Protein Tyrosine Phosphatase PRL2 Promotes MLL-Rearranged Acute Myeloid Leukemia Development through Inhibiting the p53 Pathway

Phosphatase of regenerating liver (PRL) family proteins, also known as protein tyrosine phosphatase 4A (PTP4A), have been identified as oncoproteins in various human cancers. PRL2 is highly expressed in MLL-rearranged AML. However, its role in leukemogenesis remains largely unexplored.

MLL-AF9 is the most prevalent MLL rearrangement in AML and we found that loss of Prl2 significantly delays MLL-AF9-induced leukemia development in mice. We also discovered that PRL2 is critical for leukemia-initiating cell (LIC) proliferation and maintenance. To understand how PRL2 promotes MLL-AF9-driven AML, we performed RNA-Seq analysis and found that regulation of TP53 activity gene signatures were upregulated in PRL2-/- hematopoietic stem and progenitor cells (HSPCs) expressing MLL-AF9 compared to that of wild-type (WT) HSPCs. To determine the role of p53 in PRL2 deficient HSPCs, we generated p53+/-PRL2-/- mice. We observed that loss of PRL2 significantly decreases the replating potential of p53+/- bone marrow cells in vitro and reduces the repopulating capacity of p53+/- bone marrow cells in vivo.

To further investigate the impact of PRL2 on the p53 pathway in MLL-AF9+ LICs, we conducted transplantation experiments using WT, PRL2-/-, p53+/-, or p53+/- PRL2-/- fetal liver cells expressing MLL-AF9. Loss of PRL2 significantly prolonged the survival of the recipient mice transplanted with MLL-AF9+ HSPCs, whereas recipient mice repopulated with p53+/-PRL2-/- HSPCs expressing MLL-AF9 showed accelerated disease development, suggesting that p53 pathway activation in PRL2-/- HSPCs may contribute to extended survival. Indeed, we found that loss of PRL2 activates the p53 pathway in MLL-AF9+ HSPCs, resulting in increased apoptosis of PRL2-/- HSPCs expressing MLL-AF9. Oncogene-induced senescence is a critical cancer suppression mechanism, which involves the p53 pathway. We discovered elevated senescence in MLL-AF9+ PRL2-/- HSPCs in a p53-dependent manner.

To understand how PRL2 regulates p53 activity, we knocked down PRL2 in human CD34+ cells expressing MLL-AF9 and found that PRL2 deficiency increases p53 stability in human CD34+ cells. We then performed GST pull-down assays using human CD34+ cells expressing MLL-AF9 and observed that p53 can be pulled down with GST protein expressing a dominant negative substrate-trapping PRL2 mutant (PRL2-CSDA). Thus, we demonstrated that PRL2 directly interacts with p53 in human CD34+ cells.

Given that menin-MLL interaction plays a key role in enhancing MLL-fusion proteins to dysregulate downstream pathways, inhibitors targeting this interaction have been tested in clinical trials. We found that PRL2 deficiency increases the sensitivity of MV4-11 cells to menin-MLL interaction inhibitor (MI-3454) treatment in a dose-dependent manner, suggesting that pharmacological inhibition of PRL2 may sensitize leukemia cells to menin inhibitor.

In summary, we demonstrate that PRL2 promotes MLL-AF9-driven leukemia by inhibiting the p53 tumor suppressor pathway. Our study underscores the critical role of PRL2 in MLL-rearranged AML, providing new opportunities for targeted therapies in AML.