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PML-RARalpha alleviates the transcriptional repression mediated by tumor suppressor Rb
1Laboratory of Molecular Genetics, RIKEN Tsukuba Institute, 3-1-1 Koyadai, Tsukuba, Ibaraki 305-0074, Japan.
Abstract:
A fusion between the promyelocytic leukemia (PML) protein and the retinoic acid receptor-alpha (RARalpha) results in the transforming protein of acute promyelocytic leukemia, PML-RARalpha. PML has growth-suppressive properties and is localized within distinct nuclear structures referred to as nuclear bodies. PML participates in numerous cellular functions, including transcriptional activation, apoptosis, and transcriptional repression, whereas PML-RARalpha blocks these functions. However, the role played by PML-RARalpha in leukemogenesis remains unclear. Here we report that PML is required for transcriptional repression mediated by the tumor suppressor Rb. Rb interacts with the histone decaetylase (HDAC) complex containing co-repressors and represses the transcription of the E2F target genes. Overexpression of PML enhanced Rb-mediated repression. The degree of Rb-mediated repression was weakened by injecting anti-PML antibodies and was lower in Pml-deficient mouse embryonic fibroblasts. PML-RARalpha inhibited Rb-mediated repression, and two co-repressor-interacting sites on the PML-RARalpha molecule were required for this activity. Furthermore, PML-RARalpha blocked the interaction between Rb and HDAC. Thus, aberrant binding of PML-RARalpha to co-repressor-HDAC complexes may inhibit their association with Rb, resulting in the abrogation of Rb activity. Thus, the disruption of Rb-mediated repression may be a contributory factor in leukemogenesis.
Insights
Promyelocytic leukemia (PML) protein is crucial for tumor suppressor Rb-mediated gene repression. The PML-RARalpha fusion protein disrupts this repression, potentially contributing to leukemia development.
Area of Science:
- Molecular Biology
- Cancer Biology
- Cellular Biology
Background:
- The promyelocytic leukemia (PML) protein, found in nuclear bodies, regulates gene transcription, apoptosis, and cell growth.
- Acute promyelocytic leukemia is characterized by the PML-RARalpha fusion protein, which interferes with normal cellular functions.
- The tumor suppressor Retinoblastoma protein (Rb) represses gene transcription by interacting with histone deacetylase (HDAC) complexes.
Purpose of the Study:
- To investigate the role of PML in Rb-mediated transcriptional repression.
- To determine how the PML-RARalpha fusion protein affects Rb activity and contributes to leukemogenesis.
Main Methods:
- Assessing Rb-mediated repression in Pml-deficient mouse embryonic fibroblasts.
- Using anti-PML antibodies to evaluate the impact of PML on Rb function.
- Analyzing the interaction between PML-RARalpha, Rb, and HDAC complexes.
Main Results:
- PML enhances Rb-mediated transcriptional repression of E2F target genes.
- PML deficiency or inhibition weakens Rb-mediated repression.
- PML-RARalpha inhibits Rb-mediated repression by blocking Rb's interaction with HDAC complexes.
- Two specific sites on PML-RARalpha are essential for inhibiting Rb-mediated repression.
Conclusions:
- PML is essential for proper Rb-mediated transcriptional repression.
- PML-RARalpha disrupts Rb function by interfering with HDAC complex recruitment.
- The abrogation of Rb activity by PML-RARalpha is a potential mechanism contributing to leukemogenesis.