PDGF‑stimulated dispersal of cell clusters and disruption of fibronectin matrix on three-dimensional collagen matrices requires matrix metalloproteinase-2

Redefinition of tumor capsule: Rho-dependent clustering of cancer-associated fibroblasts in favor of tensional homeostasis

Fibroblasts are the most frequent cells of the connective tissues. Having the ability to sense and respond to mechanical stimuli in addition to the biochemical ones makes them crucial for such a composite-like and tension-preserving tissue. Over the last decade, the investigation of the role of these cells in tumor progression was a hot topic of research in tumor biology. Literatures almost unanimously describe the re-education of stromal fibroblasts by tumor cells in favor of tumor progression, which resulted in the birth of a new nomenclature, the cancer-associated fibroblasts. On the other hand, some studies reported anti-tumor roles for these cells. Herein, author suggests that the previously described pro-migratory and pro-contractile contexts, which respectively results in divergent and convergent distribution of fibroblasts by changing Rho-Rac1 balance, could be applied for cancer-associated fibroblasts as well. Based on this proposed concept, stromal fibroblasts could represent different roles, either pro-tumor or anti-tumor, during the course of tumor progression. In the earlier phases, they tend to assemble along tumor-stroma interface in the form of tumor capsules in order to resist tumor growth and to maintain tensional homeostasis in stroma. But in later phases, after being chronically subjected to tumor-induced chemical and mechanical stimuli, they will gradually lose their substantial abilities to oppose tumor expansion and, in contrary, will promote tumorigenesis. In summary, this paper redefines tumor capsule from chemical and mechanical standpoints as Rho-dependent clustering of cancer-associated fibroblasts in favor of tensional homeostasis. Furthermore, it proposes that stromal fibroblasts will undergo some irreversible epigenetic changes in Rac1- and Rho-related proteins through tumor-stroma crosstalk, which irreversibly diminish their ability of capsule formation. Finally, the author discusses the possible researches helping us to assess the proposed concept and its clinical implications.

Smart mechanosensing machineries enable migration of vascular smooth muscle cells in atherosclerosis-relevant 3D matrices

At the early stage of atherosclerosis, neointima is formed due to the migration of vascular smooth muscle cells (VSMCs) from the media to the intima. VSMCs are surrounded by highly adhesive 3D matrices. They take specific strategies to cross various 3D matrices in the media, including heterogeneous collagen and mechanically strong basement membrane. Migration of VSMCs is potentially caused by biomechanical mechanism. Most in vitro studies focus on cell migration on 2D substrates in response to biochemical factors. How the cells move through 3D matrices under the action of mechanosensing machineries remains unexplored. In this review, we propose that several interesting tension-dependent machineries act as "tractor"-posterior myosin II accumulation, and "wrecker"-anterior podosome maintaining, to power VSMCs ahead. VSMCs embedded in 3D matrices may accumulate a minor myosin II isoform, myosin IIB, at the cell rear. Anisotropic myosin IIB distribution creates cell rear, polarizes cell body, pushes the nucleus and reshapes the cell body, and cooperates with a uniformly distributed myosin IIA to propel the cell forward. On the other hand, matrix digestion by podosome further promote the migration when the matrix becomes denser. Actomyosin tension activates Src to induce podosome in soft 3D matrices and retain the podosome integrity to steadily digest the matrix.

Collaboration of fibronectin matrix with other extracellular signals in morphogenesis and differentiation

Tissue formation and cell differentiation depend on a properly assembled extracellular matrix (ECM). Fibronectin is a key constituent of the pericellular ECM, forming essential connections between cell surface integrin receptors and structural components of the ECM. Recent studies using vertebrate models, conditional gene knockouts, tissue explants, and cell culture systems have identified developmental processes that depend on fibronectin and its receptor α5β1 integrin. We describe requirements for fibronectin matrix in the cardiovascular system, somite and precartilage development, and epithelial-mesenchymal transition. Information about molecular mechanisms shows the importance of fibronectin and integrins during tissue morphogenesis and cell differentiation, as well as their cooperation with growth factors to mediate changes in cell behaviors.