Multimeric complexes of the PML-retinoic acid receptor alpha fusion protein in acute promyelocytic leukemia cells and interference with retinoid and peroxisome-proliferator signaling pathways.

Abstract

The t(15;17) chromosomal translocation, specific for acute promyelocytic leukemia (APL), fuses thePML gene to the retinoic acid receptor a (RARa) gene, resulting in expression of a PML-RARa hybrid protein. In this report, we analyzed the nature of PML-RARa-containing complexes in nuclear protein extracts of t(15;17)-positive cells. We show that endogenous PML-RARa can bind to DNA as a homodimer, in contrast to RARa that requires the retinoid X receptor (RXR) dimerization partner. In addition, these cells contain oligomeric complexes of PML-RARa and endogenous RXR Treatment with retinoic acid results in a decrease of PML-RARa protein levels and, as a consequence, of DNA binding by the different complexes. Using responsive elements from various hormone signaling pathways, we show that PML-RARa homodimers have altered DNA-binding characteristics when compared to RARaRXRa heterodimers. In transfected Drosophila SL-3 cells that are devoid of endogenous retinoid receptors PML-RARa inhibits transactivation by RARa-RXRa heterodimers in a dominant fashion. In addition, we show that both normal retinoid receptors and the PML-RARa hybrid bind and activate the peroxisome proliferator-activated receptor responsive element from the AcylCoA oxidase gene, indicating that retinoids and peroxisome proliferator receptors may share common target genes. These properties of PML-RARa may contribute to the transformed phenotype of APL cells.The consistent expression of PML-retinoic acid receptor a (RARa) in the majority of cases of acute promyelocytic leukemia (APL) suggests an important role for the fusion protein during transformation of these cells. Since PML-RARa retains most of the functional domains of both PML and RARa, it may interfere with the normal function of either of the parental proteins. Retinoid receptors are ligand-inducible transcription factors that belong to the nuclear receptor superfamily. Two families of retinoid receptors have been described, each consisting of three genes. RARa, -13, and -y bind both all-trans-and 9-cis-retinoic acid (RA), whereas the three retinoid X receptors (RXRs) (a,1, and y) bind only the 9-is isomer. RARs bind with high affinity to RA responsive elements [RAREs; consisting of a directly repeated (A/G)G(T/G)TCA consensus sequence] as a heterodimer with RXRs. RXR also heterodimerizes with several other nuclear receptors, such as the vitamin D3 receptor, the thyroid hormone receptor, and the peroxisome proliferatoractivated receptor (PPAR), indicating its pivotal role in different hormone signaling pathways. When compared to normal receptors, the transactivating properties of PMLRARa are altered.

Deregulation of NPM and PLZF in a variant t(5;17) case of acute promyelocytic leukemia

“…In vitro studies have demonstrated that PML-RARa and PLZF-RARa disrupt the transactivating e ects of RARa at the RAREb 2 promoter, and that the dominant negative e ects of PML-RARa and PLZFRARa are reversed in the presence of ectopically expressed RXRa Licht et al, 1996). PML-RARa and PLZF-RARa heterodimerize with RXRa through the RARa dimerization domain retained in the RARa portion of the fusions (Jansen et al, 1995;Licht et al, 1996). Recently it has been shown that both PML-RARa and PLZF-RARa silence the transcription of RA responsive genes under physiological concentrations of RA (Grignani et al, 1998;He et al, 1998;Lin et al, 1998).…”

The acute promyelocytic leukemia PML-RARα protein induces hepatic preneoplastic and neoplastic lesions in transgenic mice

“…In contrast to RARa that requires the retinoid X receptor dimerization partner to e ciently bind DNA (Mangelsdorf and Evans, 1995a), PML-RARa can bind target sequences as a homodimer with distinct DNAbinding properties suggesting that it may interfere with other nuclear receptor pathways (Perez et al, 1993;Jansen et al, 1995). In this regard, it has been shown that the fusion protein is able to block the vitamin D3-induced di erentiation of U937 cells (Grignani et al, 1993).…”

Pathways of retinoic acid- or arsenic trioxide-induced PML/RARα catabolism, role of oncogene degradation in disease remission

“…The rate of catabolism of the fusion protein is quite variable (Duprez et al, 1996a,b;Jansen et al, 1995;Raelson et al, 1996;Yoshida et al, 1996;Zhu et al, 1997Zhu et al, , 1999. Degradation of the fusion protein is clearly responsible for the RA-induced relocalization of PML (and associated NB proteins) (Daniel et al, 1993;Dyck et al, 1994;Koken et al, 1994;Weis et al, 1994), which could promote apoptosis induction.…”

“…A ®rst mechanistical analysis demonstrated that caspase activation was responsible for cleavage of the fusion protein , accounting for the appearance of a de novo 90 kD protein upon RA exposure (Duprez et al, 1996a;Gianni et al, 1998;Jansen et al, 1995;Raelson et al, 1996;Zhu et al, 1999). The speci®c cleavage site was mapped to the Cterminus of PML (D522).…”