A-kinase anchoring proteins: scaffolding proteins in the heart

The pleiotropic cyclic nucleotide cAMP is the primary second messenger responsible for autonomic regulation of cardiac inotropy, chronotropy, and lusitropy. Under conditions of prolonged catecholaminergic stimulation, cAMP also contributes to the induction of both cardiac myocyte hypertrophy and apoptosis. The formation of localized, multiprotein complexes that contain different combinations of cAMP effectors and regulatory enzymes provides the architectural infrastructure for the specialization of the cAMP signaling network. Scaffolds that bind protein kinase A are called "A-kinase anchoring proteins" (AKAPs). In this review, we discuss recent advances in our understanding of how PKA is compartmentalized within the cardiac myocyte by AKAPs and how AKAP complexes modulate cardiac function in both health and disease.     

A-Kinase Anchoring Protein Targeting of Protein Kinase A and Regulation of HERG Channels

Adrenergic stimulation of the heart initiates a signaling cascade in cardiac myocytes that increases the concentration of cAMP. Although cAMP elevation may occur over a large area of a target-organ cell, its effects are often more restricted due to local concentration of its main effector, protein kinase A (PKA), through A-kinase anchoring proteins (AKAPs). The HERG potassium channel, which produces the cardiac rapidly activating delayed rectifying K(+) current (I (Kr)), is a target for cAMP/PKA regulation. PKA regulation of the current may play a role in the pathogenesis of hereditary and acquired abnormalities of the channel leading to cardiac arrhythmia. We examined the possible role for AKAP-mediated regulation of HERG channels. Here, we report that the PKA-RII-specific AKAP inhibitory peptide AKAP-IS perturbs the distribution of PKA-RII and diminishes the PKA-dependent phosphorylation of HERG protein. The functional consequence of AKAP-IS is a reversal of cAMP-dependent regulation of HERG channel activity. In further support of AKAP-mediated targeting of kinase to HERG, PKA activity was coprecipitated from HERG expressed in HEK cells. Velocity gradient centrifugation of solubilized porcine cardiac membrane proteins showed that several PKA-RI and PKA-RII binding proteins cosediment with ERG channels. A physical association of HERG with several specific AKAPs with known cardiac expression, however, was not demonstrable in heterologous cotransfection studies. These results suggest that one or more AKAP(s) targets PKA to HERG channels and may contribute to the acute regulation of I (Kr) by cAMP.     

A型激酶锚定蛋白及其复合物结构与功能

A型激酶锚定蛋白(A-kinase anchoring proteins,AKAPs)是一类结构不同而功能相关的蛋白家族,其主要功能是将cAMP依赖性蛋白激酶A（PKA）锚定于特定的亚细胞结构.PKA是第二信使cAMP的主要效应器,而AKAPs在靶向定位和调节PKA介导的磷酸化事件方面扮演重要角色. AKAPs更为重要的功能是与多种信号分子形成信号复合物,从时间和空间上整合cAMP-PKA和其他信号途径.本文将对AKAPs及其信号复合物的结构特点和参与细胞信号转导的功能机制及其研究现状进行概述.     

Neuronal AKAP150 coordinates PKA and Epac-mediated PKB/Akt phosphorylation

In diverse neuronal processes ranging from neuronal survival to synaptic plasticity cyclic adenosine monophosphate (cAMP)-dependent signaling is tightly connected with the protein kinase B (PKB)/Akt pathway but the precise nature of this connection remains unknown. In the current study we investigated the effect of two mainstream pathways initiated by cAMP, cAMP-dependent protein kinase (PKA) and exchange proteins directly activated by cAMP (Epac1 and Epac2) on PKB/Akt phosphorylation in primary cortical neurons and HT-4 cells. We demonstrate that PKA activation leads to a reduction of PKB/Akt phosphorylation, whereas activation of Epac has the opposite effect. This effect of Epac on PKB/Akt phosphorylation was mediated by Rap activation. The increase in PKB/Akt phosphorylation after Epac activation could be blocked by pretreatment with Epac2 siRNA and to a somewhat smaller extent by Epac1 siRNA. PKA, PKB/Akt and Epac were all shown to establish complexes with neuronal A-kinase anchoring protein150 (AKAP150). Interestingly, activation of Epac increased phosphorylation of PKB/Akt complexed to AKAP150. From experiments using PKA-binding deficient AKAP150 and peptides disrupting PKA anchoring to AKAPs, we conclude that AKAP150 acts as a key regulator in the two cAMP pathways to control PKB/Akt phosphorylation.     

AKAP proteins anchor cAMP-dependent protein kinase to KvLQT1/IsK channel complex

In cardiac myocytes, the slow component of the delayed rectifier K(+) current (I(Ks)) is regulated by cAMP. Elevated cAMP increases I(Ks) amplitude, slows its deactivation kinetics, and shifts its activation curve. At the molecular level, I(Ks) channels are composed of KvLQT1/IsK complexes. In a variety of mammalian heterologous expression systems maintained at physiological temperature, we explored cAMP regulation of recombinant KvLQT1/IsK complexes. In these systems, KvLQT1/IsK complexes were totally insensitive to cAMP regulation. cAMP regulation was not restored by coexpression with the dominant negative isoform of KvLQT1 or with the cystic fibrosis transmembrane regulator. In contrast, coexpression of the neuronal A kinase anchoring protein (AKAP)79, a fragment of a cardiac AKAP (mAKAP), or cardiac AKAP15/18 restored cAMP regulation of KvLQT1/IsK complexes inasmuch as cAMP stimulation increased the I(Ks) amplitude, increased its deactivation time constant, and negatively shifted its activation curve. However, in cells expressing an AKAP, the effects of cAMP stimulation on the I(Ks) amplitude remained modest compared with those previously reported in cardiac myocytes. The effects of cAMP stimulation were fully prevented by including the Ht31 peptide (a global disruptor of protein kinase A anchoring) in the intracellular medium. We concluded that cAMP regulation of I(Ks) requires protein kinase A anchoring by AKAPs, which therefore participate with the channel protein complex underlying I(Ks).     

Phosphorylation of the A-kinase-anchoring protein Yotiao contributes to protein kinase A regulation of a heart potassium channel

Regulation of the heart by the sympathetic nervous system, fundamental to the physiological response to stress and exercise, requires coordinated phosphorylation of multiple downstream molecular targets, including the I(Ks) (slowly activating potassium current) channel. Sympathetic nervous system stimulation increases intracellular cAMP for which targeted regulation is directed in large part by distinct scaffold or anchoring proteins. Yotiao is an A-kinase-anchoring protein (AKAP) that recruits the cyclic AMP-dependent protein kinase (protein kinase A (PKA)) and protein phosphatase 1 to the carboxyl terminus of the I(Ks) channel to form a molecular complex and control its phosphorylation state, crucial to the cardiac cellular response to sympathetic nervous system stimulation. Here we report that Yotiao itself is a substrate for PKA phosphorylation, and we identify a Yotiao amino-terminal (N-T) residue (Ser-43) that is PKA-phosphorylated in response to beta-adrenergic receptor stimulation. The replacement of Ser-43 by Ala ablates the PKA phosphorylation of N-T Yotiao and markedly diminishes the functional response of the wild type and pseudo-phosphorylated I(Ks) channel to cAMP but neither prevents the PKA phosphorylation of KCNQ1 nor its binding to Yotiao. These results suggest, for the first time, a critical role for the PKA phosphorylation of an AKAP in the functional regulation of an ion channel protein and postphosphorylation allosteric modulation of the I(Ks) channel by Yotiao.     

Essential role of A-kinase anchor protein 121 for cAMP signaling to mitochondria

A-Kinase anchor proteins (AKAPs) immobilize and concentrate protein kinase A (PKA) isoforms at specific subcellular compartments. Intracellular targeting of PKA holoenzyme elicits rapid and efficient phosphorylation of target proteins, thereby increasing sensitivity of downstream effectors to cAMP action. AKAP121 targets PKA to the cytoplasmic surface of mitochondria. Here we show that conditional expression of AKAP121 in PC12 cells selectively enhances cAMP.PKA signaling to mitochondria. AKAP121 induction stimulates PKA-dependent phosphorylation of the proapoptotic protein BAD at Ser(155), inhibits release of cytochrome c from mitochondria, and protects cells from apoptosis. An AKAP121 derivative mutant that localizes on mitochondria but does not bind PKA down-regulates PKA signaling to the mitochondria and promotes apoptosis. These findings indicate that PKA anchored by AKAP121 transduces cAMP signals to the mitochondria, and it may play an important role in mitochondrial physiology.     

D‐AKAP2:PKA RII:PDZK1 ternary complex structure: Insights from the nucleation of a polyvalent scaffold

A‐kinase anchoring proteins (AKAPs) regulate cAMP‐dependent protein kinase (PKA) signaling in space and time. Dual‐specific AKAP2 (D‐AKAP2/AKAP10) binds with high affinity to both RI and RII regulatory subunits of PKA and is anchored to transporters through PDZ domain proteins. Here, we describe a structure of D‐AKAP2 in complex with two interacting partners and the exact mechanism by which a segment that on its own is disordered presents an α‐helix to PKA and a β‐strand to PDZK1. These two motifs nucleate a polyvalent scaffold and show how PKA signaling is linked to the regulation of transporters. Formation of the D‐AKAP2: PKA binary complex is an important first step for high affinity interaction with PDZK1, and the structure reveals important clues toward understanding this phenomenon. In contrast to many other AKAPs, D‐AKAP2 does not interact directly with the membrane protein. Instead, the interaction is facilitated by the C‐terminus of D‐AKAP2, which contains two binding motifs—the D‐AKAP2_AKB and the PDZ motif—that are joined by a short linker and only become ordered upon binding to their respective partner signaling proteins. The D‐AKAP2_AKB binds to the D/D domain of the R‐subunit and the C‐terminal PDZ motif binds to a PDZ domain (from PDZK1) that serves as a bridging protein to the transporter. This structure also provides insights into the fundamental question of why D‐AKAP2 would exhibit a differential mode of binding to the two PKA isoforms.     

Spatial organisation of AKAP18 and PDE4 isoforms in renal collecting duct principal cells

A plethora of stimuli including hormones and neurotransmitters mediate a rise of the cellular level of cAMP and thereby activation of protein kinase A (PKA). PKA phosphorylates and thereby modulates the activity of a wide range of cellular targets. It is now appreciated that different stimuli induce the activation of PKA at specific sites where the kinase phosphorylates particular substrates in close proximity. The tethering of PKA to cellular compartments is facilitated by A kinase-anchoring proteins (AKAPs). The incorporation of phosphodiesterases (PDEs) into AKAP-based signalling complexes provides gradients of cAMP that regulate PKA activity locally. An example for a process depending on compartmentalised cAMP/PKA signalling is the arginine-vasopressin (AVP)-mediated water reabsorption in renal collecting duct principal cells. Upon activation through AVP, PKA phosphorylates the water channel aquaporin-2 (AQP-2) located on intracellular vesicles. The phosphorylation triggers the redistribution of AQP2 to the plasma membrane. AKAP-anchored PKA has been shown to be involved in AQP2 shuttling. Here, AKAP18 isoforms and members of the PDE4 family of PDEs are shown to be differentially localised in renal principal cells.     

Phosphodiesterase 4D and protein kinase a type II constitute a signaling unit in the centrosomal area

The mediation of cAMP effects by specific pools of protein kinase A (PKA) targeted to distinct subcellular domains raises the question of how inactivation of the cAMP signal is achieved locally and whether similar targeting of phosphodiesterases (PDEs) to sites of cAMP/PKA action could be observed. Here, we demonstrate that Sertoli cells of the testis contain an insoluble PDE4D3 isoform, which is shown by immunofluorescence to target to centrosomes. Staining of PDE4D and PKA shows co-localization of PDE4D with PKA-RIIalpha and RIIbeta in the centrosomal region. Co-precipitation of RII subunits and PDE4D3 from cytoskeletal extracts indicates a physical association of the two proteins. Distribution of PDE4D overlaps with that of the centrosomal PKA-anchoring protein, AKAP450, and AKAP450, PDE4D3, and PKA-RIIalpha co-immunoprecipitate. Finally, both PDE4D3 and PKA co-precipitate with a soluble fragment of AKAP450 encompassing amino acids 1710 to 2872 when co-expressed in 293T cells. Thus, a centrosomal complex that includes PDE4D and PKA constitutes a novel signaling unit that may provide accurate spatio-temporal modulation of cAMP signals.     

Cardiac function modulation depends on the A‐kinase anchoring protein complex

The A‐kinase anchoring proteins (AKAPs) are a group of structurally diverse proteins identified in various species and tissues. These proteins are able to anchor protein kinase and other signalling proteins to regulate cardiac function. Acting as a scaffold protein, AKAPs ensure specificity in signal transduction by enzymes close to their appropriate effectors and substrates. Over the decades, more than 70 different AKAPs have been discovered. Accumulative evidence indicates that AKAPs play crucial roles in the functional regulation of cardiac diseases, including cardiac hypertrophy, myofibre contractility dysfunction and arrhythmias. By anchoring different partner proteins (PKA, PKC, PKD and LTCCs), AKAPs take part in different regulatory pathways to function as regulators in the heart, and a damaged structure can influence the activities of these complexes. In this review, we highlight recent advances in AKAP‐associated protein complexes, focusing on local signalling events that are perturbed in cardiac diseases and their roles in interacting with ion channels and their regulatory molecules. These new findings suggest that AKAPs might have potential therapeutic value in patients with cardiac diseases, particularly malignant rhythm.     

Interaction of heterotrimeric G13 protein with an A-kinase-anchoring protein 110 (AKAP110) mediates cAMP-independent PKA activation.

Heterotrimeric G proteins and protein kinase A (PKA) are two important transmitters that transfer signals from a wide variety of cell surface receptors to generate physiological responses. The established mechanism of PKA activation involves the activation of the Gs-cAMP pathway. Binding of cAMP to the regulatory subunit of PKA (rPKA) leads to a release and subsequent activation of a catalytic subunit of PKA (cPKA). Here, we report a novel mechanism of PKA stimulation that does not require cAMP. Using yeast two-hybrid screening, we found that the alpha subunit of G13 protein interacted with a member of the PKA-anchoring protein family, AKAP110. Using in vitro binding and coimmunoprecipitation assays, we have shown that only activated G alpha 13 binds to AKAP110, suggesting a potential role for AKAP110 as a G alpha subunit effector protein. Importantly, G alpha 13, AKAP110, rPKA, and cPKA can form a complex, as shown by coimmunoprecipitation. By characterizing the functional significance of the G alpha 13-AKAP110 interaction, we have found that G alpha 13 induced release of the cPKA from the AKAP110-rPKA complex, resulting in a cAMP-independent PKA activation. Finally, AKAP110 significantly potentiated G alpha 13-induced activation of PKA. Thus, AKAP110 provides a link between heterotrimeric G proteins and cAMP-independent activation of PKA.     

Mechanism of neuroprotective mitochondrial remodeling by PKA/AKAP1

Mitochondrial shape is determined by fission and fusion reactions catalyzed by large GTPases of the dynamin family, mutation of which can cause neurological dysfunction. While fission-inducing protein phosphatases have been identified, the identity of opposing kinase signaling complexes has remained elusive. We report here that in both neurons and non-neuronal cells, cAMP elevation and expression of an outer-mitochondrial membrane (OMM) targeted form of the protein kinase A (PKA) catalytic subunit reshapes mitochondria into an interconnected network. Conversely, OMM-targeting of the PKA inhibitor PKI promotes mitochondrial fragmentation upstream of neuronal death. RNAi and overexpression approaches identify mitochondria-localized A kinase anchoring protein 1 (AKAP1) as a neuroprotective and mitochondria-stabilizing factor in vitro and in vivo. According to epistasis studies with phosphorylation site-mutant dynamin-related protein 1 (Drp1), inhibition of the mitochondrial fission enzyme through a conserved PKA site is the principal mechanism by which cAMP and PKA/AKAP1 promote both mitochondrial elongation and neuronal survival. Phenocopied by a mutation that slows GTP hydrolysis, Drp1 phosphorylation inhibits the disassembly step of its catalytic cycle, accumulating large, slowly recycling Drp1 oligomers at the OMM. Unopposed fusion then promotes formation of a mitochondrial reticulum, which protects neurons from diverse insults.     

Selectivity and regulation of A-kinase anchoring proteins in the heart. The role of autophosphorylation of the type II regulatory subunit of cAMP-dependent protein kinase

Downstream regulation of the cAMP-dependent protein kinase (PKA) pathway is mediated by anchoring proteins (AKAPs) that sequester PKA to specific subcellular locations through binding to PKA regulatory subunits (RI or RII). The RII-binding domain of all AKAPs forms an amphipathic alpha-helix with similar secondary structure. However, the importance of sequence differences in the RII-binding domains of different AKAPs is unknown, and mechanisms that regulate AKAP-PKA affinity are not clearly defined. Using surface plasmon resonance (SPR) spectroscopy, we measured real-time kinetics of RII interaction with various AKAPs. Base-line equilibrium binding constants (K(d)) for RII binding to Ht31, mAKAP, and AKAP15/18 were 10 nm, 119 nm, and 6.6 microm, respectively. PKA stimulation of intact Chinese hamster ovary cells increased RIIalpha binding to AKAP100/mAKAP and AKAP15/18 by approximately 7- and 82-fold, respectively. These results suggest that differences in primary sequence of the RII-binding domain may be responsible for the selective affinity of RII for different AKAPs. Furthermore, RII autophosphorylation may provide additional localized regulation of kinase anchoring. In cardiac myocytes, disruption of RII-AKAP interaction decreased PKA phosphorylation of the PKA substrate, myosin-binding protein C. Thus, these mechanisms may be involved in adding additional specificity in intracellular signaling in diverse cell types and under conditions of cAMP/PKA activation.     

The A-kinase-anchoring protein AKAP95 is a multivalent protein with a key role in chromatin condensation at mitosis

Protein kinase A (PKA) and the nuclear A-kinase-anchoring protein AKAP95 have previously been shown to localize in separate compartments in interphase but associate at mitosis. We demonstrate here a role for the mitotic AKAP95-PKA complex. In HeLa cells, AKAP95 is associated with the nuclear matrix in interphase and redistributes mostly into a chromatin fraction at mitosis. In a cytosolic extract derived from mitotic cells, AKAP95 recruits the RIIalpha regulatory subunit of PKA onto chromatin. Intranuclear immunoblocking of AKAP95 inhibits chromosome condensation at mitosis and in mitotic extract in a PKA-independent manner. Immunodepletion of AKAP95 from the extract or immunoblocking of AKAP95 at metaphase induces premature chromatin decondensation. Condensation is restored in vitro by a recombinant AKAP95 fragment comprising the 306-carboxy-terminal amino acids of the protein. Maintenance of condensed chromatin requires PKA binding to chromatin-associated AKAP95 and cAMP signaling through PKA. Chromatin-associated AKAP95 interacts with Eg7, the human homologue of Xenopus pEg7, a component of the 13S condensin complex. Moreover, immunoblocking nuclear AKAP95 inhibits the recruitment of Eg7 to chromatin in vitro. We propose that AKAP95 is a multivalent molecule that in addition to anchoring a cAMP/PKA-signaling complex onto chromosomes, plays a role in regulating chromosome structure at mitosis.     

cAMP/PKA signalling reinforces the LATS–YAP pathway to fully suppress YAP in response to actin cytoskeletal changes

Actin cytoskeletal damage induces inactivation of the oncoprotein YAP (Yes‐associated protein). It is known that the serine/threonine kinase LATS (large tumour suppressor) inactivates YAP by phosphorylating its Ser127 and Ser381 residues. However, the events downstream of actin cytoskeletal changes that are involved in the regulation of the LATS–YAP pathway and the mechanism by which LATS differentially phosphorylates YAP on Ser127 and Ser381 in vivo have remained elusive. Here, we show that cyclic AMP (cAMP)‐dependent protein kinase (PKA) phosphorylates LATS and thereby enhances its activity sufficiently to phosphorylate YAP on Ser381. We also found that PKA activity is involved in all contexts previously reported to trigger the LATS–YAP pathway, including actin cytoskeletal damage, G‐protein‐coupled receptor activation, and engagement of the Hippo pathway. Inhibition of PKA and overexpression of YAP cooperate to transform normal cells and amplify neural progenitor pools in developing chick embryos. We also implicate neurofibromin 2 as an AKAP (A‐kinase‐anchoring protein) scaffold protein that facilitates the function of the cAMP/PKA–LATS–YAP pathway. Our study thus incorporates PKA as novel component of the Hippo pathway.     

Characterization of an A-kinase anchoring protein in human ciliary axonemes

Although protein kinase A (PKA) activation is known to increase ciliary beat frequency in humans the molecular mechanisms involved are unknown. We demonstrate that PKA is associated with ciliary axonemes where it specifically phosphorylates a 23-kDa protein. Because PKA is often localized to subcellular compartments in proximity to its substrate(s) via interactions with A-kinase-anchoring proteins (AKAPs), we investigated whether an AKAP was also associated with ciliary axonemes. This study has identified a novel 28 kDa AKAP (AKAP28)that is highly enriched in airway axonemes. The mRNA for AKAP28 is up-regulated as primary airway cells differentiate and is specifically expressed in tissues containing cilia and/or flagella. Additionally, both Western blot and immunostaining data show that AKAP28 is enriched in airway cilia. These data demonstrate that we have identified the first human axonemal AKAP, a protein that likely plays a role in the signaling necessary for efficient modulation of ciliary beat frequency.     

Identification of a novel A-kinase anchoring protein 18 isoform and evidence for its role in the vasopressin-induced aquaporin-2 shuttle in renal principal cells

Arginine vasopressin (AVP) increases the water permeability of renal collecting duct principal cells by inducing the fusion of vesicles containing the water channel aquaporin-2 (AQP2) with the plasma membrane (AQP2 shuttle). This event is initiated by activation of vasopressin V2 receptors, followed by an elevation of cAMP and the activation of protein kinase A (PKA). The tethering of PKA to subcellular compartments by protein kinase A anchoring proteins (AKAPs) is a prerequisite for the AQP2 shuttle. During the search for AKAP(s) involved in the shuttle, a new splice variant of AKAP18, AKAP18delta, was identified. AKAP18delta functions as an AKAP in vitro and in vivo. In the kidney, it is mainly expressed in principal cells of the inner medullary collecting duct, closely resembling the distribution of AQP2. It is present in both the soluble and particulate fractions derived from renal inner medullary tissue. Within the particulate fraction, AKAP18delta was identified on the same intracellular vesicles as AQP2 and PKA. AVP not only recruited AQP2, but also AKAP18delta to the plasma membrane. The elevation of cAMP caused the dissociation of AKAP18delta and PKA. The data suggest that AKAP18delta is involved in the AQP2 shuttle.     

The biological functions of A-kinase anchor proteins

cAMP-dependent protein kinase is targeted to discrete subcellular locations by a family of specific anchor proteins (A-kinase anchor proteins, AKAPs). Localization recruits protein kinase A (PKA) holoenzyme close to its substrate/effector proteins, directing and amplifying the biological effects of cAMP signaling.AKAPs include two conserved structural modules: (i) a targeting domain that serves as a scaffold and membrane anchor; and (ii) a tethering domain that interacts with PKA regulatory subunits. Alternative splicing can shuffle targeting and tethering domains to generate a variety of AKAPs with different targeting specificity. Although AKAPs have been identified on the basis of their interaction with PKA, they also bind other signaling molecules, mainly phosphatases and kinases, that regulate AKAP targeting and activate other signal transduction pathways.We suggest that AKAP forms a "transduceosome" by acting as an autonomous multivalent scaffold that assembles and integrates signals derived from multiple pathways. The transduceosome amplifies cAMP and other signals locally and, by stabilizing and reducing the basal activity of PKA, it also exerts long-distance effects. The AKAP transduceosome thus optimizes the amplitude and the signal/noise ratio of cAMP-PKA stimuli travelling from the membrane to the nucleus and other subcellular compartments.     

Luteinizing hormone receptor activation in ovarian granulosa cells promotes protein kinase A-dependent dephosphorylation of microtubule-associated protein 2D

The actions of LH to induce ovulation and luteinization of preovulatory follicles are mediated principally by activation of cAMP-dependent protein kinase (PKA) in granulosa cells. PKA activity is targeted to specific locations in many cells by A kinase-anchoring proteins (AKAPs). We previously showed that FSH induces expression of microtubule-associated protein (MAP) 2D, an 80-kDa AKAP, in rat granulosa cells, and that MAP2D coimmunoprecipitates with PKA-regulatory subunits in these cells. Here we report a rapid and targeted dephosphorylation of MAP2D at Thr256/Thr259 after treatment with human chorionic gonadotropin, an LH receptor agonist. This event is mimicked by treatment with forskolin or a cAMP analog and is blocked by the PKA inhibitor myristoylated-PKI, indicating a role for cAMP and PKA signaling in phosphoregulation of granulosa cell MAP2D. Furthermore, we show that Thr256/Thr259 dephosphorylation is blocked by the protein phosphatase 2A (PP2A) inhibitor, okadaic acid, and demonstrate interactions between MAP2D and PP2A by coimmunoprecipitation and microcystin-agarose pull-down. We also show that MAP2D interacts with glycogen synthase kinase (GSK) 3beta and is phosphorylated at Thr256/Thr259 by this kinase in the basal state. Increased phosphorylation of GSK3beta at Ser9 and the PP2A B56delta subunit at Ser566 is observed after treatment with human chorionic gonadotropin and appears to result in LH receptor-mediated inhibition of GSK3beta and activation of PP2A, respectively. Taken together, these results show that the phosphorylation status of the AKAP MAP2D is acutely regulated by LH receptor-mediated modulation of kinase and phosphatase activities via PKA.