altered by the concomitant expression of ErbB2.