Cytotoxic T-lymphocyte-associated protein 4 (CTLA4) is an immune checkpoint protein, expressed by T cells, which has a critical role in regulating the immune response. The finely-tuned nature of CTLA4 mediated immune regulation in humans is illustrated by the fact that heterozygous loss of function mutations in CTLA4 cause a syndrome of severe autoimmunity. We recently reported that another immune regulatory disorder, very similar in appearance to haploinsufficiency of CTLA4, but caused by biallelic mutations in ?LPS- responsive vesicle trafficking, beach and anchor containing? (LRBA), is associated with functional deficiency of CTLA4 and is highly responsive to therapy with CTLA4-Ig. Furthermore, we demonstrated that LRBA interacts with the cytoplasmic tail of CTLA4, altering its intracellular distribution, and slowing lysosomal degradation. Our biochemical experiments demonstrated interaction between the BEACH domain of LRBA and the YVKM motif of CTLA4, the same motif bound by clathrin adaptors. Thus, we hypothesize that LRBA controls CTLA4 levels and localization via a direct BEACH:YVKM interaction, in competition with clathrin adaptors, preventing movement to lysosomal compartments. We propose to test this hypothesis by first assessing structural and biophysical LRBA: CTLA4 interactions. Second, we will make an unbiased assessment of interacting proteins via mass spectrometry for both LRBA and CTLA4. In so doing we will define proteins which potentially modify or mediate LRBA:CTLA4 interactions.

Public Health Relevance

Human LRBA deficiency causes a severe immune regulatory/ immune deficiency disorder. We have found that this disorder is associated with functional deficiency of CTLA4, which is the probable cause for most or all clinical manifestations. LRBA appears to control CTLA4 levels via a specific binding interaction. Our proposal seeks to better understand the nature of this interaction and how it affects CTLA4 trafficking and turnover.

Agency
National Institute of Health (NIH)
Institute
National Institute of Allergy and Infectious Diseases (NIAID)
Type
Exploratory/Developmental Grants (R21)
Project #
1R21AI132822-01
Application #
9372162
Study Section
Cellular and Molecular Immunology - A Study Section (CMIA)
Program Officer
Singleton, Kentner L
Project Start
2017-06-01
Project End
2019-05-31
Budget Start
2017-06-01
Budget End
2018-05-31
Support Year
1
Fiscal Year
2017
Total Cost
$234,000
Indirect Cost
$84,000
Name
Cincinnati Children's Hospital Medical Center
Department
Type
Independent Hospitals
DUNS #
071284913
City
Cincinnati
State
OH
Country
United States
Zip Code
45229
Herr, Andrew B (2018) Evolution of an allosteric ""off switch"" in apoptotic caspases. J Biol Chem 293:5462-5463