Caspases mediate retinoic acid-induced degradation of the acute promyelocytic leukemia PML/RARα fusion protein

Clara Nervi, Fabiana F. Ferrara, Mirco Fanelli, Maria Rita Rippo, Barbara Tomassini, Pier Francesco Ferrucci, Martin Ruthardt, Vania Gelmetti, Carlo Gambacorti-Passerini, Daniela Diverio, Francesco Grignani, Pier Giuseppe Pelicci, Roberto Testi

Research output: Contribution to journalArticle

Abstract

All-trans-retinoic acid (RA) treatment induces morphological remission in acute promyelocytic leukemia (APL) patients carrying the t(15;17) and expressing the PML/RARα product by inducing terminal differentiation of the leukemic clone. RA treatment induces downregulation of PML/RARα and reorganization of the PML-nuclear bodies. These events have been proposed to be essential for the induction of APL cell differentiation by RA. Here, we show that in the APL* derived NB4 cell line as well as in myeloid precursor U937 cells expressing the PML/RARα (U937/PR9) and in blasts from APL patients, the PML/RARα fusion protein is cleaved by a caspase 3-like activity induced by RA treatment. In fact, a caspase 3-like activity is detectable in PML/RARα expressing cells after RA treatment, and selective caspase inhibitor peptides are able to prevent the RA-induced degradation of the fusion protein in vivo and in vitro. Using recombinant caspases and PML/RARα deletion mutants we mapped a caspase 3 cleavage site (Asp 522) within the α-helix region of the PML component of the fusion protein. The extent of PML/RARα cleavage directly correlates with the ability of RA to restore the normal PML nuclear bodies (NBs) pattern. However, RA-induced differentiation is not prevented by the persistence of the fusion product and occurs in the absence of normally structured PML NBs. These results indicate that PML/RARα is directly involved in conferring RA sensitivity of APL cells and that the RA-induced reassembly of PML NBs is the consequence of the disappearance of PML/RARα.

Original languageEnglish
Pages (from-to)2244-2251
Number of pages8
JournalBlood
Volume92
Issue number7
Publication statusPublished - Oct 1 1998

ASJC Scopus subject areas

  • Hematology

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