1. Retinoic Acid Receptor Alpha (RARα) Acute Promyelocytic Leukemia (APL)

2. APL Overview Subtype of AML (5-8% of AML adults) Subtype of AML (5-8% of AML adults) Abnormal accumulation of promyelocytes resulting in decreased production of RBCs Abnormal accumulation of promyelocytes resulting in decreased production of RBCs Median age is 40 years Median age is 40 years Increased incidence in patients from Latin America Increased incidence in patients from Latin America Anemia and thrombocytopenia Anemia and thrombocytopenia

3. RARα is a transcription factor Nuclear receptor Nuclear receptor Ligand-inducible transcriptional regulator Ligand-inducible transcriptional regulator Ligand is retinoic acid (RA) Ligand is retinoic acid (RA) Cyberlipid Center; www.cyberlipid.org RARα

4. Active transcription factor is a heterodimer RARα forms heterodimer with RXRs RARα forms heterodimer with RXRs Heterodimer binds DNA sequence called RA- response element (RARE) Heterodimer binds DNA sequence called RA- response element (RARE) Marlétaz F, et al. Int J Biol Sci 2006; 2:38-47.

5. Retinoic Acid Absent RAR-RXR heterodimer is a repressor RAR-RXR heterodimer is a repressor Co-repressors modify histones Co-repressors modify histones SMRT, N-CoR SMRT, N-CoR mSin3 mSin3 HDACs HDACs Marlétaz F, et al. Int J Biol Sci 2006; 2:38-47.

6. Retinoic Acid Present Repression complex dissociates and a co- activator complex assembles Repression complex dissociates and a co- activator complex assembles Co-activator complex modifies histones to induce transcriptional activation Co-activator complex modifies histones to induce transcriptional activation Marlétaz F, et al. Int J Biol Sci 2006; 2:38-47.

7. Scientists knocked out RARα Gene in Mice Homologous recombination Homologous recombination Disrupt exon 8, which prevents synthesis of all RAR α isoforms Disrupt exon 8, which prevents synthesis of all RAR α isoforms Lufkin, Thomas, et al. Proc. Natl. Acad. Sci. USA. Vol. 90, pp. 7225-7229

8. RARα -null mutants viable but generally die before 2 months Intercross RARα heterozygotes to give RARα -null homozygotes Intercross RARα heterozygotes to give RARα -null homozygotes RARα gene disruption is not embryonic lethal RARα gene disruption is not embryonic lethal RARα, RARβ and RARγ are highly redundant RARα, RARβ and RARγ are highly redundant Lufkin, Thomas, et al. Proc. Natl. Acad. Sci. USA. Vol. 90, pp. 7225-7229

9. Testis Degeneration in RARα Mutant Mice Male RARα -null homozygotes that survived for > 2 months were sterile Male RARα -null homozygotes that survived for > 2 months were sterile Severe degeneration of germinal epithelium in testes Severe degeneration of germinal epithelium in testes Lufkin, Thomas, et al. Proc. Natl. Acad. Sci. USA. Vol. 90, pp. 7225-7229

10. Chromosomal Translocation causes mutation Chromosome 17 Chromosome 17 Fusion proteins created with 5 common partners Fusion proteins created with 5 common partners PML PML PLZF PLZF NPM NPM NuMA NuMA Stat5b Stat5b Medicine OnLine. www.meds.com

11. Fusion proteins can form homodimers Homodimer associates with multiple units of the co-repressor complex Homodimer associates with multiple units of the co-repressor complex Enhanced transcriptional repression Enhanced transcriptional repression Lin, Richard, et. al. “Transcriptional regulation in APL”

12. Fusion proteins react strongly with co-repressors to recruit HDACs Physiological [RA] will not dissociate repression complex Physiological [RA] will not dissociate repression complex Lin, Richard, et. al. “Transcriptional regulation in APL”

13. High [RA] dissociates repression complex formed by some fusion proteins PML-RARα but not PLZF-RARα PML-RARα but not PLZF-RARα Lin, Richard, et. al. “Transcriptional regulation in APL”

14. Target genes involved in myeloid proliferation and differentiation p21WAF, C/EBP, HoxA1, etc. p21WAF, C/EBP, HoxA1, etc. Inhibition blocks differentiation Inhibition blocks differentiation Lin, Richard, et. al. “Transcriptional regulation in APL”

15. Treatment Pharmacological [RA] with chemotherapy Pharmacological [RA] with chemotherapy Possibly HDAC inhibitors Possibly HDAC inhibitors Lin, Richard, et. al. “Transcriptional regulation in APL”