Insulin resistance uncoupled from dyslipidemia due to C-terminal PIK3R1 mutations
Isabel Huang-Doran, Patsy Tomlinson, Felicity Payne, Alexandra Gast, Alison Sleigh, William Bottomley, Julie Harris, Allan Daly, Nuno Rocha, Simon Rudge, Jonathan Clark, Albert Kwok, Stefano Romeo, Emma McCann, Barbara Müksch, Mehul Dattani, Stefano Zucchini, Michael Wakelam, Lazaros C. Foukas, David B. Savage, Rinki Murphy, Stephen O’Rahilly, Inês Barroso, Robert K. Semple
Isabel Huang-Doran, Patsy Tomlinson, Felicity Payne, Alexandra Gast, Alison Sleigh, William Bottomley, Julie Harris, Allan Daly, Nuno Rocha, Simon Rudge, Jonathan Clark, Albert Kwok, Stefano Romeo, Emma McCann, Barbara Müksch, Mehul Dattani, Stefano Zucchini, Michael Wakelam, Lazaros C. Foukas, David B. Savage, Rinki Murphy, Stephen O’Rahilly, Inês Barroso, Robert K. Semple
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Research Article Endocrinology Metabolism

Insulin resistance uncoupled from dyslipidemia due to C-terminal PIK3R1 mutations

Abstract

Obesity-related insulin resistance is associated with fatty liver, dyslipidemia, and low plasma adiponectin. Insulin resistance due to insulin receptor (INSR) dysfunction is associated with none of these, but when due to dysfunction of the downstream kinase AKT2 phenocopies obesity-related insulin resistance. We report 5 patients with SHORT syndrome and C-terminal mutations in PIK3R1, encoding the p85α/p55α/p50α subunits of PI3K, which act between INSR and AKT in insulin signaling. Four of 5 patients had extreme insulin resistance without dyslipidemia or hepatic steatosis. In 3 of these 4, plasma adiponectin was preserved, as in insulin receptor dysfunction. The fourth patient and her healthy mother had low plasma adiponectin associated with a potentially novel mutation, p.Asp231Ala, in adiponectin itself. Cells studied from one patient with the p.Tyr657X PIK3R1 mutation expressed abundant truncated PIK3R1 products and showed severely reduced insulin-stimulated association of mutant but not WT p85α with IRS1, but normal downstream signaling. In 3T3-L1 preadipocytes, mutant p85α overexpression attenuated insulin-induced AKT phosphorylation and adipocyte differentiation. Thus, PIK3R1 C-terminal mutations impair insulin signaling only in some cellular contexts and produce a subphenotype of insulin resistance resembling INSR dysfunction but unlike AKT2 dysfunction, implicating PI3K in the pathogenesis of key components of the metabolic syndrome.

Authors

Isabel Huang-Doran, Patsy Tomlinson, Felicity Payne, Alexandra Gast, Alison Sleigh, William Bottomley, Julie Harris, Allan Daly, Nuno Rocha, Simon Rudge, Jonathan Clark, Albert Kwok, Stefano Romeo, Emma McCann, Barbara Müksch, Mehul Dattani, Stefano Zucchini, Michael Wakelam, Lazaros C. Foukas, David B. Savage, Rinki Murphy, Stephen O’Rahilly, Inês Barroso, Robert K. Semple

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Figure 2

A de novo heterozygous nonsense mutation in PIK3R1 in a patient with severe insulin resistance.

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A de novo heterozygous nonsense mutation in PIK3R1 in a patient with sev...
(A) Genomic DNA sequence from patient 1 (P1) and her parents showing the de novo p.Tyr657X (Y657X) mutation in PIK3R1. (B) Domain structure of the protein products of PIK3R1 (p85α, p55α, and p50α) and predicted truncation site resulting from the nonsense mutation. (C) Full-length and truncated p85α, p55α, and p50α (indicated by arrowheads) and full-length p85β in EBV-transformed lymphoblastoid cells (EBVLs) from P1 and healthy controls (C1–C4), as assessed by Western blotting for total p85 (p85α/β) or p85β alone. (D) Expression of p85α or p85β in dermal fibroblasts from P1 and healthy controls (C1, C2). (E) Quantification of WT and mutant p85α expression in P1 and control fibroblasts from 4 independent Western blots, normalized to mean expression of WT p85α in controls. *P < 0.05, ***P < 0.005; 1-way ANOVA followed by post-hoc Tukey test. Total number of observations indicated in parentheses. Dot plot displays mean ± SEM. (F) Western blot of p110α after IP of total p85 in primary dermal fibroblast lysates. (G) Western blot of p110β after IP of total p85 in primary dermal fibroblast lysates.