IMMUNOLOGY
mRNA destabilization by BTG1 and BTG2 maintains
T cell quiescence
Soo Seok Hwang^1 , Jaechul Lim^1 , Zhibin Yu1,2,3, Philip Kong^1 , Esen Sefik^1 , Hao Xu^1 ,
Christian C. D. Harman^1 , Lark Kyun Kim^4 , Gap Ryol Lee^5 , Hua-Bing Li1,2,3, Richard A. Flavell1,6†
T cells maintain a quiescent state prior to activation. As inappropriate T cell activation can
cause disease, T cell quiescence must be preserved. Despite its importance, the mechanisms
underlying the“quiescent state”remain elusive. Here, we identify BTG1 and BTG2 (BTG1/2)
as factors responsible for T cell quiescence. BTG1/2-deficient T cells show an increased
proliferation and spontaneous activation duetoaglobalincreaseinmessengerRNA(mRNA)
abundance, which reduces the threshold to activation. BTG1/2 deficiency leads to an increase in
polyadenylate tail length, resulting in a greater mRNA half-life. Thus, BTG1/2 promote the
deadenylation and degradation of mRNA to secure T cell quiescence. Our study reveals a key
mechanism underlying T cell quiescence and suggests that low mRNA abundance is a crucial
feature for maintaining quiescence.
Q
uiescence is a cellular state in which
cells undergo reversible cell cycle arrest
in response to environmental challenges
or lack of stimuli ( 1 ). For T lymphocytes,
quiescence is a ground state where they
are poised in the absence of activation sig-
nals. In this state, T cells barely proliferate and
maintain a low basal metabolic rate, which is
required for survival ( 2 , 3 ). Upon encountering
cognate antigen through T cell receptor (TCR)–
costimulatory signals, naïve T cells exit quies-
cence and undergo clonal expansion and dif-
ferentiation ( 4 ). Studies have shown that T cell
quiescence is actively maintained, rather than a
default state ( 5 – 7 ). In naïve T cells, FOXO1 and
KLF2 control cell trafficking by modulating
genes such asCcr7,S1pr1, andSell( 8 , 9 ). Ad-
ditionally, cytokines and receptors impor-
tant for T cell quiescence are regulated by
FOXO1, FOXP1, and TOB ( 7 , 8 , 10 ). Metabolic
programming by TSC1 also supports T cell
quiescence ( 11 ). Although these factors play
crucial roles in T cell quiescence through
specific genes or programs, how“minimal-ism”operates in quiescent T cells remains
largely unknown.
To reveal additional factors responsible for
orchestrating quiescence in T cells, we searched
for genes regulated by super-enhancers [strong
histone H3 lysine 27 acetylation (H3K27ac)
signals] in quiescent T cells. Our rationale was
that super-enhancers are closely associated with
cell-type specificity ( 12 ). We found a super-
enhancer linked toBTG1andBTG2in the
top ~1% of hits, which was comparable to the
percentage forKLF2andIL7R(Fig. 1A and
fig. S1A). BTG1/2 belong to the B cell translo-
cation gene/Transducer of ERBB2 (BTG/TOB)
family ( 13 , 14 ), which shows antiproliferative
activity and is implicated in numerous cellular
processes ( 14 , 15 ). Notably,BTG1/ 2 were highly
expressed in lymph nodes and white blood
cells among the BTG/TOB family, suggestingRESEARCH
Hwanget al.,Science 367 , 1255–1260 (2020) 13 March 2020 1of5
(^1) Department of Immunobiology, Yale University School of
Medicine, New Haven, CT 06510, USA.^2 Shanghai Institute of
Immunology, Department of Microbiology and Immunology,
Shanghai Jiao Tong University School of Medicine
(SJTU-SM), Shanghai 200025, China.^3 Yale Center for
ImmunoMetabolism, Shanghai Jiao Tong University School of
Medicine (SJTU-SM), Shanghai 200025, China^4 Severance
Biomedical Science Institute and BK21 PLUS Project for
Medical Sciences, Gangnam Severance Hospital, Yonsei
University College of Medicine, Seoul 06230, Republic of
Korea.^5 Department of Life Science, Sogang University, Seoul
04107, Republic of Korea.^6 Howard Hughes Medical Institute,
Chevy Chase, MD 20815-6789, USA.
*These authors contributed equally to this work.
†Corresponding author. Email: [email protected]
Fig. 1. BTG1 and BTG2 are mainly expressed in
quiescent T cells.(A) Super-enhancers are ranked
by normalized H3K27ac chromatin immunoprecipitation
sequencing signals. Super-enhancer signals are
adopted from ( 12 ). (B) Tissue-specific expression of
BTG1/2 in the immune system. RNA-seq data are
adopted from Illumina Body map 2.0 project
(PRJEB2445). TPM, transcripts per million. (C) Relative
expression ofBtg1/ 2 in naïve and memory CD4 T cells.
(D) Decrease ofBtg1andBtg2expression upon
TCR stimulation. Mouse naïve CD4 and CD8 T cells
were cultured with antibodies against CD3 (a-CD3)
(5mg/ml) anda-CD28 (2mg/ml) for 5 days. The
expression ofBtg1/ 2 was quantified by reverse
transcription–quantitative polymerase chain
reaction (RT-qPCR) (top) and immunoblotting
(bottom), respectively. Error bars represent
SEM (n= 2). Each symbol represents the mean
of two independent experiments with two
technical replicates.