alpha B-crystallin interacts with cytoplasmic intermediate filament bundles during mitosis

The small heat-shock protein alpha B-crystallin interacts with intermediate filament proteins. Using cosedimentation assay, we showed previously that in vitro binding of alpha B-crystallin to peripherin and vimentin was tempe rature-dependent. Furthermore, when NIH 3T3 cells were submitted to differe nt stress conditions a dynamic reorganization of the intermediate filament network was observed concomitantly with the recruitment of alpha B-crystall ins on the intermediate filament proteins. Thus, the intracellular state of alpha B-crystallin correlated directly with the remodeling of the intermed iate filament network in response to stress. Here, we show data suggesting that alpha B-crystallin is implicated in remodeling of intermediate filamen ts during cell division. We investigated the intracellular distribution of alpha B-crystallin in naturally occurring mitotic NIH 3T3 cells and in neur oblastoma N2a and N1E115 cells. In NIH 3T3 cells, alpha B-crystallin remain ed diffused throughout the cell cycle. Subcellular fractionation of alpha B -crystallin showed that alpha B-crystallin remained in the cytosolic compar tment during mitosis. Furthermore, alpha B-crystallin accumulated in mitoti cally arrested NIH 3T3 cells. This increased level of alpha B-crystallin pr otein was due to an increased level of alpha B-crystallin mRNA in mitotic N IH 3T3 cells. In the neuroblastoma cells, the intermediate filaments were r earranged into thick cable-like structures and alpha B-crystallin was recru ited onto them. In neuroblastoma N2a cells the level of expression did not change during the cell cycle. However, a small fraction of alpha B-crystall in switched onto the insoluble fraction in mitotically arrested N2a cells. Our results suggested that depending on the state of rearrangement of the i ntermediate filament network during mitosis alpha B-crystallin was either r ecruited onto the intermediate filaments or upregulated in the cytosolic co mpartment. (C) 1999 Academic Press.