Surface plasmon resonance analysis of gp17, a natural CD4 ligand from human seminal plasma inhibiting human immunodeficiency virus type-1 gp120-mediated syncytium formation

Cytotoxic and viricidal effects of human semen on mumps virus-infected lymphocytes: In vitro studies

Viruses in human semen may be sexually transmitted via free and cell-mediated viral infection. The potential effects of semen on the infection and sexual transmission of most viruses in semen remain largely unclear. The present study elucidated the inhibitory effects of human seminal plasma (SP) on Jurkat cell (JC)-mediated mumps virus (MuV) infection. We demonstrated that MuV efficiently infected JCs and that the JCs infected by MuV (JC-MuV) mediated MuV infection of HeLa cells. Remarkably, SP was highly cytotoxic to JCs and inhibited JC-MuV infection of HeLa cells. The cytotoxic factor possessed a molecular weight of less than 3 kDa, whereas that of the viricidal factor was over 100 kDa. The cooperation of cytotoxic and viricidal factors was required for the SP inhibition of JC-MuV infection, and prostatic fluid (PF) was responsible for both the cytotoxic and viricidal effects of SP. The cytotoxic effects we observed were resistant to the treatment of PF with boiling water, proteinase K, RNase A, and DNase I. Our results provide novel insights into the antiviral properties of SP, which may limit cell-mediated sexual viral transmission.

Tear Proteomics of Children and Young Adult Soft Contact Lens, Orthokeratology and Spectacle Wearers - A Pilot Study

PURPOSE

Contact lens complications occur more often in older teenagers and young adults compared to children. This study explored differences in tear proteomics between children and young adults wearing soft contact lens (SCL), orthokeratology or spectacles for >3 years.

METHODS

Twelve children and 12 sex- and correction-matched young adults were enrolled. Tears were collected via Schirmer strips for tear proteomic analysis using mass spectrometry. Proteome Discoverer was used for protein identification. Label-Free Quantitation was generated using Scaffold software; Fisher's Exact tests were used to compare proteins by age and correction groups. Generalized linear models were used to assess differences in overall protein levels by age and correction groups. A secondary analysis of proteins presented in >50% of samples of each group was conducted using the R/Bioconductor limma package.

RESULTS

There were 385 proteins present only in young adults while 183 were unique in children. There were 528 unique proteins to SCL, 96 to orthokeratology and 149 to spectacle wearers. Based on Fisher's Exact analyses, 126 proteins were higher in young adults than children (all P < 0.048). Forty-seven protein levels were higher in SCL compared to orthokeratology (all P < 0.01), 33 protein levels were higher in SCL compared to spectacles (all P < 0.01), 15 protein levels were higher in orthokeratology compared to spectacle wearers (all P < 0.01). Based on generalized linear models, young adults had higher overall protein levels than children (P = 0.001), SCL had higher protein levels than spectacle wearers (P < 0.001) but no differences were found between orthokeratology and spectacle wearers (P = 0.79). Based on the secondary analysis, only Antileukoproteinase was higher in the young adult orthokeratology group compared to other groups (P < 0.01).

CONCLUSIONS

Tear protein type and abundance differ by age and correction. Further research is needed to understand the effects of contact lens correction in children and young adults on the tear proteome.

The Prolactin Inducible Protein Modulates Antitumor Immune Responses and Metastasis in a Mouse Model of Triple Negative Breast Cancer

The prolactin inducible protein (PIP) is expressed to varying degrees in more than 90% of breast cancers (BCs). Although high levels of PIP expression in BC has been shown to correlate with better prognosis and patient response to chemotherapy, some studies suggest that PIP may also play a role in metastasis. Here, we investigated the role of PIP in BC using the well-established 4T1 and E0771 mouse BC cell lines. Stable expression of PIP in both cell lines did not significantly alter their proliferation, migration, and response to anticancer drugs in vitro compared to empty vector control. To assess the effect of PIP expression on breast tumorigenesis in vivo, the 4T1 syngeneic transplantable mouse model was utilized. In immunocompetent syngeneic BALB/c mice, PIP-expressing 4T1 primary tumors displayed delayed tumor onset and reduced tumor growth, and this was associated with higher percentages of natural killer cells and reduced percentages of type 2 T-helper cells in the tumor environment. The delayed tumor onset and growth were abrogated in immunodeficient mice, suggesting that PIP-mediated modulation of primary tumor growth involves an intact immune system. Paradoxically, we also observed that PIP expression was associated with a higher number of 4T1 colonies in the lungs in both the immunocompetent and immunodeficient mice. Gene expression analysis of PIP-expressing 4T1 cells (4T1-PIP) revealed that genes associated with tumor metastasis such as CCL7, MMP3 and MMP13, were significantly upregulated in 4T1-PIP cells when compared to the empty vector control (4T1-EV) cells. Collectively, these studies strongly suggest that PIP may possess a double-edge sword effect in BC, enhancing both antitumor immunity as well as metastasis.

Characterization of an Antiviral Component in Human Seminal Plasma

Numerous types of viruses have been found in human semen, which raises concerns about the sexual transmission of these viruses. The overall effect of semen on viral infection and transmission have yet to be fully investigated. In the present study, we aimed at the effect of seminal plasma (SP) on viral infection by focusing on the mumps viral (MuV) infection of HeLa cells. MuV efficiently infected HeLa cells in vitro. MuV infection was strongly inhibited by the pre-treatment of viruses with SP. SP inhibited MuV infection through the impairment of the virus's attachment to cells. The antiviral activity of SP was resistant to the treatment of SP with boiling water, Proteinase K, RNase A, and DNase I, suggesting that the antiviral factor would not be proteins and nucleic acids. PNGase or PLA2 treatments did not abrogate the antiviral effect of SP against MuV. Further, we showed that the prostatic fluid (PF) showed similar inhibition as SP, whereas the epididymal fluid and seminal vesicle extract did not inhibit MuV infection. Both SP and PF also inhibited MuV infection of other cell types, including another human cervical carcinoma cell line C33a, mouse primary epididymal epithelial cells, and Sertoli cell line 15P1. Moreover, this inhibitory effect was not specific to MuV, as the herpes simplex virus 1, dengue virus 2, and adenovirus 5 infections were also inhibited by SP and PF. Our findings suggest that SP contains a prostate-derived pan-antiviral factor that may limit the sexual transmission of various viruses.

Identification of Urinary Biomarkers for Exercise-Induced Immunosuppression by iTRAQ Proteomics

Purpose

To identify noninvasive immune biomarkers of exercise-induced immunosuppression using the iTRAQ proteomics technique.

Methods

Fifteen healthy males were recruited and subjected to a four-week incremental treadmill running training program. After each week of training, WBC counts and CD4⁺ and CD8⁺ lymphocytes were measured to monitor the immune function status. iTRAQ proteomics technology was used to identify differential proteins and their characteristics in urine.

Results

Our data showed that the WBC counts, CD4⁺ lymphocytes, and CD4⁺/CD8⁺ ratio decreased by more than 10% after four weeks of training, suggesting exercise-induced immunosuppression. A total of 1854 proteins were identified in urine during the incremental running using the iTRAQ technology. Compared with the urine before training, there were 89, 52, 77, and 148 proteins significantly upregulated and 66, 27, 68, and 114 proteins significantly downregulated after each week, respectively. Among them, four upregulated proteins, SEMG-1, PIP, PDGFRL, and NDPK, increased their abundance with the increased exercise intensity. Bioinformatics analysis indicates that these proteins are involved in stress response and immune function.

Conclusion

Four weeks of incremental treadmill running induced immunosuppression in healthy males. By using iTRAQ proteomics, four proteins in the urine, SEMG-1, PIP, PDGFRL, and NDPK, were found to increase incrementally with the increased exercise intensity, which have the potential to be used as noninvasive immune biomarkers of exercise-induced immunosuppression.

From Ancient to Emerging Infections: The Odyssey of Viruses in the Male Genital Tract

The male genital tract (MGT) is the target of a number of viral infections that can have deleterious consequences at the individual, offspring, and population levels. These consequences include infertility, cancers of male organs, transmission to the embryo/fetal development abnormalities, and sexual dissemination of major viral pathogens such as human immunodeficiency virus (HIV) and hepatitis B virus. Lately, two emerging viruses, Zika and Ebola, have additionally revealed that the human MGT can constitute a reservoir for viruses cleared from peripheral circulation by the immune system, leading to their sexual transmission by cured men. This represents a concern for future epidemics and further underlines the need for a better understanding of the interplay between viruses and the MGT. We review here how viruses, from ancient viruses that integrated the germline during evolution through old viruses (e.g., papillomaviruses originating from Neanderthals) and more modern sexually transmitted infections (e.g., simian zoonotic HIV) to emerging viruses (e.g., Ebola and Zika) take advantage of genital tract colonization for horizontal dissemination, viral persistence, vertical transmission, and endogenization. The MGT immune responses to viruses and the impact of these infections are discussed. We summarize the latest data regarding the sources of viruses in semen and the complex role of this body fluid in sexual transmission. Finally, we introduce key animal findings that are relevant for our understanding of viral infection and persistence in the human MGT and suggest future research directions.

The human breast cancer-associated protein, the prolactin-inducible protein (PIP), regulates intracellular signaling events and cytokine production by macrophages

The prolactin-inducible protein (PIP) is considered a valuable biomarker that is associated with both benign and malignant pathological conditions of the mammary gland. The function of PIP in breast tumorigenesis remains unknown; however, evidence from our laboratory and others suggest that it regulates host immunity. Studies with PIP-deficient (PIP^-/-) mice demonstrated significantly lower numbers of CD4⁺ T cells in their secondary lymphoid organs, impaired Th1 response, and impaired nitric oxide (NO) production. To further delineate the immunoregulatory role of PIP, we compared the expression of IFN-γR and TLR4, pro-inflammatory cytokine production, and intracellular signaling events by IFN-γ and lipopolysaccharide (LPS)-stimulated macrophages from wild-type (WT) and PIP^-/- mice. We showed that although the expressions of IFN-γR and TLR4 were comparable, productions of pro-inflammatory cytokines were decreased in PIP^-/- macrophages. This was associated with decreased phosphorylation of mitogen-activated protein kinase (MAPK) and signal transducer of activation of transcription (STAT) proteins in macrophages from PIP^-/- mice. Interestingly, the expression of suppressors of cytokine signaling (SOCS) 1 and 3 proteins, known to suppress IFN-γ and LPS signaling, was higher in PIP^-/- macrophages compared to those from WT mice. Collectively, our studies show that deficiency of PIP significantly affects intracellular signaling events leading to decreased pro-inflammatory cytokine production, and further confirms a role for PIP as an important immunoregulatory protein. This direct link between PIP and cell-mediated immunity, a key component of the immune system that is critical for cancer control, may have significant therapeutic implications.

Deficiency of prolactin-inducible protein leads to impaired Th1 immune response and susceptibility to Leishmania major in mice

Although the strategic production of prolactin-inducible protein (PIP) at several ports of pathogen entry into the body suggests it might play a role in host defense, no study has directly implicated it in immunity against any infectious agent. Here, we show for the first time that PIP deficiency is associated with reduced numbers of CD4(+) T cells in peripheral lymphoid tissues and impaired CD4(+) Th1-cell differentiation in vitro. In vivo, CD4(+) T cells from OVA-immunized, PIP-deficient mice showed significantly impaired proliferation and IFN-γ production following in vitro restimulation. Furthermore, PIP-deficient mice were highly susceptible to Leishmani major infection and failed to control lesion progression and parasite proliferation. This susceptibility was associated with impaired NO production and leishmanicidal activity of PIP KO macrophages following IFN-γ and LPS stimulation. Collectively, our findings implicate PIP as an important regulator of CD4(+) Th1-cell-mediated immunity.

Dominant Prostasome Immunogens for Sperm-Agglutinating Autoantibodies of Infertile Men

The presence of naturally occurring anti-sperm antibodies (ASA) is a well-known cause of infertility in men and women, but the antigens for these antibodies are poorly characterized. We have previously shown that prostasomes adhere to sperm cells and that prostasomes are major targets for ASA associated with infertility. These autoantigens have not been characterized. We used 2-dimensional electrophoresis, immunoblotting, and mass-spectrometry to identify the prostasome antigens for these autoantibodies. By these techniques, we revealed that prolactin-inducible protein (PIP) and clusterin were dominant prostasome immunogens for sperm-agglutinating autoantibodies of 20 patients with immunological infertility. PIP was identified by 19 of 20 (95%) patient sera and clusterin by 17 of 20 (85%). In addition, 10 sporadically occurring prostasomal antigens were identified in this context, viz alcohol dehydrogenase [NADP+], annexin I, annexin III, BRCA1-associated ring domain protein 1, heat shock 27-kd protein, isocitrate dehydrogenase, lactoylglutathione lyase, NG,NG-dimethylarginine dimethylaminohydrolase 1, peroxiredoxin 2, and syntenin 1.

Generation and initial characterization of the prolactin-inducible protein (PIP) null mouse: accompanying global changes in gene expression in the submandibular gland

The human prolactin-inducible protein/gross cystic disease fluid protein-15 (hPIP/GCDFP-15) is a secretory glycoprotein found primarily in apocrine tissues including the breast and salivary glands. With largely unknown functions, PIP has been implicated in breast cancer and metastasis, host defense processes and T lymphocyte apoptosis. To begin to address PIP function in vivo, we generated the PIP null mouse (Pip-/-). Additionally, to determine the effect of the loss of PIP on gene expression and to gain insight into some of the molecular mechanisms underlying PIP function, microarray analysis of the submandibular gland was also undertaken. Pip-/- mice developed normally with no overt differences in behaviour or gross morphology and were fertile. However, histological examination of 3-month-old Pip-/- mice sometimes showed enlarged submandibular lymph nodes, lymphocytic aggregations within the prostate lobes, and enlarged medulla in the thymus. Functional analysis of gene expression revealed sets of multiple differentially expressed genes associated with cell death and survival, lipid metabolism, inflammation, immune disease, and cancer, as a consequence of mPIP abrogation. Taken together, these studies lend support to an immunomodulatory role for PIP in vivo and provide further insights into potentially novel signaling pathways and regulatory networks for PIP.

Cationic polypeptides contribute to the anti-HIV-1 activity of human seminal plasma

Mucosal surfaces of the reproductive tract as well as their secretions have important roles in preventing sexual transmission of HIV-1. In the current study, the majority of the intrinsic anti-HIV-1 activity of human seminal plasma (SP) was determined to reside in the cationic polypeptide fraction. Antiviral assays utilizing luciferase reporter cells and lymphocytic cells revealed the ability of whole SP to prevent HIV-1 infection, even when SP was diluted 3200-fold. Subsequent fractionation by continuous flow acid-urea (AU)-PAGE and antiviral testing revealed that cationic polypeptides within SP were responsible for the majority of anti-HIV-1 activity. A proteomic approach was utilized to resolve and identify 52 individual cationic polypeptides that contribute to the aggregate anti-HIV-1 activity of SP. One peptide fragment of semenogelin I, termed SG-1, was purified from SP by a multistep chromatographic approach, protein sequenced, and determined to exhibit anti-HIV-1 activity against HIV-1. Anti-HIV-1 activity was transient, as whole SP incubated for prolonged time intervals exhibited a proportional decrease in anti-HIV-1 activity that was directly attributed to the degradation of semenogelin I peptides. Collectively, these results indicate that the cationic polypeptide fraction of SP is active against HIV-1, and that semenogelin-derived peptides contribute to the intrinsic anti-HIV-1 activity of SP.

Crystal structure of the novel complex formed between zinc alpha2-glycoprotein (ZAG) and prolactin-inducible protein (PIP) from human seminal plasma

This is the first report on the formation of a complex between zinc alpha2-glycoprotein (ZAG) and prolactin-inducible protein (PIP). The complex was purified from human seminal plasma and crystallized using 20% polyethylene glycol 9000 and 5% hexaethylene glycol. The structure of the complex has been determined using X-ray crystallographic method and refined to an R(cryst) of 0.199 (R(free)=0.239). The structure of ZAG is broadly similar to the structure of serum ZAG. The scaffolding of PIP consists of seven beta-strands that are organized in the form of two antiparallel beta-pleated sheets, resulting in the formation of a sandwiched beta-sheet. The amino acid sequence of PIP contains one potential N-glycosylation site at Asn77, and the same is found glycosylated with four sugar residues. The structure of the complex shows that the beta-structure of PIP is ideally aligned with the beta-structure of domain alpha3 of ZAG to form a long interface between two proteins. The proximal beta-strands at the long interface are arranged in an antiparallel manner. There are 12 hydrogen bonds and three salt bridges between ZAG and PIP. At the two ends of vertical interface, two salt bridges are formed between pairs of Lys41-Asp233 and Lys68-Glu229. On the perpendicular interface involving alpha1-alpha2 domains of ZAG and a loop of PIP, another salt bridge is formed. The internal space at the corner of the L-shaped structure is filled with solvent molecules including a carbonate ion. The overall buried area in the complex is approximately 914 A(2), which is considerably higher than the 660 A(2) reported for the class I major histocompatibility complex structures.

Altered distribution of aquaporin 5 and its C-terminal binding protein in the lacrimal glands of a mouse model for Sjögren's syndrome

PURPOSE

To investigate the distribution and expression of aquaporin 5 (AQP5) and its C-terminal binding protein in the apical membrane of the lacrimal glands (LGs) in a mouse model for Sjogren's syndrome (SS).

METHODS

The LGs of NOD mice (mouse model for SS) and ICR mice (normal control) were homogenized and delivered into the affinity columns bound to synthetic AQP5 C-terminal peptide. The eluates were analyzed by electrophoresis and liquid chromatography mass spectrometry/mass spectrometry (LC-MS/MS) techniques.

RESULTS

AQP5 from the NOD mice exhibited the capacity to bind a 21-kDa protein that was lacking in the ICR mice. Instead, ICR mouse expressed a 17-kDa AQP5 binding protein that was absent in LGs of SS. LC-MS/MS analysis revealed these respective proteins to be major urinary protein 4 (MUP4) and prolactin-inducible protein (PIP). The treatment of ICR mice with antisense PIP oligonucleotides decreased immunostaining of AQP5 in the apical membrane.

CONCLUSIONS

These observations suggest that the binding of PIP to the C-terminal portion of AQP5 may cause AQP5 to be transported to the apical membrane of LGs. Correction of the aberrant binding of PIP to the AQP5 C-terminus could normalize AQP5 trafficking to the apical membrane, leading to a treatment for patients with SS.

Increased expression of secretory actin-binding protein on human spermatozoa is associated with poor semen quality

BACKGROUND

Antibodies to human sperm are useful diagnostic reagents for detection of changes in sperm protein expression and their relationship with sperm defects and male infertility. The specificity of Hs-16 monoclonal antibody (mAb) and the localization and frequency of the occurrence of Hs-16-recognized protein on human spermatozoa were investigated.

METHODS

Samples from 30 fertile men with normal spermiograms and 30 men with pathological spermiograms were studied. The specificity of Hs-16 mAb was analysed by the western blotting technique and matrix-assisted laser desorption/ionization mass spectrometry. Indirect immunofluorescence with Hs-16 antibody was used to test sperm ejaculates.

RESULTS

The Hs-16 antibody detected a human sperm and seminal plasma protein, which was determined to be secretory actin-binding protein (SABP). This specificity was also verified by co-localization of SABP and actin on spermatozoa with Hs-16 and anti-actin antibodies, and partial co-localization of these proteins was found. SABP was localized on the sperm tail, mainly in the midpiece of the tail. Other parts of spermatozoa were labelled with lower frequency. A significant difference was found in SABP labelling between men with normal spermiograms and donors with asthenozoospermia or oligoasthenoteratozoospermia (both P < 0.01), and asthenozoospermia versus oligoasthenoteratozoospermia (P < 0.05). Increased expression of SABP was observed in men with pathological spermiograms.

CONCLUSIONS

Hs-16 antibody reacts specifically with SABP. SABP can serve as a marker of defective sperm and may be associated with fertility failure.

Human seminal plasma prolactin-inducible protein is an immunoglobulin G-binding protein

Antisperm antibodies (ASA) are present in 20% of couples seeking treatment for infertility. Antibody-binding proteins in seminal plasma may protect sperm from ASA-induced damage. We have previously isolated several IgG-binding proteins from human seminal plasma using IgG affinity chromatography. Here, we report another such protein which we have identified by amino acid sequencing and confirmed by western blotting to be prolactin-inducible protein (PIP). PIP binds via the Fc fragment of IgG. We have determined the level of PIP in normal seminal plasma to be 3.4 mg/ml (interquartile range 2.0-4.4 mg/ml). We have found there is no difference in the mean level of PIP in seminal plasma from fertile or infertile men regardless of ASA status. PIP was shown to exist in several isoforms in seminal plasma by Western blot. There is a complex pattern of PIP isoform variability in seminal plasma from fertile and infertile men but one multimeric form of PIP was absent from the seminal plasma of men with ASA who were fertile. This may reflect consumption of PIP in these men. The physiological function of PIP remains unknown, but the ability of PIP to bind IgG-Fc suggests PIP may have an immunomodulatory role.

Identification of gp17 glycoprotein and characterization of prostatic acid phosphatase (PAP) and carboxypeptidase E (CPE) fragments in a human seminal plasma fraction interacting with concanavalin A

The decapacitating fraction of human seminal plasma, which strongly interacts with concanavalin A, is constituted by high mannose-type N-linked glycoproteins, most of them of less than 44 kDa. Each component with apparent molecular mass of 30, 18, and 17 kDa respectively, as judged by SDS-PAGE, was submitted to "in gel" digestion with trypsin followed by HPLC separation of the peptides and sequencing. They were characterized at microscale as gp17, an aspartyl protease that possibly contributes to liquefaction of the seminal plasma coagulum, two fragments of human acid phosphatase (17 and 30 kDa, respectively), and a 17-kDa fragment of carboxypeptidase E. Neither the fragments of prostatic acid phosphatase nor that of carboxypeptidase E had been described before in the human seminal fluid. Very weak bands, of apparent molecular masses 44 and 52 kDa, are consistent with presence of small amounts of parent compounds, prostatic acid phosphatase and carboxypeptidase E.

Structural study of GCDFP-15/gp17 in disease versus physiological conditions using a proteomic approach

Gross cystic disease fluid protein (GCDFP-15), also known as prolactin-inducible protein (PIP), is a specific breast tumor marker. GCDFP-15/PIP is also identified as gp17 and/or seminal actin-binding protein (SABP) from seminal vesicles and as extraparotid glycoprotein (EP-GP) from salivary glands. It is an aspartyl proteinase able to specifically cleave fibronectin (FN), suggesting a possible involvement in mammary tumor progression and fertilization. Other functions were attributed to this protein(s) on the basis of its ability to interact with an array of molecules such as CD4, actin, and fibrinogen. We investigated the structure of the protein(s) under disease versus physiological conditions by RP-HPLC chromatography, ProteinChip technology, and QStar MS/MS mass spectrometry. The proteins behaved differently when examined by RP-HPLC chromatography and surface-enhanced laser desorption ionization time-of-flight (SELDI-TOF) mass spectrometry, suggesting different conformations and/or tissue-specific posttranslational modifications of the proteins, although their primary structure was identical by MS/MS analysis. Both showed a single N-glycosylation site. A different N-linked glycosylation pattern was observed in pathological GCDFP-15/PIP as compared with physiological gp17/SABP protein by coupling enzymatic digestion and ProteinChip technology. Furthermore, taking advantage of ProteinChip technology, we analyzed the interaction of both proteins with CD4 and FN. We observed that the physiological form was mainly involved in the binding to CD4. Moreover, we defined the specific FN binding-domain of this protein. These data suggested that, depending on its conformational state, the protein could differently bind to its various binding molecules and change its function(s) in the microenviroments where it is expressed.

Mapping the CD4 binding domain of gp17, a glycoprotein secreted from seminal vesicles and breast carcinomas

gp17, a secretory CD4-binding factor isolated from the human seminal plasma, is identical to the gross cystic disease fluid protein-15, a specific marker for primary and metastatic breast tumors. We previously demonstrated that gp17 binds to CD4 with high affinity and strongly inhibits T lymphocyte apoptosis induced by sequential cross-linking of CD4 and T cell receptor (TCR). To further characterize the gp17/CD4 interaction and map the gp17 binding site, we produced a secreted form of recombinant gp17 fused to human IgG1 Fc, gp17-Ig. We showed that gp17-Ig exhibits a binding affinity for CD4 similar to that of native gp17. As no information about gp17 structure is presently available, 99 overlapping gp17 peptides were synthesized by the Spot method, which allowed the mapping of two CD4 binding regions. Alanine scanning of CD4-reactive peptides identified critical residues, selected for site-directed mutagenesis. Nine gp17-Ig mutants were generated and characterized. Three residues within the carboxy-terminal region were identified as the major binding domain to CD4. The Spot method combined with mutagenesis represents a refined approach to distinguish the contact residues from the ones contributing to the conformation of the CD4-binding domain.

Circulating antibodies against the breast tumor marker GCDFP-15/gp17 in mammary carcinoma patients and in patients carrying benign breast conditions

Sera samples from 111 women, including 73 breast cancer patients and 38 patients with benign diseases of the breast, were examined. These were compared with samples from healthy women or from patients carrying tumors of origin other than breast as controls. This was done to determine whether antibodies against GCDFP-15/gp17, a protein of gross cystic disease fluid also secreted by mammary apocrine tumor cells, could be found. We observed that 2.6% of mammary disease patients affected by benign conditions and 5.5% of patients carrying malignant mammary gland tumors expressed statistically significant amounts of antibodies against GCDFP-15/gp17 (p < 0.01). The highest circulating anti-GCDFP-15/gp17 antibody levels occurred in patients with highly malignant ductal or lobular carcinoma of the breast and in patients with dysplasia. No correlation was found between the presence of circulating antibodies and the size of the tumor or the age of the patients. A bimodal correlation with the percent of invaded lymph nodes was observed instead. IgM and IgG isotypes were detected among the circulating anti-GCDFP-15/gp17 antibodies, suggesting the involvement of a T-cell-mediated immunoresponse. Our findings raise the possibility that the anti-GCDFP-15/gp17 immune response may be useful as a tool for investigating some aspects of the mechanisms of breast disease progression and that GCDFP-15/gp17 may be explored as an antigen for anti-tumor vaccination. Int. J. Cancer (Pred. Oncol.) 84:568-572, 1999.

Biosynthesis and immunobiochemical characterization of gp17/GCDFP-15. A glycoprotein from seminal vesicles and from breast tumors, in HeLa cells and in Pichia pastoris yeast

The gp17 factor is a secretory product of human seminal vesicle cells which binds to CD4 and acts as a potent inhibitor of T lymphocyte apoptosis induced by CD4 crosslinking and subsequent T-cell receptor (TCR) activation. The protein is identical to gross cystic disease fluid protein-15 (GCDFP-15), a breast tumor secretory marker PIP (prolactin inducible protein), a prolactin-controlled and androgen-controlled protein; secretory actin binding protein (SABP), a seminal plasma actin binding protein and extra-parotid glycoprotein (EP-GP), a secretory protein from the salivary gland. The structure of this protein has not yet been elucidated and no biological function has been clearly attributed to date. Expression of recombinant gp17/GCDFP-15 cDNA in bacteria and insect cells leads to the production of a misfolded insoluble protein. In this study, we describe the production of gp17/GCDFP-15 in two different eukaryotic systems, namely HeLa cells and the Pichia pastoris yeast. Using constructs in which gp17/GCDFP-15 was tagged with enhanced green fluorescent protein (EGFP) in various combinations, we observed expression only when the fusion protein was directed to the secretory compartment by the correct signal peptide. The resulting fluorescent protein was inefficiently secreted, thus suggesting that gp17/GCDFP-15 is not appropriately post-translationally processed and/or transported in HeLa cells. The use of the P. pastoris secretory pathway allowed instead the accumulation in the culture medium of a GCDFP-15/gp17 species which retained the ability to bind to CD4 and also most of the biochemical and immunological properties of the native protein. The production of an active recombinant molecule opens the way to correlate the structural properties of this peculiar factor to its ability to bind several proteins, including CD4, and to block CD4-mediated T cell programmed death.

Identification of a CD4 domain required for interleukin-16 binding and lymphocyte activation

Interleukin-16 (IL-16) activates CD4(+) cells, possibly by direct interaction with CD4. IL-16 structure and function are highly conserved across species, suggesting similar conservation of a putative IL-16 binding site on CD4. Comparison of the human CD4 amino acid sequence with that of several different species revealed that immunoglobulin-like domain 4 is the most conserved extracellular region. Potential interaction of this domain with IL-16 was studied by testing murine D4 sequence-based oligopeptides for inhibition of IL-16 chemoattractant activity and inhibition of IL-16 binding to CD4 in vitro. Three contiguous 12-residue D4 region peptides (designated A, B, and C) blocked IL-16 chemoattractant activity, with peptide B the most potent. Peptides A and B were synergistic for inhibition, but peptide C was not. Peptides A and B also blocked IL-16 binding to CD4 in vitro, whereas peptide C did not. CD4, in addition to its known function as a receptor for major histocompatibility complex class II, contains a binding site for IL-16 in the D4 domain. The D4 residues required for IL-16 binding overlap those previously shown to participate in CD4-CD4 dimerization following class II major histocompatibility complex binding, providing a mechanistic explanation for the known function of IL-16 to inhibit the mixed lymphocyte reaction.

Abnormal restriction pattern of PIP gene associated with human primary prostate cancers

The PIP gene, localized in the 7q34 region that contains a number of fragile sites such as FRA 7H and FRA TI, codes for gp17/PIP, a protein secreted by breast apocrine tumors. We analyzed the integrity of this gene in 20 tumors of the urogenital tract. We found rearranged EcoRI fragments in 5 of 15 primary prostate carcinomas. No rearrangement was found in normal prostates derived from five patients undergoing prostatocystectomy during treatment of bladder cancers. By Southern blot hybridization with PIP gene exon-specific probes, the rearrangements were mapped at or near the 3' end of the gene. These abnormalities were found, not only in the neoplastic cells invading the prostatic tissues, but also in seminal vesicles without histologic tumoral features. These data suggest a critical role of the PIP gene or neighboring genes in prostate cancer.

Potent Inhibition of CD4/TCR-Mediated T Cell Apoptosis by a CD4-Binding Glycoprotein Secreted from Breast Tumor and Seminal Vesicle Cells

We previously isolated a CD4 ligand glycoprotein, gp17, from human seminal plasma; this glycoprotein is identical with gross cystic disease fluid protein-15 (GCDFP-15), a factor specifically secreted from primary and secondary breast tumors. The function of gp17/GCDFP-15 in physiological as well as in pathological conditions has remained elusive thus far. As a follow up to our previous findings that gp17 binds to CD4 with high affinity and interferes with both HIV-1 gp120 binding to CD4 and syncytium formation, we investigated whether gp17 could affect the T lymphocyte apoptosis induced by a separate ligation of CD4 and TCR. We show here that gp17/GCDFP-15 is in fact a strong and specific inhibitor of the T lymphocyte programmed cell death induced by CD4 cross-linking and subsequent TCR activation. The antiapoptotic effect observed in the presence of gp17 correlates with a moderate up-regulation of Bcl-2 expression in treated cells. The presence of gp17 also prevents the down-modulation of Bcl-2 expression in Bcl-2bright CD4+ T cells that is caused by the triggering of apoptosis. Our results suggest that gp17 may represent a new immunomodulatory CD4 binding factor playing a role in host defense against infections and tumors.

Colloidal Au-enhanced surface plasmon resonance immunosensing

Surface plasmon resonance (SPR) biosensing using colloidal Au enhancement is reported. Immobilization of approximately 11-nm-diameter colloidal Au to an evaporated Au film results in a large shift in plasmon angle, a broadened plasmon resonance, and an increase in minimum reflectance. The incorporation of colloidal Au into SPR biosensing results in increased SPR sensitivity to protein-protein interactions when a Au film-immobilized antibody and an antigen-colloidal Au conjugate comprise the binding pair. A highly specific particle-enhanced analogue of a sandwich immunoassay is also demonstrated by complexing the Au particle to a secondary antibody. A tremendous signal amplification is observed, as addition of the antibody-Au colloid conjugate results in a 25-fold larger signal than that due to addition of a free antibody solution that is 6 orders of magnitude more concentrated. Picomolar detection of human immunoglobulin G has been realized using particle enhancement, with the theoretical limits for the technique being much lower. Finally, a quasi-linear relationship between particle coverage and plasmon angle shift is presented, thereby providing for a direct correlation between plasmon shift and solution antigen concentration. Together, these results represent significant advances in the generality and sensitivity of SPR as it is applied to biosensing.

Differential antibody reactivity and CD4 binding of the mammary tumor marker protein GCDFP-15 from breast cyst and its counterparts from exocrine epithelia

Analysis of biopsies from breast cancer patients demonstrated that GCDFP-15 (gross cystic disease fluid protein-15) is a specific immunocytochemical marker of primary and secondary apocrine breast tumors. The protein has an amino acid sequence identical to SABP (secretory actin-binding protein), to PIP (prolactin-inducible protein) and to gp17, a protein isolated from human seminal plasma. The latter was found to bind to CD4, a T-cell co-receptor involved in antigen recognition, thereby inhibiting the ability of the receptor to interact with the HIV-1 envelope protein gp120. We compare here the ability of independently purified GCDFP-15, SABP and gp17 and of recombinant PIP both to cross-react with a panel of monoclonal antibodies (MAbs) raised against GCDFP-15 or gp17, respectively, and to bind to CD4. We show that, although the various factors share the ability to bind to the panel of antibodies used, differences in the pattern of MAb recognition can be demonstrated. By comparing the kinetic constants for binding of GCDFP-5 and gp17 to CD4 by biosensor technology, significant differences in binding affinities were observed between the 2 factors, thus reflecting structural differences. Surface plasmon resonance analysis also showed that anti-GCDFP-15 and anti-gp17 antibodies inhibit the binding of CD4 to GCDFP-15 and gp17, respectively, to different extents. Our data thus indicate that, while the various forms of the protein are encoded by the same cDNA, tissue specificities due to post-translational modifications exist. This information may be relevant for developing more sensitive and accurate tests for the use of GCDFP-15 as a diagnostic mammary tumor marker and, most importantly, raises the possibility that GCDFP-15 may constitute a breast tumor-specific antigen.

Expression of gross cystic disease fluid protein-15/Prolactin-inducible protein in rat salivary glands

Gross cystic disease fluid protein-15 (GCDFP-15)/prolactin-inducible protein (PIP) is present at moderate levels in human submandibular and sublingual glands and is barely detectable in human parotid gland. The rodent homologue, PIP, has previously been identified in adult submandibular and lacrimal glands. Here we present the molecular characterization of rat PIP and show that this protein is a product of neonatal and adult rat submandibular, sublingual, and parotid glands. cDNA clones encoding rat PIP were isolated and sequenced. The deduced amino acid sequence of rat PIP shows 56% overall identity and 80% similarity with mouse PIP. By SDS-PAGE, secreted rat PIP has an apparent Mr of 17,000, with a minor proportion present as Mr 20-22,000 N-glycosylated forms. PIP was localized in rat salivary glands by immunogold silver staining. PIP was identified in acinar cells of developing and mature submandibular and parotid glands and at very low levels in sublingual gland serous demilunes. Typically, rat submandibular gland secretory proteins are produced by either acinar cell progenitors (Type III cells) or mature acinar cells. The expression pattern observed for PIP is similar to that previously reported for salivary peroxidase, an important component of nonimmune mucosal defense.

BIAcore for macromolecular interaction

Examination of the literature for the period of this review revealed nearly two hundred citations that employed surface plasmon resonance (SPR) spectroscopy using BIAcore technology to evaluate biospecific interactions, demonstrating the increasing popularity of this powerful technique. Among these we noted the development of several new applications/modifications of standard techniques. In general, we find the qualitative aspects of the reported experiments to be excellent but the quantitative descriptions (kT, kon, koff, and keq) as well as the binding models still lagging behind.

CD4-mediated anchoring of the seminal antigen gp17 onto the spermatozoon surface

A soluble 1, kDa glycoprotein, namely gp17, was previously isolated from human semen and used to obtain mouse monoclonal or chicken polyclonal antibodies. This protein was shown to bind CD4+ T-cells and to soluble recombinant CD4 in vitro. Here, we report that the anti-gp17 monoclonal antibodies are captured by ejaculated spermatozoa and that gp17-like antigens are released by cell acid extraction. Immunoblotting experiments with monoclonal antibodies indicated that SDS-lysates from spermatozoa contain proteins with the same electrophoretic and antigenic properties of CD4 and gp17. Anti-CD4 mouse monoclonal antibodies were used to coprecipitate from NP40-lysate proteins reacting with chicken anti-gp17 antibodies. Analytical chromatography demonstrated that a number of gp17-like forms are present in the seminal plasma, put that only the 1 kDa species can be detected in the spermatozoa lysate. This protein was localised by immunofluorescence on the post-acrosomal region of the spermatozoon. The same surface domain was also reactive with anti-CD4 antibodies. After treatment to induce in vitro capacitation, gp17 was detected all over the spermatozoon head. Conversely, only a minor part of the treated spermatozoa exhibited CD4 immunostaining, which remained localised on the post-acrosomal region. The possible function of CD4 and gp17 on male germ cells is discussed.