A team of researchers from the Cancer Science Institute of Singapore (CSI Singapore) at the National University of Singapore (NUS), co-led by Professor Daniel G Tenen and Associate Professor Polly Chen Leilei, made an unprecedented discovery of a hitherto unappreciated mechanism leading to ADAR2 (adenosine deaminases acting on RNA) dysregulation in core binding factor acute myelogenous leukaemias (CBF-AML), and highlighted the functional relevance of the role of ADAR2 role in leukaemogenesis.

The research was published in the journal Blood on 16 February 2023.

Adenosine to inosine (A-to-I) RNA editing, catalysed by the ADAR family of enzymes ADAR1 and ADAR2, has been shown to contribute to multiple cancers.

However, little is known about their roles in haematological malignancies.

Here, the team comprehensively profiled the ADAR expression (ADAR1–3) in different subtypes of AML and found that ADAR2, but not ADAR1 and ADAR3, was differentially expressed in CBF-AML patients.

CBF-AML is characterised by the presence of either t(8;21) or inv(16) translocations, which affect the RUNX transcription factor heterodimer. 

The team also discovered a previously undescribed regulatory mechanism leading to ADAR2 down regulation in AMLs, in which the formation of the AML1-ETO fusion gene and its truncated form AE9a halts the transcription of the ADAR2 gene.

To further support their hypothesis that the loss of ADAR2 and RNA editing may specifically contribute to the development of CBF-AML, they re-expressed ADAR2 in CBF-AML and non-CBF-AML and found that leukaemogenesis was suppressed in the CBF-AML cells.

In addition, the team also discovered for the first time that the RNA editing capability of ADAR2 was essential for suppressing leukaemogenesis in an AE9a-driven AML mouse model. 

“Understanding the role of ADAR2 and ADAR2-mediated RNA editing in cancer has long been neglected, with researchers in this field being more focused on the role of ADAR1 and RNA editing in cancers, including haematological malignancies. Our motivation is to systematically investigate the potential role of ADAR-mediated RNA editing in AML,” said Associate Prof Chen, the co-lead author of this paper and an internationally-known expert in the role of RNA editing in cancer. 

This work propels the team to delve deeper into the causes and functional consequences of ADAR2 dysregulation in multiple diseases, including cancer, as well as the underlying mechanisms (editing-dependent or independent) leading to pathogenesis.

CBF-AML accounts for up to 20 per cent of AML cases.

While it has a relatively good prognosis, approximately half of AML patients will eventually relapse with subsequent poor survival rates.

Therefore, the ability to modulate the level of ADAR2 and editing frequency of its RNA substrates may hold great potential for developing RNA therapeutics against CBF-AMLs, leading to improved treatment outcomes. 

Article: Core binding factor fusion down regulation of ADAR2 RNA editing contributes to AML leukaemogenesis

Source: National University of Singapore