Translocations of retinoic acid receptor-α (), typically , are a genetic hallmark of acute promyelocytic leukemia (APL). However, because a small fraction of APL lack translocations of, we focused here on APL cases without translocation to elucidate the molecular etiology of-negative APL. We performed whole-genome sequencing, PCR, and FISH for five APL cases without translocations. Four of five-negative APL cases had translocations involving retinoic acid receptor-β () translocations, and was identified as an in-frame fusion in three cases; one case had an rearrangement detected by FISH, although the partner gene could not be identified. When transduced in cell lines, homodimerized and diminished transcriptional activity for the retinoic acid receptor pathway in a dominant-negative manner. enhanced the replating capacity of mouse bone marrow cells and inhibited myeloid maturation of human cord blood cells as did. However, the response of APL with translocation to retinoids was attenuated compared with that of , an observation in line with the clinical resistance of-positive APL to ATRA. Our results demonstrate that the majority of -negative APL have translocations, thereby forming a novel, distinct subgroup of APL. as an oncogenic protein exerts effects similar to those of, underpinning the importance of retinoic acid pathway alterations in the pathogenesis of APL. These findings report a novel and distinct genetic subtype of acute promyelocytic leukemia (APL) by illustrating that the majority of APL without RARA translocations harbor RARB translocations. .

No abstract

Mutations in the gene encoding the Wiskott-Aldrich syndrome protein (WASP) are responsible for Wiskott-Aldrich syndrome and WASP is a major actin regulator in the cytoplasm. Although rare gain-of-function mutations in the WASP gene are known to result in X-linked neutropenia (XLN), the molecular pathogenesis of XLN is not fully understood. In this study, we showed that all reported constitutively activating mutants (L270P, S272P and I294T) of WASP were hyperphosphorylated by Src family tyrosine kinases and demonstrated higher actin polymerization activities compared with wild-type (WT) WASP. Further analysis showed a tendency of activating WASP mutants to localize in the nucleus compared with WT or the Y291F mutant of WASP. In addition, we found that WASP could form a complex with nuclear RNA-binding protein, 54 kDa (p54nrb) and RNA polymerase II (RNAP II). ChIP assays revealed that WASP associated with DNA, although the affinity was relatively weaker than RNAP II. To determine whether gene transcription was affected by WASP mutation in myeloid cells, we performed microarray analysis and found different expression profiles between WT and L270P WASP-transfected K562 cells. Among the genes affected, granulocyte colony-stimulating factor receptor, Runx1, and protein tyrosine phosphatase receptor c were included. ChIP on chip analysis of genomic DNA showed WT and L270P WASP had a highly similar DNA-binding pattern but differed in binding affinity at the same locus. Therefore, our results suggest that the open conformation of WASP regulates its nuclear localization and plays requisite roles in regulating gene transcription that would contribute to the outcome in the nucleus of myeloid cells.

Acute promyelocytic leukemia (APL) is cytogenetically characterized by the t(15;17) (q24;q21), although cases without this translocation exist. These cases are referred to as “cryptic” or “masked” translocations. Additionally, fewer than 5% of APL cases have another partner gene fused to the RARA gene. The TBL1XR1‐RARA fusion gene has recently been reported as a novel RARA‐associated fusion gene. We report a case with TBL1XR1‐RARA and a masked translocation that was not detected by conventional tests for RARA‐associated translocations. Three‐year‐old girl was diagnosed with APL based morphological findings, although conventional tests for RARA‐associated chimeric genes were negative. She received all‐trans retinoic acid treatment, but that was not effective. She achieved a complete remission (CR) by conventional multidrug chemotherapy, but had extramedullary relapse 2 years after onset. She underwent cord blood transplantation (CBT) in her second CR and is currently alive. To investigate the underlying pathogenesis of this unique case, we performed whole‐genome sequencing and found a cryptic insertion of RARA gene into the TBL1XR1 gene. The transcript of the chimeric gene, TBL1XR1‐RARA, was confirmed as an in‐frame fusion by RT‐PCR. In conclusion, we found using next‐generation sequencing (NGS) a TBL1XR1‐RARA fusion in a child with variant APL without the classic karyotype. Cryptic insertion could also occur in cases other than APL with PML‐RARA. Variant APL has many variants and NGS analysis should therefore be considered for APL variant cases, even for those without RARA translocation detected by conventional analysis.