1. ¹IFOM – Institute of Molecular Oncology of the Italian Foundation for Cancer Research, Via Adamello 16, 20139 Milan, Italy
2. ²European Institute of Oncology, Via Ripamonti 435, 20141 Milan, Italy
3. ³San Raffaele Bio-medical Science Park of Rome, Via di Castel Romano 100, 00128 Rome, Italy
4. ⁴Department of Biopathology, University of Tor Vergata, Rome, Italy

Correspondence: M Alcalay, E-mail: myriam.alcalay@ifom-ieo-campus.it

Received 11 October 2004; Revised 17 December 2004; Accepted 10 January 2005; Published online 21 February 2005.

Abstract

Acute promyelocytic leukemia (APL) is a distinct subtype of acute myeloid leukemia characterized by a block of differentiation at the promyelocytic stage. APL patients respond to pharmacological concentrations of all-trans retinoic acid (RA) and disease remission correlates with terminal differentiation of leukemic blasts. The PML/RAR oncogenic transcription factor is responsible for both the pathogenesis of APL and for its sensitivity to RA. In order to identify physiological targets of RA therapy, we analysed gene expression profiles of RA-treated APL blasts and found 1056 common target genes. Comparing these results to those obtained in RA-treated U937 cell lines revealed that transcriptional response to RA is largely dependent on the expression of PML/RAR. Several genes involved in the control of differentiation and stem cell renewal are early targets of RA regulation, and may be important effectors of RA response. Modulation of chromatin modifying genes was also observed, suggesting that specific structural changes in local chromatin domains may be required to promote RA-mediated differentiation. Computational analysis of upstream genomic regions in RA target genes revealed nonrandom distribution of transcription factor binding sites, indicating that specific transcriptional regulatory complexes may be involved in determining RA response.