Stephanie Everingham

F-BAR-containing adaptor CIP4 localizes to early endosomes and regulates Epidermal Growth Factor Receptor trafficking and downregulation

Cdc42-Interacting Protein-4 (CIP4) family adaptors have been implicated in promoting Epidermal Growth Factor Receptor (EGFR) internalization, however, their unique or overlapping functions remain unclear. Here, we show that although CIP4 was not required for early events in clathrin-mediated endocytosis of EGFR, CIP4 localizes to vesicles containing EGFR and Rab5. Furthermore, expression of constitutively active Rab5 led to accumulation of CIP4 and the related adaptor Toca-1 in giant endosomes. Using a mutagenesis approach, we show that localization of CIP4 to endosomes is mediated in part via the curved phosphoinositide-binding face of the CIP4 F-BAR domain. Downregulation of CIP4 in A431 epidermoid carcinoma cells by RNA interference led to elevated EGFR levels, compared to control cells. Although surface expression of EGFR was not affected by CIP4 silencing, EGF-induced transit of EGFR from EEA1-positive endosomes to lysosomes was reduced compared to control cells. This correlated with more robust activation of ERK kinase and entry to S phase in CIP4-depleted A431 cells, compared to control cells. The combined silencing of CIP4 and Toca-1 was more effective in driving cells into S phase, suggesting a partial redundancy in their functions. Overall, our results implicate CIP4 and Toca-1 in regulating late events in EGFR trafficking from endosomes that serves to limit sustained ERK activation within the endosomal compartment.

Contributions of F-BAR and SH2 Domains of Fes Protein Tyrosine Kinase for Coupling to the FcεRI Pathway in Mast Cells

ABSTRACT This study investigates the roles of Fer-CIP4 homology (FCH)-Bin/amphiphysin/Rvs (F-BAR) and SH2 domains of Fes protein tyrosine kinase in regulating its activation and signaling downstream of the high-affinity immunoglobulin G (IgE) receptor (FcεRI) in mast cells. Homology modeling of the Fes F-BAR domain revealed conservation of some basic residues implicated in phosphoinositide binding (R113/K114). The Fes F-BAR can bind phosphoinositides and induce tubulation of liposomes in vitro. Mutation of R113/K114 to uncharged residues (RK/QQ) caused a significant reduction in phosphoinositide binding in vitro and a more diffuse cytoplasmic localization in transfected COS-7 cells. RBL-2H3 mast cells expressing full-length Fes carrying the RK/QQ mutation show defects in FcεRI-induced Fes tyrosine phosphorylation and degranulation compared to cells expressing wild-type Fes. This correlated with reduced localization to Lyn kinase-containing membrane fractions for the RK/QQ mutant compared to wild-type Fes in mast cells. The Fes SH2 domain also contributes to Fes signaling in mast cells, via interactions with the phosphorylated FcεRI β chain and the actin regulatory protein HS1. We show that Fes phosphorylates C-terminal tyrosine residues in HS1 implicated in actin stabilization. Thus, coordinated actions of the F-BAR and SH2 domains of Fes allow for coupling to FcεRI signaling and potential regulation the actin reorganization in mast cells.

SH2 Domain-Containing Phosphatase-2 Protein-Tyrosine Phosphatase Promotes FcεRI-Induced Activation of Fyn and Erk Pathways Leading to TNFα Release from Bone Marrow-Derived Mast Cells

Clustering of the high affinity IgE receptor (FcεRI) in mast cells leads to degranulation and production of numerous cytokines and lipid mediators that promote allergic inflammation. Initiation of FcεRI signaling involves rapid tyrosine phosphorylation of FcεRI and membrane-localized adaptor proteins that recruit additional SH2 domain-containing proteins that dynamically regulate downstream signaling. SH2 domain-containing phosphatase-2 (SHP2) is a protein-tyrosine phosphatase implicated in FcεRI signaling, but whose function is not well defined. In this study, using a mouse model allowing temporal shp2 inactivation in bone marrow-derived mast cells (BMMCs), we provide insights into SHP2 functions in the FcεRI pathway. Although no overt defects in FcεRI-induced tyrosine phosphorylation were observed in SHP2 knock-out (KO) BMMCs, several proteins including Lyn and Syk kinases displayed extended phosphorylation kinetics compared with wild-type BMMCs. SHP2 was dispensable for FcεRI-induced degranulation of BMMCs, but was required for maximal activation of Erk and Jnk mitogen-activated protein kinases. SHP2 KO BMMCs displayed several phenotypes associated with reduced Fyn activity, including elevated phosphorylation of the inhibitory pY531 site in Fyn, impaired signaling to Grb2-associated binder 2, Akt/PKB, and IκB kinase, and decreased TNF-α release compared with control cells. This is likely due to elevated Lyn activity in SHP2 KO BMMCs, and the ability of Lyn to antagonize Fyn activity. Overall, our study identifies SHP2 as a positive effector of FcεRI-induced activation of Fyn/Grb2-associated binder 2/Akt and Ras/Erk pathways leading to TNF-α release from mast cells.

SH2 Domain-Containing Phosphatase 2 Is a Critical Regulator of Connective Tissue Mast Cell Survival and Homeostasis in Mice

ABSTRACT Mast cells require KIT receptor tyrosine kinase signaling for development and survival. Here, we report that SH2 domain-containing phosphatase 2 (SHP2) signaling downstream of KIT is essential for mast cell survival and homeostasis in mice. Using a novel mouse model with shp2 deletion within mature mast cells (MC-shp2 knockout [KO]), we find that SHP2 is required for the homeostasis of connective tissue mast cells. Consistently with the loss of skin mast cells, MC-shp2 KO mice fail to mount a passive late-phase cutaneous anaphylaxis response. To better define the phenotype of shp2-deficient mast cells, we used an inducible shp2 knockout approach in bone marrow-derived mast cells (BMMCs) or cultured peritoneal mast cells and found that SHP2 promotes mast cell survival. We show that SHP2 promotes KIT signaling to extracellular signal-regulated kinase (ERK) mitogen-activated protein kinase and downregulation of the proapoptotic protein Bim in BMMCs. Also, SHP2-deficient BMMCs failed to repopulate mast cells in mast cell-deficient mice. Silencing of Bim partially rescued survival defects in shp2-deficient BMMCs, consistent with the importance of a KIT → SHP2 → Ras/ERK pathway in suppressing Bim and promoting mast cell survival. Thus, SHP2 is a key node in a mast cell survival pathway and a new potential therapeutic target in diseases involving mast cells.

Calpains promote neutrophil recruitment and bacterial clearance in an acute bacterial peritonitis model

Activation of the innate immune system is critical for clearance of bacterial pathogens to limit systemic infections and host tissue damage. Here, we report a key role for calpain proteases in bacterial clearance in mice with acute peritonitis. Using transgenic mice expressing Cre recombinase primarily in innate immune cells (fes‐Cre), we generated conditional capns1 knockout mice. Consistent with capns1 being essential for stability and function of the ubiquitous calpains (calpain‐1, calpain‐2), peritoneal cells from these mice had reduced levels of calpain‐2/capns1, and reduced proteolysis of their substrate selenoprotein K. Using an acute bacterial peritonitis model, we observed impaired bacterial killing within the peritoneum and development of bacteremia in calpain knockout mice. These defects correlated with significant reductions in IL‐1α release, neutrophil recruitment, and generation of reactive oxygen species in calpain knockout mice with acute bacterial peritonitis. Peritoneal macrophages from calpain knockout mice infected with enterobacteria ex vivo, were competent in phagocytosis of bacteria, but showed impaired clearance of intracellular bacteria compared with control macrophages. Together, these results implicate calpains as key mediators of effective innate immune responses to acute bacterial infections, to prevent systemic dissemination of bacteria that can lead to sepsis.

FES Kinase Promotes Mast Cell Recruitment to Mammary Tumors via the Stem Cell Factor/KIT Receptor Signaling Axis

KIT receptor is required for mast cell development, survival, and migration toward its ligand stem cell factor (SCF). Many solid tumors express SCF and this leads to mast cell recruitment to tumors and release of mediators linked to tumor angiogenesis, growth, and metastasis. Here, we investigate whether FES protein-tyrosine kinase, a downstream effector of KIT signaling in mast cells, is required for migration of mast cells toward SCF-expressing mammary tumors. Using a novel agarose drop assay for chemotaxis of bone marrow–derived mast cells (BMMC) toward SCF, we found that defects in chemotaxis of fes-null BMMCs correlated with disorganized microtubule networks in polarized cells. FES displayed partial colocalization with microtubules in polarized BMMCs and has at least two direct microtubule binding sites within its N-terminal F-BAR and SH2 domains. An oligomerization-disrupting mutation within the Fer/CIP4 homology-Bin/Amphiphysin/Rvs (F-BAR) domain had no effect on microtubule binding, whereas microtubule binding to the SH2 domain was dependent on the phosphotyrosine-binding pocket. FES involvement in mast cell recruitment to tumors was tested using the AC2M2 mouse mammary carcinoma model. These tumor cells expressed SCF and promoted BMMC recruitment in a KIT- and FES-dependent manner. Engraftment of AC2M2 orthotopic and subcutaneous tumors in control or fes-null mice, revealed a key role for FES in recruitment of mast cells to the tumor periphery. This may contribute to the reduced tumor growth and metastases observed in fes-null mice compared with control mice. Taken together, FES is a potential therapeutic target to limit the progression of tumors with stromal mast cell involvement. Mol Cancer Res; 10(7); 881–91. ©2012 AACR.

Abstract 5311: Transducer of Cdc42-dependent actin assembly-1 (Toca-1) promotes breast cancer invasion and metastasis

Metastatic breast adenocarcinomas display activation signatures for signaling pathways like Epidermal Growth Factor Receptor (EGFR) that trigger cell motility and tissue invasion. Transducer of Cdc42-dependent actin assembly-1 (Toca-1) is an adaptor protein that promotes recruitment of actin nucleation promoting factors to cellular membranes. Although these actin regulatory proteins have been linked to breast cancer invasion, the role of Toca-1 in this process has not been reported. In this study, breast cancer cell lines with a range of invasive and metastatic properties were used, including human MDA-MB-231 cells, rat MTLn3 cells, and MTLn3-B1 cells expressing human EGFR. To test the role of Toca-1 in these cell lines, we established stable Toca-1 knock-down (KD) using lentiviral delivery of shRNAs specific for human or rat Toca-1. Here, we report that Toca-1 is expressed in highly invasive breast cancers cell lines, and that Toca-1 co-localizes with components of invadopodia. Toca-1 localizes to the filamentous actin-rich core of invadopodial protrusions in breast cancer cells that are actively degrading the extracellular matrix (ECM). In MDA-MB-231 cells, Toca-1 KD led to a significant defect in EGF-induced cell migration and invasion compared to control cells. This correlated with a significant defect in EGF- and Src-induced ECM digestion in Toca-1 KD compared to control MDA-MB-231 cells. Next, control and Toca-1 KD cells were compared in orthotopic mammary tumors that were xenografted in Rag2 −/− :[[Unsupported Character - Symbol Font ]]c −/− mice. Although Toca-1 KD remained effective in primary tumors, no defects in tumor growth were observed. However, mice bearing Toca-1 KD cell tumors displayed a significant reduction in spontaneous metastases to the lung. Similar results were obtained for weakly metastatic MDA-MB-231 cells and highly metastatic MTLn3-B1 cells. In contrast, Toca-1 was not required for efficient lung seeding following tail vein injection of MTLn3-B1 cells, suggesting that Toca-1 functions at an early step in the dissemination of metastatic breast tumor cells. Taken together, this investigation identifies Toca-1 as a pro-invasive protein in breast cancer, and a potential therapeutic target to limit tumor metastasis. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 5311. doi:1538-7445.AM2012-5311