Mechanistic Investigation of Genotype-Phenotype Correlations in PIK3R1-Related Diseases
type: CreativeWork
description: The PIK3R1 gene encodes three proteins - p85$\alpha$, p50$\alpha$ and p55$\alpha$ - that are regulatory subunits of Class IA phosphoinositide 3-kinases (PI3Ks). These regulatory subunits heterodimerise with one of three catalytic subunit isoforms, namely p110$\alpha$, p110$\beta$, or p110$\delta$. Class IA PI3Ks are critical enzymes involved in fundamental metabolic and mitogenic signalling pathways. This thesis describes the delineation of biochemical and molecular mechanisms whereby PIK3R1 mutations cause diverse disease phenotypes observed in SHORT syndrome (defined by Short stature, Hyperextensibility, Ocular depression, Rieger anomaly and Teething delay), the primary immunodeficiency Activated PI3K-$\delta$ Syndrome 2 (APDS2), and cancer. Initial studies of purified wildtype or mutant PI3K complexes, utilising a modified PI3K fluorescence polarisation lipid kinase assay, established that SHORT syndrome-associated p85$\alpha$ mutations impaired phosphotyrosine peptide-stimulated PI3K activity when heterodimerised with either of the Class IA catalytic subunit isoforms. Two cancer-associated mutations assessed using the same assay demonstrated differential effects on PI3K function, causing either basal activation or impaired phosphotyrosine peptide-stimulated PI3K activity. To examine the effect of SHORT syndrome-associated p85$\alpha$ mutations in insulin-responsive cell types, 3T3-L1 preadipocyte models with conditional overexpression of p85$\alpha$ Y657X or p85$\alpha$ R649W were generated. Doxycycline-induced overexpression of mutant p85$\alpha$ attenuated insulin-stimulated Akt phosphorylation due to reduced insulin-stimulated association of p85$\alpha$/p110$\alpha$ heterodimers with either IRS1 or IRS2. This in turn resulted in impaired downstream signalling as indicated by low adipogenic efficiency. Cells and tissues isolated from Pik3r1$^{WT/Y657X}$ knock-in mice also demonstrated decreased insulin-stimulated Akt phosphorylation. Observations from a system…
abstract: The PIK3R1 gene encodes three proteins - p85$\alpha$, p50$\alpha$ and p55$\alpha$ - that are regulatory subunits of Class IA phosphoinositide 3-kinases (PI3Ks). These regulatory subunits heterodimerise with one of three catalytic subunit isoforms, namely p110$\alpha$, p110$\beta$, or p110$\delta$. Class IA PI3Ks are critical enzymes involved in fundamental metabolic and mitogenic signalling pathways. This thesis describes the delineation of biochemical and molecular mechanisms whereby PIK3R1 mutations cause diverse disease phenotypes observed in SHORT syndrome (defined by Short stature, Hyperextensibility, Ocular depression, Rieger anomaly and Teething delay), the primary immunodeficiency Activated PI3K-$\delta$ Syndrome 2 (APDS2), and cancer. Initial studies of purified wildtype or mutant PI3K complexes, utilising a modified PI3K fluorescence polarisation lipid kinase assay, established that SHORT syndrome-associated p85$\alpha$ mutations impaired phosphotyrosine peptide-stimulated PI3K activity when heterodimerised with either of the Class IA catalytic subunit isoforms. Two cancer-associated mutations assessed using the same assay demonstrated differential effects on PI3K function, causing either basal activation or impaired phosphotyrosine peptide-stimulated PI3K activity. To examine the effect of SHORT syndrome-associated p85$\alpha$ mutations in insulin-responsive cell types, 3T3-L1 preadipocyte models with conditional overexpression of p85$\alpha$ Y657X or p85$\alpha$ R649W were generated. Doxycycline-induced overexpression of mutant p85$\alpha$ attenuated insulin-stimulated Akt phosphorylation due to reduced insulin-stimulated association of p85$\alpha$/p110$\alpha$ heterodimers with either IRS1 or IRS2. This in turn resulted in impaired downstream signalling as indicated by low adipogenic efficiency. Cells and tissues isolated from Pik3r1$^{WT/Y657X}$ knock-in mice also demonstrated decreased insulin-stimulated Akt phosphorylation. Observations from a system…
author: Tomlinson, Patsy Roseanne
language: en
keywords: SHORT syndrome, Phosphoinositide 3-kinase, PI3K, Metabolism, Cell Signalling, Genotype-Phenotype
license: https://apollo8-f-pro.lib.cam.ac.uk/bitstreams/5f18872a-b299-4a50-ae54-6ca7d4f6cb50/download
license: https://www.rioxx.net/licenses/all-rights-reserved/
date published: 2018-01-24
date modified: 2026-07-22T22:24:30Z
provider: Cambridge University
publisher: Networked Digital Library of Theses and Dissertations
type: WebPage
source organization: University of Cambridge

PropertyValue
property ID: DOI
value: 10.17863/CAM.18165