are no longer expressed, showed no difference
in mRNA degradation between WT and DKO
(fig. S15), suggesting that BTG1/2 contribute to
lowering mRNA amounts through mRNA turn-
over in naïve but not activated T cells.
To examine if poly(A) length is indeed
elongated in DKO cells, we performed mTAIL-
seq (fig. S16A) ( 24 ). In line with the stabiliza-
tion of mRNA, the poly(A) tail length of DKO
T cells was longer than that of WT (Fig. 4, E
and F, and table S4). Again, mtRNA poly(A)
tail lengths were nearly unchanged (Fig. 4F),
suggesting that BTG1/2-mediated deadenyla-
tion was responsible for degrading the bulk of
cytoplasmic mRNA in naïve T cells. Notably,
the difference in poly(A) tail length in naïve
T cells was diminished in activated T cells
(fig.S16,BandC,andtableS5).
In conclusion, we propose a model to ex-
plainhowthequiescentstateinTcellsis
maintained (Fig. 4G). BTG1 and BTG2 are
highly and specifically expressed in quiescent
T cells and promote mRNA deadenylation and
degradation. Unlike BTG1/2, deadenylases ap-
pear to be ubiquitously expressed at a low level,
implying a specialized function of BTG1/2 in
immune cells (fig. S17). Because BTG1/2 inter-
actwithPABPandtheCNOTcomplex,which
bind nonspecifically to mRNAs ( 25 ), BTG1/2
can direct the down-regulation of mRNAs at
a global level. This mechanism is seemingly
inefficient in terms of cost, but the availability
of presynthesized mRNA provides a benefit to
quiescent T cells of a rapid response to acti-
vation signals. Given that naïve T cells differ-
entiate into multiple lineages, having such a
primed state on a hair trigger would be ulti-
mately beneficial. Upon activation, BTG1/2
quickly disappear, which results in an accumu-
lation of mRNAs and exit from the quiescent
state (Figs. 1D and 4G).
Here, we show the functional consequences
of BTG1/2-mediated deadenylation in vivo.
B cells may also use a similar mechanism
to maintain quiescence through BTG1/2, as
BTG1/2 are commonly dysregulated in leuke-
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other cofactors, in addition to BTG1/2, may
recruit and enhance mRNA deadenylation and
degradation in certain cell types. Thus, the
mechanism that we propose may be broadly
applicable to other cells and tissues, serving as
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ACKNOWLEDGMENTS
We are grateful to R. Medzhitov for support and discussions. We
thank J. Y. Hwang and W. J. Chae for helpful comments.
We also thank all members of the Flavell laboratory for
technical and administrative support. We thank M. Ha for the
gift of RNA spike-in and J. Choi for illustrating the graphical
abstract.Funding:This work was supported by the Howard
Hughes Medical Institute (R.A.F.). The work of S.S.H. was
supported by a Leslie H. Warner Fellowship from Yale Cancer
Center (YCC). The work of J.L. was supported by postdoctoral
fellowships from the HFSPO (LT000037/2018-L) and Jane
Coffin Childs Memorial Fund. G.R.L was supported by National
Research Foundation of Korea (NRF-2017R1A2B3008621).
H.B.L. was supported by the National Natural Science Foundation
of China (91753141) and the start-up fund from the Shanghai
Jiao Tong University School of Medicine.Author contributions:
S.S.H. conceived and initiated the project. S.S.H. and J.L. designed
the experiments, analyzed and discussed the results, and wrote
the manuscript. S.S.H. performed most of the experiments in
this study. J.L. performed total RNA-seq and mTAIL-seq, analyzed
the data, and illustrated the figures. Z.Y. and P.K. helped to
perform the FACS analysis and in vitro experiments. E.S. and
H.X. helped to carry out the colitis experiment. C.C.D.H. helped
to analyze our deep RNA-seq data. L.K.K., G.R.L., and H.-B.L.
contributed to key discussions. R.A.F. supervised the project,
participated in interpreting the results, and edited the manuscript.
Competing interests:R.A.F is a consultant for GSK and Zai Lab
Ltd. All other authors declare no competing financial interests.
Data and materials availability:Sequenced reads have been
deposited in the NCBI Gene Expression Omnibus (GEO) database
(accession no. GSE125890).SUPPLEMENTARY MATERIALS
science.sciencemag.org/content/367/6483/1255/suppl/DC1
Materials and Methods
Figs. S1 to 17
Tables S1 to S6
References ( 29 – 33 )
View/request a protocol for this paper fromBio-protocol.14 February 2019; resubmitted 22 October 2019
Accepted 19 February 2020
10.1126/science.aax0194Hwanget al.,Science 367 , 1255–1260 (2020) 13 March 2020 5of5
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