Sequence similarity between aB-crystallin and small heat shock proteins (HSPs) has prompted us to investigate whether aB-crystallin expression is induced by heat shock. Indeed, accumulation of aB-crystallin was detected immunologically in NIH 3T3 cells after incubation at elevated temperatures and after addition of Cd2+ or sodium arsenite to these cells. Two-dimensional gel electrophoresis revealed identity between aB-crystallin from eye lenses and from heattreated fibroblasts. The promoter of the aB-crystallin gene was fused to the bacterial chloramphenicol acetyltransferase gene and was shown to confer heat inducibility on this reporter gene in transient transfection assays. A perfect heat shock element within the promoter region is likely to mediate this response. Small HSPs and aB-crystallin were shown to share the following two physical properties: (i) they form supramolecular structures with sedimentation values around 17 S and (ii) they are associated with the nucleus at high temperatures and are localized in the cytoplasm under normal conditions. We conclude that aB-crystallin has to be considered a member of the class of small HSPs.Heat shock and numerous other stress conditions lead to the rapid induction of several genes whose protein products are collectively called heat shock proteins (HSPs) (for recent reviews see refs. 1-3). The HSPs have been grouped into several classes on the basis of their size and sequence homology. Members of the class of small HSPs have molecular masses in the range 15-40 kDa. All analyzed organisms possess at least one small HSP gene. In mammals, birds, and yeast this class of HSPs is represented by a single member (4-9), whereas in Drosophila melanogaster and plants there appear to be multiple small HSPs (10, 11). Small HSPs aggregate to form characteristic ring-shaped structures called heat shock granules (4,(12)(13)(14)(15). These structures resemble prosomes or proteosomes but are distinct entities (16). Their biochemical function is unknown. Under heat shock conditions the small HSPs associate with the nucleus. Following a heat shock they slowly relocalize to the cytoplasm (17)(18)(19). It is still a matter of debate whether the small HSPs are actually transported into the nucleus at high temperatures or whether they are entrapped by the intermediate filaments, which, under heat shock conditions, collapse onto the nucleus (for a review see ref.3). The amino acid sequences of the small HSPs from different organisms are only poorly conserved. However, striking sequence similarities exist between vertebrate a-crystallins and small HSPs (5, 20-23). a-Crystallins were originally found in eye lenses, where they are among the most abundant proteins (24, 25). There exist two forms of a-crystallins, aA and aB, which are closely related (26). Considerable amounts of aB-crystallin, but not aAcrystallin, are present in many nonlenticular tissues (27-31). Moreover, aB-crystallin gene expression has been observed in various diseased cells, including astrocytes of patients s...

Abstract. Stress induces the synthesis of several large and small heat shock proteins (hsp's). Two related small hap's, hsp25 and c~B crystallin exist in mice. o~B crystallin is an abundant protein in several tissues even in the absence of stress. Particularly high amounts accumulate in the eye lens. Here we show that hsp25 is likewise constitutively expressed in many normal adult tissues. In the absence of stress the protein is most abundant in the eye lens, heart, stomach, colon, lung, and bladder. The stress-independent expression pattern of the two small hsp's is distinct. In several tissues the amount of hsp25 exceeds that accumulating in NIH 3T3 fibroblasts in response to heat stress, hsp25, like orB crystallin, exists in a highly aggregated form in the eye lens. The expression of hsp25 and o~B crystallin in normal tissues suggests an essential, but distinct function of the two related proreins under standard physiological conditions.

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ocB-crystallin, a major soluble protein of vertebrate eye lenses, is a small heat shock protein which transiently accumulates in response to heat shock and other kinds of stress in mouse NIH 3T3 fibroblasts. Ectopic expression of an aeB-crystallin cDNA clone renders NIH 3T3 cells thermoresistant. avB-crystallin accumulates in response to the synthetic glucocorticoid hormone dexamethasone. Dexamethasone-treated NIH 3T3 cells become thermoresistant to the same extent as they accumulate cvB-crystallin. A cell clone in which ciB-crystallin is superinduced upon heat shock acquires augmented thermotolerance. Expression of the ras oncogene causes a rapid but transient accumulation of cfB-crystallin within 1 day. Later, sustained ras oncogene expression suppresses the dexamethasone-mediated aB-crystallin accumulation. Thus, oncogenic transformation triggered by the ras oncogene interferes with hormone-mediated accumulation of oaB-crystallin and concomitant acquisition of thermoresistance. Other known heat shock proteins do not accumulate in response to ectopic csB-crystallin expression or to dexamethasone treatment. These results indicate that aB-crystallin can protect NIH 3T3 fibroblasts from thermal shock.Studies on oncogene-induced alterations in cellular gene expression and their association with the transformation phenotype are essential for understanding the mechanisms by which oncogenes mediate the malignant phenotype (for a review, see reference 3). In an attempt to define specific cellular responses toward accumulation of oncoproteins, we have previously studied the effects of the ras and mos oncoproteins on cellular gene expression in mouse NIH 3T3 fibroblasts (34). We found that high amounts of aB-crystallin rapidly accumulate in NIH 3T3 cells in response to the expression of the c-Ha-ras and v-mos oncogenes controlled by the glucocorticoid-inducible promoter of mouse mammary tumor virus (MMTV) (32).aB-crystallin is one of the major soluble proteins of vertebrate eye lenses (for reviews, see references 51, 52, and 67). The protein shares 60% amino acid sequence homology with oA-crystallin (62). atB-crystallin is also expressed in nonocular tissues such as heart muscle, skeletal muscle, kidney, lung, brain, spermatocyte, and placenta (5, 8, 12, 23-25, 31, 40). Moreover, evidence has been accumulating that elevated levels of aB-crystallin are associated with various pathological conditions in the brain and other tissues (13,24,26,27,43,44,48). The ot-crystallins share amino acid sequence similarity with small heat shock proteins (hsps) of diverse organisms, including mycobacteria, fruit flies, plants, and mammals (for reviews, see references 39, 51, 52, 65, 66, and 67). The homology between mouse aB-crystallin (32) and hsp25 (unpublished data; 17) reaches approximately 40%. These observations suggest a possible functional relationship between a-crystallins and small hsps (11). Recently we have shown that oxB-crystallin is indeed a bona fide small hsp (33). The characteristic features shared by aB-crystallin a...

We have previously shown that alpha B-crystallin is a heat-shock protein which specifically accumulates in response to the expression of c-Ha-ras and v-mos oncogenes in mouse NIH 3T3 fibroblasts. Elevated levels of alpha B-crystallin mRNA or protein were shown to be associated with pathological conditions of the brain. Therefore, we have examined the expression of alpha B-crystallin in normal human brains and brain tumors by Western blot analysis. alpha B-crystallin is moderately expressed in adult but not fetal brain. Elevated levels of alpha B-crystallin expression are observed in glial tumors such as astrocytoma, glioblastoma multiforme, and oligodendroglioma. alpha B-crystallin in these tumors is predominately unphosphorylated. High amounts of accumulated alpha B-crystallin in astrocytic tumors are preferentially found in the more aggressive stages. Glioblastoma multiforme is exceptional in that high alpha B-crystallin expression is observed in only one half of the analyzed samples whereas no alpha B-crystallin could be detected in the other. These results indicate that alpha B-crystallin may be a useful biochemical marker for studying the pathogenesis of various human brain tumors.