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B Cell Receptor Activation Predominantly Regulates AKT-mTORC1/2 Substrates Functionally Related to RNA Processing
Dara K Mohammad1,2, Raja H Ali3, Janne J Turunen1
1Department of Laboratory Medicine, Clinical Research Center, Karolinska Institutet, Karolinska Hospital Huddinge, SE-141 86 Huddinge-Stockholm, Sweden.
Researchers identified novel protein phosphorylation events regulated by Protein kinase B (AKT) and mTORC1/2 signaling following B cell receptor activation. This revealed conserved protein targets involved in gene regulation and RNA processing.
Area of Science:
- Cellular signaling pathways
- Molecular biology
- Proteomics
Background:
- Protein kinase B (AKT) phosphorylates substrates at the RXRXXpS/T motif, facilitating 14-3-3 interactions.
- B cell receptor (BCR) activation triggers complex signaling cascades impacting cellular functions.
Purpose of the Study:
- To identify novel AKT-induced phosphorylation events after BCR activation.
- To characterize proteins regulated by this signaling pathway.
Main Methods:
- Proteomics, including phosphorylated consensus motif-specific antibody enrichment and tandem mass spectrometry.
- Biochemical assays and bioinformatics analyses.
- Inhibition studies using AKT (MK-2206) and mTORC (PP242) inhibitors.
Main Results:
- Identified 446 proteins with 186 novel phosphorylation events.
- Observed differential regulation: 85 proteins upregulated (ribosomal, translational, DNA/transcription regulation) and 277 downregulated (RNA binding, splicing, export).
- Confirmed RXRXXpS/T motif as a substrate for both AKT and mTORC1/2, with domain-specific enrichment and phylogenetic conservation.
Conclusions:
- BCR activation induces widespread phosphorylation changes mediated by AKT and mTORC1/2.
- The RXRXXpS/T motif is a key regulatory site for conserved protein functions across eukaryotes.
- Phosphorylation dynamics impact gene expression and RNA processing machinery.
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