Inhibition of the Peptidyl-Prolyl-Isomerase Pin1 Enhances the Responses of Acute Myeloid Leukemia Cells to Retinoic Acid via Stabilization of RARα and PML-RARα

Abstract

The peptidyl-prolyl-isomerase Pin1 interacts with phosphorylated proteins, altering their conformation. The retinoic acid receptor RARA and the acute-promyelocytic-leukemia-specific counterpart PML-RARA directly interact with Pin1. Overexpression of Pin1 inhibits ligand-dependent activation of RARA and PML-RARA. 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 RARA transcriptional activity. Functional inhibition of RARA and PML-RARA 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 RARA in a constitutive fashion. Suppression of Pin1 by a specific short hairpin RNA in HL-60 or NB4 cells stabilizes RARA and PML-RARA, 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. [Cancer Res 2009;69(3):1016-26]

Novel Role of Pin1 Induction in Type II Collagen-Mediated Rheumatoid Arthritis

“…In fact, anti-cancer agents such as methotrexate and azathioprine are used for the treatment of RA (48). Pin1 inhibition has anti-cancer effects in experimental studies (49,50), and recently, diverse chemical-based or peptide-based Pin1 inhibitors have been synthesized (51,52). We found that multiple treaments of 10 mg/kg juglone caused severe toxic effects in mice, such as paralysis and even death (three among seven mice).…”

p38αMAPK interacts with and inhibits RARα: suppression of the kinase enhances the therapeutic activity of retinoids in acute myeloid leukemia cells

“…23) cells, RARa À/À mouse embryo fibroblasts (MEF) 20 and freshly isolated AML blasts from the peripheral blood of four AML patients (Supplementary Table I) were cultured as described. 23 All patients gave informed consent for sample collection. The protocol for the collection of leukemic blasts from AML patients was approved by the local ethical committee.…”

“…NBT-reducing activity was measured and values are the mean ± s. Pull-down, immunoprecipitation and far-Western experiments were as described. 23 For the pull-down experiments, 23 we used GST-p38a and GSTDNp38a. For the immunoprecipitation experiments in NB4 cells, anti-RARa antibodies 23 were used.…”

“…23 For the pull-down experiments, 23 we used GST-p38a and GSTDNp38a. For the immunoprecipitation experiments in NB4 cells, anti-RARa antibodies 23 were used. For other immunoprecipitations, we transfected hRARa and PML-RARa and HA-WTp38a in COS-7 cells.…”

“…For other immunoprecipitations, we transfected hRARa and PML-RARa and HA-WTp38a in COS-7 cells. Immunoprecipitations were performed with anti-RARa 23 or anti-HA antibodies (Sigma). In the last case, proteins were precipitated with HA-Sepharose beads (Amersham, Little Chalfont, UK).…”