The transcriptional repressor Bcl6 promotes pre-TCR induced differentiation to CD4+CD8+ thymocyte and attenuates Notch1 activation

Abstract

Pre-TCR signal transduction is required for developing thymocytes to differentiate from CD4-CD8- double negative (DN) to CD4+CD8+ double positive (DP) cell. Notch signalling is required for T-cell fate specification and must be maintained throughout β-selection, but inappropriate Notch activation in DN4 and DP cells is oncogenic. Here, we show that pre-TCR signalling leads to increased expression of the transcriptional repressor Bcl6 and that Bcl6 is required for differentiation to DP. Conditional deletion of Bcl6 from thymocytes reduced pre-TCR-induced differentiation to DP cell, disrupted expansion and enrichment of icTCRβ+ cells within the DN population and increased DN4 cell death. It also increased Notch1 activation and Notch-mediated transcription in the DP population. Thus, Bcl6 is required in thymocyte development for efficient differentiation from DN3 to DP cell and to attenuate Notch1 activation in DP cells. Given the importance of inappropriate NOTCH1 signalling in T-ALL, and the involvement of Bcl6 in other types of leukaemia, this study is important to our understanding of T-ALL.

ZBTB Transcription Factors: Key Regulators of the Development, Differentiation and Effector Function of T Cells

“…Two recent studies extended roles of BCL6 in T-cell compartment from the periphery (differentiation and function) to thymus (early development) ( Figures 1A, B ) ( 137 , 138 ). Pre-TCR signal upregulates BCL6 in DN3 to DP thymocytes, and depletion of BCL6 from the DN2 stage onwards (Lck-Cre) results in a reduced proliferative burst of β-selected DN3 cells, impaired survival of DN4 thymocytes, and an aberrantly augmented NOTCH1 activation in DP thymocytes ( 138 ).…”

“…Two recent studies extended roles of BCL6 in T-cell compartment from the periphery (differentiation and function) to thymus (early development) (Figures 1A, B) (137,138). Pre-TCR signal upregulates BCL6 in DN3 to DP thymocytes, and depletion of BCL6 from the DN2 stage onwards (Lck-Cre) results in a reduced proliferative burst of b-selected DN3 cells, impaired survival of DN4 thymocytes, and an aberrantly augmented NOTCH1 activation in DP thymocytes (138). Given the ineffectiveness of BCL6-ablation in DP stage (CD4-Cre) on subsequent T-cell development (137), BCL6 seems to specifically promote the differentiation of DN3 to DP stage of conventional ab + T cells (138).…”

“…Pre-TCR signal upregulates BCL6 in DN3 to DP thymocytes, and depletion of BCL6 from the DN2 stage onwards (Lck-Cre) results in a reduced proliferative burst of β-selected DN3 cells, impaired survival of DN4 thymocytes, and an aberrantly augmented NOTCH1 activation in DP thymocytes ( 138 ). Given the ineffectiveness of BCL6-ablation in DP stage (CD4-Cre) on subsequent T-cell development ( 137 ), BCL6 seems to specifically promote the differentiation of DN3 to DP stage of conventional αβ + T cells ( 138 ). By contrast, depletion of BCL6 in DP thymocytes greatly impairs the development of iNKT and MAIT cells ( 137 ).…”

The pioneer transcription factors Foxa1 and Foxa2 regulate alternative RNA splicing during thymocyte positive selection

“…For intracellular Foxp3 and Nr4a1 staining, cells were fixed and permeabilized using the Intracellular Fixation & Permeabilization kit (eBioscience). AnnexinV staining was carried out as described ( Solanki et al, 2020 ). Samples were analysed on an Accuri C6 flow cytometer (BD Biosciences) and LSRII (BD Biosciences).…”

“…Canonical correspondence analysis is a multivariate analysis that allows the comparison of experimental transcriptome data with publicly available datasets from other laboratories ( Ono et al, 2014 ). CCA was performed using the CCA function of CRAN package vegan, as previously described ( Solanki et al, 2020 ). The GSE38909 dataset was used as the environmental variable and our dataset was regressed onto it.…”