Lipophilin, a novel heterodimeric protein of human tears

Discovery and Verification of Sjögren's Syndrome Protein Biomarkers in Tears by Targeted LC-MRM

Sjögren's syndrome (SS) is an autoimmune rheumatic disorder characterized by exocrine gland dysfunction, mainly from the lacrimal and salivary glands. The disease causes severe aqueous dry eye syndrome (DED) and is associated with high rates of complications, including corneal ulceration, scaring, and perforation. Systemic complications may occur as well as a higher risk of developing lymphoma. Diagnosis of SS-DED is often delayed and difficult to establish. With the aim of discovering biomarkers to help discriminate SS-DED patients, a combination of untargeted and targeted LC-MS/MS analyses were performed on tear samples collected on Schirmer strips and subjected to tryptic digestion. Following the analysis of three cohorts and the development of two targeted LC-sMRM methods for the verification of putative biomarkers found in the first cohort of samples, 64 proteins could be linked to Sjögren's syndrome, in the hopes of helping to confirm diagnoses as well as potentially stratifying the severity of disease in these patients. Proteins that were increased in SS-DED showed activation of the immune system and alterations in homeostasis. Several proteases and protease inhibitors were found to be significantly changing in SS-DED, as well as a consistent decrease in specific proteins known to be secreted by the lacrimal gland.

Evidence for Phospholipids on the Surface of Human Tears

Purpose

The structure of tears has been theoretically considered three tiers with lipids at the air interface, aqueous and proteins in the subphase, and anchored mucins on the corneal epithelial surface. While many lipid and protein species have been identified in tears by mass spectrometry, the localization of the major components within the tear film structure remains speculative. The most controversial components are phospholipids. Although surface active, phospholipids have been presumed to be bound entirely to protein in the aqueous portion of tears or reside at the aqueous-lipid interface. Herein, the possibility that phospholipids are adsorbed at the air-surface interface of tears is interrogated.

Methods

Polarization-modulated Fourier transform infrared reflective absorption spectroscopy (PM-IRRAS) was used to study the presence of phosphate signals at the tear surface. In order to constrain the depth of signal detection to the surface, an extreme grazing angle of incident radiation was employed. Nulling ellipsometry was used to confirm the presence of monolayers and surface thicknesses when surface active reagents were added to solutions.

Results

Surface selection of PM-IRRAS was demonstrated by suppression of water and phosphate signals in buffers with monolayers of oleic acid. Phosphate signals were shown to reflect relative concentrations. Absorption peaks attributable to phospholipids were detected by PM-IRRAS on the human tear film surface and were augmented by the addition of phospholipid.

Conclusions

The data provide strong evidence that phospholipids are present at the surface of tears.

Exploring the human lacrimal gland using organoids and single-cell sequencing

The lacrimal gland is essential for lubrication and protection of the eye. Disruption of lacrimal fluid production, composition, or release results in dry eye, causing discomfort and damage to the ocular surface. Here, we describe the establishment of long-term 3D organoid culture conditions for mouse and human lacrimal gland. Organoids can be expanded over multiple months and recapitulate morphological and transcriptional features of lacrimal ducts. CRISPR-Cas9-mediated genome editing reveals the master regulator for eye development Pax6 to be required for differentiation of adult lacrimal gland cells. We address cellular heterogeneity of the lacrimal gland by providing a single-cell atlas of human lacrimal gland tissue and organoids. Finally, human lacrimal gland organoids phenocopy the process of tear secretion in response to neurotransmitters and can engraft and produce mature tear products upon orthotopic transplantation in mouse. Together, this study provides an experimental platform to study the (patho-)physiology of the lacrimal gland.

Lipocalin-1 is the acceptor protein for phospholipid transfer protein in tears

Phospholipid transfer protein, ∼80 kDa, transfers phospholipids from micelles to lipid binding proteins. The acceptor protein in plasma is apolipoprotein-A1, 28 kDa. Previously, phospholipid transfer protein was found in tears but an acceptor protein was not identified. To search for the acceptor protein(s) in tears a fluorescent phospholipid transfer assay was altered to omit the extrinsic acceptor. Human tears were incubated with fluorescent micelles and showed marked transfer activity verifying a native acceptor protein must be present. Reconstituted tears without tear lipocalin (lipocalin-1) eliminated the transfer of phospholipids. To determine if phospholipid transfer protein is involved in carrying phospholipid to the surface of tears from tear lipocalin, a fraction enriched in phospholipid transfer protein was injected into the subphase of a tear mimicking buffer in which tear lipocalin was present. The addition of phospholipid transfer protein did not increase the thickness of the surface layer regardless of the presence of lipid bearing tear lipocalin. The data show that phospholipid transfer protein transfers phospholipid from micelles to tear lipocalin. Phospholipid transfer protein does not transport the phospholipid. While tear lipocalin has no intrinsic transfer activity from micelles, it is the acceptor protein for phospholipid transfer protein in tears.

High-resolution quantitative proteomics applied to the study of the specific protein signature in the sputum and saliva of active tuberculosis patients and their infected and uninfected contacts

Our goal was to establish panels of protein biomarkers that are characteristic of patients with microbiologically confirmed pulmonary tuberculosis (TB) and their contacts, including latent TB-infected (LTBI) and uninfected patients. Since the first pathogen-host contact occurs in the oral and nasal passages the saliva and sputum were chosen as the biological fluids to be studied. Quantitative shotgun proteomics was performed using a LTQ-Orbitrap-Elite platform. For active TB patients, both fluids exhibited a specific accumulation of proteins that were related to complement activation, inflammation and modulation of immune response. In the saliva of TB patients, a decrease of in proteins related to glucose and lipid metabolism was detected. In contrast, the sputum of uninfected contacts presented a specific proteomic signature that was composed of proteins involved in the perception of bitter taste, defense against pathogens and innate immune response, suggesting that those are key events during the initial entry of the pathogen in the host. SIGNIFICANCE: This is the first study to compare the saliva and sputum from active TB patients and their contacts. Our findings strongly suggest that TB patients show not only an activation of processes that are related to complement activation and modulation of inflammation but also an imbalance in carbohydrate and lipid metabolism. In addition, those individuals who do not get infected after direct exposure to the pathogen display a typical proteomic signature in the sputum, which is a reflection of the secretion from the nasal and oral mucosa, the first immunological barriers that M. tuberculosis encounters in the host. Thus, this result indicates the importance of the processes related to the innate immune response in fighting the initial events of the infection.

Interaction of ceramides and tear lipocalin

The distribution of lipids in tears is critical to their function. Lipids in human tears may retard evaporation by forming a surface barrier at the air interface. Lipids complexed with the major lipid binding protein in tears, tear lipocalin, reside in the bulk (aqueous) and may have functions unrelated to the surface. Many new lipids species have been revealed through recent mass spectrometric studies. Their association with lipid binding proteins has not been studied. Squalene, (O-acyl) omega-hydroxy fatty acids (OAHFA) and ceramides are examples. Even well-known lipids such as wax and cholesteryl esters are only presumed to be unbound because extracts of protein fractions of tears were devoid of these lipids. Our purpose was to determine by direct binding assays if the aforementioned lipids can bind tear lipocalin. Lipids were screened for ability to displace DAUDA from tear lipocalin in a fluorescence displacement assay. Di- and tri-glycerides, squalene, OAHFA, wax and cholesterol esters did not displace DAUDA from tear lipocalin. However, ceramides displaced DAUDA. Apparent dissociation constants for ceramide-tear lipocalin complexes using fluorescent analogs were measured consistently in the submicromolar range with 3 methods, linear spectral summation, high speed centrifugal precipitation and standard fluorescence assays. At the relatively small concentrations in tears, all ceramides were complexed to tear lipocalin. The lack of binding of di- and tri-glycerides, squalene, OAHFA, as well as wax and cholesterol esters to tear lipocalin is consonant with residence of these lipids near the air interface.

In vitro selections of mammaglobin A and mammaglobin B aptamers for the recognition of circulating breast tumor cells

Mammaglobin B (MGB2) and mammaglobin A (MGB1) are proteins expressed in metastatic breast cancers. The early detection of circulating tumor cells (CTCs) in breast cancer patients is crucial to decrease mortality rate. Herein, novel aptamers were successfully selected and characterized against MGB2 and MGB1 proteins using a hybrid SELEX approach. The potential use of the selected aptamers in breast CTC detection was studied using spiked breast cancer cells in whole blood lysate. The results obtained from this study showed that the selected aptamers (MAMB1 and MAMA2) bind to their target breast cancer cell lines with high affinity (low nanomolar Kd values) and specificity. They also bind to their free recombinant target proteins and show minimal non-specific binding to normal and other cancer cell lines. Additionally, they were able to distinguish a low number of breast cancer cells spiked in whole blood lysate containing normal blood cells. The results obtained in this study indicate the great potential for the use of aptamers to detect MGB1 and MGB2 protein biomarkers, expressed on the surface of breast CTCs.

TFOS DEWS II Tear Film Report

The members of the Tear Film Subcommittee reviewed the role of the tear film in dry eye disease (DED). The Subcommittee reviewed biophysical and biochemical aspects of tears and how these change in DED. Clinically, DED is characterized by loss of tear volume, more rapid breakup of the tear film and increased evaporation of tears from the ocular surface. The tear film is composed of many substances including lipids, proteins, mucins and electrolytes. All of these contribute to the integrity of the tear film but exactly how they interact is still an area of active research. Tear film osmolarity increases in DED. Changes to other components such as proteins and mucins can be used as biomarkers for DED. The Subcommittee recommended areas for future research to advance our understanding of the tear film and how this changes with DED. The final report was written after review by all Subcommittee members and the entire TFOS DEWS II membership.

Metabolomics and Trace Element Analysis of Camel Tear by GC-MS and ICP-MS

Camel tear metabolomics and elemental analysis are useful in getting the information regarding the components responsible for maintaining the protective system that allows living in the desert and dry regions. The aim of this study was to correlate that the camel tears can be used as artificial tears for the evaluation of dryness in the eye. Eye biomarkers of camel tears were analyzed by gas chromatography-mass spectroscopy (GC-MS) and inductively coupled plasma mass spectroscopy (ICP-MS). The major compounds detected in camel tears by GC-MS were alanine, valine, leucine, norvaline, glycine, cadaverine, urea, ribitol, sugars, and higher fatty acids like octadecanoic acid and hexadecanoic acid. GC-MS analysis of camel tears also finds several products of metabolites and its associated metabolic participants. ICP-MS analysis showed the presence of different concentration of elemental composition in the camel tears.

Identification of secretaglobin Scgb2a1 as a target for developmental reprogramming by BPA in the rat prostate

Secretoglobins are a superfamily of secreted proteins thought to participate in inflammation, tissue repair, and tumorigenesis. Secretoglobin family 2A member 1 (Scgb2a1) is a component of prostatein, a major androgen-binding protein secreted by the rat prostate. Using a rat model for developmental reprogramming of susceptibility to prostate carcinogenesis, we identified, by RNA-seq, that Scgb2a1 is significantly upregulated (>100-fold) in the prostate of adult rats neonatally exposed to bisphenol A (BPA), with increased gene expression confirmed by quantitative RT-PCR and chromatin immunoprecipitation for histone H3 lysine 9 acetylation. Bisulfite analysis of both CpG islands located within 10 kb of the Scgb2a1 promoter identified significant hypomethylation of the CpG island upstream of the transcription start site of this gene in the reprogrammed prostate. These data suggest that expression of Scgb2a1 in the adult prostate could be epigenetically reprogrammed by BPA exposure during prostate development, with potential implications for cancer risk and response to chemotherapeutics associated with prostatein binding.

The real reason for having a meibomian lipid layer covering the outer surface of the tear film - A review

This review critically evaluates a broad range of literature in order to show the relationship between meibum, tear lipids and the tear film lipid layer (TFLL). The relationship of meibum composition to dry eye syndrome is briefly discussed. The review also explores the interactions between aqueous and the TFLL by examining the correlations between meibomian lipids and lipids extracted from whole tears, and by considering protein adsorption to the TFLL from the aqueous. Although it is clear to the authors that a normal tear film resists evaporation, an emerging idea from the literature is that the main purpose of the TFLL is to allow the spread of the tear film and to prevent its collapse onto the ocular surface, rather than to be an evaporative blanket. Current models on the possible structure of the TFLL are also examined.

Identification of human tear fluid biomarkers in vernal keratoconjunctivitis using iTRAQ quantitative proteomics

BACKGROUND

Understanding and treating vernal keratoconjunctivitis (VKC) has been a challenge because the pathogenesis is unclear and antiallergic therapy often unsuccessful. The aim of the study was to analyze peptide profiles in human tears using mass spectrometry to elucidate compositional differences between healthy subjects and patients affected by VKC.

METHODS

Tears were collected from healthy subjects and VKC patients. Digested samples were treated with iTRAQ (isobaric tag for relative and absolute quantitation). Separation of tryptic peptides was realized using a MicroHPLC interfaced with a microfraction collector. MS and MS/MS mass spectra were performed using a MALDI TOF/TOF 4800 Applied Biosystem spectrometer. Protein Pilot™ software with Paragon™ algorithm v4.1.46 or GPS™ with Mascot engine was used as search engines with SwissProt or IPI human as the databases.

RESULTS

A significant number of peptides were examined, and 78 proteins were successfully identified. In all VKC samples, levels of serum albumin, transferrin, and hemopexin were found up to 100 times higher than control tear levels and correlated to the severity of disease. Hemopexin, transferrin, mammaglobin B, and secretoglobin 1D were found significantly over-expressed in VKC samples compared with the control samples. Tear samples from patients treated with topical cyclosporine or corticosteroids showed a dramatic reduction in these protein levels.

CONCLUSIONS

LC MALDI MS and isobaric tag for relative and absolute quantitation technique may be useful in the quantitative and qualitative characterization of the peptidoma of human tears. These techniques may identify target proteins to be used in the diagnosis and management of VKC and other inflammatory ocular surface conditions.

Secretoglobin expression in ovarian carcinoma: lipophilin B gene upregulation as an independent marker of better prognosis

BACKGROUND

The aim of the present study was to investigate within ovarian carcinoma and normal ovarian biopsies the gene expression of multiple secretoglobin family members relative to mammaglobin B, which we previously reported as a promising novel ovarian carcinoma prognostic marker.

METHODS

Using quantitative real-time Reverse Transcription PCR we tested 53 ovarian carcinoma and 30 normal ovaries for the expression of 8 genes belonging to the secretoglobin family: mammaglobin A, lipophilin A, lipophilin B, uteroglobin, HIN-1, UGRP-1, RYD5 and IIS. Next, we decided to expand the LipB gene expression analysis to a further 48 ovarian carcinoma samples, for a total of 101 tumor tissues of various histologies and to study its protein expression by immunohistochemistry in formalin-fixed paraffin-embedded tumors and normal ovaries. Finally, we correlated lipophilin B gene and protein expression to conventional patient clinico-pathological features and outcome.

RESULTS

We found significant mammaglobin A, lipophilin A, lipophilin B and RYD5 gene overexpression in ovarian carcinomas compared to normal ovaries. Lipophilin B mRNA showed a higher presence in tumors (75.4%) compared to normal ovaries (16.6%) and the most significant correlation with mammaglobin B mRNA (rs =0.77, p < 0.001). By immunohistochemical analysis, we showed higher lipophilin B expression in the cytoplasm of tumor cells compared to normal ovaries (p < 0.001). Moreover, lipophilin B gene overexpression was significantly associated with serous histology (serous vs clear cell p = 0.027; serous vs undifferentiated p = 0.007) and lower tumor grade (p = 0.02). Lower LipB mRNA levels (low versus high tertiles) were associated to a shorter progression-free (p = 0.03, HR = 2.2) and disease-free survival (p = 0.02, HR = 2.5) by univariate survival analysis and, importantly, they remain an independent prognostic marker for decreased disease-free (p = 0.001, HR = 3.9) and progression-free survival (p = 0.004, HR = 2.8) in multivariate Cox regression analysis.

CONCLUSIONS

The present study represents the first quantitative evaluation of secretoglobin gene expression in normal and neoplastic ovarian tissues. Our results demonstrate lipophilin B gene and protein upregulation in ovarian carcinoma compared to normal ovary. Moreover, lipophilin B gene overexpression correlates with a less aggressive tumor phenotype and represents a novel ovarian carcinoma prognostic factor.

Lacrimal proline rich 4 (LPRR4) protein in the tear fluid is a potential biomarker of dry eye syndrome

Dry eye syndrome (DES) is a complex, multifactorial, immune-associated disorder of the tear and ocular surface. DES with a high prevalence world over needs identification of potential biomarkers so as to understand not only the disease mechanism but also to identify drug targets. In this study we looked for differentially expressed proteins in tear samples of DES to arrive at characteristic biomarkers. As part of a prospective case-control study, tear specimen were collected using Schirmer strips from 129 dry eye cases and 73 age matched controls. 2D electrophoresis (2DE) and Differential gel electrophoresis (DIGE) was done to identify differentially expressed proteins. One of the differentially expressed protein in DES is lacrimal proline rich 4 protein (LPRR4). LPRR4 protein expression was quantified by enzyme immune sorbent assay (ELISA). LPRR4 was down regulated significantly in all types of dry eye cases, correlating with the disease severity as measured by clinical investigations. Further characterization of the protein is required to assess its therapeutic potential in DES.

Two dimensional electrophoretic analysis of human tears: collection method in dry eye syndrome

Tear proteomics, by 2-DE, can give a fingerprint of the protein profile, which is well suited in clinical proteomics for biomarker identification and in diagnostics. The mode of tear collection can influence the representation of the proteins in the tear and therefore it is important to use the appropriate method. In this study, capillary and Schirmer mode of tear collection was done in the healthy controls and the Schirmer method was validated in dry eye syndrome conditions. 2-D PAGE of normal and dry eye tear was performed using pH 3-10 linear IPG strips followed by 13% SDS-PAGE. The spot intensity was analyzed by the PD quest software. The two methods were compared using Bland-Altman statistical tool. The 2-D map of capillary and Schirmer tear showed 147 ± 8 spots and 145 ± 7 spots respectively. Both the collection methods were in agreement with each other and were comparable. Dry eye tear protein showed differential expression of proteins as observed in 25-35 kDa region. One of the significantly reduced protein was identified as proline-rich 4 protein. Schirmer method of tear collection is reliable in patients with dry eye, which can display the differential protein expression and help in biomarker identification.

Uteroglobin: a steroid-inducible immunomodulatory protein that founded the Secretoglobin superfamily

Blastokinin or uteroglobin (UG) is a steroid-inducible, evolutionarily conserved, secreted protein that has been extensively studied from the standpoint of its structure and molecular biology. However, the physiological function(s) of UG still remains elusive. Isolated from the uterus of rabbits during early pregnancy, UG is the founding member of a growing superfamily of proteins called Secretoglobin (Scgb). Numerous studies demonstrated that UG is a multifunctional protein with antiinflammatory/ immunomodulatory properties. It inhibits soluble phospholipase A(2) activity and binds and perhaps sequesters hydrophobic ligands such as progesterone, retinols, polychlorinated biphenyls, phospholipids, and prostaglandins. In addition to its antiinflammatory activities, UG manifests antichemotactic, antiallergic, antitumorigenic, and embryonic growth-stimulatory activities. The tissue-specific expression of the UG gene is regulated by several steroid hormones, although a nonsteroid hormone, prolactin, further augments its expression in the uterus. The mucosal epithelia of virtually all organs that communicate with the external environment express UG, and it is present in the blood, urine, and other body fluids. Although the physiological functions of this protein are still under investigation, a single nucleotide polymorphism in the UG gene appears to be associated with several inflammatory/autoimmune diseases. Investigations with UG-knockout mice revealed that the absence of this protein leads to phenotypes that suggest its critical homeostatic role(s) against oxidative damage, inflammation, autoimmunity, and cancer. Recent studies on UG-binding proteins (receptors) provide further insight into the multifunctional nature of this protein. Based on its antiinflammatory and antiallergic properties, UG is a potential drug target.

Single eye analysis and contralateral eye comparison of tear proteins in normal and dry eye model rabbits by MALDI-ToF mass spectrometry using wax-coated target plates

A study of rabbit tear protein expression in a dry eye rabbit model was performed to determine if a pattern in expressed proteins could be identified. The uniqueness of the model allows the comparison of normal (control) eye tear protein expression with surgically induced dry eye tear protein expression in individual animals. The sensitivity of the method allows for single eye analysis. One-dimensional mini-gel electrophoresis of the tear proteins did not show substantial differences between band patterns of the normal versus the dry eye, but was used to assess the molecular weight ranges of the major proteins. Specific assignments of some of the predominant proteins were obtained by tandem mass spectrometry (MS) which showed that the lower molecular weight lipid-binding proteins (approximately 10 kDa to 36 kDa) constitute a considerable amount of the observed protein, followed in lesser quantities by the transferrins which have higher molecular weights ranging from 70 kDa to 85 kDa. Enhancement of matrix-assisted laser desorption/ionization time-of-flight (MALDI-ToF) MS linear mode analysis of intact proteins in tear fluid was demonstrated through the use of wax-coated MALDI plates and spot washing. MALDI-ToF MS analysis of the expressed tear proteins illustrates that differences between normal eye tear and dry eye tear protein content are manifested in changes in the lower molecular weight lipid-binding proteins such as lipophilin which exhibits an increase in concentration in the dry eye, and beta-2 microglobulin which undergoes a decrease.

Immunohistochemical analysis of secretoglobin SCGB 2A1 expression in human ocular glands and tissues

Human secretoglobin (SCGB) 2A1 (or lipophilin C, lacryglobin, mammaglobin B) is a small protein of unknown function that forms heterodimers with secretoglobin 1D1 (lipophilin A) in tears. SCGB 2A1 is homologous to mammaglobin (mammaglobin A) and the C3 component of prostatein, the major secretory protein of the rat ventral prostate. Androgen-dependent expression of SCGB 2A1 has been observed in the prostate. Besides identification of SCGB 2A1 in the tear proteome only its mRNA had been detected in the lacrimal gland. Here, we report expression of SCGB 2A1 in all ocular glands and in the keratinized stratified squamous epithelium of the eyelid as well as in the stratified epithelium of the conjunctiva and in the orbicularis oculi muscle. Almost all of these tissues are also known to express the androgen receptor. Therefore, we conclude that presence of the androgen signalling machinery could be the main general determinant of SCGB 2A1 expression. Implications of the presence in tear fluid of an androgen-regulated secretoglobin, which most likely binds hydrophobic ligands, for tear film lipid layer formation and function is discussed.

Secretoglobin 2A1 Is under Selective Androgen Control Mediated by a Peculiar Binding Site for Sp Family Transcription Factors

Human secretoglobin (SCGB) 2A1 (or lipophilin C, lacryglobin, mammaglobin B) is a small protein of unknown function that forms heterodimers with secretoglobin 1D1 (lipophilin A) in tears and is expressed in the prostate. Here we show that SCGB 2A1 is under androgen control in the androgen-responsive prostatic cell line LNCaP and can be induced more than 20-fold by dihydrotestosterone. Only 6 h after androgen treatment, a strong DNase I-hypersensitive site is induced in the proximal promoter within chromatin. Within the boundaries of this DNase I-hypersensitive site a minimal 32-bp peculiar dimeric inverted repeat variant GC box (dim-IR-GA box) was found to confer androgen but not glucocorticoid responsiveness in gene transfer experiments. Mutations of both GA boxes that abolish binding of Sp1 and Sp3 also abrogate the androgen response. In an EMSA the DNA binding domain of the androgen receptor (AR) was not able to bind directly to the dim-IR-GA box. However, AR is functionally required for the hormone response because induction can be inhibited with the nonsteroidal antagonist bicalutamide. Chromatin immunoprecipitation experiments demonstrated that AR is recruited to the proximal promoter 10 min after androgen treatment. Therefore we propose that SCGB 2A1 represents a new class of androgen target genes that are purely under indirect AR control mediated by DNA-bound Sp factors.

Evaluation of Lipophilins as Determinants of Tumor Cell Response to Estramustine

Estramustine administered orally as estramustine phosphate (EMP) remains a major tool in hormone refractory prostate cancer chemotherapy. The presence of estramustine binding protein, prostatin, in prostate tissue may be a determinant of response to treatment. Lipophilins are secretory proteins with homology to prostatin. Reverse transcription-polymerase chain reaction was performed to estimate expression patterns of lipophilins A to C in human biopsies and cell lines resistant to estramustine. Although lipophilin A was not expressed in prostate tissue, both lipophilins B and C were expressed in normal and tumor prostate without significant differences. For lipophilin C, a somatic mutation (T to C transition at positions 409 and 412) was found in human tumor samples and absent in normal prostate tissue. No consistent response to EMP was observed in enhanced green fluorescent protein (EGFP)-tagged lipophilin C-transfected PC3 cells compared with parental controls. Among these EGFP-lipophilin C clones, no direct correlation between response to EMP treatment (IC50 values) and EGFP expression was observed (p = 0.73). Lipophilin C mRNA levels did not vary significantly between wild-type and estramustine-resistant cells in prostate (DU145 and PC3) and ovarian (SKOV3) cancer cell lines. Overall, these results suggest that lipophilins are not specific determinants of estramustine efficacy.

Secretoglobins in the human pituitary: high expression of lipophilin B and its down-regulation in pituitary adenomas

Secretoglobins are small secreted proteins, the expression of which has mostly been associated with secretory mucosal epithelia. Several secretoglobins have been implicated in the development of various human cancers. Allelic deletions of chromosome 11q13 correlates with the invasiveness of pituitary tumors. Intriguingly, several secretoglobin genes are located on 11q13; however, for most of these genes the expression in the pituitary and pituitary tumors have not been investigated. Antibodies specific for the secretoglobin lipophilin B (SCGB1D2, BU101) were developed and used in an immunohistochemical analysis of a human normal tissue microarray. Prominent lipophilin B immunoreactivity was found in the secretory cells of the anterior pituitary. Eight of nine analyzed pituitary adenomas showed a reduction in lipophilin B immunoreactivity compared to normal pituitary. However, there was no apparent association between lipophilin B immunoreactivity and hormone production or tumor invasiveness. Expression of eight different secretoglobin mRNAs were analyzed in normal pituitary and the pituitary adenoma cell line HP75 by highly specific quantitative real-time reverse transcription-PCR assays. Lipophilins B and C (SCGB2A1, mammaglobin B) were the most prominently expressed secretoglobin mRNAs in the pituitary. No secretoglobin mRNA was detected in the HP75 cells. The present report demonstrates, for the first time, lipophilin B expression in the pituitary and its apparent down-regulation in pituitary adenomas.

Identification of MGB1 as a marker in the differential diagnosis of lung tumors in patients with a history of breast cancer by analysis of publicly available SAGE data

The risk of developing second primary cancers is increased in patients with breast cancer. The lung is one of the major target organs, and therefore a differential diagnosis between primary and metastatic cancers is required for the treatment of lung tumors in patients with a history of breast cancer. However, biopsy specimens frequently result in small, fragmented tissues containing only a few, degenerated cancer cells. We attempted to find a useful marker for differential diagnosis, using the online SAGE database. We selected three molecules, small breast epithelial mucin (SBEM), prostate epithelium-specific Ets transcription factor (PDEF), and mammaglobin (MGB1), as potential markers for breast cancer. SBEM and PDEF proved of no use for practical differential diagnosis because they are expressed in the normal bronchus. In contrast, expression of MGB1 was detected in all 22 primary breast cancers, but not in 22 normal lung tissues. Furthermore, all 12 metastatic breast cancers examined demonstrated positive MGB1 transcripts, whereas one of 48 primary lung adenocarcinomas expressed MGB1. This suggests that MGB1 can serve as a differential molecular marker. In practice, prospective examination, using the nine cases with a history of breast cancer, confirmed the usefulness of MGB1 in differential diagnosis.

Purification and characterization of pheromaxein, the porcine steroid-binding protein. A member of the secretoglobin superfamily

Low molecular mass proteins are implicated in chemical communication throughout mammalian species, being involved in both perception and delivery of pheromonal compounds. In boars, pheromones are secreted in saliva to cause oestrous sows to take up the mating stance. These pheromones are the 16-androstene steroids, 5alpha-androsten-3alpha-ol and 5alpha-androsten-3-one. The submaxillary glands of boars contain a low molecular mass protein, pheromaxein, which is capable of binding these 16-androstene pheromones. Pheromaxein was purified, cloned and characterized. It was found to be a nonglycosylated heterodimeric protein, belonging to the secretoglobin superfamily and the major 16-androstene-binding protein present in submaxillary salivary glands of the boar. One subunit, pheromaxein A, was found to be homologous to prostatein peptides, C1 and C2 and lipophilin A and B, whereas the other subunit, pheromaxein C, was homologous to prostatein peptide C3 and lipophilin C. Transcription of pheromaxein A was limited to the prostate and submaxillary salivary glands from both the boar and sow, whereas transcription of the other subunit, pheromaxein C, was more widespread. This is similar to the transcription distribution of lipophilin in humans. Many isoforms of pheromaxein were found to exist, with a molecular mass range of 17,415-18,159 Da; these are probably products of a multigene family. Post-translational modifications, to generate mature pheromaxein isoforms, probably include C-terminal cleavage of pheromaxein A, followed by additional modifications.

Dysregulated secretoglobin expression in human lung cancers

Lipophilins A, B, C, mammaglobin, and uteroglobin are members of the secretoglobin family of small, secreted, proteins. The functions of these proteins are not well understood but uteroglobin has been implicated in the development of cancers. Uteroglobin is known to be highly expressed in normal lung and down-regulated in lung cancers but expression of the other secretoglobins in normal lung and lung neoplasms have not been investigated. Therefore, we developed quantitative real-time reverse transcription (RT-) PCR assays for the different secretoglobins and evaluated their expression in normal and neoplastic lung tissues. The secretoglobin transcript levels were quantitated by real-time RT-PCR in samples from three normal lungs, 24 lung tumors including six small cell lung carcinomas, seven adenocarcinomas, and five squamous cell carcinomas, and in cell lines from three small cell lung carcinomas and one mesothelioma. Uteroglobin was confirmed to be abundantly expressed in normal lung and the different lung tumors showed down-regulated uteroglobin expression. Of the other secretoglobins, only lipophilin C was detected in normal lung, albeit at low levels. The lung tumors, however, frequently showed neo- or up-regulation of lipophilins A, B, C, and mammaglobin. The results constitute the first quantitative evaluation of secretoglobin expression in normal and neoplastic human lung tissues and demonstrate dysregulation in various human lung cancers. These findings could have important biological and diagnostic implications.

Analysis of rabbit tear proteins by high-pressure liquid chromatography/electrospray ionization mass spectrometry

The aim of this study was to develop a fast and reliable analytical procedure for the display of the protein components of tears that can be used to differentiate the status of the ocular surface. Using this new procedure, we analyzed the tear protein components following a corneal wound in the rabbit. Calibrated 10-microL glass, fire-polished capillary micropipettes were used to collect tears from New Zealand White rabbits prior to and daily for 9 days following a unilateral 6-mm diameter centrally placed anterior keratectomy. Tear proteins were eluted by a reversed-phase high-performance liquid chromatography (RP-HPLC) column and the tear protein profile was monitored by electrospray ionization (ESI) mass spectrometry positive total ion current (TIC) chromatography. Tear proteins were reliably separated into 17 peaks, each of which contained one or a number of protein components. The molecular weight of each protein component was determined by on-line ESI. Major tear protein components, lactoferrin, lysozyme (minimally detectable in rabbit tears), albumin, lipocalin, lipophilin and beta2-microglobulin, were tentatively identified by this method. Based on the mass spectrometric data, beta2-microglobulin was found to be glycosylated with N-acetylhexosamine. ESI-positive TIC chromatograms and mass spectra revealed comparative differences in the tear protein spectra after corneal wounding. One day after wounding, rabbit lysozyme with a molecular weight of 14,717 Da was found to be 8-fold higher in the tears of wounded eyes when compared with tears from unwounded eyes. It dropped back to normal 3 days after wounding. The expression of an unidentified tear protein with the molecular weight of 16,060 Da was also elevated after corneal wounding and returned to normal level by day 5. In this study, LC/ESI-MS was developed as a fast, reproducible and simple method for the identification and analysis of many of the protein components of the tears. Importantly, this technique also allows quantification of each component resolved in the chromatogram. This method is very suitable for mapping peptides and proteins (<80 kDa) in tears.

Cationic polypeptides are required for antibacterial activity of human airway fluid

In a search for direct evidence leading to the biological relevance of airway secretions in innate host defense, we characterized the antibacterial function of cationic polypeptides within minimally manipulated nasal fluid. In this study, we show that cationic antimicrobial polypeptides are responsible for most of the bactericidal activity of whole nasal fluid. The removal of cationic polypeptides using a cation-exchange resin ablated the activity of nasal fluid against Escherichia coli, Listeria monocytogenes, and Pseudomonas aeruginosa. By using a novel proteomic approach, we identified a dozen cationic peptides and proteins within nasal fluid, all of which either are known antimicrobial polypeptides or have other proposed roles in host defense. Of the three most abundant cationic polypeptides in nasal fluid, lysozyme was more effective than either lactoferrin or secretory leukoprotease inhibitor in restoring the antibacterial activity of the cationic polypeptide-depleted fluid against a mucoid cystic fibrosis isolate of P. aeruginosa.

Purification and characterization of the mammaglobin/lipophilin B complex, a promising diagnostic marker for breast cancer

Mammaglobin, a promising diagnostic marker for breast cancer, forms a covalent complex with lipophilin B. mRNA levels for each component of the complex were determined for a number of breast tumors and normal tissues, and correlation of message expression was highly significant between mammaglobin and lipophilin B (p < 0.0001). The complex was purified by both standard biochemical techniques and immunoaffinity chromatography. N-Terminal sequencing revealed that mammaglobin and lipophilin B are processed as predicted by cleavage of their signal sequence after amino acids 19 and 21, respectively. Three molecular masses-representing the fully glycosylated form, the complex without one of the carbohydrate chains, and the deglycosylated proteins-are detected by ProteinChip array SELDI-TOF mass spectrometry after partial enzymatic deglycosylation. This is consistent with the two predicted N-linked glycosylation sites in the primary sequence of mammaglobin and each site having an attached sugar of approximately 3500 Da. Reducing agents release lipophilin B from mammaglobin, and the free peptides are seen at their predicted molecular masses in the deglycosylated complex. Molecular modeling, secondary structure prediction, and circular dichroism indicate that the complex is a small alpha-helical globule that has three disulfide bridges and a carbohydrate chain at each pole. LC-ESI-MS shows that mammaglobin and lipophilin B are bonded in a head to tail orientation. This work describes the biochemistry of the mammaglobin/lipophilin B complex and lays the framework for use of this complex as a novel protein-based serological marker for breast cancer.

Characterization and cloning of two isoforms of heteroglobin, a novel heterodimeric glycoprotein of the secretoglobin-uteroglobin family showing tissue-specific and sex differential expression

Heteroglobin (HGB) is a 39-kDa heterodimeric protein detected under non-reducing conditions in harderian, parotid, and submaxillary glands and saliva of the Syrian hamster with antiserum raised against the carboxyl end deduced from the female harderian gland cDNA FHG22 (Dominguez, P. (1995) FEBS Lett. 376, 257-261). After reduction, only one 5.6-kDa polypeptide, named HGB.A, was immunodetected and identified by sequencing as the mature FHG22 product. Tissue-specific expression of HGB.A and HGB mimics that of FHG22 mRNA, with sex differences in submaxillary and harderian glands. Purification of HGB revealed it consists of HGB.A disulfide bonded to HGB.B, a 33.5-kDa N-glycosylated subunit that yields a 9-kDa core polypeptide after deglycosylation. Two highly homologous (96.2%) cDNA clones (HGB.B1 and HGB.B2) encoding 94 amino acid-long isoforms were identified by screening a female harderian gland library with an HGB.B probe. The corresponding mature polypeptides are 78 amino acids long with 12 differences, but 3 putative N-glycosylation sites are maintained. The expression of HGB.B mRNAs is parallel to that of HGB and HGB.A, but no HGB.B2 mRNA was detected in submaxillary glands. Homology studies indicate that HGB.A and HGB.B1/HGB.B2 belong to different subfamilies of the secretoglobin-uteroglobin family and form heterodimers as previously described.

XPS and surface-MALDI-MS characterisation of worn HEMA-based contact lenses

XPS and MALDI-MS were used to analyse initial adsorption events in the fouling of HEMA-based contact lenses. All of the lenses tested accumulated tear film deposits within 10 min of wear. XPS indicated the presence of mainly proteinaceous deposits, with indications of some contributions by mucins or lipids on some lenses and the nature of the deposit being influenced by the lens chemistry. MALDI-MS detected the presence of surface-adsorbed species with molecular weights < 15 kDa. While lysozyme could be identified by comparison of MALDI-MS signals with known protein mass and assignments are suggested for some other signals, several other species, with MWs less than that of lysozyme, could not be identified as no ocular proteins with corresponding MWs had been reported in previous biochemical tear film analyses. These species, and others, were also detected in MALDI-MS analysis of reflex tear film, suggesting that the adsorbed unidentified species were not simply products of surface-induced dissociation of adsorbing higher-MW proteins. This short-term wear study detected rapid interface conversion and demonstrated the utility and surface sensitivity of XPS and MALDI-MS in characterising contact lens deposits at the initial stages when sub-monolayer adsorbed amounts are present on lenses.

Lacryglobin in human tears, a potential marker for cancer

Lacrygobin has been identified in human tears. This protein has high sequence homology to the mammaglobins, proteins upregulated in breast cancer and in breast cancer metastasis. In order to investigate the utility of tear screening for cancer tear samples were collected from patients with different types of cancer and compared to controls. Tear samples were taken from five controls and eight breast, six lung, five colon, one prostate and three ovary cancer patients. Tears were analysed using 2-D gel electrophoresis (n = 25) and 1-D electrophoresis (n = 3). Lacryglobin was present in the following percentage of patients: breast cancer (88%), lung (83%), colon (100%), ovary (33%), prostate (100%) and controls (60%). Two control patients with lacryglobin had a family history of breast and prostate cancer. Lacryglobin was detected in some but not all tear samples and further studies are warranted to investigate its potential as a marker for cancer.

Identification of rat prostatic steroid binding protein (PSBP) as an immunosuppressive factor

Prostatic steroid binding protein (PSBP) is the major protein produced ( approximately 20% of the total cytosolic protein) and secreted into the seminal fluid by the rat ventral prostate but its physiological function has not been elucidated yet. Since PSBP is secreted into the seminal fluid (which is itself a potent immunosuppressor) and has strong homology with uteroglobin (which possess an important anti-inflammatory function) our aim was to determine what effect, if any, PSBP would have on the immune system. With that purpose in mind we performed mononuclear cell cultures in the presence or absence of purified PSBP and analysed the effect of this protein on different functional parameters. PSBP inhibits the mitogen-induced proliferation of normal rat spleen mononuclear cells (MNC) specifically and in a dose-dependent manner. It reduces the production of IL-2 and the expression of its receptor (analysed by flow cytometry) which are important events for lymphocyte proliferation. Also, PSBP was able to inhibit OVA-specific proliferation of lymph node cells from previously primed animals. The immunosuppressive effect of PSBP is not due to an inherent toxic effect to the cells, since the cell viability was kept intact at the different times of culture studied. We also analysed the effect of rat PSBP on mitogen-induced proliferation of mouse spleen and human blood MNC. The proliferation was strongly abolished in a dose-dependent and non-species specific fashion. Moreover, PSBP strongly inhibits the human mixed lymphocyte reaction. Taken together, the present data support evidence for a new type of function for PSBP. We report that PSBP is a potent immunosuppressor factor and we describe its effect on the immune function in vitro. Here, we discuss the possible implications of these findings in the protection of sperm from immunologic damage in the feminine reproductive tract.

All human genes of the uteroglobin family are localized on chromosome 11q12.2 and form a dense cluster

Rabbit uteroglobin is the founder member of a family of mammalian proteins that has expanded to more than 20 members within the last few years. All members are small, secretory, rarely glycosylated dimeric proteins with unclear physiological functions and are mainly expressed in mucosal tissues. A phylogenetic analysis shows that the family can be grouped into five subfamilies, A to E. Subfamily A contains rabbit uteroglobin and its orthologues from various species; most of these have been described to form antiparallel homodimers via two intermolecular disulfide bonds. All other subfamily members contain a third conserved cysteine and, from existing biochemical data, it can be predicted that a member of subfamily B or C will likely form heterodimers with a partner from subfamily E or D, respectively. Besides the mentioned cysteines, only one central lysine is conserved in all family members. In the known uteroglobin structures, this lysine forms an exposed salt bridge with an aspartate side chain, which is conserved in almost all sequences. Using radiation hybrid mapping and P1 clone analysis and utilizing data from the human genome project, we show that all known five human family members (Clara cell 10-kDa protein, lipophilins A and B, lacryglobin, mammaglobin) and a new member, we call lymphoglobin, are localized on chromosome 11q12.2 in a dense cluster spanning not more than approximately 400 kbp.

The uteroglobin fold

Uteroglobin (UTG) forms a fascinating homodimeric structure that binds small- to medium-sized ligands through an internal hydrophobic cavity, located at the interface between the two monomers. Previous studies have shown that UTG fold is not limited to the UTG/CC10 family, whose sequence/structure relationships are highlighted here, but can be extended to the cap domain of Xanthobacter autotrophicus haloalkane dehalogenase. We show here that UTG fold is adopted by several other cap domains within the alpha/beta hydrolase family, making it a well-suited "geode" structure allowing it to sequester various hydrophobic molecules. Additionally, some data about a new crystal form of oxidized rabbit UTG are presented, completing previous structural studies, as well as results from molecular dynamics, suggesting an alternative way for the ligand to reach the internal cavity.

Secretory lipophilins: a tale of two species

Secretory lipophilins are "lipid-loving" proteins that are major constituents of several mammalian secretions, including the prostatic fluid of rats and the tears of humans and rabbits. These proteins form covalent heterodimers that are stabilized by three intramolecular cystine disulfide bonds. The heterodimers, some of which are glycosylated, may undergo additional non-covalent assembly to form tetramers. The peptide components found in secretory lipophilins are from two subfamilies: lipophilins A/B and lipophilin C. The C subfamily members described in this report are three rabbit and one human lipophilin, plus human mammaglobin and the C3 subunit of rat prostatein. Human A/B and C lipophilins are expressed by many tissues and are especially prominent in endocrine-responsive organs. The gene for human lipophilin B resides at chromosome 10q22-23. This region harbors the PTEN/MMAC1 gene and is believed to contain additional tumor suppressor genes. Although the functions of secretory lipophilins are imperfectly understood, their abundance in glandular secretions and in hormone-responsive tissues suggests that they deserve considerably more attention than they have received to date.