AKAP3-mediated type I PKA signaling is required for mouse sperm hyperactivation and fertility†

The protein kinase A (PKA) signaling pathway, which mediates protein phosphorylation, is important for sperm motility and male fertility. This process relies on A-kinase anchoring proteins that organize PKA and its signalosomes within specific subcellular compartments. Previously, it was found that the absence of A-kinase anchoring protein 3 (AKAP3) leads to multiple morphological abnormalities in mouse sperm. But how AKAP3 regulates sperm motility is yet to be elucidated. AKAP3 has two amphipathic domains, here named dual and RI, in its N-terminus. These domains are responsible for binding regulatory subunits I alpha (RIα) and II alpha (RIIα) of PKA and for RIα only, respectively. Here, we generated mutant mice lacking the dual and RI domains of AKAP3. It was found that the deletion of these domains caused male mouse infertile, accompanied by mild defects in the fibrous sheath of sperm tails. Additionally, the levels of serine/threonine phosphorylation of PKA substrates and tyrosine phosphorylation decreased in the mutant sperm, which exhibited a defect in hyperactivation under capacitation conditions. The protein levels of PKA subunits remained unchanged. But, interestingly, the regulatory subunit RIα was mis-localized from principal piece to midpiece of sperm tail, whereas this was not observed for RIIα. Further protein-protein interaction assays revealed a preference for AKAP3 to bind RIα over RIIα. Collectively, our findings suggest that AKAP3 is important for sperm hyperactivity by regulating type-I PKA signaling pathway mediated protein phosphorylation via its dual and RI domains.

Protein Kinase A Catalytic and Regulatory Subunits Interact Differently in Various Areas of Mouse Brain

Protein kinase A (PKA) are tetramers of two catalytic and two regulatory subunits, docked at precise intracellular sites to provide localized phosphorylating activity, triggered by cAMP binding to regulatory subunits and subsequent dissociation of catalytic subunits. It is unclear whether in the brain PKA dissociated subunits may also be found. PKA catalytic subunit was examined in various mouse brain areas using immunofluorescence, equilibrium binding and western blot, to reveal its location in comparison to regulatory subunits type RI and RII. In the cerebral cortex, catalytic subunits colocalized with clusters of RI, yet not all RI clusters were bound to catalytic subunits. In stria terminalis, catalytic subunits were in proximity to RI but separated from them. Catalytic subunits clusters were also present in the corpus striatum, where RII clusters were detected, whereas RI clusters were absent. Upon cAMP addition, the distribution of regulatory subunits did not change, while catalytic subunits were completely released from regulatory subunits. Unpredictably, catalytic subunits were not solubilized; instead, they re-targeted to other binding sites within the tissue, suggesting local macromolecular reorganization. Hence, the interactions between catalytic and regulatory subunits of protein kinase A consistently vary in different brain areas, supporting the idea of multiple interaction patterns.

[Effect of Electroacupuncture at "Zusanli"(ST 36) on the Expression of Ghrelin/cAMP/PKA in the Jejunum in Rats with Spleen Qi Deficiency Syndrome]

OBJECTIVE

To observe the effect of electroacupuncture (EA) at "Zusanli"(ST 36) on Ghrelin/cAMP/PKA expression in the jejunum in rats with spleen qi deficiency syndrome, so as to reveal its underlying mechanism in improving energy metabolism.

METHODS

Forty male SD rats were randomly divided into 4 groups:normal group, spleen qi deficiency syndrome (model) group, EA group and non-acupoint group (n=10 in each group).The model of spleen qi deficiency syndrome was established by improper diet and overstrain. EA (2 Hz/15 Hz, 0.5 mA) was applied to bilateral "Zusanli" (ST 36) in the EA group and non-acupoint in non-acupoint group for 20 min, once a day for 6 days. The pathologic changes of the jejunum tissue were detected by H&E staining. Ghrelin, ATP and cAMP levels in jejunum tissue were determined by ELISA. The expression levels of PKA protein in jejunum tissue were determined by Western blot.

RESULTS

H&E staining showed that the intestinal villi of the model group were swelling, shortening and thickening, with a damaged or broken top-part in the model group, and basically restored to normal after EA treatment. ELISA results showed that the contents of Ghrelin, ATP and cAMP in the jejunum tissue were significantly lower in the model group than in the normal group (P<0.05), while significantly higher in the EA group than in the model group (P<0.05). Western blot results showed that the expression of PKA protein in the jejunum tissue was significantly lower in the model group than in the normal group (P<0.05), and significantly higher in the EA group than in the model group and non-acupoint group (P<0.05).

CONCLUSIONS

EA at ST 36 can improve the morphological changes in the jejunum of spleen qi deficiency rats, which may be associated with its effects in increasing Ghrelin, ATP and cAMP contents, and up-regulating PKA expression, leading to an increase of energy metabolism and spleen qi at last.

Roles of phosphodiesterases in the regulation of the cardiac cyclic nucleotide cross-talk signaling network

The balanced signaling between the two cyclic nucleotides (cNs) cAMP and cGMP plays a critical role in regulating cardiac contractility. Their degradation is controlled by distinctly regulated phosphodiesterase isoenzymes (PDEs), which in turn are also regulated by these cNs. As a result, PDEs facilitate communication between the β-adrenergic and Nitric Oxide (NO)/cGMP/Protein Kinase G (PKG) signaling pathways, which regulate the synthesis of cAMP and cGMP respectively. The phenomena in which the cAMP and cGMP pathways influence the dynamics of each other are collectively referred to as cN cross-talk. However, the cross-talk response and the individual roles of each PDE isoenzyme in shaping this response remain to be fully characterized. We have developed a computational model of the cN cross-talk network that mechanistically integrates the β-adrenergic and NO/cGMP/PKG pathways via regulation of PDEs by both cNs. The individual model components and the integrated network model replicate experimentally observed activation-response relationships and temporal dynamics. The model predicts that, due to compensatory interactions between PDEs, NO stimulation in the presence of sub-maximal β-adrenergic stimulation results in an increase in cytosolic cAMP accumulation and corresponding increases in PKA-I and PKA-II activation; however, the potentiation is small in magnitude compared to that of NO activation of the NO/cGMP/PKG pathway. In a reciprocal manner, β-adrenergic stimulation in the presence of sub-maximal NO stimulation results in modest cGMP elevation and corresponding increase in PKG activation. In addition, we demonstrate that PDE2 hydrolyzes increasing amounts of cAMP with increasing levels of β-adrenergic stimulation, and hydrolyzes increasing amounts of cGMP with decreasing levels of NO stimulation. Finally, we show that PDE2 compensates for inhibition of PDE5 both in terms of cGMP and cAMP dynamics, leading to cGMP elevation and increased PKG activation, while maintaining whole-cell β-adrenergic responses similar to that prior to PDE5 inhibition. By defining and quantifying reactions comprising cN cross-talk, the model characterizes the cross-talk response and reveals the underlying mechanisms of PDEs in this non-linear, tightly-coupled reaction system.

[Effect of Bushen Tiaojing Recipe containing serum on FSH/cAMP-PKA pathway in in vitro cultured human ovarian granular cells]

OBJECTIVE

To explore the potential molecular mechanisms for Bushen Tiaojing Recipe (BTR) improving the endocrine function of ovarian granular cells by observing the effect of BTR containing serum on follicle stimulating hormone/cyclic adenosine monophosphate-protein kinase A (FSH/ cAMP-PKA) pathway in in vitro cultured human ovarian granular cells.

METHODS

The primary ovarian granular cells collected from in vitro fertilization-embryo transfer patients were cultured for 24 h. The human and rat serum containing different concentrations of BTR (low, medium, high dose), and their normal serums were co-incubated with ovarian granular cells for 48 h respectively, and then they were divided into the low, medium, high dose BTR groups and the control group. The levels of estradiol (E2), progesterone (P), and cyclic adenosine monophosphate (cAMP) in the culture medium were measured by radioimmunoassay. The protein expression of FSHR in ovarian granular cells was detected by Western Blot. The mRNA expression of follicle stimulating hormone receptor (FSHR) and P450 aromatase (P450arom) in ovarian granular cells were detected by Real-time PCR.

RESULTS

In human BTR containing serum groups: Compared with control group, the levels of E2 and cAMP in the culture medium were higher (both P < 0.05) in the medium and high dose BTR groups; the levels of P in the culture medium decreased in the medium dose BTR group (P < 0.01). The protein and mRNA expression of FSHR in ovarian granular cells increased (all P < 0.01), the mRNA expressions of P450arom in ovarian granular cells were higher (P < 0.05, P< 0.01) in the medium and high dose BTR groups. In rat BTR containing serum groups: Compared with the control group, the levels of E2 in the culture medium were higher (all P < 0.01), cAMP in the culture medium were higher (P < 0.05, P < 0.01) in the medium and high dose BTR group; the levels of P in the culture medium decreased in the medium dose BTR group (P < 0.01). The protein and mRNA expression of FSHR in ovarian granular cells were higher (all P < 0.01), the mRNA expression of P450arom in ovarian granular cells increased in the medium and high dose BTR groups (P < 0.05, P < 0.01).

CONCLUSION

BTR could possibly improve the endocrine function of ovarian granular cells by regulating main effector molecules FSHR, cAMP, P450arom, and E2 in FSH/cAMP-PKA pathway of ovarian granular cells.

[Influence of metanandamide on steroidogenesis in rat adrenocorticocytes in vitro]

It is known from literature about antioxidant, anti-inflammatory, membrane protective and adreniregulatory properties of N-acetylethanolamines, but data concerning their participation in regulation of steroidogenesis are insufficient. In order to study the influence of a synthetic analogue of endogenous canabinoid anandamide - metanandamide - on the intensity of steroidogenesis the influence of different concentrations of the drug on the contents of 11-hydroxicorticosteroides (11-HCS) in the culture medium after incubation of adrenal tissue in rats of both sexes was investigated. The quantitative determination of 11-HCS was conducted by fluorometric micromethod. It was shown that the incubation of tissue sections with metanandamide leads to a reduction of 11-HCS in males and an increase of their content in females. It was concluded that the inhibition of corticosteroid secretion and synthesis in males may be due to reduction of cAMP and inhibition of cAMP-dependent protein kinase A (PKA) under the effect of metanandamide. The opposite and dose-dependent effects of the preparation in females may be connected with the estrogen influence on the mechanisms of drug effect realization.

FSH modulates PKAI and GPR3 activities in mouse oocyte of COC in a gap junctional communication (GJC)-dependent manner to initiate meiotic resumption

Many studies have shown that cyclic adenosine-5′-monophosphate (cAMP)-dependent protein kinase A (PKA) and G-protein-coupled receptor 3 (GPR3) are crucial for controlling meiotic arrest in oocytes. However, it is unclear how gonadotropins modulate these factors to regulate oocyte maturation, especially by gap junctional communication (GJC). Using an in vitro meiosis-arrested mouse cumulus-oocyte complex (COC) culture model, we showed that there is a close relationship between follicle-stimulating hormone (FSH) and the PKA type I (PKAI) and GPR3. The effect of FSH on oocyte maturation was biphasic, initially inhibitory and then stimulatory. During FSH-induced maturation, rapid cAMP surges were observed in both cumulus cells and oocyte. Most GJC between cumulus cells and oocyte ceased immediately after FSH stimulation and recommenced after the cAMP surge. FSH-induced maturation was blocked by PKAI activator 8-AHA-cAMP. Levels of PKAI regulatory subunits and GPR3 decreased and increased, respectively, after FSH stimulation. In the presence of the GJC inhibitor carbenoxolone (CBX), FSH failed to induce the meiotic resumption and the changes in PKAI, GPR3 and cAMP surge in oocyte were no longer detected. Furthermore, GPR3 was upregulated by high cAMP levels, but not by PKAI activation. When applied after FSH stimulation, the specific phosphodiesterase 3A (PDE3A) inhibitor cilostamide immediately blocked meiotic induction, regardless of when it was administered. PKAI activation inhibited mitogen-activated protein kinase (MAPK) phosphorylation in the oocytes of COCs, which participated in the initiation of FSH-induced meiotic maturation in vitro. Just before FSH-induced meiotic maturation, cAMP, PKAI, and GPR3 returned to basal levels, and PDE3A activity and MAPK phosphorylation increased markedly. These experiments show that FSH induces a transient increase in cAMP levels and regulates GJC to control PKAI and GPR3 activities, thereby creating an inhibitory phase. After PDE3A and MAPK activities increase, meiosis resumes.

Participation of myosin Va and Pka type I in the regeneration of neuromuscular junctions

Background

The unconventional motor protein, myosin Va, is crucial for the development of the mouse neuromuscular junction (NMJ) in the early postnatal phase. Furthermore, the cooperative action of protein kinase A (PKA) and myosin Va is essential to maintain the adult NMJ. We here assessed the involvement of myosin Va and PKA in NMJ recovery during muscle regeneration.

Methodology/Principal Findings

To address a putative role of myosin Va and PKA in the process of muscle regeneration, we used two experimental models the dystrophic mdx mouse and Notexin-induced muscle degeneration/regeneration. We found that in both systems myosin Va and PKA type I accumulate beneath the NMJs in a fiber maturation-dependent manner. Morphologically intact NMJs were found to express stable nicotinic acetylcholine receptors and to accumulate myosin Va and PKA type I in the subsynaptic region. Subsynaptic cAMP signaling was strongly altered in dystrophic muscle, particularly in fibers with severely subverted NMJ morphology.

Conclusions/Significance

Our data show a correlation between the subsynaptic accumulation of myosin Va and PKA type I on the one hand and NMJ regeneration status and morphology, AChR stability and specificity of subsynaptic cAMP handling on the other hand. This suggests an important role of myosin Va and PKA type I for the maturation of NMJs in regenerating muscle.

Communication between tandem cAMP binding domains in the regulatory subunit of protein kinase A-Ialpha as revealed by domain-silencing mutations

Protein kinase A (PKA) is the main receptor for the universal cAMP second messenger. PKA is a tetramer with two catalytic (C) and two regulatory (R) subunits, each including two tandem cAMP binding domains, i.e. CBD-A and -B. Structural investigations of RIalpha have revealed that although CBD-A plays a pivotal role in the cAMP-dependent inhibition of C, the main function of CBD-B is to regulate the access of cAMP to site A. To further understand the mechanism underlying the cross-talk between CBD-A and -B, we report here the NMR investigation of a construct of R, RIalpha-(119-379), which unlike previous fragments characterized by NMR, spans in full both CBDs. Our NMR studies were also extended to two mutants, R209K and the corresponding R333K, which severely reduce the affinity of cAMP for CBD-A and -B, respectively. The comparative NMR analysis of wild-type RIalpha-(119-379) and of the two domain silencing mutations has led to the definition at an unprecedented level of detail of both intra- and interdomain allosteric networks, revealing several striking differences between the two CBDs. First, the two domains, although homologous in sequence and structure, exhibit remarkably different responses to the R/K mutations especially at the beta2-3 allosteric "hot spot." Second, although the two CBDs are reciprocally coupled at the level of local unfolding of the hinge, the A-to-B and B-to-A pathways are dramatically asymmetrical at the level of global unfolding. Such an asymmetric interdomain cross-talk ensures efficiency and robustness in both the activation and de-activation of PKA.

The differential regulation of steroidogenic acute regulatory protein-mediated steroidogenesis by type I and type II PKA in MA-10 cells

Following tropic hormone challenge, steroidogenic tissues utilize PKA to phosphorylate unique subsets of proteins necessary to facilitate steroidogenesis. This includes the PKA-dependent expression and activation of the steroidogenic acute regulatory protein (STAR), which mediates the rate-limiting step of steroidogenesis by inducing the transfer of cholesterol from the outer to the inner mitochondrial membrane. Since both type I and type II PKA are present in steroidogenic tissues, we have utilized cAMP analog pairs that preferentially activate each PKA subtype in order to examine their impact on STAR synthesis and activity. In MA-10 mouse Leydig tumor cells Star gene expression is more dependent upon type I PKA, while the post-transcriptional regulation of STAR appears subject to type II PKA. These experiments delineate the discrete effects that type I and type II PKA exert on STAR-mediated steroidogenesis, and suggest complimentary roles for each subtype in coordinating steroidogenesis.

Inhibition of T cell activation by cyclic adenosine 5'-monophosphate requires lipid raft targeting of protein kinase A type I by the A-kinase anchoring protein ezrin

cAMP negatively regulates T cell immune responses by activation of type I protein kinase A (PKA), which in turn phosphorylates and activates C-terminal Src kinase (Csk) in T cell lipid rafts. Using yeast two-hybrid screening, far-Western blot, immunoprecipitation and immunofluorescense analyses, and small interfering RNA-mediated knockdown, we identified Ezrin as the A-kinase anchoring protein that targets PKA type I to lipid rafts. Furthermore, Ezrin brings PKA in proximity to its downstream substrate Csk in lipid rafts by forming a multiprotein complex consisting of PKA/Ezrin/Ezrin-binding protein 50, Csk, and Csk-binding protein/phosphoprotein associated with glycosphingolipid-enriched microdomains. The complex is initially present in immunological synapses when T cells contact APCs and subsequently exits to the distal pole. Introduction of an anchoring disruptor peptide (Ht31) into T cells competes with Ezrin binding to PKA and thereby releases the cAMP/PKA type I-mediated inhibition of T cell proliferation. Finally, small interfering RNA-mediated knockdown of Ezrin abrogates cAMP regulation of IL-2. We propose that Ezrin is essential in the assembly of the cAMP-mediated regulatory pathway that modulates T cell immune responses.

Requirement of protein kinase type I for cAMP-mediated up-regulation of lipid-linked oligosaccharide for asparagine-linked protein glycosylation

Glycan chains of asparagine-linked (N-linked) glycoproteins play a significant role in protein structure and function, as well as in angiogenesis an essential process for breast or other solid tumor growth. Non-availability of these chains causes incorrect folding of glycoproteins and leads to programmed cell death (i.e., apoptosis) through unfolded protein response (UPR) signaling. Cells actively processing cAMP signals modulate the glycan chain biosynthesis by PKA. Glycosylation of cellular proteins in a PKA type I-deficient CHO mutant 10248 was much reduced when compared with the wild type CHO 10001. The rate of LLO biosynthesis is similar in both cell types but quantitatively it is low in the mutant. Pulse-chase experiments indicated that the t(1/2) for LLO-turnover in CHO 10248 was twice as high as that of the wild type. This correlated with the reduced DPMS activity. The Km for GDP-mannose for the DPMS activity was 3-4 folds higher in the mutant than that of the wild type with or without exogenously added Dol-P. The kcat of DPMS was also reduced in the mutant. In vitro phosphorylation of microsomes from the CHO 10248 by PKA, on the other hand, restored the DPMS activity to the normal level. The LLO biosynthesis also improved significantly in MR1, a revertant of the CHO 10248. The turnover of LLO in MR1 and the glycoprotein profile were also at par with the wild type. Therefore, we conclude that PKA type I plays an important role in modulating the protein N-glycosylation in cAMP responsive cells.