Id1 Attenuates Notch Signaling and Impairs T-Cell Commitment by Elevating Deltex1 Expression

Abstract

Complete inhibition of E protein transcription factors by Id1 blocks the developmental transition of CD4/CD8 double-negative 1 (DN1; CD44⁺ CD25⁻) thymocytes to the DN2 (CD44⁺ CD25⁺) stage. To understand the underlying mechanisms, we observed that mRNA levels of Deltex1, as well as Deltex4, were dramatically elevated in Id1-expressing thymocytes, which could result in developmental arrest by attenuating Notch function. In support of this hypothesis, we found that Deltex1 ablation enabled Id1-expressing progenitors to differentiate to the DN3 (CD44⁻ CD25⁺) stage, which was accompanied by enhanced Notch1 expression in T-cell progenitors. Consistently, constitutive activation of Notch1 drove the differentiation of Id1-expressing progenitors to the DN3 stage. Furthermore, we showed that Gfi1b levels decreased, whereas GATA3 levels increased in Id1 transgenic thymocytes. When overexpressed, GATA3 was able to upregulate Deltex1 transcription. Thus, T-cell commitment may be controlled by the interplay among E proteins, Gfi1b, and GATA3 transcription regulators, which influence Notch function through the expression of Deltex1.

ACKNOWLEDGMENTS

We thank Ying Zhao for technical assistance and members of the Sun laboratory for advice. We are grateful to Jose Alberola-Ila and Flora Ling for critical reading of the manuscript.

We wish to dedicate the manuscript to the memory of Wei-Feng Chen.

This work was supported by grants from the National Institute of Health to X.-H.S. (CA77553 and AI56129). X.-H.S. holds the Eli Lilly Distinguished Chair in Biomedical Research.