Role of CCAAT Enhancer Binding Protein Alpha in cell differentiation in leukemia and lung cancer cells
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CCAAT/Enhancer Binding Protein Alpha (C/EBPa) is transcription factor protein involved in the differentiation of many cell types, including granulocytes and pulmonary cells. Studies have found that downregulation of C/EBPa leads to tumor formation in the hematopoietic system, bones, lungs, liver, and other organs. Mutations and post translational modifications can also reduce the function of C/EBPa in humans, leading to cancers. Recent studies have made progress in treating acute promyelocytic leukemia (APL), an M3 subtype of acute myeloid leukemia (AML), by incorporating all trans retinoic acid (ATRA) in targeted treatments. ATRA increases C/EBPa expression levels, thus promoting cell differentiation and subsequent apoptosis of leukemia cells. Still, survival rates of AML patients are low. In patients diagnosed with AML subtypes M4 or higher, ATRA does not work. In addition, patients can become resistant to ATRA, making it essential to find an alternative therapy. Therefore, novel drug treatments are necessary. Through a high throughput screening method, we have determined a potent chemical compound, ICCB280, that can enhance C/EBPa expression levels. However, ICCB280’s effective concentration for cell differentiation is relatively high, so we performed a structural-activity relationship (SAR) analysis and discovered a more potent chemical, styryl quinazolinone CCAAT/Enhancer Binding Protein Compound 73 (CEBP- 73). We tested CEBP-73 with two cell lines, HL-60 and A549, which represent leukemia and lung cancer models, respectively. We found that CEBP-73 increased C/EBPa expression levels in a time-dependent, dose-responsive manner in both leukemia cells and lung cancer cells. In western blot analyses, while both ICCB280 and CEBP-73 upregulated C/EBPa protein expression, more protein was expressed in leukemia and lung cancer cells treated with CEBP-73 in a dose-dependent manner than in cells treated with ICCB280. Next, we investigated CEBP-73’s effectiveness in upregulating C/EBPa’s downstream genes. We observed enhanced expression of CEBPe (HL-60 specific downstream gene) in HL-60 cells, and enhanced SPC, NKX2-1 (codes for TTF-1), and HIF-1a (A549 specific downstream genes) expression levels in A549 cells. To investigate the mechanisms of increased C/EBPa expression, we asked whether expression of an extra coding CEBPA (ecCEBPA), a noncoding RNA for C/EBPa that prevents methylation at the CEBPA gene promoter site, will increase. We found that CEBP-73 increased not only C/EBPa expression, but also ecCEBPA in HL-60 and A549 cells. This is the first study to our knowledge that confirms styryl quinazolinone CEBP- 73 can increase ecCEBPA expression. To examine the effectiveness of CEBP-73 in vivo, EGFR-L858R-T790M (EGFRTL/CCSP-rtTA) mice were administered a vehicle solution (control), 1 mg/kg of CEBP-73, or 10 mg/kg CEBP-73. The results showed a trend in CEBP-73 concentrations; higher doses of CEBP-73 induce higher levels of C/EBPa expression in lung tissue. Fewer and smaller tumors were present in lungs treated with CEBP-73 than lungs treated with a control. These findings support the role of CEBP-73 in enhancing C/EBPa expression, including upregulation at the promoter region of the CEBPA gene and at downstream gene loci. In addition, the study’s results affirm the role of C/EBPa as an inducer of cell differentiation in leukemia and lung cancer by showing neutrophils with segmented lobes and granules, indications of cell maturity, in cells treated with compounds that enhanced C/EBPa expression. These data suggest that CEBP-73 could provide novel therapeutic approaches in treating leukemia and lung cancer and could potentially be modified to treat other cancers in targeted drug therapies.
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