cAMP Signaling Pathway: KEGG Overview and Mechanisms
By Dr. Zubair Khalid, DVM, MS, PhD ·
Introduction to the cAMP Signaling Pathway
What is cAMP?
Cyclic adenosine 3′,5′-monophosphate (cAMP) is a ubiquitous second messenger that transduces extracellular signals into intracellular responses. First discovered by Earl Sutherland in the late 1950s, cAMP is synthesized from ATP by adenylyl cyclase and degraded to 5′-AMP by phosphodiesterases. Its primary effector in mammalian cells is protein kinase A (PKA), also known as cAMP-dependent protein kinase.
The pathway is initiated when an extracellular ligand—such as a hormone, neurotransmitter, or odorant—binds to a G-protein-coupled receptor (GPCR) on the plasma membrane. This binding triggers a conformational change in the receptor, promoting the exchange of GDP for GTP on the α subunit of a heterotrimeric G protein. The activated Gα subunit then stimulates adenylyl cyclase, which catalyzes the conversion of ATP to cAMP. The resulting rise in intracellular cAMP concentration activates PKA, which phosphorylates serine and threonine residues on a wide array of downstream targets, including transcription factors, metabolic enzymes, and ion channels.
cAMP signaling is remarkably versatile. Depending on the cell type and the specific GPCR engaged, cAMP can promote glycogen breakdown in hepatocytes, stimulate steroidogenesis in adrenal cortical cells, increase heart rate in cardiac myocytes, or modulate synaptic plasticity in neurons. This versatility arises from the compartmentalization of cAMP signaling, where localized pools of cAMP activate specific PKA isoforms anchored to distinct subcellular sites via A-kinase anchoring proteins (AKAPs).
Overview of the KEGG Pathway Map
The Kyoto Encyclopedia of Genes and Genomes (KEGG) is a bioinformatics resource that integrates genomic, chemical, and systemic functional information. The cAMP signaling pathway is catalogued as KEGG pathway map hsa04024 (human) and ko04024 (ortholog). The KEGG diagram for this pathway provides a comprehensive, manually curated representation of the molecular interactions, including GPCRs, G proteins, adenylyl cyclases, phosphodiesterases, PKA substrates, and downstream transcription factors.
The KEGG map is organized into functional modules: receptor-ligand interactions at the top, signal transduction cascades in the middle, and nuclear or cytosolic effector responses at the bottom. Each node represents a gene product (protein or RNA), and each edge represents a molecular interaction (binding, phosphorylation, or activation). The map also includes cross-references to other KEGG pathways, such as the Wnt Signaling Pathway and the PI3K AKT Pathway, reflecting the extensive crosstalk between cAMP signaling and other cellular networks.
Key Components of the cAMP Pathway
G-Protein Coupled Receptors (GPCRs)
GPCRs constitute the largest family of cell-surface receptors in the human genome, with over 800 members. These seven-transmembrane-spanning proteins detect a diverse array of extracellular stimuli, including hormones (glucagon, adrenaline), neurotransmitters (dopamine, serotonin), and sensory stimuli (light, odorants). The cytoplasmic loops of GPCRs, particularly the second and third intracellular loops and the C-terminal tail, contain binding sites for heterotrimeric G proteins.
The heterotrimeric G protein consists of three subunits: Gα (39–52 kDa), Gβ (35–36 kDa), and Gγ (7–8 kDa). In the resting state, Gα binds GDP and associates with the Gβγ dimer. Upon receptor activation, the GPCR acts as a guanine nucleotide exchange factor (GEF), promoting the release of GDP from Gα and its replacement with GTP. This exchange induces a conformational change in Gα, causing it to dissociate from Gβγ and from the receptor. Both the GTP-bound Gα and the free Gβγ dimer can then modulate downstream effectors.
Gα subunits are classified into four families based on sequence homology and effector specificity: Gαs (stimulatory), Gαi/o (inhibitory), Gαq/11 (activating phospholipase C), and Gα12/13 (activating Rho GTPases). For cAMP signaling, the critical distinction is between Gαs and Gαi. Gαs activates adenylyl cyclase, increasing cAMP production, whereas Gαi inhibits adenylyl cyclase, decreasing cAMP levels. The β-adrenergic receptor (β-AR) is a canonical Gαs-coupled receptor, while the α2-adrenergic receptor and the M2 muscarinic acetylcholine receptor are classic Gαi-coupled receptors.
Adenylyl Cyclase and cAMP Production
Adenylyl cyclase (AC) is the enzyme responsible for converting ATP to cAMP and pyrophosphate. There are nine transmembrane adenylyl cyclase isoforms (AC1–AC9) and one soluble isoform (sAC) in mammals. All transmembrane ACs share a similar topology: two hydrophobic membrane-spanning domains, each containing six transmembrane helices, and two cytoplasmic catalytic domains (C1 and C2) that form the active site at their interface.
The catalytic activity of AC requires the binding of GTP-bound Gαs, which interacts with the C1 domain and stabilizes the active conformation. The substrate ATP binds in a pocket formed by both C1 and C2, with Mg²⁺ (or Mn²⁺) as a required cofactor. The reaction proceeds via a nucleophilic attack of the 3′-hydroxyl group of ATP on the α-phosphate, forming the cyclic phosphodiester bond. The Km of AC for ATP is approximately 100–200 µM, and the Vmax varies among isoforms from 0.5 to 20 µmol/min/mg.
AC isoforms differ in their regulation by calcium and protein kinases. For example, AC1 and AC8 are stimulated by Ca²⁺/calmodulin, providing a mechanism for crosstalk between calcium and cAMP signaling. AC5 and AC6 are inhibited by Gαi and by protein kinase C (PKC) phosphorylation. These isoform-specific regulatory properties allow cells to fine-tune cAMP production in response to diverse stimuli.
Protein Kinase A (PKA) and CREB
PKA is the principal effector of cAMP in most mammalian cells. The holoenzyme is a tetramer composed of two regulatory (R) subunits and two catalytic (C) subunits. There are four R subunit isoforms (RIα, RIβ, RIIα, RIIβ) and three C subunit isoforms (Cα, Cβ, Cγ). In the basal state, the R subunits bind to and inhibit the C subunits. Each R subunit contains two tandem cAMP-binding domains at its C-terminus, and the binding of four cAMP molecules (two per R subunit) causes a conformational change that releases the active C subunits.
The free C subunits are serine/threonine kinases that phosphorylate substrates containing the consensus sequence Arg-Arg-X-Ser/Thr (RRXS/T). One of the most important PKA substrates is the transcription factor cAMP response element-binding protein (CREB). PKA phosphorylates CREB at serine 133, which promotes the recruitment of the coactivator CREB-binding protein (CBP) and its paralog p300. CBP/p300 possess intrinsic histone acetyltransferase activity, which remodels chromatin and facilitates transcription of genes containing cAMP response elements (CREs) in their promoters. The consensus CRE sequence is TGACGTCA.
PKA also phosphorylates a wide range of other substrates, including glycogen phosphorylase kinase, hormone-sensitive lipase, the ryanodine receptor, and the transcription factor cAMP response element modulator (CREM). The specificity of PKA phosphorylation is achieved in part by AKAPs, which tether PKA to specific subcellular compartments, ensuring that the kinase acts on the appropriate substrates in response to localized cAMP signals.
Activation and Regulation Mechanisms
G-Protein Activation Cycle
The G-protein cycle is a tightly regulated process that ensures the duration and amplitude of cAMP signaling are precisely controlled. The cycle proceeds through the following ordered steps:
- Ligand binding: An agonist binds to the GPCR, inducing a conformational change that exposes the G-protein binding site on the intracellular face of the receptor.
- GEF activity: The activated receptor promotes the exchange of GDP for GTP on Gα. This is the rate-limiting step in G-protein activation and is accelerated by the receptor by a factor of 10³–10⁴.
- Subunit dissociation: GTP binding induces a conformational change in Gα, reducing its affinity for Gβγ and the receptor. The GTP-bound Gα and free Gβγ dissociate and interact with their respective effectors.
- Effector activation: Gαs activates adenylyl cyclase, while Gαi inhibits it. The Gβγ dimer can also activate effectors such as G-protein-coupled inwardly rectifying potassium channels (GIRKs) and certain isoforms of phospholipase C.
- GTP hydrolysis: The intrinsic GTPase activity of Gα hydrolyzes GTP to GDP, returning Gα to its inactive conformation. This hydrolysis is accelerated by regulators of G-protein signaling (RGS proteins), which act as GTPase-activating proteins (GAPs).
- Reassociation: The GDP-bound Gα reassociates with Gβγ, reforming the inactive heterotrimer, which is then available for another round of activation.
The intrinsic GTPase activity of Gα is slow, with a rate constant of approximately 0.02–0.05 min⁻¹, corresponding to a half-life of 15–35 minutes. RGS proteins accelerate this hydrolysis by up to 1000-fold, reducing the half-life to seconds. This rapid termination is essential for the temporal precision of cAMP signaling.
Termination by Phosphodiesterases
Phosphodiesterases (PDEs) are the enzymes responsible for degrading cAMP to 5′-AMP, thereby terminating the signal. The human genome encodes 21 PDE genes, grouped into 11 families (PDE1–PDE11) based on sequence homology, substrate specificity, and regulatory properties. PDE4, PDE7, and PDE8 are cAMP-specific, while PDE1, PDE2, PDE3, PDE10, and PDE11 can hydrolyze both cAMP and cGMP.
PDE4 is the most abundant cAMP-specific PDE in most tissues and is a major therapeutic target. PDE4 inhibitors such as rolipram and roflumilast elevate cAMP levels and have anti-inflammatory effects. PDE3 is inhibited by cGMP, providing a mechanism for crosstalk between the cAMP and cGMP pathways. PDE1 is activated by Ca²⁺/calmodulin, linking calcium signaling to cAMP degradation.
The Km values of PDEs for cAMP range from 0.5 to 50 µM, and their Vmax values vary widely. In cardiac myocytes, PDE3 and PDE4 account for the majority of cAMP hydrolysis, and their inhibition by milrinone (PDE3 inhibitor) is used clinically to treat heart failure. The subcellular localization of PDEs is critical for cAMP compartmentation; PDE4 isoforms are anchored to specific cellular structures via interactions with AKAPs and β-arrestins, ensuring that cAMP is degraded only in specific microdomains.
Cellular Effects of cAMP Signaling
Gene Expression Regulation
The most extensively studied effect of cAMP on gene expression is mediated by the PKA-CREB pathway. Upon phosphorylation at serine 133, CREB binds to CRE sequences in the promoters of target genes and recruits CBP/p300. This leads to histone acetylation, chromatin remodeling, and transcriptional activation. Genes regulated by CREB include those encoding gluconeogenic enzymes (phosphoenolpyruvate carboxykinase, glucose-6-phosphatase), neurotrophic factors (brain-derived neurotrophic factor, BDNF), and circadian clock components (Per1, Per2).
The duration of CREB phosphorylation is critical for the transcriptional outcome. Transient CREB phosphorylation (minutes) is insufficient to activate transcription, whereas sustained phosphorylation (hours) leads to robust gene expression. This temporal regulation is achieved through the balance between PKA activity and the dephosphorylation of CREB by protein phosphatases such as PP1 and PP2A.
cAMP also regulates gene expression through PKA-independent mechanisms. Exchange proteins activated by cAMP (Epac1 and Epac2) are guanine nucleotide exchange factors for the small GTPases Rap1 and Rap2. Epac activation leads to Rap1-GTP formation, which can activate the mitogen-activated protein kinase (MAPK) cascade and influence cell proliferation and differentiation. This pathway is particularly important in neurons, where Epac mediates cAMP-dependent effects on synaptic plasticity.
Metabolic Enzyme Modulation
cAMP exerts rapid effects on metabolism through direct phosphorylation of metabolic enzymes by PKA. In the liver, glucagon stimulates cAMP production, leading to PKA-mediated phosphorylation and activation of glycogen phosphorylase kinase. This kinase then phosphorylates and activates glycogen phosphorylase, which catalyzes the breakdown of glycogen to glucose-1-phosphate. Simultaneously, PKA phosphorylates and inactivates glycogen synthase, preventing glycogen synthesis. The net effect is a switch from glycogen storage to glucose release.
In adipose tissue, cAMP activates hormone-sensitive lipase (HSL) through PKA-mediated phosphorylation at serine 563, 659, and 660. This promotes the hydrolysis of triglycerides to free fatty acids and glycerol, which are released into the circulation for use by other tissues. In cardiac myocytes, PKA phosphorylates L-type calcium channels and the ryanodine receptor, increasing calcium influx and release from the sarcoplasmic reticulum, which enhances contractility.
The KEGG Pathway Map for cAMP Signaling
Interpreting KEGG Diagrams
KEGG pathway maps are graphical representations of molecular interaction networks. Each map is a collection of nodes (gene products) connected by edges (interactions). The nodes are color-coded: red nodes indicate human genes, blue nodes indicate other species, and white nodes indicate genes not present in the reference organism. The edges are labeled with arrows (activation), T-bars (inhibition), or lines (binding).
For the cAMP signaling pathway (hsa04024), the map is divided into several functional modules. The top section shows GPCRs and their ligands, including β-adrenergic receptors, glucagon receptor, and dopamine receptors. The middle section shows the G proteins, adenylyl cyclases, and phosphodiesterases. The bottom section shows the downstream effectors, including PKA, CREB, Epac, and ion channels.
Each node in the KEGG map is linked to detailed information in the KEGG GENES, KEGG COMPOUND, and KEGG REACTION databases. Clicking on a node reveals the gene name, species, and cross-references to other databases such as NCBI Gene and UniProt. The map also includes links to related pathways, allowing users to navigate between interconnected signaling networks.
Related KEGG Pathways
The cAMP signaling pathway does not operate in isolation. KEGG provides cross-references to several related pathways that share components or converge on common effectors. For example, the Notch Signaling Pathway and the Wnt Signaling Pathway both regulate gene expression through distinct mechanisms but can crosstalk with cAMP signaling at the level of transcription factors. The Nf Kappa B Signaling Pathway is activated by PKA in some cell types, linking cAMP to inflammatory responses. The JAK STAT Pathway and Jak2-stat3 Signaling Pathway can modulate cAMP signaling through the expression of PDEs and GPCRs. The PI3K AKT Pathway intersects with cAMP signaling at the level of cell survival and metabolism, and the Apoptosis Pathway can be regulated by cAMP through both PKA-dependent and PKA-independent mechanisms.
Methods to Study the cAMP Pathway
cAMP Assays and Biosensors
The measurement of intracellular cAMP levels is fundamental to studying this pathway. Traditional methods include radioimmunoassays (RIA) and enzyme-linked immunosorbent assays (ELISA), which require cell lysis and provide a population-average measurement. These assays typically detect cAMP in the range of 0.1–100 pmol per well and are useful for comparing cAMP levels between different conditions.
For real-time, single-cell measurements, genetically encoded FRET (Förster resonance energy transfer) biosensors are the method of choice. The most widely used cAMP biosensor is Epac1-camps, which consists of a cAMP-binding domain from Epac1 flanked by a donor fluorophore (CFP) and an acceptor fluorophore (YFP). When cAMP binds to the Epac domain, it induces a conformational change that increases the distance between the fluorophores, decreasing FRET efficiency. The change in FRET ratio (YFP/CFP emission) is proportional to the cAMP concentration, allowing quantitative measurements with a temporal resolution of seconds and a detection limit of approximately 100 nM cAMP.
Another approach is the use of the PKA-based biosensor AKAR (A-kinase activity reporter), which measures PKA activity rather than cAMP concentration. AKAR consists of a PKA substrate peptide, a phospho-binding domain (FHA1), and a FRET pair. When PKA phosphorylates the substrate, the FHA1 domain binds to the phosphopeptide, causing a conformational change that alters FRET. AKAR allows researchers to monitor PKA activity in living cells with high spatial and temporal resolution.
Use of Forskolin and Inhibitors
Pharmacological tools are essential for dissecting the cAMP pathway. Forskolin, a diterpene from the plant Coleus forskohlii, directly activates adenylyl cyclase by binding to the catalytic domain and stabilizing the active conformation. Forskolin is used at concentrations of 1–100 µM to elevate cAMP levels independent of receptor activation. It is particularly useful for studying downstream effects of cAMP without the complexity of GPCR signaling.
Specific inhibitors allow the dissection of individual pathway components. H89 is a commonly used PKA inhibitor with an IC50 of approximately 50 nM, although it also inhibits other kinases at higher concentrations. KT5720 is a more selective PKA inhibitor with an IC50 of 60 nM. Rolipram and roflumilast are PDE4 inhibitors that elevate cAMP levels by blocking its degradation. Pertussis toxin, which ADP-ribosylates Gαi and prevents its activation, is used to distinguish Gαi-mediated inhibition from Gαs-mediated stimulation of adenylyl cyclase.
Clinical Relevance and Disease Links
cAMP in Cancer
Dysregulation of cAMP signaling is implicated in several types of cancer. In some contexts, cAMP promotes cell proliferation, while in others it inhibits it, depending on the cell type and the specific downstream effectors engaged. For example, in pituitary adenomas, activating mutations in Gαs (the GNAS gene) lead to constitutive adenylyl cyclase activation and elevated cAMP levels, which drive cell proliferation and hormone hypersecretion. These mutations are found in approximately 30–40% of growth hormone-secreting pituitary adenomas.
Conversely, in many epithelial cancers, elevated cAMP levels inhibit cell growth and promote differentiation. This has led to the development of cAMP-elevating agents, such as PDE inhibitors, as potential cancer therapeutics. However, the effects are context-dependent, and chronic cAMP elevation can also promote tumor progression through the activation of Epac and the MAPK pathway. The PI3K AKT Pathway and the Apoptosis Pathway are frequently dysregulated in cancer and can interact with cAMP signaling to determine cell fate.
cAMP in Cardiovascular Disease
cAMP plays a central role in cardiac function. In cardiac myocytes, β-adrenergic receptor stimulation increases cAMP, which activates PKA and enhances contractility (positive inotropy), heart rate (positive chronotropy), and relaxation (positive lusitropy). In heart failure, chronic β-adrenergic stimulation leads to desensitization of β-ARs and downregulation of adenylyl cyclase, resulting in reduced cAMP signaling and impaired contractility.
PDE3 inhibitors such as milrinone are used clinically to treat acute heart failure by increasing cAMP levels and enhancing cardiac contractility. However, long-term use of these agents is associated with increased mortality, likely due to arrhythmias and increased myocardial oxygen demand. β-blockers, which reduce cAMP signaling, are the mainstay of chronic heart failure treatment, highlighting the complex relationship between cAMP levels and cardiac function.
Common Pitfalls and Misconceptions
Misunderstanding G-Protein Specificity
A common error is assuming that all GPCRs couple to Gαs and stimulate adenylyl cyclase. In reality, GPCRs can couple to Gαi, which inhibits adenylyl cyclase, or to Gαq, which activates phospholipase C and has no direct effect on cAMP. The same ligand can activate different GPCRs with opposing effects on cAMP. For example, adrenaline activates both β-ARs (Gαs-coupled, stimulating cAMP) and α2-ARs (Gαi-coupled, inhibiting cAMP). The net effect on cAMP depends on the relative expression of these receptors in a given cell type.
Another misconception is that Gβγ is inert. While Gα is the primary regulator of adenylyl cyclase, Gβγ can activate other effectors, including GIRK channels, phospholipase Cβ, and the MAPK pathway. In some contexts, Gβγ-mediated signaling is more important than Gα-mediated signaling, particularly in the regulation of ion channels and cell migration.
Overlooking Negative Feedback
cAMP signaling is subject to multiple layers of negative feedback that are often ignored in simplified models. PKA phosphorylates and activates PDE4, increasing cAMP degradation and terminating the signal. PKA also phosphorylates the β2-adrenergic receptor, which promotes its desensitization and internalization. Additionally, PKA phosphorylates adenylyl cyclase isoforms AC5 and AC6, reducing their activity. These feedback loops ensure that cAMP levels return to baseline after stimulation and prevent excessive signaling.
Students often assume that cAMP levels remain elevated as long as the ligand is present. In reality, the pathway adapts rapidly through receptor desensitization, PDE activation, and G-protein inactivation. This adaptation is clinically relevant; for example, chronic β-agonist use in asthma leads to reduced β-AR responsiveness due to receptor downregulation.
Summary and Study Tips
Key Takeaways
- cAMP is a second messenger synthesized from ATP by adenylyl cyclase and degraded by phosphodiesterases.
- GPCRs activate heterotrimeric G proteins, which regulate adenylyl cyclase activity: Gαs stimulates, Gαi inhibits.
- PKA is the primary effector of cAMP, phosphorylating substrates such as CREB, glycogen phosphorylase kinase, and ion channels.
- The pathway is terminated by GTP hydrolysis on Gα, PDE-mediated cAMP degradation, and receptor desensitization.
- KEGG pathway hsa04024 provides a comprehensive map of cAMP signaling components and interactions.
- cAMP signaling is dysregulated in diseases including cancer, heart failure, and endocrine disorders.
- Experimental tools include FRET biosensors, forskolin, PDE inhibitors, and PKA inhibitors.
Exam-Focused Revision
For exam preparation, focus on the following key concepts:
- The G-protein cycle: Memorize the steps of GDP-GTP exchange, subunit dissociation, effector activation, and GTP hydrolysis. Understand the role of RGS proteins in accelerating termination.
- The PKA holoenzyme: Know the structure (R₂C₂ tetramer), the mechanism of activation (cAMP binding to R subunits), and the consensus phosphorylation sequence (RRXS/T).
- The CREB pathway: Understand how PKA phosphorylates CREB at serine 133, leading to CBP recruitment and gene transcription.
- The KEGG map: Be able to identify the major components of the cAMP pathway on the KEGG diagram and explain the interactions between them.
- Pharmacological tools: Know the mechanisms of action of forskolin, H89, rolipram, and pertussis toxin.
Frequently Asked Questions
What is the cAMP signaling pathway in KEGG?
The cAMP signaling pathway in KEGG (hsa04024 for human, ko04024 for orthologs) is a curated molecular interaction map that depicts the components and reactions of cAMP-mediated signal transduction. It includes GPCRs, heterotrimeric G proteins, adenylyl cyclases, phosphodiesterases, PKA, CREB, Epac, and downstream effectors. The map is interactive and cross-referenced to other KEGG pathways and databases.
How does cAMP activate PKA?
cAMP activates PKA by binding to the regulatory (R) subunits of the inactive R₂C₂ tetramer. Each R subunit has two cAMP-binding sites, and the binding of four cAMP molecules (two per R subunit) induces a conformational change that reduces the affinity of the R subunits for the catalytic (C) subunits. The C subunits dissociate and become catalytically active, phosphorylating serine and threonine residues on downstream substrates.
What is the role of adenylyl cyclase in the cAMP pathway?
Adenylyl cyclase is the enzyme that catalyzes the conversion of ATP to cAMP and pyrophosphate. It is activated by GTP-bound Gαs and inhibited by GTP-bound Gαi. There are nine transmembrane isoforms (AC1–AC9) and one soluble isoform (sAC), each with distinct regulatory properties. Forskolin directly activates adenylyl cyclase and is used experimentally to elevate cAMP levels.
How is cAMP signaling terminated?
cAMP signaling is terminated through multiple mechanisms: (1) GTP hydrolysis by Gα, which returns the G protein to its inactive state; (2) degradation of cAMP to 5′-AMP by phosphodiesterases; (3) receptor desensitization and internalization; and (4) feedback phosphorylation of adenylyl cyclase and PDEs by PKA. RGS proteins accelerate GTP hydrolysis, while PDE inhibitors such as rolipram prolong cAMP signaling.
What are the main downstream effects of cAMP?
The main downstream effects of cAMP are mediated by PKA and Epac. PKA phosphorylates metabolic enzymes (glycogen phosphorylase kinase, hormone-sensitive lipase), ion channels (L-type calcium channels, ryanodine receptor), and transcription factors (CREB, CREM). Epac activates Rap1 and Rap2, which regulate cell adhesion, proliferation, and secretion. These effects influence metabolism, gene expression, contractility, and neuronal plasticity.
What is the KEGG pathway ID for cAMP signaling?
The KEGG pathway ID for cAMP signaling is hsa04024 for Homo sapiens and ko04024 for the KEGG ortholog (KO) reference pathway. The map can be accessed through the KEGG website and includes detailed annotations for each component.
What is the difference between Gs and Gi proteins in cAMP signaling?
Gαs (stimulatory) activates adenylyl cyclase, increasing cAMP production, whereas Gαi (inhibitory) inhibits adenylyl cyclase, decreasing cAMP production. Receptors coupled to Gαs (e.g., β-adrenergic receptors, glucagon receptor) stimulate cAMP signaling, while receptors coupled to Gαi (e.g., α2-adrenergic receptors, M2 muscarinic receptors) suppress it. Pertussis toxin blocks Gαi activation and is used experimentally to distinguish these pathways.
Key Takeaways
- cAMP is a second messenger produced by adenylyl cyclase and degraded by phosphodiesterases, with PKA as its principal effector.
- GPCRs regulate cAMP through heterotrimeric G proteins: Gαs activates adenylyl cyclase, Gαi inhibits it.
- PKA phosphorylates substrates at RRXS/T motifs, including CREB, which drives gene transcription via CRE elements.
- The pathway is terminated by GTP hydrolysis, PDE-mediated cAMP degradation, and receptor desensitization.
- KEGG map hsa04024 provides a comprehensive, interactive representation of the cAMP signaling network.
- cAMP dysregulation is implicated in cancer, heart failure, and endocrine disorders, making it a major therapeutic target.
- Experimental tools include FRET biosensors, forskolin, PDE inhibitors, and PKA inhibitors, each with specific applications and limitations.
Further Reading
- Li J et al. Tong-Qiao-Huo-Xue Decoction promotes synaptic remodeling via cAMP/PKA/CREB pathway in vascular dementia rats. Phytomedicine : international journal of phytotherapy and phytopharmacology. 2024. PubMed 39461198
- Wang G et al. Sheng-ji Hua-yu Formula promotes diabetic ulcer healing via regulating the cAMP/PKA/CREB signaling pathway. Journal of ethnopharmacology. 2025. PubMed 40484258
- Jiang Y et al. Senkyunolide H protects PC12 cells from OGD/R-induced injury via cAMP-PI3K/AKT signaling pathway. Journal of ethnopharmacology. 2022. PubMed 34543683
- Xu C et al. Steamed Panax notoginseng Saponins Ameliorate Cyclophosphamide-Induced Anemia by Attenuating Gut-Liver Injury and Activating the cAMP/PI3K/AKT Signaling Pathway. Nutrients. 2025. PubMed 41228409
- Liu Y et al. The cAMP-PKA signaling pathway induces apoptosis and promotes hypothermic liver injury. World journal of emergency medicine. 2025. PubMed 41246541
- Fu L et al. Moxibustion ameliorates osteoarthritis by regulating gut microbiota via impacting cAMP-related signaling pathway. Biomedicine & pharmacotherapy = Biomedecine & pharmacotherapie. 2024. PubMed 38113621