Retinoid receptor signaling and autophagy in acute promyelocytic leukemia

• Normal and aberrant retinoid signaling in hematopoiesis and leukemia is reviewed.
• We suggest a novel role for RARα in the development of X-RARα gene fusions in APL.
• ATRA therapy in APL activates transcription and promotes onco-protein degradation.
• Autophagy may be involved in both onco-protein degradation and differentiation.
• Pharmacologic autophagy induction may potentiate ATRA׳s therapeutic effects.

Retinoids are a family of signaling molecules derived from vitamin A with well established roles in cellular differentiation. Physiologically active retinoids mediate transcriptional effects on cells through interactions with retinoic acid (RARs) and retinoid-X (RXR) receptors. Chromosomal translocations involving the RARα gene, which lead to impaired retinoid signaling, are implicated in acute promyelocytic leukemia (APL). All-trans-retinoic acid (ATRA), alone and in combination with arsenic trioxide (ATO), restores differentiation in APL cells and promotes degradation of the abnormal oncogenic fusion protein through several proteolytic mechanisms. RARα fusion-protein elimination is emerging as critical to obtaining sustained remission and long-term cure in APL. Autophagy is a degradative cellular pathway involved in protein turnover. Both ATRA and ATO also induce autophagy in APL cells. Enhancing autophagy may therefore be of therapeutic benefit in resistant APL and could broaden the application of differentiation therapy to other cancers. Here we discuss retinoid signaling in hematopoiesis, leukemogenesis, and APL treatment. We highlight autophagy as a potential important regulator in anti-leukemic strategies.