Protein kinase A is a functional component of focal adhesions

Focal adhesions (FAs) form the junction between extracellular matrix (ECM)-bound integrins and the actin cytoskeleton and also transmit signals that regulate cell adhesion, cytoskeletal dynamics, and cell migration. While many of these signals are rooted in reversible tyrosine phosphorylation, phosphorylation of FA proteins on Ser/Thr residues is far more abundant yet its mechanisms and consequences are far less understood. The cAMP-dependent protein kinase (protein kinase A; PKA) has important roles in cell adhesion and cell migration and is both an effector and regulator of integrin-mediated adhesion to the ECM. Importantly, subcellular localization plays a critically important role in specifying PKA function. Here, we show that PKA is present in isolated FA-cytoskeleton complexes and active within FAs in live cells. Furthermore, using kinase-catalyzed biotinylation of isolated FA-cytoskeleton complexes, we identify 53 high-stringency candidate PKA substrates within FAs. From this list, we validate tensin-3 (Tns3)-a well-established molecular scaffold, regulator of cell migration, and a component of focal and fibrillar adhesions-as a novel direct substrate for PKA. These observations identify a new pathway for phospho-regulation of Tns3 and, importantly, establish a new and important niche for localized PKA signaling and thus provide a foundation for further investigation of the role of PKA in the regulation of FA dynamics and signaling.

14-3-3 interaction with phosphodiesterase 8A sustains PKA signaling and downregulates the MAPK pathway

The cAMP/PKA and mitogen-activated protein kinase (MAPK) signaling cascade control many cellular processes and are highly regulated for optimal cellular responses upon external stimuli. Phosphodiesterase 8A (PDE8A) is an important regulator that inhibits signaling via cAMP-dependent PKA by hydrolyzing intracellular cAMP pool. Conversely, PDE8A activates the MAPK pathway by protecting CRAF/Raf1 kinase from PKA-mediated inhibitory phosphorylation at Ser259 residue, a binding site of scaffold protein 14-3-3. It still remains enigmatic as to how the cross-talk involving PDE8A regulation influences cAMP/PKA and MAPK signaling pathways. Here, we report that PDE8A interacts with 14-3-3ζ in both yeast and mammalian system, and this interaction is enhanced upon the activation of PKA, which phosphorylates PDE8A's Ser359 residue. Biophysical characterization of phospho-Ser359 peptide with 14-3-3ζ protein further supports their interaction. Strikingly, 14-3-3ζ reduces the catalytic activity of PDE8A, which upregulates the cAMP/PKA pathway while the MAPK pathway is downregulated. Moreover, 14-3-3ζ in complex with PDE8A and cAMP-bound regulatory subunit of PKA, RIα, delays the deactivation of PKA signaling. Our results define 14-3-3ζ as a molecular switch that operates signaling between cAMP/PKA and MAPK by associating with PDE8A.

A versatile kinase mobility shift assay (KiMSA) for PKA analysis and cyclic AMP detection in sperm physiology (and beyond)

The cAMP-dependent protein kinase (PKA) is one of the most extensively distributed kinases among intracellular signal cascades, with a pivotal role in the regulation of various processes, including the capacitation of sperm cells. Traditional assessments of PKA activity relies on the utilization of [γ-32P] ATP and the Kemptide substrate. This methodology presents several major drawbacks, including high-costs and health risks derived from the manipulation of radioactive isotopes. In this work we introduce an enhanced non-radioactive assay for quantifying PKA activity, termed KiMSA which relies on the use of a fluorescent-labeled Kemptide (Kemptide-FITC). Once the kinase reaction is terminated, the products can be easily resolved through electrophoresis on an agarose gel and quantified by fluorescence densitometry. We show that the KiMSA assay is suitable for purified PKA, and also to address both basal and capacitation induced PKA activity in mouse sperm cells. Furthermore, the assay enables monitoring the inhibition of PKA with inhibitors such as sPKI and H-89 in live cells. Therefore, the experimental and optimal assay conditions are set so that the KiMSA assay can be used to either assess in vitro as well as in vivo PKA activity in sperm cells. Finally, this method allows for measurement of cAMP concentrations, rendering a versatile technique for the study of cAMP/PKA pathways.

Cardiac side effects of RNA-based SARS-CoV-2 vaccines: Hidden cardiotoxic effects of mRNA-1273 and BNT162b2 on ventricular myocyte function and structure

BACKGROUND AND PURPOSE

To protect against SARS-CoV-2 infection, the first mRNA-based vaccines, Spikevax (mRNA-1273, Moderna) and Comirnaty (BNT162b2, Pfizer/Biontech), were approved in 2020. The structure and assembly of the immunogen-in both cases, the SARS-CoV-2 spike (S) glycoprotein-are determined by a messenger RNA sequence that is translated by endogenous ribosomes. Cardiac side-effects, which for the most part can be classified by their clinical symptoms as myo- and/or pericarditis, can be caused by both mRNA-1273 and BNT162b2.

EXPERIMENTAL APPROACH

As persuasive theories for the underlying pathomechanisms have yet to be developed, this study investigated the effect of mRNA-1273 and BNT162b2 on the function, structure, and viability of isolated adult rat cardiomyocytes over a 72 h period.

KEY RESULTS

In the first 24 h after application, both mRNA-1273 and BNT162b2 caused neither functional disturbances nor morphological abnormalities. After 48 h, expression of the encoded spike protein was detected in ventricular cardiomyocytes for both mRNAs. At this point in time, mRNA-1273 induced arrhythmic as well as completely irregular contractions associated with irregular as well as localized calcium transients, which provide indications of significant dysfunction of the cardiac ryanodine receptor (RyR2). In contrast, BNT162b2 increased cardiomyocyte contraction via significantly increased protein kinase A (PKA) activity at the cellular level.

CONCLUSION AND IMPLICATIONS

Here, we demonstrated for the first time, that in isolated cardiomyocytes, both mRNA-1273 and BNT162b2 induce specific dysfunctions that correlate pathophysiologically to cardiomyopathy. Both RyR2 impairment and sustained PKA activation may significantly increase the risk of acute cardiac events.

From membrane to nucleus: A three-wave hypothesis of cAMP signaling

For many decades, our understanding of G protein-coupled receptor (GPCR) activity and cyclic AMP (cAMP) signaling was limited exclusively to the plasma membrane. However, a growing body of evidence has challenged this view by introducing the concept of endocytosis-dependent GPCR signaling. This emerging paradigm emphasizes not only the sustained production of cAMP but also its precise subcellular localization, thus transforming our understanding of the spatiotemporal organization of this process. Starting from this alternative point of view, our recent work sheds light on the role of an endocytosis-dependent calcium release from the endoplasmic reticulum in the control of nuclear cAMP levels. This is achieved through the activation of local soluble adenylyl cyclase, which in turn regulates the activation of local protein kinase A (PKA) and downstream transcriptional events. In this review, we explore the dynamic evolution of research on cyclic AMP signaling, including the findings that led us to formulate the novel three-wave hypothesis. We delve into how we abandoned the paradigm of cAMP generation limited to the plasma membrane and the changing perspectives on the rate-limiting step in nuclear PKA activation.

Drug discovery for heart failure targeting myosin-binding protein C

Cardiac MyBP-C (cMyBP-C) interacts with actin and myosin to fine-tune cardiac muscle contractility. Phosphorylation of cMyBP-C, which reduces the binding of cMyBP-C to actin and myosin, is often decreased in patients with heart failure (HF) and is cardioprotective in model systems of HF. Therefore, cMyBP-C is a potential target for HF drugs that mimic its phosphorylation and/or perturb its interactions with actin or myosin. We labeled actin with fluorescein-5-maleimide (FMAL) and the C0-C2 fragment of cMyBP-C (cC0-C2) with tetramethylrhodamine (TMR). We performed two complementary high-throughput screens (HTS) on an FDA-approved drug library, to discover small molecules that specifically bind to cMyBP-C and affect its interactions with actin or myosin, using fluorescence lifetime (FLT) detection. We first excited FMAL and detected its FLT, to measure changes in fluorescence resonance energy transfer (FRET) from FMAL (donor) to TMR (acceptor), indicating binding. Using the same samples, we then excited TMR directly, using a longer wavelength laser, to detect the effects of compounds on the environmentally sensitive FLT of TMR, to identify compounds that bind directly to cC0-C2. Secondary assays, performed on selected modulators with the most promising effects in the primary HTS assays, characterized the specificity of these compounds for phosphorylated versus unphosphorylated cC0-C2 and for cC0-C2 versus C1-C2 of fast skeletal muscle (fC1-C2). A subset of identified compounds modulated ATPase activity in cardiac and/or skeletal myofibrils. These assays establish the feasibility of the discovery of small-molecule modulators of the cMyBP-C-actin/myosin interaction, with the ultimate goal of developing therapies for HF.

Impact of interorganelle coordination between the conventional early secretory pathway and autophagy in cellular homeostasis and stress response

The conventional early secretory pathway and autophagy are two essential interconnected cellular processes that are crucial for maintaining cellular homeostasis. The conventional secretory pathway is an anabolic cellular process synthesizing and delivering proteins to distinct locations, including different organelles, the plasma membrane, and the extracellular media. On the other hand, autophagy is a catabolic cellular process that engulfs damaged organelles and aberrant cytosolic constituents into the double autophagosome membrane. After fusion with the lysosome and autolysosome formation, this process triggers digestion and recycling. A growing list of evidence indicates that these anabolic and catabolic processes are mutually regulated. While knowledge about the molecular actors involved in the coordination and functional cooperation between these two processes has increased over time, the mechanisms are still poorly understood. This review article summarized and discussed the most relevant evidence about the key molecular players implicated in the interorganelle crosstalk between the early secretory pathway and autophagy under normal and stressful conditions.

Specific phosphorylation of microtubule-associated protein 2c by extracellular signal-regulated kinase reduces interactions at its Pro-rich regions

Microtubule-associated protein 2 (MAP2) is an important neuronal target of extracellular signal-regulated kinase 2 (ERK2) involved in Raf signaling pathways, but mechanistic details of MAP2 phosphorylation are unclear. Here, we used NMR spectroscopy to quantitatively describe the kinetics of phosphorylation of individual serines and threonines in the embryonic MAP2 variant MAP2c. We carried out real-time monitoring of phosphorylation to discover major phosphorylation sites that were not identified in previous studies relying on specific antibodies. Our comparison with phosphorylation of MAP2c by a model cyclin-dependent kinase CDK2 and with phosphorylation of the MAP2c homolog Tau revealed differences in phosphorylation profiles that explain specificity of regulation of biological functions of MAP2c and Tau. To probe the molecular basis of the regulatory effect of ERK2, we investigated the interactions of phosphorylated and unphosphorylated MAP2c by NMR with single-residue resolution. As ERK2 phosphorylates mostly outside the regions binding microtubules, we studied the binding of proteins other than tubulin, namely regulatory subunit RIIα of cAMP-dependent protein kinase (PKA), adaptor protein Grb2, Src homology domain 3 of tyrosine kinases Fyn and Abl, and ERK2 itself. We found ERK2 phosphorylation interfered mostly with binding to proline-rich regions of MAP2c. Furthermore, our NMR experiments in SH-SY5Y neuroblastoma cell lysates showed that the kinetics of dephosphorylation are compatible with in-cell NMR studies and that residues targeted by ERK2 and PKA are efficiently phosphorylated in the cell lysates. Taken together, our results provide a deeper characterization of MAP2c phosphorylation and its effects on interactions with other proteins.

Raf Kinase Inhibitory Protein regulates the cAMP-dependent protein kinase signaling pathway through a positive feedback loop

Raf Kinase Inhibitory Protein (RKIP) maintains cellular robustness and prevents the progression of diseases such as cancer and heart disease by regulating key kinase cascades including MAP kinase and protein kinase A (PKA). Phosphorylation of RKIP at S153 by Protein Kinase C (PKC) triggers a switch from inhibition of Raf to inhibition of the G protein coupled receptor kinase 2 (GRK2), enhancing signaling by the β-adrenergic receptor (β-AR) that activates PKA. Here we report that PKA-phosphorylated RKIP promotes β-AR-activated PKA signaling. Using biochemical, genetic, and biophysical approaches, we show that PKA phosphorylates RKIP at S51, increasing S153 phosphorylation by PKC and thereby triggering feedback activation of PKA. The S51V mutation blocks the ability of RKIP to activate PKA in prostate cancer cells and to induce contraction in primary cardiac myocytes in response to the β-AR activator isoproterenol, illustrating the functional importance of this positive feedback circuit. As previously shown for other kinases, phosphorylation of RKIP at S51 by PKA is enhanced upon RKIP destabilization by the P74L mutation. These results suggest that PKA phosphorylation at S51 may lead to allosteric changes associated with a higher-energy RKIP state that potentiates phosphorylation of RKIP at other key sites. This allosteric regulatory mechanism may have therapeutic potential for regulating PKA signaling in disease states.

Breadth and Specificity in Pleiotropic Protein Kinase A Activity and Environmental Responses

Protein Kinase A (PKA) is an essential kinase that is conserved across eukaryotes and plays fundamental roles in a wide range of organismal processes, including growth control, learning and memory, cardiovascular health, and development. PKA mediates these responses through the direct phosphorylation of hundreds of proteins-however, which proteins are phosphorylated can vary widely across cell types and environmental cues, even within the same organism. A major question is how cells enact specificity and precision in PKA activity to mount the proper response, especially during environmental changes in which only a subset of PKA-controlled processes must respond. Research over the years has uncovered multiple strategies that cells use to modulate PKA activity and specificity. This review highlights recent advances in our understanding of PKA signaling control including subcellular targeting, phase separation, feedback control, and standing waves of allosteric regulation. We discuss how the complex inputs and outputs to the PKA network simultaneously pose challenges and solutions in signaling integration and insulation. PKA serves as a model for how the same regulatory factors can serve broad pleiotropic functions but maintain specificity in localized control.

Choosing Kinase Inhibitors for Androgen Deprivation Therapy-Resistant Prostate Cancer

Androgen deprivation therapy (ADT) is a systemic therapy for advanced prostate cancer (PCa). Although most patients initially respond to ADT, almost all cancers eventually develop castration resistance. Castration-resistant PCa (CRPC) is associated with a very poor prognosis, and the treatment of which is a serious clinical challenge. Accumulating evidence suggests that abnormal expression and activation of various kinases are associated with the emergence and maintenance of CRPC. Many efforts have been made to develop small molecule inhibitors to target the key kinases in CRPC. These inhibitors are designed to suppress the kinase activity or interrupt kinase-mediated signal pathways that are associated with PCa androgen-independent (AI) growth and CRPC development. In this review, we briefly summarize the roles of the kinases that are abnormally expressed and/or activated in CRPC and the recent advances in the development of small molecule inhibitors that target kinases for the treatment of CRPC.

LRRK2 at Striatal Synapses: Cell-Type Specificity and Mechanistic Insights

Mutations in leucine-rich repeat kinase 2 (LRRK2) cause Parkinson’s disease with a similar clinical presentation and progression to idiopathic Parkinson’s disease, and common variation is linked to disease risk. Recapitulation of the genotype in rodent models causes abnormal dopamine release and increases the susceptibility of dopaminergic neurons to insults, making LRRK2 a valuable model for understanding the pathobiology of Parkinson’s disease. It is also a promising druggable target with targeted therapies currently in development. LRRK2 mRNA and protein expression in the brain is highly variable across regions and cellular identities. A growing body of work has demonstrated that pathogenic LRRK2 mutations disrupt striatal synapses before the onset of overt neurodegeneration. Several substrates and interactors of LRRK2 have been identified to potentially mediate these pre-neurodegenerative changes in a cell-type-specific manner. This review discusses the effects of pathogenic LRRK2 mutations in striatal neurons, including cell-type-specific and pathway-specific alterations. It also highlights several LRRK2 effectors that could mediate the alterations to striatal function, including Rabs and protein kinase A. The lessons learned from improving our understanding of the pathogenic effects of LRRK2 mutations in striatal neurons will be applicable to both dissecting the cell-type specificity of LRRK2 function in the transcriptionally diverse subtypes of dopaminergic neurons and also increasing our understanding of basal ganglia development and biology. Finally, it will inform the development of therapeutics for Parkinson’s disease.

Apoptotic and anti-angiogenic effects of propolis against human bladder cancer: molecular docking and in vitro screening

INTRODUCTION

Bladder cancer is still of unknown initiation and progression, it is difficult to treat the patient once bladder cancer have a distant metastasis.

MATERIALS AND METHODS

In the present study, propolis extract was evaluated against bladder cancer cells (T24). Two independent pathways were investigated, apoptosis and angiogenesis, Bax, Bcl-2, P53, and caspase-3 for apoptosis, vascular endothelial growth factor receptor and protein kinase A as angiogenesis potential targets.

OBJECTIVES

Molecular docking studies will be conducted for the major known constituents of Egyptian propolis into apoptotic and angiogenic protein targets, to give better insights to the possible binding mode and interactions and investigate the ability of propolis constituents to target both apoptotic and angiogenic pathways.

RESULTS

Propolis showed anti-proliferative activity against T24 cancer cell line, the IC₅₀ value was 6.36 µg/ml. Also significant effects of propolis on Bax, Bcl-2, P53, and caspase-3 were observed.

DISCUSSION

These obtained results proved the ability of propolis to induce cell death. Also it has revealed noticeable effects on protein kinase A and vascular endothelial growth factor receptor.

CONCLUSION

The obtained results can encourage us to say that propolis extract can induce a programmed cell death in human bladder cancer cells, and also affect angiogenesis.

Monoamine Oxidase-B Inhibitor Reduction in Pro-Inflammatory Cytokines Mediated by Inhibition of cAMP-PKA/EPAC Signaling

Mucosal epithelial cell integrity is an important component of innate immunity and it protects the host from an environment rich in microorganisms. Virulence factors from Gram-negative bacteria [e.g. lipopolysaccharide (LPS)] induce significant pro-inflammatory cytokine expression. Monoamine oxidase (MAO) inhibitors reduce cytokine expression in a variety of inflammatory models and may therefore have therapeutic potential for a number of inflammatory diseases. We tested the anti-inflammatory therapeutic potential of a recently developed reversible MAO-B inhibitor (RG0216) with reduced transport across the blood–brain barrier. In an epithelial cell culture model, RG0216 significantly decreased LPS-induced interleukin (IL)-6 and IL-1β gene and protein expression and was as effective as equimolar concentrations of deprenyl (an existing irreversible MAO-B inhibitor). Hydrogen peroxide and modulating dopamine receptor signaling had no effect on cytokine expression. We showed that LPS-induced expression of IL-6 and IL-1β was cAMP dependent, that IL-6 and IL-1β expression were induced by direct cAMP activation (forskolin) and that RG0216 and deprenyl effectively reduced cAMP-mediated cytokine expression. Targeted protein kinase A (PKA) and Exchange Protein Activated by cAMP (EPAC) activation regulated IL-6 and IL-1β expression, albeit in different ways, but both cytokines were effectively decreased with RG0216. RG0216 reduction of LPS-induced cytokine expression occurred by acting downstream of the cAMP-PKA/EPAC signaling cascade. This represents a novel mechanism by which MAO-B selective inhibitors regulate LPS-induced IL-6 and IL-1β expression.

Abnormal Calcium Handling in Atrial Fibrillation Is Linked to Changes in Cyclic AMP Dependent Signaling

Both, the decreased L-type Ca²⁺ current (I_Ca,L) density and increased spontaneous Ca²⁺ release from the sarcoplasmic reticulum (SR), have been associated with atrial fibrillation (AF). In this study, we tested the hypothesis that remodeling of 3′,5′-cyclic adenosine monophosphate (cAMP)-dependent protein kinase A (PKA) signaling is linked to these compartment-specific changes (up- or down-regulation) in Ca²⁺-handling. Perforated patch-clamp experiments were performed in atrial myocytes from 53 patients with AF and 104 patients in sinus rhythm (Ctl). A significantly higher frequency of transient inward currents (I_TI) activated by spontaneous Ca²⁺ release was confirmed in myocytes from AF patients. Next, inhibition of PKA by H-89 promoted a stronger effect on the I_TI frequency in these myocytes compared to myocytes from Ctl patients (7.6-fold vs. 2.5-fold reduction), while the β-agonist isoproterenol (ISO) caused a greater increase in Ctl patients (5.5-fold vs. 2.1-fold). I_Ca,L density was larger in myocytes from Ctl patients at baseline (p < 0.05). However, the effect of ISO on I_Ca,L density was only slightly stronger in AF than in Ctl myocytes (3.6-fold vs. 2.7-fold). Interestingly, a significant reduction of I_Ca,L and Ca²⁺ sparks was observed upon Ca²⁺/Calmodulin-dependent protein kinase II inhibition by KN-93, but this inhibition had no effect on I_TI. Fluorescence resonance energy transfer (FRET) experiments showed that although AF promoted cytosolic desensitization to β-adrenergic stimulation, ISO increased cAMP to similar levels in both groups of patients in the L-type Ca²⁺ channel and ryanodine receptor compartments. Basal cAMP signaling also showed compartment-specific regulation by phosphodiesterases in atrial myocytes from 44 Ctl and 43 AF patients. Our results suggest that AF is associated with opposite changes in compartmentalized PKA/cAMP-dependent regulation of I_Ca,L (down-regulation) and I_TI (up-regulation).

Exogenous Albumin Is Crucial for Pig Sperm to Elicit In Vitro Capacitation Whereas Bicarbonate Only Modulates Its Efficiency

Simple Summary

In this work, we addressed if the presence of exogenous bicarbonate required for pig sperm capacitation, which is a necessary step to acquire fertilizing ability. While sperm incubated in media without BSA or BSA/bicarbonate did not achieve in vitro capacitation, those incubated with BSA reached that status under any bicarbonate concentration, even when bicarbonate was absent. Interestingly, there were differences related to the concentration of bicarbonate, since sperm incubated in media with BSA and with no bicarbonate or 5 mM bicarbonate showed lower overall efficiency in achieving in vitro capacitation than those incubated in the presence of BSA and higher concentration of bicarbonate. Additionally, at the end of the experiment, sperm incubated in the presence of BSA and 38 mM bicarbonate showed lower motility and plasma membrane integrity than those incubated in media with BSA and lower concentrations of bicarbonate. In conclusion, BSA is crucial in for pig sperm to elicit in vitro capacitation and trigger the subsequent progesterone-induced acrosome exocytosis. In contrast, although exogenous bicarbonate does not appear to be indispensable, it shortens the time needed to reach that capacitated status.

Abstract

This work sought to address whether the presence of exogenous bicarbonate is required for pig sperm to elicit in vitro capacitation and further progesterone-induced acrosome exocytosis. For this purpose, sperm were either incubated in a standard in vitro capacitation medium or a similar medium with different concentrations of bicarbonate (either 0 mM, 5 mM, 15 mM or 38 mM) and BSA (either 0 mg/mL or 5 mg/mL). The achievement of in vitro capacitation and progesterone-induced acrosomal exocytosis was tested through the analysis of sperm motility, plasma membrane integrity and lipid disorder, acrosome exocytosis, intracellular calcium levels, mitochondria membrane potential, O₂ consumption rate and the activities of both glycogen synthase kinase 3 alpha (GSK3α) and protein kinase A (PKA). While sperm incubated in media without BSA or BSA/bicarbonate, they did not achieve in vitro capacitation; those incubated in media with BSA achieved the capacitated status under any bicarbonate concentration, even when bicarbonate was absent. Moreover, there were differences related to the concentration of bicarbonate, since sperm incubated in media with BSA and with no bicarbonate or 5 mM bicarbonate showed lower overall efficiency in achieving in vitro capacitation than those incubated in the presence of BSA and 15 mM or 38 mM bicarbonate. Additionally, at the end of the experiment, sperm incubated in the presence of BSA and 38 mM bicarbonate showed significantly (p < 0.05) lower values of motility and plasma membrane integrity than those incubated in media with BSA and lower concentrations of bicarbonate. In conclusion, BSA is instrumental for pig sperm to elicit in vitro capacitation and trigger the subsequent progesterone-induced acrosome exocytosis. Furthermore, while exogenous bicarbonate does not seem to be essential to launch sperm capacitation, it does modulate its efficiency.

Role of transient receptor potential vanilloid-1 in behavioral thermoregulation of the Mongolian gerbil Meriones unguiculatus

Ambient temperature considerably affects the physiology and behavior of mammals. Thermosensory and thermoregulatory abilities play an important role in the response to changing ambient temperature in endotherms. However, the molecular mechanisms of behavioral thermoregulation remain poorly understood. Transient receptor potential vanilloid-1 (TRPV1) is activated by changes in ambient temperature and is involved in acute thermoregulation. Here, we aimed to determine whether TRPV1 is involved in behavioral thermoregulation in wild rodents by conducting 2 experiments. In the first, 42 adult Mongolian gerbils (Meriones unguiculatus; 14 per treatment) were randomly assigned to 3 housing temperatures (4, 23, and 36°C) for 4 weeks. In the second, 20 gerbils (10 per treatment) were randomly injected with capsaicin (TRPV1 agonist) or AMG517 (TRPV1 antagonist). The results showed a significant decrease in food intake and non-shivering thermogenesis in the gerbils housed at 36°C. Additionally, there was a significant increase in the preference of gerbils housed at 4°C to low temperatures. The expression of TRPV1 protein in the brown adipose tissue (BAT) and liver was significantly positively correlated with that of protein kinase A (PKA). The expression of TRPV1 and PKA proteins in the BAT was positively correlated with the temperature preference of the gerbils. The gerbils injected with capsaicin preferred significantly lower temperatures than the control group gerbils. These findings suggest that TRPV1 and PKA are involved in behavioral thermoregulation in Mongolian gerbils.

Control of the Hedgehog pathway by compartmentalized PKA in the primary cilium

The Hedgehog (Hh) signaling is one of the essential signaling pathways during embryogenesis and in adults. Hh signal transduction relies on primary cilium, a specialized cell surface organelle viewed as the hub of cell signaling. Protein kinase A (PKA) has been recognized as a potent negative regulator of the Hh pathway, raising the question of how such a ubiquitous kinase specifically regulates one signaling pathway. We reviewed recent genetic, molecular and biochemical studies that have advanced our mechanistic understanding of PKA's role in Hh signaling in vertebrates, focusing on the compartmentalized PKA at the centrosome and in the primary cilium. We outlined the recently developed genetic and optical tools that can be harvested to study PKA activities during the course of Hh signal transduction.

PINK1-induced phosphorylation of mitofusin 2 at serine 442 causes its proteasomal degradation and promotes cell proliferation in lung cancer and pulmonary arterial hypertension

Impaired mitochondrial fusion, due in part to decreased mitofusin 2 (Mfn2) expression, contributes to unrestricted cell proliferation and apoptosis-resistance in hyperproliferative diseases like pulmonary arterial hypertension (PAH) and non-small cell lung cancer (NSCLC). We hypothesized that Mfn2 levels are reduced due to increased proteasomal degradation of Mfn2 triggered by its phosphorylation at serine 442 (S442) and investigated the potential kinase mediators. Mfn2 expression was decreased and Mfn2 S442 phosphorylation was increased in pulmonary artery smooth muscle cells from PAH patients and in NSCLC cells. Mfn2 phosphorylation was mediated by PINK1 and protein kinase A (PKA), although only PINK1 expression was increased in these diseases. We designed a S442 phosphorylation deficient Mfn2 construct (PD-Mfn2) and a S442 constitutively phosphorylated Mfn2 construct (CP-Mfn2). The effects of these modified Mfn2 constructs on Mfn2 expression and biological function were compared with those of the wildtype Mfn2 construct (WT-Mfn2). WT-Mfn2 increased Mfn2 expression and mitochondrial fusion in both PAH and NSCLC cells resulting in increased apoptosis and decreased cell proliferation. Compared to WT-Mfn2, PD-Mfn2 caused greater Mfn2 expression, suppression of proliferation, apoptosis induction, and cell cycle arrest. Conversely, CP-Mfn2 caused only a small increase in Mfn2 expression and did not restore mitochondrial fusion, inhibit cell proliferation, or induce apoptosis. Silencing PINK1 or PKA, or proteasome blockade using MG132, increased Mfn2 expression, enhanced mitochondrial fusion and induced apoptosis. In a xenotransplantation NSCLC model, PD-Mfn2 gene therapy caused greater tumor regression than did therapy with WT-Mfn2. Mfn2 deficiency in PAH and NSCLC reflects proteasomal degradation triggered by Mfn2-S442 phosphorylation by PINK1 and/or PKA. Inhibiting Mfn2 phosphorylation has potential therapeutic benefit in PAH and lung cancer.

The Marine-Derived Natural Product Epiloliolide Isolated from Sargassum horneri Regulates NLRP3 via PKA/CREB, Promoting Proliferation and Anti-Inflammatory Effects of Human Periodontal Ligament Cells

Currently, periodontitis treatment relies on surgical operations, anti-inflammatory agents, or antibiotics. However, these treatments cause pain and side effects, resulting in a poor prognosis. Therefore, in this study, we evaluated the impact of the compound epiloliolide isolated from Sargassum horneri on the recovery of inflammatory inhibitors and loss of periodontal ligaments, which are essential treatment strategies for periodontitis. Here, human periodontal ligament cells stimulated with PG-LPS were treated with the compound epiloliolide, isolated from S. horneri. In the results of this study, epiloliolide proved the anti-inflammatory effect, cell proliferation capacity, and differentiation potential of periodontal ligament cells into osteoblasts, through the regulation of the PKA/CREB signaling pathway. Epiloliolide effectively increased the proliferation and migration of human periodontal ligament cells without cytotoxicity and suppressed the protein expression of proinflammatory mediators and cytokines, such as iNOS, COX-2, TNF-α, IL-6, and IL-1β, by downregulating NLRP3 activated by PG-LPS. Epiloliolide also upregulated the phosphorylation of PKA/CREB proteins, which play an important role in cell growth and proliferation. It was confirmed that the anti-inflammatory effect in PG-LPS-stimulated large cells was due to the regulation of PKA/CREB signaling. We suggest that epiloliolide could serve as a potential novel therapeutic agent for periodontitis by inhibiting inflammation and restoring the loss of periodontal tissue.

Cardiac myosin-binding protein C interaction with actin is inhibited by compounds identified in a high-throughput fluorescence lifetime screen

Cardiac myosin-binding protein C (cMyBP-C) interacts with actin and myosin to modulate cardiac muscle contractility. These interactions are disfavored by cMyBP-C phosphorylation. Heart failure patients often display decreased cMyBP-C phosphorylation, and phosphorylation in model systems has been shown to be cardioprotective against heart failure. Therefore, cMyBP-C is a potential target for heart failure drugs that mimic phosphorylation or perturb its interactions with actin/myosin. Here we have used a novel fluorescence lifetime-based assay to identify small-molecule inhibitors of actin-cMyBP-C binding. Actin was labeled with a fluorescent dye (Alexa Fluor 568, AF568) near its cMyBP-C binding sites; when combined with the cMyBP-C N-terminal fragment, C0-C2, the fluorescence lifetime of AF568-actin decreases. Using this reduction in lifetime as a readout of actin binding, a high-throughput screen of a 1280-compound library identified three reproducible hit compounds (suramin, NF023, and aurintricarboxylic acid) that reduced C0-C2 binding to actin in the micromolar range. Binding of phosphorylated C0-C2 was also blocked by these compounds. That they specifically block binding was confirmed by an actin-C0-C2 time-resolved FRET (TR-FRET) binding assay. Isothermal titration calorimetry (ITC) and transient phosphorescence anisotropy (TPA) confirmed that these compounds bind to cMyBP-C, but not to actin. TPA results were also consistent with these compounds inhibiting C0-C2 binding to actin. We conclude that the actin-cMyBP-C fluorescence lifetime assay permits detection of pharmacologically active compounds that affect cMyBP-C-actin binding. We now have, for the first time, a validated high-throughput screen focused on cMyBP-C, a regulator of cardiac muscle contractility and known key factor in heart failure.

Tolerance to nascent protein misfolding stress requires fine-tuning of the cAMP/PKA pathway

Protein aggregation is the abnormal association of misfolded proteins into larger, often insoluble structures that can be toxic during aging and in protein aggregation-associated diseases. Previous research has established a role for the cytosolic Tsa1 peroxiredoxin in responding to protein misfolding stress. Tsa1 is also known to downregulate the cAMP/protein kinase A (PKA) pathway as part of the response to hydrogen peroxide stress. However, whether the cAMP/PKA pathway is involved in protein misfolding stress is not known. Using transcriptomics, we examined the response to protein misfolding stress and found upregulation of numerous stress gene functions and downregulation of many genes related to protein synthesis and other growth-related processes consistent with the well-characterized environmental stress response. The scope of the transcriptional response is largely similar in wild-type and tsa1 mutant strains, but the magnitude is dampened in the strain lacking Tsa1. We identified a direct protein interaction between Tsa1 and the Bcy1 regulatory subunit of PKA that is present under normal growth conditions and explains the observed differences in gene expression profiles. This interaction is increased in a redox-dependent manner in response to nascent protein misfolding, via Tsa1-mediated oxidation of Bcy1. Oxidation of Bcy1 causes a reduction in cAMP binding by Bcy1, which dampens PKA pathway activity, leading to a targeted reprogramming of gene expression. Redox regulation of the regulatory subunit of PKA provides a mechanism to mitigate the toxic consequences of protein misfolding stress that is distinct to stress caused by exogenous sources of reactive oxygen species.

Cholesterol Activates Cyclic AMP Signaling in Metaplastic Acinar Cells

Cholesterol is a non-essential metabolite that exerts both structural and signaling functions. However, cholesterol biosynthesis is elevated, and actively supports, pancreatic carcinogenesis. Our previous work showed that statins block the reprogramming of mutant KRAS-expressing acinar cells, that spontaneously undergo a metaplastic event termed acinar-to-ductal metaplasia (ADM) to initiate carcinogenesis. Here we tested the impact of cholesterol supplementation on isolated primary wild-type acinar cells and observed enhanced ductal transdifferentiation, associated with generation of the second messenger cyclic adenosine monophosphate (cAMP) and the induction of downstream protein kinase A (PKA). Inhibition of PKA suppresses cholesterol-induced ADM ex vivo. Live imaging using fluorescent biosensors dissected the temporal and spatial dynamics of PKA activation upon cholesterol addition and showed uneven activation both in the cytosol and on the outer mitochondrial membrane of primary pancreatic acinar cells. The ability of cholesterol to activate cAMP signaling is lost in tumor cells. Qualitative examination of multiple normal and transformed cell lines supports the notion that the cAMP/PKA axis plays different roles during multi-step pancreatic carcinogenesis. Collectively, our findings describe the impact of cholesterol availability on the cyclic AMP/PKA axis and plasticity of pancreatic acinar cells.

AKAP79/150 coordinates leptin-induced PKA signaling to regulate KATP channel trafficking in pancreatic β-cells

The adipocyte hormone leptin regulates glucose homeostasis both centrally and peripherally. A key peripheral target is the pancreatic β-cell, which secretes insulin upon glucose stimulation. Leptin is known to suppress glucose-stimulated insulin secretion by promoting trafficking of K_ATP channels to the β-cell surface, which increases K⁺ conductance and causes β-cell hyperpolarization. We have previously shown that leptin-induced K_ATP channel trafficking requires protein kinase A (PKA)-dependent actin remodeling. However, whether PKA is a downstream effector of leptin signaling or PKA plays a permissive role is unknown. Using FRET-based reporters of PKA activity, we show that leptin increases PKA activity at the cell membrane and that this effect is dependent on N-methyl-D-aspartate receptors, CaMKKβ, and AMPK, which are known to be involved in the leptin signaling pathway. Genetic knockdown and rescue experiments reveal that the increased PKA activity upon leptin stimulation requires the membrane-targeted PKA-anchoring protein AKAP79/150, indicating that PKA activated by leptin is anchored to AKAP79/150. Interestingly, disrupting protein phosphatase 2B (PP2B) anchoring to AKAP79/150, known to elevate basal PKA signaling, leads to increased surface K_ATP channels even in the absence of leptin stimulation. Our findings uncover a novel role of AKAP79/150 in coordinating leptin and PKA signaling to regulate K_ATP channel trafficking in β-cells, hence insulin secretion. The study further advances our knowledge of the downstream signaling events that may be targeted to restore insulin secretion regulation in β-cells defective in leptin signaling, such as those from obese individuals with type 2 diabetes.

Phosphorylation of a chronic pain mutation in the voltage-gated sodium channel Nav1.7 increases voltage sensitivity

Mutations in voltage-gated sodium channels (Navs) can cause alterations in pain sensation, such as chronic pain diseases like inherited erythromelalgia. The mutation causing inherited erythromelalgia, Nav1.7 p.I848T, is known to induce a hyperpolarized shift in the voltage dependence of activation in Nav1.7. So far, however, the mechanism to explain this increase in voltage sensitivity remains unknown. In the present study, we show that phosphorylation of the newly introduced Thr residue explains the functional change. We expressed wildtype human Nav1.7, the I848T mutant, or other mutations in HEK293T cells and performed whole-cell patch-clamp electrophysiology. As the insertion of a Thr residue potentially creates a novel phosphorylation site for Ser/Thr kinases and because Nav1.7 had been shown in Xenopus oocytes to be affected by protein kinases C and A, we used different nonselective and selective kinase inhibitors and activators to test the effect of phosphorylation on Nav1.7 in a human system. We identify protein kinase C, but not protein kinase A, to be responsible for the phosphorylation of T848 and thereby for the shift in voltage sensitivity. Introducing a negatively charged amino acid instead of the putative phosphorylation site mimics the effect on voltage gating to a lesser extent. 3D modeling using the published cryo-EM structure of human Nav1.7 showed that introduction of this negatively charged site seems to alter the interaction of this residue with the surrounding amino acids and thus to influence channel function. These results could provide new opportunities for the development of novel treatment options for patients with chronic pain.

Cyclic nucleotide selectivity of protein kinase G isozymes

The intrinsic activity of the C-terminal catalytic (C) domain of cyclic guanosine monophosphate (cGMP)-dependent protein kinases (PKG) is inhibited by interactions with the N-terminal regulatory (R) domain. Selective binding of cGMP to cyclic nucleotide binding (CNB) domains within the R-domain disrupts the inhibitory R-C interaction, leading to the release and activation of the C-domain. Affinity measurements of mammalian and plasmodium PKG CNB domains reveal different degrees of cyclic nucleotide affinity and selectivity; the CNB domains adjacent to the C-domain are more cGMP selective and therefore critical for cGMP-dependent activation. Crystal structures of isolated CNB domains in the presence and absence of cyclic nucleotides reveal isozyme-specific contacts that explain cyclic nucleotide selectivity and conformational changes that accompany CNB. Crystal structures of tandem CNB domains identify two types of CNB-mediated dimeric contacts that indicate cGMP-driven reorganization of domain-domain interfaces that include large conformational changes. Here, we review the available structural and functional information of PKG CNB domains that further advance our understanding of cGMP mediated regulation and activation of PKG isozymes.

Receptor-independent modulation of cAMP-dependent protein kinase and protein phosphatase signaling in cardiac myocytes by oxidizing agents

The contraction and relaxation of the heart is controlled by stimulation of the β1-adrenoreceptor (AR) signaling cascade, which leads to activation of cAMP-dependent protein kinase (PKA) and subsequent cardiac protein phosphorylation. Phosphorylation is counteracted by the main cardiac protein phosphatases, PP2A and PP1. Both kinase and phosphatases are sensitive to intramolecular disulfide formation in their catalytic subunits that inhibits their activity. Additionally, intermolecular disulfide formation between PKA type I regulatory subunits (PKA-RI) has been described to enhance PKA's affinity for protein kinase A anchoring proteins, which alters its subcellular distribution. Nitroxyl donors have been shown to affect contractility and relaxation, but the mechanistic basis for this effect is unclear. The present study investigates the impact of several nitroxyl donors and the thiol-oxidizing agent diamide on cardiac myocyte protein phosphorylation and oxidation. Although all tested compounds equally induced intermolecular disulfide formation in PKA-RI, only 1-nitrosocyclohexalycetate (NCA) and diamide induced reproducible protein phosphorylation. Phosphorylation occurred independently of β1-AR activation, but was abolished after pharmacological PKA inhibition and thus potentially attributable to increased PKA activity. NCA treatment of cardiac myocytes induced translocation of PKA and phosphatases to the myofilament compartment as shown by fractionation, immunofluorescence, and proximity ligation assays. Assessment of kinase and phosphatase activity within the myofilament fraction of cardiac myocytes after exposure to NCA revealed activation of PKA and inhibition of phosphatase activity thus explaining the increase in phosphorylation. The data suggest that the NCA-mediated effect on cardiac myocyte protein phosphorylation orchestrates alterations in the kinase/phosphatase balance.

Cysteine Sulfoxides Enhance Steroid Hormone Production via Activation of the Protein Kinase A Pathway in Testis-Derived I-10 Tumor Cells

Testosterone plays an important role in male sexual characteristics and maturation, and decreased testosterone levels increase the risk of several diseases. Recently, onion extract rich in cysteine sulfoxides, which are amino acids unique to onions, has been reported to alleviate age-related symptoms resulting from decreased testosterone levels in males. However, the mechanism underlying the suppression of low testosterone levels by cysteine sulfoxides has not been elucidated. In this study, we found that onion extract containing cysteine sulfoxides enhanced progesterone, a precursor of testosterone, in mouse testis-derived I-10 tumor cells. Furthermore, cysteine sulfoxides activated protein kinase A (PKA) and cyclic adenosine monophosphate response element-binding protein, which are key factors in steroidogenesis. These results suggest that cysteine sulfoxides enhance steroid hormone production via activation of the PKA signaling pathway.

CaMKK2 is inactivated by cAMP-PKA signaling and 14-3-3 adaptor proteins

The calcium-calmodulin-dependent protein kinase kinase-2 (CaMKK2) is a key regulator of cellular and whole-body energy metabolism. It is known to be activated by increases in intracellular Ca²⁺, but the mechanisms by which it is inactivated are less clear. CaMKK2 inhibition protects against prostate cancer, hepatocellular carcinoma, and metabolic derangements induced by a high-fat diet; therefore, elucidating the intracellular mechanisms that inactivate CaMKK2 has important therapeutic implications. Here we show that stimulation of cAMP-dependent protein kinase A (PKA) signaling in cells inactivates CaMKK2 by phosphorylation of three conserved serine residues. PKA-dependent phosphorylation of Ser⁴⁹⁵ directly impairs calcium-calmodulin activation, whereas phosphorylation of Ser¹⁰⁰ and Ser⁵¹¹ mediate recruitment of 14-3-3 adaptor proteins that hold CaMKK2 in the inactivated state by preventing dephosphorylation of phospho-Ser⁴⁹⁵ We also report the crystal structure of 14-3-3ζ bound to a synthetic diphosphorylated peptide that reveals how the canonical (Ser⁵¹¹) and noncanonical (Ser¹⁰⁰) 14-3-3 consensus sites on CaMKK2 cooperate to bind 14-3-3 proteins. Our findings provide detailed molecular insights into how cAMP-PKA signaling inactivates CaMKK2 and reveals a pathway to inhibit CaMKK2 with potential for treating human diseases.

Phosphorylation on Ser-359 of the α2 subunit in GABA type A receptors down-regulates their density at inhibitory synapses

GABA type A receptors (GABA_ARs) mediate fast synaptic inhibition and are trafficked to functionally diverse synapses. However, the precise molecular mechanisms that regulate the synaptic targeting of these receptors are unclear. Whereas it has been previously shown that phosphorylation events in α4, β, and γ subunits of GABA_ARs govern their function and trafficking, phosphorylation of other subunits has not yet been demonstrated. Here, we show that the α2 subunit of GABA_ARs is phosphorylated at Ser-359 and enables dynamic regulation of GABA_AR binding to the scaffolding proteins gephyrin and collybistin. We initially identified Ser-359 phosphorylation by MS analysis, and additional experiments revealed that it is regulated by the activities of cAMP-dependent protein kinase (PKA) and the protein phosphatase 1 (PP1) and/or PP2A. GST-based pulldowns and coimmunoprecipitation experiments demonstrate preferential binding of both gephyrin and collybistin to WT and an S359A phosphonull variant, but not to an S359D phosphomimetic variant. Furthermore, the decreased capacity of the α2 S359D variant to bind collybistin and gephyrin decreased the density of synaptic α2-containing GABA_AR clusters and caused an absence of α2 enrichment in the axon initial segment. These results suggest that PKA-mediated phosphorylation and PP1/PP2A-dependent dephosphorylation of the α2 subunit play a role in the dynamic regulation of GABA_AR accumulation at inhibitory synapses, thereby regulating the strength of synaptic inhibition. The MS data have been deposited to ProteomeXchange, with the data set identifier PXD019597.

Induction of UCP1 and thermogenesis by a small molecule via AKAP1/PKA modulation

Strategies to increase energy expenditure are an attractive approach to reduce excess fat storage and body weight to improve metabolic health. In mammals, uncoupling protein-1 (UCP1) in brown and beige adipocytes uncouples fatty acid oxidation from ATP generation in mitochondria and promotes energy dissipation as heat. We set out to identify small molecules that enhance UCP1 levels and activity using a high-throughput screen of nearly 12,000 compounds in mouse brown adipocytes. We identified a family of compounds that increase Ucp1 expression and mitochondrial activity (including un-coupled respiration) in mouse brown adipocytes and human brown and white adipocytes. The mechanism of action may be through compound binding to A kinase anchoring protein (AKAP) 1, modulating its localization to mitochondria and its interaction with protein kinase A (PKA), a known node in the β-adrenergic signaling pathway. In mice, the hit compound increased body temperature, UCP1 protein levels, and thermogenic gene expression. Some of the compound effects on mitochondrial function were UCP1- or AKAP1-independent, suggesting compound effects on multiple nodes of energy regulation. Overall, our results highlight a role for AKAP1 in thermogenesis, uncoupled respiration, and regulation energy balance.

A-kinase-anchoring protein 1 (dAKAP1)-based signaling complexes coordinate local protein synthesis at the mitochondrial surface

Compartmentalization of macromolecules is a ubiquitous molecular mechanism that drives numerous cellular functions. The appropriate organization of enzymes in space and time enables the precise transmission and integration of intracellular signals. Molecular scaffolds constrain signaling enzymes to influence the regional modulation of these physiological processes. Mitochondrial targeting of protein kinases and protein phosphatases provides a means to locally control the phosphorylation status and action of proteins on the surface of this organelle. Dual-specificity protein kinase A anchoring protein 1 (dAKAP1) is a multivalent binding protein that targets protein kinase A (PKA), RNAs, and other signaling enzymes to the outer mitochondrial membrane. Many AKAPs recruit a diverse set of binding partners that coordinate a broad range of cellular processes. Here, results of MS and biochemical analyses reveal that dAKAP1 anchors additional components, including the ribonucleoprotein granule components La-related protein 4 (LARP4) and polyadenylate-binding protein 1 (PABPC1). Local translation of mRNAs at organelles is a means to spatially control the synthesis of proteins. RNA-Seq data demonstrate that dAKAP1 binds mRNAs encoding proteins required for mitochondrial metabolism, including succinate dehydrogenase. Functional studies suggest that the loss of dAKAP1-RNA interactions reduces mitochondrial electron transport chain activity. Hence, dAKAP1 plays a previously unappreciated role as a molecular interface between second messenger signaling and local protein synthesis machinery.

The first DEP domain of the RhoGEF P-Rex1 autoinhibits activity and contributes to membrane binding

Phosphatidylinositol (3,4,5)-trisphosphate (PIP₃)-dependent Rac exchanger 1 (P-Rex1) catalyzes the exchange of GDP for GTP on Rac GTPases, thereby triggering changes in the actin cytoskeleton and in transcription. Its overexpression is highly correlated with the metastasis of certain cancers. P-Rex1 recruitment to the plasma membrane and its activity are regulated via interactions with heterotrimeric Gβγ subunits, PIP₃, and protein kinase A (PKA). Deletion analysis has further shown that domains C-terminal to its catalytic Dbl homology (DH) domain confer autoinhibition. Among these, the first dishevelled, Egl-10, and pleckstrin domain (DEP1) remains to be structurally characterized. DEP1 also harbors the primary PKA phosphorylation site, suggesting that an improved understanding of this region could substantially increase our knowledge of P-Rex1 signaling and open the door to new selective chemotherapeutics. Here we show that the DEP1 domain alone can autoinhibit activity in context of the DH/PH-DEP1 fragment of P-Rex1 and interacts with the DH/PH domains in solution. The 3.1 Å crystal structure of DEP1 features a domain swap, similar to that observed previously in the Dvl2 DEP domain, involving an exposed basic loop that contains the PKA site. Using purified proteins, we show that although DEP1 phosphorylation has no effect on the activity or solution conformation of the DH/PH-DEP1 fragment, it inhibits binding of the DEP1 domain to liposomes containing phosphatidic acid. Thus, we propose that PKA phosphorylation of the DEP1 domain hampers P-Rex1 binding to negatively charged membranes in cells, freeing the DEP1 domain to associate with and inhibit the DH/PH module.

The interaction of the mitochondrial protein importer TOMM34 with HSP70 is regulated by TOMM34 phosphorylation and binding to 14-3-3 adaptors

Translocase of outer mitochondrial membrane 34 (TOMM34) orchestrates heat shock protein 70 (HSP70)/HSP90-mediated transport of mitochondrial precursor proteins. Here, using in vitro phosphorylation and refolding assays, analytical size-exclusion chromatography, and hydrogen/deuterium exchange MS, we found that TOMM34 associates with 14-3-3 proteins after its phosphorylation by protein kinase A (PKA). PKA preferentially targeted two serine residues in TOMM34: Ser93 and Ser160, located in the tetratricopeptide repeat 1 (TPR1) domain and the interdomain linker, respectively. Both of these residues were necessary for efficient 14-3-3 protein binding. We determined that phosphorylation-induced structural changes in TOMM34 are further augmented by binding to 14-3-3, leading to destabilization of TOMM34's secondary structure. We also observed that this interaction with 14-3-3 occludes the TOMM34 interaction interface with ATP-bound HSP70 dimers, which leaves them intact and thereby eliminates an inhibitory effect of TOMM34 on HSP70-mediated refolding in vitro In contrast, we noted that TOMM34 in complex with 14-3-3 could bind HSP90. Both TOMM34 and 14-3-3 participated in cytosolic precursor protein transport mediated by the coordinated activities of HSP70 and HSP90. Our results provide important insights into how PKA-mediated phosphorylation and 14-3-3 binding regulate the availability of TOMM34 for its interaction with HSP70.

The KDM Inhibitor GSKJ4 Triggers CREB Downregulation via a Protein Kinase A and Proteasome-Dependent Mechanism in Human Acute Myeloid Leukemia Cells

Acute myeloid leukemia (AML) is a progressive hematopoietic-derived cancer arising from stepwise genetic mutations of the myeloid lineage. cAMP response element-binding protein (CREB) is a nuclear transcription factor, which plays a key role in the multistep process of leukemogenesis, thus emerging as an attractive potential drug target for AML treatment. Since epigenetic dysregulations, such as DNA methylation, histone modifications, as well as chromatin remodeling, are a frequent occurrence in AML, an increasing and selective number of epi-drugs are emerging as encouraging therapeutic agents. Here, we demonstrate that the histone lysine demethylases (KDMs) JMJD3/UTX inhibitor GSKJ4 results in both proliferation decrease and CREB protein downregulation in AML cells. We found that GSKJ4 clearly decreases CREB protein, but not CREB mRNA levels. By cycloheximide assay, we provide evidence that GSKJ4 reduces CREB protein stability; moreover, proteasome inhibition largely counteracts the GSKJ4-induced CREB downregulation. Very interestingly, a rapid CREB phosphorylation at the Ser133 residue precedes CREB protein decrease in response to GSKJ4 treatment. In addition, protein kinase A (PKA) inhibition, but not extracellular signal-regulated kinase (ERK)1/2 inhibition, almost completely prevents both GSKJ4-induced p-Ser133-CREB phosphorylation and CREB protein downregulation. Overall, our study enforces the evidence regarding CREB as a potential druggable target, identifies the small epigenetic molecule GSKJ4 as an “inhibitor” of CREB, and encourages the design of future GSKJ4-based studies for the development of innovative approaches for AML therapy.

Transforming growth factor β (TGF-β) receptor signaling regulates kinase networks and phosphatidylinositol metabolism during T-cell activation

The cytokine content in tissue microenvironments shapes the functional capacity of a T cell. This capacity depends on the integration of extracellular signaling through multiple receptors, including the T-cell receptor (TCR), co-receptors, and cytokine receptors. Transforming growth factor β (TGF-β) signals through its cognate receptor, TGFβR, to SMAD family member proteins and contributes to the generation of a transcriptional program that promotes regulatory T-cell differentiation. In addition to transcription, here we identified specific signaling networks that are regulated by TGFβR. Using an array of biochemical approaches, including immunoblotting, kinase assays, immunoprecipitation, and flow cytometry, we found that TGFβR signaling promotes the formation of a SMAD3/4-protein kinase A (PKA) complex that activates C-terminal Src kinase (CSK) and thereby down-regulates kinases involved in proximal TCR activation. Additionally, TGFβR signaling potentiated CSK phosphorylation of the P85 subunit in the P85-P110 phosphoinositide 3-kinase (PI3K) heterodimer, which reduced PI3K activity and down-regulated the activation of proteins that require phosphatidylinositol (3,4,5)-trisphosphate (PtdIns(3,4,5)P3) for their activation. Moreover, TGFβR-mediated disruption of the P85-P110 interaction enabled P85 binding to a lipid phosphatase, phosphatase and tensin homolog (PTEN), aiding in the maintenance of PTEN abundance and thereby promoting elevated PtdIns(4,5)P2 levels in response to TGFβR signaling. Taken together, these results highlight that TGF-β influences the trajectory of early T-cell activation by altering PI3K activity and PtdIns levels.

Reduction of protein phosphatase 2A (PP2A) complexity reveals cellular functions and dephosphorylation motifs of the PP2A/B'δ holoenzyme

Protein phosphatase 2A (PP2A) is a large enzyme family responsible for most cellular Ser/Thr dephosphorylation events. PP2A substrate specificity, localization, and regulation by second messengers rely on more than a dozen regulatory subunits (including B/R2, B'/R5, and B″/R3), which form the PP2A heterotrimeric holoenzyme by associating with a dimer comprising scaffolding (A) and catalytic (C) subunits. Because of partial redundancy and high endogenous expression of PP2A holoenzymes, traditional approaches of overexpressing, knocking down, or knocking out PP2A regulatory subunits have yielded only limited insights into their biological roles and substrates. To this end, here we sought to reduce the complexity of cellular PP2A holoenzymes. We used tetracycline-inducible expression of pairs of scaffolding and regulatory subunits with complementary charge-reversal substitutions in their interaction interfaces. For each of the three regulatory subunit families, we engineered A/B charge-swap variants that could bind to one another, but not to endogenous A and B subunits. Because endogenous Aα was targeted by a co-induced shRNA, endogenous B subunits were rapidly degraded, resulting in expression of predominantly a single PP2A heterotrimer composed of the A/B charge-swap pair and the endogenous catalytic subunit. Using B'δ/PPP2R5D, we show that PP2A complexity reduction, but not PP2A overexpression, reveals a role of this holoenzyme in suppression of extracellular signal-regulated kinase signaling and protein kinase A substrate dephosphorylation. When combined with global phosphoproteomics, the PP2A/B'δ reduction approach identified consensus dephosphorylation motifs in its substrates and suggested that residues surrounding the phosphorylation site play roles in PP2A substrate specificity.

A-kinase anchoring protein 8L interacts with mTORC1 and promotes cell growth

mTOR complex 1 (mTORC1) senses nutrients to mediate anabolic processes within the cell. Exactly how mTORC1 promotes cell growth remains unclear. Here, we identified a novel mTORC1-interacting protein called protein kinase A anchoring protein 8L (AKAP8L). Using biochemical assays, we found that the N-terminal region of AKAP8L binds to mTORC1 in the cytoplasm. Importantly, loss of AKAP8L decreased mTORC1-mediated processes such as translation, cell growth, and cell proliferation. AKAPs anchor protein kinase A (PKA) through PKA regulatory subunits, and we show that AKAP8L can anchor PKA through regulatory subunit Iα. Reintroducing full-length AKAP8L into cells restored mTORC1-regulated processes, whereas reintroduction of AKAP8L missing the N-terminal region that confers the interaction with mTORC1 did not. Our results suggest a multifaceted role for AKAPs in the cell. We conclude that mTORC1 appears to regulate cell growth, perhaps in part through AKAP8L.

Disruption of AKAP-PKA Interaction Induces Hypercontractility With Concomitant Increase in Proliferation Markers in Human Airway Smooth Muscle

With the ability to switch between proliferative and contractile phenotype, airway smooth muscle (ASM) cells can contribute to the progression of airway diseases such as asthma and chronic obstructive pulmonary disease (COPD), in which airway obstruction is associated with ASM hypertrophy and hypercontractility. A-kinase anchoring proteins (AKAPs) have emerged as important regulatory molecules in various tissues, including ASM cells. AKAPs can anchor the regulatory subunits of protein kinase A (PKA), and guide cellular localization via various targeting domains. Here we investigated whether disruption of the AKAP-PKA interaction, by the cell permeable peptide stearated (st)-Ht31, alters human ASM proliferation and contractility. Treatment of human ASM with st-Ht31 enhanced the expression of protein markers associated with cell proliferation in both cultured cells and intact tissue, although this was not accompanied by an increase in cell viability or cell-cycle progression, suggesting that disruption of AKAP-PKA interaction on its own is not sufficient to drive ASM cell proliferation. Strikingly, st-Ht31 enhanced contractile force generation in human ASM tissue with concomitant upregulation of the contractile protein α-sm-actin. This upregulation of α-sm-actin was independent of mRNA stability, transcription or translation, but was dependent on proteasome function, as the proteasome inhibitor MG-132 prevented the st-Ht31 effect. Collectively, the AKAP-PKA interaction appears to regulate markers of the multi-functional capabilities of ASM, and this alter the physiological function, such as contractility, suggesting potential to contribute to the pathophysiology of airway diseases.

Human cardiac myosin-binding protein C restricts actin structural dynamics in a cooperative and phosphorylation-sensitive manner

Cardiac myosin-binding protein C (cMyBP-C) is a thick filament-associated protein that influences actin-myosin interactions. cMyBP-C alters myofilament structure and contractile properties in a protein kinase A (PKA) phosphorylation-dependent manner. To determine the effects of cMyBP-C and its phosphorylation on the microsecond rotational dynamics of actin filaments, we attached a phosphorescent probe to F-actin at Cys-374 and performed transient phosphorescence anisotropy (TPA) experiments. Binding of cMyBP-C N-terminal domains (C0-C2) to labeled F-actin reduced rotational flexibility by 20-25°, indicated by increased final anisotropy of the TPA decay. The effects of C0-C2 on actin TPA were highly cooperative (n = ∼8), suggesting that the cMyBP-C N terminus impacts the rotational dynamics of actin spanning seven monomers (i.e. the length of tropomyosin). PKA-mediated phosphorylation of C0-C2 eliminated the cooperative effects on actin flexibility and modestly increased actin rotational rates. Effects of Ser to Asp phosphomimetic substitutions in the M-domain of C0-C2 on actin dynamics only partially recapitulated the phosphorylation effects. C0-C1 (lacking M-domain/C2) similarly exhibited reduced cooperativity, but not as reduced as by phosphorylated C0-C2. These results suggest an important regulatory role of the M-domain in cMyBP-C effects on actin structural dynamics. In contrast, phosphomimetic substitution of the glycogen synthase kinase (GSK3β) site in the Pro/Ala-rich linker of C0-C2 did not significantly affect the TPA results. We conclude that cMyBP-C binding and PKA-mediated phosphorylation can modulate actin dynamics. We propose that these N-terminal cMyBP-C-induced changes in actin dynamics help explain the functional effects of cMyBP-C phosphorylation on actin-myosin interactions.

The phosphorylation status of Ser-637 in dynamin-related protein 1 (Drp1) does not determine Drp1 recruitment to mitochondria

Recruitment of the GTPase dynamin-related protein 1 (Drp1) to mitochondria is a central step required for mitochondrial fission. Reversible Drp1 phosphorylation has been implicated in the regulation of this process, but whether Drp1 phosphorylation at Ser-637 determines its subcellular localization and fission activity remains to be fully elucidated. Here, using HEK 293T cells and immunofluorescence, immunoblotting, RNAi, subcellular fractionation, co-immunoprecipitation assays, and CRISPR/Cas9 genome editing, we show that Drp1 phosphorylated at Ser-637 (Drp1^pS637) resides both in the cytosol and on mitochondria. We found that the receptors mitochondrial fission factor (Mff) and mitochondrial elongation factor 1/2 (MIEF1/2) interact with and recruit Drp1^pS637 to mitochondria and that elevated Mff or MIEF levels promote Drp1^pS637 accumulation on mitochondria. We also noted that protein kinase A (PKA), which mediates phosphorylation of Drp1 on Ser-637, is partially present on mitochondria and interacts with both MIEFs and Mff. PKA knockdown did not affect the Drp1-Mff interaction, but slightly enhanced the interaction between Drp1 and MIEFs. In Drp1-deficient HEK 293T cells, both phosphomimetic Drp1-S637D and phospho-deficient Drp1-S637A variants, like wild-type Drp1, located to the cytosol and to mitochondria and rescued a Drp1 deficiency-induced mitochondrial hyperfusion phenotype. However, Drp1-S637D was less efficient than Drp1-WT and Drp1-S637A in inducing mitochondrial fission. In conclusion, the Ser-637 phosphorylation status in Drp1 is not a determinant that controls Drp1 recruitment to mitochondria.

The peptide hormone adropin regulates signal transduction pathways controlling hepatic glucose metabolism in a mouse model of diet-induced obesity

The peptide hormone adropin regulates energy metabolism in skeletal muscle and plays important roles in the regulation of metabolic homeostasis. Besides muscle, the liver has an essential role in regulating glucose homeostasis. Previous studies have reported that treatment of diet-induced obese (DIO) male mice with adropin34-76 (the putative secreted domain) reduces fasting blood glucose independently of body weight changes, suggesting that adropin suppresses glucose production in the liver. Here, we explored the molecular mechanisms underlying adropin's effects on hepatic glucose metabolism in DIO mice. Male DIO B6 mice maintained on a high-fat diet received five intraperitoneal injections of adropin34-76 (450 nmol/kg/injection) over a 48-h period. We found that adropin34-76 enhances major intracellular signaling activities in the liver that are involved in insulin-mediated regulation of glucose homeostasis. Moreover, treatment with adropin34-76 alleviated endoplasmic reticulum stress responses and reduced activity of c-Jun N-terminal kinase in the liver, explaining the enhanced activities of hepatic insulin signaling pathways observed with adropin34-76 treatment. Furthermore, adropin34-76 suppressed cAMP activated protein kinase A (PKA) activities, resulting in reduced phosphorylation of inositol trisphosphate receptor, which mediates endoplasmic reticulum calcium efflux, and of cAMP-responsive element-binding protein, a key transcription factor in hepatic regulation of glucose metabolism. Adropin34-76 directly affected liver metabolism, decreasing glucose production and reducing PKA-mediated phosphorylation in primary mouse hepatocytes in vitro Our findings indicate that major hepatic signaling pathways contribute to the improved glycemic control achieved with adropin34-76 treatment in situations of obesity.

AKAP6 and phospholamban colocalize and interact in HEK-293T cells and primary murine cardiomyocytes

Phospholamban (PLN) is an important Ca²⁺ modulator at the sarcoplasmic reticulum (SR) of striated muscles. It physically interacts and inhibits sarcoplasmic reticulum Ca²⁺ATPase (SERCA2) function, whereas a protein kinase A (PKA)‐dependent phosphorylation at its serine 16 reverses the inhibition. The underlying mechanism of this post‐translational modification, however, remains not fully understood. Using publicly available databases, we identified A‐kinase anchoring protein 6 (AKAP6) as a candidate that might play some roles in PLN phosphorylation. Immunofluorescence showed colocalization between GFP‐AKAP6 and PLN in transfected HEK‐293T cells and cultured mouse neonatal cardiomyocytes (CMNCs). Co‐immunoprecipitation confirmed the functional interaction between AKAP6 and PLN in HEK‐293T and isolated adult rat cardiomyocytes in response to isoproterenol stimulation. Functionally, AKAP6 promoted Ca²⁺ uptake activity of SERCA1 in cotransfected HEK‐293T cells despite the presence of PLN. These results were further confirmed in adult rat cardiomyocytes. Immunofluorescence showed colocalization of both proteins around the perinuclear region, while protein–protein interaction was corroborated by immunoprecipitation of the nucleus‐enriched fraction of rat hearts. Our findings suggest AKAP6 as a novel interacting partner to PLN in HEK‐293T and murine cardiomyocytes.

FSH/LH-Dependent Upregulation of Ahr in Murine Granulosa Cells Is Controlled by PKA Signaling and Involves Epigenetic Regulation

The aryl hydrocarbon receptor (Ahr) is a ligand-activated transcription factor primarily known for its toxicological functions. Recent studies have established its importance in many physiological processes including female reproduction, although there is limited data about the precise mechanisms how Ahr itself is regulated during ovarian follicle maturation. This study describes the expression of Ahr in ovarian granulosa cells (GCs) of immature mice in a gonadotropin-dependent manner. We show that Ahr upregulation in vivo requires both follicle stimulating hormone (FSH) and luteinizing hormone (LH) activities. FSH alone increased Ahr mRNA, but had no effect on Ahr protein level, implicating a possible LH-dependent post-transcriptional regulation. Also, the increase in Ahr protein is specific to large antral follicles in induced follicle maturation. We show that Ahr expression in GCs of mid-phase follicular maturation is downregulated by protein kinase A (PKA) signaling and activation of Ahr promoter is regulated by chromatin remodeling.

Reversible phosphorylation: a birthday tribute to Herb Tabor

Herb Tabor was the Editor-in-Chief of the Journal of Biological Chemistry (JBC) spanning the years 1971-2010. This year, Herb turns 100. What do you give a person turning 100? Our answer to this question was to dedicate two of our favorite JBC papers to Herb. Both of these papers focus on reversible phosphorylation, which we briefly review. In addition, we delve into a new finding that centers around a novel family of secreted kinases, suggesting that there are many new and exciting discoveries yet to explore.

Protein kinase A-mediated phosphorylation of naked cuticle homolog 2 stimulates cell-surface delivery of transforming growth factor-α for epidermal growth factor receptor transactivation

The classic mode of G protein-coupled receptor (GPCR)-mediated transactivation of the receptor tyrosine kinase epidermal growth factor receptor (EGFR) transactivation occurs via matrix metalloprotease (MMP)-mediated cleavage of plasma membrane-anchored EGFR ligands. Herein, we show that the Gαs-activating GPCR ligands vasoactive intestinal peptide (VIP) and prostaglandin E2 (PGE2 ) transactivate EGFR through increased cell-surface delivery of the EGFR ligand transforming growth factor-α (TGFα) in polarizing madin-darby canine kidney (MDCK) and Caco-2 cells. This is achieved by PKA-mediated phosphorylation of naked cuticle homolog 2 (NKD2), previously shown to bind TGFα and direct delivery of TGFα-containing vesicles to the basolateral surface of polarized epithelial cells. VIP and PGE2 rapidly activate protein kinase A (PKA) that then phosphorylates NKD2 at Ser-223, a process that is facilitated by the molecular scaffold A-kinase anchoring protein 12 (AKAP12). This phosphorylation stabilized NKD2, ensuring efficient cell-surface delivery of TGFα and increased EGFR activation. Thus, GPCR-triggered, PKA/AKAP12/NKD2-regulated targeting of TGFα to the cell surface represents a new mode of EGFR transactivation that occurs proximal to ligand cleavage by MMPs.

Phosphorylation of HSP90 by protein kinase A is essential for the nuclear translocation of androgen receptor

The androgen receptor (AR) is often activated in prostate cancer patients undergoing androgen-ablative therapy because of the activation of cellular pathways that stimulate the AR despite low androgen levels. In many of these tumors, the cAMP-dependent protein kinase A (PKA) pathway is activated. Previous studies have shown that PKA can synergize with low levels of androgen to enhance androgen signaling and consequent cell proliferation, leading to castration-resistant prostate cancer. However, the mechanism by which PKA causes AR stimulation in the presence of low/no androgen is not established yet. Here, using immunofluorescence immunoblotting assays, co-immunoprecipitation, siRNA-mediated gene silencing, and reporter gene assays, we demonstrate that PKA activation is necessary for the phosphorylation of heat shock protein (HSP90) that binds to unliganded AR in the cytoplasm, restricting its entry into the nucleus. We also found that PKA-mediated phosphorylation of the Thr⁸⁹ residue in HSP90 releases AR from HSP90, enabling AR binding to HSP27 and its migration into the nucleus. Substitution of the Thr⁸⁹ in HSP90 prevented its phosphorylation by PKA and significantly reduced AR transactivation and cellular proliferation. We further observed that the transcription of AR target genes, such as prostate-specific antigen (PSA), is also lowered in the HSP90 Thr⁸⁹ variant. These results suggest that using a small-molecule inhibitor against the HSP90 Thr⁸⁹ residue in conjunction with existing androgen-ablative therapy may be more effective than androgen-ablative therapy alone in the treatment of prostate cancer patients.

cAMP-dependent activation of the Rac guanine exchange factor P-REX1 by type I protein kinase A (PKA) regulatory subunits

Regulatory subunits of protein kinase A (PKA) inhibit its kinase subunits. Intriguingly, their potential as cAMP-dependent signal transducers remains uncharacterized. We recently reported that type I PKA regulatory subunits (RIα) interact with phosphatidylinositol 3,4,5-trisphosphate-dependent Rac exchange factor 1 (P-REX1), a chemotactic Rac guanine exchange factor (RacGEF). Because P-REX1 is known to be phosphorylated and inhibited by PKA, its interaction with RIα suggests that PKA regulatory and catalytic subunits may fine-tune P-REX1 activity or those of its target pools. Here, we tested whether RIα acts as a cAMP-dependent factor promoting P-REX1-mediated Rac activation and cell migration. We observed that Gs-coupled EP2 receptors indeed promote endothelial cell migration via RIα-activated P-REX1. Expression of the P-REX1-PDZ1 domain prevented RIα/P-REX1 interaction, P-REX1 activation, and EP2-dependent cell migration, and P-REX1 silencing abrogated RIα-dependent Rac activation. RIα-specific cAMP analogs activated P-REX1, but lost this activity in RIα-knockdown cells, and cAMP pulldown assays revealed that P-REX1 preferentially interacts with free RIα. Moreover, purified RIα directly activated P-REX1 in vitro We also found that the RIα CNB-B domain is critical for the interaction with P-REX1, which was increased in RIα mutants, such as the acrodysostosis-associated mutant, that activate P-REX1 at basal cAMP levels. RIα and Cα PKA subunits targeted distinct P-REX1 molecules, indicated by an absence of phosphorylation in the active fraction of P-REX1. This was in contrast to the inactive fraction in which phosphorylated P-REX1 was present, suggesting co-existence of dual stimulatory and inhibitory effects. We conclude that PKA's regulatory subunits are cAMP-dependent signal transducers.

Preferential generation of Ca2+-permeable AMPA receptors by AKAP79-anchored protein kinase C proceeds via GluA1 subunit phosphorylation at Ser-831

AMPA-type glutamate receptors (AMPARs) mediate fast excitatory neurotransmission in the mammalian central nervous system. Preferential AMPAR subunit assembly favors heteromeric GluA1/GluA2 complexes. The presence of the GluA2 subunit generates Ca²⁺-impermeable (CI) AMPARs that have linear current-voltage (I-V) relationships. However, diverse forms of synaptic plasticity and pathophysiological conditions are associated with shifts from CI to inwardly rectifying, GluA2-lacking, Ca²⁺-permeable (CP) AMPARs on time scales ranging from minutes to days. These shifts have been linked to GluA1 phosphorylation at Ser-845, a protein kinase A (PKA)-targeted site within its intracellular C-terminal tail, often in conjunction with protein kinase A anchoring protein 79 (AKAP79; AKAP150 in rodents), which targets PKA to GluA1. However, AKAP79 may impact GluA1 phosphorylation at other sites by interacting with other signaling enzymes. Here, we evaluated the ability of AKAP79, its signaling components, and GluA1 phosphorylation sites to induce CP-AMPARs under conditions in which CI-AMPARs normally predominate. We found that GluA1 phosphorylation at Ser-831 is sufficient for the appearance of CP-AMPARs and that AKAP79-anchored protein kinase C (PKC) primarily drives the appearance of these receptors via this site. In contrast, other AKAP79-signaling components and C-terminal tail GluA1 phosphorylation sites exhibited a permissive role, limiting the extent to which AKAP79 promotes CP-AMPARs. This may reflect the need for these sites to undergo active phosphorylation/dephosphorylation cycles that control their residency within distinct subcellular compartments. These findings suggest that AKAP79, by orchestrating phosphorylation, represents a key to a GluA1 phosphorylation passcode, which allows the GluA1 subunit to escape GluA2 dominance and promote the appearance of CP-AMPARs.

Depletion of dAKAP1-protein kinase A signaling islands from the outer mitochondrial membrane alters breast cancer cell metabolism and motility

Breast cancer screening and new precision therapies have led to improved patient outcomes. Yet, a positive prognosis is less certain when primary tumors metastasize. Metastasis requires a coordinated program of cellular changes that promote increased survival, migration, and energy consumption. These pathways converge on mitochondrial function, where distinct signaling networks of kinases, phosphatases, and metabolic enzymes regulate these processes. The protein kinase A-anchoring protein dAKAP1 compartmentalizes protein kinase A (PKA) and other signaling enzymes at the outer mitochondrial membrane and thereby controls mitochondrial function and dynamics. Modulation of these processes occurs in part through regulation of dynamin-related protein 1 (Drp1). Here, we report an inverse relationship between the expression of dAKAP1 and mesenchymal markers in breast cancer. Molecular, cellular, and in silico analyses of breast cancer cell lines confirmed that dAKAP1 depletion is associated with impaired mitochondrial function and dynamics, as well as with increased glycolytic potential and invasiveness. Furthermore, disruption of dAKAP1-PKA complexes affected cell motility and mitochondrial movement toward the leading edge in invasive breast cancer cells. We therefore propose that depletion of dAKAP1-PKA "signaling islands" from the outer mitochondrial membrane augments progression toward metastatic breast cancer.