Related Experiment Videos
Retinoic acid receptor alpha suppresses transformation by v-myb
J Smarda1, J Sugarman, C Glass
1Department of Genetics and Molecular Biology, Faculty of Science, Masaryk University, Brno, Czech Republic.
Abstract:
Retinoic acid (RA) is capable of inducing the differentiation of various myelomonocytic cell lines. During this differentiation process, the levels of c-myb expression decline, suggesting that the RA receptor (RAR) may act in part by down-regulating this proto-oncogene. We have now investigated whether the RAR can also inhibit the function of Myb proteins themselves. We have found that transcriptional activation of a Myb-responsive reporter gene can be inhibited by RA in a human monocytic cell line. This inhibition could not be overcome by the expression of exogenous Myb. The RAR did not interfere with DNA binding by Myb proteins in vitro, suggesting that the functional inhibition occurs at the level of transcriptional activation. To determine the biological relevance of the inhibition of Myb proteins by the RAR, we have used v-myb-transformed monoblasts. These cells differentiate into macrophages in the presence of phorbol ester (tetradecanoyl phorbol acetate [TPA]) but are normally unresponsive to RA treatment. The introduction of an inducible, exogenous RAR alpha into v-myb-transformed monoblasts permitted an RA-dependent differentiation into macrophage-like cells similar to those induced by TPA. These results demonstrate that transformation by v-myb is recessive to RAR alpha and imply that many types of non-RA-responsive leukemia cells may become responsive following the introduction of the RAR.
Insights
Retinoic acid (RA) inhibits Myb protein function, promoting cell differentiation. Introducing the RA receptor alpha (RARα) into leukemia cells can restore RA responsiveness, offering a potential therapeutic strategy.
Area of Science:
- Cell Biology
- Molecular Biology
- Oncology
Background:
- Retinoic acid (RA) induces differentiation in myelomonocytic cell lines.
- RA treatment down-regulates c-myb proto-oncogene expression.
- The role of RA receptor (RAR) in inhibiting Myb protein function is unclear.
Purpose of the Study:
- To investigate if RAR can inhibit Myb protein function.
- To determine the mechanism of RAR-mediated inhibition of Myb.
- To assess the biological relevance of RAR inhibition of Myb in leukemia cells.
Main Methods:
- Assessed inhibition of Myb-responsive reporter gene by RA in monocytic cells.
- Examined effects of exogenous Myb expression on RA inhibition.
- Studied RAR's effect on Myb DNA binding in vitro.
- Utilized v-myb-transformed monoblasts and introduced exogenous RAR alpha.
Main Results:
- RA inhibited transcriptional activation of a Myb-responsive reporter gene.
- RAR did not interfere with Myb DNA binding, suggesting inhibition at transcriptional activation level.
- Exogenous RAR alpha enabled RA-dependent differentiation in v-myb-transformed monoblasts, previously unresponsive to RA.
- v-myb transformation was recessive to RAR alpha.
Conclusions:
- RAR inhibits Myb protein function at the transcriptional activation level.
- RAR alpha can overcome v-myb-mediated transformation.
- Introducing RAR may render non-RA-responsive leukemia cells sensitive to RA treatment.