αB-Crystallin Interacts with Cytoplasmic Intermediate Filament Bundles during Mitosis

The small heat-shock protein αB-crystallin interacts with intermediate filament proteins. Using cosedimentation assay, we showed previously that in vitro binding of αB-crystallin to peripherin and vimentin was temperature-dependent. Furthermore, when NIH 3T3 cells were submitted to different stress conditions a dynamic reorganization of the intermediate filament network was observed concomitantly with the recruitment of αB-crystallins on the intermediate filament proteins. Thus, the intracellular state of αB-crystallin correlated directly with the remodeling of the intermediate filament network in response to stress. Here, we show data suggesting that αB-crystallin is implicated in remodeling of intermediate filaments during cell division. We investigated the intracellular distribution of αB-crystallin in naturally occurring mitotic NIH 3T3 cells and in neuroblastoma N2a and N1E115 cells. In NIH 3T3 cells, αB-crystallin remained diffused throughout the cell cycle. Subcellular fractionation of αB-crystallin showed that αB-crystallin remained in the cytosolic compartment during mitosis. Furthermore, αB-crystallin accumulated in mitotically arrested NIH 3T3 cells. This increased level of αB-crystallin protein was due to an increased level of αB-crystallin mRNA in mitotic NIH 3T3 cells. In the neuroblastoma cells, the intermediate filaments were rearranged into thick cable-like structures and αB-crystallin was recruited onto them. In neuroblastoma N2a cells the level of expression did not change during the cell cycle. However, a small fraction of αB-crystallin switched onto the insoluble fraction in mitotically arrested N2a cells. Our results suggested that depending on the state of rearrangement of the intermediate filament network during mitosis αB-crystallin was either recruited onto the intermediate filaments or upregulated in the cytosolic compartment.