The mammalian target of rapamycin (mTOR) drives lymphocyte growth, division, and differentiation following antigen stimulation. mTOR is a protein kinase that functions in two complexes, mTORC1 and mTORC2. Rapamycin is an allosteric mTORC1 inhibitor that profoundly suppresses B cell proliferation and differentiation. Conversely, elevated mTORC1 activity is seen in lymphocytes from patients with autoantibody-driven disorders including arthritis and lupus. However, the mechanisms by which mTORC1 signaling promotes B cell differentiation remain poorly defined. We have reported that genetic or pharmacological inhibition of mTORC1 suppresses antibody class switching in activated B cells. Subsequently we identified novel roles for eukaryotic initiation factor 4E (eIF4E), a downstream mTORC1 effector, in promoting B cell proliferation and antibody class switching. eIF4E regulates the translation of subsets of mRNAs in a cell type-specific manner, and is opposed by eIF4E-binding proteins (4E-BPs) that are direct substrates of mTORC1. Using novel chemical tools and genetic mouse models we have determined that the roles of mTORC1, 4E-BPs and eIF4E in class switching can be separated from their roles in proliferation. The general goal of this proposal is to define the mechanisms by which mTORC1 and eIF4E promote antibody class switching.
The first Aim i s to test the hypothesis that efficient class switching requires eIF4E an is opposed by 4E-BPs. We will measure isotype switching in activated B cells from mice with increased or decreased expression of eIF4E or 4E-BPs, in the presence or absence of RAP. Novel compounds that inhibit mTORC1 through an ATP-competitive manner will also be used. The role of the 4E-BP/eIF4E signaling axis will also be tested in vivo by measuring antibody responses and germinal center formation in immunized mice.
The second Aim will define the mechanisms by which eIF4E regulates translation of mRNAs involved in B cell differentiation. Increasing evidence indicates that translation efficiency varies widely among individual mRNAs, and that regulated translation modulates the proteome to a similar degree as transcriptional and epigenetic regulation. In accord, genome-wide translatome studies have uncovered novel regulatory mechanisms in tumorigenesis and other processes. We will use ribosome profiling for global, unbiased identification of eIF4E targets that are differentially translated in activated B cells undergoing antibody class switching. This project is significant because a greater understanding of the translatome controlled by eIF4E and suppressed by mTORC1 inhibition might reveal novel strategies for suppressing pathogenic autoantibody responses, with a better therapeutic window than rapamycin. This work will also shed light on potential immunosuppressive effects of eIF4E inhibitors under development for cancer.

Public Health Relevance

Rapamycin is an immunosuppressive drug that blocks activity of enzyme called mTOR. The goal of this project is to gain new insight into how mTOR signals to a translation factor called eIF4E to promote synthesis of proteins necessary for antibody class switching. We will achieve this using innovative chemical tools, new mouse models, and genomic technology. The results of this project might reveal novel targets for immunosuppression with a better therapeutic window than rapamycin.

Agency
National Institute of Health (NIH)
Institute
National Institute of Allergy and Infectious Diseases (NIAID)
Type
Exploratory/Developmental Grants (R21)
Project #
1R21AI124146-01
Application #
9092908
Study Section
Cellular and Molecular Immunology - A Study Section (CMIA)
Program Officer
Ferguson, Stacy E
Project Start
2016-03-16
Project End
2018-02-28
Budget Start
2016-03-16
Budget End
2017-02-28
Support Year
1
Fiscal Year
2016
Total Cost
$222,886
Indirect Cost
$67,036
Name
University of California Irvine
Department
Biochemistry
Type
Schools of Arts and Sciences
DUNS #
046705849
City
Irvine
State
CA
Country
United States
Zip Code
92617
Chiu, Honyin; Jackson, Leandra V; Oh, Kwon Ik et al. (2018) The mTORC1/4E-BP/eIF4E Axis Promotes Antibody Class Switching in B Lymphocytes. J Immunol :
Fruman, David A; Chiu, Honyin; Hopkins, Benjamin D et al. (2017) The PI3K Pathway in Human Disease. Cell 170:605-635