Non-canonical dynamic mechanisms of interaction between the p66Shc protein and Met receptor.

Met receptor tyrosine kinase (RTK) is known to bind to the three distinct protein isoforms encoded by the ShcA (Shc) gene. Structure-function studies have unveiled critical roles for p52Shc-dependent signalling pathways in Met-regulated biological functions. The molecular basis of the interaction between the Met and p52Shc proteins is well-defined, but not for the longest protein isoform, p66Shc. In the present study, co-immunoprecipitation assays were performed in human embryonic kidney 293 (HEK293) cells, transiently co-transfected with Met and p66Shc mutants, in order to define the molecular determinants involved in mediating Met-p66Shc interaction. Our results show that p66Shc interacts constitutively with the receptor Met, and the Grb2 (growth factor receptor-bound protein-2) and Gab1 (Grb2-associated binder-1) adaptor proteins. Although its phosphotyrosine-binding domain (PTB) and Src homology 2 (SH2) domains co-ordinate p66Shc binding to non-activated Met receptor, these phosphotyrosine-binding modules, and its collagen homology domain 2 (CH2) region, exert negative constraints. In contrast, p66Shc interaction with the activated Met depends mainly on the integrity of its PTB domain, and to a lesser extent of its SH2 domain. Even though not required for the recruitment of p66Shc, tyrosine phosphorylation of p66Shc by activated Met enhances these interactions by mechanisms not reliant on the integrity of the Met multisubstrate-binding site. In turn, this increases phosphotyrosine-dependent p66Shc-Grb2-Gab1 complex formation away from the receptor, while blocking Grb2 and Gab1 recruitment to activated Met. In conclusion, we identify, for the first time, a novel non-canonical dynamic mode of interaction between Met and the p66 protein isoform of Shc and its effects on rewiring binding effector complexes according to the activation state of the receptor.

SOCS1 in cancer: An oncogene and a tumor suppressor.

The Suppressor Of Cytokine Signaling 1 (SOCS1) has been extensively investigated in immune cells where it works as a potent inhibitor of inflammation by negative feedback regulation of the cytokine-activated JAK-STAT signaling pathways. SOCS1 is also recognized as a tumor suppressor in numerous cancers and its critical functional relevance in non-immune cells, including epithelial cells, has just begun to emerge. Most notably, conflicting results from clinical and experimental studies suggest that SOCS1 may function as either a tumor suppressor or a tumor promoter, in a cell context-dependent manner. Here, we present an overview of the mechanisms underlying SOCS1 function as a tumor suppressor and discuss the emerging evidences of SOCS1 activity as an oncogene.

Met receptor-induced Grb2 or Shc signals both promote transformation of intestinal epithelial cells, albeit they are required for distinct oncogenic functions.

BACKGROUND: Deregulation of receptor tyrosine kinases (RTK) contributes to the initiation and progression of intestinal-derived epithelial cancers, including colorectal cancer (CRC). However, the roles of the proximal signaling molecules engaged by RTKs in different oncogenic functions of CRC remain unclear. METHODS: Herein, the functional impact of expressing variant forms of the oncogenic Met receptor (Tpr-Met) that selectively recruit the adaptor proteins Grb2 or Shc was investigated in a model derived from normal intestinal epithelial cells (IEC-6). An RNA interference (RNAi) approach was used to define the requirement of Grb2 or Shc in Tpr-Met-transformed IEC-6 cells. Since Grb2 and Shc couple RTKs to the activation of the Ras/MEK/Erk and PI3K/Akt pathways, Erk and Akt phosphorylation/activation states were monitored in transformed IEC-6 cells, and a pharmacological approach was employed to provide insights into the roles of these pathways in oncogenic processes evoked by activated Met, and downstream of Grb2 and Shc. RESULTS: We show, for the first time, that constitutive activation of either Grb2 or Shc signals in IEC-6 cells, promotes morphological transformation associated with down-regulation of E-cadherin, as well as increased cell growth, loss of growth contact inhibition, anchorage-independent growth, and resistance to serum deprivation and anoikis. Oncogenic activation of Met was revealed to induce morphological transformation, E-cadherin down-regulation, and protection against anoikis by mechanisms dependent on Grb2, while Shc was shown to be partly required for enhanced cell growth. The coupling of activated Met to the Ras/MEK/Erk and PI3K/Akt pathways, and the sustained engagement of Grb2 or Shc in IECs, was shown to trigger negative feedback, limiting the extent of activation of these pathways. Nonetheless, morphological alterations and E-cadherin down-regulation induced by the oncogenic Tpr-Met, and by Grb2 or Shc signals, were blocked by MEK, but not PI3K, inhibitors while the enhanced growth and resistance to anoikis induced by Tpr-Met were nearly abolished by co-treatment with both inhibitors. CONCLUSION: Overall, these results identify Grb2 and Shc as central signaling effectors of Met-driven progression of intestinal epithelial-derived cancers. Notably, they suggest that Grb2 may represent a promising target for the design of novel CRC therapies.

FOXL1+ Telocytes in mouse colon orchestrate extracellular matrix biodynamics and wound repair resolution.

Recent studies have identified FoxL1+-telocytes (TCFoxL1+) as key players in gut epithelial-mesenchymal interactions which can determine the colonic microenvironment. Bone morphogenetic protein signaling disruption in TCFoxL1+ alters the physical and cellular microenvironment and leads to colon pathophysiology. This suggests a role for TCFoxL1+ in stromagenesis, but it is hard to identify the specific contribution of TCFoxL1+ when analyzing whole tissue profiling studies. We performed ex vivo deconstruction of control and BmpR1a△FoxL1+ colon samples, isolated the mesenchyme-enriched fractions, and determined the protein composition of the in vivo extracellular matrix (ECM) to analyze microenvironment variation. Matrisomic analysis of mesenchyme fractions revealed modulations in ECM proteins with functions associated with innate immunity, epithelial wound healing, and the collagen network. These results show that TCFoxL1+ is critical in orchestrating the biodynamics of the colon ECM. TCFoxL1+ disfunction reprograms the gut's microenvironment and drives the intestinal epithelium toward colonic pathologies. SIGNIFICANCE: In this study, the method that was elected to isolate ECM proteins might not encompass the full extent of ECM proteins in a tissue, due to the protocol chosen, as this protocol by Naba et al., targets more the insoluble part of the matrisome and eliminates the more soluble components in the first steps. However, this ECM-enrichment strategy represents an improvement and interesting avenue to study ECM proteins in the colon compared to total tissue analysis with a background of abundant cellular protein. Thus, the matrisomic approach presented in this study, and its target validation delivered a broader evaluation of the matrix remodeling occurring in the colonic sub-epithelial mesenchyme of the BmpR1a△FoxL1+ mouse model.

Comprehensive Profiling of Early Neoplastic Gastric Microenvironment Modifications and Biodynamics in Impaired BMP-Signaling FoxL1+-Telocytes.

FoxL1+telocytes (TCFoxL1+) are novel gastrointestinal subepithelial cells that form a communication axis between the mesenchyme and epithelium. TCFoxL1+ are strategically positioned to be key contributors to the microenvironment through production and secretion of growth factors and extracellular matrix (ECM) proteins. In recent years, the alteration of the bone morphogenetic protein (BMP) signaling in TCFoxL1+ was demonstrated to trigger a toxic microenvironment with ECM remodeling that leads to the development of pre-neoplastic gastric lesions. However, a comprehensive analysis of variations in the ECM composition and its associated proteins in gastric neoplasia linked to TCFoxL1+ dysregulation has never been performed. This study provides a better understanding of how TCFoxL1+ defective BMP signaling participates in the gastric pre-neoplastic microenvironment. Using a proteomic approach, we determined the changes in the complete matrisome of BmpR1a△FoxL1+ and control mice, both in total antrum as well as in isolated mesenchyme-enriched antrum fractions. Comparative proteomic analysis revealed that the deconstruction of the gastric antrum led to a more comprehensive analysis of the ECM fraction of gastric tissues microenvironment. These results show that TCFoxL1+ are key members of the mesenchymal cell population and actively participate in the establishment of the matrisomic fraction of the microenvironment, thus influencing epithelial cell behavior.

SOCS1 controls liver regeneration by regulating HGF signaling in hepatocytes.

BACKGROUND & AIMS: Frequent repression of the Socs1 (suppressor of cytokine signaling 1) gene in hepatocellular carcinoma (HCC) and increased susceptibility of SOCS1-deficient mice to hepatocarcinogens suggest a tumor suppressor role for SOCS1 in the liver, but the underlying mechanisms remain unclear. Here we investigated the role of SOCS1 in regulating hepatocyte proliferation following partial hepatectomy and HGF stimulation. METHODS: Because Socs1(-/-) mice die prematurely due to deregulated IFNγ signaling, we used Socs1(-/-)Ifng(-/-) mice to study the role of SOCS1 in liver regeneration following partial hepatectomy. We examined the activation of signaling molecules downstream of IL-6 and hepatocyte growth factor (HGF) receptors in the regenerating liver, primary hepatocytes, and in human hepatoma cells. We examined the interaction between SOCS1 and the HGF receptor c-Met by reciprocal immunoprecipitation. RESULTS: Socs1(-/-)Ifng(-/-) mice displayed accelerated liver regeneration with increased DNA synthesis compared to Ifng(-/-) and wild type mice. The regenerating liver of Socs1(-/-)Ifng(-/-) mice did not show increased IL-6 signaling, but displayed earlier phosphorylation of Gab1, a signaling adaptor downstream of c-Met. Following HGF stimulation, hepatocytes from Socs1(-/-)Ifng(-/-) mice displayed increased phosphorylation of c-Met and Gab1, cell migration and proliferation. Accordingly, SOCS1 overexpression attenuated HGF-induced phosphorylation of c-Met, Gab1, and ERK1/2 in hepatoma cells, and decreased their proliferation and migration. SOCS1 interacted with the Tpr-Met, an oncogenic form of the Met receptor. CONCLUSIONS: SOCS1 attenuates c-Met signaling and thus negative regulation of HGF signaling could be an important mechanism underlying the anti-tumor role of SOCS1 in the liver.

Altered Mucus Barrier Integrity and Increased Susceptibility to Colitis in Mice upon Loss of Telocyte Bone Morphogenetic Protein Signalling.

FoxL1+-Telocytes (TCFoxL1+) are subepithelial cells that form a network underneath the epithelium. We have shown that without inflammatory stress, mice with loss of function in the BMP signalling pathway in TCFoxL1+ (BmpR1aΔFoxL1+) initiated colonic neoplasia. Although TCFoxL1+ are modulated in IBD patients, their specific role in this pathogenesis remains unclear. Thus, we investigated how the loss of BMP signalling in TCFoxL1+ influences the severity of inflammation and fosters epithelial recovery after inflammatory stress. BmpR1a was genetically ablated in mouse colonic TCFoxL1+. Experimental colitis was performed using a DSS challenge followed by recovery steps to assess wound healing. Physical barrier properties, including mucus composition and glycosylation, were assessed by alcian blue staining, immunofluorescences and RT-qPCR. We found that BmpR1aΔFoxL1+ mice had impaired mucus quality, and upon exposure to inflammatory challenges, they had increased susceptibility to experimental colitis and delayed healing. In addition, defective BMP signalling in TCFoxL1+ altered the functionality of goblet cells, thereby affecting mucosal structure and promoting bacterial invasion. Following inflammatory stress, TCFoxL1+ with impaired BMP signalling lose their homing signal for optimal distribution along the epithelium, which is critical in tissue regeneration after injury. Overall, our findings revealed key roles of BMP signalling in TCFoxL1+ in IBD pathogenesis.

Oncogenic engagement of the Met receptor is sufficient to evoke angiogenic, tumorigenic, and metastatic activities in rat intestinal epithelial cells.

The deregulation of Met/hepatocyte growth factor (HGF) receptor tyrosine kinase signaling constitutes a common event in colorectal cancers. However, the physiopathological functions of such a deregulation remain poorly understood. In the present study, we investigated the role of the deregulation of Met receptor in the neoplastic transformation of intestinal epithelial cells. To do so, the normal, well-established and characterized rat intestinal epithelial IEC-6 cells were transduced with a retrovirus carrying the oncogenic constitutive active form of Met receptor, Tpr-Met. Herein, we show that compared with control IEC-6 cells, Tpr-Met-IEC-6 cells exhibit enhanced proliferation, loss of growth-contact inhibition, cell morphological alterations, actin cytoskeletal reorganization, loss of E-cadherin expression and anchorage-independent growth. Moreover, Tpr-Met-IEC-6 cells are conferred the capacity to produce the proangiogenic factor VEGF and to reduce the potent antiangiogenic factor thrombospondin-1. Of significance, Tpr-Met-IEC-6 cells are endowed with the ability to elicit angiogenic responses and to form tumors and metastases in vivo. Hence, our study demonstrates for the first time that the sole oncogenic engagement of Met receptor in normal intestinal epithelial cells is sufficient to induce a wide array of cancerous biological processes that are fundamental to the initiation and malignant progression of colorectal cancers.

Adenovirus IL-13-induced airway disease in mice: a corticosteroid-resistant model of severe asthma.

Interleukin 13 (IL-13) is considered to be a key driver of the development of airway allergic inflammation and remodeling leading to airway hyperresponsiveness (AHR). How precisely IL-13 leads to the development of airway inflammation, AHR, and mucus production is not fully understood. In order to identify key mediators downstream of IL-13, we administered adenovirus IL-13 to specifically induce IL-13-dependent inflammation in the lungs of mice. This approach was shown to induce cardinal features of lung disease, specifically airway inflammation, elevated cytokines, AHR, and mucus secretion. Notably, the model is resistant to corticosteroid treatment and is characterized by marked neutrophilia, two hallmarks of more severe forms of asthma. To identify IL-13-dependent mediators, we performed a limited-scale two-dimensional SDS-PAGE proteomic analysis and identified proteins significantly modulated in this model. Intriguingly, several identified proteins were unique to this model, whereas others correlated with those modulated in a mouse ovalbumin-induced pulmonary inflammation model. We corroborated this approach by illustrating that proteomic analysis can identify known pathways/mediators downstream of IL-13. Thus, we have characterized a murine adenovirus IL-13 lung model that recapitulates specific disease traits observed in human asthma, and have exploited this model to identify effectors downstream of IL-13. Collectively, these findings will enable a broader appreciation of IL-13 and its impact on disease pathways in the lung.

Loss of mesenchymal bone morphogenetic protein signaling leads to development of reactive stroma and initiation of the gastric neoplastic cascade.

Bmps are morphogens involved in various gastric cellular functions. Studies in genetically-modified mice have shown that Bmp disruption in gastric epithelial and stromal cell compartments leads to the development of tumorigenesis. Our studies have demonstrated that abrogation of gastric epithelial Bmp signaling alone was not sufficient to recapitulate the neoplastic features associated with total gastric loss of Bmp signaling. Thus, epithelial Bmp signaling does not appear to be a key player in gastric tumorigenesis initiation. These observations suggest a greater role for stromal Bmp signaling in gastric polyposis initiation. In order to identify the specific roles played by mesenchymal Bmp signaling in gastric homeostasis, we generated a mouse model with abrogation of Bmp signaling exclusively in the gastro-intestinal mesenchyme (Bmpr1a(ΔMES)). We were able to expose an unsuspected role for Bmp loss of signaling in leading normal gastric mesenchyme to adapt into reactive mesenchyme. An increase in the population of activated-fibroblasts, suggesting mesenchymal transdifferentiation, was observed in mutant stomach. Bmpr1a(ΔMES) stomachs exhibited spontaneous benign polyps with presence of both intestinal metaplasia and spasmolytic-polypeptide-expressing metaplasia as early as 90 days postnatal. These results support the novel concept that loss of mesenchymal Bmp signaling cascade acts as a trigger in gastric polyposis initiation.

Tumour-promoting role of SOCS1 in colorectal cancer cells.

The SOCS1 (Suppressor Of Cytokine Signalling 1) protein is considered a tumour suppressor. Notably, the SOCS1 gene is frequently silenced in cancer by hypermethylation of its promoter. Besides blocking inflammation, SOCS1 tumour suppressor activity involves Met receptor inhibition and enhancement of p53 tumour suppressor activity. However, the role of SOCS1 in colorectal cancer (CRC) remains understudied and controversial. Here, we investigated SOCS1 relevance for CRC by querying gene expression datasets of human CRC specimens from The Cancer Genome Atlas (TCGA), and by SOCS1 gain/loss-of-function analyses in murine and human colon carcinoma cells. Our results show that SOCS1 mRNA levels in tumours were more often elevated than reduced with respect to matched adjacent normal tissue of CRC specimens (n = 41). The analysis of TCGA dataset of 431 CRC patients revealed no correlation between SOCS1 expression and overall survival. Overexpression of SOCS1 in CRC cells triggered cell growth enhancement, anchorage-independent growth and resistance to death stimuli, whereas knockdown of SOCS1 reduced these oncogenic features. Moreover, SOCS1 overexpression in mouse CT26 cells increased tumourigenesis in vivo. Biochemical analyses showed that SOCS1 pro-oncogenic activity correlated with the down-modulation of STAT1 expression. Collectively, these results suggest that SOCS1 may work as an oncogene in CRC.