A Multipathway Phosphopeptide Standard for Rapid Phosphoproteomics Assay Development

Recent advances in methodology have made phosphopeptide analysis a tractable problem for many proteomics researchers. There are now a wide variety of robust and accessible enrichment strategies to generate phosphoproteomes while free or inexpensive software tools for quantitation and site localization have simplified phosphoproteome analysis workflow tremendously. As a research group under the Association for Biomolecular Resource Facilities umbrella, the Proteomics Standards Research Group has worked to develop a multipathway phosphopeptide standard based on a mixture of heavy-labeled phosphopeptides designed to enable researchers to rapidly develop assays. This mixture contains 131 mass spectrometry vetted phosphopeptides specifically chosen to cover as many known biologically interesting phosphosites as possible from seven different signaling networks: AMPK signaling, death and apoptosis signaling, ErbB signaling, insulin/insulin-like growth factor-1 signaling, mTOR signaling, PI3K/AKT signaling, and stress (p38/SAPK/JNK) signaling. Here, we describe a characterization of this mixture spiked into a HeLa tryptic digest stimulated with both epidermal growth factor and insulin-like growth factor-1 to activate the MAPK and PI3K/AKT/mTOR pathways. We further demonstrate a comparison of phosphoproteomic profiling of HeLa performed independently in five labs using this phosphopeptide mixture with data-independent acquisition. Despite different experimental and instrumentation processes, we found that labs could produce reproducible, harmonized datasets by reporting measurements as ratios to the standard, while intensity measurements showed lower consistency between labs even after normalization. Our results suggest that widely available, biologically relevant phosphopeptide standards can act as a quantitative "yardstick" across laboratories and sample preparations enabling experimental designs larger than a single laboratory can perform. Raw data files are publicly available in the MassIVE dataset MSV000090564.

Charge-based interactions through peptide position 4 drive diversity of antigen presentation by human leukocyte antigen class I molecules

Human leukocyte antigen class I (HLA-I) molecules bind and present peptides at the cell surface to facilitate the induction of appropriate CD8+ T cell-mediated immune responses to pathogen- and self-derived proteins. The HLA-I peptide-binding cleft contains dominant anchor sites in the B and F pockets that interact primarily with amino acids at peptide position 2 and the C-terminus, respectively. Nonpocket peptide-HLA interactions also contribute to peptide binding and stability, but these secondary interactions are thought to be unique to individual HLA allotypes or to specific peptide antigens. Here, we show that two positively charged residues located near the top of peptide-binding cleft facilitate interactions with negatively charged residues at position 4 of presented peptides, which occur at elevated frequencies across most HLA-I allotypes. Loss of these interactions was shown to impair HLA-I/peptide binding and complex stability, as demonstrated by both in vitro and in silico experiments. Furthermore, mutation of these Arginine-65 (R65) and/or Lysine-66 (K66) residues in HLA-A*02:01 and A*24:02 significantly reduced HLA-I cell surface expression while also reducing the diversity of the presented peptide repertoire by up to 5-fold. The impact of the R65 mutation demonstrates that nonpocket HLA-I/peptide interactions can constitute anchor motifs that exert an unexpectedly broad influence on HLA-I-mediated antigen presentation. These findings provide fundamental insights into peptide antigen binding that could broadly inform epitope discovery in the context of viral vaccine development and cancer immunotherapy.

Neoantigen vaccination induces clinical and immunologic responses in non-small cell lung cancer patients harboring EGFR mutations

Background

Neoantigen (NeoAg) peptides displayed at the tumor cell surface by human leukocyte antigen molecules show exquisite tumor specificity and can elicit T cell mediated tumor rejection. However, few NeoAgs are predicted to be shared between patients, and none to date have demonstrated therapeutic value in the context of vaccination.

Methods

We report here a phase I trial of personalized NeoAg peptide vaccination (PPV) of 24 stage III/IV non-small cell lung cancer (NSCLC) patients who had previously progressed following multiple conventional therapies, including surgery, radiation, chemotherapy, and tyrosine kinase inhibitors (TKIs). Primary endpoints of the trial evaluated feasibility, tolerability, and safety of the personalized vaccination approach, and secondary trial endpoints assessed tumor-specific immune reactivity and clinical responses. Of the 16 patients with epidermal growth factor receptor (EGFR) mutations, nine continued TKI therapy concurrent with PPV and seven patients received PPV alone.

Results

Out of 29 patients enrolled in the trial, 24 were immunized with personalized NeoAg peptides. Aside from transient rash, fatigue and/or fever observed in three patients, no other treatment-related adverse events were observed. Median progression-free survival and overall survival of the 24 vaccinated patients were 6.0 and 8.9 months, respectively. Within 3–4 months following initiation of PPV, seven RECIST-based objective clinical responses including one complete response were observed. Notably, all seven clinical responders had EGFR-mutated tumors, including four patients that had continued TKI therapy concurrently with PPV. Immune monitoring showed that five of the seven responding patients demonstrated vaccine-induced T cell responses against EGFR NeoAg peptides. Furthermore, two highly shared EGFR mutations (L858R and T790M) were shown to be immunogenic in four of the responding patients, all of whom demonstrated increases in peripheral blood neoantigen-specific CD8+ T cell frequencies during the course of PPV.

Conclusions

These results show that personalized NeoAg vaccination is feasible and safe for advanced-stage NSCLC patients. The clinical and immune responses observed following PPV suggest that EGFR mutations constitute shared, immunogenic neoantigens with promising immunotherapeutic potential for large subsets of NSCLC patients. Furthermore, PPV with concurrent EGFR inhibitor therapy was well tolerated and may have contributed to the induction of PPV-induced T cell responses.

Vestigial-like 1 is a shared targetable cancer-placenta antigen expressed by pancreatic and basal-like breast cancers

Cytotoxic T lymphocyte (CTL)-based cancer immunotherapies have shown great promise for inducing clinical regressions by targeting tumor-associated antigens (TAA). To expand the TAA landscape of pancreatic ductal adenocarcinoma (PDAC), we performed tandem mass spectrometry analysis of HLA class I-bound peptides from 35 PDAC patient tumors. This identified a shared HLA-A*0101 restricted peptide derived from co-transcriptional activator Vestigial-like 1 (VGLL1) as a putative TAA demonstrating overexpression in multiple tumor types and low or absent expression in essential normal tissues. Here we show that VGLL1-specific CTLs expanded from the blood of a PDAC patient could recognize and kill in an antigen-specific manner a majority of HLA-A*0101 allogeneic tumor cell lines derived not only from PDAC, but also bladder, ovarian, gastric, lung, and basal-like breast cancers. Gene expression profiling reveals VGLL1 as a member of a unique group of cancer-placenta antigens (CPA) that may constitute immunotherapeutic targets for patients with multiple cancer types.

Beyond COX-1: the effects of aspirin on platelet biology and potential mechanisms of chemoprevention

After more than a century, aspirin remains one of the most commonly used drugs in western medicine. Although mainly used for its anti-thrombotic, anti-pyretic, and analgesic properties, a multitude of clinical studies have provided convincing evidence that regular, low-dose aspirin use dramatically lowers the risk of cancer. These observations coincide with recent studies showing a functional relationship between platelets and tumors, suggesting that aspirin's chemopreventive properties may result, in part, from direct modulation of platelet biology and biochemistry. Here, we present a review of the biochemistry and pharmacology of aspirin with particular emphasis on its cyclooxygenase-dependent and cyclooxygenase-independent effects in platelets. We also correlate the results of proteomic-based studies of aspirin acetylation in eukaryotic cells with recent developments in platelet proteomics to identify non-cyclooxygenase targets of aspirin-mediated acetylation in platelets that may play a role in its chemopreventive mechanism.

Glioblastoma stem cell-derived exosomes induce M2 macrophages and PD-L1 expression on human monocytes

Exosomes can mediate a dynamic method of communication between malignancies, including those sequestered in the central nervous system and the immune system. We sought to determine whether exosomes from glioblastoma (GBM)-derived stem cells (GSCs) can induce immunosuppression. We report that GSC-derived exosomes (GDEs) have a predilection for monocytes, the precursor to macrophages. The GDEs traverse the monocyte cytoplasm, cause a reorganization of the actin cytoskeleton, and skew monocytes toward the immune suppresive M2 phenotype, including programmed death-ligand 1 (PD-L1) expression. Mass spectrometry analysis demonstrated that the GDEs contain a variety of components, including members of the signal transducer and activator of transcription 3 (STAT3) pathway that functionally mediate this immune suppressive switch. Western blot analysis revealed that upregulation of PD-L1 in GSC exosome-treated monocytes and GBM-patient-infiltrating CD14⁺ cells predominantly correlates with increased phosphorylation of STAT3, and in some cases, with phosphorylated p70S6 kinase and Erk1/2. Cumulatively, these data indicate that GDEs are secreted GBM-released factors that are potent modulators of the GBM-associated immunosuppressive microenvironment.

KAT2A coupled with the α-KGDH complex acts as a histone H3 succinyltransferase

Histone modifications, such as the frequently occurring lysine succinylation, are central to the regulation of chromatin-based processes. However, the mechanism and functional consequences of histone succinylation are unknown. Here we show that the α-ketoglutarate dehydrogenase (α-KGDH) complex is localized in the nucleus in human cell lines and binds to lysine acetyltransferase 2A (KAT2A, also known as GCN5) in the promoter regions of genes. We show that succinyl-coenzyme A (succinyl-CoA) binds to KAT2A. The crystal structure of the catalytic domain of KAT2A in complex with succinyl-CoA at 2.3 Å resolution shows that succinyl-CoA binds to a deep cleft of KAT2A with the succinyl moiety pointing towards the end of a flexible loop 3, which adopts different structural conformations in succinyl-CoA-bound and acetyl-CoA-bound forms. Site-directed mutagenesis indicates that tyrosine 645 in this loop has an important role in the selective binding of succinyl-CoA over acetyl-CoA. KAT2A acts as a succinyltransferase and succinylates histone H3 on lysine 79, with a maximum frequency around the transcription start sites of genes. Preventing the α-KGDH complex from entering the nucleus, or expression of KAT2A(Tyr645Ala), reduces gene expression and inhibits tumour cell proliferation and tumour growth. These findings reveal an important mechanism of histone modification and demonstrate that local generation of succinyl-CoA by the nuclear α-KGDH complex coupled with the succinyltransferase activity of KAT2A is instrumental in histone succinylation, tumour cell proliferation, and tumour development.

Proteomics Profiling of Exosomes from Primary Mouse Osteoblasts under Proliferation versus Mineralization Conditions and Characterization of Their Uptake into Prostate Cancer Cells

Osteoblasts communicate both with normal cells in the bone marrow and with tumor cells that metastasized to bone. Here we show that osteoblasts release exosomes, we termed osteosomes, which may be a novel mechanism by which osteoblasts communicate with cells in their environment. We have isolated exosomes from undifferentiated/proliferating (D0 osteosomes) and differentiated/mineralizing (D24 osteosomes) primary mouse calvarial osteoblasts. The D0 and D24 osteosomes were found to be vesicles of 130-140 nm by dynamic light scattering analysis. Proteomics profiling using tandem mass spectrometry (LC-MS/MS) identified 206 proteins in D0 osteosomes and 336 in D24 osteosomes. The proteins in osteosomes are mainly derived from the cytoplasm (∼47%) and plasma membrane (∼31%). About 69% of proteins in osteosomes are also found in Vesiclepedia, and these canonical exosomal proteins include tetraspanins and Rab family proteins. We found that there are differences in both protein content and levels in exosomes isolated from undifferentiated and differentiated osteoblasts. Among the proteins that are unique to osteosomes, 169 proteins are present in both D0 and D24 osteosomes, 37 are unique to D0, and 167 are unique to D24. Among those 169 proteins present in both D0 and D24 osteosomes, 10 proteins are likely present at higher levels in D24 than D0 osteosomes based on emPAI ratios of >5. These results suggest that osteosomes released from different cellular state of osteoblasts may mediate distinct functions. Using live-cell imaging, we measured the uptake of PKH26-labeled osteosomes into C4-2B4 and PC3-mm2 prostate cancer cells. In addition, we showed that cadherin-11, a cell adhesion molecule, plays a role in the uptake of osteosomes into PC3-mm2 cells as osteosome uptake was delayed by neutralizing antibody against cadherin-11. Together, our studies suggest that osteosomes could have a unique role in the bone microenvironment under both physiological and pathological conditions.

Abstract 3474: Depletion of SPECC1L inhibits colorectal cancer cell proliferation

Introduction: Despite the numerous drugs available for patients with metastatic colorectal cancer (mCRC), median overall survival for this group of patients remains at ~20-24 months, with no significant advances in the last 7 years. In the US ~50,000 patients die each year from mCRC refractory to systemic therapy. Inhibiting angiogenesis as a therapy has led to a great deal of enthusiasm. However, the overall benefit of classical-antiangiogenic therapy remains modest and has not lived up to their expectations in treating CRC. Our recent studies suggest that VEGF intracrine signaling, rather than autocrine/paracrine signaling, regulates cell survival in CRC cells. Further studies to understand the significance and mechanisms of this novel function have led us to identify factors that intracellularly interact with VEGF. Our studies further indicate that one such interacting protein, SPECC1L, may have a significant role in CRC cell proliferation and may be a potential target in mCRC therapy.

Methods: Lysates from CRC cells expressing Myc-tagged VEGF protein were immunoprecipitated and analyzed by mass spectrometry to identify VEGF-interacting protiens. SPECC1L was identified as a co-precipitated protein with high level of confidence. SPECC1L was depleted using siRNA and effects of such depletion on CRC cell growth and morphology were measured by cell growth assays (MTT), microscopy, FACS and western blot analyses. Localization of the protein and its interaction with microtubules and actin were visualized by immunostaining of FLAG-tagged recombinant SPECC1L protein.

Results: SPECC1L was identified as a protein that co-immunoprecipitated with Myc-tagged VEGF in CRC cells using mass spectroscopy. Previous literature suggests a role for SPECC1L in cell division. As a fraction of VEGF overexpressing CRC cells have a large multinucleated phenotype, likely arising due to defects in cell division, it was hypothesized that a VEGF mediated regulation of SPECC1L may lead to such phenotype. Depletion of SPECC1L by siRNAs in multiple CRC cell lines led to strong defects in cell division. The effects of SPECC1L depletion were manifested as accumulation of doublet-cells failing to complete cytokinesis following mitosis and resulted in reduced cell proliferation. Failure to complete cell division also led to the formation of multinucleated cells and enhanced cell death.

Conclusions: Inhibition of SPECC1L strongly inhibits CRC cell proliferation and enhances cell death. Thus targeting SPECC1L has the potential for developing therapeutics that reduce viability of CRC cells and improve survival of colorectal cancer patients.

*** These studies were supported by the Gillson-Longenbaugh Foundation.

Citation Format: Rajat Bhattacharya, Ling Xia, Fan Fan, Rui Wang, Delphine Boulbes, Xiang-Cang Ye, David Hawke, Lee Ellis. Depletion of SPECC1L inhibits colorectal cancer cell proliferation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3474. doi:10.1158/1538-7445.AM2017-3474

SLC45A2: A Melanoma Antigen with High Tumor Selectivity and Reduced Potential for Autoimmune Toxicity

Cytotoxic T lymphocyte (CTL)-based immunotherapies have had remarkable success at generating objective clinical responses in patients with advanced metastatic melanoma. Although the melanocyte differentiation antigens (MDA) MART-1, PMEL, and tyrosinase were among the first melanoma tumor-associated antigens identified and targeted with immunotherapy, expression within normal melanocytes of the eye and inner ear can elicit serious autoimmune side effects, thus limiting their clinical potential as CTL targets. Using a tandem mass spectrometry (MS) approach to analyze the immunopeptidomes of 55 melanoma patient-derived cell lines, we identified a number of shared HLA class I-bound peptides derived from the melanocyte-specific transporter protein SLC45A2. Antigen-specific CTLs generated against HLA-A*0201- and HLA-A*2402-restricted SLC45A2 peptides effectively killed a majority of HLA-matched cutaneous, uveal, and mucosal melanoma cell lines tested (18/25). CTLs specific for SLC45A2 showed significantly reduced recognition of HLA-matched primary melanocytes that were, conversely, robustly killed by MART1- and PMEL-specific T cells. Transcriptome analysis revealed that SLC45A2 mRNA expression in normal melanocytes was less than 2% that of other MDAs, therefore providing a more favorable melanoma-to-melanocyte expression ratio. Expression of SLC45A2 and CTL sensitivity could be further upregulated in BRAF(V600E)-mutant melanoma cells upon treatment with BRAF or MEK inhibitors, similarly to other MDAs. Taken together, our study demonstrates the feasibility of using tandem MS as a means of discovering shared immunogenic tumor-associated epitopes and identifies SLC45A2 as a promising immunotherapeutic target for melanoma with high tumor selectivity and reduced potential for autoimmune toxicity. Cancer Immunol Res; 5(8); 618-29. ©2017 AACR.

Phosphoglycerate Kinase 1 Phosphorylates Beclin1 to Induce Autophagy

Autophagy is crucial for maintaining cell homeostasis. However, the precise mechanism underlying autophagy initiation remains to be defined. Here, we demonstrate that glutamine deprivation and hypoxia result in inhibition of mTOR-mediated acetyl-transferase ARD1 S228 phosphorylation, leading to ARD1-dependent phosphoglycerate kinase 1 (PGK1) K388 acetylation and subsequent PGK1-mediated Beclin1 S30 phosphorylation. This phosphorylation enhances ATG14L-associated class III phosphatidylinositol 3-kinase VPS34 activity by increasing the binding of phosphatidylinositol to VPS34. ARD1-dependent PGK1 acetylation and PGK1-mediated Beclin1 S30 phosphorylation are required for glutamine deprivation- and hypoxia-induced autophagy and brain tumorigenesis. Furthermore, PGK1 K388 acetylation levels correlate with Beclin1 S30 phosphorylation levels and poor prognosis in glioblastoma patients. Our study unearths an important mechanism underlying cellular-stress-induced autophagy initiation in which the protein kinase activity of the metabolic enzyme PGK1 plays an instrumental role and reveals the significance of the mutual regulation of autophagy and cell metabolism in maintaining cell homeostasis.

Abstract 4715: Regulation of the PI3K pathway through a p85α monomer-homodimer equilibrium

The canonical action of the p85α regulatory subunit of phosphatidylinositol 3-kinase (PI3K) is mediated by association with the p110 catalytic subunit to allow stimuli-dependent activation of the PI3K pathway. Although the best-characterized role of p85α is p110-dependent, intermolecular interactions of p85α protomers have been suggested to result in p85α homodimerization. However, the function of the p85α homodimer remains to be elucidated. Through structural modeling and biochemical analyses, we demonstrate the p110α-independent role of homodimerized p85α in the positive regulation of PTEN. p110α-free p85α homodimerizes via SH3:proline rich domain and BH:BH intermolecular interactions to selectively bind unphosphorylated activated PTEN. p85α homodimer competes for PTEN binding with the E3 ligase WWP2. As a consequence, homodimeric but not monomeric p85α suppresses the PI3K pathway by protecting PTEN from WWP2-mediated proteasomal degradation. Further, p85α homodimer enhances the lipid phosphatase activity and membrane association of PTEN. Importantly, the homodimerization surface and the PTEN-interaction interface are targeted in cancer patient-derived p85α mutants, providing a plausible mechanism for tumor development. These p85α mutants are oncogenic by destabilizing PTEN and inducing PI3K pathway activation. Together, we provide a mechanistic model of how p85α plays a dual role in regulating the PI3K pathway through forming p85α homodimer or p110-bound heterodimer. Our data suggest that the monomer-dimer equilibrium of p85α regulates the PI3K pathway and thereby associates with cancer development.

Citation Format: Lydia WT Cheung, Katarzyna W. Walkiewicz, Tabot Besong, David Hawke, Stefan T. Arold, Gordon B. Mills. Regulation of the PI3K pathway through a p85α monomer-homodimer equilibrium. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 4715. doi:10.1158/1538-7445.AM2015-4715

Aberrant fucosylation of glycosphingolipids in human hepatocellular carcinoma tissues

BACKGROUNDS & AIMS

Glycosylation promoting or inhibiting tumour cell invasion and metastasis is of crucial importance in current cancer research. Tumour-associated carbohydrate antigens are predominantly expressed on the tumour cell surface. Glycosphingolipids (GSLs) are members of the family. To perform glycosphingolipidomic assays on neutral GSLs obtained from solid hepatocellular carcinoma (HCC) tissues and paired peritumoural tissues by linear ion trap quadrupole-electrospray ionization mass spectrometry.

METHODS

Qualitative and quantitative analysis of fucosylated neutral GSLs was performed in the positive ion mode on the LTQ-XL mass spectrometer and MALDI-TOF-MS.

RESULTS

A group of fucosylated neutral GSLs in HCC was found to be expressed higher in the tumour tissues, as their proportion in total cellular GSLs was 3.3-fold higher in the tumour tissues than in the peritumoural tissues (P < 0.01). Moreover, qualitative analysis of the aberrant fucosylated GSLs were completed, and seven types of fucosylated GSLs that contained terminal Fuca2Gal- structure were identified by mass spectrometry.

CONCLUSIONS

Our results may lead to improved immunotherapy of HCC and contribute to understanding the role of aberrant fucosylated GSLs in the development and progress of HCC in following studies.

Mass spectrometric analysis of glycosphingolipid antigens

Glycosphingolipids (GSL's) belong to the glycoconjugate class of biomacromolecules, which bear structural information for significant biological processes such as embryonic development, signal transduction, and immune receptor recognition^1-2. They contain complex sugar moieties in the form of isomers, and lipid moieties with variations including fatty acyl chain length, unsaturation, and hydroxylation. Both carbohydrate and ceramide portions may be basis of biological significance. For example, tri-hexosylceramides include globotriaosylceramide (Galα4Galβ4Glcβ1Cer) and isoglobotriaosylceramide (Galα3Galβ4Glcβ1Cer), which have identical molecular masses but distinct sugar linkages of carbohydrate moiety, responsible for completely different biological functions^3-4. In another example, it has been demonstrated that modification of the ceramide part of alpha-galactosylceramide, a potent agonist ligand for invariant NKT cells, changes their cytokine secretion profiles and function in animal models of cancer and auto-immune diseases⁵. The difficulty in performing a structural analysis of isomers in immune organs and cells serve as a barrier for determining many biological functions⁶.

Here, we present a visualized version of a method for relatively simple, rapid, and sensitive analysis of glycosphingolipid profiles in immune cells^7-9. This method is based on extraction and chemical modification (permethylation, see below Figure 5A, all OH groups of hexose were replaced by MeO after permethylation reaction) of glycosphingolipids^10-15, followed by subsequent analysis using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF/MS) and ion trap mass spectrometry. This method requires 50 million immune cells for a complete analysis. The experiments can be completed within a week. The relative abundance of the various glycosphingolipids can be delineated by comparison to synthetic standards. This method has a sensitivity of measuring 1% iGb3 among Gb3 isomers, when 2 fmol of total iGb3/Gb3 mixture is present⁹.

Ion trap mass spectrometry can be used to analyze isomers. For example, to analyze the presence of globotriaosylceramide and isoglobtriaosylceramide in the same sample, one can use the fragmentation of glycosphingolipid molecules to structurally discriminate between the two (see below Figure 5). Furthermore, chemical modification of the sugar moieties (through a permethylation reaction) improves the ionization and fragmentation efficiencies for higher sensitivity and specificity, and increases the stability of sialic acid residues. The extraction and chemical modification of glycosphingolipids can be performed in a classic certified chemical hood, and the mass spectrometry can be performed by core facilities with ion trap MS instruments.

Lack of iGb3 and Isoglobo-Series Glycosphingolipids in Pig Organs Used for Xenotransplantation: Implications for Natural Killer T-Cell Biology

α-1,3-Terminated galactose residues on glycoproteins and glycosphingolipids are recognized by natural anti-α-1,3-galactose antibodies in human serum and cause hyperacute rejection in pig-to-human xenotransplantation. Genetic depletion of α-1,3-galactosyltransferase-1 in pigs abolishes the hyperacute rejection reaction. However, the isoglobotriosylceramide (iGb3) synthase in pigs may produce additional α-1,3-terminated galactose residues on glycosphingolipids. In both α-1,3-galactosyltranserase-1 knockout mice and pigs, cytotoxic anti-α-1,3-galactose antibodies could be induced; thus, a paradox exists that anti-α-1,3-galactose antibodies are present in animals with functional iGb3 synthases. Furthermore, iGb3 has been found to be an endogenous antigen for natural killer T (NKT) cells, an innate type of lymphocyte that may initiate the adaptive immune responses. It has been reasoned that iGb3 may trigger the activation of NKT cells and cause the rejection of α-1,3-galactosyltransferase-1-deficient organs through the potent stimulatory effects of NKT cells on adaptive immune cells (see ref.([20])). In this study, we examined the expression of iGb3 and the isoglobo-series glycosphingolipids in pig organs, including the heart, liver, pancreas, and kidney, by ion-trap mass spectrometry, which has a sensitivity of measuring 1% iGb3 among Gb3 isomers, when 5 μg/mL of the total iGb3/Gb3 mixture is present (see ref.([35])). We did not detect iGb3 or other isoglobo-series glycosphingolipids in any of these organs, although they were readily detected in mouse and human thymus and dendritic cells. The lack of iGb3 and isoglobo-series glycosphingolipids in pig organs indicates that iGb3 is unlikely to be a relevant immune epitope in xenotransplantation.

Glioma pathogenesis-related protein 1 induces prostate cancer cell death through Hsc70-mediated suppression of AURKA and TPX2

In this study we report that expression of glioma pathogenesis-related protein 1 (GLIPR1) regulated numerous apoptotic, cell cycle, and spindle/centrosome assembly-related genes, including AURKA and TPX2, and induced apoptosis and/or mitotic catastrophe (MC) in prostate cancer (PCa) cells, including p53-mutated/deleted, androgen-insensitive metastatic PCa cells. Mechanistically, GLIPR1 interacts with heat shock cognate protein 70 (Hsc70); this interaction is associated with SP1 and c-Myb destabilization and suppression of SP1- and c-Myb-mediated AURKA and TPX2 transcription. Inhibition of AURKA and TPX2 using siRNA mimicked enforced GLIPR1 expression in the induction of apoptosis and MC. Recombinant GLIPR1-ΔTM protein inhibited AURKA and TPX2 expression, induced apoptosis and MC, and suppressed orthotopic xenograft tumor growth. Our results define a novel GLIPR1-regulated signaling pathway that controls apoptosis and/or mitotic catastrophe in PCa cells and establishes the potential of this pathway for targeted therapies.

PKM2 phosphorylates histone H3 and promotes gene transcription and tumorigenesis

Tumor-specific pyruvate kinase M2 (PKM2) is essential for the Warburg effect. In addition to its well-established role in aerobic glycolysis, PKM2 directly regulates gene transcription. However, the mechanism underlying this nonmetabolic function of PKM2 remains elusive. We show here that PKM2 directly binds to histone H3 and phosphorylates histone H3 at T11 upon EGF receptor activation. This phosphorylation is required for the dissociation of HDAC3 from the CCND1 and MYC promoter regions and subsequent acetylation of histone H3 at K9. PKM2-dependent histone H3 modifications are instrumental in EGF-induced expression of cyclin D1 and c-Myc, tumor cell proliferation, cell-cycle progression, and brain tumorigenesis. In addition, levels of histone H3 T11 phosphorylation correlate with nuclear PKM2 expression levels, glioma malignancy grades, and prognosis. These findings highlight the role of PKM2 as a protein kinase in its nonmetabolic functions of histone modification, which is essential for its epigenetic regulation of gene expression and tumorigenesis.

Characterization of a human 12/15-lipoxygenase promoter variant associated with atherosclerosis identifies vimentin as a promoter binding protein

Background

Sequence variation in the human 12/15 lipoxygenase (ALOX15) has been associated with atherosclerotic disease. We functionally characterized an ALOX15 promoter polymorphism, rs2255888, previously associated with carotid plaque burden.

Methodology/Principal Findings

We demonstrate specific in vitro and in vivo binding of the cytoskeletal protein, vimentin, to the ALOX15 promoter. We show that the two promoter haplotypes carrying alternate alleles at rs2255888 exhibit significant differences in promoter activity by luciferase reporter assay in two cell lines. Differences in in-vitro vimentin-binding to and formation of DNA secondary structures in the polymorphic promoter sequence are also detected by electrophoretic mobility shift assay and biophysical analysis, respectively. We show regulation of ALOX15 protein by vimentin.

Conclusions/Significance

This study suggests that vimentin binds the ALOX15 promoter and regulates its promoter activity and protein expression. Sequence variation that results in changes in DNA conformation and vimentin binding to the promoter may be relevant to ALOX15 gene regulation.

AKT-dependent phosphorylation of Niban regulates nucleophosmin- and MDM2-mediated p53 stability and cell apoptosis

Although Niban is highly expressed in human cancer cells, the cellular functions of Niban remain largely unknown. We demonstrate here that ultraviolet irradiation induces phosphorylation of Niban at S602 by AKT, which increases the association of Niban with nucleophosmin and disassociation of nucleophosmin from the MDM2 complex. This leads to the promotion of MDM2-p53 interaction and subsequent p53 degradation, thereby providing an antiapoptotic effect. Conversely, depletion of or deficiency in Niban expression promotes stabilization of p53 with increased cell apoptosis. Our findings illustrate a pivotal role for AKT-mediated phosphorylation of Niban in protecting cells from genotoxic stress-induced cell apoptosis.

Evaluation of changes in serum protein profiles during neoadjuvant chemotherapy in HER2-positive breast cancer using an LC-MALDI-TOF/MS procedure

Comparison of protein profiles of sera acquired before and after preoperative chemotherapy for breast cancer may reveal tumor markers that could be used to monitor tumor response. In this study, we analyzed pre- and post-chemotherapy protein profiles of sera from 39 HER2-postive breast cancer patients (n=78 samples) who received 6 months of preoperative chemotherapy using LC-MALDI-TOF/MS technology. We detected qualitative and quantitative differences in pair-wise comparison of pre- and post chemotherapy samples that were different in patients who achieved pathological complete response (pCR, n=21) compared with those with residual disease (n=18). We identified 2329 and 3152 peaks as differentially expressed in the pre-chemotherapy samples of the responders and non-responders. Comparison of matching pre- and post-chemotherapy samples identified 34 (32 decreased, two increased) and 304 peaks (157 decreased, 147 increased) that significantly changed (p<0.01, false discovery rate ≤ 20%) after treatment in responders and non-responders, respectively. The top 11 most significantly altered peptide peaks with the greatest change in intensity were positively identified. These corresponded to eight proteins including α-2-macroglobulin, complement 3, hemopexin, and serum amyloid P in the responder group and chains C and A of apolipoprotein A-I, hemopexin precursor, complement C, and amyloid P component in the non-responding groups. All proteins decreased after therapy, except chain C apolipoprotein A and hemopexin precursor that increased. These results suggest that changes in serum protein levels occur in response to chemotherapy and these changes partly appear different in patients who are highly sensitive to chemotherapy compared with those with lesser response.

EGF-induced ERK activation promotes CK2-mediated disassociation of alpha-Catenin from beta-Catenin and transactivation of beta-Catenin

Increased transcriptional activity of beta-catenin resulting from Wnt/Wingless-dependent or -independent signaling has been detected in many types of human cancer, but the underlying mechanism of Wnt-independent regulation remains unclear. We demonstrate here that EGFR activation results in disruption of the complex of beta-catenin and alpha-catenin, thereby abrogating the inhibitory effect of alpha-catenin on beta-catenin transactivation via CK2alpha-dependent phosphorylation of alpha-catenin at S641. ERK2, which is activated by EGFR signaling, directly binds to CK2alpha via the ERK2 docking groove and phosphorylates CK2alpha primarily at T360/S362, subsequently enhancing CK2alpha activity toward alpha-catenin phosphorylation. In addition, levels of alpha-catenin S641 phosphorylation correlate with levels of ERK1/2 activity in human glioblastoma specimens and with grades of glioma malignancy. This EGFR-ERK-CK2-mediated phosphorylation of alpha-catenin promotes beta-catenin transactivation and tumor cell invasion. These findings highlight the importance of the crosstalk between EGFR and Wnt pathways in tumor development.

Evaluation of Changes in Plasma Protein Profiles during Neoadjuvant Chemotherapy in HER2-Positive Breast Cancer Using MALDI-TOF/MS Procedure

Background: Comparison of protein profiles of the plasma before chemotherapy and after completion of neoadjuvant chemotherapy may reveal tumor markers that could be used to monitor tumor response.Patients and Methods: We examined matching pre- and post-treatment serum samples 39 HER2-postive breast cancer patients (n=78 samples) who all received 6 months of preoperative chemotherapy with or without trastuzumab in the context of a randomized clinical trial. Serum was analyzed with an Applied Biosystems 4700 Proteomics Analyzer matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometer. Samples were grouped and pooled into those who achieved pathological complete response (pCR, n=20) and those who had residual disease (RD, n=19). We compared matching baseline and post-chemotherapy/pre-surgery samples separately in both response groups and also compared baseline samples between the two response groups.Results: MALDI-TOF analysis revealed a total of 2329 and 3152 peaks in pooled samples of cases with pCR and RD, respectively. A total of 32 peaks were differentially expressed between base line and post-chemotherapy pCR samples and 643 peaks in cases with RD (false discovery rate ≤ 20%). A total of 8 differentially expressed proteins were identified in the before- and after-chemotherapy samples from their peptides after digestion and LC-MALDI-TOF/TOF. These included 4 AFM, C3, hemopexin, SAP in pCR samples and AP1, hemopexin, Complement B, amyloid P component in the RD group.Conclusion: Our study suggests that MALDI mass spectrometry may be used to detect differences in baseline serum profiles of patients who are highly sensitive to chemotherapy and those who are less sensitive. Also, changes occur in the serum during chemotherapy and this may offer the possibility of monitoring response to treatment in the future.

Citation Information: Cancer Res 2009;69(24 Suppl):Abstract nr 2037.

FAK phosphorylation by ERK primes ras-induced tyrosine dephosphorylation of FAK mediated by PIN1 and PTP-PEST

Activated Ras has been found in many types of cancer. However, the mechanism underlying Ras-promoted tumor metastasis remains unclear. We demonstrate here that activated Ras induces tyrosine dephosphorylation and inhibition of FAK mediated by the Ras downstream Fgd1-Cdc42-PAK1-MEK-ERK signaling cascade. ERK phosphorylates FAK S910 and recruits PIN1 and PTP-PEST, which colocalize with FAK at the lamellipodia of migrating cells. PIN1 binding and prolyl isomerization of FAK cause PTP-PEST to interact with and dephosphorylate FAK Y397. Inhibition of FAK mediated by this signal relay promotes Ras-induced cell migration, invasion, and metastasis. These findings uncover the importance of sequential modification of FAK-by serine phosphorylation, isomerization, and tyrosine dephosphorylation--in the regulation of FAK activity and, thereby, in Ras-related tumor metastasis.

Immunologic glycosphingolipidomics and NKT cell development in mouse thymus

Invariant NKT cells are a hybrid cell type of Natural Killer cells and T cells, whose development is dependent on thymic positive selection mediated by double positive thymocytes through their recognition of natural ligands presented by CD1d, a nonpolymorphic, non-MHC, MHC-like antigen presenting molecule. Genetic evidence suggested that beta-glucosylceramide derived glycosphingolipids (GSLs) are natural ligands for NKT cells. N-butyldeoxygalactonojirimycin (NB-DGJ), a drug that specifically inhibits the glucosylceramide synthase, inhibits the endogenous ligands for NKT cells. Furthermore, we and others have found a beta-linked glycosphingolipid, isoglobotriaosylceramide (iGb3), is a stimulatory NKT ligand. The iGb3 synthase knockout mice have a normal NKT development and function, indicating that other ligands exist and remain to be identified. In this study, we have performed a glycosphingolipidomics study of mouse thymus, and studied mice mutants which are deficient in beta-hexosaminidase b or alpha-galactosidase A, two glycosidases that are up- and downstream agents of iGb3 turnover, respectively. Our mass spectrometry methods generated a first database for glycosphingolipids expressed in mouse thymus, which are specifically regulated by rate-limiting glycosidases. Among the identified thymic glycosphingolipids, only iGb3 is a stimulatory ligand for NKT cells, suggesting that large-scale fractionation, enrichment and characterization of minor species of glycosphingolipids are necessary for identifying additional ligands for NKT cells. Our results also provide early insights into cellular lipidomics studies, with a specific focus on the important immunological functions of glycosphingolipids.

Evaluation of serum profiles changes after neoadjuvant chemotherapy for breast cancer using MALDI-TOF/MS procedure

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Evaluation of serum profiles changes after neoadjuvant chemotherapy for breast cancer using MALDI-TOF / MS procedure. Background: Response to primary chemotherapy (CT) for breast cancer is heterogeneous among patients and a more tailored treatment would be beneficial in term of reducing exposure to an unnecessary toxicity and optimization of response rates. Mass spectrometry analysis of serum might be helpful in detecting specific changes in response to primary CT. Methods: An applied Biosystems 4700 Proteomics Analyzer matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometer was used. A breast cancer cohort of 78 sera samples from 39 HER2 positive patients consisting of matched pretreatment and (6 months) posttreatment samples was used. Blood samples were collected serially before each treatment cycle every 3 weeks of neoadjuvant CT. Samples were divided into those who achieved pathological complete response (pCR, n= 20) and those who had residual disease (RD, n=19). Low-mass differentially expressed peptides were identified using MALDI-TOF/TOF. Results: This procedure yielded a total of 2329 and 3152 peaks respectively, for the responders and non-responders. Biological variation analysis revealed a total of 32 peaks for responders and 643 peaks for non-responders to be differentially regulated with a false discovery rate less than 20%. A total of 8 differentially expressed proteins were identified from their peptides after digestion and LC-MALDI-TOF/TOF. Four in tumors with pCR (AFM, C3, hemopexin, SAP) and four proteins in the RD group were identified (AP1, hemopexin, Complement B, amyloid P component) Conclusions: Our study suggests that MALDI mass spectrometry may be used to predict the tumor response to neoadjuvant chemotherapy. Proteomic analysis may be useful in developing tailored chemotherapy for breast cancer.

No significant financial relationships to disclose.

Stimulation of lung innate immunity protects against lethal pneumococcal pneumonia in mice

RATIONALE

The lungs are a common site of serious infection in both healthy and immunocompromised subjects, and the most likely route of delivery of a bioterror agent. Since the airway epithelium shows great structural plasticity in response to inflammatory stimuli, we hypothesized it might also show functional plasticity.

OBJECTIVES

To test the inducibility of lung defenses against bacterial challenge.

METHODS

Mice were treated with an aerosolized lysate of ultraviolet-killed nontypeable (unencapsulated) Haemophilus influenzae (NTHi), then challenged with a lethal dose of live Streptococcus pneumoniae (Spn) delivered by aerosol.

MEASUREMENTS AND MAIN RESULTS

Treatment with the NTHi lysate induced complete protection against challenge with a lethal dose of Spn if treatment preceded challenge by 4 to 24 hours. Lesser levels of protection occurred at shorter (83% at 2 h) and longer (83% at 48-72 h) intervals between treatment and challenge. There was also some protection when treatment was given 2 hours after challenge (survival increased from 14 to 57%), but not 24 hours after challenge. Protection did not depend on recruited neutrophils or resident mast cells and alveolar macrophages. Protection was specific to the airway route of infection, correlated in magnitude and time with rapid bacterial killing within the lungs, and was associated with increases of multiple antimicrobial polypeptides in lung lining fluid.

CONCLUSIONS

We infer that protection derives from stimulation of local innate immune mechanisms, and that activated lung epithelium is the most likely cellular effector of this response. Augmentation of innate antimicrobial defenses of the lungs might have therapeutic value.

Phosphorylation of beta-catenin by AKT promotes beta-catenin transcriptional activity

Increased transcriptional activity of beta-catenin resulting from Wnt/Wingless-dependent or -independent signaling has been detected in many types of human cancer, but the underlying mechanism of Wnt-independent regulation is poorly understood. We have demonstrated that AKT, which is activated downstream from epidermal growth factor receptor signaling, phosphorylates beta-catenin at Ser552 in vitro and in vivo. AKT-mediated phosphorylation of beta-catenin causes its disassociation from cell-cell contacts and accumulation in both the cytosol and the nucleus and enhances its interaction with 14-3-3zeta via a binding motif containing Ser552. Phosphorylation of beta-catenin by AKT increases its transcriptional activity and promotes tumor cell invasion, indicating that AKT-dependent regulation of beta-catenin plays a critical role in tumor invasion and development.

Serum amyloid A as a tumor marker in sera of nude mice with orthotopic human pancreatic cancer and in plasma of patients with pancreatic cancer

We screened an orthotopic nude mouse model of human pancreatic cancer for candidate serum biomarkers and examined their presence in the plasma of pancreatic cancer patients. Nude mice were injected in the pancreas with L3.9pl human pancreatic cancer cells. One week later, the mice were randomized into 4 treatment groups: i) control, saline; ii) oral STI 571; iii) intraperitoneal gemcitabine; and iv) STI 571 and gemcitabine. After 1, 2, and 3 weeks of treatment, sera and tumors were collected from mice in each group as well as uninjected mice. All sera were analyzed by surface enhanced laser desorption ionization mass spectrometry using ProteinChip technology. Protein profiles were analyzed with the Biomarker Wizard software package. The concentration of candidate proteins was evaluated in mouse sera and plasma from 135 pancreatic cancer patients, 7 pancreatitis patients, and 113 healthy volunteers. The combination therapy inhibited tumor growth. A 11.7-kDa protein peak correlating with tumor weight was purified by gel filtration, separated by SDS-PAGE, and identified as mouse serum amyloid A (SAA) by amino acid sequencing and public database searches. The expression of SAA in mouse sera was confirmed by Western blotting and correlated with tumor weight. The level of SAA in plasma of pancreatic cancer patients correlated with clinical stage and was significantly higher than in normal volunteers (mean value: 180.1 microg/ml vs 27.9 microg/ml: P<0.01) or pancreatitis patients. For SAA used as a single tumor marker with a cut-off of 75 microg/ml, the sensitivity for pancreatic cancer was 96.5% and specificity was 31.9%. Our search for specific marker proteins to identify pancreatic cancer was unsuccessful. Although SAA is not specific for pancreatic cancer and not sensitive enough to detect stage I patients, it may be a candidate biomarker for detecting and monitoring the progressive growth of pancreatic cancer.

A role for cell-cycle-regulated histone H3 lysine 56 acetylation in the DNA damage response

DNA breaks are extremely harmful lesions that need to be repaired efficiently throughout the genome. However, the packaging of DNA into nucleosomes is a significant barrier to DNA repair, and the mechanisms of repair in the context of chromatin are poorly understood. Here we show that lysine 56 (K56) acetylation is an abundant modification of newly synthesized histone H3 molecules that are incorporated into chromosomes during S phase. Defects in the acetylation of K56 in histone H3 result in sensitivity to genotoxic agents that cause DNA strand breaks during replication. In the absence of DNA damage, the acetylation of histone H3 K56 largely disappears in G2. In contrast, cells with DNA breaks maintain high levels of acetylation, and the persistence of the modification is dependent on DNA damage checkpoint proteins. We suggest that the acetylation of histone H3 K56 creates a favourable chromatin environment for DNA repair and that a key component of the DNA damage response is to preserve this acetylation.

Developing an understanding of proteomics: an introduction to biological mass spectrometry

Three components form the foundation of the rapidly growing field of proteomics research: traditional protein chemistry experiments, separations science, and biological mass spectrometry. The increasing demand for proteomics, as well as the presentation of the 2003 Nobel Prize to John Fenn and Koichi Tanaka for ion source development, has placed biological mass spectrometry in the scientific spotlight. A basic understanding of mass spectrometry is increasingly important for basic, translational, and clinical research. This review article presents an introduction to mass spectrometry, a brief description of different mass spectrometry experiments, and new developments in the field.

A circulating ligand for galectin-3 is a haptoglobin-related glycoprotein elevated in individuals with colon cancer

BACKGROUND & AIMS

Galectin-3 is a beta-galactoside-binding protein implicated in tumor progression and metastasis of colorectal cancers. To determine whether circulating galectin-3 ligands are related to the presence of colon cancer, we sought to identify and quantify ligands in serum that bind to galectin-3.

METHODS

Sera from patients with colon cancer, adenomas, and normal individuals were desialylated, reduced, and separated by sodium dodecyl sulfate/polyacrylamide gel electrophoresis (SDS-PAGE) and blots probed with biotinylated galectin-3.

RESULTS

In colon cancer sera, the major galectin-3 ligand was a 40-kilodalton band distinct from mucin, carcinoembryonic antigen, and Mac-2 binding protein. Serum 40-kilodalton ligand was 10- to 30-fold higher in patients with colon cancer than in healthy subjects. Ligand was purified by gel filtration, affinity precipitation on galectin-3/agarose, and SDS-PAGE. When tryptic peptides were analyzed by matrix-assisted laser-desorption ionization mass spectrometry and protein database searching, the 40-kilodalton ligand was identified as haptoglobin beta subunit. In confirmation of this finding, depletion of haptoglobin by immunoprecipitation also eliminated the 40-kilodalton ligand. Colon cancer sera had only a modest increase in total haptoglobin as compared with healthy subjects, suggesting that the structure rather than the amount of haptoglobin is altered in patients with colon cancer. Immunohistochemical staining confirmed the absence of haptoglobin in normal colon and the ectopic expression of haptoglobin in colon cancers and adenomatous polyps.

CONCLUSIONS

A major circulating ligand for galectin-3, which is elevated in the sera of patients with colon cancer, is a cancer-associated glycoform of haptoglobin.

Human p32, interacts with B subunit of the CCAAT-binding factor, CBF/NF-Y, and inhibits CBF-mediated transcription activation in vitro

To understand the role of the CCAAT-binding factor, CBF, in transcription, we developed a strategy to purify the heterotrimeric CBF complex from HeLa cell extracts using two successive immunoaffinity chromatography steps. Here we show that the p32 protein, previously identified as the ASF/SF2 splicing factor-associated protein, copurified with the CBF complex. Studies of protein-protein interaction demonstrated that p32 interacts specifically with CBF-B subunit and also associates with CBF-DNA complex. Cellular localization by immunofluorescence staining revealed that p32 is present in the cell throughout the cytosol and nucleus, whereas CBF is present primarily in the nucleus. A portion of the p32 colocalizes with CBF-B in the nucleus. Interestingly, reconstitution of p32 in an in vitro transcription reaction demonstrated that p32 specifically inhibits CBF-mediated transcription activation. Altogether, our study identified p32 as a novel and specific corepressor of CBF-mediated transcription activation in vitro.

Tumor suppressor ARF degrades B23, a nucleolar protein involved in ribosome biogenesis and cell proliferation

The tumor suppressor ARF induces a p53-dependent and -independent cell cycle arrest. Unlike the nucleoplasmic MDM2 and p53, ARF localizes in the nucleolus. The role of ARF in the nucleolus, the molecular target, and the mechanism of its p53-independent function remains unclear. Here we show that ARF interacts with B23, a multifunctional nucleolar protein involved in ribosome biogenesis, and promotes its polyubiquitination and degradation. Overexpression of B23 induces a cell cycle arrest in normal fibroblasts, whereas in cells lacking p53 it promotes S phase entry. Conversely, knocking down B23 inhibits the processing of preribosomal RNA and induces cell death. Further, oncogenic Ras induces B23 only in ARF null cells, but not in cells that retain wild-type ARF. Together, our results reveal a molecular mechanism of ARF in regulating ribosome biogenesis and cell proliferation via inhibiting B23, and suggest a nucleolar role of ARF in surveillance of oncogenic insults.

Expression and purification of the angiogenesis inhibitor 16-kDa prolactin fragment from insect cells

The 16-kDa fragment of prolactin (16-kDa PRL), derived from proteolytic cleavage of 23-kDa PRL, was shown to have antiangiogenic activity. Previous studies have shown that recombinant 16-kDa PRL produced from bacteria often contained endotoxins, which are cytotoxic to endothelial cells, and varied in its biological activity due to changes in its refolding from inclusion bodies. These problems limited the use of recombinant 16-kDa PRL. To improve the generation of recombinant 16-kDa PRL, we expressed 16-kDa PRL in Sf9 insect cells using a baculoviral expression system. The signal sequence of the human PRL gene and codons for seven histidines were added to the N- and C-termini, respectively, of the 16-kDa PRL cDNA construct. Recombinant 16-kDa PRL was detected in both the cell pellet and the medium. About 0.28 mg purified protein was isolated from the cell pellet of 4 x 10(7) infected cells using nickel affinity chromatography. Sixteen kilodalton PRL was posttranslationally modified with apparent molecular weights of 16 and 18 kDa on SDS-PAGE. The level of 18-kDa protein was significantly reduced after digestion with peptidyl-N-glycosidase, suggesting that the heterogeneity was due to glycosylation of 16-kDa PRL. N-terminal sequence analysis confirmed the fact that both proteins were human 16-kDa PRL and the signal sequences were cleaved at the same position as that of human PRL. Consistent with its role as an angiogenesis inhibitor, purified recombinant 16-kDa PRL inhibits the proliferation of endothelial cells with a potency similar to that previously reported for the protein generated in Escherichia coli. This 16-kDa PRL expressed in Sf9 cells is a useful reagent for functional studies and for the purification and identification of its receptor.

Immunoglobulin variable-region-like domains of diverse sequence within the major histocompatibility complex of the chicken

The highly polymorphic B-G antigens are considered to be part of the major histocompatibility complex (MHC) of the chicken, the B system of histocompatibility, because they are encoded in a family of genes tightly linked with the genes encoding MHC class I and class II antigens. To better understand these unusual MHC antigens, full-length B-G cDNA clones were isolated from B21 embryonic erythroid cell cDNA library, restriction-mapped, and sequenced. Five transcript types were identified. Analysis of the deduced amino acid sequences suggests that the B-G polypeptides are composed of single extracellular domains that resemble immunoglobulin domains of the variable-region (V) type, single membrane-spanning domains typical of integral membrane proteins, and long cytoplasmic tails. Sequence diversity among the five transcript types was found in all domains, notably including the B-G immunoglobulin V-like domains. The cytoplasmic tails of the B-G antigens are made up entirely of units of seven amino acid residues (heptads) that are typical of an alpha-helical coiled-coil conformation. The heptads vary in number and sequence between the different transcripts. The presence within B-G polypeptides of polymorphic immunoglobulin V-like domains warrants further investigations to determine the degree and nature of variability within this domain in these unusual MHC antigens.

Purification of somatostatin from frog brain: coisolation with retinal somatostatin-like immunoreactivity

Somatostatin-like immunoreactivity (SLI) was purified from frog brain and retina, and the structure of the brain peptide was determined. Frog brain (101 g) and retinal (45 g) tissues were extracted with 3% acetic acid, yielding 9.6 and 0.44 nmol of SLI, respectively. SLI was further purified by chromatography on a somatostatin immunoaffinity column followed by sequential application to reverse-phase C-18 HPLC columns. The brain and retinal peptides, purified roughly 100,000-fold with net yields of 7.5 and 2.3%, respectively, appeared identical in the final steps of purification. The amino acid sequence of brain SLI, as determined by a gas-phase automated Edman degradation technique, was as follows: Ala-Gly-(Cys)-Lys-Asn-Phe-Phe-Trp-Lys-Thr-Phe-Thr-Ser-(Cys). Our data indicate that despite structural variations in somatostatins of other lower vertebrates, the amino acid sequence of frog brain and, by deduction, retinal SLI is identical to that of somatostatin tetradecapeptide. These findings support the physiological relevance of studies directed at elucidating the neurotransmitter function of somatostatin using the well-established models of frog brain and retina.