编者按：这来自于2003年末的美国血液学协会年会上的精彩报告
5qNCA, the Putative del(5q) Tumor Suppressor Gene, Is a Co-Repressor of the Retinoic Acid Receptor and Binds c-Myb.
Brenton G. Mar, Jelena Kravarusic, Tiffany L. Sharma, Heiner Wolfes, Carol A. Westbrook Section of Hematology/Oncology, Dept of Medicine, University of Illinois at Chicago, Chicago, IL, USA; Department of Biochemistry, Medical University of Hannover, Institute for Biophysical Chemistry, Hannover, Germany
5qNCA is a 191-kd protein that was originally identified as a candidate for the tumor suppressor gene in myeloid malignancies that have chromosome 5q deletions. The gene, located within the chromosome 5q deletion interval, is mutated in the KG1 myeloblastic/promyelocytic cell line (ALA256) and has a limited tissue distribution, including peripheral blood leukocytes. Because it contains a nuclear receptor binding NR box motif and shares homology with two thyroid hormone receptor (THR) interacting proteins, TRIP8 and Hairless (Hr), we tested whether 5qNCA also interacted functionally with nuclear receptors. Reporter assays were used to test interactions with retinoic acid receptor (RAR). CV-1 cells were co-transfected with expression plasmids for 5qNCA, RAR
, and a retinoic acid response element (RARE)-luciferase reporter; it was found that 5qNCA inhibits RAR-mediated transcription from the RARE in the presence of its ligand ATRA, with no effect on basal (unliganded) transcription. Both the native and ALA256-mutated forms of 5qNCA showed a similar degree of repression. We conclude that 5qNCA is a ligand-dependent inhibitor of RAR. Next, we tested whether 5qNCA binds c-Myb in vivo, since the two proteins have been shown to interact in vitro using a yeast two-hybrid system (unpublished result). By co-expressing c-Myb and a Flag-epitope-tagged 5qNCA in 293T cells, we demonstrated that the two proteins co-immunoprecipitate, and thus interact in vivo. Interestingly, neither Hr nor TRIP8 shows homology to the c-Myb-binding region of 5qNCA, located at the N-terminal region near the ALA256 mutation, suggesting its nuclear hormone corepressor activity may be independent of its ability to bind c-Myb. Nonetheless, the interaction of 5qNCA with c-Myb and RAR, both of which regulate myeloid differentiation and are mutually antagonistic, suggests that 5qNCA is involved in this process as well. Using realtime RT-PCR measurements, we showed that expression of 5qNCA is transiently increased in HL60-cells within 10 hours of ATRA-induced neutrophil differentiation. Taken together, our studies suggest that 5qNCA has a combinatorial role in the interaction of c-Myb and RAR during physiologic differentiation of neutrophils. Efforts are underway to determine the function this gene, the effects of the ALA256 KG1 mutation on this function, and the implication for del(5q) leukemia.
Abstract #3174 appears in Blood, Volume 102, issue 11, November 16, 2003
