alphaB-crystallin interacts with cytoplasmic intermediate filament bundles during mitosis.

The small heat-shock protein alphaB-crystallin interacts with intermediate filament proteins. Using cosedimentation assay, we showed previously that in vitro binding of alphaB-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 alphaB-crystallins on the intermediate filament proteins. Thus, the intracellular state of alphaB-crystallin correlated directly with the remodeling of the intermediate filament network in response to stress. Here, we show data suggesting that alphaB-crystallin is implicated in remodeling of intermediate filaments during cell division. We investigated the intracellular distribution of alphaB-crystallin in naturally occurring mitotic NIH 3T3 cells and in neuroblastoma N2a and N1E115 cells. In NIH 3T3 cells, alphaB-crystallin remained diffused throughout the cell cycle. Subcellular fractionation of alphaB-crystallin showed that alphaB-crystallin remained in the cytosolic compartment during mitosis. Furthermore, alphaB-crystallin accumulated in mitotically arrested NIH 3T3 cells. This increased level of alphaB-crystallin protein was due to an increased level of alphaB-crystallin mRNA in mitotic NIH 3T3 cells. In the neuroblastoma cells, the intermediate filaments were rearranged into thick cable-like structures and alphaB-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 alphaB-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 alphaB-crystallin was either recruited onto the intermediate filaments or upregulated in the cytosolic compartment.

Epithelial cell proliferation, apoptosis, and apoptosis inhibition in inverted papillomas.

Inverted papillomas (IPs) are rare benign tumors of nasal epithelium with high recurrence rates and malignant transformation potential. Their etiology is still uncertain, and the mechanism of their growth has not yet been fully described. The purpose of this study was to detect, quantify, and compare cell proliferation, apoptosis, and apoptosis inhibition in hyperplastic epithelium from IPs and in inflammatory nasal polyps (NPs). IP samples were obtained after surgical removal of tumor in 13 patients, and NPs were sampled during endoscopic ethmoidectomy in 10 patients with nasal polyposis. Cell proliferation and apoptosis inhibition, respectively, were assessed by immunohistochemical identification of the proliferating cell nuclear antigen (PCNA) and the oncoprotein Bcl-2. Apoptosis was evaluated by analyzing the DNA fragmentation. Cell proliferation and apoptosis were significantly higher in IPs than in NPs (P = .0002 and P = .043, respectively), while apoptosis inhibition was significantly lower in IPs than in NPs (P = .001). Concerning IPs, cell proliferation was significantly higher than apoptosis (P = .0029) and apoptosis inhibition (P = .0015). The increase in epithelial cell proliferation seemed to be greater in IPs with dysplasia than in IPs without dysplasia. Increased epithelial cell proliferation, but not apoptosis and apoptosis inhibition, seems to be involved in the development of IP.