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A regulatory subunit of phosphoinositide 3-kinase increases the nuclear accumulation of X-box–binding protein-1 to modulate the unfolded protein response

Nature Medicine volume 16, pages 438–445 (2010)Cite this article

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Abstract

Class Ia phosphoinositide 3-kinase (PI3K), an essential mediator of the metabolic actions of insulin, is composed of a catalytic (p110α or p110β) and regulatory (p85αα, p85βα or p55α) subunit. Here we show that p85αα interacts with X-box–binding protein-1 (XBP-1), a transcriptional mediator of the unfolded protein response (UPR), in an endoplasmic reticulum (ER) stress-dependent manner. Cell lines with knockout or knockdown of p85αα show marked alterations in the UPR, including reduced ER stress–dependent accumulation of nuclear XBP-1, decreased induction of UPR target genes and increased rates of apoptosis. This is associated with a decreased activation of inositol-requiring protein-1α (IRE1α) and activating transcription factor-6αα (ATF6α). Mice with deletion of p85α in liver (L-Pik3r1−/−) show a similar attenuated UPR after tunicamycin administration, leading to an increased inflammatory response. Thus, p85αα forms a previously unrecognized link between the PI3K pathway, which is central to insulin action, and the regulation of the cellular response to ER stress, a state that when unresolved leads to insulin resistance.

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Figure 1: Identification and characterization of XBP-1 as a p85α interacting protein.
Figure 2: Evaluation of ER stress and UPR signaling dynamics in p85α-deficient fibroblasts.
Figure 3: Evaluation of XBP-1 target-gene transcription, UPR-dependent gene expression and apoptosis.
Figure 4: Evaluation of the UPR in livers from control and L-Pik3r1−/− mice.
Figure 5: Analysis of gene expression, XBP-1 splicing and XBP-1 stability in livers from Pik3r1lox/lox and L-Pik3r1−/− mice after 72 h of vehicle or tunicamycin treatment (n = 5 per group).
Figure 6: Analysis of liver from control and L-Pik3r1−/− mice after tunicamycin treatment.

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Acknowledgements

We would like to thank D. Ron (New York University School of Medicine) for providing the Flag–XBP-1u and Flag–XBP-1s expression plasmids. This work was supported by US National Institutes of Health grant DK55545 and National Institutes of Health training grant DK07260-30, as well as Core laboratory support from the Joslin Diabetes and Endocrine Research Center grant DK36836. We would also like to thank U. Ozcan for useful advice and discussion and S. Green and S. Flaherty for assistance in preparation of this manuscript.

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  1. Jeremie Boucher and Marcelo A Mori: These authors contributed equally to this work.

Authors and Affiliations

  1. Research Division, Section on Integrative Physiology and Metabolism, Joslin Diabetes Center, Harvard Medical School, Boston, Massachusetts, USA

    Jonathon N Winnay, Jeremie Boucher, Marcelo A Mori & C Ronald Kahn

  2. Department of Metabolic Diseases, Graduate School of Medicine, The University of Tokyo, Tokyo, Japan

    Kohjiro Ueki

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Contributions

J.N.W. came up with the hypothesis, designed and performed the experiments, analyzed the data and wrote the manuscript. J.B. and M.A.M. designed and performed the experiments and analyzed the data. K.U. came up with the hypothesis and generated reagents. C.R.K. came up with the hypothesis, helped analyze the data and wrote the manuscript.

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Correspondence to C Ronald Kahn.

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Winnay, J., Boucher, J., Mori, M. et al. A regulatory subunit of phosphoinositide 3-kinase increases the nuclear accumulation of X-box–binding protein-1 to modulate the unfolded protein response. Nat Med 16, 438–445 (2010). https://doi.org/10.1038/nm.2121

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