Ectopic expression of alpha B-crystallin in Chinese hamster ovary cells suggests a nuclear role for this protein.
alpha B-crystallin (alpha B) is known to be a cytosolic, small heat shock-like multimeric protein that has anti-aggregation, chaperone-like properties. The expression of the alpha B-crystallin gene is developmentally regulated and is induced by a variety of stress stimuli. Importantly, alpha B-crystallin expression is enhanced during oncogenic transformation of cells, in a number of tumors, and most notably, in many neurodegenerative disorders, including Alzheimer's disease and multiple sclerosis. Other than its perceived role as a structural protein in the ocular lens, the actual function of alpha B-crystallin in cellular physiology remains unknown. We have stably transfected CHO cells with an inducible alpha B-cDNA-MMTV-promoter construct that allows the synthesis of recombinant alpha B-crystallin only upon exposure of these cells to dexamethasone. Using immunostaining and conventional and confocal microscopy, we have examined the subcellular distribution of the ectopically expressed alpha B-crystallin. We find that in addition to being in the cytoplasm, the protein resides in the nuclear interior in the interphase nucleus. Double labeling with anti alpha B-crystallin and anti-tubulin, concanavallin, and wheat germ agglutinin, respectively, revealed that during cell division alpha B-crystallin is excluded from condensed chromatin 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.
Bhat
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SP
Jules Stein Eye Institute, UCLA School of Medicine 90095-7000, USA. hbat@jsei.ucla.edu
Hale
I L
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Matsumoto
B
B
Elghanayan
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D
D000818:Animals; D016466:CHO Cells; D002455:Cell Division / Q000502:physiology; D002467:Cell Nucleus / Q000378:metabolism*; D006224:Cricetinae; D003459:Crystallins / Q000096:biosynthesis* / Q000235:genetics / Q000502:physiology*; D003599:Cytoskeleton / Q000378:metabolism; D003907:Dexamethasone / Q000494:pharmacology; D015870:Gene Expression / Q000187:drug effects; D007150:Immunohistochemistry; D015388:Organelles / Q000378:metabolism; D014162:Transfection
D003459:Crystallins; D003907:Dexamethasone