Induction of p38, tumour necrosis factor-α and RANTES by mechanical stretching of keratinocytes expressing mutant keratin 10R156H

Desmosomes and Intermediate Filaments: Their Consequences for Tissue Mechanics

Adherens junctions (AJs) and desmosomes connect the actin and keratin filament networks of adjacent cells into a mechanical unit. Whereas AJs function in mechanosensing and in transducing mechanical forces between the plasma membrane and the actomyosin cytoskeleton, desmosomes and intermediate filaments (IFs) provide mechanical stability required to maintain tissue architecture and integrity when the tissues are exposed to mechanical stress. Desmosomes are essential for stable intercellular cohesion, whereas keratins determine cell mechanics but are not involved in generating tension. Here, we summarize the current knowledge of the role of IFs and desmosomes in tissue mechanics and discuss whether the desmosome-keratin scaffold might be actively involved in mechanosensing and in the conversion of chemical signals into mechanical strength.

Multiple roles for keratin intermediate filaments in the regulation of epithelial barrier function and apico-basal polarity

As multicellular organisms evolved a family of cytoskeletal proteins, the keratins (types I and II) expressed in epithelial cells diversified in more than 20 genes in vertebrates. There is no question that keratin filaments confer mechanical stiffness to cells. However, such a number of genes can hardly be explained by evolutionary advantages in mechanical features. The use of transgenic mouse models has revealed unexpected functional relationships between keratin intermediate filaments and intracellular signaling. Accordingly, loss of keratins or mutations in keratins that cause or predispose to human diseases, result in increased sensitivity to apoptosis, regulation of innate immunity, permeabilization of tight junctions, and mistargeting of apical proteins in different epithelia. Precise mechanistic explanations for these phenomena are still lacking. However, immobilization of membrane or cytoplasmic proteins, including chaperones, on intermediate filaments (“scaffolding”) appear as common molecular mechanisms and may explain the need for so many different keratin genes in vertebrates.

ERBB2 overexpression triggers transient high mechanoactivity of breast tumor cells

Biomechanical properties of tumor cells play an important role for the metastatic capacity of cancer. Cellular changes of viscoelastic features are prerequisite for cancer progression since they are essential for proliferation and metastasis. However, only little is known about the way how expression of oncogenes influences these biomechanical properties. To address this aspect we used a breast cancer cell line with inducible expression of an oncogenic version of ERBB2. ERBB2 is known to be correlated with bad prognosis in breast cancer. Cell elasticity was determined by the Optical Stretcher, where suspended cells are deformed by two slightly divergent laser beams. We found that induction of ERBB2 caused remarkable biomechanical alterations of the MCF-7 cells after 24 h: the cells actively contracted in response to mechanical stimuli, a phenomenon known as mechanoactivation. After this period, as the cells became senescent, the mechanoactivity returned to control levels. Time-resolved gene array analysis revealed that mechanoactivation was accompanied by temporal upregulation of 46 cytoskeletal genes. A possible role of these genes in tumor progression was investigated by expression analyses of 766 breast cancer patients. This showed an association of 12 out of these 46 genes with increased risk of metastasis. Our results demonstrate that overexpression of ERBB2 causes mechanoactivation of tumor cells, which may enhance tumor cell motility fostering distant metastasis.