TG-Interacting Factor Regulates Proliferation and Differentiation of Human Myeloid Leukemia Cells

Transforming growth-interacting factor (TGIF) is a homeobox transcriptional repressor that has been implicated in holoprosencephaly and various types of cancer. TGIF is expressed in hematopoietic stem cells and modulates TGF-β and retinoic acid (RA) signaling, both of which play an important role in hematopoiesis. We recently reported that TGIF’s levels correlate inversely with survival in patients with acute myelogenous leukemia. Here we present the first direct evidence of a role for TGIF in myelopoiesis. We used short hairpin RNA interference to define the effects of TGIF knockdown on proliferation and differentiation of myeloid leukemia-derived cell lines. We show that TGIF levels increase with myeloid differentiation and its knockdown resulted in reduced proliferation and differentiation, and lower expression of CEBPβ, CEBPε, PU.1 and RUNX1, key myeloid transcription factors. The reduction in proliferation was not attributable to a block at a particular stage of cell cycle or a significant increase in apoptosis. Furthermore, we show that TGIF knockdown results in increased TGF-β and decreased RA signaling. Consistent with our progenitor cell line results, bone marrow cells derived from Tgif-null mice produced reduced number of colonies in methylcellulose colony forming assays. Insights into the molecular basis of TGIF’s effects were provided by a genome-wide chromatin immunoprecipitation-based elucidation of TGIF target genes. Together, these data suggest that TGIF has a role in regulating the balance between proliferation and differentiation. Reduced TGIF expression could tip the balance toward quiescent leukemic cells (including leukemic stem cells), providing them protection from anti-cycle agents.