Fusion proteins of the retinoic acid receptor-α recruit histone deacetylase in promyelocytic leukaemia

Abstract

The transforming proteins of acute promyelocytic leukaemias (APL) are fusions of the promyelocytic leukaemia (PML) and the promyelocytic leukaemia zinc-finger (PLZF) proteins with retinoic acid receptor-alpha (RARalpha). These proteins retain the RARalpha DNA- and retinoic acid (RA)-binding domains, and their ability to block haematopoietic differentiation depends on the RARalpha DNA-binding domain. Thus RA-target genes are downstream effectors. However, treatment with RA induces differentiation of leukaemic blast cells and disease remission in PML-RARalpha APLs, whereas PLZF-RARa APLs are resistant to RA. Transcriptional regulation by RARs involves modifications of chromatin by histone deacetylases, which are recruited to RA-target genes by nuclear co-repressors. Here we show that both PML-RARalpha and PLZF-RARalpha fusion proteins recruit the nuclear co-repressor (N-CoR)-histone deacetylase complex through the RARalpha CoR box. PLZF-RARalpha contains a second, RA-resistant binding site in the PLZF amino-terminal region. High doses of RA release histone deacetylase activity from PML-RARalpha, but not from PLZF-RARalpha. Mutation of the N-CoR binding site abolishes the ability of PML-RARalpha to block differentiation, whereas inhibition of histone deacetylase activity switches the transcriptional and biological effects of PLZF-RARalpha from being an inhibitor to an activator of the RA signalling pathway. Therefore, recruitment of histone deacetylase is crucial to the transforming potential of APL fusion proteins, and the different effects of RA on the stability of the PML-RARalpha and PLZF-RARalpha co-repressor complexes determines the differential response of APLs to RA.

Human endogenous retrovirus protein cORF supports cell transformation and associates with the promyelocytic leukemia zinc finger protein

“…The promyelocytic zinc ®nger protein PLZF is a transcriptional repressor that was originally identi®ed as part of a fusion with the retinoic acid receptor alpha (RARa) implicated in acute promyelocytic leukemia (APL; Chen et al, 1993a,b). In attempts to identify protein binding partners, several interacting proteins such as the co-repressors N-CoR, SMRT, Sin3A and HDAC1 were found to associate with the N-terminal POZ domain of PLFZ (Hong et al, 1997;He et al, 1998;Lin et al, 1998;Grignani et al, 1998;David et al, 1998). cORF is the third PLZF binding partner aside from the promyelocytic leukemia protein (PML; Melnick and and the epsin 1 protein that has been shown to target the boundary region of the proline-rich domain and the proximal of the nine zinc®ngers.…”

“…It recognizes speci®c DNA sequences via its C-terminal zinc ®nger domain consisting of nine KruÈ ppel-like C2H2 elements (Li et al, 1997). However, PLZF does not function as a transactivator; rather, target genes are suppressed upon DNA binding by the interaction of the N-terminal POZ domain with the co-repressors N-CoR, SMRT, Sin3A and HDAC1 (histone deacetylase 1; Hong et al, 1997;He et al, 1998;Lin et al, 1998;Grignani et al, 1998;David et al, 1998). Other factors bind to PLZF and may modulate its function as a transcriptional repressor (Melnick and Licht, 1999).…”

Evidence of epigenetic changes affecting the chromatin state of the retinoic acid receptor β2 promoter in breast cancer cells

“…Knowledge of RARb2-methylation state of primary breast cancers might be useful to identify tumors that are more likely to respond to RA-therapy. Finally, the possibility to re-induce RARb activity in RA-resistant breast cancer cells, using both TSA and RA, a combination proven to be e ective for treating leukemia (Grignani et al, 1998;Guidez et al, 1998;Lin et al, 1998;Warrell et al, 1998), might have therapeutic implications also in the treatment of RA-resistant breast tumors.…”

Overexpressed BCL6 (LAZ3) oncoprotein triggers apoptosis, delays S phase progression and associates with replication foci

“…Five mg of total RNA were harvested after 48 h, loaded and hybridized with a probe Growth suppression and apoptosis by BCL6 (LAZ3) O Albagli et al tion at least in part by locally inducing a repressive (hypoacetylated) chromatin structure. This mechanism appears to be shared by other POZ/zinc ®nger (POK) transcriptional repressors since PLZF, a relative of BCL6 involved in certain cases of acute promyelocytic leukemia, recruits the same SIN3/ SMRT(NcoR)/HDAC complex and also depends upon HDAC activity to repress transcription (Dhordain et al, 1997;Hong et al, 1997;David et al, 1998;Dhordain et al, 1998;Grignani et al, 1998;Guidez et al, 1998;Lin et al, 1998;Wong and Privalsky, 1998;Huynh and Bardwell, 1998). BCL6 is expressed in most tissues and in many cell types in vitro (Kerckaert et al, 1993;Fukuda et al, 1995;Allman et al, 1996;Albagli et al, 1998).…”