Deficiency of the protein-tyrosine phosphatase DEP-1/PTPRJ promotes matrix metalloproteinase-9 expression in meningioma cells

Disrupting PTPRJ transmembrane-mediated oligomerization counteracts oncogenic receptor tyrosine kinase FLT3 ITD

The receptor protein tyrosine phosphatase (RPTP) PTPRJ (also known as DEP-1) has been identified as a negative regulator of the receptor tyrosine kinase FLT3 signalling in vitro. The inactivation of the PTPRJ gene in mice expressing the constitutively active, oncogenic receptor tyrosine kinase FLT3 ITD aggravated known features of leukaemogenesis, revealing PTPRJ's antagonistic role. FLT3 ITD mutations resulting in constitutively kinase activity and cell transformation frequently occur in patients with acute myeloid leukaemia (AML). Thus, in situ activation of PTPRJ could be used to abrogate oncogenic FLT3 signalling. The activity of PTPRJ is suppressed by homodimerization, which is mediated by transmembrane domain (TMD) interactions. Specific Glycine-to-Leucine mutations in the TMD disrupt oligomerization and inhibit the Epidermal Growth Factor Receptor (EGFR) and EGFR-driven cancer cell phenotypes. To study the effects of PTPRJ TMD mutant proteins on FLT3 ITD activity in cell lines, endogenous PTPRJ was inactivated and replaced by stable expression of PTPRJ TMD mutants. Autophosphorylation of wild-type and ITD-mutated FLT3 was diminished in AML cell lines expressing the PTPRJ TMD mutants compared to wild-type-expressing cells. This was accompanied by reduced FLT3-mediated global protein tyrosine phosphorylation and downstream signalling. Further, PTPRJ TMD mutant proteins impaired the proliferation and in vitro transformation of leukemic cells. Although PTPRJ's TMD mutant proteins showed impaired self-association, the specific phosphatase activity of immunoprecipitated proteins remained unchanged. In conclusion, this study demonstrates that the destabilization of PTPRJ TMD-mediated self-association increases the activity of PTPRJ in situ and impairs FLT3 activity and FLT3-driven cell phenotypes of AML cells. Thus, disrupting the oligomerization of PTPRJ in situ could prove a valuable therapeutic strategy to restrict oncogenic FLT3 activity in leukemic cells.

AKT1E17K -mutated meningioma cell lines respond to treatment with the AKT inhibitor AZD5363

AIMS

Meningiomas are the most frequent primary brain tumours. Recently, knowledge about the molecular drivers underlying aggressive meningiomas has been expanded. A hotspot mutation in the AKT1 gene (AKT1^E17K ), which is found in meningiomas at the convexity and especially at the skull base, has been associated with earlier tumour recurrence.

METHODS

Here, we analysed the effects of the AKT1^E17K mutation and treatment response to the Akt inhibitor AZD5363 in transgenic meningioma cell clones and mouse xenografts modelling convexity or skull base meningiomas.

RESULTS

We show that the AKT^E17K mutation significantly enhances meningioma cell proliferation and colony size in vitro, resulting in significantly shortened survival times of mice carrying convexity or skull base AKT1^E17K xenografts. Treatment of mutant cells or xenografts (150 mg/kg/d) with AZD5363 revealed a significant decrease in cell proliferation and colony size and a prolongation of mouse survival. Western blots revealed activation of AKT1 kinase (phosphorylation at Ser273 and Thr308) by the E17K mutation in human meningioma samples and in our in vitro and in vivo models.

CONCLUSIONS

Our data suggest that AKT1^E17K mutated meningiomas are a promising selective target for AZD5363.

Molecular Mechanism and Approach in Progression of Meningioma

Meningioma is the most common tumor of the central nervous system, most of which is benign. Even after complete resection, a high rate of recurrence of meningioma is observed. From in-depth study of its pathogenesis, it has been found that a number of chromosomal variations and abnormal molecular signals are closely related to the occurrence and development of malignancy in meningioma, which may provide the theoretical basis and potential direction for accurate and targeted treatment. We have reviewed advances in chromosomal variations and molecular mechanisms involved in the progression of meningioma, and have highlighted the association with malignant biological behavior including cell proliferation, angiogenesis, increased invasiveness, and inhibition of apoptosis. In addition, the chemotherapy of meningioma is summarized and discussed.

Loss of PTPRJ/DEP-1 enhances NF2/Merlin-dependent meningioma development

INTRODUCTION

Meningiomas are common tumors in adults, which develop from the meningeal coverings of the brain and spinal cord. Loss-of-function mutations or deletion of the NF2 gene, resulting in loss of the encoded Merlin protein, lead to Neurofibromatosis type 2 (NF2), but also cause the formation of sporadic meningiomas. It was shown that inactivation of Nf2 in mice caused meningioma formation. Another meningioma tumor-suppressor candidate is the receptor-like density-enhanced phosphatase-1 (DEP-1), encoded by PTPRJ. Loss of DEP-1 enhances meningioma cell motility in vitro and invasive growth in an orthotopic xenograft model. Ptprj-deficient mice develop normally and do not show spontaneous tumorigenesis. Another genetic lesion may be required to interact with DEP-1 loss in meningioma genesis.

METHODS

In the present study we investigated in vitro and in vivo whether the losses of DEP-1 and Merlin/NF2 may have a combined effect.

RESULTS

Human meningioma cells deficient for DEP-1, Merlin/NF2 or both showed no statistically significant changes in cell proliferation, while DEP-1 or DEP1/NF2 deficiency led to moderately increased colony size in clonogenicity assays. In addition, the loss of any of the two genes was sufficient to induce a significant reduction of cell size (p < .05) and profound morphological changes. Most important, in Ptprj knockout mice Cre/lox mediated meningeal Nf2 knockout elicited a four-fold increased rate of meningioma formation within one year compared with mice with Ptprj wild type alleles (25% vs 6% tumor incidence).

CONCLUSIONS

Our data suggest that loss of DEP-1 and Merlin/NF2 synergize during meningioma genesis.