ABSTRACT
Retinoic acid (RA) has broad clinical applications for the treatment of various cancers, particularly acute promyelocytic leukemia. However, RA-based therapy is limited by relapse in patients associated with RA resistance, the mechanism of which is poorly understood. Here, we suggest a new molecular mechanism of RA resistance by a repressor, named RA resistance factor (RaRF). RaRF suppressed transcriptional activity of the RA receptor (RAR) by directly interacting with and sequestering RAR to the nucleolus in response to RA. RaRF was highly expressed in RA-resistant leukemia cells and its expression was strongly correlated with RA sensitivity. MCL1 was upregulated by RA treatment upon RaRF depletion, accompanying leukemic myeloblast differentiation, which is negatively regulated by ectopic RaRF expression. Collectively, we propose that RaRF may be a factor in the resistance mechanism and thus a potential target for leukemia therapy using RA.
Subject(s)
Cell Nucleolus/metabolism , Drug Resistance, Neoplasm , Leukemia, Promyelocytic, Acute/drug therapy , Myeloid Cell Leukemia Sequence 1 Protein/metabolism , Receptors, Retinoic Acid/metabolism , Repressor Proteins/metabolism , Tretinoin/therapeutic use , Cell Differentiation/drug effects , Cell Line, Tumor , Datasets as Topic , Gene Expression Regulation, Leukemic , Granulocyte Precursor Cells/drug effects , Granulocyte Precursor Cells/pathology , Humans , Kaplan-Meier Estimate , Leukemia, Promyelocytic, Acute/genetics , Leukemia, Promyelocytic, Acute/mortality , Leukemia, Promyelocytic, Acute/pathology , Receptors, Retinoic Acid/genetics , Up-RegulationABSTRACT
Estrogen receptor alpha (ERα) has a pivotal role in breast carcinogenesis by associating with various cellular factors. Selective expression of additional sex comb-like 2 (ASXL2) in ERα-positive breast cancer cells prompted us to investigate its role in chromatin modification required for ERα activation and breast carcinogenesis. Here, we observed that ASXL2 interacts with ligand E2-bound ERα and mediates ERα activation. Chromatin immunoprecipitation-sequencing analysis supports a positive role of ASXL2 at ERα target gene promoters. ASXL2 forms a complex with histone methylation modifiers including LSD1, UTX and MLL2, which all are recruited to the E2-responsive genes via ASXL2 and regulate methylations at histone H3 lysine 4, 9 and 27. The preferential binding of the PHD finger of ASXL2 to the dimethylated H3 lysine 4 may account for its requirement for ERα activation. On ASXL2 depletion, the proliferative potential of MCF7 cells and tumor size of xenograft mice decreased. Together with our finding on the higher ASXL2 expression in ERα-positive patients, we propose that ASXL2 could be a novel prognostic marker in breast cancer.
