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Regulation of Sperm Capacitation and the Acrosome Reaction by PIP 2 and Actin Modulation.

Breitbart H, Finkelstein M - Asian J. Androl. (2015 Jul-Aug)

Bottom Line: Stimulation of phospholipase C, by Ca 2 + -ionophore or by activating the epidermal-growth-factor-receptor, inhibits tyrosine phosphorylation of gelsolin and enhances enzyme activity.In conclusion, these data indicate that the increase of PIP 2 and/or F-actin in the head during capacitation enhances gelsolin translocation to the head.As a result, the decrease of gelsolin in the tail allows the maintenance of high levels of F-actin in this structure, which is essential for the development of HA motility.

View Article: PubMed Central - PubMed

Affiliation: The Mina and Everard Faculty of Life Sciences, Bar-Ilan University, Ramat-Gan, Israel.

ABSTRACT
Actin polymerization and development of hyperactivated (HA) motility are two processes that take place during sperm capacitation. Actin polymerization occurs during capacitation and prior to the acrosome reaction, fast F-actin breakdown takes place. The increase in F-actin during capacitation depends upon inactivation of the actin severing protein, gelsolin, by its binding to phosphatydilinositol-4, 5-bisphosphate (PIP 2 ) and its phosphorylation on tyrosine-438 by Src. Activation of gelsolin following its release from PIP 2 is known to cause F-actin breakdown and inhibition of sperm motility, which can be restored by adding PIP 2 to the cells. Reduction of PIP 2 synthesis inhibits actin polymerization and motility, while increasing PIP 2 synthesis enhances these activities. Furthermore, sperm demonstrating low motility contained low levels of PIP 2 and F-actin. During capacitation there was an increase in PIP 2 and F-actin levels in the sperm head and a decrease in the tail. In spermatozoa with high motility, gelsolin was mainly localized to the sperm head before capacitation, whereas in low motility sperm, most of the gelsolin was localized to the tail before capacitation and translocated to the head during capacitation. We also showed that phosphorylation of gelsolin on tyrosine-438 depends upon its binding to PIP 2 . Stimulation of phospholipase C, by Ca 2 + -ionophore or by activating the epidermal-growth-factor-receptor, inhibits tyrosine phosphorylation of gelsolin and enhances enzyme activity. In conclusion, these data indicate that the increase of PIP 2 and/or F-actin in the head during capacitation enhances gelsolin translocation to the head. As a result, the decrease of gelsolin in the tail allows the maintenance of high levels of F-actin in this structure, which is essential for the development of HA motility.

No MeSH data available.


Related in: MedlinePlus

Inactivation of gelsolin by Src-dependent tyrosine phosphorylation: the tyrosine kinase Src is activated by the HCO3−/sAC/cAMP/PKA system leading to gelsolin phosphorylation on Tyr-483 which is stimulated by gelsolin binding to PIP2. Under these conditions p-gelsolin is inactive and actin polymerization occurs.
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Figure 3: Inactivation of gelsolin by Src-dependent tyrosine phosphorylation: the tyrosine kinase Src is activated by the HCO3−/sAC/cAMP/PKA system leading to gelsolin phosphorylation on Tyr-483 which is stimulated by gelsolin binding to PIP2. Under these conditions p-gelsolin is inactive and actin polymerization occurs.

Mentions: Since F-actin levels are increased during capacitation, it is likely that gelsolin is inactive during this period of time. Gelsolin can be inhibited by its Src-dependent phosphorylation on tyr-438 and/or it's binding to PIP2, two processes that occur during sperm capacitation. In human sperm, Src is involved in regulating capacitation, Ca fluxes, protein tyrosine phosphorylation and the AR.313233 Previous studies suggested that Src is not directly involved in protein tyrosine phosphorylation but rather inhibits protein phosphatase resulting in an increase in tyrosine phosphorylation of proteins.34 It was shown elsewhere that capacitation is regulated by two parallel pathways, activation of PKA activates Src leading to inactivation of Ser/Thr phosphatase.3235 (Figure 3). We have recently shown that activation of Src by PKA, inhibits the Ser/Thr phosphatase PP1 resulting in CaMKII activation leading to activation of Pyk2 which phosphorylates PI3K on tyrosine-845.3 Src was found in sperm tail and head and is localized to the membrane fraction,35 similar to gelsolin localization and consistent with our assumption about its inactivating function. These assumptions were verified when Src-dependent phosphorylation of gelsolin on tyr-438 during sperm capacitation was found.23 In addition, we found that activation of PKA/Src caused F-actin formation, which was inhibited by inhibiting Src activity,22 suggesting that activation of Src causes gelsolin inhibition and an increase in F-actin. Also, PBP10-induced F-actin depolymerization is inhibited by activating Src or by inhibition of tyrosine-phosphatase suggesting that although gelsolin is released from its binding to PIP2, it is still highly phosphorylated and inactive. The levels of tyr-p-gelsolin are enhanced by elevating the cellular levels of PIP2 and vice versa,23 suggesting that binding of gelsolin to PIP2 increase its phosphorylation/inhibition. These findings are further supported by showing a decrease in tyr-p-gelsolin by activation of PLC to hydrolyse PIP2 or by releasing gelsolin from PIP2 using PBP10. These observations also suggest that free tyr-p-gelsolin is more sensitive to tyr-phosphatase activity compared to the PIP2-bound p-gelsolin. Also, activation of sperm EGFR caused PLC-dependent dephosphorylation of p-gelsolin, after 1 h of incubation under capacitation conditions.24 These results confirm our hypothesis that gelsolin is inhibited during capacitation due to its binding to PIP2 and tyr-phosphorylation by Src.


Regulation of Sperm Capacitation and the Acrosome Reaction by PIP 2 and Actin Modulation.

Breitbart H, Finkelstein M - Asian J. Androl. (2015 Jul-Aug)

Inactivation of gelsolin by Src-dependent tyrosine phosphorylation: the tyrosine kinase Src is activated by the HCO3−/sAC/cAMP/PKA system leading to gelsolin phosphorylation on Tyr-483 which is stimulated by gelsolin binding to PIP2. Under these conditions p-gelsolin is inactive and actin polymerization occurs.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4492050&req=5

Figure 3: Inactivation of gelsolin by Src-dependent tyrosine phosphorylation: the tyrosine kinase Src is activated by the HCO3−/sAC/cAMP/PKA system leading to gelsolin phosphorylation on Tyr-483 which is stimulated by gelsolin binding to PIP2. Under these conditions p-gelsolin is inactive and actin polymerization occurs.
Mentions: Since F-actin levels are increased during capacitation, it is likely that gelsolin is inactive during this period of time. Gelsolin can be inhibited by its Src-dependent phosphorylation on tyr-438 and/or it's binding to PIP2, two processes that occur during sperm capacitation. In human sperm, Src is involved in regulating capacitation, Ca fluxes, protein tyrosine phosphorylation and the AR.313233 Previous studies suggested that Src is not directly involved in protein tyrosine phosphorylation but rather inhibits protein phosphatase resulting in an increase in tyrosine phosphorylation of proteins.34 It was shown elsewhere that capacitation is regulated by two parallel pathways, activation of PKA activates Src leading to inactivation of Ser/Thr phosphatase.3235 (Figure 3). We have recently shown that activation of Src by PKA, inhibits the Ser/Thr phosphatase PP1 resulting in CaMKII activation leading to activation of Pyk2 which phosphorylates PI3K on tyrosine-845.3 Src was found in sperm tail and head and is localized to the membrane fraction,35 similar to gelsolin localization and consistent with our assumption about its inactivating function. These assumptions were verified when Src-dependent phosphorylation of gelsolin on tyr-438 during sperm capacitation was found.23 In addition, we found that activation of PKA/Src caused F-actin formation, which was inhibited by inhibiting Src activity,22 suggesting that activation of Src causes gelsolin inhibition and an increase in F-actin. Also, PBP10-induced F-actin depolymerization is inhibited by activating Src or by inhibition of tyrosine-phosphatase suggesting that although gelsolin is released from its binding to PIP2, it is still highly phosphorylated and inactive. The levels of tyr-p-gelsolin are enhanced by elevating the cellular levels of PIP2 and vice versa,23 suggesting that binding of gelsolin to PIP2 increase its phosphorylation/inhibition. These findings are further supported by showing a decrease in tyr-p-gelsolin by activation of PLC to hydrolyse PIP2 or by releasing gelsolin from PIP2 using PBP10. These observations also suggest that free tyr-p-gelsolin is more sensitive to tyr-phosphatase activity compared to the PIP2-bound p-gelsolin. Also, activation of sperm EGFR caused PLC-dependent dephosphorylation of p-gelsolin, after 1 h of incubation under capacitation conditions.24 These results confirm our hypothesis that gelsolin is inhibited during capacitation due to its binding to PIP2 and tyr-phosphorylation by Src.

Bottom Line: Stimulation of phospholipase C, by Ca 2 + -ionophore or by activating the epidermal-growth-factor-receptor, inhibits tyrosine phosphorylation of gelsolin and enhances enzyme activity.In conclusion, these data indicate that the increase of PIP 2 and/or F-actin in the head during capacitation enhances gelsolin translocation to the head.As a result, the decrease of gelsolin in the tail allows the maintenance of high levels of F-actin in this structure, which is essential for the development of HA motility.

View Article: PubMed Central - PubMed

Affiliation: The Mina and Everard Faculty of Life Sciences, Bar-Ilan University, Ramat-Gan, Israel.

ABSTRACT
Actin polymerization and development of hyperactivated (HA) motility are two processes that take place during sperm capacitation. Actin polymerization occurs during capacitation and prior to the acrosome reaction, fast F-actin breakdown takes place. The increase in F-actin during capacitation depends upon inactivation of the actin severing protein, gelsolin, by its binding to phosphatydilinositol-4, 5-bisphosphate (PIP 2 ) and its phosphorylation on tyrosine-438 by Src. Activation of gelsolin following its release from PIP 2 is known to cause F-actin breakdown and inhibition of sperm motility, which can be restored by adding PIP 2 to the cells. Reduction of PIP 2 synthesis inhibits actin polymerization and motility, while increasing PIP 2 synthesis enhances these activities. Furthermore, sperm demonstrating low motility contained low levels of PIP 2 and F-actin. During capacitation there was an increase in PIP 2 and F-actin levels in the sperm head and a decrease in the tail. In spermatozoa with high motility, gelsolin was mainly localized to the sperm head before capacitation, whereas in low motility sperm, most of the gelsolin was localized to the tail before capacitation and translocated to the head during capacitation. We also showed that phosphorylation of gelsolin on tyrosine-438 depends upon its binding to PIP 2 . Stimulation of phospholipase C, by Ca 2 + -ionophore or by activating the epidermal-growth-factor-receptor, inhibits tyrosine phosphorylation of gelsolin and enhances enzyme activity. In conclusion, these data indicate that the increase of PIP 2 and/or F-actin in the head during capacitation enhances gelsolin translocation to the head. As a result, the decrease of gelsolin in the tail allows the maintenance of high levels of F-actin in this structure, which is essential for the development of HA motility.

No MeSH data available.


Related in: MedlinePlus