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Cancer Res. 2009 Feb 1;69(3):1016-26. doi: 10.1158/0008-5472.CAN-08-2603. Epub 2009 Jan 20.

Inhibition of the peptidyl-prolyl-isomerase Pin1 enhances the responses of acute myeloid leukemia cells to retinoic acid via stabilization of RARalpha and PML-RARalpha.

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  • 1Laboratory of Molecular Biology, Istituto di Ricerche Farmacologiche Mario Negri, Milan, Italy. egarattini@marionegri.it

Abstract

The peptidyl-prolyl-isomerase Pin1 interacts with phosphorylated proteins, altering their conformation. The retinoic acid receptor RARalpha and the acute-promyelocytic-leukemia-specific counterpart PML-RARalpha directly interact with Pin1. Overexpression of Pin1 inhibits ligand-dependent activation of RARalpha and PML-RARalpha. Inhibition is relieved by Pin1-targeted short interfering RNAs and by pharmacologic inhibition of the catalytic activity of the protein. Mutants of Pin1 catalytically inactive or defective for client-protein-binding activity are incapable of inhibiting ligand-dependent RARalpha transcriptional activity. Functional inhibition of RARalpha and PML-RARalpha by Pin1 correlates with degradation of the nuclear receptors via the proteasome-dependent pathway. In the acute myelogenous leukemia cell lines HL-60 and NB4, Pin1 interacts with RARalpha in a constitutive fashion. Suppression of Pin1 by a specific short hairpin RNA in HL-60 or NB4 cells stabilizes RARalpha and PML-RARalpha, resulting in increased sensitivity to the cytodifferentiating and antiproliferative activities of all-trans retinoic acid. Treatment of the two cell lines and freshly isolated acute myelogenous leukemia blasts (M1 to M4) with ATRA and a pharmacologic inhibitor of Pin1 causes similar effects. Our results add a further layer of complexity to the regulation of nuclear retinoic acid receptors and suggest that Pin1 represents an important target for strategies aimed at increasing the therapeutic index of retinoids.

PMID:
19155306
[PubMed - indexed for MEDLINE]
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