ABSTRACT
Oncogenic transformation requires unlimited self-renewal. Currently, it remains unclear whether a normal capacity for self-renewal is required for acquiring an aberrant self-renewal capacity. Our results in a new conditional transgenic mouse showed that a mixed lineage leukemia (MLL) fusion oncogene, MLL-ENL, at an endogenous-like expression level led to leukemic transformation selectively in a restricted subpopulation of hematopoietic stem cells (HSCs) through upregulation of promyelocytic leukemia zinc finger (Plzf). Interestingly, forced expression of Plzf itself immortalized HSCs and myeloid progenitors in vitro without upregulation of Hoxa9/Meis1, which are well-known targets of MLL fusion proteins, whereas its mutant lacking the BTB/POZ domain did not. In contrast, depletion of Plzf suppressed the MLL-fusion-induced leukemic transformation of HSCs in vitro and in vivo. Gene expression analyses of human clinical samples showed that a subtype of PLZF-high MLL-rearranged myeloid leukemia cells was closely associated with the gene expression signature of HSCs. These findings suggested that MLL fusion protein enhances the self-renewal potential of normal HSCs to develop leukemia, in part through a Plzf-driven self-renewal program.
Subject(s)
Cell Transformation, Neoplastic/genetics , Cell Transformation, Neoplastic/pathology , Hematopoietic Stem Cells/pathology , Kruppel-Like Transcription Factors/metabolism , Leukemia/etiology , Myeloid Progenitor Cells/pathology , Myeloid-Lymphoid Leukemia Protein/genetics , Oncogene Proteins, Fusion/genetics , Animals , Biomarkers, Tumor/genetics , Biomarkers, Tumor/metabolism , Blotting, Western , Cell Differentiation , Cell Proliferation , Cell Transformation, Neoplastic/metabolism , Flow Cytometry , Gene Expression Profiling , Hematopoietic Stem Cells/metabolism , Humans , Kruppel-Like Transcription Factors/antagonists & inhibitors , Kruppel-Like Transcription Factors/genetics , Leukemia/metabolism , Leukemia/pathology , Mice , Mice, Inbred C57BL , Mice, Transgenic , Myeloid Progenitor Cells/metabolism , Oligonucleotide Array Sequence Analysis , Promyelocytic Leukemia Zinc Finger Protein , RNA, Messenger/genetics , Real-Time Polymerase Chain Reaction , Retroviridae/genetics , Reverse Transcriptase Polymerase Chain ReactionABSTRACT
Multiple mutations contribute to establish cancers. We have searched for potential oncogenes by screening cDNA libraries derived from gastric cancer cell lines, pancreatic cancer cell lines and glioma cell lines, using retrovirus-mediated expression cloning. Two types of interleukin-3 (IL-3)-dependent cell lines, Ba/F3 and HF6, were transduced with the cDNA libraries and several genes that render these cells factor-independent were identified including PIM-1, PIM-2, PIM-3, GADD45B and reproductive homeobox genes on the X chromosome gene F2 (RHOXF2). Although no mutation in these genes was found, these molecules were highly expressed in cancer cell lines and they may play important roles in cell transformation. Among them, we focused on a transcriptional repressor RHOXF2. Transduction of RHOXF2 rendered HF6 cells factor-independent, while knockdown of RHOXF2 inhibited growth of the HGC27 gastric cancer cell line which highly expresses RHOXF2. In addition, RHOXF2-transduced HF6 cells quickly induced leukemia when transplanted into sublethally irradiated mice. Moreover, RHOXF2 is highly expressed in some leukemia cell lines and a variety of human cancer samples including colon and lung cancers. Thus, these results indicate that RHOXF2 is involved in carcinogenesis.
