In vitro phosphorylation of von Willebrand factor by FAM20c enhances its ability to support platelet adhesion

Essentials Platelet adhesion to von Willebrand factor (VWF) is critical for hemostasis and thrombosis. Whether VWF can undergo phosphorylation is unknown. Family with sequence similarity 20 kinase phosphorylates VWF A2 domain at S1517 and S1613. Phosphorylation of VWF and VWF A1A2A3 domain at S1613 enhances platelet adhesion. SUMMARY: Background von Willebrand factor (VWF) mediates platelet adhesion and contributes to hemostasis at sites of vascular injury as well as to arterial thrombosis. The A1A2A3 domains of VWF contain important sites that differentially participate in supporting platelet adhesion. FAM20c (family with sequence similarity 20, member C) has emerged as a serine/threonine kinase, which phosphorylates extracellular proteins containing the S-X-E/pS motifs that are also found within the VWF A domains. This is of interest because we and others have shown that structural modifications within these A domains influence the ability of VWF to support platelet adhesion. Objective We assessed if VWF A domains can be phosphorylated and the functional consequence of phosphorylated VWF. Results Here, we show that FAM20c phosphorylated purified plasma VWF, VWF A1A2A3 protein, isolated A2 domain, but not A1 and A3 domain proteins, in vitro. FAM20c phosphorylated the isolated A2 domain at S1517 and S1613 within the S-X-E recognition motif, with S1613 being the major phosphorylation site. Mass spectrometry analysis of purified plasma VWF from healthy donors revealed several phosphorylation sites, including the S1613 in the A2 domain. VWF A1A2A3 domain protein phosphorylated at S1613 promoted stable platelet adhesion and microthrombi at high shear stress. Lastly, under high shear stress VWF treated with FAM20c and ATP robustly supported platelet adhesion, compared to VWF treated with FAM20c in the absence of ATP. Conclusion These outcomes indicate that VWF can be phosphorylated by FAM20c in vitro, and this novel post-translational modification enhances the adhesiveness of VWF to platelets.

Aurora kinase B dependent phosphorylation of 53BP1 is required for resolving merotelic kinetochore-microtubule attachment errors during mitosis

Defects in resolving kinetochore-microtubule attachment mistakes during mitosis is linked to chromosome instability associated with carcinogenesis as well as resistance to cancer therapy. Here we report for the first time that tumor suppressor p53-binding protein 1 (53BP1) is phosphorylated at serine 1342 (S1342) by Aurora kinase B both in vitro and in human cells, which is required for optimal recruitment of 53BP1 at kinetochores. Furthermore, 53BP1 staining normally localized on the outer kinetochore, extended to the whole kinetochore when it is merotelically-attached, in concert with mitotic centromere-associated kinesin. Kinetochore-binding of pS1342-53BP1 is essential for efficient resolving of merotelic attachment, a spontaneous kinetochore-microtubule connection error that usually causes aneuploidy. Consistently, loss of 53BP1 results in significant increase in lagging chromosome events, micronuclei formation and aneuploidy, due to the unresolved merotely in both cancer and primary cells, which is prevented by ectopic wild type 53BP1 but not by the nonphophorylable S1342A mutant. We thus document a novel DNA damage-independent function of 53BP1 in maintaining faithful chromosome segregation during mitosis.

Proteomic Profiling of a Biomimetic Drug Delivery Platform

Current delivery platforms are typically designed for prolonged circulation that favors superior accumulation of the payload in the targeted tissue. The design of efficient surface modifications determines both a longer circulation time and targeting abilities of particles. The optimization of synthesis protocols to efficiently combine targeting molecules and elements that allow for an increased circulation time can be challenging and almost impossible when several functional elements are needed. On the other hand, in the last decade, the development of bioinspired technologies was proposed as a new approach with which to increase particle safety, biocompatibility and targeting, while maintaining the synthesis protocols simple and reproducible. Recently, we developed a new drug delivery system inspired by the biology of immune cells called leukolike vector (LLV) and formed by a nanoporous silicon core and a shell derived from the leucocyte cell membrane. The goal of this study is to investigate the protein content of the LLV. Here we report the proteomic profiling of the LLV and demonstrate that our approach can be used to modify the surface of synthetic particles with more than 150 leukocyte membrane associated proteins that determine particle safety, circulation time and targeting abilities towards inflamed endothelium.

Expression and purification of an engineered, yeast-expressed Leishmania donovani nucleoside hydrolase with immunogenic properties

Leishmania donovani is the major cause of visceral leishmaniasis (kala-azar), now recognized as the parasitic disease with the highest level of mortality second only to malaria. No human vaccine is currently available. A 36 kDa L. donovani nucleoside hydrolase (LdNH36) surface protein has been previously identified as a potential vaccine candidate antigen. Here we present data on the expression of LdNH36 in Pichia pastoris and its purification at the 20 L scale to establish suitability for future pilot scale manufacturing. To improve efficiency of process development and ensure reproducibility, 4 N-linked glycosylation sites shown to contribute to heterogeneous high-mannose glycosylation were mutated to glutamine residues. The mutant LdNH36 (LdNH36-dg2) was expressed and purified to homogeneity. Size exclusion chromatography and light scattering demonstrated that LdNH36-dg2 existed as a tetramer in solution, similar to the wild-type recombinant L. major nucleoside hydrolase. The amino acid mutations do not affect the tetrameric interface as confirmed by theoretical modeling, and the mutated amino acids are located outside the major immunogenic domain. Immunogenic properties of the LdNH36-dg2 recombinant protein were evaluated in BALB/c mice using formulations that included a synthetic CpG oligodeoxynucleotide, together with a microparticle delivery platform (poly(lactic-co-glycolic acid)). Mice exhibited high levels of IgG1, IgG2a, and IgG2b antibodies that were reactive to both LdNH36-dg2 and LdNH36 wild-type. While the point mutations did affect the hydrolase activity of the enzyme, the IgG antibodies elicited by LdNH36-dg2 were shown to inhibit the hydrolase activity of the wild-type LdNH36. The results indicate that LdNH36-dg2 as expressed in and purified from P. pastoris is suitable for further scale-up, manufacturing, and testing in support of future first-in-humans phase 1 clinical trials.

Optimization and revision of the production process of the Necator americanus glutathione S-transferase 1 (Na-GST-1), the lead hookworm vaccine recombinant protein candidate

Infection by the human hookworm Necator americanus is a leading cause of anemia and disability in the developing countries of Africa, Asia, and the Americas. In order to prevent childhood hookworm disease in resource poor settings, a recombinant vaccine is under development by the Sabin Vaccine Institute and Texas Children’s Hospital Center for Vaccine Development, a Product Development Partnership (PDP). Previously, we reported on the expression and purification of a highly promising hookworm vaccine candidate, Na-GST-1, an N. americanus glutathione s-transferase expressed in Pichia pastoris (yeast), which led to production of 1.5 g of 95% pure recombinant protein at a 20L scale.^{1, 2, 3} This yield and purity of Na-GST-1 was sufficient for early pilot manufacturing and initial phase 1 clinical testing. However, based on the number of doses which would be required to allow mass vaccination and a potential goal to deliver a vaccine as inexpensively as possible, a higher yield of expression of the recombinant antigen at the lowest possible cost is highly desirable. Here we report on modifications to the fermentation (upstream process) of the antigen expressed in P. pastoris, and to the purification (downstream process) of the recombinant protein that allowed for a 2–3-fold improvement in the final yield of Na-GST-1 purified protein. The major improvements included upstream process changes such as the addition of a sorbitol pulse and co-feed during methanol induction as well as an extension of the induction stage to approximately 96 hours; downstream process changes included modifying the UFDF to flat sheet with a 10 kDa Molecular Weight cut-off (MWCO), adjusting the capacity of an ion-exchange chromatography step utilizing a gradient elution as opposed to the original step elution, and altering the hydrophobic interaction chromatography conditions. The full process, as well as the purity and stability profiles of the target Na-GST-1, and its formulation on Alhydrogel^®, is described.

Performance and System Validation of a New Cellular-Enabled Blood Glucose Monitoring System Using a New Standard Reference Measurement Procedure of Isotope Dilution UPLC-MRM Mass Spectrometry

BACKGROUND

We evaluated the accuracy, precision, and linearity of the In Touch blood glucose monitoring system (BGMS), a new color touch screen and cellular-enabled blood glucose meter, using a new rapid, highly precise and accurate (13)C6 isotope-dilution liquid chromatography-mass spectrometry method (IDLC-MS).

METHODS

Blood glucose measurements from the In Touch BGMS were referenced to a validated UPLC-MRM standard reference measurement procedure previously shown to be highly accurate and precise. Readings from the In Touch BGMS were taken over the blood glucose range of 24-640 mg/dL using 12 concentrations of blood glucose. Ten In Touch BGMS and 3 lots of test strips were used with 10 replicates at each concentration. A lay user study was also performed to assess the ease of use.

RESULTS

At blood glucose concentrations <75 mg/dL 100% of the measurements are within ±8 mg/dL from the true reference standard; at blood glucose levels >75 mg/dL 100% of the measurements are within ±15% of the true reference standard. 100% of the results are within category A of the consensus grid. Within-run precision show CV < 3.72% between 24-50 mg/dL and CV<2.22% between 500 and 600 mg/dL. The results show that the In Touch meter exceeds the minimum criteria of both the ISO 15197:2003 and ISO 15197:2013 standards. The results from a user panel show that 100% of the respondents reported that the color touch screen, with its graphic user interface (GUI), is well labeled and easy to navigate.

CONCLUSIONS

To our knowledge this is the first touch screen glucose meter and the first study where accuracy of a new BGMS has been measured against a true primary reference standard, namely IDLC-MS.

Development and Validation of a Rapid (13)C6-Glucose Isotope Dilution UPLC-MRM Mass Spectrometry Method for Use in Determining System Accuracy and Performance of Blood Glucose Monitoring Devices

BACKGROUND

There is currently considerable discussion about the accuracy of blood glucose concentrations determined by personal blood glucose monitoring systems (BGMS). To date, the FDA has allowed new BGMS to demonstrate accuracy in reference to other glucose measurement systems that use the same or similar enzymatic-based methods to determine glucose concentration. These types of reference measurement procedures are only comparative in nature and are subject to the same potential sources of error in measurement and system perturbations as the device under evaluation. It would be ideal to have a completely orthogonal primary method that could serve as a true standard reference measurement procedure for establishing the accuracy of new BGMS.

METHODS

An isotope-dilution liquid chromatography/mass spectrometry (ID-UPLC-MRM) assay was developed using (13)C6-glucose as a stable isotope analogue to specifically measure glucose concentration in human plasma, and validated for use against NIST standard reference materials, and against fresh isolates of whole blood and plasma into which exogenous glucose had been spiked. Assay performance was quantified to NIST-traceable dry weight measures for both glucose and (13)C6-glucose.

RESULTS

The newly developed assay method was shown to be rapid, highly specific, sensitive, accurate, and precise for measuring plasma glucose levels. The assay displayed sufficient dynamic range and linearity to measure across the range of both normal and diabetic blood glucose levels. Assay performance was measured to within the same uncertainty levels (<1%) as the NIST definitive method for glucose measurement in human serum.

CONCLUSIONS

The newly developed ID UPLC-MRM assay can serve as a validated reference measurement procedure to which new BGMS can be assessed for glucose measurement performance.

Thyroid hormone induction of human cholesterol 7 alpha-hydroxylase (Cyp7a1) in vitro

Thyroid hormone (TH) modulates serum cholesterol by acting on TH receptor β1 (TRβ1) in liver to regulate metabolic gene sets. In rodents, one important TH regulated step involves induction of Cyp7a1, an enzyme in the cytochrome P450 family, which enhances cholesterol to bile acid conversion and plays a crucial role in regulation of serum cholesterol levels. Current models suggest, however, that Cyp7a1 has lost the capacity to respond to THs in humans. We were prompted to re-examine TH effects on cholesterol metabolic genes in human liver cells by a recent study of a synthetic TH mimetic which showed that serum cholesterol reductions were accompanied by increases in a marker for bile acid synthesis in humans. Here, we show that TH effects upon cholesterol metabolic genes are almost identical in mouse liver, mouse and human liver primary cells and human hepatocyte cell lines. Moreover, Cyp7a1 is a direct TR target gene that responds to physiologic TR levels through a set of distinct response elements in its promoter. These findings suggest that THs regulate cholesterol to bile acid conversion in similar ways in humans and rodent experimental models and that manipulation of hormone signaling pathways could provide a strategy to enhance Cyp7a1 activity in human patients.

Characterization of p38 MAPK isoforms for drug resistance study using systems biology approach

MOTIVATION

p38 mitogen-activated protein kinase activation plays an important role in resistance to chemotherapeutic cytotoxic drugs in treating multiple myeloma (MM). However, how the p38 mitogen-activated protein kinase signaling pathway is involved in drug resistance, in particular the roles that the various p38 isoforms play, remains largely unknown.

METHOD

To explore the underlying mechanisms, we developed a novel systems biology approach by integrating liquid chromatography-mass spectrometry and reverse phase protein array data from human MM cell lines with computational pathway models in which the unknown parameters were inferred using a proposed novel algorithm called modularized factor graph.

RESULTS

New mechanisms predicted by our models suggest that combined activation of various p38 isoforms may result in drug resistance in MM via regulating the related pathways including extracellular signal-regulated kinase (ERK) pathway and NFкB pathway. ERK pathway regulating cell growth is synergistically regulated by p38δ isoform, whereas nuclear factor kappa B (NFкB) pathway regulating cell apoptosis is synergistically regulated by p38α isoform. This finding that p38δ isoform promotes the phosphorylation of ERK1/2 in MM cells treated with bortezomib was validated by western blotting. Based on the predicted mechanisms, we further screened drug combinations in silico and found that a promising drug combination targeting ERK1/2 and NFκB might reduce the effects of drug resistance in MM cells. This study provides a framework of a systems biology approach to studying drug resistance and drug combination selection.

AVAILABILITY AND IMPLEMENTATION

RPPA experimental Data and Matlab source codes of modularized factor graph for parameter estimation are freely available online at http://ctsb.is.wfubmc.edu/publications/modularized-factor-graph.php.

A peptide-free, liposome-based oligosaccharide vaccine, adjuvanted with a natural killer T cell antigen, generates robust antibody responses in vivo

Due to the prevalence of oligo- and polysaccharides on the surfaces of pathogenic organisms, carbohydrates are primary targets for recognition by antibodies generated by the immune systems of higher organisms. Consequently, substantial effort has been expended in efforts to develop vaccines based on carbohydrate epitopes. Typical approaches involve multivalent presentation of carbohydrate targets on antigenic peptides or proteins, which often involve substantial synthetic commitments and/or vaccines that are heterogeneous and difficult to characterize. We have developed a simple, liposome-based approach to generate multivalent carbohydrate vaccines, and in place of an antigenic peptide or protein, we have used a potent antigen for natural killer T cells. This vaccine, based on the Streptococcus pneumoniae serotype 14 polysaccharide, gave a response superior to that from a clinically used vaccine (Prevnar). The dependence of this response on liposome formation was demonstrated by comparison to a simple mixture of the oligosaccharide and the natural killer T cell adjuvant. The importance of the strength of the adjuvant was observed by use of a potent synthetic adjuvant and a weaker, bacterial derived glycolipid adjuvant. These results demonstrate the effectiveness of this novel and relatively simple means of generating carbohydrate-based vaccines.

Loss of LKB1 and PTEN tumor suppressor genes in the ovarian surface epithelium induces papillary serous ovarian cancer

Epithelial ovarian cancer presents mostly with serous, endometrioid or mucinous histology but is treated as a single disease. The development of histotype-specific therapy has been challenging because of the relative lack of studies attributing disrupted pathways to a distinct histotype differentiation. mTOR activation is frequently associated with poor prognosis in serous ovarian cancer, which is the most common and most deadly histotype. However, the mechanisms dysregulating mTOR in the pathogenesis of ovarian cancer are unknown. We detected copy number loss and correlated lower expression levels of LKB1, TSC1, TSC2 and PTEN tumor suppressor genes for upstream regulators of mTOR activity in up to 80% in primary ovarian serous tumor databases, with LKB1 allelic loss-predominant. Reduced LKB1 protein was usually associated with increased mTOR activity in both serous ovarian cancer cell lines and primary tumors. Conditional deletion of Lkb1 in murine ovarian surface epithelial (OSE) cells caused papillary hyperplasia and shedding but not tumors. Simultaneous deletion of Lkb1 and Pten, however, led to development of high-grade ovarian serous histotype tumors with 100% penetrance that expressed WT1, ERα, PAX8, TP53 and cytokeratin 8, typical markers used in the differential diagnosis of serous ovarian cancer. Neither hysterectomy nor salpingectomy interfered with progression of ovarian tumorigenesis, suggesting that neither uterine nor Fallopian tube epithelial cells were contributing to tumorigenesis. These results implicate LKB1 loss in the OSE in the pathogenesis of serous ovarian cancer and provide a compelling rationale for investigating the therapeutic potential of targeting LKB1 signaling in patients with this deadly disease.

Activation of the ATM-Snail pathway promotes breast cancer metastasis

The DNA damage response (DDR) is critical for the maintenance of genetic stability and serves as an anti-cancer barrier during early tumorigenesis. However, the role of the DDR in tumor progression and metastasis is less known. Here, we demonstrate that the ATM kinase, one of the critical DDR elements, is hyperactive in late stage breast tumor tissues with lymph-node metastasis and this hyperactivity correlates with elevated expression of the epithelial-mesenchymal transition marker, Snail. At the molecular level, we demonstrate that ATM regulates Snail stabilization by phosphorylation on Serine-100. Using mass spectrometry, we identified HSP90 as a critical binding protein of Snail in response to DNA damage. HSP90 binds to and stabilizes phosphorylated Snail. We further provide in vitro and in vivo evidence that activation of ATM-mediated Snail phosphorylation promotes tumor invasion and metastasis. Finally, we demonstrate that Snail Serine-100 phosphorylation is elevated in breast cancer tissues with lymph-node metastasis, indicating clinical significance of the ATM-Snail pathway. Together, our findings provide strong evidence that the ATM-Snail pathway promotes tumor metastasis, highlighting a previously undescribed role of the DDR in tumor invasion and metastasis.

Genome wide DNA copy number analysis of serous type ovarian carcinomas identifies genetic markers predictive of clinical outcome

Ovarian cancer is the fifth leading cause of cancer death in women. Ovarian cancers display a high degree of complex genetic alterations involving many oncogenes and tumor suppressor genes. Analysis of the association between genetic alterations and clinical endpoints such as survival will lead to improved patient management via genetic stratification of patients into clinically relevant subgroups. In this study, we aim to define subgroups of high-grade serous ovarian carcinomas that differ with respect to prognosis and overall survival. Genome-wide DNA copy number alterations (CNAs) were measured in 72 clinically annotated, high-grade serous tumors using high-resolution oligonucleotide arrays. Two clinically annotated, independent cohorts were used for validation. Unsupervised hierarchical clustering of copy number data derived from the 72 patient cohort resulted in two clusters with significant difference in progression free survival (PFS) and a marginal difference in overall survival (OS). GISTIC analysis of the two clusters identified altered regions unique to each cluster. Supervised clustering of two independent large cohorts of high-grade serous tumors using the classification scheme derived from the two initial clusters validated our results and identified 8 genomic regions that are distinctly different among the subgroups. These 8 regions map to 8p21.3, 8p23.2, 12p12.1, 17p11.2, 17p12, 19q12, 20q11.21 and 20q13.12; and harbor potential oncogenes and tumor suppressor genes that are likely to be involved in the pathogenesis of ovarian carcinoma. We have identified a set of genetic alterations that could be used for stratification of high-grade serous tumors into clinically relevant treatment subgroups.

Genome-wide comparison of paired fresh frozen and formalin-fixed paraffin-embedded gliomas by custom BAC and oligonucleotide array comparative genomic hybridization: facilitating analysis of archival gliomas

Array comparative genomic hybridization (aCGH) is a powerful tool for detecting DNA copy number alterations (CNA). Because diffuse malignant gliomas are often sampled by small biopsies, formalin-fixed paraffin-embedded (FFPE) blocks are often the only tissue available for genetic analysis; FFPE tissues are also needed to study the intratumoral heterogeneity that characterizes these neoplasms. In this paper, we present a combination of evaluations and technical advances that provide strong support for the ready use of oligonucleotide aCGH on FFPE diffuse gliomas. We first compared aCGH using bacterial artificial chromosome (BAC) arrays in 45 paired frozen and FFPE gliomas, and demonstrate a high concordance rate between FFPE and frozen DNA in an individual clone-level analysis of sensitivity and specificity, assuring that under certain array conditions, frozen and FFPE DNA can perform nearly identically. However, because oligonucleotide arrays offer advantages to BAC arrays in genomic coverage and practical availability, we next developed a method of labeling DNA from FFPE tissue that allows efficient hybridization to oligonucleotide arrays. To demonstrate utility in FFPE tissues, we applied this approach to biphasic anaplastic oligoastrocytomas and demonstrate CNA differences between DNA obtained from the two components. Therefore, BAC and oligonucleotide aCGH can be sensitive and specific tools for detecting CNAs in FFPE DNA, and novel labeling techniques enable the routine use of oligonucleotide arrays for FFPE DNA. In combination, these advances should facilitate genome-wide analysis of rare, small and/or histologically heterogeneous gliomas from FFPE tissues.

Clinical value of plasma hepatocyte growth factor measurement for the diagnosis of periampullary cancer and prognosis after pancreaticoduodenectomy

BACKGROUND

Previous studies suggest that serum hepatocyte growth factor (HGF) level may be a useful diagnostic and prognostic biomarker for various tumors. We investigated the utility of plasma HGF level measurements in diagnosing periampullary cancer (PAC).

METHODS

Of the patients enrolled in this pilot study (n = 118), 57 had PAC, 21 had benign pancreatic tumor (BPT), 20 had chronic pancreatitis (CP), and 20 were healthy controls. Plasma HGF was measured with ELISA kits. It was measured again at 10 days and 1, 2, 3, 6, and 12 months after pancreaticoduodenectomy (PD).

RESULTS

Plasma HGF levels were significantly higher in PAC patients than in BPT patients, CP patients, or healthy controls. When a cutoff value of 1,120  pg/ml was used, 48/57 (84%) patients with PAC were positive for elevated HGF, but only 6/20 (30%) of patients with CP and none of the controls or patients with BPT were positive for elevated HGF. After PD, HGF levels were significantly elevated at day 10.

CONCLUSIONS

Plasma HGF level discriminates well between PAC and other, benign diseases. Therefore, HGF measurement could be a useful addition to the existing array of diagnostic tools for PAC pancreatic cancer. The higher postoperative value may reflect the stress of surgery.

Chemical composition-oriented receptor selectivity of L5, a naturally occurring atherogenic low-density lipoprotein

Anion-exchange chromatography resolves human plasma low-density lipoprotein (LDL) into 5 subfractions, with increasing negative surface charge in the direction of L1 to L5. Unlike the harmless L1 to L4, the exclusively atherogenic L5 is rejected by the normal LDL receptor (LDLR) but endocytosed into vascular endothelial cells through the lectin-like oxidized LDL receptor-1 (LOX-1). Analysis with SDS-PAGE and 2-dimensional electrophoresis showed that the protein framework of L1 was composed mainly of apolipoprotein (apo) B100, with an isoelectric point (pI) of 6.620. There was a progressively increased association of additional proteins, including apoE (pI 5.5), apoAI (pI 5.4), apoCIII (pI 5.1), and apo(a) (pI 5.5), from L1 to L5. LC/MSE was used to quantify protein distribution in all subfractions. On the basis of weight percentages, L1 contained 99% apoB-100 and trace amounts of other proteins. In contrast, L5 contained 60% apoB100 and substantially increased amounts of apo(a), apoE, apoAI, and apoCIII. The compositional characteristics contribute to L5's electronegativity, rendering it unrecognizable by LDLR. LOX-1, which has a high affinity for negatively charged ligands, is known to mediate the signaling of proinflammatory cytokines. Thus, the chemical composition-oriented receptor selectivity hinders normal metabolism of L5, enhancing its atherogenicity through abnormal receptors, such as LOX-1.

Developmental regulation of mitochondrial biogenesis and function in the mouse mammary gland during a prolonged lactation cycle

The regulation of mitochondrial biogenesis and function in the lactating mammary cell is poorly understood. The goal of this study was to use proteomics to relate temporal changes in mammary cell mitochondrial function during lactation to changes in the proteins that make up this organelle. The hypothesis tested was that changes in mammary cell mitochondrial biogenesis and function during lactation would be accounted for by coordinated changes in the proteins of the electron transport chain and that some of these proteins might be linked by their expression patterns to PPARGC1α and AMP kinase. The mitochondrial proteome was studied along with markers of mitochondrial biogenesis and function in mammary tissue collected from mice over the course of a single prolonged lactation cycle. Mammary tissue concentrations of AMP and ADP were increased (P < 0.05) during early lactation and then declined with prolonged lactation. Similar changes were also observed for mitochondrial ATP synthesis activity, mitochondrial mass and DNA copy number. Analysis of the mammary cell mitochondrial proteome identified 244 unique proteins. Of these, only two proteins of the electron transport chain were found to increase during early lactation. In contrast, coordinated changes in numerous electron transport chain proteins were observed both during mid- and late lactation. There were six proteins that could be directly linked to PPARGC1α through network analysis. Abundance of PPARGC-1α and phosphorylation of AMP kinase was highest on day 2 postpartum. The results suggest that the increases in mammary mitochondria ATP synthesis activity during early lactation results from changes in only a limited number proteins. In addition, decreases in a handful of proteins linked to lipid oxidation could be temporally linked to decreases in PPARGC1α and phospho-AMP kinase suggesting potential roles for these proteins in coordinating mammary gland metabolism during early lactation.

Genomic profiling distinguishes familial multiple and sporadic multiple meningiomas

Background

Meningiomas may occur either as familial tumors in two distinct disorders, familial multiple meningioma and neurofibromatosis 2 (NF2), or sporadically, as either single or multiple tumors in individuals with no family history. Meningiomas in NF2 and approximately 60% of sporadic meningiomas involve inactivation of the NF2 locus, encoding the tumor suppressor merlin on chromosome 22q. This study was undertaken to establish whether genomic profiling could distinguish familial multiple meningiomas from sporadic solitary and sporadic multiple meningiomas.

Methods

We compared 73 meningiomas presenting as sporadic solitary (64), sporadic multiple (5) and familial multiple (4) tumors using genomic profiling by array comparative genomic hybridization (array CGH).

Results

Sporadic solitary meningiomas revealed genomic rearrangements consistent with at least two mechanisms of tumor initiation, as unsupervised cluster analysis readily distinguished tumors with chromosome 22 deletion (associated with loss of the NF2 tumor suppressor) from those without chromosome 22 deletion. Whereas sporadic meningiomas without chromosome 22 loss exhibited fewer chromosomal imbalance events overall, tumors with chromosome 22 deletion further clustered into two major groups that largely, though not perfectly, matched with their benign (WHO Grade I) or advanced (WHO Grades II and III) histological grade, with the latter exhibiting a significantly greater degree of genomic imbalance (P < 0.001). Sporadic multiple meningiomas showed a frequency of genomic imbalance events comparable to the atypical grade solitary tumors. By contrast, familial multiple meningiomas displayed no imbalances, supporting a distinct mechanism for the origin for these tumors.

Conclusion

Genomic profiling can provide an unbiased adjunct to traditional meningioma classification and provides a basis for exploring the different genetic underpinnings of tumor initiation and progression. Most importantly, the striking difference observed between sporadic and familial multiple meningiomas indicates that genomic profiling can provide valuable information for differential diagnosis of subjects with multiple meningiomas and for considering the risk for tumor occurrence in their family members.

High-dose methotrexate for elderly patients with primary CNS lymphoma

The introduction of methotrexate (MTX)-based chemotherapy has improved median survival for patients with primary CNS lymphoma (PCNSL). Older age is a negative prognostic marker in patients with PCNSL and may increase the likelihood of MTX toxicity. We studied the response and adverse effects of intravenous high-dose MTX in patients who were 70 or more years of age at the time of diagnosis. We identified 31 patients at our institution diagnosed with PCNSL at age > or =70 years (median, 74 years) who were treated with high-dose MTX (3.5-8 g/m(2)) as initial therapy from 1992 through 2006. The best response to MTX was determined by contrast-enhanced MRI. Toxicity was analyzed by chart review. These 31 patients received a total of 303 cycles of MTX (median, eight cycles per patient). Overall, 87.9% of the cycles required dose reduction because of impaired creatinine clearance. In 30 evaluable patients, the overall radiographic response rate was 96.7%, with 18 complete responses (60%) and 11 partial responses (36.7%). Progression-free survival and overall survival were 7.1 months and 37 months, respectively. Grade I-IV toxicities were observed in 27 of 31 patients and included gastrointestinal disturbances in 58% (3.2% grade III), hematological complications in 80.6% (6.5% grade III), and renal toxicity in 29% (0% grade III/IV). High-dose MTX is associated with a high proportion of radiographic responses and a low proportion of grade III/IV toxicity in patients 70 or more years of age. High-dose MTX should be considered as a feasible treatment option in elderly patients with PCNSL.

Role of NonO-histone interaction in TNFalpha-suppressed prolyl-4-hydroxylase alpha1

Inflammation is a key process in cardiovascular diseases. The extracellular matrix (ECM) of the vasculature is a major target of inflammatory cytokines, and TNFalpha regulates ECM metabolism by affecting collagen production. In this study, we have examined the pathways mediating TNFalpha-induced suppression of prolyl-4 hydroxylase alpha1 (P4Halpha1), the rate-limiting isoform of P4H responsible for procollagen hydroxylation, maturation, and organization. Using human aortic smooth muscle cells, we found that TNFalpha activated the MKK4-JNK1 pathway, which induced histone (H) 4 lysine 12 acetylation within the TNFalpha response element in the P4Halpha1 promoter. The acetylated-H4 then recruited a transcription factor, NonO, which, in turn, recruited HDACs and induced H3 lysine 9 deacetylation, thereby inhibiting transcription of the P4Halpha1 promoter. Furthermore, we found that TNFalpha oxidized DJ-1, which may be essential for the NonO-P4Halpha1 interaction because treatment with gene specific siRNA to knockout DJ-1 eliminated the TNFalpha-induced NonO-P4Halpha1 interaction and its suppression. Our findings may be relevant to aortic aneurysm and dissection and the stability of the fibrous cap of atherosclerotic plaque in which collagen metabolism is important in arterial remodeling. Defining this cytokine-mediated regulatory pathway may provide novel molecular targets for therapeutic intervention in preventing plaque rupture and acute coronary occlusion.

Water-soluble fullerene (C60) derivatives as nonviral gene-delivery vectors

A new class of water-soluble C60 transfecting agents has been prepared using Hirsch-Bingel chemistry and assessed for their ability to act as gene-delivery vectors in vitro. In an effort to elucidate the relationship between the hydrophobicity of the fullerene core, the hydrophilicity of the water-solubilizing groups, and the overall charge state of the C60 vectors in gene delivery and expression, several different C60 derivatives were synthesized to yield either positively charged, negatively charged, or neutral chemical functionalities under physiological conditions. These fullerene derivatives were then tested for their ability to transfect cells grown in culture with DNA carrying the green fluorescent protein (GFP) reporter gene. Statistically significant expression of GFP was observed for all forms of the C60 derivatives when used as DNA vectors and compared to the ability of naked DNA alone to transfect cells. However, efficient in vitro transfection was only achieved with the two positively charged C60 derivatives, namely, an octa-amino derivatized C60 and a dodeca-amino derivatized C60 vector. All C60 vectors showed an increase in toxicity in a dose-dependent manner. Increased levels of cellular toxicity were observed for positively charged C60 vectors relative to the negatively charged and neutral vectors. Structural analyses using dynamic light scattering and optical microscopy offered further insights into possible correlations between the various derivatized C60 compounds, the C60 vector/DNA complexes, their physical attributes (aggregation, charge) and their transfection efficiencies. Recently, similar Gd@C60-based compounds have demonstrated potential as advanced contrast agents for magnetic resonance imaging (MRI). Thus, the successful demonstration of intracellular DNA uptake, intracellular transport, and gene expression from DNA using C60 vectors suggests the possibility of developing analogous Gd@C60-based vectors to serve simultaneously as both therapeutic and diagnostic agents.

Electronegative LDL circulating in smokers impairs endothelial progenitor cell differentiation by inhibiting Akt phosphorylation via LOX-1

Endothelial progenitor cells (EPCs), important for endothelial regeneration and vasculogenesis, are reduced by cigarette smoking. To elucidate the mechanisms, we examined the effects of electronegative LDL, circulating in chronic smokers, on EPC differentiation. Using ion-exchange chromatography, we purified smoker LDL into five subfractions, L1-L5. In matched, nonsmoking healthy subjects, L5, the most electronegative subfraction, was either absent or scanty. Sustained L5 treatment inhibited CD31 and KDR expression and EPC differentiation, whereas L1-L4 had no effect. L5 also inhibited telomerase activity to accelerate EPC senescence in correlation with reduced Akt phosphorylation. Transfection of day 3 EPCs with dominant negative Akt constructs inhibited CD31 and KDR expression, stalled EPC differentiation, and promoted early senescence. In contrast, transfection with constitutively active Akt rendered the EPCs resistant to L5, allowing normal maturation. L5 upregulated the lectin-like oxidized low density lipoprotein receptor 1 (LOX-1), and pretreatment of EPCs with TS20, a LOX-1-neutralizing antibody, blocked internalization of L5 by EPCs and prevented L5-mediated inhibition of EPC differentiation. Mixing L5 with L1 to physiological L5/L1 ratios did not attenuate L5's effects. These findings suggest that cigarette smoking is associated with the formation of L5, which inhibits EPC differentiation by impairing Akt phosphorylation via the LOX-1 receptor.

Proteomic identification of in vivo substrates for matrix metalloproteinases 2 and 9 reveals a mechanism for resolution of inflammation

Clearance of allergic inflammatory cells from the lung through matrix metalloproteinases (MMPs) is necessary to prevent lethal asphyxiation, but mechanistic insight into this essential homeostatic process is lacking. In this study, we have used a proteomics approach to determine how MMPs promote egression of lung inflammatory cells through the airway. MMP2- and MMP9-dependent cleavage of individual Th2 chemokines modulated their chemotactic activity; however, the net effect of complementing bronchoalveolar lavage fluid of allergen-challenged MMP2(-/-)/MMP9(-/-) mice with active MMP2 and MMP9 was to markedly enhance its overall chemotactic activity. In the bronchoalveolar fluid of MMP2(-/-)/MMP9(-/-) allergic mice, we identified several chemotactic molecules that possessed putative MMP2 and MMP9 cleavage sites and were present as higher molecular mass species. In vitro cleavage assays and mass spectroscopy confirmed that three of the identified proteins, Ym1, S100A8, and S100A9, were substrates of MMP2, MMP9, or both. Function-blocking Abs to S100 proteins significantly altered allergic inflammatory cell migration into the alveolar space. Thus, an important effect of MMPs is to differentially modify chemotactic bioactivity through proteolytic processing of proteins present in the airway. These findings provide a molecular mechanism to explain the enhanced clearance of lung inflammatory cells through the airway and reveal a novel approach to target new therapies for asthma.

Glioma test array for use with formalin-fixed, paraffin-embedded tissue: array comparative genomic hybridization correlates with loss of heterozygosity and fluorescence in situ hybridization

Array-based comparative genomic hybridization (aCGH) is a powerful, high-throughput tool for whole genome analysis. Until recently, aCGH could only be reproducibly performed on frozen tissue samples and with significant tissue amounts. For brain tumors however, paraffin-embedded tissue blocks from small stereotactic biopsies may be the only tissue routinely available. The development of methods to analyze formalin-fixed, paraffin-embedded (FFPE) material therefore has the potential to impact molecular diagnosis in a significant way. To this end, we constructed a BAC array representing chromosomes 1, 7, 19, and X because 1p/19q deletion and EGFR gene amplification provide clinically relevant information for glioma diagnosis. We also optimized a two-step labeling procedure using an amine-modified nucleotide for generating aCGH probes. Using this approach, we analyzed a series of 28 FFPE oligodendroglial tumors for alterations of chromosomes 1, 7, and 19. We also independently assayed these tumors for 1p/19q deletion by fluorescence in situ hybridization and by loss of heterozygosity analyses. The concordance between aCGH, standard loss of heterozygosity and fluorescence in situ hybridization was nearly 100% for the chromosomes analyzed. These results suggest that aCGH could offer an improved molecular diagnostic approach for gliomas because of its ability to detect clinically relevant molecular alterations in small FFPE specimens.

A pseudolikelihood approach for simultaneous analysis of array comparative genomic hybridizations

DNA sequence copy number has been shown to be associated with cancer development and progression. Array-based comparative genomic hybridization (aCGH) is a recent development that seeks to identify the copy number ratio at large numbers of markers across the genome. Due to experimental and biological variations across chromosomes and hybridizations, current methods are limited to analyses of single chromosomes. We propose a more powerful approach that borrows strength across chromosomes and hybridizations. We assume a Gaussian mixture model, with a hidden Markov dependence structure and with random effects to allow for intertumoral variation, as well as intratumoral clonal variation. For ease of computation, we base estimation on a pseudolikelihood function. The method produces quantitative assessments of the likelihood of genetic alterations at each clone, along with a graphical display for simple visual interpretation. We assess the characteristics of the method through simulation studies and analysis of a brain tumor aCGH data set. We show that the pseudolikelihood approach is superior to existing methods both in detecting small regions of copy number alteration and in accurately classifying regions of change when intratumoral clonal variation is present. Software for this approach is available at http://www.biostat.harvard.edu/ approximately betensky/papers.html.

Nuclear accumulation of exogenous DNA fragments in viable cells mediated by FGF-2 and DNA release upon cellular injury

We and others have previously shown that basic fibroblast growth factor (FGF-2 or bFGF) can be used as a targeting molecule to help carry plasmid DNA into cells when the growth factor molecule is physically coupled to the DNA molecule being delivered. Herein we report our observations on the FGF-mediated uptake of exogenous labeled DNA into cultured cells in a manner that is representative of that which may occur under physiological conditions at sites of wounded tissue. Cellular debris at such sites contains nucleic acid fragments released from dead cells, as well as growth factors such as FGF-2 that function early in the wound repair process. Using a cell culture model designed to mimic the local environment of a wound with respect to the presence of soluble FGF-2 and DNA fragments, we have shown that FGF-2 is able to direct the cellular uptake and nuclear localization of fragments of exogenous DNA via the FGF receptor into intact and healthy cells. Furthermore, we can monitor and quantitate this type of FGF-mediated DNA delivery by using indirect immunofluorescence of bromodeoxyuridine-labeled exogenous DNA. Our results suggest that this type of FGF-mediated DNA fragment uptake could allow for the transduction of viable nearest neighbor cells at sites of injury in vivo. Such a phenomenon may lead to mutational aberrations in the recipient cells and enhance the probability of wound carcinogenesis.

Nonthrombogenic, adhesive cellular lining for left ventricular assist devices

BACKGROUND

The textured, blood-contacting surfaces of the Thermocardiosystems HeartMate left ventricular assist device (LVAD) promote the passivation of the biomaterial caused by the accumulation of an integral coagulum. Commonly, acute, postimplantation thrombocytopenia causes significant bleeding, requiring surgery or blood transfusions. Chronic complications include thromboembolic microevents that can affect central nervous system function. Pumps, explanted during donor organ transplantation, are often found to have an extensive cellular panus associated with the blood-contacting surfaces of the device. This natural cellular lining suggests a possible strategy for improving the blood biocompatibility of the HeartMate. Therefore, seeding of LVADs with cells genetically engineered to enhance their antithrombotic properties before implantation was investigated as a means to improve biocompatibility for long-term use.

METHODS AND RESULTS

Bovine vascular smooth muscle cells genetically engineered to produce nitric oxide were seeded on LVAD biomaterials and exposed to elevated shear stresses to determine cell-adhesive capabilities. Comparative studies were performed with vascular endothelial cells isolated from the same vessel. To assess the thrombogenic potential of the genetically engineered smooth muscle cells, monolayers were exposed to whole blood in parallel plate flow chambers and were platelet-adhesion quantified. This procedure used scanning electron microscopy and computer image-capture software. Endothelial cell monolayers and mock-transduced smooth muscle cells were assayed in a comparative manner. LVADs were seeded with genetically engineered smooth muscle cells and maintained under cell culture conditions for 96 hours. Thereafter, seeded LVADs were incorporated into in vitro flow loops. Cell retention within the pump was determined by sampling the effluent culture medium downstream of the pump and cell counting in a Coulter counter. After 18 hours of in vitro flow, a seeded pump was implanted into the abdominal cavity of a calf and anastomosed to the apex of the heart and to the descending aorta. More genetically engineered smooth muscle cells were retained on the surface of LVAD biomaterials when they were subjected to shear stresses up to 75 dyne/cm than endothelial cells assayed in the identical manner. Adherence of platelets to the surface of smooth muscle cells was significantly reduced after their transduction with nitric oxide synthase with GTP cyclohydrolase genes. Platelet deposition on the genetically modified myocyte layers was similar to that associated with endothelial cell layers. Cell loss from cell-seeded LVADs incorporated into in vitro flow loops remained < 5% of the total cell number seeded regardless of the duration of flow.

CONCLUSIONS

LVADs seeded with smooth muscle cells, transduced with the genes to optimize nitric oxide production, adhered well to the pump surface under in vitro and in vivo flow conditions.

Stimulation of growth and migration of vascular endothelial cells by vascular endothelial growth factor transduced smooth muscle cells in co-culture

Vascular endothelial growth factor (VEGF) is a secreted mitogen with high specificity toward endothelial cells. Expression of VEGF by smooth muscle cells in vivo may be an important stimulus for the regrowth of the endothelium after damage caused by interventions such as angioplasty. The levels of VEGF secreted by cultured smooth muscle cells minimally stimulated growth of endothelial cells in co-culture. Full length cDNA for the 165 amino acid residue, bovine VEGF (VEGF165), was isolated from calf liver total RNA by reverse transcriptase polymerase chain reaction (RT-PCR) techniques, and used to generate plasmid constructs for transfection. Bovine aortic smooth muscle cells (BSMC), stably transfected with VEGF165 plasmid DNA, secreted mitogen into conditioned culture medium at levels that are physiologically relevant (2-4 ng/ml). Transformed BSMC stimulated growth of bovine aortic endothelial cells (BAEC) in co-culture, to a significantly greater extent than mock transfected BSMC. Migration of BAEC was also enhanced by the presence of VEGF transduced BSMC. These data suggest that smooth muscle cells, genetically engineered to produce VEGF, may provide biologic linings in cardiovascular prostheses that could promote the growth of endogenous endothelial cells.

Liposomal induction of NO synthase expression in cultured vascular smooth muscle cells

Transfection of bovine smooth muscle cells with plasmid constructs containing the full coding sequence for endothelial NO synthase (NOS3) using liposome mediated gene transfer gave rise to cells that produced high levels of NO. Western analysis indicated that transfected cells were indeed expressing NOS3 protein, but in addition expression of inducible NO synthase (NOS2) was detected. The latter accounted for the high levels of NO produced by transfectants. Treatment of bovine or rat smooth muscle cells or 3T3 fibroblasts with only liposome preparations resulted in the induction of NOS2 expression and NO production. All liposomal reagents were shown to be endotoxin free. Direct induction of gene expression by liposomes alone suggests caution in interpretation of data for which gene transfer is mediated by liposomal preparations.

Genetically engineered smooth muscle cells as linings to improve the biocompatibility of cardiovascular prostheses

BACKGROUND

The seeding of the blood-contacting surfaces of cardiovascular prostheses with autologous endothelial cells to improve their biocompatibility has had little success. In most instances, cells have sloughed off under flow conditions. The performance of left ventricular assist devices (LVADs) designed to stabilize patients awaiting donor hearts for transplantation has been remarkably good. After prolonged implantation, pump surfaces become covered with a pannus of smooth muscle-like cells (myofibroblasts). Occasional islands of endothelial cells have been identified on top of such cell layers. Therefore, in an attempt to accelerate the beneficial conditioning and improve biomaterial-blood compatibility of LVAD internal surfaces, their seeding with autologous, genetically engineered smooth muscle cells (SMCs) was investigated.

METHODS AND RESULTS

Since routine testing of the Thermocardiosystems HeartMate LVAD is carried out in calves, SMCs were isolated from calves, propagated in culture, and transduced with NO synthase genes to yield stable production of NO. Previous studies had demonstrated that SMCs attached strongly to the biomaterials that compose the internal surfaces of LVADs. Transduction of NO synthase gene expression in the SMCs was achieved by electroporation and antibiotic (G418) selection. Inhibition of smooth muscle cell proliferation by NO has been documented, and the same molecule has been shown to inhibit platelet adhesion to cell surfaces. Cells transduced with NO synthase expressed enzyme protein at consistently high levels for several passages in culture; however, NO production was dependent on the supplementation of culture medium with a source of tetrahydrobiopterin (sepiapterin). Under such conditions, transduced cells were growth-inhibited compared with mock-transfected controls. Induction of GTP cyclohydrolase (the rate-limiting enzyme for the production of tetrahydrobiopterin) expression also resulted in NO production by NO synthase-transduced cells.

CONCLUSIONS

Preliminary studies have shown that SMCs form strong attachments to the surface materials of LVADs and that their proliferation rates could be controlled after transformation with NO synthase under conditions that support production of NO. Therefore, genetically engineered SMCs may provide an improved blood biomaterial interface for cardiovascular prostheses.

Critical functional requirement for the guanidinium group of the arginine 41 side chain of human epidermal growth factor as revealed by mutagenic inactivation and chemical reactivation

In a preliminary study we demonstrated that the formation of the epidermal growth factor (EGF) receptor-ligand complex requires the participation of the highly conserved arginine 41 side chain of the growth factor peptide (Engler, D.A., Montelione, G.T., and Niyogi, S.K. (1990) FEBS Lett. 271, 47-50). In an attempt to gain further insight into the nature of this interaction(s), we used both site-directed mutagenesis and chemical modification reagents to produce human EGF (hEGF) analogues with altered chemical properties of the residue 41 side chain. Eight mutant analogues of hEGF were generated, substituting arginine 41 with lysine, glutamine, isoleucine, tyrosine, glycine, alanine, aspartate, or glutamate. Although each of the mutant analogues was able to displace wild-type hEGF fully in receptor competition binding assays, affinity of the receptor for the mutants was substantially reduced, varying from 0.4 to less than 0.01% of that observed for wild-type growth factor. At sufficiently high concentrations these mutants were able to stimulate DNA synthesis in mouse keratinocytes. Substitution of lysine for arginine 41 reduced the receptor affinity 250-fold from that observed for wild type, despite retention of the positive electrostatic charge. The lysine substitution leaves a reactive amine at position 41 and made it possible, using amine-specific chemical modification reagents, to produce selected arginine homologues that were tested for their effects on receptor binding, receptor tyrosine kinase activation, and stimulation of DNA synthesis in mouse keratinocytes. The reaction of lysine 41 with methyl acetimidate resulted in a lysineacetamidine product which only partially restored activity of the lysine hEGF mutant. However, reaction with O-methylisourea resulted in generation of an arginine 41 homologue (homoarginine) which restored full activity. The results indicate that the chemical properties inherent in the guanidinium group of the arginine 41 side chain of hEGF are responsible for optimal receptor-ligand association.

Fluorescence studies with human epidermal growth factor

Steady-state and time-resolved fluorescence studies have been performed with human epidermal growth factor, a small globular protein having two adjacent tryptophan residues near its C-terminus. Based on the relatively red fluorescence and accessibility to solute quenchers, the two tryptophan residues are found to be exposed to solvent. Anisotropy decay measurements show the dominant depolarizing process to have a sub-nanosecond rotational correlation time indicating the existence of rapid segmental motion of the fluorescing tryptophan residues. From an analysis of the low-temperature excitation anisotropy spectrum of the protein (and in comparison with that of tryptophan, the peptide melittin, and the dipeptide trp-trp), it is concluded that homo-energy transfer and/or exciton interaction occurs between the adjacent tryptophan residues. A thermal transition in the structure of the protein, which is observed by circular dichroism measurements, is not sensed by the steady-state fluorescence of the protein. This result, in conjunction with the anisotropy decay results, indicates that the two tryptophan residues are in a highly flexible C-terminus segment, which is not an integral part of the three-dimensional structure of the protein. Fluorescence measurements with three site-directed mutants also show very little variation.

Aromaticity at position 37 in human epidermal growth factor is not obligatory for activity

The third disulfide loop (amino acids 33 to 42) of human epidermal growth factor (hEGF) encompasses the region of highest amino acid conservation among all of the EGF-like family of molecules. The importance of some of these highly conserved residues for the maintenance of biological activity, especially the aromatic amino acid tyrosine at position 37, has until now been considered essential on the basis of previous studies with the EGF-like molecule transforming growth factor alpha. Variants at the Tyr-37 position of hEGF were constructed by site-directed mutagenesis. The substituting amino acids were phenylalanine, histidine, serine, alanine, aspartic acid, arginine, and glycine. The variants were tested for their ability to competitively displace native [125I]hEGF from its receptor and to stimulate the protein-tyrosine kinase activity of the receptor; the order of efficacy of substituting amino acids was Phe greater than His greater than Ser greater than Ala greater than Asp greater than Arg greater than Gly in both assays. All were effective, with no or only moderate reduction in potency, in stimulating the incorporation of [3H]thymidine into acid-insoluble material of quiescent mouse A31 cells. Only Tyr-37----Ala, Tyr-37----Arg and Tyr-37----Gly were slightly less potent in the cell assay. Thus, neither tyrosine nor another aromatic amino acid at position 37 in hEGF is essential for full biological activity.

Biochemical properties of site-directed mutants of human epidermal growth factor: importance of solvent-exposed hydrophobic residues of the amino-terminal domain in receptor binding

Eight analogues of human epidermal growth factor (hEGF) having specific amino acid substitutions in the beta-sheet structure (residues 19-31) of the amino-terminal domain were generated by site-directed mutagenesis. Affinity of the epidermal growth factor (EGF) receptor for each of these mutant hEGF analogues was measured by both radioreceptor competition binding and receptor tyrosine kinase stimulation assays. The relative binding affinities obtained by these two methods were generally in agreement for each hEGF species. The results indicate that hydrophobic residues on the exposed surface of the beta-sheet structure of the amino-terminal domain of hEGF have an important role in the formation of the active EGF-receptor complex. The substitution of hydrophobic amino acid residues, Val-19----Gly, Met-21----Thr, Ile-23----Thr, and Leu-26----Gly, resulted in decreased binding affinity, with the most severe reductions observed with the last two mutants. The mutations Ala-25----Val and Lys-28----Arg introduced amino acid residues resulting in slightly increased receptor binding affinity. Similar to previous results with acidic residues in this region [Engler, D.A., Matsunami, R.K., Campion, S.R., Stringer, C.D., Stevens, A., & Niyogi, S.K. (1988) J. Biol. Chem. 263, 12384-12390], removal of the positive charge in the Lys-28----Leu substitution had almost no effect on binding affinity, indicating the lack of any absolute requirement for ionic interactions at this site. Substitution of Tyr-22, which resulted in decreased receptor binding affinity, provides further indication of the importance of aromatic residues in this region of the molecule, as found earlier with Tyr-29 (cf. reference above).(ABSTRACT TRUNCATED AT 250 WORDS)

Human epidermal growth factor. Distinct roles of tyrosine 37 and arginine 41 in receptor binding as determined by site-directed mutagenesis and nuclear magnetic resonance spectroscopy

Site-directed mutagenesis was employed to examine the function of two highly conserved residues, Tyr-37 and Arg-41, of human EGF (hEGF) in receptor binding. Both a conservative change to phenylalanine and a semi-conservative change to histidine at position 37 yield proteins with receptor affinity similar to wild-type hEGF. A non-conservative change to alanine results in a molecule with about 40% of the receptor affinity, indicating that an aromatic residue is not essential at this position. Both conservative (to lysine) and non-conservative (to alanine) substitutions at position 41 drastically reduced receptor binding to less than 0.5% of the wild-type activity. 1D-NMR data indicate that the replacement of Arg-41 by lysine does not significantly alter the native protein conformation. Thus, Arg-41 may be directly involved in ligand receptor interaction, whereas the side chain of Tyr-37, although possibly important structurally, is not essential for receptor binding.

Cloning of authentic human epidermal growth factor as a bacterial secretory protein and its initial structure-function analysis by site-directed mutagenesis

A synthetic chimeric gene, coding for the human epidermal growth factor fused to the signal peptide of Escherichia coli alkaline phosphatase, was cloned into E. coli under the transcriptional control of the trp-lac (tac) promoter. Following induction with isopropylthiogalactoside, the secretion of the correctly processed protein product into the bacterial periplasm was detected and quantitated by its specific binding to the epidermal growth factor receptor. The purified protein was identical to authentic human epidermal growth factor in size, amino acid composition, primary sequence, receptor binding, and stimulation of receptor protein-tyrosine kinase activity. Based on interspecies homologies, structural considerations, and reported studies with peptide fragments, structure-function analysis was initiated with alterations of targeted amino acid residues by oligonucleotide-directed mutagenesis. The receptor binding affinity of each mutant, relative to the wild type, was measured by both radioreceptor competition and receptor tyrosine kinase stimulation assays. In general, the values obtained by the two methods were in agreement for each species of epidermal growth factor and followed the order: wild type greater than Glu24----Gly greater than Asp27----Gly much greater than Pro7----Thr greater than Tyr29----Gly greater than Leu47----His. The relatively low values obtained with the last two mutants suggest that Tyr29 and Leu47 may be important for the biological activity of human epidermal growth factor.