ABSTRACT
Acute myeloid leukemia (AML) is characterized by increased proliferation and reduced differentiation of myeloid lineage cells. AML is frequently associated with mutations or chromosomal rearrangements involving transcription factors. PU.1 (encoded by Sfpi1) is an E26 transformation-specific family transcription factor that is required for myeloid differentiation. Reduced PU.1 levels, caused by either mutation or repression, are associated with human AML and are sufficient to cause AML in mice. The objective of this study was to determine whether reduced PU.1 expression induces deregulation of the cell cycle in the myeloid lineage. Our results showed that immature myeloid cells expressing reduced PU.1 levels (Sfpi1(BN/BN) myeloid cells) proliferated indefinitely in cell culture and expanded in vivo. Transplantation of Sfpi1(BN/BN) cells induced AML in recipient mice. Cultured Sfpi1(BN/BN) cells expressed elevated messenger RNA transcript and protein levels of E2F1, an important regulator of cell cycle entry. Restoration of PU.1 expression in Sfpi1(BN/BN) myeloid cells blocked proliferation, induced differentiation, and reduced E2F1 expression. Taken together, these data show that PU.1 controls cell cycle exit in the myeloid lineage associated with downregulation of E2F1 expression.
Subject(s)
Cell Cycle/physiology , E2F1 Transcription Factor/metabolism , Myeloid Cells/metabolism , Proto-Oncogene Proteins/physiology , Trans-Activators/physiology , Acute Disease , Animals , Animals, Newborn , Cell Cycle/genetics , Cells, Cultured , Down-Regulation , Doxycycline/pharmacology , E2F1 Transcription Factor/genetics , Female , Immunoblotting , Interleukin Receptor Common gamma Subunit/deficiency , Interleukin Receptor Common gamma Subunit/genetics , Leukemia, Myeloid/genetics , Leukemia, Myeloid/metabolism , Leukemia, Myeloid/pathology , Male , Mice , Mice, Inbred C57BL , Mice, Inbred NOD , Mice, Knockout , Mice, SCID , Myeloid Cells/drug effects , Myeloid Cells/transplantation , Oligonucleotide Array Sequence Analysis , Proto-Oncogene Proteins/deficiency , Proto-Oncogene Proteins/genetics , Reverse Transcriptase Polymerase Chain Reaction , Spleen/cytology , Spleen/metabolism , Survival Analysis , Trans-Activators/deficiency , Trans-Activators/genetics , Transcriptome/drug effects , Transcriptome/geneticsABSTRACT
The E26 transformation-specific (Ets) transcription factor PU.1 is required to generate lymphoid progenitor cells from hematopoietic stem cells, but it is not required to generate B cells from committed B-cell lineage progenitors. We hypothesized that PU.1 function in B-cell differentiation is complemented by the related Ets transcription factor Spi-B. To test this hypothesis, mice were generated lacking both PU.1 and Spi-B in the B-cell lineage. Unlike mice lacking PU.1 or Spi-B, mice deficient in both PU.1 and Spi-B in the B-cell lineage had reduced frequencies of B cells as well as impaired B-cell differentiation. Strikingly, all PU.1 and Spi-B-deficient mice developed pre-B cell acute lymphoblastic leukemia before 30 weeks of age. Pre-B cells accumulated in the thymus resulting in massive thymic enlargement and dyspnea. These findings demonstrate that PU.1 and Spi-B are essential transcriptional regulators of B-cell differentiation as well as novel tumor suppressors in the B-cell lineage.
