Biased binding of class IA phosphatidyl inositol 3-kinase subunits to inducible costimulator (CD278)
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- Acosta, Y.Y., Zafra, M.P., Ojeda, G. et al. Cell. Mol. Life Sci. (2011) 68: 3065. doi:10.1007/s00018-010-0606-1
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To better understand T lymphocyte costimulation by inducible costimulator (ICOS; H4; CD278), we analyzed proteins binding to ICOS peptides phosphorylated at the Y191MFM motif. Phosphorylated ICOS binds class IA phosphatidyl inositol 3-kinase (PI3-K) p85α, p50-55α and p85β regulatory subunits and p110α, p110δ and p110β catalytic subunits. Intriguingly, T cells expressed high levels of both p110α or p110δ catalytic subunits, yet ICOS peptides, cell surface ICOS or PI3-kinase class IA regulatory subunits preferentially coprecipitated p110α catalytic subunits. Silencing p110α or p110δ partially inhibited Akt/PKB activation induced by anti-CD3 plus anti-ICOS antibodies. However, silencing p110α enhanced and silencing p110δ inhibited Erk activation. Both p110α- and p110δ-specific inhibitors blocked cytokine secretion induced by TCR/CD3 activation with or without ICOS costimulus, but only p110α inhibitors blocked ICOS-induced cell elongation. Thus, p110α and p110δ are essential to optimal T cell activation, but their abundance and activity differentially tune up distinct ICOS signaling pathways.