Genome-wide screen reveals WNT11, a non-canonical WNT gene, as a direct target of ETS transcription factor ERG

Abstract

E26 transforming sequence-related gene (ERG) is a transcription factor involved in normal hematopoiesis and is dysregulated in leukemia. ERG mRNA overexpression was associated with poor prognosis in a subset of patients with T-cell acute lymphoblastic leukemia (T-ALL) and acute myeloid leukemia (AML). Herein, a genome-wide screen of ERG target genes was conducted by chromatin immunoprecipitation-on-chip (ChIP-chip) in Jurkat cells. In this screen, 342 significant annotated genes were derived from this global approach. Notably, ERG-enriched targets included WNT signaling genes: WNT11, WNT2, WNT9A, CCND1 and FZD7. Furthermore, chromatin immunoprecipitation (ChIP) of normal and primary leukemia bone marrow material also confirmed WNT11 as a target of ERG in six of seven patient samples. A larger sampling of patient diagnostic material revealed that ERG and WNT11 mRNA were coexpressed in 80% of AML (n ¼ 30) and 40% in T-ALL (n ¼ 30) bone marrow samples. Small interfering RNA (siRNA)-mediated knockdown of ERG confirmed downregulation of WNT11 transcripts. Conversely, in a tet-on ERG-inducible assay, WNT11 transcripts were costimulated. A WNT pathway agonist, 6-bromoindirubin-3-oxime (BIO), was used to determine the effect of cell growth on the ERG-inducible cells. The addition of BIO resulted in an ERG-dependent proliferative growth advantage over ERG-uninduced cells. Finally, ERG induction prompted morphological transformation whereby round unpolarized K562 cells developed elongated protrusions and became polarized. This morphological transformation could effectively be inhibited with BIO and with siRNA knockdown of WNT11. In conclusion, ERG transcriptional networks in leukemia converge on WNT signaling targets. Specifically, WNT11 emerged as a direct target of ERG. Potent ERG induction promoted morphological transformation through WNT11 signals. The findings in this study unravel new ERG-directed molecular signals that may contribute to the resistance of current therapies in acute leukemia patients with poor prognosis characterized by high ERG mRNA expression.

Strong expression of the neuronal transcription factor FOXP2 is linked to an increased risk of early PSA recurrence in ERG fusion-negative cancers

“…Activation of ERG expression by TMPRSS2:ERG gene fusion results in aberrant activation of different signalling cascades in ERG fusion-positive as compared with ERG fusion-negative prostate cancers 27 32–34. One of the best known consequences of ERG expression is activation of WNT signalling26 27 35 It is tempting to speculate that FOXP2 and ERG, or their target genes, interfere with pathways governing tumour aggressiveness, possibly including the WNT pathway, which is subsequently reflected by the different clinical course in ERG-positive and ERG-negative cancers. The genes or mechanisms mediating this effect remain to be identified.…”

Molecular mechanisms of ETS transcription factor-mediated tumorigenesis

“…There is also little information on downstream targets of ERG that contribute to malignant leukemogenesis. A genome wide screen of ERG target genes conducted with ChIP-chip in Jurkat cells included the WNT signaling genes WNT11, WNT2, WNT9A, CCND1 , and FZD7 (Mochmann et al, 2011). Sampling of patient diagnostic material showed that ERG and WNT1 were co-expressed in 80% of AML, whereas knockdown of ERG1 by siRNA lead to WNT1 transcript down-regulation and WNT1 transcripts could be stimulated with tet-on ERG inducible assay.…”

FAT1 expression and mutations in adult acute lymphoblastic leukemia

“…7, 12 Deregulation of the WNT pathway has been linked to leukemogenesis in T-ALL. 13, 14 The previously unreported FAT1 mutation rate of 15% in adult T-ALL stresses the importance of the WNT pathway in T-ALL.…”