WNK1 inhibition induces AML differentiation via ERK-CEBPbeta signaling

Impaired differentiation is a key pathological feature of Acute Myeloid Leukemia (AML). AML differentiation-inducing agents such as all-trans retinoic acid (ATRA) have shown great promise to treat AML patients as seen by improved overall survival and relapse rates. However, this success has been limited to a subset of AML patients, namely those with Acute Promyelocytic Leukemia (APL). This highlights the need to identify more differentiation therapy options that could be effective for other AML subtypes. In this study, we identified With-no-Lysine(K) kinase 1 (WNK1) as a novel regulator of AML differentiation arrest. We show evidence of WNK1 dysregulation in AML patients demonstrated by its increased expression and activity compared to healthy controls. Targeting WNK1 through genetic or pharmacologic inhibition induced granulocytic differentiation of AML cell lines in vitro. WNK1 inhibition also caused cell cycle arrest and apoptosis. Furthermore, oral administration of WNK1 inhibitor reduced leukemic burden in AML xenograft models. We observed that knocking down expression of WNK1 substrates SPAK and OSR1 mirrored the effects of WNK1 inhibition suggesting their involvement in mediating pro-leukemic functions of WNK1. Mechanistically, we show that WNK1 inhibition induces differentiation by promoting MEK-ERK activity and increasing C/EBPbeta activity and expression, resulting in increased transcription of myeloid differentiation genes. Finally, we illustrate that combining WNK1 inhibition with ATRA further boosts ATRA's efficacy, synergistically increasing differentiation, apoptosis, and cell cycle arrest. C/EBPbeta expression was also enhanced by this combination treatment, suggesting a role for C/EBPbeta in mediating these anti-leukemic effects. Taken together, our findings suggest that WNK1 negatively regulates ERK phosphorylation and activity, likely through SPAK/OSR1. Inhibiting WNK1 releases ERK suppression, increasing C/EBPbeta activity and expression which leads to myeloid differentiation. Overall, our findings reveal a novel role for WNK1 in promoting differentiation arrest and highlight its potential as a new therapeutic target for AML treatment.