Antisense knockout of HOXB4 blocks 1,25-dihydroxyvitamin D3 inhibition of c-myc expression.
The expression of c-myc is decreased by 1,25-(OH)2D(3) during HL-60 cell differentiation. Concomitantly, 1,25-(OH)2D(3) increases the expression and DNA binding activity of HOXB4, a homeobox gene. HOXB4 binds to the c-my c gene at sites involved in blocking c-myc transcription elongation. In this study, a phosphorothioate antisense oligonucleotide targeted against HOXB4 was examined for its effect on 1,25-(OH)2D(3) inhibition of c-myc expression. Alone, 1,25-(OH)2D(3) (20 nM) increased HOXB4 levels by 103+/-7% (mean+/-s.e., n=3) and decreased c-myc levels by 89+/-5% (mean+/-s.e.m., n=3) at 48 h of treatment. HOXB4 antisense treatment completely blocked the induction of HOXB4 by 1,25-(OH)2D(3). In addition, HOXB4 antisense partially blocked 1,25-(OH)2D(3)-mediated decrease in c-myc levels (46+/-6% inhibition) and promotion of HL-60 cell differentiation (20+/-2% and 25+/-3% inhibition as assessed by nitroblue tetrazolium and non-specific esterase assays respectively). The data further establish that HOXB4 levels are regulated by 1,25-(OH)2D(3) and reveal that HOXB4 participates in the down-regulation of c-myc expression.
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Department of Pharmacology, University of Michigan, School of Medicine, 1301 MSRB III, 1150 West Medical Center Drive, Ann Arbor, Michigan 48109-0632, USA.
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D000470:Alkaloids; D053119:Benzophenanthridines; D015153:Blotting, Western; D002117:Calcitriol / Q000494:pharmacology*; D002454:Cell Differentiation / Q000235:genetics; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology; D017353:Gene Deletion; D005786:Gene Expression Regulation / Q000235:genetics*; D018922:HL-60 Cells / Q000187:drug effects / Q000378:metabolism*; D018398:Homeodomain Proteins / Q000235:genetics*; D006801:Humans; D016376:Oligonucleotides, Antisense / Q000494:pharmacology; D010617:Phenanthridines / Q000494:pharmacology; D011493:Protein Kinase C / Q000037:antagonists & inhibitors; D016271:Proto-Oncogene Proteins c-myc / Q000235:genetics*; D014157:Transcription Factors / Q000235:genetics*
D000470:Alkaloids; D053119:Benzophenanthridines; D004791:Enzyme Inhibitors; C090460:HOXB4 protein, human; D018398:Homeodomain Proteins; D016376:Oligonucleotides, Antisense; D010617:Phenanthridines; D016271:Proto-Oncogene Proteins c-myc; D014157:Transcription Factors; C016299:chelerythrine; D011493:Protein Kinase C; D002117:Calcitriol