Snail1 expression in mesenchimal cells promotes tumorigenesis and tumor progression

Snail transcription factor 1 triggers epithelial to mesenchymal transition. In cancer, this process provides tumoral epithelial cells with invasive characteristics. In this thesis, we demonstrated that the function of Snail1 in fibroblasts and mesenchymal stem cells (MSCs) also contributes to tumor progression. In tumors with a mesenchymal origin, expression of Snail1 in oncogenic MSCs is needed to maintain their tumorigenic capacity and is required in vivo for tumor formation. Therefore, its deletion results in the absence of tumors. In tumors with an epithelial origin, we demonstrated that Snail1 expression in stromal fibroblasts is required to promote tumor cell invasion. Fibroblasts are activated in a Snail1-dependent manner by factors such as TGF- released by epithelial tumor cells. As response, fibroblasts secrete prostaglandin E2 which contributes to tumor invasion. Consequently, depletion of Snail1 in in vivo cancer models reduces the invasion to adjacent tissues and decreases metastasis. These results suggest a key role for Snail1 in tumor progression that is not limited to its expression in epithelial cells.El factor de transcripción Snail1 es necesario para iniciar la transición epitelio-mesénquima. En cáncer, este proceso provee a las células epiteliales tumorales con características invasivas. En esta tesis demostramos que la función de Snail1 en fibroblastos y en células madre mesenquimales (MSCs) también contribuye a la progresión tumoral. En tumores de origen mesenquimal la expresión de Snail1 en MSCs es necesaria para mantener sus capacidades tumorigénicas e in vivo es necesaria para la formación del tumor. En tumores de origen epitelial, la expresión de Snail1 en los fibroblastos del estroma es necesaria para promover la invasión de las células tumorales. Los fibroblastos son activados de manera dependiente de Snail1 gracias a factores liberados por las células epiteliales del tumor; por ejemplo TGF-. Uno de los efectos de esta activación es la secreción de prostaglandina E2 la cual contribuye a la invasión tumoral. En consecuencia, la depleción de Snail1 en modelos tumorales in vivo reduce la invasión a tejidos adyacentes y disminuye la aparición de metástasis. Estos resultados sugieren un rol clave de Snail1 durante la progresión tumoral que no está limitado a su expresión en células epiteliales

Multivesicular GSK3 sequestration upon wnt signaling is controlled by p120-catenin/cadherin interaction with LRP5/6

The Wnt canonical ligands elicit the activation of β-catenin transcriptional activity, a response dependent on, but not limited to, β-catenin stabilization through the inhibition of GSK3 activity. Two mechanisms have been proposed for this inhibition, one dependent on the binding and subsequent block of GSK3 to LRP5/6 Wnt coreceptor and another one on its sequestration into multivesicular bodies (MVBs). Here we report that internalization of the GSK3-containing Wnt-signalosome complex into MVBs is dependent on the dissociation of p120-catenin/cadherin from this complex. Disruption of cadherin-LRP5/6 interaction is controlled by cadherin phosphorylation and requires the previous separation of p120-catenin; thus, p120-catenin and cadherin mutants unable to dissociate from the complex block GSK3 sequestration into MVBs. These mutants substantially inhibit, but do not completely prevent, the β-catenin upregulation caused by Wnt3a. These results, besides elucidating how GSK3 is sequestered into MVBs, support this mechanism as cause of β-catenin stabilization by Wnt.This work was funded by grants from the Ministerio de Economía (BFU2012-31554 to M.D. and SAF2010-16089 to A.G.H.) and Fundació La Marató de TV3 (120130) to M.D. and A.G.H. Support from Fundación Científica de la Asociación Española contra el Cáncer, ISCIII/FEDER (RD12/0036/005) and Generalitat de Catalunya (2009SGR867) is also appreciated. M.V. and L.A.-C. were recipients of predoctoral fellowships from FPI, and R.V.-C. was a recipient of a fellowship from ISCII

Snail1 is required for the maintenance of the pancreatic acinar phenotype

The Snail1 transcriptional factor is required for correct embryonic development, yet its expression in adult animals is very limited and its functional roles are not evident. We have now conditionally inactivated Snail1 in adult mice and analyzed the phenotype of these animals. Snail1 ablation rapidly altered pancreas structure: one month after Snail1 depletion, acinar cells were markedly depleted, and pancreas accumulated adipose tissue. Snail1 expression was not detected in the epithelium but was in pancreatic mesenchymal cells (PMCs). Snail1 ablation in cultured PMCs downregulated the expression of several β-catenin/Tcf-4 target genes, modified the secretome of these cells and decreased their ability to maintain acinar markers in cultured pancreas cells. Finally, Snail1 deficiency modified the phenotype of pancreatic tumors generated in transgenic mice expressing c-myc under the control of the elastase promoter. Specifically, Snail1 depletion did not significantly alter the size of the tumors but accelerated acinar-ductal metaplasia. These results demonstrate that Snail1 is expressed in PMCs and plays a pivotal role in maintaining acinar cells within the pancreas in normal and pathological conditions

Glutamine-directed migration of cancer-activated fibroblasts facilitates epithelial tumor invasion

Tumors are complex tissues composed of transformed epithelial cells as well as cancer-activated fibroblasts (CAF) that facilitate epithelial tumor cell invasion. We show here that CAFs and other mesenchymal cells rely much more on glutamine than epithelial tumor cells; consequently, they are more sensitive to inhibition of glutaminase. Glutamine dependence drove CAF migration toward this amino acid when cultured in low glutamine conditions. CAFs also invaded a Matrigel matrix following a glutamine concentration gradient and enhanced the invasion of tumor cells when both cells were cocultured. Accordingly, glutamine directed invasion of xenografted tumors in immunocompromised mice. Stimulation of glutamine-driven epithelial tumor invasion by fibroblasts required previous CAF activation, which involved the TGFβ/Snail1 signaling axis. CAFs moving toward Gln presented a polarized Akt2 distribution that was modulated by the Gln-dependent activity of TRAF6 and p62 in the migrating front, and depletion of these proteins prevented Akt2 polarization and Gln-driven CAF invasion. Our results demonstrate that glutamine deprivation promotes CAF migration and invasion, which in turn facilitates the movement of tumor epithelial cells toward nutrient-rich territories. These results provide a novel molecular mechanism for how metabolic stress enhances invasion and metastasis. SIGNIFICANCE: Cancer-associated fibroblasts migrate and invade toward free glutamine and facilitate invasion of tumor epithelial cells, accounting for their movement away from the hostile conditions of the tumor towards nutrient-rich adjacent tissues. GRAPHICAL ABSTRACT: http://cancerres.aacrjournals.org/content/canres/81/2/438/F1.large.jpg.We thank Drs. J. Moscat for advice, J. Yélamos, M. Birnbaum and L. Tío for cell lines and reagents and M. Iglesias for assistance. This study was funded by grants awarded by Ministerio de Ciencia, Innovación y Universidades -Agencia Estatal de Investigación (Retos de Investigación) and FEDER (SAF2016-76461-R and PID2019-104698RB-I00 to AGH and RTI2018-099719-B-100 to MD). We also acknowledge support from the Instituto Carlos III (PIE15/00008). AMF was funded by a Predoctoral FI Contract by the Secretaria d'Universitats i Recerca del Departament d'Empresa i Coneixement de la Generalitat de Catalunya (FI-DGR 2016); MBO and LAC were recipients of FPI contracts awarded by Ministerio de Ciencia y Tecnologia