The RARA gene encodes for the retinoic acid receptor alpha, which is a transcription factor activated by retinoic acid and is critical for cellular differentiation and proliferation. In acute promyelocytic leukemia (APL), a translocation mutation creates a dominant-negative fusion protein (PML-RARA) that inhibits normal differentiation of promyelocytes, leading to leukemia. Treatments like all-trans retinoic acid (ATRA) can restore differentiation by degrading the fusion protein and activating differentiation pathways.

1. RARA
Retinoic Acid Receptor Alpha
Taylor Beard

2. Big Picture
• RARA encodes ligand activated transcription
factor RARα protein
• RARα promotes transcription of genes involved in
differentiation and proliferation
• Activated by Retinoic Acid (RA) ligand and co-
activators
• Acts in a dominant negative manner in Acute
Promyelocytic Leukemia (APL) due to an
oncogenic translocation mutation
• Translocation fusion protein PML-RARα inhibits
differentiation of promyelocytes
• ATRA (All-Trans Retinoic Acid) treatment restores
differentiation

3. RARA Protein Structure
• N-terminal: transcription modulation region
 AF-1 & AF-2
• DNA-binding domain (DBD): Zinc fingers
• Hinge region: allows rotation
• Ligand binding region (LBD): ligand binding,
dimerization, and transactivation
• C-terminal: function unknown
• Phosphorylation: Ser 369 residue of LBD
Vigue (2010) Atlas of Genetics and Cytogenetics in Oncology and Haematology

4. RARα Function
• Ligand activated transcription factor
– Ligand = Retinoic Acid (RA)
• RAR/RXR heterodimers bind to Retinoic Acid
Response Elements (RAREs) in target genes
– heterodimer formed via binding of DBD domains
– Target genes: differentiation & proliferation
• Absence of RA:
– Recruit corepressors NCoR & SMRT
– Histone deacetylase activity: ↑ chromatin compaction
– transcriptional repression
• Presence of RA:
– ligand-induced conformational changes
– Dissociate corepressors & recruit co-activators (SRC/p160)
– Histone acetyl- & methylation : ↓ chromatin compaction
– transcription promotion

5. RARα Mechanism of Action
COREPRESSORS (NCoR, SMRT)
CO-ACTIVATORS (SRC/p160, p300/CBP, CARM-1)
+ RA
(ligand)
Niederreither & Dolle (2008) Nature 9:541–553

6. Hematopoiesis|----------------BoneMarrow---------------||--Blood--|
Focosi (2001)

7. RARA Oncogenic Gene
Transformation in APL
• t(15;17)  PML-RARA fusion gene
- Recruits tightly bound corepressors
- Physiological doses of RA inadequate for
activation
• Dominant-negative inhibitor of RA signaling
pathway
• Inhibits differentiation of promyelocytes
Melnick & Licht JD (1999) Blood. 93:3167–3215

8. Oncogenic
Activity in APL
Goal of APL
Treatment
title
(Promyelocyte) (Mature WBC)
Pitha-Rowe et al. (2003) Leukemia 17:1723–1730

9. PML-RARα Inhibits Differentiation
Figure 1. Expression of PML-RARα inhibits normal expression of
differentiation markers in myeloid precursor cell lines.
(Control) (PML-RARα)
Grignani et al. (1993) Cell 74:423–431

10. ATRA Restores Differentiation
Figure 2. (below) Northern
blot. ATRA treatment
increases mRNA expression
of differentiation transcription
factor PU.1
Figure 3. (above) Western
blot. ATRA treatment results in
loss of PML-RARA fusion
protein expression and
induction of PU.1 protein
expression.
Mueller et al. (2006) Blood 107:3330–3338

11. Acute Promyelocytic Leukemia (APL)
• A type of acute myeloid leukemia - AML M3
• Deficiency of mature WBCs and excess of promyelocytes
• Incidence
– Rare: 5% of all AML cases
– Higher in Italy and the Americas
• Risk factors
– No known environmental risk factors
– Any age (mean 40-50 yrs); equal in M/F
• Symptoms: the ‘classic triad’
– Fatigue
– Bruising and bleeding
– Infections and weight loss
• Prognosis
– 5 year survival rate: 58.5%

12. APL Treatment
• Substitution Therapy
– Stabilize bleeding tendency
• All-Trans-Retinoic Acid (ATRA)
– Promotes differentiation via PML-RARα cleavage
and degradation
• Chemotherapy
– Eliminates existing tumor cells
• Arsenic Trioxide (ATO)
– Degrades PML-RARα via a different pathway than
ATRA

13. References
• Bastien J, Rochette-Egly C. 2004. Nuclear retinoid receptors and the transcription of retinoid-target genes
Gene. Gene 328:1–16.
• Focosi D. 2001. Physiology of adult homo sapiens - blood (haematology : plasma, blood cells, and
coagulation) and lymph [Internet]. Available from:
http://www.ufrgs.br/imunovet/molecular_immunology/blood.html
• Grignani Francesco, Ferucci PF, Testa U, Talamo G, Fagioli M, Alcalay M, Mencarelli A, Grignani Fausto,
Peschle C, Nicholetti I, et al. 1993. The acute promyelocytic leukemia-specific PML-RARα fusion protein
inhibits differentiation and promotes survival of myeloid precursor cells Cell. Cell 74:423–431.
• Lingfelder E, Niederwieser D, Platzbecker U, Schlenk RF, Wörmann J. 2012. Acute Promyelocytic Leukemia
(APL) [Internet]. (onkopedia, editor.). Available from: https://www.onkopedia-
guidelines.info/en/onkopedia/guidelines/acute-promyelocytic-leukemia-
apl/@@view/html/index.html#ID0EG
• Melnick A, Licht JD. 1999. Deconstructing a Disease: RARα, Its Fusion Partners, and Their Roles in the
Pathogenesis of Acute Promyelocytic Leukemia Blood. Blood 93:3167–3215.
• Mueller BU, Pabst T, Fos J, Fey MF, Asou N, Buergi U, Tenen DG. 2006. ATRA resolves the differentiation
block in t(15;17) acute myeloid leukemia by restoring PU.1 expression Blood. Blood 107:3330–3338.
• Niederreither K, Dolle P. 2008. Retinoic acid in development: towards an integrated view Nature Reviews
Genetics. Nature 9:541–553.
• Pitha-Rowe I, Petty WJ, Kitaweeran S, Dmitrovsky E. 2003. Retinoid target genes in acute promyelocytic
leukemia Leukemia. Leukemia 17:1723–1730.
• Vigue F. 2010. RARA (Retinoic acid receptor, alpha) [Internet]. (Atlas of Genetics and Cytogenetics in
Oncology and Haematology, editor.). Available from:
http://atlasgeneticsoncology.org/Genes/RARAID46.html