The Catalytic Activity of the Mitogen-Activated Protein Kinase Extracellular Signal-Regulated Kinase 3 Is Required To Sustain CD4⁺ CD8⁺ Thymocyte Survival

Abstract

Extracellular signal-regulated kinase 3 (ERK3) is an atypical member of the mitogen-activated protein kinase (MAPK) family whose function is largely unknown. Given the central role of MAPKs in T cell development, we hypothesized that ERK3 may regulate thymocyte development. Here we have shown that ERK3 deficiency leads to a 50% reduction in CD4⁺ CD8⁺ (DP) thymocyte number. Analysis of hematopoietic chimeras revealed that the reduction in DP thymocytes is intrinsic to hematopoietic cells. We found that early thymic progenitors seed the Erk3^−/− thymus and can properly differentiate and proliferate to generate DP thymocytes. However, ERK3 deficiency results in a decrease in the DP thymocyte half-life, associated with a higher level of apoptosis. As a consequence, ERK3-deficient DP thymocytes are impaired in their ability to make successful secondary T cell receptor alpha (TCRα) gene rearrangement. Introduction of an already rearranged TCR transgene restores thymic cell number. We further show that knock-in of a catalytically inactive allele of Erk3 fails to rescue the loss of DP thymocytes. Our results uncover a unique role for ERK3, dependent on its kinase activity, during T cell development and show that this atypical MAPK is essential to sustain DP survival during RAG-mediated rearrangements.

ACKNOWLEDGMENTS

We thank members of the laboratory for helpful discussion. We acknowledge C. Perreault, S. Lesage, and H. Melichar for critical reading of the manuscript. We thank N. Henley and M. Dupuis for cell sorting, C. Beauchamp, J. Rooney, M. Saba El Leil, and K. Lévesque for technical assistance, M. Chagnon for statistical analysis, and the staff of the Animal Facility for mouse care.

This work was supported by grants from the Natural Sciences and Engineering Council of Canada (NSERC) (grant number 262146-2009) to N.L. and the Canadian Institutes of Health Research (CIHR) (MOP-93729) to S. Meloche. M.M. was supported by the Cole Foundation and the University of Montreal. S.B. was supported by a CIHR Fellowship, and K.C. was supported by an NSERC summer studentship. S. Meloche holds the Canada Research Chair in Cellular Signaling. N.L. was supported by a CIHR New Investigator Award and a Senior Scholarship of the Fonds de la Recherche en Santé du Québec.