SHP2/PTPN11 PROTEIN-TYROSINE PHOSPHATASE PROMOTES MAST CELL HOMEOSTASIS AND SYSTEMIC MASTOCYTOSIS
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KIT receptor (CD117) is a receptor tyrosine kinase crucial for homeostasis of mast cells (MCs) in tissues and recruitment to sites of inflammation and tumors in response to its ligand Stem cell factor (SCF). Gain of function mutations in KIT (e.g. D816V) are frequently observed in systemic mastocytosis and other cancer types. Src Homology 2 domain containing phosphatase-2 (SHP2 or PTPN11) is a protein tyrosine phosphatase that promotes cell proliferation, survival and motility in multiple pathways and cell types. To study SHP2 function in MCs, we generated novel MC-specific Shp2 knock-out (KO) mice (MC-shp2 KO). These mice had reduced numbers of MCs in skin and peritoneum, and defective contact hypersensitivity responses compared to control mice, consistent with SHP2 promoting MC homeostasis. Using an inducible SHP2 KO bone marrow-derived MC (BMMC) culture model, we found that SHP2 KO cells were prone to apoptosis and had no MC repopulating activity in vivo. Mechanistically, SHP2 enhanced ERK activation and downregulation of pro-apoptotic protein Bim. SHP2 KO BMMCs also had defects in chemotaxis towards SCF, due to impaired activation of a Lyn/Vav/Rac pathway in SHP2 KO BMMCs. This correlated with defects in cell spreading, and F-actin polymerization in response to SCF. Treatment of BMMCs with a SHP2 inhibitor (II-B08) also led to reduced chemotaxis, consistent with SHP2 phosphatase activity being required for KIT-induced chemotaxis. Lastly, we tested whether SHP2 regulates oncogenic KIT signaling using a P815 mouse mastocytoma model. Stable silencing of SHP2 in P815 cells led to reduced cell growth and survival in vitro, and less aggressive systemic mastocytosis development in syngeneic mice. Overall, these studies identify SHP2 as a key node in SCF/KIT and oncogenic KIT pathways, and as a potential therapeutic target in several human diseases.