The basement membrane in epidermal polarity, stemness, and regeneration

The epidermis is a specialized epithelium that constitutes the outermost layer of the skin, and it provides a protective barrier against environmental assaults. Primarily consisting of multilayered keratinocytes, the epidermis is continuously renewed by proliferation of stem cells and the differentiation of their progeny, which undergo terminal differentiation as they leave the basal layer and move upward toward the surface, where they die and slough off. Basal keratinocytes rest on a basement membrane at the dermal-epidermal junction that is composed of specific extracellular matrix proteins organized into interactive and mechanically supportive networks. Firm attachment of basal keratinocytes, and their dynamic regulation via focal adhesions and hemidesmosomes, is essential for maintaining major skin processes, such as self-renewal, barrier function, and resistance to physical and chemical stresses. The adhesive integrin receptors expressed by epidermal cells serve structural, signaling, and mechanosensory roles that are critical for epidermal cell anchorage and tissue homeostasis. More specifically, the basement membrane components play key roles in preserving the stem cell pool, and establishing cell polarity cues enabling asymmetric cell divisions, which result in the transition from a proliferative basal cell layer to suprabasal cells committed to terminal differentiation. Finally, through a well-regulated sequence of synthesis and remodeling, the components of the dermal-epidermal junction play an essential role in regeneration of the epidermis during skin healing. Here too, they provide biological and mechanical signals that are essential to the restoration of barrier function

Laminin 332 processing impacts cellular behavior

Laminin 332, composed of the α3, β3 and γ2 chains, is an epithelial-basement membrane specific laminin variant. Its main role in normal tissues is the maintenance of epithelial-mesenchymal cohesion in tissues exposed to external forces, including skin and stratified squamous mucosa. After being secreted and deposited in the extracellular matrix, laminin 332 undergoes physiological maturation processes consisting in the proteolytic processing of domains located within the α3 and the γ2 chains. These maturation events are essential for laminin 332 integration into the basement membrane where it plays an important function in the nucleation and maintenance of anchoring structures. Studies in normal and pathological situations have revealed that laminin 332 can trigger distinct cellular events depending on the level of its proteolytic cleavages. In this review, the biological and structural characteristics of laminin 332 domains are presented and we discuss whether they trigger specific functions

EGF controls the in vivo developmental potential of a mammary epithelial cell line possessing progenitor properties

The bilayered mammary epithelium comprises a luminal layer of secretory cells and a basal layer of myoepithelial cells. Numerous data suggest the existence of self-renewing, pluripotent mammary stem cells; however, their molecular characteristics and differentiation pathways are largely unknown. BC44 mammary epithelial cells in culture, display phenotypic characteristics of basal epithelium, i.e., express basal cytokeratins 5 and 14 and P-cadherin, but no smooth muscle markers. In vivo, after injection into the cleared mammary fat pad, these cells gave rise to bilayered, hollow, alveolus-like structures comprising basal cells expressing cytokeratin 5 and luminal cells positive for cytokeratin 8 and secreting β-casein in a polarized manner into the lumen. The persistent stimulation of EGF receptor signaling pathway in BC44 cells in culture resulted in the loss of the in vivo morphogenetic potential and led to the induction of active MMP2, thereby triggering cell scattering and motility on laminin 5. These data (a) suggest that BC44 cells are capable of asymmetric division for self-renewal and the generation of a differentiated progeny restricted to the luminal lineage; (b) clarify the function of EGF in the control of the BC44 cell phenotypic plasticity; and (c) suggest a role for this phenomenon in the mammary gland development

Laminin isoforms in human embryonic stem cells : synthesis, receptor usage and growth support

Sanna Vuoristo, Ismo Virtanen, Minna Takkunen, Jaan Palgi, Yamato Kikkawa, Patricia Rousselle, Kiyotoshi Sekiguchi, Timo Tuuri, and Timo Otonkoski, "Laminin isoforms in human embryonic stem cells: synthesis, receptor usage and growth support", Journal of Cellular and Molecular Medicine, 13, 8b, pp. 2622-2633, Wiley, 200

Designed Ankyrin Repeat Proteins provide insights into the structure and function of CagI and are potent inhibitors of CagA translocation by the Helicobacter pylori type IV secretion system

The bacterial human pathogen Helicobacter pylori produces a type IV secretion system ( cag T4SS) to inject the oncoprotein CagA into gastric cells. The cag T4SS external pilus mediates attachment of the apparatus to the target cell and the delivery of CagA. While the composition of the pilus is unclear, CagI is present at the surface of the bacterium and required for pilus formation. Here, we have investigated the properties of CagI by an integrative structural biology approach. Using Alpha Fold 2 and Small Angle X-ray scattering, it was found that CagI forms elongated dimers mediated by rod-shape N-terminal domains (CagI N ) prolonged by globular C-terminal domains (CagI C ). Three Designed Ankyrin Repeat Proteins (DARPins) K2, K5 and K8 selected against CagI interacted with CagI C with subnanomolar affinities. The crystal structures of the CagI:K2 and CagI:K5 complexes were solved and identified the interfaces between the molecules, thereby providing a structural explanation for the difference in affinity between the two binders. Purified CagI and CagI C were found to interact with adenocarcinoma gastric (AGS) cells, induced cell spreading and the interaction was inhibited by K2. The same DARPin inhibited CagA translocation by up to 65% in AGS cells while inhibition levels were 40% and 30% with K8 and K5, respectively. Our study suggests that CagI C plays a key role in cag T4SS-mediated CagA translocation and that DARPins targeting CagI represent potent inhibitors of the cag T4SS, a crucial risk factor for gastric cancer development.Bases structurale du système de secretion de type IV d'Helicobacter pyloriBases structurales et moléculaires de l'exploitation de l'integrin a5ß1 par le système de sécrétion de type IV d'Helicobacter pylor

Laminine 5, migration cellulaire et cancer

La laminine 5 est exprimée dans les lames basales des épithéliums squameux et transitionnels spécialisés. Ses propriétés structurales lui permettent de maintenir la cohésion épithélio-mésenchymateuse. Elle induit des signaux biologiques déterminants, responsable de l’assemblage des structures d’adhérence cellulaires stables que sont les hémidesmosomes. Des études récentes montrent son implication dans la migration des cellules métastatiques au cours de la progression tumorale et cet article fait le point sur les différentes hypothèses proposées à ce jour

EFFET DU TGF-BETA 1 SUR LES INTERACTIONS ENTRE LES KERATINOCYTES ET LA LAMININE 5 (IMPLICATION POTENTIELLE AU COURS DE LA CICATRISATION CUTANEE)

LYON1-BU Santé (693882101) / SudocPARIS-BIUM (751062103) / SudocPARIS-BIUP (751062107) / SudocSudocFranceF

Laminins and matrix metalloproteinases connection: a subtle relationship that can go wrong in a tumor context, particularly if CD44 gets involved

Laminins (LM) are large extracellular glycoproteins involved in several biological processes, including cellular interactions, self-polymerization, and binding with other extracellular matrix proteins. LMs influence cell function by inducing various signaling pathways via cell membrane receptors and have multiple, often cell type-specific, functions in, for example, adhesion, differentiation, migration, and phenotype maintenance, and they also provide resistance to apoptosis. They are also important components of basement membranes. The basement membrane is partly degraded in the course of tumor growth, facilitating the invasion of budding cells and their migration to lymphatic or blood vessels. In this context, LMs undergo proteolytic cleavage, which disrupts their involvement in maintaining the structural and biological properties of the basement membrane. LMs are also involved via their participation in cancer cell adhesion and migration processes. These events are either supported by their major cell binding domains or triggered by cryptic interaction sites revealed by matrix metalloproteinase (MMP)-induced proteolytic cleavage. While being ideal targets for MMPs, LM can enhance their expression and activity. They appear to be key matrix elements in the regulation of MMP activity via the recruitment of the CD44 receptor, a multiple MMP-interacting and activating platform playing an important role in cancer progression