A stepwise and digital pattern of RSK phosphorylation determines the outcome of thymic selection

Shintaro Funasaki; Atsushi Hatano; Hirokazu Nakatsumi; Daisuke Koga; Osamu Sugahara; Kanae Yumimoto; Masaya Baba; Masaki Matsumoto; Keiichi I Nakayama

doi:10.1016/j.isci.2023.107552

A stepwise and digital pattern of RSK phosphorylation determines the outcome of thymic selection

iScience. 2023 Aug 9;26(9):107552. doi: 10.1016/j.isci.2023.107552. eCollection 2023 Sep 15.

Authors

Shintaro Funasaki^{1

2}, Atsushi Hatano³, Hirokazu Nakatsumi¹, Daisuke Koga¹, Osamu Sugahara¹, Kanae Yumimoto¹, Masaya Baba², Masaki Matsumoto^{1

3}, Keiichi I Nakayama^{1

4}

Affiliations

¹ Department of Molecular and Cellular Biology, Medical Institute of Bioregulation, Kyushu University, Fukuoka, Fukuoka 812-8582, Japan.
² Laboratory of Cancer Metabolism, International Research Center for Medical Sciences (IRCMS), Kumamoto University, Kumamoto, Kumamoto 860-0811, Japan.
³ Department of Omics and Systems Biology, Graduate School of Medical and Dental Sciences, Niigata University, Niigata, Niigata 951-8510, Japan.
⁴ Anticancer Strategies Laboratory, TMDU Advanced Research Institute, Tokyo Medical and Dental University, Bunkyo-ku, Tokyo 113-8510, Japan.

Abstract

Developing CD4⁺CD8⁺ double-positive (DP) thymocytes with randomly generated T cell receptors (TCRs) undergo positive (maturation) or negative (apoptosis) selection on the basis of the strength of TCR stimulation. Selection fate is determined by engagement of TCR ligands with a subtle difference in affinity, but the molecular details of TCR signaling leading to the different selection outcomes have remained unclear. We performed phosphoproteome analysis of DP thymocytes and found that p90 ribosomal protein kinase (RSK) phosphorylation at Thr⁵⁶² was induced specifically by high-affinity peptide ligands. Such phosphorylation of RSK triggered its translocation to the nucleus, where it phosphorylated the nuclear receptor Nur77 and thereby promoted its mitochondrial translocation for apoptosis induction. Inhibition of RSK activity protected DP thymocytes from antigen-induced cell death. We propose that RSK phosphorylation constitutes a mechanism by which DP thymocytes generate a stepwise and binary signal in response to exposure to TCR ligands with a graded affinity.

Keywords: Cell biology; Immunology.