A requirement for sustained ERK signaling during thymocyte positive selection in vivo

doi:10.1073/pnas.0505110102

A requirement for sustained ERK signaling during thymocyte positive selection in vivo

Center for Immunology, Department of Laboratory Medicine and Pathology, University of Minnesota, Minneapolis, MN 55455

Edited by Harvey Cantor, Harvard Medical School, Boston, MA, and approved July 28, 2005 (received for review June 17, 2005)

Abstract

It is unknown how the contrasting events of positive and negative selection can lead to the distinct biological outcomes of life or death. An increasing body of evidence suggests that the duration of extracellular signal-regulated kinase (ERK) signaling plays a role in thymocyte selection. However, it remains unclear what the kinetics of ERK activation are during positive selection in vivo. In this study, we examined the magnitude and duration of ERK signaling in intact murine thymic tissues cultured under conditions of negative or positive selection. We found that negative selection induced a rapid and robust ERK activation that is associated with death, whereas positive selection stimulated a lower intensity and brief ERK activation that quickly declined and then gradually increased and was sustained over several days. The expression pattern of Egr-1 (early growth response-1), a downstream ERK effector, correlates with the biphasic kinetics of ERK during positive selection. Id3 (inhibitor of differentiation/DNA binding 3) also exhibits biphasic kinetics but appeared to be independent of ERK signaling. Furthermore, inhibitors of T cell receptor ligation and ERK activation block maturation of CD8 single-positive thymocytes even when added after 24 h. These results demonstrate that the in vivo duration of ERK signaling must be sustained to support positive selection.

T cell development

Footnotes

↵ * To whom correspondence should be addressed at: Center for Immunology, University of Minnesota, Mayo Mail Code 334, 420 Delaware Street SE, Minneapolis, MN 55455. E-mail: hogqu001{at}umn.edu.
This paper was submitted directly (Track II) to the PNAS office.
Abbreviations: ERK, extracellular signal-regulated kinase; FTOC, fetal thymic organ culture; DP, CD4⁺ CD8⁺ double-positive; SP, single-positive; IEG, immediate early gene; Egr-1, early growth response-1; Id3, inhibitor of differentiation/DNA binding 3; βCATp, β-catenin peptide; MAPK, mitogen-activated protein kinase; TCR, T cell receptor; MEK, MAPK kinase; OVA, ovalbumin; TAP, transporter associated with antigen processing; APC, antigen-presenting cell; MFI, mean fluorescence intensity.