Leukemia Research 37 (2013) 1744–1749 Contents lists available at ScienceDirect Leukemia Research journa l h o me pag e: www.elsevier.com/locate/leukres WT1 isoform expression pattern in acute myeloid leukemia Irene Luna a,∗ , Esperanza Such a , Jose Cervera a , Eva Barragán b , Mariam Iba ˜ nez a , Inés Gómez-Seguí a , María López-Pavía a , Marta Llop b , Oscar Fuster b , Sandra Dolz b , Silvestre Oltra c , Carmen Alonso a , Belén Vera a , Ignacio Lorenzo a , David Martínez-Cuadrón a , Pau Montesinos a , M. Leonor Senent a , Federico Moscardó a , Pascual Bolufer b , Miguel A. Sanz a,d a Department of Hematology, Hospital Universitari i Politècnic La Fe, Valencia, Spain b Laboratory of Molecular Biology, Department of Medical Pathology, Hospital Universitario La Fe, Valencia, Spain c Genetic Unit, Hospital Universitario La Fe, Valencia, Spain d Facultad de Medicina, Universidad de Valencia, Spain a r t i c l e i n f o Article history: Received 10 May 2013 Received in revised form 11 September 2013 Accepted 11 October 2013 Available online 22 October 2013 Keywords: Acute myeloid leukemia WT1 isoforms a b s t r a c t WT1 plays a dual role in leukemia development, probably due to an imbalance in the expression of the 4 main WT1 isoforms. We quantify their expression and evaluate them in a series of AML patients. Our data showed a predominant expression of isoform D in AML, although in a lower quantity than in normal CD34+ cells. We found a positive correlation between the total WT1 expression and A, B and C isoforms. The overexpression of WT1 in AML might be due to a relative increase in A, B and C isoforms, together with a relative decrease in isoform D expression. © 2013 Elsevier Ltd. All rights reserved. 1. Introduction Wilms’ tumor gene 1 (WT1) was initially described as a tumor suppressor gene based on the loss-of-function muta- tions in pediatric nephroblastoma [1,2], but its accurate role in leukemia development has not been completely understood. Pre- vious reports have shown that the WT1 gene is overexpressed in primary human leukemia, being correlated with poor prognosis [3,4]. Additionally, the growth of WT1-expressing leukemia cells is inhibited by treatment with WT1 antisense oligomers [5–7], thus indicating an oncogenic rather than a tumor-suppressor role in leukemogenesis. On the contrary, the identification of inactivating mutations in leukemia patients suggests that WT1 may work as a tumor suppressor gene [8–15]. WT1 gene encodes a zinc finger transcription factor that can be translated into multiple isoforms due to alternative mRNA splicing in addition to other translational and post-translational modifica- tions. The 4 main isoforms are generated by 2 alternative splicing events [16,17]: Alternative splice I comprises exon 5, encoding 17 amino acids (51 nucleotides) that are inserted between the ∗ Corresponding author at: Hospital Universitario La Fe, Avenida Campanar 21, 46009 Valencia, Spain. Tel.: +34 961973232; fax: +34 961973281. E-mail address: luna ire@gva.es (I. Luna). transactivation and DNA binding domains. Alternative splice II results from the presence or absence of tripeptide KTS, which is 9 nucleotides at the end of exon 9, between the third and fourth zinc fingers of the WT1 protein. So that, the distinct isoforms are labeled as isoform A (-5/-KTS), B (+5/-KTS), C (-5/+KTS) and D (+5/+KTS). It has been previously proposed that the various WT1 pro- teins might have different functions in hematopoietic proliferation and differentiation, and even different prognostic values. Several studies suggest that the form of WT1 that lacks the KTS insertion (WT1 -KTS) acts as a transcription factor, as it binds discrete DNA sequences with high affinity, and can interact with transcriptional cofactors [18]. The isoforms containing KTS (WT1 +KTS) are pre- sumably involved in post-transcriptional mRNA processing as they may bind mRNA and display a reduced DNA binding affinity com- pared to the -KTS forms [19–21]. Concerning splicing of exon 5, it has been shown that the forms containing the 17-amino-acid seg- ment may have an antiapoptotic role upstream of the mitochondria in the intrinsic apoptosis pathway [22,23], and could be implicated in leukemia relapse by blocking differentiation and repressing apo- ptosis [24]. The mRNA splice isoforms are thought to occur in fixed ratios that are constant in all tissues expressing WT1 during development and are conserved between species [16]. A possible imbalance in the proportion of the main WT1 isoforms in acute leukemia could 0145-2126/$ – see front matter © 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.leukres.2013.10.009