RARα1/RARα2-PML mRNA Expression in Acute Promyelocytic Leukemia Cells: A Molecular and Laboratory-Clinical Correlative Study

Abstract

In addition to the major fusion gene PML-RARα, the t(15; 17) in acute promyelocytic leukemia (APL) produces the reciprocal fusion gene RARα-PML. To determine the scope of RARα-containing mRNA expression in APL cells, we tested PML-RARα–positive APL cells for the presence of mRNAs initiated from two distinct RARα gene promoters, α1 and α2. From the normal allele, both RARα1 and RARα2 mRNAs were expressed in all APL cases (N = 24). From the translocated allele, RARα1-PML mRNA was expressed in 77% and RARα2-PML mRNA in 28% of cases (N = 98). RARα2-PML mRNA was not observed in the absence of RARα1-PML mRNA. There was no association between RARα1-PML or RARα2-PML mRNA expression and the type of PML-RARα mRNA formed by either 5′ or 3′ breaksites in the PML gene. RARα1-PML mRNAs and RARα2-PML mRNAs from 5′ PML breaksite cases coded for full-length RARα-PML proteins but RARα2-PML mRNAs from 3′ PML breaksite cases encoded a truncated RARα2 peptide. RARα1/α2-PML mRNA expression was not associated with differences in APL cell sensitivity to all-trans retinoic acid(tRA)-induced differentiation in vitro or in clinical outcome after tRA or chemotherapy induction therapy (protocol E2491). Our analysis indicated that RARα1/α2-PML mRNA expression markedly differs from normal RARα1/α2 mRNA expression, that the difference in RARα1-PML and RARα2-PML mRNA expression frequency is primarily related to the genomic separation of the RARα1 and RARα2 coding exons, and that variations in RARα1/α2-PML mRNA expression likely have no clinically relevant function in APL cells.

Retinoic acid receptors: From molecular mechanisms to cancer therapy

“…hRARα2 (NP_001019980.1) is expressed specifically in the intestine, lung, and liver (Leroy et al, 1991a), and is upregulated upon RA-or granulocyte colony-stimulating factorinduced differentiation (Jing et al, 1996;Li et al, 1997a). This isoform is encoded by the transcript variant 2 (NM_001024809.3) and is composed of 457 amino acids; the DBD and the LBD are comprised between amino acids 77-161 and 181-411, respectively (http://www.ncbi.nlm.nih .gov/protein/NP_001019980.1) (Figure 4 and section 7.1.…”

“…Three regions of the PML locus are involved in the translocation breakpoints: intron 3 (i.e., bcr3), exon 6 (i.e., bcr2), and intron 6 (i.e., bcrl). Bcr1, Bcr2 and Bcr3 breakpoints lead to the expression of the long (PML(L)-RARα), variable (PML(V)-RARα) and short (PML(S)-RARα) isoform of the fusion protein, respectively (Alcalay et al, 1992;Chang et al, 1992Chang et al, , 1995de Thé et al, 1991;Dong et al, 1993;Fenaux and Chomienne, 1996;Geng et al, 1993;Jansen et al, 1995;Kakizuka et al, 1991;Kastner et al, 1992;Li et al, 1997a;Melnick and Licht, 1999;Pandolfi et al, 1991Pandolfi et al, , 1992Slack et al, 1997). among patients is generated by heterogeneous breakpoint cluster regions as well as by alternative splicing (Chang et al, 1992;Dong et al, 1993;Geng et al, 1993;Pandolfi et al, 1992).…”

Pathogenetic implication of fusion genes in acute promyelocytic leukemia and their diagnostic utility

“…Furthermore, RT‐PCR helps to determine PML breakpoint patterns which have prognostic significance . Diagnostic RT‐PCR also helps in revealing reciprocal RARα‐PML transcripts which are detectable in approximately 75% of patients …”

“…Therefore, expression of the reciprocal gene is not required for the development of APL. Furthermore, there are no differences in ATRA sensitivities or clinical outcomes between patients who do or do not express the RARα‐PML transcripts …”

The pathogenesis of acute promyelocytic leukaemia: evaluation of the role of molecular diagnosis and monitoring in the management of the disease

“…There has been considerable interest to determine whether the reciprocal fusion protein plays a significant role in the pathogenesis of APL. However, analysis of large patient groups entered into clinical trials would suggest that this is unlikely to be the case, particularly because RARα‐PML is not expressed in approximately 25% patients with APL (Grimwade et al , 1996b; Li, Y.‐P., et al , 1997), whereas in the remaining group expression of reciprocal transcripts does not appear to influence disease behaviour or prognosis (Burnett et al , 1999).…”