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AML1 stimulates G1 to S progression via its transactivation domain
Florence Bernardin1, Alan D Friedman
1Division of Pediatric Oncology, Cancer Research Building, Room 253, The Johns Hopkins Oncology Center, 1650 Orleans Street, Baltimore, MD 21231, USA.
Abstract:
Inhibition of AML1-mediated transactivation potently slows G1 to S cell cycle progression. In Ba/F3 cells, activation of exogenous AML1 (RUNX1)-ER with 4-hydroxytamoxifen prevents inhibition of G1 progression mediated by CBFbeta-SMMHC, a CBF oncoprotein. We expressed three AML1-ER variants with CBFbeta-SMMHC in Ba/F3 cells. In these lines, CBFbeta-SMMHC expression is regulated by the zinc-responsive metallothionein promoter. Deletion of 72 AML1 C-terminal residues, which includes a transrepression domain, did not alter the activity of AML1-ER, whereas further deletion of 98 residues, removing the most potent AML1 transactivation domain (TAD), prevented rescue of cell cycle inhibition. Notably, the two variants which did not stimulate G1 exacerbated CBFbeta-SMMHC-mediated cell cycle arrest, suggesting that they dominantly inhibit AML1 activities. In addition, the two variants which stimulated G1 also induced apoptosis in 5-15% of the cells, an effect consistent with excessive G1 stimulation. These observations indicate that AML1 activates transcription of one or more genes critical for the G1 to S transition via its C-terminal transactivation domain. Inactivation of AML in acute leukemia is expected to slow proliferation unless additional genetic alterations co-exist which accelerate G1.
Insights
Acute myeloid leukemia (AML) oncoprotein CBFbeta-SMMHC inhibits cell cycle progression. AML1 (RUNX1) transactivation domain is critical for overcoming this arrest, with its inactivation slowing proliferation in leukemia.
Area of Science:
- Molecular Biology
- Cell Biology
- Cancer Research
Background:
- Acute myeloid leukemia (AML) is often associated with genetic alterations affecting cell cycle regulation.
- The AML1 (RUNX1) transcription factor plays a crucial role in normal hematopoiesis and can be involved in leukemogenesis.
- CBFbeta-SMMHC is an oncoprotein that inhibits cell cycle progression.
Purpose of the Study:
- To investigate the role of AML1 (RUNX1) transactivation domain in regulating G1 to S cell cycle progression.
- To determine how AML1 (RUNX1) variants interact with the CBFbeta-SMMHC oncoprotein.
- To elucidate the mechanisms by which AML1 (RUNX1) influences cell cycle arrest and apoptosis.
Main Methods:
- Expression of AML1 (RUNX1)-ER variants and CBFbeta-SMMHC in Ba/F3 cells.
- Utilizing the zinc-responsive metallothionein promoter for inducible gene expression.
- Analyzing cell cycle progression and apoptosis rates following experimental manipulations.
Main Results:
- Deletion of the AML1 (RUNX1) transactivation domain (TAD) abrogated its ability to rescue cell cycle inhibition.
- AML1 (RUNX1) variants lacking TAD exacerbated CBFbeta-SMMHC-mediated cell cycle arrest.
- AML1 (RUNX1) variants that promoted G1 progression also induced apoptosis, suggesting a role in cell cycle control.
Conclusions:
- AML1 (RUNX1) activates transcription of genes essential for G1 to S phase transition via its C-terminal TAD.
- Inactivation of AML1 (RUNX1) is predicted to impede leukemia cell proliferation unless compensatory mechanisms exist.
- Targeting AML1 (RUNX1) activity may offer therapeutic strategies for AML.