Changes in Carboxy Methylation and Tyrosine Phosphorylation of Protein Phosphatase PP2A Are Associated with Epididymal Sperm Maturation and Motility

Mammalian sperm contain the serine/threonine phosphatases PP1γ2 and PP2A. The role of sperm PP1γ2 is relatively well studied. Here we confirm the presence of PP2A in sperm and show that it undergoes marked changes in methylation (leucine 309), tyrosine phosphorylation (tyrosine 307) and catalytic activity during epididymal sperm maturation. Spermatozoa isolated from proximal caput, distal caput and caudal regions of the epididymis contain equal immuno-reactive amounts of PP2A. Using demethyl sensitive antibodies we show that PP2A is methylated at its carboxy terminus in sperm from the distal caput and caudal regions but not in sperm from the proximal caput region of the epididymis. The methylation status of PP2A was confirmed by isolation of PP2A with microcystin agarose followed by alkali treatment, which causes hydrolysis of protein carboxy methyl esters. Tyrosine phosphorylation of sperm PP2A varied inversely with methylation. That is, PP2A was tyrosine phosphorylated when it was demethylated but not when methylated. PP2A demethylation and its reciprocal tyrosine phosphorylation were also affected by treatment of sperm with L-homocysteine and adenosine, which are known to elevate intracellular S-adenosylhomocysteine, a feedback inhibitor of methyltransferases. Catalytic activity of PP2A declined during epididymal sperm maturation. Inhibition of PP2A by okadaic acid or by incubation of caudal epididymal spermatozoa with L-homocysteine and adenosine resulted in increase of sperm motility parameters including percent motility, velocity, and lateral head amplitude. Demethylation or pharmacological inhibition of PP2A also leads to an increase in phosphorylation of glycogen synthase kinase-3 (GSK3). Our results show for the first time that changes in PP2A activity due to methylation and tyrosine phosphorylation occur in sperm and that these changes may play an important role in the regulation of sperm function.     

A maturation-related differential phosphorylation of the plasma membrane proteins of the epididymal spermatozoa of the hamster by endogenous protein kinases

When the plasma membranes of caput and cauda epididymal spermatozoa of hamster were evaluated for their ability to undergo phosphorylation, a differential phosphorylation of the membrane proteins was observed. In the plasma membranes of the caput epididymal spermatozoa (immature), twelve proteins were phosphorylated (100, 76, 67, 65, 55, 52, 47, 42, 38, 32, 30, and 20 kD), whereas in the plasma membranes of cauda epididymal spermatozoa (mature), a differential phosphorylation pattern was observed with respect to the 94, 67, 52, and 47 kD proteins. The 94 kD protein was found to be phosphorylated and the 67 kD protein was found to be not phosphorylated in cauda spermatozoal plasma membrane (Cd SPM) in contrast to this protein in caput spermatozoal plasma membrane (Cpt SPM). The 52 and 47 kD proteins were also more intensely phosphorylated in Cd SPM than Cpt SPM. The 100 kilodalton protein, although present in both Cpt and Cd sperm plasma membranes, was found to be phosphorylated at the tyrosine residues only in the Cd SPM, as indicated by the Western blot using antiphosphotyrosine antibody. Further, a differential phosphorylation of the substrate proteins present in the Cpt and Cd SPM was seen when Mg²⁺ in the assay buffer was replaced by other divalent cations. For instance, Zn²⁺ stimulated the phosphorylation of an 85 kD protein in cauda SPM and not in the caput SPM and Ca²⁺ stimulated the phosphorylation of a 76 kD protein only in the cauda SPM. The phosphoproteins in both the plasma membranes were found to be phosphorylated predominantly at the tyrosine residue. The differential phosphorylation of a 100 kD protein at tyrosine in the Cd SPM (Western blot), which is absent in the immature Cpt SPM, also indicated that certain proteins in the hamster spermatozoa are phosphorylated in a maturation-specific manner. Mol. Reprod. Dev. 47:341–350, 1997. © 1997 Wiley-Liss, Inc.     

Tyrosine phosphorylation as evidence of epididymal cauda participation in the sperm maturation process of Corynorhinus mexicanus bat

The bat Corynorhinus mexicanus provides an interesting experimental model for the study of epididymal sperm maturation because after spermatogenesis and the regression of the testes, this bat stores sperm in the epididymal cauda for several months. Earlier research conducted by our group suggested that sperm maturation in this species must be completed in the caudal region of the epididymis. One of the major signal transduction events during sperm maturation is the tyrosine phosphorylation of sperm proteins. The aim of the present study was to comparatively evaluate tyrosine phosphorylation in spermatozoa obtained from the caput, corpus and cauda of the epididymis during the sperm storage period. The maturation status of the sperm was determined by the percentage of capacitation and tyrosine phosphorylation in sperm obtained from the epididymis. The highest proportion of tyrosine phosphorylation was registered after the sperm had reached the cauda epididymis during the middle of the storage period. In conclusion, in Corynorhinus mexicanus and most likely in other chiropteran species with an asynchronous male reproductive pattern, epididymal sperm maturation ends in the caudal region of the epididymis and is related to the time that the sperm remains in the epididymis before mating activity.     

Responses of monkey epididymal sperm of different maturational status to second messengers mediating protein tyrosine phosphorylation,acrosome reaction,and motility

The maturation of various aspects of sperm function have been demonstrated in monkey and human epididymal sperm, including the ability to undergo the acrosome reaction. The present study aimed to investigate the maturational changes in non‐human primate sperm in the signal transduction mechanisms leading to the acrosome reaction involving cyclic AMP, Ca²⁺ influx, protein kinase C, and protein tyrosine phosphorylation. Sperm from the caput, corpus, and cauda epididymidis of cynomolgus monkeys were incubated in a complete medium for 2.5 hr, followed by 30 min stimulation with 1 mM dibutyryl cAMP and 1 mM caffeine, 50 μM 1,2‐dioctanoyl‐sn‐glycerol (DOG), and 50 μM Ca²⁺‐ionophore A23187. Quantitative Western blotting revealed little difference in tyrosine phosphorylated proteins among the caput, corpus, and cauda sperm without stimulation. Incubation with cAMP increased the amount of tyrosine phosphorylated proteins up to 10‐fold in the corpus and cauda sperm, but to a lower extent in the caput sperm. Ca²⁺‐ionophore attenuated the cAMP stimulation but had no effect on its own. Such responses in tyrosine phosphorylated proteins were in great contrast to the responses in the acrosome reaction, where A23187 was the strongest stimulant, resulting in induction of the reaction in 50 ± 5%, 11 ± 5%, and 8 ± 4% cauda, corpus and caput sperm, respectively (mean ± sem, n = 6). DOG and cAMP in combination induced acrosome reactions in about 10% of viable cells in the cauda and corpus but not caput sperm. Caput sperm responded to cAMP with increases in percentage motility without forward progression whereas cauda sperm displayed marked kinematic changes expected of hyperactivation. Comparisons of responses suggest that the major tyrosine phosphorylated proteins detected are unlikely to be involved immediately in the precipitation of the acrosome reaction, but more related to flagellar motion. Development of signal transduction pathways is part of the epididymal maturational process. Mol. Reprod. Dev. 54:194–202, 1999. © 1999 Wiley‐Liss, Inc.     

Tyrosine phosphorylation of cytochrome c as a signaling event in frozen thawed buffalo spermatozoa at the cross-roads of capacitation and apoptosis

Considering the importance of cytochrome c in both life and death, it was of significant interest to investigate the expression of cytochrome c, its tyrosine phosphorylation status and immunolocalization patterns in a frozen-thawed buffalo sperm cell in comparison to in vitro capacitated [heparin (10 μg/ml) induced, for 4 h] and stress [apoptotic (10 μM staurosporine), oxidative (25 μM H₂O₂) and osmotic (180 mM NaCl) for 4 h] induced conditions. Proteins were subjected to immunoblotting and probed by using monoclonal anti-phosphotyrosine antibodies. A significant (p < 0.05) increase in expression of tyrosine phosphorylated cytochrome c was observed in capacitated buffalo sperm in comparison to frozen-thawed samples. cAMP protein kinase-A dependent and extracellular signal-regulated kinase independent tyrosine phosphorylation of cytochrome c was found during in vitro capacitation of buffalo spermatozoa. Localized increase in cytochrome c and tyrosine phosphorylated proteins were observed in frozen thawed and capacitated sperm. The information generated in this study can be used to understand the molecular mechanism of regulation of an apoptotic protein (cytochrome c) by tyrosine phosphorylation (a capacitation marker) in a frozen thawed sperm cell which could be a good target to combat apoptosis.     

Binding and Function of Phosphotyrosines of the Ephrin A2 (EphA2) Receptor Using Synthetic Sterile α Motif (SAM) Domains

The sterile α motif (SAM) domain of the ephrin receptor tyrosine kinase, EphA2, undergoes tyrosine phosphorylation, but the effect of phosphorylation on the structure and interactions of the receptor is unknown. Studies to address these questions have been hindered by the difficulty of obtaining site-specifically phosphorylated proteins in adequate amounts. Here, we describe the use of chemically synthesized and specifically modified domain-length peptides to study the behavior of phosphorylated EphA2 SAM domains. We show that tyrosine phosphorylation of any of the three tyrosines, Tyr⁹²¹, Tyr⁹³⁰, and Tyr⁹⁶⁰, has a surprisingly small effect on the EphA2 SAM structure and stability. However, phosphorylation at Tyr⁹²¹ and Tyr⁹³⁰ enables differential binding to the Src homology 2 domain of the adaptor protein Grb7, which we propose will lead to distinct functional outcomes. Setting up different signaling platforms defined by selective interactions with adaptor proteins thus adds another level of regulation to EphA2 signaling.     

A role for phosphorylation of glycogen synthase kinase-3alpha in bovine sperm motility regulation

The long-term goal of our work is to understand biochemical mechanisms underlying sperm motility and fertility. In a recent study we showed that tyrosine phosphorylation of a 55-kDa protein varied in direct proportion to motility. Tyrosine phosphorylation of the protein was low in immotile compared to motile epididymal sperm. Inhibition or stimulation of motility by high calcium levels or cAMP, respectively, results in a corresponding decrease or increase in tyrosine phosphorylation of the 55-kDa protein. Here we report purification and identification of this motility-associated protein. Soluble extracts from bovine caudal epididymal sperm were subjected to DEAE-cellulose, Affi-Gel blue, and cellulose phosphate chromatography. Tyrosine phosphate immunoreactive fractions contained glycogen synthase kinase-3 (GSK-3) activity, suggesting a possible correspondence between these proteins. This suggestion was verified by Western blot analyses following one-dimensional and two-dimensional gel electrophoresis of the purified protein using monoclonal and affinity-purified polyclonal antibodies against the catalytic amino-terminus and carboxy-terminus regions of GSK-3. Further confirmation of the identity of these proteins came from Western blot analysis using antibodies specific to the tyrosine phosphorylated GSK-3. Using this antibody, we also showed that GSK-3 tyrosine phosphorylation was high in motile compared to immotile sperm. Immunocytochemistry revealed that GSK-3 is present in the flagellum and the anterior portion of the sperm head. These data suggest that GSK-3, regulated by phosphorylation, could be a key element underlying motility initiation in the epididymis and regulation of mature sperm function.     

Autophosphorylation of brain microtubule protein: evidence for endogenous protein kinase/phosphoprotein phosphatase cycling and multiple phosphorylation of a microtubule associated protein

Brain microtubule protein, prepared by two types of recycling methods, undergoes “flash” phosphorylation in the presence of [γ-³²p]ATP through sequential action of protein kinase and phosphoprotein phosphatase present in microtubule protein. SDS electrophoretic analysis indicates that MAP₁, tau protein, and tubulin are poorly phosphorylated, and MAP₂ is the major site of phosphorylation. To improve [³²P]phosphoprotein stability in the presence of the kinase/phosphatase cycle, 3′,5′-cyclicAMP, orthophosphate, or fluoride ion may be added. After separation from tubulin by phosphocellulose chromatography, the MAP fraction exhibits autophosphorylation. Finally, the maximal extent of autophosphorylation is observed with an ATP regenerating system using ADP, [³²P]acetyl-P, and bacterial acetate kinase; this results in the incorporation of 3–4 phosphoryl groups per MAP₂ subunit.     

Assessment of human sperm protein tyrosine phosphorylation by immunocytochemistry in a clinical andrology laboratory. Preliminary data

Abstract

We propose that evaluation of protein tyrosine phosphorylation (TP) status in ejaculated spermatozoa under capacitating conditions in an experiment that mimics “in vitro” the physiology of sperm from ejaculation through the female genital tract could potentially be used as a prognostic test for functional competence of sperm in fertilization. Our purpose was to elucidate whether there is a relation between conventional sperm parameters, occurrence of TP and pregnancy outcome obtained from intrauterine insemination (IUI). Semen samples were analyzed according to WHO criteria. TP levels were determined by immunocytochemistry under four different conditions: 1) ejaculated sperm, 2) postselection sperm, 3) postselection sperm incubated 5 h at 37° C and 5% CO₂, and 4) postselection sperm incubated overnight at 37° C and 5% CO₂. Data on sperm tyrosine phosphorylated proteins did not correlate with sperm concentration, progressive motility or normal sperm morphology. TP increased under capacitating conditions and showed a time dependent pattern except for five outlier cases. IUI was performed in 12 selected couples who had neither female nor male infertility factors. The three pregnancies had a time dependent pattern for TP. Of the unsuccessful cases, one had an outlier TP pattern. It appears that a TP time dependent pattern is necessary for fertilization.     

Iberiotoxin and clofilium regulate hyperactivation,acrosome reaction,and ion homeostasis synergistically during human sperm capacitation

Potassium channels play essential roles in the regulation of male fertility. However, potassium channels mediating K⁺ currents in human sperm (I_KSper) remain controversial. Besides SLO3, the SLO1 potassium channel is a potential candidate for human sperm KSper. This study intends to elucidate the function of SLO1 potassium channel during human sperm capacitation. Human sperm were treated with iberiotoxin (IbTX, a SLO1 specific inhibitor) and clofilium (SLO3 inhibitor) separately or simultaneously during in vitro capacitation. A computer-assisted sperm analyzer was used to assess sperm motility. The sperm acrosome reaction (AR) was analyzed using fluorescein isothiocyanate-conjugated Pisum sativum agglutinin staining. Sperm protein tyrosine phosphorylation was studied using western blotting. Intracellular Ca²⁺, K⁺, Cl⁻, and pH were analyzed using ion fluorescence probes. Independent inhibition with IbTX or clofilium decreased the sperm hyperactivation, AR, and protein tyrosine phosphorylation, and was accompanied by an increase in [K⁺]_i, [Cl⁻]_i, and pH_i, but a decrease in [Ca²⁺]_i. Simultaneously inhibition with IbTX and clofilium lower sperm hyperactivation and AR more than independent inhibition. The increase in [K⁺]_i, [Cl⁻]_i, and pH_i, and the decrease in [Ca²⁺]_i were more pronounced. This study suggested that the SLO1 potassium channel may have synergic roles with SLO3 during human sperm capacitation.     

Capacitation-associated protein tyrosine phosphorylation starts early in buffalo (Bubalus bubalis) spermatozoa as compared to cattle

A comparative study was conducted on protein tyrosine phosphorylation events of capacitating sperm of two ruminant species, cattle and buffalo. Ejaculated cattle and buffalo bull spermatozoa were suspended separately in sp-TALP medium at 50 × 10⁶ mL⁻¹ and incubated at 38.5 °C with 5% CO₂ in air in the absence or presence of heparin for a period of 6 h. The extent of sperm capacitation after various periods of incubations was assessed by lysophosphatidyl choline-induced acrosome reaction followed by a triple-staining technique and capacitation-associated tyrosine-phosphorylated proteins were detected by immunoblotting technique using a monoclonal antiphosphotyrosine antibody. In the same media, over a time-period, a significant increase in capacitation percentage was observed even in control group of buffalo spermatozoa as compared to a non-significant increase in that of cattle sperm. In both cattle and buffalo spermatozoa, at 6 h, four proteins of molecular weight 49, 45, 32, and 20 kDa (designated as p49, p45, p32, and p20) were tyrosine phosphorylated. However, in buffalo, two additional proteins of 38 and 30 kDa were also tyrosine phosphorylated. In a time-course study, p20 appeared as early as at 0 h in capacitated buffalo spermatozoa as compared to 4 h in cattle. Further, in heparin-treated buffalo spermatozoa, with a time-dependent increase in tyrosine phosphorylation of some proteins, there was time-dependent dephosphorylation of some other proteins that was never seen in heparin-treated cattle sperm. Thus, the present findings revealed that though buffalo sperm takes more time than cattle for capacitation but its associated protein tyrosine phosphorylation event starts very early as compared to cattle.     

Stimulation of protein phosphorylation during fertilization-induced maturation of Urechis caupo oocytes

Protein phosphorylation was studied during fertilization of Urechis caupo oocytes both in vivo, by measuring [³²P]phosphate incorporation into ³²P preloaded oocytes and in vitro, by measuring endogenous protein kinase and phosphatase activities in homogenates. During fertilization (and maturation) the rate of protein phosphorylation is dramatically increased. No change in the [³²P]phosphate uptake, or the nucleotide levels was observed at fertilization, so the increase cannot be attributed to changes in substrate availability. In vitro enzyme assays showed changes in protein kinase activity which approximately mirrored the changes in the in vivo phosphorylation pattern. As there were no changes in protein phosphatase activity, these results suggest the phosphorylation change results from an increase in protein kinase activity. The pattern of change, investigated by SDS-polyacrylamide gel electrophoresis, shows that proteins that were phosphorylated in the unfertilized egg become phosphorylated to a greater degree after fertilization. One protein (48 kd) undergoes an increase followed by a decrease of its phosphorylation level.     

Regulation of tyrosine kinase activity during capacitation in goat sperm

Protein tyrosine phosphorylation is a key event accompanying sperm capacitation. Although this signaling cascade generates an array of tyrosine-phosphorylated polypeptides, their molecular characterization is still limited. It is necessary to differentiate the localization of the tyrosine-phosphorylated proteins in spermatozoa to understand the link between the different phosphorylated proteins and the corresponding regulated sperm function. cAMP plays a pivotal role in the regulation of tyrosine phosphorylation. The intracellular cAMP levels were raised in goat spermatozoa by the addition of the phosphodiesterase inhibitor, IBMX in conjugation with caffeine. Tyrosine phosphorylation was significantly up-regulated following treatment with these two reagents. Treatment of caudal spermatozoa with IBMX and caffeine, time dependent up-regulated phosphorylation of the protein of molecular weights 50 and 200 kDa was observed. Increased phosphorylation was observed with a combination of IBMX and caffeine treatment. Tyrosine phosphorylation in caput spermatozoa was not affected significantly under these conditions. The expression level of tyrosine kinase in sperm was examined with specific inhibitors and with anti-phosphotyrosine antibody. The indirect immunofluorescence staining was carried out on ethanol permeabilized sperm using anti-phosphotyrosine antibody. Western blot analysis was done using two separate PKA antibodies: anti-PKA catalytic and anti-PKA RIα. Almost no difference was found in the intracellular presence of the PKA RIα and RIIα subunits in caput and caudal epididymal spermatozoa. However, the catalytic subunit seemed to be present in higher amount in caudal spermatozoa. The results show that caprine sperm displays an enhancement of phosphorylation in the tyrosine residues of specific proteins under in vitro capacitation conditions.     

Tyrosine phosphorylation of HSP-90 during mammalian sperm capacitation

The process of sperm capacitation is correlated with activation of a signal transduction pathway leading to protein tyrosine phosphorylation. Whereas phosphotyrosine expression is an essential prerequisite for fertilization, the proteins that are phosphorylated during capacitation have not yet been identified. In the present study, we observed that a major target of this signaling pathway is the molecular chaperone protein, heat shock protein (HSP)-86, a member of the HSP-90 family of HSPs. We used cross-immunoprecipitation experiments to confirm the tyrosine phosphorylation of HSP-86, a process that is not inhibited by the ansamycin antibiotic, geldanamycin. The general significance of these findings was confirmed by studies in which HSP-90 was also found to be tyrosine phosphorylated in human and rat spermatozoa when incubated under conditions that support capacitation. To our knowledge, these results represent the first report of a protein that undergoes tyrosine phosphorylation during mouse sperm capacitation and the first study implicating molecular chaperones in the processes by which mammalian spermatozoa gain the ability to fertilize the oocyte.     

Phosphorylation of Mycobacterium tuberculosis Ser/Thr phosphatase by PknA and PknB

Background

The integrated functions of 11 Ser/Thr protein kinases (STPKs) and one phosphatase manipulate the phosphorylation levels of critical proteins in Mycobacterium tuberculosis. In this study, we show that the lone Ser/Thr phosphatase (PstP) is regulated through phosphorylation by STPKs.

Principal Findings

PstP is phosphorylated by PknA and PknB and phosphorylation is influenced by the presence of Zn²⁺-ions and inorganic phosphate (Pi). PstP is differentially phosphorylated on the cytosolic domain with Thr¹³⁷, Thr¹⁴¹, Thr¹⁷⁴ and Thr²⁹⁰ being the target residues of PknB while Thr¹³⁷ and Thr¹⁷⁴ are phosphorylated by PknA. The Mn²⁺-ion binding residues Asp³⁸ and Asp²²⁹ are critical for the optimal activity of PstP and substitution of these residues affects its phosphorylation status. Native PstP and its phosphatase deficient mutant PstP_c ^D38G are phosphorylated by PknA and PknB in E. coli and addition of Zn²⁺/Pi in the culture conditions affect the phosphorylation level of PstP. Interestingly, the phosphorylated phosphatase is more active than its unphosphorylated equivalent.

Conclusions and Significance

This study establishes the novel mechanisms for regulation of mycobacterial Ser/Thr phosphatase. The results indicate that STPKs and PstP may regulate the signaling through mutually dependent mechanisms. Consequently, PstP phosphorylation may play a critical role in regulating its own activity. Since, the equilibrium between phosphorylated and non-phosphorylated states of mycobacterial proteins is still unexplained, understanding the regulation of PstP may help in deciphering the signal transduction pathways mediated by STPKs and the reversibility of the phenomena.     

Discordance between phosphorylation and recruitment of 53BP1 in response to DNA double-strand breaks

During the DNA damage response (DDR), chromatin modifications contribute to localization of 53BP1 to sites of DNA double-strand breaks (DSBs). 53BP1 is phosphorylated during the DDR, but it is unclear whether phosphorylation is directly coupled to chromatin binding. In this study, we used human diploid fibroblasts and HCT116 tumor cells to study 53BP1 phosphorylation at Serine-25 and Serine-1778 during endogenous and exogenous DSBs (DNA replication and whole-cell or sub-nuclear microbeam irradiation, respectively). In non-stressed conditions, endogenous DSBs in S-phase cells led to accumulation of 53BP1 and γH2AX into discrete nuclear foci. Only the frank collapse of DNA replication forks following hydroxyurea treatment initiated 53BP1^Ser25 and 53BP1^Ser1778 phosphorylation. In response to exogenous DSBs, 53BP1^Ser25 and 53BP1^Ser1778 phosphoforms localized to sites of initial DSBs in a cell cycle-independent manner. 53BP1 phosphoforms also localized to late residual foci and associated with PML-NBs during IR-induced senescence. Using isogenic cell lines and small-molecule inhibitors, we observed that DDR-induced 53BP1 phosphorylation was dependent on ATM and DNA-PKcs kinase activity but independent of MRE11 sensing or RNF168 chromatin remodeling. However, loss of RNF168 blocked recruitment of phosphorylated 53BP1 to sites of DNA damage. Our results uncouple 53BP1 phosphorylation from DSB localization and support parallel pathways for 53BP1 biology during the DDR. As relative 53BP1 expression may be a biomarker of DNA repair capacity in solid tumors, the tracking of 53BP1 phosphoforms in situ may give unique information regarding different cancer phenotypes or response to cancer treatment.     

Receptor-Recognized α2-Macroglobulin Binds to Cell Surface-Associated GRP78 and Activates mTORC1 and mTORC2 Signaling in Prostate Cancer Cells

Objective

Tetrameric α₂-macroglobulin (α₂M), a plasma panproteinase inhibitor, is activated upon interaction with a proteinase, and undergoes a major conformational change exposing a receptor recognition site in each of its subunits. Activated α₂M (α₂M*) binds to cancer cell surface GRP78 and triggers proliferative and antiapoptotic signaling. We have studied the role of α₂M* in the regulation of mTORC1 and TORC2 signaling in the growth of human prostate cancer cells.

Methods

Employing immunoprecipitation techniques and Western blotting as well as kinase assays, activation of the mTORC1 and mTORC2 complexes, as well as down stream targets were studied. RNAi was also employed to silence expression of Raptor, Rictor, or GRP78 in parallel studies.

Results

Stimulation of cells with α₂M* promotes phosphorylation of mTOR, TSC2, S6-Kinase, 4EBP, Akt^T308, and Akt^S473 in a concentration and time-dependent manner. Rheb, Raptor, and Rictor also increased. α₂M* treatment of cells elevated mTORC1 kinase activity as determined by kinase assays of mTOR or Raptor immunoprecipitates. mTORC1 activity was sensitive to {"type":"entrez-nucleotide","attrs":{"text":"LY294002","term_id":"1257998346","term_text":"LY294002"}}LY294002 and rapamycin or transfection of cells with GRP78 dsRNA. Down regulation of Raptor expression by RNAi significantly reduced α₂M*-induced S6-Kinase phosphorylation at T389 and kinase activity in Raptor immunoprecipitates. α₂M*-treated cells demonstrate about a twofold increase in mTORC2 kinase activity as determined by kinase assay of Akt^S473 phosphorylation and levels of p-Akt^S473 in mTOR and Rictor immunoprecipitates. mTORC2 activity was sensitive to {"type":"entrez-nucleotide","attrs":{"text":"LY294002","term_id":"1257998346","term_text":"LY294002"}}LY294002 and transfection of cells with GRP78 dsRNA, but insensitive to rapamycin. Down regulation of Rictor expression by RNAi significantly reduces α₂M*-induced phosphorylation of Akt^S473 phosphorylation in Rictor immunoprecipitates.

Conclusion

Binding of α₂M* to prostate cancer cell surface GRP78 upregulates mTORC1 and mTORC2 activation and promotes protein synthesis in the prostate cancer cells.     

The effect of oviductal fluid on protein tyrosine phosphorylation in cryopreserved boar spermatozoa differs with the freezing method

Sperm capacitation takes place in the oviduct and protein tyrosine phosphorylation of sperm proteins is a crucial step in capacitation and acquisition of fertilizing potential. Cryopreserved spermatozoa show altered expression of protein tyrosine phosphorylation in the oviduct. The present study compared two freezing methods (conventional-conventional freezing (CF) and simplified-simplified freezing (SF) methods) for their effect on the ability of boar spermatozoa to undergo protein tyrosine phosphorylation in response to oviductal fluid (ODF). Cryopreserved boar-spermatozoa were incubated with pre- and post-ovulatory ODF for 6 h at 38 °C under 5% CO₂. Aliquots of sperm samples were taken at hourly intervals and analyzed for kinematics and protein tyrosine phosphorylation. Global protein tyrosine phosphorylation in spermatozoa was measured using flow cytometry and different patterns of phosphorylation were assessed using confocal microscopy. Immediately after thawing, no significant difference was observed in post-thaw sperm motility, velocity and global tyrosine phosphorylation between the two methods of freezing although the freezing method significantly (P < 0.05) influenced the effect of oviductal fluid on these parameters during incubation. While spermatozoa frozen by the CF method showed a significantly higher (P < 0.001) proportion of phosphorylation in response to preovulatory ODF during incubation, spermatozoa frozen by the SF method did not elicit such significant response as there was no significant difference in the proportion of tyrosine phosphorylated spermatozoa between treatments at any given time during incubation. If the CF method was used, the proportion of spermatozoa displaying either tail or full sperm phosphorylation increased in response to both preovulatory (EODF) and postovulatory oviductal fluid. However, if the SF method was used, a significant increase in these patterns was noticed only in the EODF treated group. The present study demonstrates that preovulatory isthmic ODF induce tyrosine phosphorylation in a higher proportion of boar spermatozoa compared to the post-ovulatory fluid and that the method of freezing significantly influences the response of post-thaw spermatozoa to porcine ODF.