Keratin

Keratin is a family of structural intermediate filament proteins abundant in epithelial cells. Compatible type I and type II keratins assemble together into filaments, which distribute mechanical stresses across a cell and connect to junctional structures such as desmosomes. Keratin is therefore part of a cellular load-bearing system rather than a molecular motor. ^[ref]

The connection to desmosomes explains how force can pass between neighbouring cells while each cell retains its own boundary. Hair and the outer layers of skin are familiar keratin-rich materials, but living epithelial cells also use keratin networks internally. Different keratin expression patterns can identify cellular states without proving identical mechanical behaviour in every tissue.