The keratin-filament cycle of assembly and disassembly.
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.
Kölsch
Anne
A
Institute of Molecular and Cellular Anatomy, RWTH Aachen University, 52074 Aachen, Germany.
Windoffer
Reinhard
R
Würflinger
Thomas
T
Aach
Til
T
Leube
Rudolf E
RE
D008841:Actin Cytoskeleton / Q000378:metabolism; D002460:Cell Line; D002465:Cell Movement / Q000502:physiology; D002467:Cell Nucleus / Q000378:metabolism; D003513:Cycloheximide / Q000378:metabolism; D003599:Cytoskeleton / Q000378:metabolism* / Q000648:ultrastructure; D036681:Fluorescence Recovery After Photobleaching; D006801:Humans; D007633:Keratins / Q000378:metabolism* / Q000648:ultrastructure; D008870:Microtubules / Q000378:metabolism; D021122:Protein Subunits / Q000378:metabolism; D011500:Protein Synthesis Inhibitors / Q000378:metabolism; D011554:Pseudopodia / Q000378:metabolism; D011691:Puromycin / Q000378:metabolism
D021122:Protein Subunits; D011500:Protein Synthesis Inhibitors; D011691:Puromycin; D007633:Keratins; D003513:Cycloheximide