PKA compartmentalization links cAMP signaling and autophagy

Promoting proteostasis by cAMP/PKA and cGMP/PKG

Proteasome functional insufficiency (PFI) is implicated in neurodegeneration and heart failure, where aberrant protein aggregation is common and impairs the ubiquitin (Ub)-proteasome system (UPS), exacerbating increased proteotoxic stress (IPTS) and creating a vicious circle. Breaking this circle represents a key to treating these diseases. Protein kinase (PK)-A and PKG can activate the proteasome and promote proteasomal degradation of misfolded proteins. PKA does so by phosphorylating Ser14-RPN6/PSMD11, but how PKG activates the proteasome remains unknown. Emerging evidence supports a strategy to treat diseases with IPTS by augmenting cAMP/PKA and cGMP/PKG. Conceivably, targeted activation of PKA and PKG at proteasome nanodomains would minimize the undesired effects from their actions on other targets. In this review, we discuss PKA and PKG regulation of proteostasis via the UPS.

Translocon Subunits of the COP9 Signalosome Complex Are a Central Hub for Regulating Multiple Photoresponsive Processes and Autophagic Flux in Magnaporthe oryzae

Photodependent processes, including circadian rhythm, autophagy, ubiquitination, neddylation/deneddylation, and metabolite biosynthesis, profoundly influence microbial pathogenesis. Although a photomorphogenesis signalosome (COP9/CSN) has been identified, the mechanism by which this large complex contributes to the pathophysiological processes in filamentous fungi remains unclear. Here, we identified eight CSN complex subunits in the rice blast fungus Magnaporthe oryzae and functionally characterized the translocon subunits containing a nuclear export or localization signal (NES/NLS). Targeted gene replacement of these CSN subunits, including MoCSN3, MoCSN5, MoCSN6, MoCSN7, and MoCSN12, attenuated vegetative growth and conidiation and rendered the deletion strains nonpathogenic. MoCSN7 deletion significantly suppressed arachidonic acid catabolism, and compromised cell wall integrity in M. oryzae. Surprisingly, we also discovered that MoCSN subunits, particularly MoCsn7, are required for the cAMP-dependent regulation of autophagic flux. Therefore, MoCSN significantly contributes to morphological, physiological, and pathogenic differentiation in M. oryzae by fostering cross-talk between multiple pathways.

Biochemical pharmacology of adenylyl cyclases in cancer

Globally, despite extensive research and pharmacological advancement, cancer remains one of the most common causes of mortality. Understanding the signaling pathways involved in cancer progression is essential for the discovery of new drug targets. The adenylyl cyclase (AC) superfamily comprises glycoproteins that regulate intracellular signaling and convert ATP into cyclic AMP, an important second messenger. The present review highlights the involvement of ACs in cancer progression and suppression, broken down for each specific mammalian AC isoform. The precise mechanisms by which ACs contribute to cancer cell proliferation and invasion are not well understood and are variable among cancer types; however, AC overactivation, along with that of downstream regulators, presents a potential target for novel anticancer therapies. The expression patterns of ACs in numerous cancers are discussed. In addition, we highlight inhibitors of AC-related signaling that are currently under investigation, with a focus on possible anti-cancer strategies. Recent discoveries with small molecules regarding more direct modulation AC activity are also discussed in detail. A more comprehensive understanding of different components in AC-related signaling could potentially lead to the development of novel therapeutic strategies for personalized oncology and might enhance the efficacy of chemoimmunotherapy in the treatment of various cancers.

PMP22 duplication dysregulates lipid homeostasis and plasma membrane organization in developing human Schwann cells

Charcot-Marie-Tooth disease type 1A (CMT1A) is the most common inherited peripheral neuropathy caused by a 1.5 Mb tandem duplication of chromosome 17 harbouring the PMP22 gene. This dose-dependent overexpression of PMP22 results in disrupted Schwann cell myelination of peripheral nerves. To obtain better insights into the underlying pathogenic mechanisms in CMT1A, we investigated the role of PMP22 duplication in cellular homeostasis in CMT1A mouse models and in patient-derived induced pluripotent stem cells differentiated into Schwann cell precursors (iPSC-SCPs). We performed lipidomic profiling and bulk RNA sequencing (RNA-seq) on sciatic nerves of two developing CMT1A mouse models and on CMT1A patient-derived iPSC-SCPs. For the sciatic nerves of the CMT1A mice, cholesterol and lipid metabolism was downregulated in a dose-dependent manner throughout development. For the CMT1A iPSC-SCPs, transcriptional analysis unveiled a strong suppression of genes related to autophagy and lipid metabolism. Gene ontology enrichment analysis identified disturbances in pathways related to plasma membrane components and cell receptor signalling. Lipidomic analysis confirmed the severe dysregulation in plasma membrane lipids, particularly sphingolipids, in CMT1A iPSC-SCPs. Furthermore, we identified reduced lipid raft dynamics, disturbed plasma membrane fluidity and impaired cholesterol incorporation and storage, all of which could result from altered lipid storage homeostasis in the patient-derived CMT1A iPSC-SCPs. Importantly, this phenotype could be rescued by stimulating autophagy and lipolysis. We conclude that PMP22 duplication disturbs intracellular lipid storage and leads to a more disordered plasma membrane owing to an alteration in the lipid composition, which might ultimately lead to impaired axo-glial interactions. Moreover, targeting lipid handling and metabolism could hold promise for the treatment of patients with CMT1A.

Autophagosomes coordinate an AKAP11-dependent regulatory checkpoint that shapes neuronal PKA signaling

Protein Kinase A (PKA) is regulated spatially and temporally via scaffolding of its catalytic (Cα/β) and regulatory (RI/RII) subunits by the A-kinase-anchoring proteins (AKAP). PKA engages in poorly understood interactions with autophagy, a key degradation pathway for neuronal cell homeostasis, partly via its AKAP11 scaffold. Mutations in AKAP11 drive schizophrenia and bipolar disorders (SZ-BP) through unknown mechanisms. Through proteomic-based analysis of immunopurified lysosomes, we identify the Cα-RIα-AKAP11 holocomplex as a prominent autophagy-associated protein kinase complex. AKAP11 scaffolds Cα-RIα to the autophagic machinery via its LC3-interacting region (LIR), enabling both PKA regulation by upstream signals, and its autophagy-dependent degradation. We identify Ser83 on the RIα linker-hinge region as an AKAP11-dependent phospho-residue that modulates RIα-Cα binding and cAMP-induced PKA activation. Decoupling AKAP11-PKA from autophagy alters Ser83 phosphorylation, supporting an autophagy-dependent checkpoint for PKA signaling. Ablating AKAP11 in induced pluripotent stem cell-derived neurons reveals dysregulation of multiple pathways for neuronal homeostasis. Thus, the autophagosome is a novel platform that modulate PKA signaling, providing a possible mechanistic link to SZ/BP pathophysiology.

GLP-1R agonist therapy and vaccine response: Neglected implications

Glucagon-like peptide-1 receptor agonists (GLP-1RAs), such as semaglutide (Ozempic®), have emerged as effective treatments for diabetes and weight management. However, recent evidence indicates that GLP-1R signalling influences various tissues, including the immune system. Notably, GLP-1 has a short half-life (< 5 minutes) and exists in the picomolar range, while GLP-1RAs like semaglutide have extended half-lives of several days and are administered at supraphysiological doses. This review explores the potential impact of these medications on vaccine efficacy. We examine evidence suggesting that GLP-1RAs may attenuate vaccine responses through direct effects on immune cells and modulation of other tissues. Additionally, we discuss how GLP-1R signalling may create a tolerogenic environment, potentially reducing vaccine immunogenicity. Given the widespread use of GLP-1RAs, it is crucial to understand their impact on immune responses and the translational implications for vaccination outcomes.

Adenosine A2A Receptor Antagonist Sch58261 Improves the Cognitive Function in Alzheimer's Disease Model Mice Through Activation of Nrf2 via an Autophagy-Dependent Pathway

Aims: Adenosine, an important endogenous neuromodulator, contributes to a broad set of several neurodegenerative diseases. The adenosine A2A receptor (A2AR) is the most involved in neuropathological effects and plays an important role in the pathogenesis of Alzheimer's disease (AD). However, the effect of A2AR antagonist and the underlying mechanism in AD model mice remains unclear. Results: The amyloid beta (Aβ)1-42-induced mice AD models were used in this study. Several behavioral experiments were performed to evaluate the improvement of AD mice treated with A2AR antagonist. For mechanism analysis, autophagy-related proteins, Kelch-like ECH-associated protein1 (Keap1)-nuclear factor erythroid-derived factor 2-related factor (Nrf2) pathway activation, and synaptic function were studied using Western blot, immunofluorescence, immunohistochemistry, transmission electron microscope, real-time quantitative PCR, and patch clamp. Pharmacological blockade of adenosine A2AR by SCH58261 (SCH) ameliorated cognitive deficits and decreased expression levels of several AD biomarkers, including Aβ and hyperphosphorylation of Tau. Moreover, SCH activated the Nrf2 pathway through autophagy mediated Keap1 degradation, resulting in the improvement of neuron autophagy dysfunction, synaptic plasticity, and synaptic transmission. Innovation: Our data clarified that the SCH (an antagonist of A2AR) could increase the level of autophagy, promote the ability of antioxidative stress by the activation of Keap1-Nrf2 pathway, and improve the synaptic function in Aβ1-42-induced AD mice or cell model, which provided a potential therapeutic strategy for AD. Conclusion: A2AR antagonism represents a promising strategy for the anti-AD agent development through autophagy-dependent pathway.

PKA Activity-Driven Modulation of Bidirectional Long-Distance transport of Lysosomal vesicles During Synapse Maintenance

The bidirectional long-distance transport of organelles is crucial for cell body-synapse communication. However, the mechanisms by which this transport is modulated for synapse formation, maintenance, and plasticity are not fully understood. Here, we demonstrate through quantitative analyses that maintaining sensory neuron-motor neuron synapses in the Aplysia gill-siphon withdrawal reflex is linked to a sustained reduction in the retrograde transport of lysosomal vesicles in sensory neurons. Interestingly, while mitochondrial transport in the anterograde direction increases within 12 hours of synapse formation, the reduction in lysosomal vesicle retrograde transport appears three days after synapse formation. Moreover, we find that formation of new synapses during learning induced by neuromodulatory neurotransmitter serotonin further reduces lysosomal vesicle transport within 24 hours, whereas mitochondrial transport increases in the anterograde direction within one hour of exposure. Pharmacological inhibition of several signaling pathways pinpoints PKA as a key regulator of retrograde transport of lysosomal vesicles during synapse maintenance. These results demonstrate that synapse formation leads to organelle-specific and direction specific enduring changes in long-distance transport, offering insights into the mechanisms underlying synapse maintenance and plasticity.

OPA1 mutation affects autophagy and triggers senescence in autosomal dominant optic atrophy plus fibroblasts

In several cases of mitochondrial diseases, the underlying genetic and bioenergetic causes of reduced oxidative phosphorylation (OxPhos) in mitochondrial dysfunction are well understood. However, there is still limited knowledge about the specific cellular outcomes and factors involved for each gene and mutation, which contributes to the lack of effective treatments for these disorders. This study focused on fibroblasts from a patient with Autosomal Dominant Optic Atrophy (ADOA) plus syndrome harboring a mutation in the Optic Atrophy 1 (OPA1) gene. By combining functional and transcriptomic approaches, we investigated the mitochondrial function and identified cellular phenotypes associated with the disease. Our findings revealed that fibroblasts with the OPA1 mutation exhibited a disrupted mitochondrial network and function, leading to altered mitochondrial dynamics and reduced autophagic response. Additionally, we observed a premature senescence phenotype in these cells, suggesting a previously unexplored role of the OPA1 gene in inducing senescence in ADOA plus patients. This study provides novel insights into the mechanisms underlying mitochondrial dysfunction in ADOA plus and highlights the potential importance of senescence in disease progression.

Metabolic control of mitophagy

Mitochondrial dysfunction is a major hallmark of ageing and related chronic disorders. Controlled removal of damaged mitochondria by the autophagic machinery, a process known as mitophagy, is vital for mitochondrial homeostasis and cell survival. The central role of mitochondria in cellular metabolism places mitochondrial removal at the interface of key metabolic pathways affecting the biosynthesis or catabolism of acetyl-coenzyme A, nicotinamide adenine dinucleotide, polyamines, as well as fatty acids and amino acids. Molecular switches that integrate the metabolic status of the cell, like AMP-dependent protein kinase, protein kinase A, mechanistic target of rapamycin and sirtuins, have also emerged as important regulators of mitophagy. In this review, we discuss how metabolic regulation intersects with mitophagy. We place special emphasis on the metabolic regulatory circuits that may be therapeutically targeted to delay ageing and mitochondria-associated chronic diseases. Moreover, we identify outstanding knowledge gaps, such as the ill-defined distinction between basal and damage-induced mitophagy, which must be resolved to boost progress in this area.

β-asarone improves cognitive impairment and alleviates autophagy in mice with vascular dementia via the cAMP/PKA/CREB pathway

BACKGROUND

Vascular dementia (VD) is the second most common type of dementia after Alzheimer's disease. β-asarone, a major component of Acorus tatarinowii Schott, is important in neurodegenerative and neurovascular diseases. Studies have confirmed that β-asarone can mitigate autophagy and reduce damage in hypoxic cells. We also reported that β-asarone improves learning and memory. This study further clarifies whether β-asarone attenuates cerebral ischaemic injury by acting through the cAMP/PKA/CREB pathway in VD model mice.

METHODS

Here, genes and potential pathways that may be targeted by β-asarone for the treatment of transient cerebral ischaemia (TCI) and cognitive impairment (CI) were obtained using network pharmacology. The two-vessel occlusion method was used to establish the VD model. The Morris water maze test was used to evaluate the effects on memory. Then, the protein levels of mitofusin-2 (Mfn2), brain-derived neurotrophic factor (BDNF), optic atrophy 1 (OPA1), cyclic adenosine monophosphate (cAMP), myelin basic protein (MBP), matrix metalloproteinase-9 (MMP9) and neuron specific enolase (NSE) were determined by ELISA. The levels of superoxide dismutase (SOD) and malonaldehyde (MDA) were measured using commercial kits. Then, qRT-PCR was employed to investigate the expression of the candidate genes screened from the protein-protein interaction (PPI) network. Furthermore, the expression of the autophagy-related proteins Beclin-1, (microtubule-associated protein light chain 3) LC3, p62, postsynaptic density protein 95 (PSD95), protein kinase A (PKA), pPKA, cyclic-AMP response binding protein (CREB), and pCREB was determined by western blotting. The expression of autophagy-related proteins, PSD95 and translocase of outer mitochondrial membrane 20 (TOM20) was determined by immunofluorescence analyses.

RESULTS

The network pharmacological analysis showed 234 targets related to β-asarone, 1,118 genes related to TCI and 2,039 genes associated with CI. Our results confirm that β-asarone treatment not only alleviated brain damage in the VD model by improving mitochondrial and synaptic function, reducing neuronal injury and upregulating the expression of antioxidants but also effectively improved the cognitive behaviour of VD model mice. Moreover, β-asarone downregulated VD-induced RELA and CCND1 mRNA expression. In addition, we validated that β-asarone increased the phosphorylation of PKA and CREB and upregulated cAMP protein expression. The results showed that the cAMP/PKA/CREB signalling pathway was upregulated. Moreover, β-asarone administration decreased the protein expression levels of Beclin-1 and LC3 and increased the expression levels of p62 in VD model mice.

CONCLUSIONS

β-asarone inhibits Beclin-1-dependent autophagy and upregulates the cAMP/PKA/CREB signalling pathway to attenuate mitochondrial and synaptic damage from cerebral ischaemia and improve learning and cognitive abilities in VD model mice.

Crystal Structures Reveal Hidden Domain Mechanics in Protein Kinase A (PKA)

Cyclic-AMP-dependent protein kinase A (PKA) is a critical enzyme involved in various signaling pathways that plays a crucial role in regulating cellular processes including metabolism, gene transcription, cell proliferation, and differentiation. In this study, the mechanisms of allostery in PKA were investigated by analyzing the vast repertoire of crystal structures available in the RCSB database. From existing structures of murine and human PKA, we elucidated the conformational ensembles and protein dynamics that are altered in a ligand-dependent manner. Distance metrics to analyze conformations of the G-loop were proposed to delineate different states of PKA and were compared to existing structural metrics. Furthermore, ligand-dependent flexibility was investigated through normalized B'-factors to better understand the inherent dynamics in PKA. The presented study provides a contemporary approach to traditional methods in engaging the use of crystal structures for understanding protein dynamics. Importantly, our studies provide a deeper understanding into the conformational ensemble of PKA as the enzyme progresses through its catalytic cycle. These studies provide insights into kinase regulation that can be applied to both PKA individually and protein kinases as a class.

Cyclic AMP induces reversible EPAC1 condensates that regulate histone transcription

The second messenger cyclic AMP regulates many nuclear processes including transcription, pre-mRNA splicing and mitosis. While most functions are attributed to protein kinase A, accumulating evidence suggests that not all nuclear cyclic AMP-dependent effects are mediated by this kinase, implying that other effectors may be involved. Here we explore the nuclear roles of Exchange Protein Activated by cyclic AMP 1. We find that it enters the nucleus where forms reversible biomolecular condensates in response to cyclic AMP. This phenomenon depends on intrinsically disordered regions present at its amino-terminus and is independent of protein kinase A. Finally, we demonstrate that nuclear Exchange Protein Activated by cyclic AMP 1 condensates assemble at genomic loci on chromosome 6 in the proximity of Histone Locus Bodies and promote the transcription of a histone gene cluster. Collectively, our data reveal an unexpected mechanism through which cyclic AMP contributes to nuclear spatial compartmentalization and promotes the transcription of specific genes.

MAGED2 Depletion Promotes Stress-Induced Autophagy by Impairing the cAMP/PKA Pathway

Melanoma-associated antigen D2 (MAGED2) plays an essential role in activating the cAMP/PKA pathway under hypoxic conditions, which is crucial for stimulating renal salt reabsorption and thus explaining the transient variant of Bartter's syndrome. The cAMP/PKA pathway is also known to regulate autophagy, a lysosomal degradation process induced by cellular stress. Previous studies showed that two members of the melanoma-associated antigens MAGE-family inhibit autophagy. To explore the potential role of MAGED2 in stress-induced autophagy, specific MAGED2-siRNA were used in HEK293 cells under physical hypoxia and oxidative stress (cobalt chloride, hypoxia mimetic). Depletion of MAGED2 resulted in reduced p62 levels and upregulation of both the autophagy-related genes (ATG5 and ATG12) as well as the autophagosome marker LC3II compared to control siRNA. The increase in the autophagy markers in MAGED2-depleted cells was further confirmed by leupeptin-based assay which concurred with the highest LC3II accumulation. Likewise, under hypoxia, immunofluorescence in HEK293, HeLa and U2OS cell lines demonstrated a pronounced accumulation of LC3B puncta upon MAGED2 depletion. Moreover, LC3B puncta were absent in human fetal control kidneys but markedly expressed in a fetal kidney from a MAGED2-deficient subject. Induction of autophagy with both physical hypoxia and oxidative stress suggests a potentially general role of MAGED2 under stress conditions. Various other cellular stressors (brefeldin A, tunicamycin, 2-deoxy-D-glucose, and camptothecin) were analyzed, which all induced autophagy in the absence of MAGED2. Forskolin (FSK) inhibited, whereas GNAS Knockdown induced autophagy under hypoxia. In contrast to other MAGE proteins, MAGED2 has an inhibitory role on autophagy only under stress conditions. Hence, a prominent role of MAGED2 in the regulation of autophagy under stress conditions is evident, which may also contribute to impaired fetal renal salt reabsorption by promoting autophagy of salt-transporters in patients with MAGED2 mutation.

The interrelation of galectins and autophagy

Autophagy is a vital physiological process that maintains intracellular homeostasis by removing damaged organelles and senescent or misfolded molecules. However, excessive autophagy results in cell death and apoptosis, which will lead to a variety of diseases. Galectins are a type of animal lectin that binds to β-galactosides and can bind to the cell surface or extracellular matrix glycans, affecting a variety of immune processes in vivo and being linked to the development of many diseases. In many cases, galectins and autophagy both play important regulatory roles in the cellular life course, yet our understanding of the relationship between them is still incomplete. Galectins and autophagy may share common etiological cofactors for some diseases. Hence, we summarize the relationship between galectins and autophagy, aiming to draw attention to the existence of multiple associations between galectins and autophagy in a variety of physiological and pathological processes, which provide new ideas for etiological diagnosis, drug development, and therapeutic targets for related diseases.

WGCNA based identification of hub genes associated with cold response and development in Apis mellifera metamorphic pupae

Honeybee is a crucial pollinator in nature, and plays an indispensable role in both agricultural production and scientific research. In recent decades, honeybee was challenged with health problems by biotic and abiotic stresses. As a key ecological factor, temperature has been proved to have an impact on the survival and production efficiency of honeybees. Previous studies have demonstrated that low temperature stress can affect honeybee pupation and shorten adult longevity. However, the molecular mechanism underlying the effects of low temperatures on honeybee growth and development during their developmental period remain poorly understood. In this paper, the weighted gene co-expression analysis (WGCNA) was employed to explore the molecular mechanisms underpinnings of honeybees' respond to low temperatures (20°C) during four distinct developmental stages: large-larvae, prepupae, early-pupae and mid-pupae. Through an extensive transcriptome analysis, thirteen gene co-expression modules were identified and analyzed in relation to honeybee development and stress responses. The darkorange module was found to be associated with low temperature stress, with its genes primarily involved in autophagy-animal, endocytosis and MAPK signaling pathways. Four hub genes were identified within this module, namely, loc726497, loc409791, loc410923, and loc550857, which may contribute to honeybee resistance to low temperature and provide insight into the underlying mechanism. The gene expression patterns of grey60 and black modules were found to correspond to the developmental stages of prepupae and early-pupae, respectively, with the hub genes loc409494, loc725756, loc552457, loc726158, Ip3k and Lcch3 in grey60 module likely involved in brain development, and the hub genes loc410555 in black module potentially related to exoskeleton development. The brown module genes exhibited a distinct pattern of overexpression in mid-pupae specimens, with genes primarily enriched in oxidative phosphorylation, citrate cycle and other pathways, which may be related to the formation of bee flying muscle. No related gene expression module was found for mature larvae stage. These findings provide valuable insights into the developmental process of honeybees at molecular level during the capped brood stage.

Impact of context-dependent autophagy states on tumor progression

Macroautophagy is a cellular quality-control process that degrades proteins, protein aggregates and damaged organelles. Autophagy plays a fundamental role in cancer where, in the presence of stressors (for example, nutrient starvation, hypoxia, mechanical pressure), tumor cells activate it to degrade intracellular substrates and provide energy. Cell-autonomous autophagy in tumor cells and cell-nonautonomous autophagy in the tumor microenvironment and in the host converge on mechanisms that modulate metabolic fitness, DNA integrity and immune escape and, consequently, support tumor growth. In this Review, we will discuss insights into the tumor-modulating roles of autophagy in different contexts and reflect on how future studies using physiological culture systems may help to understand the complexity and open new therapeutic avenues.

Defective BVES-mediated feedback control of cAMP in muscular dystrophy

Biological processes incorporate feedback mechanisms to enable positive and/or negative regulation. cAMP is an important second messenger involved in many aspects of muscle biology. However, the feedback mechanisms for the cAMP signaling control in skeletal muscle are largely unknown. Here we show that blood vessel epicardial substance (BVES) is a negative regulator of adenylyl cyclase 9 (ADCY9)-mediated cAMP signaling involved in maintaining muscle mass and function. BVES deletion in mice reduces muscle mass and impairs muscle performance, whereas virally delivered BVES expressed in Bves-deficient skeletal muscle reverses these defects. BVES interacts with and negatively regulates ADCY9's activity. Disruption of BVES-mediated control of cAMP signaling leads to an increased protein kinase A (PKA) signaling cascade, thereby promoting FoxO-mediated ubiquitin proteasome degradation and autophagy initiation. Our study reveals that BVES functions as a negative feedback regulator of ADCY9-cAMP signaling in skeletal muscle, playing an important role in maintaining muscle homeostasis.

Forskolin affects proliferation, migration and Paclitaxel-mediated cytotoxicity in non-small-cell lung cancer cell lines via adenylyl cyclase/cAMP axis

Non-Small-Cell Lung Cancer (NSCLC) is considered one of the most frequently diagnosed cancers and the leading cause of cancer-related deaths worldwide. Despite the undoubted therapeutic advances that have occurred in clinical practice over time, due to its high degree in both heterogeneity and resistance, NSCLC remains largely incurable. As a natural cAMP elevating agent, Forskolin has shown anti-cancer properties in different tumor types, thus supposing its possible usage in treating malignancies. In this study, we investigated the Forskolin outcome in H1299 and A549 NSCLC cell lines, either alone or in combination with Paclitaxel. We proved that Forskolin impairs cell growth and migration ability of these cells, concurrently. Albeit with a different extent between H1299 and A549, changes in cell-cycle progression and epithelial-mesenchymal markers were observed in response to Forskolin administration. Interestingly, comparable cell growth impairment was also obtained with the cAMP phosphodiesterase inhibitor IBMX, while the employment of adenylyl cyclase inhibitor SQ22536 counteracted, at least in part, the Forskolin-mediated anticancer effects. Besides as a single agent, we also demonstrated that Forskolin strongly enhances Paclitaxel-induced cytotoxicity, affecting cell death mainly via apoptosis induction. Notably, H89-mediated protein kinase A (PKA) inhibition further deteriorated the combination outcome. Altogether, our data designate Forskolin as a possible anticancer molecule in NSCLC, and recognize the adenylyl cyclase/cAMP axis as one of the pathways involved in. Although achieved at preclinical stage, our findings encourage the design of future studies aimed at further exploring the Forskolin employment in NSCLC treatment.

Nalfurafine Hydrochloride, a κ-Opioid Receptor Agonist, Induces Melanophagy via PKA Inhibition in B16F1 Cells

Selective autophagy controls cellular homeostasis by degrading unnecessary or damaged cellular components. Melanosomes are specialized organelles that regulate the biogenesis, storage, and transport of melanin in melanocytes. However, the mechanisms underlying melanosomal autophagy, known as the melanophagy pathway, are poorly understood. To better understand the mechanism of melanophagy, we screened an endocrine-hormone chemical library and identified nalfurafine hydrochlorides, a κ-opioid receptor agonist, as a potent inducer of melanophagy. Treatment with nalfurafine hydrochloride increased autophagy and reduced melanin content in alpha-melanocyte-stimulating hormone (α-MSH)-treated cells. Furthermore, inhibition of autophagy blocked melanosomal degradation and reversed the nalfurafine hydrochloride-induced decrease in melanin content in α-MSH-treated cells. Consistently, treatment with other κ-opioid receptor agonists, such as MCOPPB or mianserin, inhibited excessive melanin production but induced autophagy in B16F1 cells. Furthermore, nalfurafine hydrochloride inhibited protein kinase A (PKA) activation, which was notably restored by forskolin, a PKA activator. Additionally, forskolin treatment further suppressed melanosomal degradation as well as the anti-pigmentation activity of nalfurafine hydrochloride in α-MSH-treated cells. Collectively, our data suggest that stimulation of κ-opioid receptors induces melanophagy by inhibiting PKA activation in α-MSH-treated B16F1 cells.

The cAMP-PKA signalling pathway regulates hyphal growth, conidiation, trap morphogenesis, stress tolerance, and autophagy in Arthrobotrys oligospora

The cyclic adenosine monophosphate-protein kinase A (cAMP-PKA) signalling pathway is evolutionarily conserved in eukaryotes and plays a crucial role in defending against external environmental challenges, which can modulate the cellular response to external stimuli. Arthrobotrys oligospora is a typical nematode-trapping fungus that specializes in adhesive networks to kill nematodes. To elucidate the biological roles of the cAMP-PKA signalling pathway, we characterized the orthologous adenylate cyclase AoAcy, a regulatory subunit (AoPkaR), and two catalytic subunits (AoPkaC1 and AoPkaC2) of PKA in A. oligospora by gene disruption, transcriptome, and metabolome analyses. Deletion of Aoacy significantly reduced the levels of cAMP and arthrobotrisins. Results revealed that Aoacy, AopkaR, and AopkaC1 were involved in hyphal growth, trap morphogenesis, sporulation, stress resistance, and autophagy. In addition, Aoacy and AopkaC1 were involved in the regulation of mitochondrial morphology, thereby affecting energy metabolism, whereas AopkaC2 affected sporulation, nuclei, and autophagy. Multi-omics results showed that the cAMP-PKA signalling pathway regulated multiple metabolic and cellular processes. Collectively, these data highlight the indispensable role of cAMP-PKA signalling pathway in the growth, development, and pathogenicity of A. oligospora, and provide insights into the regulatory mechanisms of signalling pathways in sporulation, trap formation, and lifestyle transition.

An appressorium membrane protein, Pams1, controls infection structure maturation and virulence via maintaining endosomal stability in the rice blast fungus

The rice blast fungus Magnaporthe oryzae spores differentiate and mature into functional appressoria by sensing the host surface signals. Environmental stimuli are transduced into cells through internalization during appressorium formation, such as in the cAMP-PKA pathway. Here, we describe a novel contribution to how appressoria mature on the surface of a leaf, and its connection to endosomes and the cAMP-PKA pathway. An appressorium membrane-specific protein, Pams1, is required for maintaining endosomal structure, appressorium maturation, and virulence in M. oryzae. During appressorium development, Pams1 was translocated from the cell membrane to the endosomal membrane. Deletion of PAMS1 led to the formation of two types of abnormal appressoria after 8 h post inoculation (hpi): melanized type I had a reduced virulence, while pale type II was dead. Before 8 hpi, Δpams1 formed appressoria that were similar to those of the wild type. After 8 hpi, the appressoria of Δpams1 was differentiated into two types: (1) the cell walls of type I appressoria were melanized, endosomes were larger, and had a different distribution from the wild type and (2) Type II appressoria gradually stopped melanization and began to die. The organelles, including the nucleus, endosomes, mitochondria, and endoplasmic reticula, were degraded, leaving only autophagic body-like vesicles in type II appressoria. The addition of exogenous cAMP to Δpams1 led to the formation of a greater proportion of type I appressoria and a smaller proportion of type II appressoria. Thus, defects in endosomal structure and the cAMP-PKA pathway are among the causes of the defective appressorium maturation and virulence of Δpams1.

Yeast Protein Kinase A Isoforms: A Means of Encoding Specificity in the Response to Diverse Stress Conditions?

Eukaryotic cells have developed a complex circuitry of signalling molecules which monitor changes in their intra- and extracellular environments. One of the most widely studied signalling pathways is the highly conserved cyclic AMP (cAMP)/protein kinase A (PKA) pathway, which is a major glucose sensing circuit in the yeast Saccharomyces cerevisiae. PKA activity regulates diverse targets in yeast, positively activating the processes that are associated with rapid cell growth (e.g., fermentative metabolism, ribosome biogenesis and cell division) and negatively regulating the processes that are associated with slow growth, such as respiratory growth, carbohydrate storage and entry into stationary phase. As in higher eukaryotes, yeast has evolved complexity at the level of the PKA catalytic subunit, and Saccharomyces cerevisiae expresses three isoforms, denoted Tpk1-3. Despite evidence for isoform differences in multiple biological processes, the molecular basis of PKA signalling specificity remains poorly defined, and many studies continue to assume redundancy with regards to PKA-mediated regulation. PKA has canonically been shown to play a key role in fine-tuning the cellular response to diverse stressors; however, recent studies have now begun to interrogate the requirement for individual PKA catalytic isoforms in coordinating distinct steps in stress response pathways. In this review, we discuss the known non-redundant functions of the Tpk catalytic subunits and the evolving picture of how these isoforms establish specificity in the response to different stress conditions.

Abnormal Cyclic Nucleotide Signaling at the Outer Mitochondrial Membrane In Sympathetic Neurons During the Early Stages of Hypertension

Disruption of cyclic nucleotide signaling in sympathetic postganglionic neurons contributes to impaired intracellular calcium handling (Ca²⁺) and the development of dysautonomia during the early stages of hypertension, although how this occurs is poorly understood. Emerging evidence supports the uncoupling of signalosomes in distinct cellular compartments involving cyclic nucleotide–sensitive PDEs (phosphodiesterases), which may underpin the autonomic phenotype in stellate neurons.

The Secrets of Alternative Autophagy

For many years, it was thought that ATG5 and ATG7 played a pivotal role in autophagy, and that the knockdown of one of these genes would result in its inhibition. However, cells with ATG5 or ATG7 depletion still generate autophagic vacuoles with mainly trans-Golgi-originated isolation membranes and do not die. This indicates that autophagy can occur via ATG5/ATG7-independent alternative autophagy. Its molecular mechanism differs from that of the canonical pathway, including inter alia the phosphorylation of ULK1, and lack of LC3 modifications. As the alternative autophagy pathway has only recently been described, little is known of its precise role; however, a considerable body of evidence suggests that alternative autophagy participates in mitochondrion removal. This review summarizes the latest progress made in research on alternative autophagy and describes its possible molecular mechanism, roles and methods of detection, and possible modulators. There is a need for further research focused on types of autophagy, as this can elucidate the functioning of various cell types and the pathogenesis of human and animal diseases.

The Cell Wall Integrity Receptor Mtl1 Contributes to Articulate Autophagic Responses When Glucose Availability Is Compromised

Mtl1protein is a cell wall receptor belonging to the CWI pathway. Mtl1 function is related to glucose and oxidative stress signaling. In this report, we show data demonstrating that Mtl1 plays a critical role in the detection of a descent in glucose concentration, in order to activate bulk autophagy machinery as a response to nutrient deprivation and to maintain cell survival in starvation conditions. Autophagy is a tightly regulated mechanism involving several signaling pathways. The data here show that in Saccharomyces cerevisiae, Mtl1 signals glucose availability to either Ras2 or Sch9 proteins converging in Atg1 phosphorylation and autophagy induction. TORC1 complex function is not involved in autophagy induction during the diauxic shift when glucose is limited. In this context, the GCN2 gene is required to regulate autophagy activation upon amino acid starvation independent of the TORC1 complex. Mtl1 function is also involved in signaling the autophagic degradation of mitochondria during the stationary phase through both Ras2 and Sch9, in a manner dependent on either Atg33 and Atg11 proteins and independent of the Atg32 protein, the mitophagy receptor. All of the above suggest a pivotal signaling role for Mtl1 in maintaining correct cell homeostasis function in periods of glucose scarcity in budding yeast.

PRKA/PKA signals and autophagy: space matters

Macroautophagy/autophagy is the cellular process responsible for the elimination and recycling of aggregated proteins and damaged organelles. Whereas autophagy is strictly regulated by several signaling cascades, the link between this process and the subcellular distribution of its regulatory pathways remains to be established. Our recent work suggests that the compartmentalization of PRKA/PKA (protein kinase cAMP-activated) determines its effects on autophagy. We found that increased cAMP levels generate dramatically different PRKA activity "signatures" mainly dependent on the actions of phosphatases and the distribution of the PRKA holoenzymes containing type II regulatory subunits (PRKAR2A and PRKAR2B; RII). In this punctum we discuss how compartmentalized PRKA signaling events are generated and affect the autophagic flux in specific cell types.