Interactions of the male contraceptive target EPPIN with semenogelin-1 and small organic ligands

Novel male contraceptives will promote gender equality in sharing contraceptive responsibility. The sperm-associated protein epididymal protease inhibitor (EPPIN) is a promising target for non-hormonal male contraception. EPPIN interacts with the semen coagulum protein semenogelin-1 (SEMG1) on the sperm surface, leading to transient inhibition of sperm motility after ejaculation. Small organic molecules targeting EPPIN's SEMG1-binding are under development as male contraceptives. Here, we combined computational approaches to uncover key aspects underlying EPPIN binding to SEMG1 and small organic ligands. We generated a human EPPIN model showing a typical arrangement of the WFDC (Whey-acid four disulfide core)-type and Kunitz-type domains, connected by a hinge region. Determining the EPPIN model's intrinsic motion by molecular dynamics simulations and normal mode analysis revealed a conformation, presenting a binding pocket that accommodates SEMG1Glu229-Gln247, EP055, and EP012. EPPIN's residues Phe63 and Lys68 (WFDC domain), Asp71 (hinge region), and Asn113, Asn114, and Asn115 (Kunitz domain) were identified as hot spots for SEMG1, EP055, and EP012 binding. Moreover, hydrophobic and hydrophilic residues in the WFDC and Kunitz domains allow plasma membrane anchoring, orienting the EPPIN binding pocket to the solvent. Targeting EPPIN's essential residues for its biomolecular interactions may improve the rational design of EPPIN ligands as spermiostatic compounds.

Non-hormonal male contraception: A review and development of an Eppin based contraceptive

Developing a non-hormonal male contraceptive requires identifying and characterizing an appropriate target and demonstrating its essential role in reproduction. Here we review the development of male contraceptive targets and the current therapeutic agents under consideration. In addition, the development of EPPIN as a target for contraception is reviewed. EPPIN is a well characterized surface protein on human spermatozoa that has an essential function in primate reproduction. EPPIN is discussed as an example of target development, testing in non-human primates, and the search for small organic compounds that mimic contraceptive antibodies; binding EPPIN and blocking sperm motility. Although many hurdles remain before the success of a non-hormonal male contraceptive, continued persistence should yield a marketable product.

Epididymal protease inhibitor (EPPIN) is differentially expressed in the male rat reproductive tract and immunolocalized in maturing spermatozoa

EPPIN (epididymal protease inhibitor; SPINLW1), an antimicrobial cysteine-rich protein containing both Kunitz and whey acidic protein (WAP)-type four disulfide core protease inhibitor consensus sequences, is a target for male contraception because of its critical role in sperm motility. Here, we characterized EPPIN's expression and cellular distribution in rat tissues and its in vivo regulation by androgens in the epididymis. EPPIN (mRNA and protein) was abundantly expressed in the rat testis and epididymis; we also found that the vas deferens, seminal vesicles, and brain were novel sites of EPPIN expression. PCR studies demonstrated that in addition to Sertoli cells, spermatogenic cells expressed Eppin mRNA. EPPIN was immunolocalized in Sertoli cells and spermatogenic cells (pachytene spermatocytes and round and elongated spermatids) and in epithelial cells and spermatozoa from efferent ductules and epididymis. EPPIN staining was observed on the middle and principal pieces of the flagellum of testicular spermatozoa. Epididymal spermatozoa had more intense EPPIN staining on the flagellum, and the EPPIN staining became apparent on the head and neck regions. This suggested that the EPPIN found on maturing spermatozoa was secreted primarily by the epithelial cells of the epididymis. Surgical castration down-regulated EPPIN expression levels (mRNA and protein) in the caput and cauda epididymis, an effect reversed by testosterone replacement. Altogether, our data suggested that EPPIN expression in rats is more widespread than in humans and mice, and is androgen-dependent in the epididymis. This species could be used as an experimental model to further study EPPIN's role in male fertility.

Characterization of EPPIN's semenogelin I binding site: a contraceptive drug target

Epididymal protease inhibitor (EPPIN) is found on the surface of spermatozoa and works as a central hub for a sperm surface protein complex (EPPIN protein complex [EPC]) that inhibits sperm motility on the binding of semenogelin I (SEMG1) during ejaculation. Here, we identify EPPIN's amino acids involved in the interactions within the EPC and demonstrate that EPPIN's sequence C102-P133 contains the major binding site for SEMG1. Within the same region, the sequence F117-P133 binds the EPC-associated protein lactotransferrin (LTF). We show that residues Cys102, Tyr107, and Phe117 in the EPPIN C-terminus are required for SEMG1 binding. Additionally, residues Tyr107 and Phe117 are critically involved in the interaction between EPPIN and LTF. Our findings demonstrate that EPPIN is a key player in the protein-protein interactions within the EPC. Target identification is an important step toward the development of a novel male contraceptive, and the functionality of EPPIN's residues Cys102, Tyr107, and Phe117 offers novel opportunities for contraceptive compounds that inhibit sperm motility by targeting this region of the molecule.

Loss of calcium in human spermatozoa via EPPIN, the semenogelin receptor

The development of a new male contraceptive requires a transition from animal model to human and an understanding of the mechanisms involved in the target's inhibition of human spermatozoan fertility. We now report that semenogelin (SEMG1) and anti-EPPIN antibodies to a defined target site of 21 amino acids on the C terminal of EPPIN cause the loss of intracellular calcium, as measured by Fluo-4. The loss of intracellular calcium explains our previous observations of an initial loss of progressive motility and eventually the complete loss of motility when spermatozoa are treated with SEMG1 or anti-EPPIN antibodies. Thimerosal can rescue the effects of SEMG1 on motility, implying that internal stores of calcium are not depleted. Additionally, SEMG1 treatment of spermatozoa decreases the intracellular pH, and motility can be rescued by ammonium chloride. The results of this study demonstrate that EPPIN controls sperm motility in the ejaculate by binding SEMG1, resulting in the loss of calcium, most likely through a disturbance of internal pH and an inhibition of uptake mechanisms. However, the exact steps through which the EPPIN-SEMG1 complex exerts its effect on internal calcium levels are unknown. Anti-EPPIN antibodies can substitute for SEMG1, and, therefore, small-molecular weight compounds that mimic anti-EPPIN binding should be able to substitute for SEMG1, providing the basis for a nonantibody, nonhormonal male contraceptive.

Therapeutic ultrasound as a potential male contraceptive: power, frequency and temperature required to deplete rat testes of meiotic cells and epididymides of sperm determined using a commercially available system

BACKGROUND

Studies published in the 1970s by Mostafa S. Fahim and colleagues showed that a short treatment with ultrasound caused the depletion of germ cells and infertility. The goal of the current study was to determine if a commercially available therapeutic ultrasound generator and transducer could be used as the basis for a male contraceptive.

METHODS

Sprague-Dawley rats were anesthetized and their testes were treated with 1 MHz or 3 MHz ultrasound while varying power, duration and temperature of treatment.

RESULTS

We found that 3 MHz ultrasound delivered with 2.2 Watt per square cm power for fifteen minutes was necessary to deplete spermatocytes and spermatids from the testis and that this treatment significantly reduced epididymal sperm reserves. 3 MHz ultrasound treatment reduced total epididymal sperm count 10-fold lower than the wet-heat control and decreased motile sperm counts 1,000-fold lower than wet-heat alone. The current treatment regimen provided nominally more energy to the treatment chamber than Fahim's originally reported conditions of 1 MHz ultrasound delivered at 1 Watt per square cm for ten minutes. However, the true spatial average intensity, effective radiating area and power output of the transducers used by Fahim were not reported, making a direct comparison impossible. We found that germ cell depletion was most uniform and effective when we rotated the therapeutic transducer to mitigate non-uniformity of the beam field. The lowest sperm count was achieved when the coupling medium (3% saline) was held at 37 degrees C and two consecutive 15-minute treatments of 3 MHz ultrasound at 2.2 Watt per square cm were separated by 2 days.

CONCLUSIONS

The non-invasive nature of ultrasound and its efficacy in reducing sperm count make therapeutic ultrasound a promising candidate for a male contraceptive. However, further studies must be conducted to confirm its efficacy in providing a contraceptive effect, to test the result of repeated use, to verify that the contraceptive effect is reversible and to demonstrate that there are no detrimental, long-term effects from using ultrasound as a method of male contraception.

Depletion of the histone chaperone tNASP inhibits proliferation and induces apoptosis in prostate cancer PC-3 cells

BACKGROUND

NASP (Nuclear Autoantigenic Sperm Protein) is a histone chaperone that is present in all dividing cells. NASP has two splice variants: tNASP and sNASP. Only cancer, germ, transformed, and embryonic cells have a high level of expression of the tNASP splice variant. We examined the consequences of tNASP depletion for prostate cancer PC-3 cells.

METHODS

tNASP was depleted from prostate cancer PC-3 cells, cervical cancer HeLa cells, and prostate epithelial PWR-1E cells using lentivirus expression of tNASP shRNA. Cell cycle changes were studied by proliferation assay with CFSE labeling and double thymidine synchronization. Gene expression profiles were detected using RT(2)Profiler PCR Array, Western and Northern blotting.

RESULTS

PC-3 and HeLa cells showed inhibited proliferation, increased levels of cyclin-dependant kinase inhibitor p21 protein and apoptosis, whereas non-tumorigenic PWR-1E cells did not. All three cell types showed decreased levels of HSPA2. Supporting in vitro experiments demonstrated that tNASP, but not sNASP is required for activation of HSPA2.

CONCLUSIONS

Our results demonstrate that PC-3 and HeLa cancer cells require tNASP to maintain high levels of HSPA2 activity and therefore viability, while PWR-1E cells are unaffected by tNASP depletion. These different cellular responses most likely arise from changes in the interaction between tNASP and HSPA2 and disturbed tNASP chaperoning of linker histones. This study has demonstrated that tNASP is critical for the survival of prostate cancer cells and suggests that targeting tNASP expression can lead to a new approach for prostate cancer treatment.

Analysis of the expression of human tumor antigens in ovarian cancer tissues

Biomarkers for early detection of cancer have great clinical diagnostic potential. Numerous reports have documented the generation of humoral immune responses that are triggered in response to changes in protein expression patterns in tumor tissues and these biomarkers are referred to as tumor associated antigens (TAAs). Using a high-throughput technology, we previously identified 65 proteins as diagnostically useful TAAs by profiling the humoral immune responses in ovarian cancer (OVCA) patients. Here we determined the expression status of some of those TAAs in tissues from OVCA patients. The protein expression patterns of 4 of those 65 antigens, namely NASP, RCAS1, Nijmegen breakage syndrome1 (NBS1) and eIF5A, along with p53 and Her2 (known molecular prognosticators) and two proteins that interact with NBS1, MRE11 and RAD50, were assessed by immunohistochemistry (IHC). NASP and RCAS1 proteins were more frequently expressed in ovarian cancer tissues than with normal ovarian tissue and serous cystadenomas and MRE11 was less frequently expressed. When evaluated simultaneously, only NASP and MRE11 remained statistically significant with sensitivity of 66% and specificity of 89%. None of these proteins' expression levels were prognostic for survival. Together, our results indicate that occurrence of humoral immune responses against some of these TAAs in OVCA patients is triggered by antigen protein overexpression.

Analysis of recombinant human semenogelin as an inhibitor of human sperm motility

Eppin (epididymal protease inhibitor [SPINLW1]) is present in a protein complex on the human sperm surface that contains lactotransferrin, clusterin, and semenogelin (SEMG1). During ejaculation the presence of semenogelin inhibits sperm progressive motility until semenogelin is hydrolyzed by prostate-specific antigen (PSA). Although eppin binds all three components in its protein complex, the binding of semenogelin to eppin appears to be critical for the inhibition of progressive motility. The effect of the originally identified seminal plasma motility inhibitor fragment has not been clearly defined on live spermatozoa. Therefore, we have used recombinant semenogelin (rSEMG1) and its fragments, including a semenogelin mutant in which cysteine 239 was changed to glycine, coupled with a computer assisted sperm analysis assay to study the motility inhibitory properties of semenogelin. Each fragment and the mutant were tested for their effects on motility. Recombinant semenogelin significantly inhibited sperm progressive motility in a dose- and time-dependent manner. The C-terminal semenogelin fragment (amino acids 164-283) containing cysteine 239 significantly inhibited sperm progressive motility, whereas the N-terminal fragment (amino acids 24-163), a short C-terminal fragment (amino acids 172-215) without cysteine 239, and the mutant fragment (amino acids 24-283 with glycine 239) did not inhibit motility. After treatment with recombinant semenogelin, spermatozoa could be washed and treated with PSA, partially reversing the inhibition of progressive motility. Cysteine 239 of rSEMG1 appears to be the critical amino acid for both binding to eppin and inhibiting sperm motility.

Linker histones stimulate HSPA2 ATPase activity through NASP binding and inhibit CDC2/Cyclin B1 complex formation during meiosis in the mouse

In mammalian spermatocytes, cell division cycle protein 2 (CDC2)/cyclin B1 and the chaperone heat shock protein A2 (HSPA2) are required for the G2-->M transition in prophase I. Here, we demonstrate that in primary spermatocytes, linker histone chaperone testis/embryo form of nuclear autoantigenic sperm protein (tNASP) binds the heat shock protein HSPA2, which localizes on the synaptonemal complex of spermatocytes. Significantly, the tNASP-HSPA2 complex binds linker histones and CDC2, forming a larger complex. We demonstrate that increasing amounts of tNASP favor tNASP-HSPA2-CDC2 complex formation. Binding of linker histones to tNASP significantly increases HSPA2 ATPase activity and the capacity of tNASP to bind HSPA2 and CDC2, precluding CDC2/cyclin B1 complex formation and, consequently, decreasing CDC2/cyclin B1 kinase activity. Linker histone binding to NASP controls the ability of HSPA2 to activate CDC2 for CDC2/cyclin B1 complex formation; therefore, tNASP's role is to provide the functional link between linker histones and cell cycle progression during meiosis.

Analysis of gene expression profiles in HeLa cells in response to overexpression or siRNA-mediated depletion of NASP

BACKGROUND

NASP (Nuclear Autoantigenic Sperm Protein) is a linker histone chaperone required for normal cell division. Changes in NASP expression significantly affect cell growth and development; loss of gene function results in embryonic lethality. However, the mechanism by which NASP exerts its effects in the cell cycle is not understood. To understand the pathways and networks that may involve NASP function, we evaluated gene expression in HeLa cells in which NASP was either overexpressed or depleted by siRNA.

METHODS

Total RNA from HeLa cells overexpressing NASP or depleted of NASP by siRNA treatment was converted to cRNA with incorporation of Cy5-CTP (experimental samples), or Cy3-CTP (control samples). The labeled cRNA samples were hybridized to whole human genome microarrays (Agilent Technologies, Wilmington, Delaware, USA). Various gene expression analysis techniques were employed: Significance Analysis of Microarrays (SAM), Expression Analysis Systematic Explorer (EASE), and Ingenuity Pathways Analysis (IPA).

RESULTS

From approximately 36 thousand genes present in a total human genome microarray, we identified a set of 47 up-regulated and 7 down-regulated genes as a result of NASP overexpression. Similarly we identified a set of 56 up-regulated and 71 down-regulated genes as a result of NASP siRNA treatment. Gene ontology, molecular network and canonical pathway analysis of NASP overexpression demonstrated that the most significant changes were in proteins participating in organismal injury, immune response, and cellular growth and cancer pathways (major "hubs": TNF, FOS, EGR1, NFkappaB, IRF7, STAT1, IL6). Depletion of NASP elicited the changed expression of proteins involved in DNA replication, repair and development, followed by reproductive system disease, and cancer and cell cycle pathways (major "hubs": E2F8, TP53, FGF, FSH, FST, hCG, NFkappaB, TRAF6).

CONCLUSION

This study has demonstrated that NASP belongs to a network of genes and gene functions that are critical for cell survival. We have confirmed the previously reported interactions between NASP and HSP90, HSP70, histone H1, histone H3, and TRAF6. Overexpression and depletion of NASP identified overlapping networks that included TNF as a core protein, confirming that both high and low levels of NASP are detrimental to cell cycle progression. Networks with cancer-related functions had the highest significance, however reproductive networks containing follistatin and FSH were also significantly affected, which confirmed NASP's important role in reproductive tissues. This study revealed that, despite some overlap, each response was associated with a unique gene signature and placed NASP in important cell regulatory networks.

Inhibition of human sperm motility by contraceptive anti-eppin antibodies from infertile male monkeys: effect on cyclic adenosine monophosphate

Epididymal protease inhibitor (eppin [official symbol, SPINLW1]) is of interest as a male contraceptive target because of its specificity and location on the human sperm surface. We have examined the effect of anti-eppin antibodies from infertile male monkeys and the effect of recombinant human semenogelin on human sperm motility. Anti-eppin antibodies significantly decreased the progressive motility of human spermatozoa as measured by decreased total distance traveled, decreased straight-line distance, and decreased velocity. Anti-eppin treatment of spermatozoa significantly increased the amount of cAMP present in nonprogressive spermatozoa; however, approximately 25% of antibody-treated spermatozoa could be rescued by the addition of cAMP-acetoxymethyl ester, indicating that anti-eppin-treated spermatozoa have a compromised ability to utilize cAMP. Addition of recombinant human semenogelin has a concentration-dependent inhibitory effect on progressive motility (increased tortuosity and decreased velocity). We tested the hypothesis that anti-eppin antibodies bound to eppin would subsequently block semenogelin binding to eppin. Anti-eppin antibodies from infertile monkeys inhibited eppin from binding to semenogelin. Addition of affinity-purified antibodies made to the dominant C-terminal epitope of eppin had an inhibitory effect on progressive motility (increased tortuosity, decreased velocity, and straight distance). Our results suggest that the eppin-semenogelin binding site is critical for the removal of semenogelin in vivo during semen liquefaction and for the initiation of progressive motility. We conclude that the eppin-semenogelin binding site on the surface of human spermatozoa is an ideal target for a nonsteroidal male contraceptive.

Characterization of an eppin protein complex from human semen and spermatozoa

Eppin (SPINLW1; serine peptidase inhibitor-like with Kunitz and WAP domains 1 (eppin); epididymal protease inhibitor) coats the surface of human ejaculate spermatozoa and originates from Sertoli and epididymal epithelial cells. In this study, we have isolated native eppin from ejaculate supernatants (seminal plasma) and washed ejaculate spermatozoa using column chromatography and two-dimensional SDS-PAGE, and identified by mass spectrometry and Western blots an eppin protein complex (EPC) containing lactotransferrin (LTF; also known as lactoferrin), clusterin (CLU), and semenogelin (SEMG1). To confirm the association of eppin with LTF, CLU, and SEMG1, antibodies to CLU and LTF were used to immunoprecipitate CLU and LTF from human sperm lysates. In both cases identical results were obtained, namely, the immunoprecipitate of the EPC. Additionally, we localized eppin, LTF, and CLU in human Sertoli cells and on human testicular and ejaculate spermatozoa, implying that the EPC is present on spermatozoa from the time they leave the seminiferous tubule. On ejaculate spermatozoa eppin, LTF, and CLU colocalize on the tail. The identification of the EPC components suggests that LTF, CLU, and/or eppin receptors may function as sperm plasma membrane receptors for the EPC, implicating the complex as a central player in a network of protein-protein interactions on the human sperm surface. The EPC may provide a surface network with microbicidal properties that protects spermatozoa as well as regulates the sperm's transition to a motile, capacitated sperm.

Eppin: an epididymal protease inhibitor and a target for male contraception

Eppin (epididymal protease inhibitor) is one of several serine protease (or serine protease-like) inhibitors that are encoded by genes on human chromosome 20 and on mouse chromosome 2. Here we review our current knowledge of human and mouse Eppin genes and the Eppin protein in the context of protease inhibitors. Antibodies to Eppin in immunized male monkeys provide an effective and reversible contraceptive and these antibodies may be effective by interfering with Eppin's interaction with semenogelin during ejaculation. We review Eppin-semenogelin interaction and present a working model in the context of the hydrolysis of semenogelin by prostate specific antigen.

Nuclear autoantigenic sperm protein (NASP), a linker histone chaperone that is required for cell proliferation

A multichaperone nucleosome-remodeling complex that contains the H1 linker histone chaperone nuclear autoantigenic sperm protein (NASP) has recently been described. Linker histones (H1) are required for the proper completion of normal development, and NASP transports H1 histones into nuclei and exchanges H1 histones with DNA. Consequently, we investigated whether NASP is required for normal cell cycle progression and development. We now report that without sufficient NASP, HeLa cells and U2OS cells are unable to replicate their DNA and progress through the cell cycle and that the NASP(-/-) null mutation causes embryonic lethality. Although the null mutation NASP(-/-) caused embryonic lethality, null embryos survive until the blastocyst stage, which may be explained by the presence of stored NASP protein in the cytoplasm of oocytes. We conclude from this study that NASP and therefore the linker histones are key players in the assembly of chromatin after DNA replication.

Eppin: an effective target for male contraception

Eppin (epididymal protease inhibitor) is a member of the whey acidic protein (WAP)-type four-disulfide core (WFDC) gene family. This study provides updated information on Eppin and the Eppin-like genes within the Eppin cluster on human chromosome 20. A virtual structural model of the Eppin protein demonstrates that the C-terminal half of Eppin is structurally homologous to the Kunitz-type trypsin inhibitor. The Eppin N-terminal may have structural similarities to defensin-type molecules, rather than to that of the WAP consensus sequence. Human spermatozoa have a receptor for Eppin. When recombinant semenogelin (Sg) is digested with PSA many low molecular weight fragments are produced. However, when Eppin is bound to Sg, digestion by PSA is modulated. Addition of antibodies to the C-terminal of Eppin resulted in blocking PSA activity modulation. We can hypothesize from our analysis of anti-Eppin epitopes on Eppin that when anti-Eppin antibodies are bound to Eppin on the sperm surface they block the binding site for semenogelin.

Mass spectrometry identification of NASP binding partners in HeLa cells

Nuclear autoantigenic sperm protein (NASP) is a linker histone binding protein that is cell-cycle regulated. Synchronized HeLa cells are delayed in progression through the G1/S border when transiently transfected to overexpress full-length NASP, but not the histone-binding site (HBS) deletion mutant (NASP-DeltaHBS). The purpose of the current study was to identify possible NASP-associated proteins in HeLa cell nuclei that could elucidate NASP's influence on the cell cycle and chromatin remodeling. For this purpose, we employed a new approach: mass spectrometry identification of initially cross-linked proteins after their separation in a second dimension by reducing SDS-polyacrylamide gel electrophoresis (SDS-PAGE). Of the twelve proteins identified, three appear to be relevant to NASP's function: heat shock protein 90 (HSP90), DNA-activated protein kinase, and ATP-dependent DNA helicase II (70-kDa subunit). Individual protein-protein interactions were tested by immunoprecipitation techniques. This new method can be used for expedited identification of binding partners of different proteins in enriched fractions and as a complementary or alternative strategy to the yeast two-hybrid system and immunoprecipitation methods.

Characterization of the NASP promoter in 3T3 fibroblasts and mouse spermatogenic cells

NASP (nuclear autoantigenic sperm protein) is a histone H1 binding protein expressed in all cells undergoing division. We have previously reported the sequence for the mouse NASP gene and analyzed its proximal promoter region in silico to determine putative regulatory regions. In this report we describe various factors regulating the transcription of NASP. Luciferase assays using 3T3 fibroblasts show that the region +9 to -135 nt (PR1C) provides the core transcriptional activity for NASP and that extending this region out to -976 nucleotides partially represses activity. However, when luciferase reporter assays were done in transfected pachytene spermatocytes, the cells that exhibit the highest NASP expression, a different gene regulation picture was revealed. In spermatogenic cells, PR1C is still a relatively strong core promoter, but unlike 3T3 cells, if the construct is extended to -3002 nucleotides there is marked enhancement of transcription. Electrophoretic mobility shift assays with 3T3 nuclear extracts were used to study the PR1C core promoter in greater detail. In the region immediately upstream of the transcription initiation site we identified two closely associated Sp1 binding sites and a binding site for an Ets family member. Supershift assays further confirmed the presence of Sp1 bound to their respective sites suggesting that Sp1 and Ets are the primary activators of the NASP promoter.

Association of eppin with semenogelin on human spermatozoa

Eppin (SPINLW1; GeneID, 57119) is a single-copy gene encoding a cysteine-rich protein found only in the testis and epididymis, which contains both Kunitz-type and WAP-type four disulfide core protease inhibitor consensus sequences. This study demonstrates that, in seminal plasma and on human spermatozoa following ejaculation, Eppin is bound to semenogelin I (Sg). Six different experimental approaches: 1) immunoprecipitation from spermatozoa and seminal plasma with anti-Eppin, 2) colocalization in semen and spermatozoa, 3) incubation of recombinant Eppin (rEppin) and rSg and immunoprecipitation with either anti-Eppin or anti-Sg, 4) far-Western blotting of Eppin and Sg, 5) Saturation binding of 125I-Sg to Eppin, which is competed by unlabeled Sg, and 6) direct binding of 125I-Sg to Eppin on a blot, all demonstrate that Eppin and Sg bind to each other. To study the specificity of binding, recombinant fragments of Eppin and Sg were made and demonstrate that the Eppin(75-133) C-terminal fragment binds the Sg(164-283) fragment containing the only cysteine in human Sg I (Cys-239). Reduction and carboxymethylation of Cys239 blocks binding of 125I-rEppin, indicating that a disulfide bond may be necessary for Eppin binding. The physiological significance of the Eppin-semenogelin complex bound on the surface of ejaculate spermatozoa lies in its ability to provide antimicrobial activity for spermatozoa, which has been reported for both Eppin and semenogelin-derived peptides, and in its ability to provide for the survival and preparation of spermatozoa for fertility in the female reproductive tract.

Association of NASP with HSP90 in mouse spermatogenic cells: stimulation of ATPase activity and transport of linker histones into nuclei

NASP (nuclear autoantigenic sperm protein) is a linker histone-binding protein found in all dividing cells that is regulated by the cell cycle (Richardson, R. T., Batova, I. N., Widgren, E. E., Zheng, L. X., Whitfield, M., Marzluff, W. F., and O'Rand, M. G. (2000) J. Biol. Chem. 275, 30378-30386), and in the nucleus linker histones not bound to DNA are bound to NASP (Alekseev, O. M., Bencic, D. C., Richardson R. T., Widgren E. E., and O'Rand, M. G. (2003) J. Biol. Chem. 278, 8846-8852). In mouse spermatogenic cells tNASP binds the testis-specific linker histone H1t. Utilizing a cross-linker, 3,3'-dithiobissulfosuccinimidyl propionate, and mass spectrometry, we have identified HSP90 as a testis/embryo form of NASP (tNASP)-binding partner. In vitro assays demonstrate that the association of tNASP with HSP90 stimulated the ATPase activity of HSP90 and increased the binding of H1t to tNASP. HSP90 and tNASP are present in both nuclear and cytoplasmic fractions of mouse spermatogenic cells; however, HSP90 bound to NASP only in the cytoplasm. In vitro nuclear import assays on permeabilized HeLa cells demonstrate that tNASP, in the absence of any other cytoplasmic factors, transports linker histones into the nucleus in an energy and nuclear localization signal-dependent manner. Consequently we hypothesize that in the cytoplasm linker histones are bound to a complex containing NASP and HSP90 whose ATPase activity is stimulated by binding NASP. NASP-H1 is subsequently released from the complex and translocates to the nucleus where the H1 is released for binding to the DNA.

Association of sperm protein 17 with A-kinase anchoring protein 3 in flagella

BACKGROUND

Sperm protein 17 (Sp17) is a three-domain protein that contains: 1) a highly conserved N-terminal domain that is 45% identical to the human type II alpha regulatory subunit (RII alpha) of protein kinase A (PKA); 2) a central sulphated carbohydrate-binding domain; and 3) a C-terminal Ca++/calmodulin (CaM) binding domain. Although Sp17 was originally discovered and characterized in spermatozoa, its mRNA has now been found in a variety of normal mouse and human tissues. However, Sp17 protein is found predominantly in spermatozoa, cilia and human neoplastic cell lines. This study demonstrates that Sp17 from spermatozoa binds A-kinase anchoring protein 3 (AKAP3), confirming the functionality of the N-terminal domain.

METHODS

In this study in vitro precipitation and immunolocalization demonstrate that Sp17 binds to AKAP3 (AKAP110) in spermatozoa.

RESULTS

Sp17 is present in the head and tail of spermatozoa, in the tail it is in the fibrous sheath, which contains AKAP3 and AKAP4. Recombinant AKAP3 and AKAP4 RII binding domains were synthesized as glutathione S-transferase (GST) fusion proteins immobilized on glutathione-agarose resin and added to CHAPS extracts of human spermatozoa. Western blots of bound and eluted proteins probed with anti-Sp17 revealed that AKAP3 bound and precipitated a significant level of Sp17 while AKAP4 did not. AKAP4 binds AKAP3 and expression of AKAP3 is reduced in AKAP4 knockout sperm, therefore we tested AKAP4 knockout spermatozoa for Sp17 and found that there was a reduction in the amount of Sp17 expressed when compared to wild type spermatozoa. Co-localization of AKAP3 and Sp17 by immunofluorescence was demonstrated along the length of the principal piece of the flagella.

CONCLUSIONS

As predicted by its N-terminal domain that is 45% identical to the human RIIalpha of PKA, Sp17 from spermatozoa binds the RII binding domain of AKAP3 along the length of the flagella.

LCN6, a novel human epididymal lipocalin

BACKGROUND

The lipocalin (LCN) family of structurally conserved hydrophobic ligand binding proteins is represented in all major taxonomic groups from prokaryotes to primates. The importance of lipocalins in reproduction and the similarity to known epididymal lipocalins prompted us to characterize the novel human epididymal LCN6.

METHODS AND RESULTS

LCN6 cDNA was identified by database analysis in a comprehensive human library sequencing program. Macaca mulatta (rhesus monkey) cDNA was obtained from an epididymis cDNA library and is 93% homologous to the human. The gene is located on chromosome 9q34 adjacent LCN8 and LCN5. LCN6 amino acid sequence is most closely related to LCN5, but the LCN6 beta-barrel structure is best modeled on mouse major urinary protein 1, a pheromone binding protein. Northern blot analysis of RNAs isolated from 25 human tissues revealed predominant expression of a 1.0 kb mRNA in the epididymis. No other transcript was detected except for weak expression of a larger hybridizing mRNA in urinary bladder. Northern hybridization analysis of LCN6 mRNA expression in sham-operated, castrated and testosterone replaced rhesus monkeys suggests mRNA levels are little affected 6 days after castration. Immunohistochemical staining revealed that LCN6 protein is abundant in the caput epithelium and lumen. Immunofluorescent staining of human spermatozoa shows LCN6 located on the head and tail of spermatozoa with the highest concentration of LCN6 on the post-acrosomal region of the head, where it appeared aggregated into large patches.

CONCLUSIONS

LCN6 is a novel lipocalin closely related to Lcn5 and Lcn8 and these three genes are likely products of gene duplication events that predate rodent-primate divergence. Predominant expression in the epididymis and location on sperm surface are consistent with a role for LCN6 in male fertility.

Characterization of mouse Eppin and a gene cluster of similar protease inhibitors on mouse chromosome 2

We have recently described a novel gene on human chromosome 20q 12-13.2 called Eppin (Epididymal protease inhibitor) that expresses three mRNAs encoding two isoforms of a cysteine-rich protein containing both Kunitz-type and WAP-type (four disulfide core) consensus sequences (Richardson et al., 2001). To further our studies on Eppin, we have cloned, sequenced and characterized mouse Eppin and report that it lies within a 200 Kb cluster of putative Eppin-like genes on mouse chromosome 2. Analysis of the homologies between the genes in the human and mouse Eppin clusters indicates that the first part of the cluster immediately surrounding Eppin represents a conserved linkage because the order of homologous genes is conserved. Sequencing of reverse transcription polymerase chain reaction (RT-PCR) products confirmed the expression of five of these novel Eppin-like genes in the mouse, which include the mouse homologue of HE-4. These genes are characterized by having either one or both of the Kunitz-type and WAP-type consensus sequences. Additional RT-PCR experiments revealed that expression of some of the Eppin-like genes is restricted to epididymis and testis while others are expressed in several somatic tissues. Northern blot analysis of 22 different mouse tissues identified Eppin transcripts only in the epididymis and testis. Immunostaining of Eppin with anti-recombinant mouse Eppin demonstrated Eppin predominantly on the postacrosomal region of mouse spermatozoa, in Sertoli cells, Leydig cells, and round spermatids in the testis, and in the principal cells of the cauda epididymidis epithelium. Eppin is first expressed by Sertoli cells of 12-day-old mice and subsequently in round spermatids, which is consistent with androgen regulation. Our results demonstrate that mouse chromosome 2 contains a conserved linkage of Eppin-like protease inhibitor genes that are expressed in the epididymis.

Overexpression of the Linker histone-binding protein tNASP affects progression through the cell cycle

NASP is an H1 histone-binding protein that is cell cycle-regulated and occurs in two major forms: tNASP, found in gametes, embryonic cells, and transformed cells; and sNASP, found in all rapidly dividing somatic cells (Richardson, R. T., Batova, I. N., Widgren, E. E., Zheng, L. X., Whitfield, M., Marzluff, W. F., and O'Rand, M. G. (2000) J. Biol. Chem. 275, 30378-30386). When full-length tNASP fused to green fluorescent protein (GFP) is transiently transfected into HeLa cells, it is efficiently transported into the nucleus within 2 h after translation in the cytoplasm, whereas the NASP nuclear localization signal (NLS) deletion mutant (NASP-DeltaNLS-GFP) is retained in the cytoplasm. In HeLa cells synchronized by a double thymidine block and transiently transfected to overexpress full-length tNASP or NASP-DeltaNLS, progression through the G(1)/S border is delayed. Cells transiently transfected to overexpress the histone-binding site (HBS) deletion mutant (NASP-DeltaHBS) or sNASP were not delayed in progression through the G(1)/S border. By using a DNA supercoiling assay, in vitro binding data demonstrate that H1 histone-tNASP complexes can transfer H1 histones to DNA, whereas NASP-DeltaHBS cannot. Measurement of NASP mobility in the nucleus by fluorescence recovery after photobleaching indicates that NASP mobility is virtually identical to that reported for H1 histones. These data suggest that NASP-H1 complexes exist in the nucleus and that tNASP can influence cell cycle progression through the G(1)/S border through mediation of DNA-H1 histone binding.

Cystatin 11: a new member of the cystatin type 2 family

Cystatin (CST)11, a novel member of the CST type 2 family of cysteine protease inhibitors, was identified in Macaca mulatta epididymis by subtractive hybridization cloning. The human CST11 gene on chromosome 20p11.2 is located near three other CST genes expressed predominantly in the male reproductive tract. The CST11 gene spans three exons, a structure similar to that of other CST family 2 genes. An exon 2-deleted alternative transcript (CST11Delta2) was also identified. CST11 mRNA is expressed only in the epididymis as judged by Northern blot hybridization and is androgen regulated. The protein is most abundant in the initial segment, but is detected throughout the epididymis and on ejaculated human sperm. The calculated tertiary structure of CST11 reveals that the three regions corresponding to the protease inhibitory wedge of CST3 are similarly juxtaposed in CST11, consistent with protease inhibitor function. Intact and exon 2-deleted CST11 recombinant proteins were tested for antibacterial activity. After a 2-h incubation of Escherichia coli with 50 microg/ml recombinant CST11 or CST11Delta2, bacterial colony-forming units were reduced to 30% of control, indicating that both forms have antimicrobial activity.

Analysis of recombinant mouse zona pellucida protein 2 (ZP2) constructs for immunocontraception

In this study we have examined the potential of recombinant mouse zona pellucida glycoprotein 2 (ZP2) as a target for immunocontraception. Immunogenicity studies and fertility trials were performed in outbred Swiss-Webster mice using four ZP2 constructs: Val(35)-Gly(200) (ZP2(V35-G200)), Val(35)-Leu(331) (ZP2(V35-L331)), Pro(325)-Ala(637) (ZP2(P325-A637)), and Val(35)-Ala(637) (ZP2(V35-A637)). A significant antibody response occurred to three of the four immunogens, however antibodies capable of recognizing native ZP occurred only after immunization with ZP2(V35-A637) and ZP2(P325-A637). Only immunization with ZP2(V35-A637) correlated with a reduction in fertility. Examination of the physiological basis for infertility revealed that: (1) passive transfer of ZP2 antiserum induced infertility in non-immune mice; (2) ovaries of infertile mice appeared histologically normal; (3) infertile mice produced normal numbers of eggs and (4) ZP of ovulated eggs from infertile mice demonstrated a significant reduction in the number of sperm bound compared to eggs from adjuvant controls. Infertility can be caused entirely by ZP2 antibodies without the incidence of significant ovarian pathology. This study also demonstrated that immunization with the bioactive (sperm binding) region of ZP2, recombinant ZP2(V35-G200), did not result in a significant immune response that recognized native ZP or inhibited fertility. Consequently we designed a ZP2-sperm antigen construct, replacing the C-terminal region of ZP2 with Sp17. This construct proved to be immunogenic and reduce fertility while directing the immune response to the Val(35)-Gly(200) region of ZP2.

Zonadhesin: characterization, localization, and zona pellucida binding

Zonadhesin is a multiple-domain transmembrane protein that is believed to function as a sperm-zona pellucida binding protein. In this study we sequenced zonadhesin from rabbit testis and analyzed its processing, expression, localization, and zona pellucida binding. We show that the precursor protein occurs exclusively in the testis and that proteolytic processing results in the formation of three fragments: p43 (D1 domain), p97 (D2-D4 domains), and p58 (D4 domain-C-terminal). In mature spermatozoa the p43 and p97 fragments exist as disulfide-bonded dimers. During spermatogenesis, synthesis of zonadhesin mRNA chiefly occurs in primary spermatocytes, whereas the protein is abundant in both Sertoli cells and spermatids. In spermatozoa the protein is localized exclusively to the anterior acrosome but is not available for binding antibody on live spermatozoa. Once the acrosome reaction is induced, zonadhesin is lost from the spermatozoon, but remains with the acrosomal shroud. We show that recombinant D4 domain can bind zona pellucida, and we propose that zonadhesin functions after the acrosome reaction has been initiated to bind the acrosomal shroud to the zona pellucida.

Primate epididymis-specific proteins: characterization of ESC42, a novel protein containing a trefoil-like motif in monkey and human

Epididymal secreted proteins promote sperm maturation and fertilizing capacity by interacting with sperm during passage through the epididymis. Here we investigate the molecular basis of sperm maturation by isolating cDNA clones for novel epididymis-specific expressed sequences. Thirty-six novel cDNAs were isolated and sequenced from a subtracted Macaca mulatta epididymis library. The clones encode proteins with a range of motifs characteristic of protein-modifying enzymes, protease inhibitors, hydrophobic ligand-binding and transport proteins, extracellular matrix-interacting proteins, and transcription regulatory factors. The full length coding sequences were obtained for 11 clones representing a range of abundance levels. Expression of each is regionally localized and androgen regulated. The most abundant, ESC42, contains a cysteine-rich region similar to the signature binding domain of the trefoil family of motogenic wound repair proteins. The monkey and human proteins are nearly 90% identical. Immunohistochemical staining revealed that the protein is most abundant in the epithelium of the caput and is also present in the lumen and bound to sperm. The ESC42 gene, located on chromosome 20q11, contains two exons encoding two nearly identical predicted signal peptides and a third exon encoding the rest of the protein.

Comparison of mouse and human NASP genes and expression in human transformed and tumor cell lines

We previously cloned and sequenced cDNAs encoding mouse NASP (mNASP), a cell cycle regulated histone H1 binding protein. Here we report the genomic sequence and organization for mNASP along with its 5' regulatory region and compare these with human NASP (hNASP). The mNASP gene contains 16 exons interrupted by 15 introns. The sequence encoding testis mNASP uses all 16 exons while the somatic form uses 13 exons by differential splicing. All the exons conform to the AG/GT splicing rule. Putative TATA box-containing transcription initiation sites are present for somatic NASP in human and mouse and for testis hNASP. Comparison of the promoter regions of mNASP and hNASP approximately 1 kb upstream of the transcription start sites for the two splice variants revealed a number of possible transcription factor binding sites relevant to specific patterns of NASP tissue expression. The presence of single bands on Southern blots of mouse genomic DNA suggests that mNASP is a single copy gene although pseudogenes exist in both the mouse and human genomes. Chromosome fluorescence by in situ hybridization revealed that mNASP is present on chromosome 4, in an area that corresponds to band 4D1, a region syntenic to the locus of hNASP on chromosome 1. Additionally, we report that human somatic and testis NASP mRNAs are expressed at varying levels in all the transformed cell lines and human tumors tested, further supporting NASP's role in the cell cycle of dividing cells.

Characterization of Sp17: a ubiquitous three domain protein that binds heparin

Sp17 is a protein that was originally thought to be expressed exclusively in the testis and whose primary function was binding to the extracellular matrix of the oocyte. Several recent reports have implicated Sp17 as having a role in cell-cell adhesion and/or cell migration in transformed, lymphocytic and haematopoietic cells, possibly through its interaction with extracellular heparan sulphate. In the present study, we report that Sp17's central domain (amino acids 61-117), spanning exon 3, is critical for heparin binding. Sp17 has two additional functional domains, an N-terminal domain similar to the dimer-interaction site in the cAMP-dependent protein kinase IIalpha regulatory subunit and a C-terminal calmodulin-binding domain. The mouse gene for Sp17 is 6.5 kb and contains four exons. Although Sp17 expression is highest in the testis, it is present in all of the mouse somatic tissues examined and is highly conserved throughout all mammalian species. Sp17's central domain, which is necessary for heparin binding, exhibits the greatest sequence divergence of all three domains. The Sp17 gene is induced in metastatic cells and during mucosal immune responses, and the protein appears to play an important role in cell migration and/or adhesion in somatic cells, as well as in male germ cells.

Characterization of the histone H1-binding protein, NASP, as a cell cycle-regulated somatic protein

Nuclear autoantigenic sperm protein (NASP), initially described as a highly autoimmunogenic testis and sperm-specific protein, is a histone-binding protein that is a homologue of the N1/N2 gene expressed in oocytes of Xenopus laevis. Here, we report a somatic form of NASP (sNASP) present in all mitotic cells examined, including mouse embryonic cells and several mouse and human tissue culture cell lines. Affinity chromatography and histone isolation demonstrate that NASP from myeloma cells is complexed only with H1, linker histones. Somatic NASP is a shorter version of testicular NASP (tNASP) with two deletions in the coding region arising from alternative splicing and differs from tNASP in its 5' untranslated regions. We examined the relationship between NASP mRNA expression and the cell cycle and report that in cultures of synchronized mouse 3T3 cells and HeLa cells sNASP mRNA levels increase during S-phase and decline in G(2), concomitant with histone mRNA levels. NASP protein levels remain stable in these cells but become undetectable in confluent cultures of nondividing CV-1 cells and in nonmitotic cells in various body tissues. Expression of sNASP mRNA is regulated during the cell cycle and, consistent with a role as a histone transport protein, NASP mRNA expression parallels histone mRNA expression.

Analysis of the autoimmune epitopes on human testicular NASP using recombinant and synthetic peptides

The human nuclear autoantigenic sperm protein, NASP, is a testicular histone-binding protein of 787 amino acids to which most vasectomized men develop autoantibodies. In this study to define the boundaries of antigenic regions and epitope recognition pattern, recombinant deletion mutants spanning the entire protein coding sequence and a human NASP cDNA sublibrary were screened with vasectomy patients' sera. Employing panel sera from 21 vasectomy patients with anti-sperm antibodies, a heterogeneous pattern of autoantibody binding to the recombinant polypeptides was detected in ELISA and immunoblotting. The majority of sera (20/21) had antibodies to one or more of the NASP fusion proteins. Antigenic sites preferentially recognized by the individual patients' sera were located within aa 32-352 and aa 572-787. Using a patient's serum selected for its reactivity to the whole recombinant protein in Western blots, cDNA clones positive for the C-terminal domain of the molecule were identified. The number and location of linear epitopes in this region were determined by synthetic peptide mapping and inhibition studies. The epitope-containing segment was delimited to the sequence aa 619-692 and analysis of a series of 74 concurrent overlapping 9mer synthetic peptides encompassing this region revealed four linear epitopes: amino acid residues IREKIEDAK (aa 648-656), KESQRSGNV (aa 656-664), AELALKATL (aa 665-673) and GFTPGGGGS (aa 680-688). All individual patients' sera reacted with epitopes within the sequence IREellipsis.GGS (aa 648-688). The strongest reactivity was displayed by peptides corresponding to the sequence AELALKATL (aa 665-673). Thus, multiple continuous autoimmune epitopes in NASP involving sequences in the conserved C-terminal domain as well as in the less conserved testis-specific N-terminal region comprising the histone-binding sites, as predicted for an antigen-driven immune response, may be a target of autoantibodies in vasectomized men and may provide a relevant laboratory variable to describe more accurately the spectrum of autoantibody specificities associated with the clinical manifestation of vasectomy.

HE2beta and HE2gamma, new members of an epididymis-specific family of androgen-regulated proteins in the human

HE2 is an epididymis-specific sperm-binding secretory protein. We isolated a family of HE2-related complementary DNAs from a human caput/corpus library. The transcripts code for identical 71-amino acid N-termini and different C-termini, and 5'- and 3'-untranslated regions. Compared with the original HE2, HE2beta and HE2gamma proteins have a 25-amino acid deletion near the C-terminus, and HE2gamma isoforms have a second deletion. These frame-shifting deletions result in C-termini differing in length, amino acid sequence, including number of cysteines, and isoelectric point. Identical sequences and deletion start and stop points indicate the HE2 isoforms are derived from alternative splicing of 8 or more exons of a single gene. Northern hybridization revealed that the 0.9-kb messenger RNA (mRNA) is most abundant in human caput; there is much less of it (20%) in corpus and little (<5%) in cauda. In castrated Macaca mulatta, HE2 mRNA decreased to 10% of sham-operated levels. Testosterone replacement maintained HE2 mRNA 3- to 5-fold higher than castrate levels, indicating its androgen dependence. Immunohistochemical staining revealed that the beta1 form is highly expressed in principal cells of the initial segment and caput. It is secreted into the lumen and binds to the sperm surface in the postacrosomal and neck regions. The beta2 form is expressed in principal cells primarily in efferent ducts.

Cloning and characterization of an androgen-dependent acidic epididymal glycoprotein/CRISP1-like protein from the monkey

A cDNA encoding an acidic epididymal glycoprotein (AEG)-like, CRISP1 (cysteine-rich secretory protein) protein from the monkey (Macaca mullata) epididymis has been cloned and sequenced. The monkey AEG (mAEG) has an open reading frame that encodes a protein containing 249 amino acids with a deduced molecular mass of 28 kDa. The mAEG protein sequence is 85% identical to human and 44% identical to mouse CRISP1, including all 16 conserved cysteine residues. mAEG also shows a significant amino acid homology with other CRISP proteins, rat AEG/DE, human TPX1/CRISP2, and guinea pig acrosomal autoantigen 1 (AA1). In addition, mAEG shows somewhat less homology to a toxin from the Mexican beaded lizard and to a human glioma pathogenesis-related protein. Northern blot analysis shows that the mRNA for mAEG is expressed in all the regions of the epididymis except the caput and was not detected in the testis, prostate, seminal vesicle, and brain. In castrated animals, mAEG gene expression in the epididymis is significantly diminished; however, testosterone enanthate replacement restored the normal level of expression, demonstrating that expression of mAEG is androgen dependent. Western blot analysis of monkey epididymal regions using mouse antirecombinant human AEG identified a 28-kDa protein only in the caudal region. Immunohistochemical analysis identified mAEG only in the principal cells of the cauda epididymal epithelium. Immunofluorescence analysis identified mAEG on the principal piece of the sperm tail and as small patches over the middle piece and head regions. The results described in the present study suggest that mAEG (CRISP1) is secreted in the monkey epididymis, regulated by androgens and present on epididymal spermatozoa.

A chimeric sperm peptide induces antibodies and strain-specific reversible infertility in mice

The development of a contraceptive vaccine based on a gamete-specific antigen requires knowledge of the ability of the antigen to elicit an immune response that inhibits fertilization. A well-defined immune response, as elicited by a synthetic peptide comprising a dominant B-cell epitope coupled to a common promiscuous T-cell epitope, might be preferable. In this study, the immunodominant B-cell epitope of sperm antigen Sp17 has been identified and synthesized as a chimeric peptide with the promiscuous T-cell epitope bovine RNase[94-104] at the N terminal. Immunization of female BALB/c mice with this peptide induced a dose-dependent reduction in fertility. Although antibodies to recombinant and native Sp17 were elicited in these mice, there was no strict correlation between the level of these antibodies and the reduction in fertility. Moreover, the induction of infertility was strain-specific since no effect on fertility could be induced in B6AF1 mice. To understand the mechanism behind this apparent strain-specific infertility induction, a more extended study on both the humoral and the cellular immune response to the chimeric peptide was performed. The antigen-specific T-cell response and the levels of antigen-specific cytokines are the major factors that affect fertility outcome.

Immune response to immunization with sperm antigens in the macaque oviduct

The oviduct of most mammalian species is the site where spermatozoa first encounter the oocyte and the process of fertilization is initiated. It should therefore be considered an important focus of study for the development of an effective gamete immunocontraceptive with the goal of immunologically interfering with spermatozoon function. The study reported here used the cynomolgus macaque as a nonhuman primate model in which to analyze the serum and oviductal fluid immune response to immunization with the human sperm protein Sp17 and synthetic peptides derived from Sp17. Human and macaque Sp17 were shown to share a very high degree of identity (96.7%), confirming this species as a suitable model in which to study the antibody response and recognition of spermatozoa. The oviductal fluid antibody titer varied with respect to serum titer both over time for individual monkeys and between different monkeys. In all cases, however, the antibody response was restricted solely to the immunoglobulin G class. Finally, both serum and oviductal fluid antibodies were directed against identical Sp17 B-cell epitopes and both recognized native macaque Sp17 in spermatozoa.

Designing an effective immunocontraceptive

The immunological inhibition of fertilization is the goal of gamete immunocontraception. To achieve this goal a gamete-specific antigen target must be defined and the presentation of the immunogen to the immune system must be clearly understood in order to elicit a defined immune response which will target the native gamete molecule. Almost 20 years ago C.B. Metz suggested six studies which would answer the questions necessary for the development of a successful immunocontraceptive, and although much work has gone into answering each of these questions, none has been completed. Hyaluronidase is an example of a well studied sperm antigen whose native, membrane bound form (PH-20) is a successful immunocontraceptive in female guinea pigs. However, it remains to be demonstrated that a successful native antigen can be a successful synthetic or recombinant gamete immunocontraceptive (GAMICON). The problem of converting a successful native contraceptive antigen into an effective synthetic or recombinant GAMICON is at the heart of the problem of GAMICON design. If the epitopes of native and synthetic immunogens are not the same, then can a conversion ever be made? One approach to understanding how to make this conversion is to use defined, synthetic B- T-cell epitopes as specific B-cell epitopes on native antigens affect fertility.

Sequence and characterization of the sperm protein Sp17 from the baboon

In this study, cDNAs encoding the sperm protein Sp17 from the baboon (Papio papio) have been cloned and sequenced. Three clones, differing in the lengths of their 3' untranslated regions, were identified, which were encoded by mRNA transcripts of 0.8-1.35 kb. The open reading frame encodes 163 amino acids with a predicted molecular mass of 18.8 kDa. The baboon Sp17 protein sequence is 97% identical to human Sp17 but differs significantly by the addition of 12 amino acids at the C-terminal, providing an additional potential protein kinase C phosphorylation site. Northern blot analysis demonstrated that the baboon Sp17 mRNA was specific to the baboon testes and was not detected in the ovary, placenta, or any of the other somatic tissues tested. Western blot analysis using anti-Sp17 antibodies demonstrated that the native baboon sperm Sp17 protein consists of a doublet with an apparent M(r) of 26.5 and 27.2 kDa. Immunocytochemical staining of baboon testis with anti-Sp17 antibodies demonstrated Sp17 in spermatocytes, spermatids, and spermatozoa within the seminiferous epithelium. No specific staining was observed on spermatogonia, Sertoli cells, Leydig cells, or other somatic cell types.

Autoimmunogenicity of the human sperm protein Sp17 in vasectomized men and identification of linear B cell epitopes

OBJECTIVE

To assess whether human sera positive for antisperm antibodies have detectable levels of Sp17 autoantibodies and to determine the linear B cell epitopes to which these are raised for both native and recombinant Sp17.

DESIGN

Enzyme-linked immunoaborbent assays were performed against recombinant HSp17 on 15 serum samples from prevasovasostomy and postvasovasostomy patients. Positive sera then were used in mimotope analyses to determine HSp17 immunodominant linear B cell epitopes. These were compared with the linear B cell epitopes of recombinant HSp17.

SETTING

University research laboratory.

PATIENT(S)

Fifteen vasectomized or vasovasostomized men.

MAIN OUTCOME MEASURE(S)

Serum antibody reactivity to human Sp17.

RESULT(S)

Sera from vasectomized and vasovasostomized men exhibit Sp17 antibodies raised predominantly to two immunodominant linear B cell epitopes (amino acids 4 to 19 and amino acids 118 to 127), which differed from those of recombinant HSp17 (amino acids 52 to 79 and amino acids 124 to 136).

CONCLUSION(S)

The results show that Sp17 is an antigen to which vasectomized men raise autoantibodies. Two linear B cell epitopes predominate in native Sp17 and these differ from (but overlap with) those of the bacterially expressed recombinant protein.

Site-directed mutagenesis of rabbit proacrosin. Identification of residues involved in zona pellucida binding

The mammalian acrosomal sperm protease proacrosin plays a role in fertilization by proteolysis of the oocyte's outer investments. In addition to its serine protease activity, acrosin from several species is known to have binding activity for the zona pellucida, and this action may serve to anchor sperm during zona penetration. In this study, proacrosin was purified from acid extracts of rabbit sperm and shown to bind to homologous zona pellucida using an in vitro assay. Measurement of this binding activity indicated a high affinity saturable interaction with a KD = 1.4 x 10(-8) M. Using cDNAs obtained from previously cloned and sequenced rabbit proacrosin and a splice variant that encodes a shorter form of acrosin (Richardson, R. T., and O'Rand, M. G. (1994) Biochim. Biophys. Acta 1219, 215-218), constructs of various sizes were produced using polymerase chain reaction and expressed as recombinant proteins. In the same in vitro zona binding assay, a construct representing residues 1-279 of rabbit proacrosin was found to bind to zona with a high affinity similar to that of native proacrosin, KD = 2.1 x 10(-8) M. By making smaller recombinant fragments and assaying them for zona binding activity, the location of the binding site was mapped to residues 47-94. Protein modeling of rabbit proacrosin using chymotrypsinogen A as a three-dimensional model indicated that an exposed loop Asp35 to His40 in chymotrypsinogen A is extended with an additional five amino acid residues in rabbit proacrosin from Ile43 to His53 containing arginine residues Arg47, Arg50 and Arg51. Site-directed mutagenesis of arginine residues Arg50 and Arg51 to alanine produced a recombinant without significant zona binding activity. These results are consistent with the hypothesis that rabbit proacrosin contains a specific zona pellucida binding site and that the loop containing arginine residues 50 and 51 is critical for zona binding activity.

Cloning and sequencing of cDNAs encoding the human sperm protein, Sp17

In the present study we have cloned and sequenced two testis-specific cDNAs (1.3 kb and 1.6 kb) encoding a human sperm protein, designated HSp17. Each cDNA gave rise to identical protein sequences and differed only in the 5' untranslated region. The predicted amino-acid sequence revealed a protein of 17.5 kDa which exhibited a high degree of homology with both rabbit and mouse Sp17. Analysis of native and recombinant Sp17 by SDS-PAGE has shown the apparent molecular weight of the protein to be 24.5 kDa.

Histone-binding domains in a human nuclear autoantigenic sperm protein

In one of our previous studies, the deduced amino acid sequence of the human nuclear autoantigenic sperm protein (hNASP) revealed two conserved histone-binding domains when compared to the Xenopus N1/N2 protein sequence. These histone-binding domains of Xenopus N1/N2 are known to be functional; however, their function in hNASP is unknown. In this study we have determined the number, location, and activity of the histone-binding domains on the primary sequence of hNASP. Purified recombinant polypeptides expressing the full-length hNASP and various deletion constructs covering the entire length of the hNASP sequence were tested by Western blotting and in ELISA for binding to biotin-labeled histones. A positive reaction was detected for the full-length recombinant protein and for the polypeptides spanning the N-terminal region (amino acids [aa] 32-192), and two additional regions: aa 193-352 and aa 353-572. The lack of binding to the expressed C-terminal (aa 573-787), which also contains polyacidic amino acids, suggests that the binding of hNASP to the somatic core histones is a sequence-specific as well as an electrostatic interaction. The removal of flanking sequences from the binding domains did not abrogate their ability to bind histones. We conclude that there are at least three functional histone-binding domains in hNASP, two of them encompassing the predicted histone binding sites homologous to the N1/N2 protein, and a third novel domain. Therefore, hNASP may be defined as a nuclear histone-binding protein found in human testis.

Sequence and localization of the mouse sperm autoantigenic protein, Sp17

The present study characterizes the sperm protein Sp17 in the mouse. Sp17 is a mammalian testis- and sperm-specific protein that has been isolated, sequenced, and characterized from rabbit testis and spermatozoa. In this study, a rabbit Sp17 cDNA probe representing the entire protein coding region was used to screen a mouse testis cDNA library to obtain the mouse Sp17 sequence. The mouse mRNa for Sp17 encodes a 149-amino acid protein with a predicted molecular weight of 17,296. The mouse Sp17 (MSp17) cDNA sequence is 82% identical to the rabbit Sp17 cDNA sequence while the MSp17 protein sequence is 74% identical to the rabbit protein sequence. The presence of native Sp17 in mouse spermatozoa and testis was demonstrated by Western blot analysis, immunoprecipitation, and immunolocalization. After SDS-PAGE, the native Sp17 has an apparent molecular mass of 24 kDa. The sequence of the native Sp17 was confirmed by Western blots of mouse testis and spermatozoa probed with two anti-peptide antibodies--one, anti-G22C, made against amino acids 61-82 in the rabbit sequence (61-83 in the mouse), and a second, anti-K18C, made against amino acids 120-136 in the C-terminal region in the human sequence (118-134 in the mouse sequence). In the absence of proteolytic inhibitors, part of the C-terminal of native MSp17 is cleaved, giving rise to an 18-kDa band. Sp17 is present in spermatocytes and spermatids in the testis. In spermatozoa, Sp17 is not available to bind antibody on the surface of live, acrosome-intact spermatozoa, but it is present on the equatorial surface of live, acrosome-reacted spermatozoa. In fixed spermatozoa, staining is observed along the length of the principal piece, weakly along the midpiece, and over the acrosomal region of the head. When the acrosome reaction begins, acrosomal staining is seen throughout the equatorial region of the acrosome. Using mimotope analysis, this study has also demonstrated that native Sp17 is a sperm autoantigen and that recombinant mouse Sp17 is immunogenic in males with a highly restricted linear epitope.

Expression of the rabbit sperm protein Sp17 in COS cells and interaction of recombinant Sp17 with the rabbit zona pellucida

This study extends our analysis of rabbit recombinant Sp17 (rSp17) by examining whether rSp17 synthesized in transfected COS cells will show a particular localization within the cell and whether the COS cell will bind with zona pellucida. We show, using the crosslinking, reagent DSS that rSp17 can bind to rabbit zona glycoprotein R45 or R55.

Sequence of a rabbit sperm zona pellucida binding protein and localization during the acrosome reaction

The interaction of the mammalian spermatozoon with the oocyte's extracellular matrix or zona pellucida is a critical first step leading to successful fertilization. In this cell-extracellular matrix interaction it is the carbohydrate of the zona pellucida which serves as the sperm receptor and the surface of the spermatozoon which provides the lectin-like adhesion molecules. To better understand sperm-zona pellucida binding we have analyzed one specific zona binding protein (ZBP). This study has determined the mRNA sequence encoding a mammalian testis and sperm specific protein of 16,891 Da, which we have designated Sp17. Analysis of Sp17 revealed that the mRNA is present in rabbit, mouse, and human testes but not in any somatic tissue tested. In the rabbit, Sp17 is the 17-kDa member of the rabbit sperm autoantigen family of sperm specific autoantigens and is encoded by two mRNAs of 0.9 and 1.1 kb. Each mRNA has a unique 5' untranslated region but both have identical coding regions. The deduced amino acid sequence of the Sp17 ZBP showed several interesting features, including a similarity to the N-terminal of human testis cAMP-dependent protein kinase. Localization of Sp17 on live spermatozoa using antibodies to recombinant Sp17 or to the Sp17 peptide, G22C, revealed that the peptide backbone of Sp17 is inaccessible until the acrosome reaction begins. However, on paraformaldehyde fixed, acrosome intact spermatozoa, the peptide backbone is accessible to the antibodies which localize Sp17 to the apical surface. In the rabbit as well as other similar species in which the corona radiata (granulosa) cells adhere tightly to the zona pellucida and synthesize zona glycoproteins, the fertilizing spermatozoon may have already begun the acrosome reaction within the cumulus oophorus. Thus, the rabbit sperm surface would be modified to expose the Sp17 polypeptide during the final phase of cumulus passage and consequently Sp17 would be available for initial zona binding. The present study has also demonstrated that recombinant Sp17 can bind zona pellucida, dextran, and dextran sulfate.

Cloning and sequencing of cDNAs for rabbit preproacrosin and a novel preproacrosin-related cDNA

A 1414 bp cDNA for rabbit preproacrosin (RPA) and a related short preproacrosin (shRPA) cDNA of 951 bp were cloned and sequenced. RPA's 431 amino acid open reading frame encodes a 46,422 kDa protein. shRPA is identical to RPA except that it lacks an internal stretch of 468 bp, such that the encoded protein has a deduced molecular mass of 29,965 kDa. Antiserum against a synthetic peptide representing the light chain of rabbit proacrosin was used on Western blots of rabbit testis and sperm. Under reducing conditions, it revealed two major groups of bands at 50-57 and 29-32 kDa. Several lines of evidence suggest that shRPA is a splice variant of proacrosin and that it encodes a 30-33 kDa protein similar to sperminogen (Siegel, M. et al. (1987) Biol. Reprod. 36, 1063-1068), but apparently lacking proteinase activity.

Identification of sperm antigen targets for immunocontraception: B-cell epitope analysis of Sp17

The selection of immunological targets present on gametes is an important first step in the successful production of animal or human vaccines for immunocontraception. One strategy with regard to sperm antigens is to select antigens with physiological roles in gamete interaction, obtain the mRNA sequence for such an antigen, and then determine which region or domain of the molecule is available to the immune system when spermatozoa are presented to the female reproductive system. To illustrate this strategy, we have used the rabbit sperm antigen Sp17 (RSA-3), which has been cloned and sequenced. The peptide pin-block method of Chiron Mimotopes, Australia, has been used to analyse the 146 amino acids of Sp17 with various homologous and heterologous antisera. This study demonstrates that such an analysis can lead to the identification of a B-cell epitope with strong immunocontraceptive potential.