PRL2 inhibition elevates PTEN protein and ameliorates progression of acute myeloid leukemia

PRL2 negatively regulates FcεRI mediated activation of mast cells

Mast cells play a central role in allergic reactions, acting as key effector cells that initiate and amplify the inflammatory response. In this study, we demonstrate that phosphatase of regenerating liver 2 (PRL2) functions as a negative regulator of FcεRI-mediated mast cell activation. In PRL2-deficient myeloid cells, PRL2 conditional knockout mice developed more severe passive systemic anaphylaxis (PSA). Although PRL2 deficiency does not impact mast cell development, in the absence of PRL2 FcεRI-mediated mast cell activation is enhanced. In the presence of IgE the expression of mast cell PRL2 is downregulated, leading to modulation of the cellular response. In PRL2-deficient mast cells, the PI3K signaling pathway is upregulated, resulting in increased calcium influx. This, in turn, enhances mast cell degranulation and the production of inflammatory mediators. Moreover, hydroxychloroquine (an inhibitor of PRL2 degradation) reduces the severity of PSA in wild-type mice. Our findings suggest that PRL2 acts as a negative regulator of FcεRI-mediated mast cell activation. Therefore, therapeutic strategies aimed at enhancing PRL2 activity in mast cells may offer a promising approach for the treatment of allergic disorders.

The PRL2 phosphatase up-regulates miR-21 through activation of the JAK2/STAT3 pathway to down-regulate the PTEN tumor suppressor

The phosphatases of regenerating liver (PRLs) are members of the protein tyrosine phosphatase (PTP) superfamily that play pro-oncogenic roles in cell proliferation, migration, and survival. We previously demonstrated that PRLs can post-translationally down-regulate PTEN, a tumor suppressor frequently inactivated in human cancers, by dephosphorylating PTEN at Tyr336, which promotes the NEDD4-mediated PTEN ubiquitination and proteasomal degradation. Here, we report that PRLs can also reduce PTEN expression by up-regulating microRNA-21 (miR-21), which is one of the most frequently overexpressed miRNAs in solid tumors. We observe a broad correlation between PRL and miR-21 levels in multiple human cancers. Mechanistically, PRL2, the most abundant and ubiquitously expressed PRL family member, promotes the JAK2/STAT3 pathway-mediated miR-21 expression by directly dephosphorylating JAK2 at Tyr570. Finally, we confirm that the PRL2-mediated miR-21 expression contributes to its oncogenic potential in breast cancer cells. Our study defines a new functional role of PRL2 in PTEN regulation through a miR-21-dependent post-transcriptional mechanism, in addition to our previously reported NEDD4-dependent post-translational PTEN regulation. Together, these studies further establish the PRLs as negative regulators of PTEN.

Targeting PRL phosphatases in hematological malignancies

INTRODUCTION

Phosphatase of regenerating liver (PRL) family proteins, also known as protein tyrosine phosphatase 4A (PTP4A), have been implicated in many types of cancers. The PRL family of phosphatases consists of three members, PRL1, PRL2, and PRL3. PRLs have been shown to harbor oncogenic potentials and are highly expressed in a variety of cancers. Given their roles in cancer progression and metastasis, PRLs are potential targets for anticancer therapies. However, additional studies are needed to be performed to fully understand the roles of PRLs in blood cancers.

AREAS COVERED

In this review, we will summarize recent studies of PRLs in normal and malignant hematopoiesis, the role of PRLs in regulating various signaling pathways, and the therapeutic potentials of targeting PRLs in hematological malignancies. We will also discuss how to improve current PRL inhibitors for cancer treatment.

EXPERT OPINION

Although PRL inhibitors show promising therapeutic effects in preclinical studies of different types of cancers, moving PRL inhibitors from bench to bedside is still challenging. More potent and selective PRL inhibitors are needed to target PRLs in hematological malignancies and improve treatment outcomes.

Protein Tyrosine Phosphatase PRL-3: A Key Player in Cancer Signaling

Protein phosphatases are primarily responsible for dephosphorylation modification within signal transduction pathways. Phosphatase of regenerating liver-3 (PRL-3) is a dual-specific phosphatase implicated in cancer pathogenesis. Understanding PRL-3's intricate functions and developing targeted therapies is crucial for advancing cancer treatment. This review highlights its regulatory mechanisms, expression patterns, and multifaceted roles in cancer progression. PRL-3's involvement in proliferation, migration, invasion, metastasis, angiogenesis, and drug resistance is discussed. Regulatory mechanisms encompass transcriptional control, alternative splicing, and post-translational modifications. PRL-3 exhibits selective expressions in specific cancer types, making it a potential target for therapy. Despite advances in small molecule inhibitors, further research is needed for clinical application. PRL-3-zumab, a humanized antibody, shows promise in preclinical studies and clinical trials. Our review summarizes the current understanding of the cancer-related cellular function of PRL-3, its prognostic value, and the research progress of therapeutic inhibitors.

Inhibition of PRL2 Upregulates PTEN and Attenuates Tumor Growth in Tp53-deficient Sarcoma and Lymphoma Mouse Models

The phosphatases of regenerating liver (PRL) are oncogenic when overexpressed. We previously found that PRL2 deletion increases PTEN, decreases Akt activity, and suppresses tumor development in a partial Pten-deficient mouse model. The current study aims to further establish the mechanism of PTEN regulation by PRL2 and expand the therapeutic potential for PTEN augmentation mediated by PRL2 inhibition in cancers initiated without PTEN alteration. The TP53 gene is the most mutated tumor suppressor in human cancers, and heterozygous or complete deletion of Tp53 in mice leads to the development of sarcomas and thymic lymphomas, respectively. There remains a lack of adequate therapies for the treatment of cancers driven by Tp53 deficiency or mutations. We show that Prl2 deletion leads to PTEN elevation and attenuation of Akt signaling in sarcomas and lymphomas developed in Tp53 deficiency mouse models. This results in increased survival and reduced tumor incidence because of impaired tumor cell proliferation. In addition, inhibition of PRL2 with a small-molecule inhibitor phenocopies the effect of genetic deletion of Prl2 and reduces Tp53 deficiency-induced tumor growth. Taken together, the results further establish PRL2 as a negative regulator of PTEN and highlight the potential of PRL2 inhibition for PTEN augmentation therapy in cancers with wild-type PTEN expression.

SIGNIFICANCE

Prl2 deletion attenuates Tp53 deficiency-induced tumor growth by increasing PTEN and reducing Akt activity. Targeting Tp53-null lymphoma with PRL inhibitors lead to reduced tumor burden, providing a therapeutic approach via PTEN augmentation.