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Updated: May 9, 2026
Oligopeptide Competition Assay for Phosphorylation Site Determination
Published on: May 18, 2017
Coordinate phosphorylation of multiple residues on single AKT1 and AKT2 molecules
1Department of Systems Biology, The University of Texas MD Anderson Cancer Center, Houston, TX, USA.
Abstract:
Aberrant AKT activation is prevalent across multiple human cancer lineages providing an important new target for therapy. Twenty-two independent phosphorylation sites have been identified on specific AKT isoforms likely contributing to differential isoform regulation. However, the mechanisms regulating phosphorylation of individual AKT isoform molecules have not been elucidated because of the lack of robust approaches able to assess phosphorylation of multiple sites on a single AKT molecule. Using a nanofluidic proteomic immunoassay (NIA), consisting of isoelectric focusing followed by sensitive chemiluminescence detection, we demonstrate that under basal and ligand-induced conditions that the pattern of phosphorylation events is markedly different between AKT1 and AKT2. Indeed, there are at least 12 AKT1 peaks and at least 5 AKT2 peaks consistent with complex combinations of phosphorylation of different sites on individual AKT molecules. Following insulin stimulation, AKT1 was phosphorylated at Thr308 in the T-loop and Ser473 in the hydrophobic domain. In contrast, AKT2 was only phosphorylated at the equivalent sites (Thr309 and Ser474) at low levels. Further, Thr308 and Ser473 phosphorylation occurred predominantly on the same AKT1 molecules, whereas Thr309 and Ser474 were phosphorylated primarily on different AKT2 molecules. Although basal AKT2 phosphorylation was sensitive to inhibition of phosphatidylinositol 3-kinase (PI3K), basal AKT1 phosphorylation was essentially resistant. PI3K inhibition decreased pThr451 on AKT2 but not pThr450 on AKT1. Thus, NIA technology provides an ability to characterize coordinate phosphorylation of individual AKT molecules providing important information about AKT isoform-specific phosphorylation, which is required for optimal development and implementation of drugs targeting aberrant AKT activation.
Insights
Aberrant AKT activation, a cancer target, shows distinct phosphorylation patterns between AKT1 and AKT2 isoforms. New nanofluidic proteomic immunoassay (NIA) reveals isoform-specific signaling crucial for developing targeted therapies.
Area of Science:
- Biochemistry
- Molecular Biology
- Cancer Research
Background:
- Aberrant activation of AKT (also known as Protein Kinase B) signaling is a common driver in numerous human cancers, making it a critical therapeutic target.
- Understanding the precise mechanisms of AKT isoform regulation, particularly the phosphorylation patterns on individual molecules, is essential for effective drug development.
- Existing methods lack the resolution to analyze multiple phosphorylation sites on single AKT molecules, hindering detailed mechanistic studies.
Purpose of the Study:
- To develop and apply a novel nanofluidic proteomic immunoassay (NIA) capable of assessing the phosphorylation status of multiple sites on individual AKT molecules.
- To investigate and compare the isoform-specific phosphorylation patterns of AKT1 and AKT2 under basal and stimulated conditions.
- To elucidate the role of phosphatidylinositol 3-kinase (PI3K) in the regulation of AKT1 and AKT2 phosphorylation.
Main Methods:
- Utilized a nanofluidic proteomic immunoassay (NIA) combining isoelectric focusing and chemiluminescence detection.
- Analyzed AKT1 and AKT2 phosphorylation patterns in response to insulin stimulation.
- Assessed the sensitivity of basal AKT phosphorylation to phosphatidylinositol 3-kinase (PI3K) inhibition.
Main Results:
- NIA revealed distinct phosphorylation profiles for AKT1 (≥12 peaks) and AKT2 (≥5 peaks), indicating complex site occupancy on individual molecules.
- Insulin stimulation led to dual phosphorylation (Thr308/Ser473) on AKT1 molecules, whereas AKT2 showed low-level phosphorylation at equivalent sites (Thr309/Ser474), often on different molecules.
- Basal AKT2 phosphorylation was sensitive to PI3K inhibition, unlike basal AKT1 phosphorylation; PI3K inhibition affected pThr451 on AKT2 but not pThr450 on AKT1.
Conclusions:
- The NIA technology enables detailed characterization of coordinate phosphorylation events on single AKT molecules.
- Significant differences in AKT1 and AKT2 phosphorylation patterns and regulation were identified, highlighting isoform-specific signaling.
- These findings provide crucial insights into AKT isoform biology, essential for the rational design and implementation of targeted cancer therapies.
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