PTPRG and PTPRC modulate nilotinib response in chronic myeloid leukemia cells.

The introduction of second-generation tyrosine kinase inhibitors (TKIs) targeting the protein-tyrosine kinase (PTK) BCR-ABL1 has improved treatment response in chronic myeloid leukemia (CML). However, in some patients response still remains suboptimal. Protein-tyrosine phosphatases (PTPs) are natural counter-actors of PTK activity and can affect TKI sensitivity, but the impact of PTPs on treatment response to second-generation TKIs is unknown. We assessed the mRNA expression level of 38 PTPs in 66 newly diagnosed CML patients and analyzed the potential relation with treatment outcome after 9 months of nilotinib medication. A significantly positive association with response was observed for higher PTPN13, PTPRA, PTPRC (also known as CD45), PTPRG, and PTPRM expression. Selected PTPs were then subjected to a functional analysis in CML cell line models using PTP gene knockout by CRISPR/Cas9 technology or PTP overexpression. These analyses revealed PTPRG positively and PTPRC negatively modulating nilotinib response. Consistently, PTPRG negatively and PTPRC positively affected BCR-ABL1 dependent transformation. We identified BCR-ABL1 signaling events, which were affected by modulating PTP levels or nilotinib treatment in the same direction. In conclusion, the PTP status of CML cells is important for the response to second generation TKIs and may help in optimizing therapeutic strategies.

The Neurobeachin-like 2 Protein Regulates Mast Cell Homeostasis.

The neurobeachin-like 2 protein (Nbeal2) belongs to the family of beige and Chediak-Higashi (BEACH) domain proteins. Loss-of-function mutations in the human NBEAL2 gene or Nbeal2 deficiency in mice cause gray platelet syndrome, a bleeding disorder characterized by macrothrombocytopenia, splenomegaly, and paucity of α-granules in megakaryocytes and platelets. We found that in mast cells, Nbeal2 regulates the activation of the Shp1-STAT5 signaling axis and the composition of the c-Kit/STAT signalosome. Furthermore, Nbeal2 mediates granule formation and restricts the expression of the transcription factors, IRF8, GATA2, and MITF as well as of the cell-cycle inhibitor p27, which are essential for mast cell differentiation, proliferation, and cytokine production. These data demonstrate the relevance of Nbeal2 in mast cells above and beyond granule biosynthesis.

The receptor tyrosine kinase c-Kit controls IL-33 receptor signaling in mast cells.

Members of the Toll/interleukin-1 receptor (TIR) family are of importance for host defense and inflammation. Here we report that the TIR-family member interleukin-33R (IL-33R) cross-activates the receptor tyrosine kinase c-Kit in human and murine mast cells. The IL-33R-induced activation of signal transducer and activator of transcription 3 (STAT3), extracellular signal-regulated kinase 1/2 (Erk1/2), protein kinase B (PKB), and Jun NH(2)-terminal kinase 1 (JNK1) depends on c-Kit and is required to elicit optimal effector functions. Costimulation with the c-Kit ligand stem cell factor (SCF) is necessary for IL-33-induced cytokine production in primary mast cells. The structural basis for this cross-activation is the complex formation between c-Kit, IL-33R, and IL-1R accessory protein (IL-1RAcP). We found that c-Kit and IL-1RAcP interact constitutively and that IL-33R joins this complex upon ligand binding. Our findings support a model in which signals from seemingly disparate receptors are integrated for full cellular responses.