Fibronectin Extra Domains tune cellular responses and confer topographically distinct features to fibril networks.

Cellular fibronectin (FN; also known as FN1) variants harboring one or two alternatively spliced so-called extra domains (EDB and EDA) play a central bioregulatory role during development, repair processes and fibrosis. Yet, how the extra domains impact fibrillar assembly and function of the molecule remains unclear. Leveraging a unique biological toolset and image analysis pipeline for direct comparison of the variants, we demonstrate that the presence of one or both extra domains impacts FN assembly, function and physical properties of the matrix. When presented to FN-null fibroblasts, extra domain-containing variants differentially regulate pH homeostasis, survival and TGF-ß signaling by tuning the magnitude of cellular responses, rather than triggering independent molecular switches. Numerical analyses of fiber topologies highlight significant differences in variant-specific structural features and provide a first step for the development of a generative model of FN networks to unravel assembly mechanisms and investigate the physical and functional versatility of extracellular matrix landscapes.This article has an associated First Person interview with the first author of the paper.

Pluripotent stem cell model reveals essential roles for miR-450b-5p and miR-184 in embryonic corneal lineage specification.

Approximately 6 million people worldwide are suffering from severe visual impairments or blindness due to corneal diseases. Corneal allogeneic transplantation is often required to restore vision; however, shortage in corneal grafts and immunorejections remain major challenges. The molecular basis of corneal diseases is poorly understood largely due to lack of appropriate cellular models. Here, we described a robust differentiation of human-induced pluripotent stem cells (hiPSCs) derived from hair follicles or skin fibroblasts into corneal epithelial-like cells. We found that BMP4, coupled with corneal fibroblast-derived conditioned medium and collagen IV allowed efficient corneal epithelial commitment of hiPSCs in a manner that recapitulated corneal epithelial lineage development with high purity. Organotypic reconstitution assays suggested the ability of these cells to stratify into a corneal-like epithelium. This model allowed us identifying miR-450b-5p as a molecular switch of Pax6, a major regulator of eye development. miR-450b-5p and Pax6 were reciprocally distributed at the presumptive epidermis and ocular surface, respectively. miR-450b-5p inhibited Pax6 expression and corneal epithelial fate in vitro, altogether, suggesting that by repressing Pax6, miR-450b-5p triggers epidermal specification of the ectoderm, while its absence allows ocular epithelial development. Additionally, miR-184 was detectable in early eye development and corneal epithelial differentiation of hiPSCs. The knockdown of miR-184 resulted in a decrease in Pax6 and K3, in line with recent findings showing that a point mutation in miR-184 leads to corneal dystrophy. Altogether, these data indicate that hiPSCs are valuable for modeling corneal development and may pave the way for future cell-based therapy.

TAp63 is important for cardiac differentiation of embryonic stem cells and heart development.

p63, a member of the p53 family, is essential for skin morphogenesis and epithelial stem cell maintenance. Here, we report an unexpected role of TAp63 in cardiogenesis. p63 null mice exhibit severe defects in embryonic cardiac development, including dilation of both ventricles, a defect in trabeculation and abnormal septation. This was accompanied by myofibrillar disarray, mitochondrial disorganization, and reduction in spontaneous calcium spikes. By the use of embryonic stem cells (ESCs), we show that TAp63 deficiency prevents expression of pivotal cardiac genes and production of cardiomyocytes. TAp63 is expressed by endodermal cells. Coculture of p63-knockdown ESCs with wild-type ESCs, supplementation with Activin A, or overexpression of GATA-6 rescue cardiogenesis. Therefore, TAp63 acts in a non-cell-autonomous manner by modulating expression of endodermal factors. Our findings uncover a critical role for p63 in cardiogenesis that could be related to human heart disease.

Tenascin-C Orchestrates an Immune-Suppressive Tumor Microenvironment in Oral Squamous Cell Carcinoma.

Inherent immune suppression represents a major challenge in the treatment of human cancer. The extracellular matrix molecule tenascin-C promotes cancer by multiple mechanisms, yet the roles of tenascin-C in tumor immunity are incompletely understood. Using a 4NQO-induced oral squamous cell carcinoma (OSCC) model with abundant and absent tenascin-C, we demonstrated that tenascin-C enforced an immune-suppressive lymphoid stroma via CCL21/CCR7 signaling, leading to increased metastatic tumors. Through TLR4, tenascin-C increased expression of CCR7 in CD11c+ myeloid cells. By inducing CCL21 in lymphatic endothelial cells via integrin α9ß1 and binding to CCL21, tenascin-C immobilized CD11c+ cells in the stroma. Inversion of the lymph node-to-tumor CCL21 gradient, recruitment of T regulatory cells, high expression of anti-inflammatory cytokines, and matrisomal components were hallmarks of the tenascin-C-instructed lymphoid stroma. Ablation of tenascin-C or CCR7 blockade inhibited the lymphoid immune-suppressive stromal properties, reducing tumor growth, progression, and metastasis. Thus, targeting CCR7 could be relevant in human head and neck tumors, as high tenascin-C expression and an immune-suppressive stroma correlate to poor patient survival.

Embryonic stem cells as a cellular model for neuroectodermal commitment and skin formation.

Embryonic stem (ES) cells can be differentiated into many cell types in vitro, thus providing a potential unlimited supply of cells for cognitive in vitro studies and cell-based therapy. We recently reported the efficient derivation of ectodermal and epidermal cells from murine ES cells. These differentiated ES cells were able to form, in culture, a multilayered epidermis coupled with an underlying dermal compartment, similar to native skin. We clarified the function of BMP-4 in the binary neuroectodermal choice by stimulating sox-1(+) neural precursors to undergo specific apoptosis while inducing epidermal differentiation through DeltaNp63 gene activation. We further demonstrated that DeltaNp63 enhances ES-derived ectodermal cell proliferation and is necessary for epidermal commitment. This unique cellular model further provides a powerful tool for identifying the molecular mechanisms controlling normal skin development and for investigating p63-ectodermal dysplasia human congenital pathologies.

Fibronectin-guided migration of carcinoma collectives.

Functional interplay between tumour cells and their neoplastic extracellular matrix plays a decisive role in malignant progression of carcinomas. Here we provide a comprehensive data set of the human HNSCC-associated fibroblast matrisome. Although much attention has been paid to the deposit of collagen, we identify oncofetal fibronectin (FN) as a major and obligate component of the matrix assembled by stromal fibroblasts from head and neck squamous cell carcinomas (HNSCC). FN overexpression in tumours from 435 patients corresponds to an independent unfavourable prognostic indicator. We show that migration of carcinoma collectives on fibrillar FN-rich matrices is achieved through αvß6 and α9ß1 engagement, rather than α5ß1. Moreover, αvß6-driven migration occurs independently of latent TGF-ß activation and Smad-dependent signalling in tumour epithelial cells. These results provide insights into the adhesion-dependent events at the tumour-stroma interface that govern the collective mode of migration adopted by carcinoma cells to invade surrounding stroma in HNSCC.

Unique DNA methylation signature in HPV-positive head and neck squamous cell carcinomas.

BACKGROUND: Head and neck squamous cell carcinomas (HNSCCs) represent a heterogeneous group of cancers for which human papilloma virus (HPV) infection is an emerging risk factor. Previous studies showed promoter hypermethylation in HPV(+) oropharyngeal cancers, but only few consistent target genes have been so far described, and the evidence of a functional impact on gene expression is still limited. METHODS: We performed global and stratified pooled analyses of epigenome-wide data in HNSCCs based on the Illumina HumanMethylation450 bead-array data in order to identify tissue-specific components and common viral epigenetic targets in HPV-associated tumours. RESULTS: We identified novel differentially methylated CpGs and regions associated with viral infection that are independent of the anatomic site. In particular, most hypomethylated regions were characterized by a marked loss of CpG island boundaries, which showed significant correlations with expression of neighbouring genes. Moreover, a subset of only five CpGs in a few hypomethylated regions predicted HPV status with a high level of specificity in different cohorts. Finally, this signature was a better predictor of survival compared with HPV status determined by viral gene expression by RNA sequencing in The Cancer Genome Atlas cohort. CONCLUSIONS: We identified a novel epigenetic signature of HPV infection in HNSCCs which is independent of the anatomic site, is functionally correlated with gene expression and may be leveraged for improved stratification of prognosis in HNSCCs.

Elevated Src family kinase activity stabilizes E-cadherin-based junctions and collective movement of head and neck squamous cell carcinomas.

EGF receptor (EGFR) overexpression is thought to drive head and neck carcinogenesis however clinical responses to EGFR-targeting agents have been modest and alternate targets are actively sought to improve results. Src family kinases (SFKs), reported to act downstream of EGFR are among the alternative targets for which increased expression or activity in epithelial tumors is commonly associated to the dissolution of E-cadherin-based junctions and acquisition of a mesenchymal-like phenotype. Robust expression of total and activated Src was observed in advanced stage head and neck tumors (N=60) and in head and neck squamous cell carcinoma lines. In cultured cancer cells Src co-localized with E-cadherin in cell-cell junctions and its phosphorylation on Y419 was both constitutive and independent of EGFR activation. Selective inhibition of SFKs with SU6656 delocalized E-cadherin and disrupted cellular junctions without affecting E-cadherin expression and this effect was phenocopied by knockdown of Src or Yes. These findings reveal an EGFR-independent role for SFKs in the maintenance of intercellular junctions, which likely contributes to the cohesive invasion E-cadherin-positive cells in advanced tumors. Further, they highlight the need for a deeper comprehension of molecular pathways that drive collective cell invasion, in absence of mesenchymal transition, in order to combat tumor spread.

DeltaNp63 is essential for epidermal commitment of embryonic stem cells.

In vivo studies have demonstrated that p63 plays complex and pivotal roles in pluristratified squamous epithelial development, but its precise function and the nature of the isoform involved remain controversial. Here, we investigate the role of p63 in epithelial differentiation, using an in vitro ES cell model that mimics the early embryonic steps of epidermal development. We show that the DeltaNp63 isoform is activated soon after treatment with BMP-4, a morphogen required to commit differentiating ES cells from a neuroectodermal to an ectodermal cell fate. DeltaNp63 gene expression remains high during epithelial development. P63 loss of function drastically prevents ectodermal cells to commit to the K5/K14-positive stratified epithelial pathway while gain of function experiments show that DeltaNp63 allows this commitment. Interestingly, other epithelial cell fates are not affected, allowing the production of K5/K18-positive epithelial cells. Therefore, our results demonstrate that DeltaNp63 may be dispensable for some epithelial differentiation, but is necessary for the commitment of ES cells into K5/K14-positive squamous stratified epithelial cells.

Key role of p63 in BMP-4-induced epidermal commitment of embryonic stem cells.

In vivo studies, transgenic and knock-out mice have demonstrated that p63 isoforms play pivotal roles in ectodermal and epidermal development but their respective function remains highly controversial. Since embryonic stem (ES) cells can be differentiated into many cell types, they represent an effective tool to recapitulate in vitro the main steps of embryonic development. We recently reported the efficient derivation of ectodermal and epidermal cells from murine ES cells and clarified the function of BMP-4 in the binary neuroectodermal choice by stimulating sox-1(+) neural precursors to undergo specific apoptosis while inducing epidermal differentiation through DeltaNp63 gene activation. DeltaNp63 is not required for ectodermal fate but enhances ES-derived ectodermal cell proliferation and epidermal commitment. This unique cellular model should further provide a powerful tool for identifying the molecular mechanisms controlling normal skin development and in p63-ectodermal dysplasia human congenital pathologies.