Abstract 198: The phosphatase PRL-3 is expressed in primary B-ALL cells and is important for adhesion and migration
Authors: Hjort Magnus Aassved A. , Abdollahi Pegah , Vandsemb Esten , Slørdahl Tobias Schmidt , Lund Bendik , Børset Magne , Rø. Torstein Baade 
Published: July 2016

Introduction: Phosphatase of regenerating liver -3 (PRL-3) is a dual specificity phosphatase, and is associated with aggressiveness and metastatic disease in a number of solid tumors. Less is known about its role in hematological cancer, but we have previously shown that PRL-3 is expressed in primary multiple myeloma (MM) cells and MM cell lines. More recently PRL-3 is shown to be expressed in acute myeloid leukemia (AML), and associated with poor prognosis. Acute lymphoblastic leukemia (ALL) is the most common childhood cancer. Despite progress in treatment and survival, treatment related toxicity is a major concern. Therefore, it is a need for new clinical markers and therapy targets to optimize the treatment. We hypothesized that PRL-3 is expressed, and have oncogenic functions in B-ALL, and can be a possible clinical marker and a novel drug target.

Methods: Primary ALL cells from peripheral blood were obtained from The Regional Biobank of Central Norway, and PRL-3 mRNA expression was measured with qRT-PCR. The PreB-ALL cell lines Reh and MHH-CALL-4 were used for further experiments. IL-7 (100 ng/mL) were used for stimulation. ShRNA against PRL-3 was used to knock down PRL-3 in Reh (shPRL-3) and for empty vector control (shMOCK) by use of lentiviral transduction. To study adhesion we used fibronectin (20 μg/mL) and stimulated with IL-7, IL-8 and IGF-1 (all 100 ng/mL) for 45 min in 37°C. Migration was studied with transwell permeable plates (pore size 3 μm) using SDF1α (75 ng/mL) as a chemoattractant. Further we examined the effect of the small molecular inhibitor PRL-3 Inhibitor I on ALL cell lines. Apoptosis and cell viability was determined by Annexin-FITC/-PI with flow cytometry, and by CellTiter-Glo® Luminescent Cell Viability assay kit, after 24-72 hours incubation with PRL-3 Inhibitor I.

Results: 89% (16 of 18) of primary B-ALL samples expressed PRL-3, and 33% (6 of 18) at high levels. Stimulation with IL-7 induced expression of PRL-3 in a dose-dependent manner in Reh and MHH-CALL-4. The knock down of PRL-3 by shRNA was 80% efficient. Reh shMOCK cells were significantly more adherent to fibronectin after stimulation with IL-7, IL-8 and IGF-1 compared to Reh shPRL3. The cells’ ability to migrate towards a SDF1α gradient were significantly reduced in Reh shPRL-3 cells compared with Reh shMOCK. PRL-3 inhibitor I also reduced the viability and induced apoptosis in Reh cell line in a dose-dependent manner, but not in MHH-CALL-4 cell line, at a concentration of 40-80 μM.

Conclusion: PRL-3 was expressed in 89% of primary B-ALL samples. Knock down of PRL-3 clearly reduced cell adhesion and migration. PRL-3 inhibitor I induced apoptosis and reduced cell viability in Reh, but not in MHH-CALL-4. This study indicates that PRL-3 could be important in the pathogenesis of B-ALL, and might be a suitable target for treatment in the future.

Citation Format: Magnus Aassved A. Hjort, Pegah Abdollahi, Esten Vandsemb, Tobias Schmidt Slørdahl, Bendik Lund, Magne Børset, Torstein Baade Rø. The phosphatase PRL-3 is expressed in primary B-ALL cells and is important for adhesion and migration. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 198.