Roles of TIF1β in Leukemic Stem Cell Through SETDB1-Dependent and Independent Mechanisms.

TIF1β/TRIM28/KAP1 has been recognized as a scaffold protein that partners with KRAB-ZFPs and heterochromatin complexes to enforce gene silencing. In embryonic and pluripotent stem cells, it maintains self-renewal by silencing endogenous retroelements through the establishment of heterochromatin. While these canonical functions have been extensively examined in embryonic stem (ES) cells, accumulating evidence also highlights its diverse contributions to cancer biology. We herein focused on the oncogenic role of TIF1β in leukemic progression, contrasting this with its physiological roles in hematopoietic stem cell maintenance, differentiation, and immune regulation, thereby providing a comparative perspective on H3K9 methyltransferase SETDB1-dependent and -independent mechanisms. TIF1β-mediated epigenetic plasticity was recently shown to establish a leukemic chromatin environment for promoting oncogenic transcriptional programs while repressing lineage-differentiation regulators, which drives leukemic progression in a context-dependent manner. This review summarizes the dual role of TIF1β as a chromatin modulator, functioning both as a canonical transcriptional co-repressor and as a context-dependent co-activator, and also discusses how these modalities cooperate to sustain leukemic stem cell programs.