TULA-2 Protein Phosphatase Suppresses Activation of Syk through the GPVI Platelet Receptor for Collagen by Dephosphorylating Tyr(P)346, a Regulatory Site of Syk.

Protein-tyrosine phosphatase TULA-2 has been shown to regulate receptor signaling in several cell types, including platelets. Platelets are critical for maintaining vascular integrity; this function is mediated by platelet aggregation in response to recognition of the exposed basement membrane collagen by the GPVI receptor, which is non-covalently associated with the signal-transducing FcRγ polypeptide chain. Our previous studies suggested that TULA-2 plays an important role in negatively regulating signaling through GPVI-FcRγ and indicated that the tyrosine-protein kinase Syk is a key target of the regulatory action of TULA-2 in platelets. However, the molecular basis of the down-regulatory effect of TULA-2 on Syk activation via FcRγ remained unclear. In this study, we demonstrate that suppression of Syk activation by TULA-2 is mediated, to a substantial degree, by dephosphorylation of Tyr(P)346, a regulatory site of Syk, which becomes phosphorylated soon after receptor ligation and plays a critical role in initiating the process that yields fully activated Syk. TULA-2 is capable of dephosphorylating Tyr(P)346 with high efficiency, thus controlling the overall activation of Syk, but is less efficient in dephosphorylating other regulatory sites of this kinase. Therefore, dephosphorylation of Tyr(P)346 may be considered an important "checkpoint" in the regulation of Syk activation process. Putative biological functions of TULA-2-mediated dephosphorylation of Tyr(P)346 may include deactivation of receptor-activated Syk or suppression of Syk activation by suboptimal stimulation.

Tumor Explants Elucidate a Cascade of Paracrine SHH, WNT, and VEGF Signals Driving Pancreatic Cancer Angiosuppression.

The sparse vascularity of pancreatic ductal adenocarcinoma (PDAC) presents a mystery: What prevents this aggressive malignancy from undergoing neoangiogenesis to counteract hypoxia and better support growth? An incidental finding from prior work on paracrine communication between malignant PDAC cells and fibroblasts revealed that inhibition of the Hedgehog (HH) pathway partially relieved angiosuppression, increasing tumor vascularity through unknown mechanisms. Initial efforts to study this phenotype were hindered by difficulties replicating the complex interactions of multiple cell types in vitro. Here we identify a cascade of paracrine signals between multiple cell types that act sequentially to suppress angiogenesis in PDAC. Malignant epithelial cells promote HH signaling in fibroblasts, leading to inhibition of noncanonical WNT signaling in fibroblasts and epithelial cells, thereby limiting VEGFR2-dependent activation of endothelial hypersprouting. This cascade was elucidated using human and murine PDAC explant models, which effectively retain the complex cellular interactions of native tumor tissues. SIGNIFICANCE: We present a key mechanism of tumor angiosuppression, a process that sculpts the physiologic, cellular, and metabolic environment of PDAC. We further present a computational and experimental framework for the dissection of complex signaling cascades that propagate among multiple cell types in the tissue environment. This article is featured in Selected Articles from This Issue, p. 201.

A novel histidine tyrosine phosphatase, TULA-2, associates with Syk and negatively regulates GPVI signaling in platelets.

T-cell ubiquitin ligand-2 (TULA-2) is a recently discovered histidine tyrosine phosphatase thought to be ubiquitously expressed. In this work, we have investigated whether TULA-2 has a key role in platelet glycoprotein VI (GPVI) signaling. This study indicates that TULA-2 is expressed in human and murine platelets and is able to associate with Syk and dephosphorylate it. Ablation of TULA-2 resulted in hyperphosphorylation of Syk and its downstream effector phospholipase C-γ2 as well as enhanced GPVI-mediated platelet functional responses. In addition, shorter bleeding times and a prothrombotic phenotype were observed in mice lacking TULA-2. We therefore propose that TULA-2 is the primary tyrosine phosphatase mediating the dephosphorylation of Syk and thus functions as a negative regulator of GPVI signaling in platelets.

Stromal elements act to restrain, rather than support, pancreatic ductal adenocarcinoma.

Sonic hedgehog (Shh), a soluble ligand overexpressed by neoplastic cells in pancreatic ductal adenocarcinoma (PDAC), drives formation of a fibroblast-rich desmoplastic stroma. To better understand its role in malignant progression, we deleted Shh in a well-defined mouse model of PDAC. As predicted, Shh-deficient tumors had reduced stromal content. Surprisingly, such tumors were more aggressive and exhibited undifferentiated histology, increased vascularity, and heightened proliferation--features that were fully recapitulated in control mice treated with a Smoothened inhibitor. Furthermore, administration of VEGFR blocking antibody selectively improved survival of Shh-deficient tumors, indicating that Hedgehog-driven stroma suppresses tumor growth in part by restraining tumor angiogenesis. Together, these data demonstrate that some components of the tumor stroma can act to restrain tumor growth.

Head and neck squamous cell carcinoma in pregnant women.

BACKGROUND: The aim of this study was to investigate oral cancer in pregnant women, a rare but therapeutically challenging patient subset. METHODS: After institutional review board approval, an EMERSE search was used to identify all women treated at the University of Michigan from 1998 to 2010 with head and neck squamous cell carcinoma (HNSCC) during pregnancy. This identified 4 patients with tongue cancer. Biomarkers and human papillomavirus (HPV) were assessed by immunohistochemistry and multiplex PCR/mass spectrometry, respectively. RESULTS: Two patients responded well to therapy and are alive more than 10 years after diagnosis; 2 patients died of disease. All tumors overexpressed EGFR and Bcl-xL, 3 of 4 overexpressed c-Met, both tumors that progressed overexpressed p53. All tumors were negative for HPV, p16, estrogen receptor, progesterone receptor, and HER-2. CONCLUSIONS: Biomarkers of aggressive tumors (high EGFR, c-Met; high Bcl-xL-low p53) did not correlate with outcome. Additional studies are needed to determine whether perineural invasion, delay in diagnosis, and p53 overexpression are factors in poor survival.