Ectopic expression of alpha B-crystallin in Chinese hamster ovary cells suggests a nuclear role for this protein

alpha B-crystallin (alpha E) is known to be a cytosolic, small heat shock-l ike multimeric protein that has anti-aggregation, chaperone-like properties . The expression of the alpha B-crystallin gene is developmentally regulate d and is induced by a variety of stress stimuli. importantly, alpha B-cryst allin expression is enhanced during oncogenic transformation of cells, in a number of tumors, and most notably, in many neurodegenerative disorders, i ncluding Alzheimer's disease and multiple sclerosis, Other than its perceiv ed role as a structural protein in the ocular lens, the actual function of alpha B-crystallin in cellular physiology remains unknown, We have stably t ransfected CHO cells with an inducible alpha B-cDNA-MMTV-promoter construct that allows the synthesis of recombinant alpha B-crystallin only upon expo sure of these cells to dexamethasone. Using immunostaining and conventional and confocal microscopy we have examined the subcellular distribution of t he ectopically expressed alpha B-crystallin. We find that in addition to be ing in the cytoplasm, the protein resides in the nuclear interior in the in terphase nucleus. Double labeling with anti alpha B-crystallin and anti-tub ulin, concanavallin, and wheat germ agglutinin, respectively, revealed that during cell division alpha B-crystallin is excluded from condensed chromat in and the nascent nuclei. However, the protein again appears in the newly formed nuclei after the completion of cytokinesis suggesting a conditional, regulatory role for alpha B-crystallin in the nucleus.