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The Gfi-1B proto-oncoprotein represses p21WAF1 and inhibits myeloid cell differentiation
1Fox Chase Cancer Center, Philadelphia, Pennsylvania 19111, USA.
Abstract:
Gfi-1 is a cellular proto-oncogene that was identified as a target of provirus integration in T-cell lymphoma lines selected for interleukin-2 (IL-2) independence in culture and in primary retrovirus-induced lymphomas. Gfi-1 encodes a zinc finger protein that functions as a transcriptional repressor. Here we show that Gfi-1B, a Gfi-1 related gene expressed in bone marrow and spleen, also encodes a transcriptional repressor. IL-6-induced G1 arrest and differentiation of the myelomonocytic cell line M1 were linked to the downregulation of Gfi-1B and the parallel induction of the cyclin-dependent kinase inhibitor p21WAF1. Experiments addressing the potential mechanism of the apparent coordinate regulation of these genes revealed that Gfi-1B represses p21WAF1 directly by binding to a high-affinity site at -1518 to -1530 in the p21WAF1 promoter. Forced expression of Gfi-1B, but not of Gfi-1B deletion mutants lacking the repressor domain, blocked the IL-6-mediated induction of p21WAF1 and inhibited G1 arrest and differentiation. We conclude that Gfi-1B is a direct repressor of the p21WAF1 promoter, the first such repressor identified to date, and that sustained expression of Gfi-1B blocks IL-6-induced G1 arrest and differentiation of M1 cells perhaps because it prevents p21WAF1 induction by IL-6.
Insights
Growth factor independence 1B (Gfi-1B) acts as a transcriptional repressor, directly inhibiting the p21WAF1 promoter. Sustained Gfi-1B expression blocks IL-6-induced cell differentiation and G1 arrest in M1 cells.
Area of Science:
- Molecular Biology
- Cell Biology
- Cancer Research
Background:
- Gfi-1 (Growth factor independence 1) is a proto-oncogene encoding a transcriptional repressor, implicated in T-cell lymphomas.
- Gfi-1B, a related gene in bone marrow and spleen, also functions as a transcriptional repressor.
- Interleukin-6 (IL-6) induces G1 arrest and differentiation in M1 myelomonocytic cells, involving p21WAF1 induction.
Purpose of the Study:
- To investigate the role of Gfi-1B in IL-6-mediated G1 arrest and differentiation of M1 cells.
- To determine if Gfi-1B directly regulates the p21WAF1 promoter.
- To elucidate the mechanism by which Gfi-1B influences cell cycle progression and differentiation.
Main Methods:
- Analysis of Gfi-1B expression in relation to IL-6 treatment in M1 cells.
- Reporter assays to assess Gfi-1B's effect on the p21WAF1 promoter activity.
- Site-directed mutagenesis to identify the Gfi-1B binding site on the p21WAF1 promoter.
- Forced expression of wild-type and mutant Gfi-1B in M1 cells.
Main Results:
- IL-6 treatment downregulates Gfi-1B and induces p21WAF1 in M1 cells.
- Gfi-1B directly represses the p21WAF1 promoter by binding to a specific site (-1518 to -1530).
- Forced expression of Gfi-1B inhibits IL-6-induced p21WAF1 expression, G1 arrest, and differentiation.
Conclusions:
- Gfi-1B is identified as the first direct repressor of the p21WAF1 promoter.
- Sustained Gfi-1B expression blocks IL-6-mediated G1 arrest and differentiation by preventing p21WAF1 induction.
- Gfi-1B plays a critical role in regulating cell cycle progression and differentiation in myelomonocytic cells.