The keratin-filament cycle of assembly and disassembly

Abstract

Continuous and regulated remodelling of the cytoskeleton is crucial for many basic cell functions. In contrast to actin filaments and microtubules, it is not understood how this is accomplished for the third major cytoskeletal filament system, which consists of intermediate-filament polypeptides. Using time-lapse fluorescence microscopy of living interphase cells, in combination with photobleaching, photoactivation and quantitative fluorescence measurements, we observed that epithelial keratin intermediate filaments constantly release non-filamentous subunits, which are reused in the cell periphery for filament assembly. This cycle is independent of protein biosynthesis. The different stages of the cycle occur in defined cellular subdomains: assembly takes place in the cell periphery and newly formed filaments are constantly transported toward the perinuclear region while disassembly occurs, giving rise to diffusible subunits for another round of peripheral assembly. Remaining juxtanuclear filaments stabilize and encage the nucleus. Our data suggest that the keratin-filament cycle of assembly and disassembly is a major mechanism of intermediate-filament network plasticity, allowing rapid adaptation to specific requirements, notably in migrating cells.

Force transduction and strain dynamics in actin stress fibres in response to nanonewton forces

“…Creating a series of photobleached regions across SFs (Kolsch et al, 2010) allowed us to determine the strain dynamics occurring along cellular SFs in response to mechanical stimulation. Strain dynamics along SFs and throughout the cell were highly heterogeneous and time variant.…”

“…Actin SFs are thought to be tension-bearing structures that are able to contract and stretch through actomyosin-mediated processes. To investigate changes in tension along SFs we designed an experiment in which cells expressing actin-EGFP were photobleached to produce a regular pattern of low and high intensity regions, spaced every 5 mm, along the SFs in the cell (Kolsch et al, 2010). This resulted in intact SFs that were segmented and resembled dashed lines (Fig.…”

“…Cells transiently expressing actin-EGFP had a series of lines photobleached into the SFs before experimentation (Kolsch et al, 2010). A series of regions of interest (ROI) were created from 1.5 mm wide parallel lines spaced every 5 mm.…”

A novel mechanism of keratin cytoskeleton organization through casein kinase Iα and FAM83H in colorectal cancer

“…The keratin cytoskeleton is an important structural stabilizer of epithelial cells (Moll et al, 2008). However, to achieve various dynamic cellular processes, including epithelial cell polarization and migration, keratin filament networks need to be dynamically reorganized (Ameen et al, 2001;Beil et al, 2003;Kölsch et al, 2010;Oriolo et al, 2007;Salas et al, 1997;Windoffer et al, 2011).…”

An Approach to Visualize the Deformation of the Intermediate Filament Cytoskeleton in Response to Locally Applied Forces

“…This was accomplished by creating cells transiently expressing a GFP-vimentin-labeled IF CSK. We then nondestructively photobleached a well-defined grid pattern into the IF CSK [23]. Once the grid was created, the cell was imaged for several minutes under an applied load from the AFM or under no load.…”