Genetic Control of Splicing at SIRPG Modulates Risk of Type 1 Diabetes
figure
posted on 2021-11-22, 21:05 authored by Morgan J. Smith, Lucia Pastor, Jeremy R.B. Newman, Patrick ConcannonSignal regulatory protein SIRPγ
(CD172G) is expressed on the surface of lymphocytes where it acts by engaging
its ligand, CD47. SIRPG, which encodes
SIRPγ, contains a non-synonymous coding variant, rs6043409, which is significantly
associated with risk for type 1 diabetes. SIRPG
produces multiple transcript isoforms via alternative splicing, all encoding
potentially functional proteins. We show that rs6043409 alters a predicted
exonic splicing enhancer, resulting in significant shifts in the distribution
of SIRPG transcript isoforms. All of
these transcript isoforms produced protein upon transient expression in vitro. However, CRISPR targeting of one
of the alternatively spliced exons in SIRPG
eliminated all SIRPγ expression in Jurkat T cells. These targeted cells formed fewer
cell-cell conjugates with each other than with wild type Jurkat cells, expressed
reduced levels of genes associated with CD47 signaling and had significantly
increased levels of cell surface CD47. In primary CD4+ and CD8+
T cells cell surface SIRPγ levels in response to anti-CD3 stimulation varied quantitatively
by rs6043409 genotype. Our results suggest that SIRPG is the most likely causative gene for type 1 diabetes risk in
the 20p13 region and highlight the role of alternative splicing in lymphocytes
in mediating the genetic risk for autoimmunity.
