Valosine containing protein is a substrate of cAMP-activated boar sperm tyrosine kinase

ACRBP (Sp32) is involved in priming sperm for the acrosome reaction and the binding of sperm to the zona pellucida in a porcine model

In boar sperm, we have previously shown that capacitation is associated with the appearance of the p32 tyrosine phosphoprotein complex. The principal tyrosine phosphoprotein involved in this complex is the acrosin-binding protein (ACRBP), which regulates the autoconversion of proacrosin to intermediate forms of acrosin in both boar and mouse sperm. However, the complete biological role of ACRBP has not yet been elucidated. In this study, we tested the hypothesis that tyrosine phophorylation and the presence of the ACRBP in the sperm head are largely necessary to induce capacitation, the acrosome reaction (AR) and sperm-zona pellucida (ZP) binding, all of which are necessary steps for fertilization. In vitro fertilization (IVF) was performed using matured porcine oocytes and pre-capacitated boar sperm cultured with anti-phosphotyrosine antibodies or antibodies against ACRBP. Anti-ACRBP antibodies reduced capacitation and spontaneous AR (P<0.05). Sperm-ZP binding declined in the presence of anti-phosphotyrosine or anti-ACRBP antibodies. The localisation of anti-ACRBP antibodies on the sperm head, reduced the ability of the sperm to undergo the AR in response to solubilized ZP or by inhibiting the sarco/endoplasmic reticulum Ca2+-ATPase. These results support our hypothesis that tyrosine phosphorylated proteins and ACRBP are present upon the sperm surface in order to participate in sperm-ZP binding, and that ACRBP upon the surface of the sperm head facilitates capacitation and the AR in the porcine.

Regulation of Sperm Capacitation by the 26S Proteasome: An Emerging New Paradigm in Spermatology

The ubiquitin proteasome system (UPS) participates in many biological processes ranging from cell cycle and antigen processing to cellular defense and signaling. Work of the last decade has made it evident that the UPS is involved in many sperm-related processes leading up to and as part of fertilization. The current knowledge of UPS involvement and changes during sperm capacitation are reviewed together with a list of known proteasome-associated sperm proteins and a discussion of the relationships between these proteins and the proteasome. Proteasomal inhibitors such as MG-132 and epoxomicin significantly alter capacitation and prevent acrosome reaction. The 26S proteasome degrades AKAP3, an A-kinase anchoring protein, partially regulating the release of protein-kinase A (PKA), a vital component necessary for the steps leading up to capacitation. Further, changes occur in 20S core subunit localization and abundance throughout capacitation. Proteasome-interacting valosine-containing protein (VCP) undergoes tyrosine phosphorylation; however, its physiological roles in capacitation and fertilization remain unknown. The E1-type ubiquitin-activating enzyme (UBA1) inhibitor PYR-41 also alters acrosomal membrane remodeling during capacitation. Furthermore, after capacitation, the acrosomal proteasomes facilitate the degradation of zona pellucida glycoproteins leading up to fertilization. Methods to modulate the sperm proteasome activity during sperm storage and capacitation may translate to increased reproductive efficiency in livestock animals. Human male infertility diagnostics may benefit from incorporation of research outcomes built upon relationships between UPS and capacitation. Altogether, the studies reviewed here support the involvement of UPS in sperm capacitation and present opportunities for new discoveries.

Motility of carp spermatozoa is associated with profound changes in the sperm proteome

In freshwater cyprinids, spermatozoa are quiescent in seminal plasma and sperm motility is initiated by a decrease in osmolality (hypo-osmotic shock) after discharge into the aqueous environment. However, it is unknown at present if and to what extent changes in proteins are involved in carp sperm motility. Therefore, the aim of our study was to identify proteins related to carp sperm motility through a comparison of immobilized and activated carp spermatozoa using a 2D-DIGE approach. Our results, for the first time indicated that carp sperm motility is associated with changes in protein content. Seventy-two differentially expressed proteins were identified. These proteins are mainly involved in ubiquitin-proteasome pathways, glycolysis, the TCA cycle, remodeling and are putatively related to sperm energy metabolism and motility. Moreover proteins associated with oxidative stress responses, signal transduction by Ca(2+)-dependent MAPK cascades, and PKC and protein folding have been identified. The proteins involved in carp sperm motility were localized to the cytoplasm, mitochondria, cytoskeleton, nucleus and sperm membrane. The identification of a high number of proteins involved in carp sperm motility would contribute to current knowledge about the molecular mechanisms of sperm motility in freshwater fish.

BIOLOGICAL SIGNIFICANCE

To the best of our knowledge, few changes in proteins involved in the initiation of fish sperm motility have been identified. This is a limited number of proteins compared with the 80 recently identified proteins involved in human sperm motility. However, no proteomic studies of sperm motility have yet been performed on freshwater fish. Our present study allowed for the first time a comprehensive characterization of the proteins associated with carp sperm motility and a better understanding of the molecular mechanisms underlying sperm motility activation and maintenance. The application of 2D-DIGE facilitated the identification proteins crucial for sperm structural organization and motility. The identification of a high number of proteins involved in carp sperm motility would contribute appreciably to the presently limited information available on the mechanisms of sperm motility in freshwater fish. Moreover the identified list of proteins will create a platform for future studies designed to assess the functional significance of specific proteins in sperm motility.

Target antigens for Hs-14 monoclonal antibody and their various expression in normozoospermic and asthenozoospermic men

Background

Poor semen quality is one of the main causes of infertility. We have generated a set of monoclonal antibodies to human sperm and used them to investigate sperm quality. Some of these antibodies found differences in the expression of proteins between normal sperm and pathological sperm displaying severe defects. One of them was the Hs-14 antibody.

The aim of this paper was to determine the target protein of the Hs-14 monoclonal antibody and to investigate the expression of the Hs-14-reacting protein on the sperm of asthenozoospermic men with sperm motility defect and of healthy normozoospermic men.

Methods

Indirect immunofluorescence, one-dimensional and two-dimensional polyacrylamide gel electrophoresis, immunoblotting and mass spectrometry.

Results

The Hs-14 antibody binds fibronectin, β-tubulin and valosin-containing protein - new name for this protein is transitional endoplasmic reticulum ATPase (TERA). Since the Hs-14 reaction with TERA remained the strongest at the highest antibody dilution, and Hs-14 consistently labelled the same spot or band as the monospecific anti-TERA antibody on immunoblots, we assume that TERA is an Hs-14-specific protein. Binding of fibronectin and β-tubulin might represent nonspecific cross-reactivity or Hs-14 reaction with similar epitopes of these proteins.

A significant difference (P < 0.001) in immunofluorescence staining with Hs-14 was found between the normozoospermic and asthenozoospermic men.

Conclusion

The Hs-14 antibody enables discrimination between sterile or subfertile asthenozoospermic and fertile normozoospermic men. Decreased levels of TERA in men can be used as a biomarker of reduced fertility.

Electronic supplementary material

The online version of this article (doi:10.1186/s12610-015-0025-0) contains supplementary material, which is available to authorized users.

Sperm proteasome and fertilization

The omnipresent ubiquitin–proteasome system (UPS) is an ATP-dependent enzymatic machinery that targets substrate proteins for degradation by the 26S proteasome by tagging them with an isopeptide chain composed of covalently linked molecules of ubiquitin, a small chaperone protein. The current knowledge of UPS involvement in the process of sperm penetration through vitelline coat (VC) during human and animal fertilization is reviewed in this study, with attention also being given to sperm capacitation and acrosome reaction/exocytosis. In ascidians, spermatozoa release ubiquitin-activating and conjugating enzymes, proteasomes, and unconjugated ubiquitin to first ubiquitinate and then degrade the sperm receptor on the VC; in echinoderms and mammals, the VC (zona pellucida/ZP in mammals) is ubiquitinated during oogenesis and the sperm receptor degraded during fertilization. Various proteasomal subunits and associated enzymes have been detected in spermatozoa and localized to sperm acrosome and other sperm structures. By using specific fluorometric substrates, proteasome-specific proteolytic and deubiquitinating activities can be measured in live, intact spermatozoa and in sperm protein extracts. The requirement of proteasomal proteolysis during fertilization has been documented by the application of various proteasome-specific inhibitors and antibodies. A similar effect was achieved by depletion of sperm-surface ATP. Degradation of VC/ZP-associated sperm receptor proteins by sperm-borne proteasomes has been demonstrated in ascidians and sea urchins. On the applied side, polyspermy has been ameliorated by modulating sperm-associated deubiquitinating enzymes. Diagnostic and therapeutic applications could emerge in human reproductive medicine. Altogether, the studies on sperm proteasome indicate that animal fertilization is controlled in part by a unique, gamete associated, extracellular UPS.

The optimization of the protocol for immunofluorescence on fish spermatozoa

In comparison with mammals, the fertilization of fish occurs predominantly outside the organism in a water environment, where fish spermatozoa require specific conditions to interact with oocytes. It is evident that optimal conditions for fish and mammalian spermatozoa are quite different. This paper describes a special approach to handling fish (common carp and Siberian sturgeon) spermatozoa in comparison with the samples originating from mammals (boar). This approach concerns not only the differences in the composition of the media applied but also primarily emphasizes the concrete parts of the immunofluorescence protocol determining accurate results. Individual parts of the protocol for indirect immunofluorescence of mammalian sperm were changed step by step and modified protocols were applied to immunofluorescence experiments with carp and sturgeon spermatozoa. By evaluating the changes in the integrity of the fish sperm head and flagellum, we selected the steps and corresponding conditions that are crucial for handling the fish spermatozoa. Based on our results, it may be concluded that when working with fish spermatozoa, the cells attached to the microscopic slides must not desiccate prior to the fixation, which is a usual step when working with mammalian sperm. The second crucial step is the necessity to fix the fish spermatozoa, especially when the research is focused on the structure of the flagellum. The impact of the temperature conditions is rather low, but working at low temperatures, except for the period of incubation with antibodies, leads to a higher number of unaffected cells.

Valosine-containing proteins (VCP) in an annelid: Identification of a novel spermatogenesis related factor

Two cDNAs similar to mammalian valosine-containing proteins (VCPs) were isolated from the common lumbricid earthworm Eisenia fetida (Savigny, 1826). The primary sequences, referred to as eVCP-1 and eVCP-2, display a similarity of 74%. Despite of the variable C-termini, both eVCPs have a conserved intron/exon organization spanning 14 kb, which is also conserved to their mammalian counterparts. Although this finding strongly suggests VCPs have a common ancestral origin, phylogenetic analysis predicts that eVCP-2 may be distinct. An investigation by reverse transcription-polymerase chain reaction (RT-PCR) revealed that, whilst evcp-1 was ubiquitously expressed during all developmental stages, evcp-2 was specifically expressed in the anterior segments of sexually mature earthworms. In situ hybridization clearly demonstrated that evcp-2 is expressed in the seminal vesicles, the location of spermatogenesis, and more precisely within the cytophores surrounded by secondary spermatocytes or spermatids. Taken together, this evidence leads to the notion that eVCP-2 is a likely component involved in the final modulation of spermatogenesis.

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Akt-mediated valosin-containing protein 97 phosphorylation regulates its association with ubiquitinated proteins

Hypoxia is a common environmental stress that influences signaling pathways and cell function. Previous studies from our laboratory have identified significant differences in cellular responses to sustained or intermittent hypoxia with the latter proving more cytotoxic. We hypothesized that differences in susceptibility of neurons to intermittent (IH) and sustained hypoxia (SH) are mediated by altered Akt signaling. SH, but not IH, induced a significant increase in Akt activation in rat CA1 hippocampal region extracts compared with room air controls. Akt immunoprecipitations followed by proteomic analysis identified valosin-containing protein (VCP) as an Akt-binding protein. In addition, VCP expression and association with Akt was enhanced during SH, and this association was decreased upon phosphoinositide 3-kinase/Akt pathway blockade with LY294002. Active recombinant Akt phosphorylated recombinant VCP in vitro. Site-directed mutagenesis studies identified Ser352, Ser746, and Ser748 as Akt phosphorylation sites on VCP. In addition, rat CA1 hippocampal tissue exposed to SH exhibited an acidic pI shift of VCP. Protein phosphatase 2A treatment inhibited this acidic shift consistent with SH-induced phosphorylation of VCP in vivo. PC-12 cells transfected with active Akt, but not dominant negative Akt or vector, induced VCP expression and an acidic shift in VCP pI, which was inhibited by protein phosphatase 2A treatment. Furthermore, VCP association with ubiquitinated proteins was demonstrated in vector-transfected PC-12 cell lysates, whereas active Akt-transfected cells demonstrated a marked decrease in association of VCP with ubiquitinated proteins. We concluded that Akt phosphorylates VCP in vitro and in vivo, and VCP phosphorylation releases it from ubiquitinated substrate protein(s) possibly allowing ubiquitinated protein(s) to be degraded by the proteosome.

Evidence for chaperone heterocomplexes containing both Hsp90 and VCP

With assistance from co-chaperone partner proteins, Hsp90 plays an essential positive role in supporting the structure and function of numerous client proteins in vivo. Hsp90's co-chaperone partnerships are believed to regulate and/or target its function. Here we describe associations between Hsp90 chaperone machinery and another chaperone, the 97-kDa valosin-containing protein VCP. Coimmunoadsorption assays indicate that VCP occurs in one or more native heterocomplexes containing Hsp90 and the Hsp90 partner proteins Cdc37, FKBP52, and p23. Functional characterizations indicate that VCP is not an Hsp90 substrate, but rather demonstrate the biochemical hallmarks of an Hsp90 co-chaperone. Potential roles for a collaboration between for Hsp90 and VCP are discussed.

A cyclic adenosine 3',5'-monophosphate-induced tyrosine phosphorylation of Syk protein tyrosine kinase in the flagella of boar spermatozoa

A cyclic adenosine 3',5'-monophosphate (cAMP)-dependent protein tyrosine phosphorylation is involved in the expression of fertilizing ability in mammalian spermatozoa. However, there are only limited data concerning the identification of protein tyrosine kinase (PTK) that is activated by the cAMP signaling. In this study, we have shown data supporting that boar sperm flagellum possesses a unique cAMP-protein kinase A (PKA) signaling cascade leading to phosphorylation of Syk PTK at the tyrosine residues of the activation loop. Ejaculated spermatozoa were washed and then incubated in a modified Krebs-Ringer HEPES medium (mKRH) containing polyvinyl alcohol (PVA) plus 0.1 mM cBiMPS (a cell-permeable cAMP analog), 0.25 mM sodium orthovanadate (Na3VO4) (a protein tyrosine phosphatase (PTP) inhibitor) or both at 38.5 degrees C for 180 min. Aliquots of the sperm suspensions were recovered before and after incubation and then used to detect sperm tyrosine-phosphorylated proteins by Western blotting and indirect immunofluorescence. In the Western blotting, the anti-phosphotyrosine monoclonal antibody (4G10) recognized several bands including 72-kDa protein in the protein extracts from spermatozoa that were incubated solely with cBiMPS. The tyrosine phosphorylation in these sperm proteins was dependent on cBiMPS and enhanced by the addition of Na3VO4. The 72-kDa tyrosine-phosphorylated protein was apparently reacted with the anti-phospho-Syk antibody (Tyr525/526). Indirect immunofluorescence revealed that the connecting and principal pieces of spermatozoa incubated with cBiMPS and Na3VO4 were stained with the anti-phospho-Syk antibody. However, the reactivity of the 72-kDa protein with the anti-phospho-Syk antibody was reduced by the addition of H-89 (a PKA inhibitor, 0.01-0.1 mM) to the sperm suspensions but not affected by the pretreatment of spermatozoa with BAPTA-AM (an intracellular Ca2+ chelator, 0.1 mM). Fractionation of phosphorylated proteins from the spermatozoa with a detergent Nonidet P-40 suggested that the 72-kDa tyrosine-phosphorylated protein might be a cytoskeletal component. Based on these findings, we have concluded that the cAMP-PKA signaling is linked to the Ca2+-independent tyrosine phosphorylation of Syk in the connecting and principal pieces of boar spermatozoa.

Viability and protein phosphorylation patterns of boar spermatozoa agglutinated by treatment with a cell-permeable cyclic adenosine 3',5'-monophosphate analog

Boar spermatozoa become agglutinated with one another at the head when their intracellular cyclic adenosine 3',5'-monophosphate (cAMP)-signaling cascades are activated in the head. The aim of the present study is to examine viability and protein phosphorylation patterns of cAMP-dependently agglutinated boar spermatozoa. Ejaculated spermatozoa were washed and then incubated in a modified Krebs-Ringer HEPES medium containing polyvinyl alcohol (mKRH-PVA) plus 0.1 mM Sp-5,6-dichloro-1-beta-D-ribofuranosyl-benzimidazole-3',5'-monophosphorothioate (cBiMPS, a cell-permeable cAMP analog) at 38.5 degrees C up to 180 minutes. Aliquots of the sperm suspensions were recovered after various incubation periods and then used to examine the state of agglutination, the viability by SYBR14-PI staining and motility assay, and the state of protein phosphorylation by Western blotting and indirect immunofluorescence. In the control samples incubated without cBiMPS for 180 minutes, less than 30% of the total spermatozoa were agglutinated with one another at the heads, and more than 70% of the agglutinated spermatozoa were propidium iodide (PI)-positive (dead). However, the incubation with cBiMPS rapidly increased the percentages of head-to-head agglutinated spermatozoa to approximately 60% within 30 minutes, but did not significantly change them thereafter. In the samples incubated with cBiMPS for 180 minutes, moreover, the percentages of PI-positive cells of the agglutinated spermatozoa (approximately 30%) were significantly lower than those obtained in the control samples (more than 70%). This result was supported by the observation that the percentages of motile cells of the agglutinated spermatozoa were much higher in the samples incubated with cBiMPS for 180 minutes than in the control samples incubated without cBiMPS. As revealed by Western blotting and indirect immunofluorescence, cBiMPS-induced serine/threonine phosphorylation of the proteins (eg, >220 kd, 220 kd, 180 kd, 84 kd, and 54 kd) appeared mainly in the connecting and principal pieces of both agglutinated and free spermatozoa within 30 minutes, and additional phosphorylation occurred in the middle piece later than 30 minutes. Moreover, tyrosine phosphorylation of the proteins (eg, >220 kd, 190 kd, 93 kd, 59 kd, 54 kd, and 32 kd) was induced intensely in the connecting and principal pieces and moderately in the middle piece of almost one half of the agglutinated spermatozoa after incubation with cBiMPS for more than 30 minutes, but rarely in those of the free spermatozoa. These findings are consistent with the following suggestions: activation of the cAMP-signaling cascades leads to rapid (within 30 minutes) head-to-head agglutination in live spermatozoa; rapid (within 30 minutes) protein serine/threonine phosphorylation in the connecting and principal pieces of both cAMP-dependently agglutinated and free spermatozoa and subsequent (later than 30 minutes) phosphorylation in the middle piece of them; and slow (later than 30 minutes) protein tyrosine phosphorylation in the connecting, middle, and principal pieces of the cAMP-dependently agglutinated spermatozoa. Based on these suggestions, we conclude that many of cAMP-dependently agglutinated spermatozoa are live cells in which cAMP-signaling cascades leading to protein serine/threonine and tyrosine phosphorylation are activated in the whole flagellum.