Insulin signalling represents one of the most pivotal molecular pathways governing metabolic regulation in mammalian physiology. At its core, this network controls the delicate balance of nutrient availability, orchestrating the metabolism of carbohydrates, lipids, and proteins with exceptional spatial and temporal precision. Recent advances in high-resolution phosphoproteomics have provided unprecedented insights into the complexity and dynamics of insulin signalling, revealing layers of regulation that were previously unappreciated. These studies underscore the centrality of protein phosphorylation events, particularly those mediated by the serine/threonine kinase AKT, in translating extracellular insulin cues into finely tuned cellular responses.
At the molecular level, the initiation of insulin signalling begins with the binding of insulin to its receptor, a receptor tyrosine kinase embedded in the plasma membrane. This interaction triggers autophosphorylation of the insulin receptor and recruitment of adapter proteins such as insulin receptor substrates (IRS), which are themselves phosphorylated on numerous tyrosine residues. These modifications create docking platforms that enable the activation of downstream kinases including phosphoinositide 3-kinase (PI3K). PI3K activation converts phosphatidylinositol (4,5)-bisphosphate (PIP2) to phosphatidylinositol (3,4,5)-trisphosphate (PIP3), a second messenger that recruits and activates AKT via its pleckstrin homology domain.
AKT serves as a central hub within the insulin signalling network, phosphorylating an extensive array of substrates to mediate cellular processes such as glucose uptake through GLUT4 translocation, glycogen synthesis via glycogen synthase kinase-3 (GSK3) inhibition, lipogenesis, and protein synthesis. The exquisite control of AKT’s activity is achieved through its phosphorylation at multiple sites, including the critical threonine and serine residues. The dynamic modulation of these phosphorylation events permits temporal tuning of insulin responses, ensuring metabolic processes are appropriately aligned with physiological demands.
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Feedback mechanisms and crosstalk represent additional layers of complexity within the insulin signalling pathway. For instance, IRS proteins undergo serine/threonine phosphorylation at a plethora of sites that can either enhance or attenuate signalling, acting as a molecular rheostat. These phosphorylation events integrate diverse cellular signals and modulate insulin sensitivity. Furthermore, intersecting pathways such as those governed by AMPK or mTOR reciprocally interact with the insulin network, collectively coordinating anabolic and catabolic activities.
The advent of phosphoproteomic technologies leveraging mass spectrometry has dramatically expanded our understanding of insulin signalling architecture. By capturing temporal snapshots of phosphorylation patterns in response to insulin stimulation, researchers have delineated substrate specificity and kinase activity profiles with remarkable depth. This has illuminated not only canonical pathways but also unveiled novel phosphorylation sites and signalling nodes, broadening the scope of insulin action beyond traditional models.
Importantly, these advances have shed light on the molecular underpinnings of insulin resistance, a hallmark of cardiometabolic diseases including type 2 diabetes and obesity. Phosphoproteomic analyses reveal that in insulin-resistant states, the signalling network undergoes profound rewiring characterized by disrupted phosphorylation at known regulatory sites along with the emergence of aberrant sites absent in healthy conditions. This altered phosphorylation landscape compromises the fidelity of insulin signalling, impairing metabolic regulation and fostering pathological outcomes.
Genetic predisposition and environmental inputs such as nutrient excess and inflammation contribute synergistically to these signalling perturbations. Variations in genes encoding components of the insulin pathway can predispose individuals to dysregulated phosphorylation dynamics. Concurrently, metabolic stressors provoke maladaptive phosphorylation via stress kinases, further skewing signal transduction fidelity. This multifactorial disruption underscores the complexity of targeting insulin resistance therapeutically.
Detailed kinetic studies of AKT activation have revealed that its phosphorylation and subsequent substrate engagement occur through a multi-step process governed by fine-tuned regulatory nodes. The interplay between upstream kinases such as PDK1 and mTORC2 governs AKT’s activation state, while phosphatases like PP2A and PHLPP impose negative regulation by dephosphorylation. This balance ensures precise modulation in response to fluctuating insulin levels, preventing aberrant signalling that could disrupt metabolic homeostasis.
Beyond AKT, other kinase families integral to insulin signal transduction—such as the MAPK cascade and atypical PKCs—work in concert to effectuate the diverse physiological actions of insulin. These kinases contribute to gene expression regulation, cell growth, and differentiation, linking metabolic control to broader cellular functions. Such multi-faceted control highlights the expansive repertoire of insulin’s biological effects.
The integration of multidisciplinary approaches combining phosphoproteomics with computational modelling and genetic manipulation offers a promising avenue to unravel the full complexity of insulin signalling. Through these strategies, it is becoming possible to map signalling networks with unprecedented resolution, predict emergent behaviours, and identify critical nodes susceptible to pharmacological intervention. This systems biology approach promises to redefine therapeutic strategies for metabolic diseases.
Furthermore, the identification of novel phosphorylation sites unique to insulin-resistant tissues presents exciting opportunities for biomarker development and targeted therapy. By selectively modulating aberrant phosphorylation events or restoring normal phosphorylation dynamics, it may be feasible to re-establish insulin sensitivity and counteract disease progression. This precision medicine approach holds considerable promise to transcend the limitations of current treatments.
Collectively, the evolving picture of insulin signalling emphasizes not only its intricacy but also its adaptability. The pathway’s capacity to integrate multiple cues and adjust its signalling output ensures metabolic flexibility. However, when these regulatory processes fail, the ensuing disruption sets the stage for profound metabolic dysfunction. Understanding these mechanisms at a molecular level is critical to advancing clinical interventions.
In conclusion, insulin signalling is a highly complex and dynamically regulated network whose precise orchestration is crucial for metabolic health. The central role of AKT and its extensive substrate network exemplifies the intricate kinase-mediated control processes critical for maintaining nutrient homeostasis. Advances in phosphoproteomics continue to unravel the pathway’s depth, reveal the perturbations underlying insulin resistance, and open new therapeutic vistas for combating cardiometabolic diseases. As research progresses, the translation of these mechanistic insights into clinical practice will be essential for addressing the global burden of metabolic disorders.
Subject of Research: insulin signalling network and its regulation through phosphorylation, with focus on AKT kinase and phosphoproteomics insights into metabolic regulation and insulin resistance.
Article Title: The insulin signalling network.
Article References:
Burchfield, J.G., Diaz-Vegas, A. & James, D.E. The insulin signalling network.
Nat Metab (2025). https://doi.org/10.1038/s42255-025-01349-z
Image Credits: AI Generated
Tags: adapter proteins in insulin signallingcellular responses to insulindownstream kinases in metabolismdynamics of insulin signallinghigh-resolution phosphoproteomicsinsulin receptor tyrosine kinaseinsulin signalling pathwaymetabolic regulation in mammalsnutrient metabolism regulationphosphoinositide 3-kinase activationprotein phosphorylation and insulinrole of AKT in insulin signalling
