Retinoic Acid Receptor α Acute Promyelocytic Leukemia Michi Nair

Retinoic Acid Heavily involved in CNS development –Gradient patterns axes –Neuronal development and differentiation –Terminal myeloid and granulocyte differentiation © 2000 by Sinauer Associates, Inc.by Sinauer Associates, Inc.

Retinoic Acid Retinoid, derived from Vitamin A (retinol) Synthesized RA binds activates transcription factors in the nucleus

Retinoic Acid Receptors © 2002 by Bruce Alberts, Alexander Johnson, Julian Lewis, Martin Raff, Keith Roberts, and Peter Walter. Ligand activated nuclear transcription factors Heterodimers of RAR & RXR Recognize RAREs Downstream targets regulate cell proliferation and differentiation

RARa Transcription control In absence of RA, transcription is repressed –Corepressors and histone deacetylases (HDAC) –Histone deacetylation condenses chromatin RA activates transcription –Induces HDACs to dissociate –Binding of activation complex He, Li-Zhen et. Al; In vivo analysis of the molecular pathogenesis of acute promyelocytic leukemia in the mouse and its therapeutic implications, Oncogene 1999

Acute Promyelocytic Leukemia Bone marrow malignancy Excess of immature promyelocytes Symptoms: –Fatigue –Increased tendency to bleed –Anemia –Minor infections He, Li-Zhen; Oncogene

APL: RAR fusion proteins Kufe, Donald W; Cancer Medicine, 6 th ed. Translocation occurs between RAR and PML –Other partner genes: PLZF, NPM, NuMA, Stat5b

X-RARα blocks RA induced transcription

Reciprocal Protein Function © 2002 by Bruce Alberts, Alexander Johnson, Julian Lewis, Martin Raff, Keith Roberts, and Peter Walter.

X-RARα Fusion Protein ‘Double dominant negative’ oncogene Chimeric protein prevents cell differentiation Chromosome breakage produces reciprocal proteins Kufe, Donald W; Cancer Medicine, 6 th ed.

Knock Out Experiments RARα1-/- mutant Redundant function of receptors RARα null mice –10% survive to 2 months –Cannibalized –Slow growth, emaciation –Developmental defects

Double negative functions PML Knock outs –Increased infections –Increased susceptibility to tumor formation –Undifferentiated myeloid cells –Uninhibited growth

Differentiation Therapy Accompanied by chemotherapy ATRA overrides mutant receptors Problems with PLZF/RARα ATRA syndrome HDAC inhibitors Arsenic Trioxide © 2003 BC Decker IncBC Decker Inc

Differentiation Therapy © 2003 BC Decker IncBC Decker Inc

Retinoic Acid Receptor α Acute Promyelocytic Leukemia t(15;17) causes RARα-X fusion protein Fusion protein retains repressors in presence of RA Fusion protein prevents transcription of genes that drive myelocytes into differentiation Higher levels of RA releases repressors from RARα-X