Prostate-specific membrane antigen (PSMA) glycoforms in prostate cancer patients seminal plasma

INTRODUCTION

Prostate-specific membrane antigen (PSMA) is a US Food and Drug Administration-approved theranostic target for prostate cancer (PCa). Although PSMA is known to be glycosylated, the composition and functional roles of its N-linked glycoforms have not been fully characterized.

METHODS

PSMA was isolated from pooled seminal plasma from low-risk grade Groups 1 and 2 PCa patients. Intact glycopeptides were analyzed by mass spectrometry to identify site-specific glycoforms.

RESULTS

We observed a rich distribution of PSMA glycoforms in seminal plasma from low and low-intermediate-risk PCa patients. Some interesting generalities can be drawn based on the predicted topology of PSMA on the plasma membrane. The glycoforms at ASN-459, ASN-476, and ASN-638 residues that are located at the basal domain facing the plasma membrane in cells, are predominantly high mannose glycans. ASN-76 which is located in the interdomain region adjacent to the apical domain of the protein shows a mixture of high mannose glycans and complex glycans, whereas ASN-121, ASN-195 and ASN-336 that are located and are exposed at the apical domain of the protein predominantly possess complex sialylated and fucosylated N-linked glycans. These highly accessible glycosites display the greatest diversity in isoforms across the patient samples.

CONCLUSIONS

Our study provides novel qualitative insights into PSMA glycoforms that are present in the seminal fluid of PCa patients. The presence of a rich diversity of glycoforms in seminal plasma provides untapped potential for glycoprotein biomarker discovery and as a clinical sample for noninvasive diagnostics of male urological disorders and diseases including PCa. Specifically, our glycomics approach will be critical in uncovering PSMA glycoforms with utility in staging and risk stratification of PCa.

MDA-9/Syntenin in the tumor and microenvironment defines prostate cancer bone metastasis

Bone metastasis is a frequent and incurable consequence of advanced prostate cancer (PC). An interplay between disseminated tumor cells and heterogeneous bone resident cells in the metastatic niche initiates this process. Melanoma differentiation associated gene-9 (mda-9/Syntenin/syndecan binding protein) is a prometastatic gene expressed in multiple organs, including bone marrow-derived mesenchymal stromal cells (BM-MSCs), under both physiological and pathological conditions. We demonstrate that PDGF-AA secreted by tumor cells induces CXCL5 expression in BM-MSCs by suppressing MDA-9-dependent YAP/MST signaling. CXCL5-derived tumor cell proliferation and immune suppression are consequences of the MDA-9/CXCL5 signaling axis, promoting PC disease progression. mda-9 knockout tumor cells express less PDGF-AA and do not develop bone metastases. Our data document a previously undefined role of MDA-9/Syntenin in the tumor and microenvironment in regulating PC bone metastasis. This study provides a framework for translational strategies to ameliorate health complications and morbidity associated with advanced PC.

Site-Specific Intact N-Linked Glycopeptide Characterization of Prostate-Specific Membrane Antigen from Metastatic Prostate Cancer Cells

The composition of N-linked glycans that are conjugated to the prostate-specific membrane antigen (PSMA) and their functional significance in prostate cancer progression have not been fully characterized. PSMA was isolated from two metastatic prostate cancer cell lines, LNCaP and MDAPCa2b, which have different tissue tropism and localization. Isolated PSMA was trypsin-digested, and intact glycopeptides were subjected to LC-HCD-EThcD-MS/MS analysis on a Tribrid Orbitrap Fusion Lumos mass spectrometer. Differential qualitative and quantitative analysis of site-specific N-glycopeptides was performed using Byonic and Byologic software. Comparative quantitative analysis demonstrates that multiple glycopeptides at asparagine residues 51, 76, 121, 195, 336, 459, 476, and 638 were in significantly different abundance in the two cell lines (p < 0.05). Biochemical analysis using endoglycosidase treatment and lectin capture confirm the MS and site occupancy data. The data demonstrate the effectiveness of the strategy for comprehensive analysis of PSMA glycopeptides. This approach will form the basis of ongoing experiments to identify site-specific glycan changes in PSMA isolated from disease-stratified clinical samples to uncover targets that may be associated with disease progression and metastatic phenotypes.

Abstract 520: MYB exhibits racially disparate overexpression and clinicopathologic association in prostate cancer: significance as a predictor of biochemical recurrence

Prostate cancer (PCa) is the most diagnosed non-cutaneous malignancy and the second leading cause of cancer-related death in American men. Significant racial disparities also exist in incidence and clinical outcome. African American (AA) men are nearly two times more likely to be diagnosed with PCa and have more than twice mortality rate than their Caucasian American (CA) counterparts. Despite an early diagnosis in majority of the cases, about one-third patients face biochemical recurrence following local therapy, with a likelihood of developing distant metastasis. Gleason score used as a prognosticator exhibits discrepancy between AA and CA men highlighting the need for better predictive markers. We previously demonstrated functional significance of MYB in PCa growth, aggressiveness, and castration-resistance. We also showed a role of MYB in sustained androgen receptor (AR) signaling under androgen-deprived condition and prostate-specific antigen (PSA) expression. Here, we studied the expression of MYB in PCa by immunohistochemistry and examined if it varied between AA and CA PCa cases and had any clinicopathological correlation. A total of 105 PCa [CA (n=50) and AA (n=55)] cases with available clinicopathologic data were included. MYB expression was also studied in adjacent benign prostatic hyperplasia (BPH) and high-grade prostate intraepithelial neoplastic (HGPIN) lesions. Stained slides were scanned and digitally analyzed for the measurement of percent positivity (0-100%) and staining intensity (1+, 2+ and 3+). Significant overexpression of MYB (p&lt;0.0001) was reported in PCa relative to HGPIN and BPH. PCa predominantly exhibited moderate to strong staining, compared to weak to moderate staining with low precent positivity rate in HGPIN and weak MYB staining with low percent positivity in BPH. A significantly higher expression of MYB (p&lt;0.0001) was noted in high Gleason score (8-9) PCa, compared to the low-medium Gleason score (≤7) PCa. Interestingly, MYB expression was significantly (p= 0.024) higher in AA PCa than CA PCa in overall and Gleason score wise comparisons. Correlation analysis of MYB showed its inverse association with time to BCR (r =-0.467, 95% CI=-0.675 to -0.190, p=0.002). Altogether, our findings establish MYB as a potentially useful biomarker for PCa diagnosis and prognosis and provide clinical support to our prior findings on the pathobiological role of MYB in PCa.

Citation Format: Mohammad Aslam Khan, Srijan Acharya, Shashi Anand, Fnu Sameeta, James E. Carter, Oliver J. Semmes, Dean A. Troyer, Seema Singh, Santanu Dasgupta, Ajay P. Singh. MYB exhibits racially disparate overexpression and clinicopathologic association in prostate cancer: significance as a predictor of biochemical recurrence [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 520.

Prostate Cancer Biomarker Development: National Cancer Institute's Early Detection Research Network Prostate Cancer Collaborative Group Review

Prostate cancer remains the most common non-skin cancer and second leading cause of death among men in the United States. Although progress has been made in diagnosis and risk assessment, many clinical questions remain regarding early identification of prostate cancer and management. The early detection of aggressive disease continues to provide high curative rates if diagnosed in a localized state. Unfortunately, prostate cancer displays significant heterogeneity within the prostate organ and between individual patients making detection and treatment strategies complex. Although prostate cancer is common among men, the majority will not die from prostate cancer, introducing the issue of overtreatment as a major concern in clinical management of the disease. The focus of the future is to identify those at highest risk for aggressive prostate cancer and to develop prevention and screening strategies, as well as discerning the difference in malignant potential of diagnosed tumors. The Prostate Cancer Research Group of the National Cancer Institute's Early Detection Research Network has contributed to the progress in addressing these concerns. This summary is an overview of the activities of the group.See all articles in this CEBP Focus section, "NCI Early Detection Research Network: Making Cancer Detection Possible."

Targeted Mass Spectrometry of a Clinically Relevant PSA Variant from Post-DRE Urines for Quantitation and Genotype Determination

Purpose

The rs17632542 single nucleotide polymorphism (SNP) results in lower serum prostate specific antigen (PSA) levels which may further mitigate against its clinical utility as a prostate cancer biomarker. Post‐digital rectal exam (post‐DRE) urine is a minimally invasive fluid that is currently utilized in prostate cancer diagnosis. To detect and quantitate the variant protein in urine.

Experimental design

Fifty‐three post‐DRE urines from rs17632542 genotyped individuals processed and analyzed by liquid chromatography/mass spectrometry (LC‐MS) in a double‐blinded randomized study. The ability to distinguish between homozygous wild‐type, heterozygous, or homozygous variant is examined before unblinding.

Results

Stable‐isotope labeled peptides are used in the detection and quantitation of three peptides of interest in each sample using parallel reaction monitoring (PRM). Using these data, groupings are predicted using hierarchical clustering in R. Accuracy of the predictions show 100% concordance across the 53 samples, including individuals homozygous and heterozygous for the SNP.

Conclusions and clinical relevance

The study demonstrates that MS based peptide variant quantitation in urine could be useful in determining patient genotype expression. This assay provides a tool to evaluate the utility of PSA variant (rs17632542) in parallel with current and forthcoming urine biomarker panels.

Complex-I Alteration and Enhanced Mitochondrial Fusion Are Associated With Prostate Cancer Progression

Mitochondria (mt) encoded respiratory complex-I (RCI) mutations and their pathogenicity remain largely unknown in prostate cancer (PCa). Little is known about the role of mtDNA loss on mt integrity in PCa. We determined mtDNA mutation in human and mice PCa and assessed the impact of mtDNA depletion on mt integrity. We also examined whether the circulating exosomes from PCa patients are transported to mt and carry mtDNA or mt proteins. We have employed next generation sequencing of the whole mt genome in human and Hi-myc PCa. The impact of mtDNA depletion on mt integrity, presence of mtDNA, and protein in sera exosomes was determined. A co-culture of human PCa cells and the circulating exosomes followed by confocal imaging determined co-localization of exosomes and mt. We observed frequent RCI mutations in human and Hi-myc PCa which disrupted corresponding complex protein expression. Depletion of mtDNA in PCa cells influenced mt integrity, increased expression of MFN1, MFN2, PINK1, and decreased expression of MT-TFA. Increased mt fusion and expression of PINK1 and DNM1L were also evident in the Hi-myc tumors. RCI-mtDNA, MFN2, and IMMT proteins were detected in the circulating exosomes of men with benign prostate hyperplasia (BPH) and progressive PCa. Circulating exosomes and mt co-localized in PCa cells. Our study identified new pathogenic RCI mutations in PCa and defined the impact of mtDNA loss on mt integrity. Presence of mtDNA and mt proteins in the circulating exosomes implicated their usefulness for biomarker development.

MDA-9/Syntenin regulates differentiation and angiogenesis programs in head and neck squamous cell carcinoma

Little is known about the molecular pathways regulating poor differentiation and invasion of head and neck squamous cell carcinoma (HNSCC). In the present study, we aimed to determine the role of MDA-9/Syntenin, a metastasis associated molecule in HNSCC tumorigenesis. Elevated MDA-9/Syntenin expression was evident in 67% (54/81) primary HNSCC tumors (p=0.001-0.002) and 69% (9/13) pre-neoplastic tissues (p=0.02-0.03). MDA-9/Syntenin overexpression was associated with the stage (p=0.001), grade (p=0.001) and lymph node metastasis (p=0.0001). Silencing of MDA-9/Syntenin in 3 poorly differentiated HNSCC cell lines induced squamous epithelial cell differentiation, disrupted angiogenesis and reduced tumor growth in vitro and in vivo. We confirmed SPRR1B and VEGFR1 as the key molecular targets of MDA-9/Syntenin on influencing HNSCC differentiation and angiogenesis respectively. MDA-9/Syntenin disrupted SPRR1B expression interacting through its PDZ1 domain and altered VEGFR1 expression in vitro and in vivo. VEGFR1 co-localized with MDA-9/Syntenin in HNSCC cell lines and primary tumor. Downregulation of growth regulatory molecules CyclinD1, CDK4, STAT3, PI3K and CTNNB1 was also evident in the MDA-9/Syntenin depleted cells, which was reversed following over-expression of MDA-9/Syntenin in immortalized oral epithelial cells. Our results suggest that early induction of MDA-9/Syntenin expression influences HNSCC progression and should be further evaluated for potential biomarker development.

Molecular pathology of prostate cancer

This chapter includes discussion of the molecular pathology of tissue, blood, urine, and expressed prostatic secretions. Because we are unable to reliably image the disease in vivo, a 12 core method that oversamples the peripheral zone is widely used. This generates large numbers of cores that need to be carefully processed and sampled. In spite of the large number of tissue cores, the amount of tumor available for study is often quite limited. This is a particular challenge for research, as new biomarker assays will need to preserve tissue architecture intact for histopathology. Methods of processing and reporting pathology are discussed. With the exception of ductal variants, recognized subtypes of prostate cancer are largely confined to research applications, and most prostate cancers are acinar. Biomarker discovery in urine and expressed prostatic secretions would be useful since these are readily obtained and are proximate fluids. The well-known challenges of biomarker discovery in blood and urine are referenced and discussed. Mediators of carcinogenesis can serve as biomarkers as exemplified by mutations in PTEN and TMPRSS2:ERG fusion. The use of proteomics in biomarker discovery with an emphasis on imaging mass spectroscopy of tissues is discussed. Small RNAs are of great interest, however, their usefulness as biomarkers in clinical decision making remains the subject of ongoing research. The chapter concludes with an overview of blood biomarkers such as circulating nucleic acids and tumor cells and bound/free isoforms of prostate specific antigen (PSA).

Characterization of a pigment-dispersing hormone in eyestalks of the fiddler crab Uca pugilator

A pigment-dispersing hormone (PDH) from eyestalks of the fiddler crab Uca pugilator has been purified by gel filtration, ion-exchange chromatography, partition chromatography, and reversed-phase liquid chromatography. Based on automated gas-phase sequencing and subsequent identification of carboxyl-terminal amide, we have assigned the primary structure of this peptide as Asn-Ser-Glu-Leu-Ile-Asn-Ser-Ile-Leu-Gly-Leu-Pro-Lys-Val-Met-Asn-Asp-Ala-NH (2). We have confirmed the sequence by synthesizing this peptide and demonstrating that the synthetic PDH and the native PDH display identical chromatographic behavior and biological activity. This hormone is a member of a family of invertebrate neuropeptides that includes a light-adapting/pigment-dispersing octadecapeptide hormone from the prawn Pandalus borealis. In assays for melanophore pigment dispersion in destalked fiddler crabs, Uca PDH was 21-fold more potent than Pandalus PDH. These two hormones share a hexapeptide core sequence (residues 5-10: -Ile-Asn-Ser-Ile-Leu-Gly-) as well as the amino- and carboxyl-terminal residues but differ at positions 3, 4, 11, 13, 16, and 17. These results point to speciesrelated or group-specific structural differences among crustacean PDHs.

Purification of FANCD2 sub-complexes

Fanconi anaemia (FA) is a recessive genetic disorder characterized by bone marrow failure, birth defects and cancer. Cells from FA patients are particularly defective in removing DNA interstrand crosslinks. We have developed a working chromatography purification scheme for FANCD2, a pivotal player in the FA DNA repair pathway, to facilitate identification of FANCD2 interacting partners. In doing so, at least three distinct FANCD2 subcomplexes were found to be present, designated as large, middle, and small complexes. The small complex is composed of tetramer of FANCD2 polypeptides, which may be the building block for other FANCD2 subcomplexes.

Abstract 3307: Cell-surface glycoproteomics identifies CUB-domain containing protein 1 to be associated with prostate cancer metastasis

Prostate cancer is still the most common and second leading cause of cancer death in men in the United States and is overwhelmingly lethal when metastatic. Evidence from histochemical analysis and experimental tumor models indicates alterations in cell-surface sialylation as a general observation associated with the metastatic potential of tumor cells. Our preliminary data from lectin staining also demonstrates changes of cell-surface sialylation in a syngeneic prostate cancer cell model, which includes two PC3 sublines, N2 (non-metastatic) and ML2 (highly metastatic). Characterization of cell-surface sialylated glycoproteins in this model system could provide new information related to the metastatic phenotype in prostate cancer. Thus, cell-surface sialoglycoproteins in the N2 and ML2 cell lines were metabolicly labeled with with an unnatural mannose analogue (AC4ManNAz); This was followed by chemoselective conjugation of the azido sugars with a biotinylated alkyne capture reagent via Cu (I) catalyzed click chemistry and affinity detection and enrichment by streptavidin-conjugated beads (or fluorescein). Captured glycoproteins were separated by 1D gel electrophoresis, in-gel proteolytic digestion, and protein identification by means of tandem mass spectrometry (LC-MS/MS). The expression of the targeted sialoglycoproteins was verified in our prostate cancer cell lines and clinical samples by means of Western blot, confocal microscopy and fluorescent immunohistochemistry. Forty three cell-surface N-linked glycoproteins were identified as differentially expressed between the PC3 metastasis variants, including CUB-domain containing protein 1 (CDCP1). Western blot analysis of the cell-surface glycoprotein enriched fractions and total cell lysate confirmed that CDCP1 was over-expressed in the metastatic ML2 cells. Expression of CDCP1 is dysregulated in prostate cancer tissues, with malignant glands showing a more intense cell surface staining pattern, whereas normal glands demonstrated weak membrane and intracellular granular staining on the basal side. We conclude that glycan metabolic labeling technology combined with mass spectrometry analysis provides a powerful tool for the identification of specific cell-surface glycoproteins that may contribute to prostate cancer metastasis, like CDCP1. Further studies are warranted to evaluate the clinical value of CDCP1 and to understand its function in prostate cancer progression.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3307.

A Bayesian network approach to feature selection in mass spectrometry data

Background

Time-of-flight mass spectrometry (TOF-MS) has the potential to provide non-invasive, high-throughput screening for cancers and other serious diseases via detection of protein biomarkers in blood or other accessible biologic samples. Unfortunately, this potential has largely been unrealized to date due to the high variability of measurements, uncertainties in the distribution of proteins in a given population, and the difficulty of extracting repeatable diagnostic markers using current statistical tools. With studies consisting of perhaps only dozens of samples, and possibly hundreds of variables, overfitting is a serious complication. To overcome these difficulties, we have developed a Bayesian inductive method which uses model-independent methods of discovering relationships between spectral features. This method appears to efficiently discover network models which not only identify connections between the disease and key features, but also organizes relationships between features--and furthermore creates a stable classifier that categorizes new data at predicted error rates.

Results

The method was applied to artificial data with known feature relationships and typical TOF-MS variability introduced, and was able to recover those relationships nearly perfectly. It was also applied to blood sera data from a 2004 leukemia study, and showed high stability of selected features under cross-validation. Verification of results using withheld data showed excellent predictive power. The method showed improvement over traditional techniques, and naturally incorporated measurement uncertainties. The relationships discovered between features allowed preliminary identification of a protein biomarker which was consistent with other cancer studies and later verified experimentally.

Conclusions

This method appears to avoid overfitting in biologic data and produce stable feature sets in a network model. The network structure provides additional information about the relationships among features that is useful to guide further biochemical analysis. In addition, when used to classify new data, these feature sets are far more consistent than those produced by many traditional techniques.

Physical and in silico approaches identify DNA-PK in a Tax DNA-damage response interactome

Background

We have initiated an effort to exhaustively map interactions between HTLV-1 Tax and host cellular proteins. The resulting Tax interactome will have significant utility toward defining new and understanding known activities of this important viral protein. In addition, the completion of a full Tax interactome will also help shed light upon the functional consequences of these myriad Tax activities. The physical mapping process involved the affinity isolation of Tax complexes followed by sequence identification using tandem mass spectrometry. To date we have mapped 250 cellular components within this interactome. Here we present our approach to prioritizing these interactions via an in silico culling process.

Results

We first constructed an in silico Tax interactome comprised of 46 literature-confirmed protein-protein interactions. This number was then reduced to four Tax-interactions suspected to play a role in DNA damage response (Rad51, TOP1, Chk2, 53BP1). The first-neighbor and second-neighbor interactions of these four proteins were assembled from available human protein interaction databases. Through an analysis of betweenness and closeness centrality measures, and numbers of interactions, we ranked proteins in the first neighborhood. When this rank list was compared to the list of physical Tax-binding proteins, DNA-PK was the highest ranked protein common to both lists. An overlapping clustering of the Tax-specific second-neighborhood protein network showed DNA-PK to be one of three bridge proteins that link multiple clusters in the DNA damage response network.

Conclusion

The interaction of Tax with DNA-PK represents an important biological paradigm as suggested via consensus findings in vivo and in silico. We present this methodology as an approach to discovery and as a means of validating components of a consensus Tax interactome.

Human T-cell leukemia virus I tax protein sensitizes p53-mutant cells to DNA damage

Mutations in p53 are a common cause of resistance of cancers to standard chemotherapy and, thus, treatment failure. Reports have shown that Tax, a human T-cell leukemia virus type I encoded protein that has been associated with genomic instability and perturbation of transcription and cell cycle, sensitizes HeLa cells to UV treatment. The extent to which Tax can sensitize cells and the mechanism by which it exerts its effect are unknown. In this study, we show that Tax sensitizes p53-mutant cells to a broad range of DNA-damaging agents, including mitomycin C, a bifunctional alkylator, etoposide, a topoisomerase II drug, and UV light, but not ionizing radiation, a double-strand break agent, or vinblastine, a tubulin poison. Tax caused hypersensitivity in all p53-deleted cell lines and several, but not all, mutant-expressed p53-containing cell lines, while unexpectedly being protective in p53 wild-type (wt) cells. The effect observed in p53-deleted lines could be reversed for this by transfection of wt p53. We also show that Tax activates a p53-independent proapoptotic program through decreased expression of the retinoblastoma protein and subsequent increased E2F1 expression. The expression of several proapoptotic proteins was also induced by Tax, including Puma and Noxa, culminating in a substantial increase in Bax dimerization. Our results show that Tax can sensitize p53-mutant cells to DNA damage while protecting p53 wt cells, a side benefit that might result in reduced toxicity in normal cells. Such studies hold the promise of a novel adjunctive therapy that could make cancer chemotherapy more effective.

Optimization of MALDI-TOF MS detection for enhanced sensitivity of affinity-captured proteins spanning a 100 kDa mass range

Analysis of complex biological samples by MALDI-TOF mass spectrometry has been generally limited to the detection of low-mass protein (or protein fragment) peaks. We have extended the mass range of MALDI-TOF high-sensitivity detection by an order of magnitude through the combined optimization of instrument parameters, data processing, and sample preparation procedures for affinity capture. WCX, C3, and IMAC magnetic beads were determined to be complementary and most favorable for broad mass range protein profiling. Key instrument parameters for extending mass range included adjustment of the ADC offset and preamplifier filter values of the TOF detector. Data processing was improved by a combination of constant and quadratic down-sampling, preceded by exponential baseline subtraction, to increase sensitivity of signal peaks. This enhancement in broad mass range detection of protein signals will be of direct benefit in MS expression profiling studies requiring full linear range mass detection.

Overexpression of alpha-defensin is associated with bladder cancer invasiveness

Alpha-defensin (alpha-defensin) has been identified as a potential marker for bladder cancer in urine by surface enhanced laser desorption ionization studies, and confirmed using both immunoabsorption and immunodepletion studies. The objective of this study was to investigate the role of alpha-defensin in bladder cancer. Immunohistochemical analysis of tissue sections showed that alpha-defensin peptides are frequently expressed in bladder cancer cells. It is noteworthy that expression of alpha-defensins increased with tumor invasiveness. Surface enhanced laser desorption ionization analysis showed the presence of alpha-defensin in the T24 and A498 cancer cell lines. These cell lines show higher classically aggressive in vitro characteristics compared with the J82 cells that did not express alpha-defensin. Exogenously added alpha-defensin increased the proliferation and motility/invasiveness of these cell lines using respective assays. It is interesting that alpha-defensin peptides increased intracellular calcium ions (Ca2+). These data are consistent with a role for alpha-defensin in bladder cancer via modulation of cell motility and invasiveness using common intracellular signals, such as Ca2+. We propose that autocrine tumor expression of alpha-defensins may play an important role in facilitating the invasive phenotype of bladder cancer in patients.

Discrete serum protein signatures discriminate between human retrovirus-associated hematologic and neurologic disease

The human T-cell leukemia virus type I (HTLV-I) is the causative agent for adult T-cell leukemia (ATL) and HTLV-I-associated myelopathy/tropical spastic paraparesis (HAM/TSP). Approximately 5% of infected individuals will develop either disease and currently there are no diagnostic tools for early detection or accurate assessment of disease state. We have employed high-throughput expression profiling of serum proteins using mass spectrometry to identify protein expression patterns that can discern between disease states of HTLV-I-infected individuals. Our study group consisted of 42 ATL, 50 HAM/TSP, and 38 normal controls. Spectral peaks corresponding to peptide ions were generated from MS-TOF data. We applied Classification and Regression Tree analysis to build a decision algorithm, which achieved 77% correct classification rate across the three groups. A second cohort of 10 ATL, 10 HAM and 10 control samples was used to validate this result. Linear discriminate analysis was performed to verify and visualize class separation. Affinity and sizing chromatography coupled with tandem mass spectrometry was used to identify three peaks specifically overexpressed in ATL: an 11.7 kDa fragment of alpha trypsin inhibitor, and two contiguous fragments (19.9 and 11.9 kDa) of haproglobin-2. To the best of our knowledge, this is the first application of protein profiling to distinguish between two disease states resulting from a single infectious agent.

Proteomic approaches to biomarker discovery in prostate and bladder cancers

Proteomic technologies, including high resolution two-dimensional electrophoresis (2-DE), antibody/protein arrays, and advances in mass spectrometry (MS), are providing the tools needed to discover and identify disease associated biomarkers. Although application of these technologies to search for potential diagnostic/prognostic biomarkers associated with prostate and bladder cancer have been somewhat limited to date, proteins either overexpressed or underexpressed have been detected in both these urological cancers. Recent advances in mass spectrometry, especially platforms that permit rapid "fingerprint" profiling of multiple biomarkers, and tandem mass spectrometers for protein identification, will most assuredly enhance the discovery, identification, and characterization of potential cancer associated biomarkers. Furthermore, application of laser capture microdissection microscopes has provided a rapid and reproducible approach to procure pure populations of cells. This technology coupled to 2-DE and MS has significantly aided the elucidation of the differential expression profiles between disease, benign and normal prostate and bladder cell populations. Finally, development and application of learning algorithms and bioinformatics to the data generated by these proteomic technologies will be essential in determining the clinical potential of a protein biomarker. The purpose of this review is to provide the reader with an overview of the application of these technologies in the search and identification of potential diagnostic/prognostic biomarkers for prostate and bladder cancers.

Proteomic approaches to biomarker discovery in prostate and bladder cancers

Proteomic technologies, including high resolution two-dimensional electrophoresis (2-DE), antibody/protein arrays, and advances in mass spectrometry (MS), are providing the tools needed to discover and identify disease associated biomarkers. Although application of these technologies to search for potential diagnostic/prognostic biomarkers associated with prostate and bladder cancer have been somewhat limited to date, proteins either overexpressed or underexpressed have been detected in both these urological cancers. Recent advances in mass spectrometry, especially platforms that permit rapid "fingerprint" profiling of multiple biomarkers, and tandem mass spectrometers for protein identification, will most assuredly enhance the discovery, identification, and characterization of potential cancer associated biomarkers. Furthermore, application of laser capture microdissection microscopes has provided a rapid and reproducible approach to procure pure populations of cells. This technology coupled to 2-DE and MS has significantly aided the elucidation of the differential expression profiles between disease, benign and normal prostate and bladder cell populations. Finally, development and application of learning algorithms and bioinformatics to the data generated by these proteomic technologies will be essential in determining the clinical potential of a protein biomarker. The purpose of this review is to provide the reader with an overview of the application of these technologies in the search and identification of potential diagnostic/prognostic biomarkers for prostate and bladder cancers.

Properties of two EBV Mta nuclear export signal sequences

The Epstein-Barr virus (EBV) Mta protein is a posttranscriptional regulator of EBV lytic gene expression that affects RNA splicing and transport. Mta mediates cytoplasmic accumulation of unspliced EBV replication gene transcripts and shuttles between the nucleus and cytoplasm. Mta contains a recognized leucine-rich, putative nuclear export signal (NES) between aa 227 and 236. Deletion of this signal sequence eliminated shuttling, while mutation of the core LXL motif in the putative NES diminished but did not abolish the ability of Mta to shuttle from donor to recipient cells in a heterokaryon assay. A double mutation of the LXL motif plus an upstream VTL motif eliminated shuttling, suggesting that Mta may have two NES motifs. In confirmation of this, transfer of either the sequence encoding the leucine-rich aa 227-236 motif or that encoding the adjacent hydrophobic aa 218-227 sequence to a GFP-NLS-pyruvate kinase reporter protein conferred the property of cytoplasmic accumulation onto the heterologous protein. Cytoplasmic accumulation of both the aa 225-237 and 218-227 containing reporters was minimal in the presence of the inhibitor leptomycin B, indicating that both motifs mediated Crm-1-dependent export. Mutations in the NES signal sequences abolished the ability of Mta to mediate cytoplasmic accumulation of BALF2 replication gene transcripts. This included mutation of the LXL motif which still showed cytoplasmic shuttling, suggesting that the NES mutations might have additional effects on Mta function. Wild-type Mta co-immunoprecipitated with the splicing factor SC35 and colocalized with SC35 in transfected cells, modifying endogenous SC35 distribution within the nucleus to give more intense, rounded spots. Interestingly, the NES mutant proteins appeared to have altered interactions with the splicing complex, binding more tightly to SC35 in co-immunoprecipitation assays. These observations suggest a linkage between the splicing and export functions of Mta.

Human T-cell leukemia virus type 1 Tax shuttles between functionally discrete subcellular targets

Human T-cell leukemia virus type 1 (HTLV-1) Tax is a nuclear protein with striking pleiotropic functionality. We recently demonstrated that Tax localizes to a multicomponent nuclear speckled structure (Tax speckled structure [TSS]). Here, we examine these structures further and identify a partial overlap of TSS with transcription hot spots. We used a strategy of directed expression via fusion proteins to determine if these transcription sites are the subtargets within TSS required for Tax function. When fused to human immunodeficiency virus type 1 (HIV-1) Tat, the resulting Tat-Tax fusion protein displayed neither a Tat-like nor a Tax-like pattern but rather was targeted specifically to the transcription subsites. The Tat-Tax fusion was able to activate both the HIV-1 long terminal repeat (LTR) and the HTVL-1 LTR at the same level as the individual component; thus, targeting proteins to transcription hot spots was compatible with both Tax and Tat transcription function. In contrast, the fusion with HIV-1 Rev, Rev-Tax, resulted in a pattern of expression that was largely Rev-like (nucleolar and cytoplasmic). The reduced localization of Rev-Tax to transcription sites was reflected in a 10-fold drop in activation of the HTLV-1 LTR. However, there was no loss in the ability of Tax to activate via NF-kappaB. Thus, NF-kappaB-dependent Tax function does not require targeting of Tax to these transcription sites and suggests that activation via NF-kappaB is a cytoplasmic function. Selective mutation of the nuclear localization signal site in the Rev portion resulted in retargeting of Rev-Tax to TSS and subsequent restoration of transcription function, demonstrating that inappropriate localization preceded loss of function. Mutation of the nuclear export signal site in the Rev portion had no effect on transcription, although the relative amount of Rev-Tax in the cytoplasm was reduced. Finally, in explaining how Tax can occupy multiple subcellular sites, we show that Tax shuttles from the nucleus to the cytoplasm in a heterokaryon fusion assay. Thus, pleiotropic functionality by Tax is regulatable via shuttling between discrete subcellular compartments.

Analysis of potential phosphorylation sites in human T cell leukemia virus type 1 Tax

The human T cell leukemia virus type 1 (HTLV-1) Tax is a phosphoprotein, however, the contribution of phosphorylation to Tax activity is unknown. Previous studies have shown that phosphorylation of Tax occurs on serine residue(s), within one tryptic fragment, in response to 4beta-phorbol-12beta-myristate-13alpha-acetate, in both mouse and human cells. Studies were conducted in multiple cell lines to identify the specific phosphorylated serines as a prelude to functional analysis. The phosphorylation pattern of Tax was found to be different in 293T and COS-7 cells in comparison with MT-4 and Px-1 cells. However, one tryptic fragment remained consistent in comigration analyses among all cell lines. Using selected Tax serine mutants a tryptic fragment containing a serine at residue 113 believed to be the site of phosphorylation of Tax did not comigrate with the common phosphorylated tryptic fragment. Analysis of selected Tax mutants for ability to trans-activate the cytomegalovirus promoter demonstrated mutation of serine 77 to alanine reduced trans-activation by 90% compared to wild-type Tax. However, examination of the phosphorylation pattern of the serine 77 mutant demonstrated that it is not the site of phosphorylation. These studies demonstrate the importance of using relevant cell lines to characterize the role of phosphorylation in protein function.

Mta has properties of an RNA export protein and increases cytoplasmic accumulation of Epstein-Barr virus replication gene mRNA

The Epstein-Barr virus (EBV) Zta and Mta regulatory proteins were previously found to be required for efficient replication of oriLyt in cotransfection-replication assays, but the contribution of Mta to the replication process was unknown. We now demonstrate that Mta regulates replication gene expression. Using the polymerase processivity factor BMRF1 as an example, we found that in transfected cells, total BMRF1 mRNA levels were unaffected by Mta but that the amounts of cytoplasmic BMRF1 RNA and protein were greatly increased in the presence of Mta. Mta also increased cytoplasmic accumulation of the BALF2, BALF5, BSLF1, and BBLF4 replication gene mRNAs but did not affect cytoplasmic levels of BBLF2/3 mRNA. Thus, five of the six core replication genes require Mta for efficient accumulation of cytoplasmic RNA. The contribution of Mta to posttranscriptional RNA processing was examined. Examination of Mta localization in transfected cells by indirect immunofluorescence revealed that Mta colocalized with the splicing factor SC35. We also found that Mta has RNA binding activity. Glutathione S-transferase-Mta bound to BMRF1 and BMLF1 transcripts but not to a control cellular gene RNA. Mta contains a consensus leucine-rich nuclear export signal. Such signal sequences are characteristic of proteins that undergo nuclear export. Examination of Mta localization in a heterokaryon assay provided evidence that Mta shuttles between the nucleus and the cytoplasm. Our experiments indicate that Mta functions in RNA processing and transport and mediates cytoplasmic accumulation of a number of EBV early mRNAs.

The Epstein-Barr virus lytic transactivator Zta interacts with the helicase-primase replication proteins

The Epstein-Barr virus transactivator Zta triggers lytic gene expression and is essential for replication of the lytic origin, oriLyt. Previous analysis indicated that the Zta activation domain contributed a replication-specific function. We now show that the Zta activation domain interacts with components of the EBV helicase-primase complex. The three helicase-primase proteins BBLF4 (helicase), BSLF1 (primase), and BBLF2/3 (primase-associated factor) were expressed fused to the Myc epitope. When expression plasmids for BBLF4 or BBLF2/3 plus BSLF1 (primase subcomplex) were separately transfected, the proteins localized to the cytoplasm. Interaction between Zta and the components of the helicase-primase complex was tested by examining the ability of Zta to alter the intracellular localization of these proteins. Cotransfection of Zta with Myc-BBLF4 resulted in nuclear translocation of Myc-BBLF4; similarly, cotransfection of Zta with the primase subcomplex led to nuclear translocation of the Myc-BSLF1 and Myc-BBLF2/3 proteins. This relocalization provides evidence for an interaction between Zta and the helicase and Zta and the primase subcomplex. An affinity assay using glutathione S-transferase-Zta fusion proteins demonstrated that Myc-BBLF4 and Myc-BBLF2/3 plus BSLF1 bound to the Zta activation domain (amino acids 1 to 133). In the nuclear relocalization assay, the amino-terminal 25 amino acids of Zta were required for efficient interaction with the primase subcomplex but not for interaction with BBLF4. Evidence for interaction between oriLyt bound Zta and the helicase-primase complex was obtained in a superactivation assay using an oriLyt-chloramphenicol acetyltransferase (CAT) reporter. Zta activated expression from a CAT reporter containing the complete oriLyt region and regulated by the oriLyt BHLF1 promoter. Cotransfection of the helicase-primase proteins, one of which was fused to a heterologous activation domain, led to Zta-dependent superactivation of CAT expression. This assay also provided evidence for an interaction between the single-stranded DNA binding protein, BALF2, and the Zta-tethered helicase-primase complex. The helicase-primase interaction is consistent with a role for Zta in stabilizing the formation of an origin-bound replication complex.

Modulation of Sp1 phosphorylation by human immunodeficiency virus type 1 Tat

We previously reported (K. T. Jeang, R. Chun, N. H. Lin, A. Gatignol, C. G. Glabe, and H. Fan, J. Virol. 67: 6224-6233, 1993) that human immunodeficiency virus type 1 (HIV-1) Tat and Sp1 form a protein-protein complex. Here, we have characterized the physical interaction and a functional consequence of Tat-Sp1 contact. Using in vitro protein chromatography, we mapped the region in Tat that contacts Sp1 to amino acids 30 to 55. We found that in cell-free reactions, Tat augmented double-stranded DNA-dependent protein kinase (DNA-PK)-mediated Sp1 phosphorylation in a contact-dependent manner. Tat mutants that do not bind Sp1 failed to influence phosphorylation of the latter. In complementary experiments, we also found that Tat forms protein-protein contacts with DNA-PK. We confirmed that in HeLa and Jurkat cells, Tat expression indeed increased the intracellular amount of phosphorylated Sp1 in a manner consistent with the results of cell-free assays. Furthermore, using two phosphatase inhibitors and a kinase inhibitor, we demonstrated a modulation of reporter gene expression as a consequence of changes in Sp1 phosphorylation. Taken together, these findings suggest that activity at the HIV-1 promoter is influenced by phosphorylation of Sp1 which is affected by Tat and DNA-PK.

A human T-cell leukemia virus Tax variant incapable of activating NF-kappaB retains its immortalizing potential for primary T-lymphocytes

The human T-cell leukemia virus type 1 (HTLV-1) transactivator (Tax) has been shown to interfere with regulated cellular proliferation. Many studies have focused on the ability of Tax to transform rodent fibroblasts; however, none has defined the molecular requirements for Tax transformation of human lymphoid cells. We show here that tax induces permanent growth of human primary T-lymphocytes by using a transformation/immortalization defective rhadinovirus vector. The cells phenotypically resemble HTLV-immortalized lymphocytes and contain episomally persisting recombinant rhadinoviral sequences, which stably express functional Tax protein. As Tax can activate major cellular signal transducing pathways including NF-kappaB and cAMP-responsive element binding protein (CREB), we asked for the relevance of these routes in the immortalization of human lymphocytes. By using Tax mutants that either activate exclusively CREB/activating transcription factor or are defective in activating this signaling pathway, we delineated that Tax can induce immortalization of primary human T-lymphocytes through a mechanism independent of NF-kappaB activation.

Localization of human T-cell leukemia virus type 1 tax to subnuclear compartments that overlap with interchromatin speckles

Tax, the virally encoded activator of the human T-cell leukemia virus type 1 long terminal repeats, regulates the expression of many cellular genes. This protein has been implicated in transformation events leading to the development of adult T-cell leukemia. Because subcellular localization contributes importantly to protein function, we determined the compartment(s) within the cell in which Tax is found. Using confocal microscopy, we found that Tax localizes to subnuclear domains which overlap with structures previously identified as interchromatin granules or spliceosomal speckles. These Tax speckled structures are coincident with a subset of nuclear transcriptional hot spots. Disruption of the Tax speckled structures by heat shock revealed the existence of different populations of Tax. One population of Tax is tightly associated with nuclear speckles. A second population exists outside of the speckles and is transcriptionally active for some promoters.

Human T-cell leukemia virus type I tax masks c-Myc function through a cAMP-dependent pathway

Human T-cell leukemia virus type I Tax is a pleiotropic gene regulator that functions through CREB/ATF- and NF-kappaB-mediated pathways. In most contexts, Tax is a potent gene activator. Here, we describe an unexpected finding of Myc repression by Tax. In cells that overexpress human T-cell leukemia virus type I Tax, the detection of c-Myc protein in the nucleus by a monoclonal antibody was masked. Tax prevented immunological visualization of a Myc epitope contained within amino acids 45-104, resulting in interference with Myc function in transcription and in anchorage-independent cell growth. Tax did not affect steady-state protein levels since detection of c-Myc with other antibodies was unperturbed. Four observations suggest that this Tax-Myc interaction is mediated through CREB/ATF signal transduction. 1) Tax point mutants, selectively defective for activation of CREB/ATF but not NF-kappaB, failed to mask c-Myc; 2) masking of Myc was abolished when Tax-expressing cells were treated with protein kinase inhibitor H-9; 3) Tax-specific shielding of Myc is absent in cells (B1R) that are genetically defective for cAMP signaling; and 4) forskolin treatment of cells mimicked Tax in masking the Myc epitope. Considered collectively, these findings suggest a regulation of Myc function at the level of localized protein conformation.

HTLV-I and HTLV-II Tax: differences in induction of micronuclei in cells and transcriptional activation of viral LTRs

Human T-cell leukemia virus (HTLV) types I and II are highly related viruses that differ in disease manifestations. HTLV-I has been linked unmistakably to adult T-cell leukemia-lymphoma. On the other hand, there is little evidence that prior infection with HTLV-II increases risk for lymphoproliferative disorders. Both viruses encode homologous transcriptional-activating proteins (respectively designated as Tax1 and Tax2) which have been suggested to be important mediators of viral pathogenesis. Previously, we reported that Tax1 is a potent inducer of micronuclei formation in cells. Here, we present evidence that Tax2 lacks micronuclei inductive ability. We contrast this phenotypic difference between Tax1 and Tax2 at the cellular level with their similarities at the molecular level in transcriptional activation.

The amino terminus of Tax is required for interaction with the cyclic AMP response element binding protein

Tax of human T-cell leukemia virus type 1 was analyzed for interaction with the cyclic AMP response element binding protein (CREB) in vitro with and without Tax response element DNA. Mutations in the carboxy terminus of Tax (L296G and L320G) did not affect binding to CREB and led to supershifts. In contrast, mutants with changes in the amino-terminal cysteine-rich region lost the ability to bind to CREB. The S10A mutant protein bound moderately. Thus, the amino terminus of Tax is essential for Tax-CREB interaction.

Definition of a minimal activation domain in human T-cell leukemia virus type I Tax

Fourteen mutants were used to delineate a minimal activation domain in the Tax protein of human T-cell leukemia virus type I. In an assay using a Gal4-Tax (GalTx) fusion protein and a responsive promoter containing Gal4 consensus binding sites, we found that activation was "squelched" by coexpression of wild-type Tax protein in trans. When Tax mutants were tested for squelching, many competed effectively against GalTx. However, those containing changes in amino acids 289 to 322 failed to inhibit activity. In particular, three mutants that were expressed stably, with changes at amino acids 289, 296, and 320 respectively, did not squelch GalTx activity. On the other hand, mutants with individual changes at amino acid 3, 9, 29, 41, 273, and 337 efficiently inhibited GalTx function. Three other mutants failed to be stably expressed. In separate experiments, when fused alone to the DNA-binding domain of Gal4, amino acids 289 to 322 of Tax conferred trans activation ability. This fusion protein was able to activate a core promoter. These findings suggest that amino acids 289 to 322 define a region that contacts an essential transcription factor and that this region is a modular activation domain.

Induction of micronuclei by HTLV-I Tax: a cellular assay for function

Cellular chromosomal damage is ubiquitously seen in HTLV-I-transformed lymphocytes. It is also characteristic of cells that have been exposed to mutagens. A sensitive measurement for mutagen-induced DNA damage is the formation of micronuclei in treated cells. Because current evidence suggests that HTLV-I Tax is etiologically linked to transformation, we tested for its activity in inducing micronuclei. We show here that transfection into cells of a Tax-producing plasmid rapidly induced the formation of micronuclei. This effect cooperated with that of a mutagen (mitomycin C) and was correlated with the inherent trans-activation capacity of Tax. These findings suggest that a commonly used mutagen assay could be a quick biological test for putatively oncogenic proteins.

Mutational analysis of human T-cell leukemia virus type I Tax: regions necessary for function determined with 47 mutant proteins

We have made 47 mutations that span the length of the human T-cell leukemia virus type I (HTLV-I) Tax open reading frame. Of the 47 mutations, 38 were substitutions of single amino acids, 5 were missense changes in two or more amino acids, and 4 were deletions. A subset of these mutations includes individual changes of all 26 naturally occurring serines to alanines. By assaying each mutant protein separately on the HTLV-I long terminal repeat (LTR) and the human immunodeficiency virus type 1 (HIV-1) LTR in parallel, we were able to identify regions of Tax selectively necessary for each promoter. A small region in the carboxyl terminus, amino acids 315 to 325, was found to be selectively important for activation of the HTLV-I LTR. Three changes at serine 113, serine 160, and serine 258 were found to specifically affect function on the HIV-1 LTR. Surprisingly, we found that the great preponderance of missense changes (32 of 42) in Tax did not affect function.

HTLV-I Tax is a zinc-binding protein: role of zinc in Tax structure and function

We have examined the functional significance of the cysteine- and histidine-rich region (amino acids 22-53) of HTLV-I Tax. A modeling of this region suggests two possible overlapping zinc-finger-like motifs. Using a zinc blotting technique, we show that Tax binds zinc. An N-terminal deletion in Tax that removed this zinc-finger region abolished the ability to bind zinc. Site-directed mutagenesis was used to generate 10 separate mutations so as to discriminate between the two alternative zinc-binding structures. Each Tax mutant was studied for its ability to trans-activate the HTLV-I LTR. Five of the ten mutations inactivated trans-activation. Our results support that one of the two putative zinc fingers is an integral element of Tax structure.

Tunicamycin inhibits function and expression of the high-affinity IL-2 receptor in a murine IL-2-dependent cell line

Murine interleukin-2-dependent T-lymphocytes (CT6) were treated with tunicamycin, an inhibitor of both glycoprotein and ganglioside synthesis, to study the involvement of glycosylation in the IL-2 proliferative response. Tunicamycin inhibited proliferation in a dose-dependent manner at concentrations which did not inhibit protein synthesis (10-50 ng/ml). Swainsonine, a glycoprotein processing inhibitor, had no effect on proliferation. Inhibition of proliferation by tunicamycin was accompanied by an inhibition of binding of 125I-IL-2 to its high-affinity receptor. Scatchard analysis showed that receptor number was decreased by tunicamycin treatment. On the other hand, tunicamycin did not affect either the binding of the monoclonal antibody 7D4, specific for the 55 kDa low-affinity protein subunit of the IL-2 receptor, or the recycling of the IL-2 receptor. To determine the specific effects of tunicamycin on the biosynthesis of particular CT6 glycoconjugates, cells were radiolabeled with 3H-glucosamine and incorporation into ganglioside, neutral glycolipid and glycoprotein fractions was measured. Low doses of tunicamycin inhibited ganglioside synthesis and glycoprotein glycosylation to the same extent, whereas no effect on neutral glycolipid synthesis was observed. These results suggest that glycosylation of glycoprotein and/or gangliosides might play an important role in the formation of a functional high-affinity IL-2 receptor complex in CT6 cells.

HTLV-I trans-activator protein, tax, is a trans-repressor of the human beta-polymerase gene

Human T cell leukemia virus type I (HTLV-I) is the etiological agent for adult T cell leukemia (ATL). The HTLV-I trans-activator protein Tax can activate the expression of its own long terminal repeat (LTR) and many cellular and viral genes. Tax down-regulated the expression of human beta-polymerase (hu beta-pol), a cellular enzyme involved in host cell DNA repair. This finding suggests a possible correlation between HTLV-I infection and host chromosomal damage, which is often seen in ATL cells.

C-terminal deletion analogs of a crustacean pigment-dispersing hormone

This study deals with the effect of deamidation and C-terminal truncation on the potency of an octadecapeptide pigment-dispersing hormone (PDH: Asn-Ser-Gly-Met-Ile-Asn-Ser-Ile-Leu-Gly-Ile-Pro-Arg-Val-Met-Thr-Glu-Ala- NH2), first described as light-adapting distal retinal pigment hormone (DRPH) from Pandalus borealis. Bioassay of synthetic analogs for melanophore pigment dispersion in destalked fiddler crabs (Uca pugilator) showed that deamidation causes a 300-fold decrease in potency. The analogs 1-17 NH2 and 1-16 NH2 were about 3 times more potent than 1-18-OH. Further truncation led to decreases in potency, with the peptide 1-9-NH2 being the smallest C-terminal deletion analog to display activity (0.001% potency). Smaller analogs (1-8-NH2, 1-6-NH2 and 1-4-NH2) were inactive when tested in doses as high as 500 nmoles/crab. On the basis of our earlier work on N-terminal deletion analogs and the present findings the residues 6 to 9 seem to be important for PDH action.

Substitution of norleucine for methionine residues in a crustacean pigment-dispersing hormone

In order to evaluate the structural/functional roles of Met residues in an octadecapeptide pigment-dispersing hormone (PDH: Asn-Ser-Gly-Met-Ile-Asn-Ser-Ile-Leu-Gly-Ile-Pro-Arg-Val-Met-Thr-Glu-Ala- NH2), first described as light-adapting distal retinal pigment hormone (DRPH) from Pandalus, three analogs were synthesized: Nle4-PDH, Nle15-PDH, and Nle4,15-PDH. When tested for melanophore pigment-dispersing activity in destalked Uca, all three Nle-analogs were more potent than unsubstituted PDH. Performic acid oxidation caused a marked loss of potency of PDH, Nle4-PDH, and Nle15-PDH. The analog Nle4,15-PDH was resistant to oxidation and displayed 6-fold higher potency than PDH. Thus Met4 and Met15 are not essential for the PDH activity. The oxidation-induced loss of activity of unsubstituted PDH may result from introduction of oxygen (in methionine sulfone) and a consequent conformational change in the octadecapeptide.