Phosphatase of regenerating liver-3 (PRL-3) is overexpressed in classical Hodgkin lymphoma and promotes survival and migration

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.

PRL3 as a therapeutic target for novel cancer immunotherapy in multiple cancer types

Phosphatase of Regenerating Liver-3 (PRL3) was discovered in 1998 and was subsequently found to be correlated with cancer progression and metastasis in 2001. Extensive research in the past two decades has produced significant findings on PRL3-mediated cancer signaling and functions, as well as its clinical relevance in diverse types of cancer. PRL3 has been established to play a role in many cancer-related functions, including but not limited to metastasis, proliferation, and angiogenesis. Importantly, the tumor-specific expression of PRL3 protein in multiple cancer types has made it an attractive therapeutic target. Much effort has been made in developing PRL3-targeted therapy with small chemical inhibitors against intracellular PRL3, and notably, the development of PRL3-zumab as a novel cancer immunotherapy against PRL3. In this review, we summarize the current understanding of the role of PRL3 in cancer-related cellular functions, its prognostic value, as well as perspectives on PRL3 as a target for unconventional immunotherapy in the clinic with PRL3-zumab.

Phosphatase of regenerating liver-3 regulates cancer cell metabolism in multiple myeloma

Cancer cells often depend on microenvironment signals from molecules such as cytokines for proliferation and metabolic adaptations. PRL-3, a cytokine-induced oncogenic phosphatase, is highly expressed in multiple myeloma cells and associated with poor outcome in this cancer. We studied whether PRL-3 influences metabolism. Cells transduced to express PRL-3 had higher aerobic glycolytic rate, oxidative phosphorylation, and ATP production than the control cells. PRL-3 promoted glucose uptake and lactate excretion, enhanced the levels of proteins regulating glycolysis and enzymes in the serine/glycine synthesis pathway, a side branch of glycolysis. Moreover, mRNAs for these proteins correlated with PRL-3 expression in primary patient myeloma cells. Glycine decarboxylase (GLDC) was the most significantly induced metabolism gene. Forced GLDC downregulation partly counteracted PRL-3-induced aerobic glycolysis, indicating GLDC involvement in a PRL-3-driven Warburg effect. AMPK, HIF-1α, and c-Myc, important metabolic regulators in cancer cells, were not mediators of PRL-3's metabolic effects. A phosphatase-dead PRL-3 mutant, C104S, promoted many of the metabolic changes induced by wild-type PRL-3, arguing that important metabolic effects of PRL-3 are independent of its phosphatase activity. Through this study, PRL-3 emerges as one of the key mediators of metabolic adaptations in multiple myeloma.

PRL-3 induces a positive signaling circuit between glycolysis and activation of STAT1/2

Multiple myeloma (MM) is an incurable hematologic malignancy resulting from the clonal expansion of plasma cells. MM cells are interacting with components of the bone marrow microenvironment such as cytokines to survive and proliferate. Phosphatase of regenerating liver (PRL)-3, a cytokine-induced oncogenic phosphatase, is highly expressed in myeloma patients and is a mediator of metabolic reprogramming of cancer cells. To find novel pathways and genes regulated by PRL-3, we characterized the global transcriptional response to PRL-3 overexpression in two MM cell lines. We used pathway enrichment analysis to identify pathways regulated by PRL-3. We further confirmed the hits from the enrichment analysis with in vitro experiments and investigated their function. We found that PRL-3 induced expression of genes belonging to the type 1 interferon (IFN-I) signaling pathway due to activation of signal transducer and activator of transcription (STAT) 1 and STAT2. This activation was independent of autocrine IFN-I secretion. The increase in STAT1 and STAT2 did not result in any of the common consequences of increased IFN-I or STAT1 signaling in cancer. Knockdown of STAT1/2 did not affect the viability of the cells, but decreased PRL-3-induced glycolysis. Interestingly, glucose metabolism contributed to the activation of STAT1 and STAT2 and expression of IFN-I-stimulated genes in PRL-3-overexpressing cells. In summary, we describe a novel signaling circuit where the key IFN-I-activated transcription factors STAT1 and STAT2 are important drivers of the increase in glycolysis induced by PRL-3. Subsequently, increased glycolysis regulates the IFN-I-stimulated genes by augmenting the activation of STAT1/2.

Protein tyrosine phosphatases in multiple myeloma

Many cell signaling pathways are activated or deactivated by protein tyrosine phosphorylation and dephosphorylation, catalyzed by protein tyrosine kinases (PTKs) and protein tyrosine phosphatases (PTPs), respectively. Even though PTPs are as important as PTKs in this process, their role has been neglected for a long time. Multiple myeloma (MM) is a cancer of plasma cells, which is characterized by production of monoclonal immunoglobulin, anemia and destruction of bone. MM is still incurable with high relapse frequency after treatment. In this review, we highlight the PTPs that were previously described in MM or have a role that can be relevant in a myeloma context. Our purpose is to show that despite the importance of PTPs in MM pathogenesis, many unanswered questions in this field need to be addressed. This might help to detect novel treatment strategies for MM patients.

Structure of the Complex of an Iminopyridinedione Protein Tyrosine Phosphatase 4A3 Phosphatase Inhibitor with Human Serum Albumin

Protein tyrosine phosphatase (PTP) 4A3 is frequently overexpressed in human solid tumors and hematologic malignancies and is associated with tumor cell invasion, metastasis, and a poor patient prognosis. Several potent, selective, and allosteric small molecule inhibitors of PTP4A3 were recently identified. A lead compound in the series, JMS-053 (7-imino-2-phenylthieno[3,2-c]pyridine-4,6(5H,7H)-dione), has a long plasma half-life (∼ 24 hours) in mice, suggesting possible binding to serum components. We confirmed by isothermal titration calorimetry that JMS-053 binds to human serum albumin. A single JMS-053 binding site was identified by X-ray crystallography in human serum albumin at drug site 3, which is also known as subdomain IB. The binding of JMS-053 to human serum albumin, however, did not markedly alter the overall albumin structure. In the presence of serum albumin, the potency of JMS-053 as an in vitro inhibitor of PTP4A3 and human A2780 ovarian cancer cell growth was reduced. The reversible binding of JMS-053 to serum albumin may serve to increase JMS-053's plasma half-life and thus extend the delivery of the compound to tumors. SIGNIFICANCE STATEMENT: X-ray crystallography revealed that a potent, reversible, first-in-class small molecule inhibitor of the oncogenic phosphatase protein tyrosine phosphatase 4A3 binds to at least one site on human serum albumin, which is likely to extend the compound's plasma half-life and thus assist in drug delivery into tumors.

Effect of Pharmacological Inhibition of the Catalytic Activity of Phosphatases of Regenerating Liver in Early T Cell Receptor Signaling Dynamics and IL-2 Production

We have previously shown the delivery of phosphatase of regenerating liver-1 (PRL-1) to the immunological synapse (IS) and proposed a regulatory role of the catalytic activity of PRLs (PRL-1, PRL-2 and PRL-3) in antigen-induced IL-2 production. Nonetheless, the expression in T cells and delivery to the IS of the highly homologous PRL-3, as well as the role of the catalytic activity of PRLs in antigen-induced early signaling, has not been investigated. Here, the expression of PRL-3 protein was detected in primary CD4 T cells and in the CD4 T cell line Jurkat (JK), in which an overexpressed GFP-PRL-3 fluorescent fusion protein trafficked through the endosomal recycling compartment and co-localized with PLCγ1 signaling sites at the IS. Pharmacological inhibition was used to compare the role of the catalytic activity of PRLs in antigen-induced early signaling and late IL-2 production. Although the phosphatase activity of PRLs was not critical for early signaling triggered by antigen, it seemed to regulate signaling dynamics and was necessary for proper IL-2 production. We propose that enzymatic activity of PRLs has a higher significance for cytokine production than for early signaling at the IS. However, further research will be necessary to deeply understand the regulatory role of PRLs during lymphocyte activation and effector function.

Migration Properties Distinguish Tumor Cells of Classical Hodgkin Lymphoma from Anaplastic Large Cell Lymphoma Cells

Anaplastic large cell lymphoma (ALCL) and classical Hodgkin lymphoma (cHL) are lymphomas that contain CD30-expressing tumor cells and have numerous pathological similarities. Whereas ALCL is usually diagnosed at an advanced stage, cHL more frequently presents with localized disease. The aim of the present study was to elucidate the mechanisms underlying the different clinical presentation of ALCL and cHL. Chemokine and chemokine receptor expression were similar in primary ALCL and cHL cases apart from the known overexpression of the chemokines CCL17 and CCL22 in the Hodgkin and Reed-Sternberg (HRS) cells of cHL. Consistent with the overexpression of these chemokines, primary cHL cases encountered a significantly denser T cell microenvironment than ALCL. Additionally to differences in the interaction with their microenvironment, cHL cell lines presented a lower and less efficient intrinsic cell motility than ALCL cell lines, as assessed by time-lapse microscopy in a collagen gel and transwell migration assays. We thus propose that the combination of impaired basal cell motility and differences in the interaction with the microenvironment hamper the dissemination of HRS cells in cHL when compared with the tumor cells of ALCL.

PRL-3 exerts oncogenic functions in myeloid leukemia cells via aberrant dephosphorylation of stathmin and activation of STAT3 signaling

PRL-3, an oncogenic dual-specificity phosphatase, is overexpressed in 50% of acute myeloid leukemia patients. Stathmin has been identified as a downstream target of PRL-3 in colorectal cancer. However, the correlation between PRL-3 and stathmin in myeloid leukemia is unclear. In this study, we revealed the positive correlation between PRL-3 and stathmin in myeloid leukemia. Knockdown of the PRL-3 gene by shRNA reduced the expression of downstream stathmin, suppressed cell proliferation, induced G2/M arrest and cell apoptosis, and inhibited migration and invasion in myeloid leukemia cells. Moreover, our study was the first to provide evidence that silencing PRL-3 increased the phosphorylation level in Ser16, Ser25, Ser38, and Ser63 of stathmin, and in turn inhibited the STAT3 and STAT5 signaling in myeloid leukemia cells. This evidence points to a promoted role for PRL-3 in the progression of myeloid leukemia, and PRL-3 could be a possible new treatment target.