Novel roles for TCF-1 and LEF-1 in directing CD4+ T cell fate and silencing CD4 in CD8+ T cells

Abstract

I would like to thank the University of Iowa Flow Cytometry Facility and its engineers, Justin Fishbaugh, Heath Vignes and George Rasmussen for their cordial and knowledgeable support of my research. They always performed their work humbly, yet flawlessly and exhibited a professionalism matched only by their compassion. Thank you for your patience and help over the years.I need to thank all who have guided and supported me from the beginnings of my passion for science, including those who have unknowingly made me a dedicated scientist. To all of my friends, including the golden oldies, the new colleagues who've formed summer softball teams and social outings in Iowa City, and various teammates from tennis club and Trihawks, thanks for being an understanding and wholesome outlet.To the middle school science teachers, the variety of coaches and especially the family members who have always encouraged the pursuit of knowledge and happiness -thank you.v ABSTRACT CD4 + and CD8 + T cells, the essential mediators of cellular immune responses, are produced in the thymus following sequential maturation stages. Hematopoietic progenitors first seed the thymus and make T cell lineage specification and commitment decisions within the CD4 − CD8 − double negative (DN) compartment. Thymocytes then mature to the CD4 + CD8 + double positive (DP) stage, followed by vigorous negative and positive selection processes. The positively selected DP thymocytes first give rise to CD4 + CD8 lo intermediate (IM) cells which then differentiate into MHC class II-restricted CD4 + and MHC class I-restricted CD8 + T cells, a crucial decision known as CD4 + vs.The lineage choice decision is influenced by the timing, intensity, and duration of signals derived from the TCR and cytokines, and recent studies have identified a number of transcriptional factors that intrinsically regulate this critical fate decision. Among these, Th-POK (encoded by Zbtb7b, called Thpok here for simplicity and consistency with the literature) is specifically required for CD4 + differentiation while Runx factors promote CD8 + T cell production and repress Cd4 in CD8 + lineage committed cells.Upregulation of Thpok is most evident in the CD4 + 8 lo IM cells and is required to antagonize Runx3 activity and expression to promote CD4 + lineage commitment.Collectively, the Th-POK-Runx3 axis appears to be a critical convergence point in the CD4 + vs. CD8 + lineage choice.After committing to either CD4 + or CD8 + thymocytes, lineage-inappropriate genes are silenced to ensure the distinct identity and functional divergence between these two cell types. Repression of the Cd4 gene on CD8 + lineage committed cells is mediated vi by a ~430 bp silencer sequence in its first intron. Likewise, Thpok is repressed in CD8 + T cells by a ~560 bp sequence upstream of the Thpok exon 1a, and both Cd4 and Thpok silencers contain consensus binding motifs for Runx factors, which are necessary for CD8 + lineage commitment.T cell factor 1 (TCF-1) and lymphoid enhancer binding factor 1 (LEF-1) are me...