Genomic variability and alternative splicing generate multiple PML/RAR alpha transcripts that encode aberrant PML proteins and PML/RAR alpha isoforms in acute promyelocytic leukaemia.

Abstract

The acute promyelocytic leukaemia (APL) 15;17 translocation generates a PML/RAR alpha chimeric gene which is transcribed as a fusion PML/RAR alpha mRNA. Molecular studies on a large series of APLs revealed great heterogeneity of the PML/RAR alpha transcripts due to: (i) variable breaking of chromosome 15 within three PML breakpoint cluster regions (bcr1, bcr2 and bcr3), (ii) alternative splicings of the PML portion and (iii) alternative usage of two RAR alpha polyadenylation sites. Nucleotide sequence analysis predicted two types of proteins: multiple PML/RAR alpha and aberrant PML. The PML/RAR alpha proteins varied among bcr1, 2 and 3 APL cases and within single cases. The fusion proteins contained variable portions of the PML N terminus joined to the B‐F RAR alpha domains; the only PML region retained was the putative DNA binding domain. The aberrant PML proteins lacked the C terminus, which had been replaced by from two to ten amino acid residues from the RAR alpha sequence. Multiple PML/RAR alpha isoforms and aberrant PML proteins were found to coexist in all APLs. These findings indicate that two potential oncogenic proteins are generated by the t(15;17) and suggest that the PML activation pathway is altered in APLs.

SUMO modification of E1B-55K oncoprotein regulates isoform-specific binding to the tumour suppressor protein PML

“…Interestingly, most so far known interaction partners of E1B-55K are transient components of the nuclear promyelocytic leukaemia (PML) bodies (Van Damme et al, 2010). The PML protein has first been described as the causal agent in acute promyelocytic leukaemia as a fusion with the RARa receptor generated by the chromosomal translocation t(15;17) (Ascoli and Maul, 1991;de The et al, 1991;Kakizuka et al, 1991;Chang et al, 1992;Goddard et al, 1992;Kastner et al, 1992;Pandolfi et al, 1992;Dyck et al, 1994;Koken et al, 1994;Weis et al, 1994;Melnick and Licht, 1999;. Since these initial findings, it has become evident that PML is a general tumour suppressor frequently deregulated in various tumour types (Gurrieri et al, 2004) most presumably involving secondary effects of PML bodies as sites of protein degradation (Lallemand-Breitenbach et al, 2001), transcriptional regulation (Li et al, 2000;Zhong et al, 2000), cellular senescence (Ferbeyre et al, 2000;Pearson et al, 2000;Bischof et al, 2002;Langley et al, 2002), tumour suppression (Salomoni and Pandolfi, 2002;Salomoni et al, 2008), DNA repair (Bischof et al, 2001;Carbone et al, 2002), apoptosis (Hofmann and Will, 2003;Takahashi et al, 2004) and epigenetic regulation (Torok et al, 2009).…”

Acute leukemia with promyelocytic features in PML/RARα transgenic mice

“…The common feature of the four translocations is the involvement of chromosome 17 and of the RAR␣ locus (2). The 15;17 translocation results in the production of two fusion genes that encode a PML͞RAR␣ fusion protein (9)(10)(11), an RAR␣͞PML fusion protein (16), and an aberrant PML protein that lacks the PML C-terminal end and its phosphorylation site (12). Because the PML͞RAR␣ hybrid retains most of the functional domains of its parental proteins and can heterodimerize with PML and retinoid-X-receptor (RXR), the chimeric proteins might act as doubly dominant negative oncogenic products, interfering with both PML and RAR͞RXR pathways (17,18).…”

Pro-proliferative function of the long isoform of PML-RARα involved in acute promyelocytic leukemia

“…Three major breakpoints clusters within the PML gene have been described: intron 3 (bcr3), exon 6 (bcr2) and intron 6 (bcr1) (Figure 1). Patients with chromosomal breakpoints in bcr1, bcr2 or bcr3 express either the long (L), the medium (M) or the short (S) isoform of the PML-RARa protein (Pandolfi et al, 1992). The RNA encoding the PML-RARa L isoform can be alternatively spliced to give PML-RARa M (medium) isoform, which is usually coexpressed with the long isoform in a given patient (Zelent et al, 2001).…”