Heat-induced preferential synthesis and redistribution of HSP 70 and 28 families in Chinese hamster ovary cells

Dynamic O-GlcNAcylation of the small heat shock protein alpha B-crystallin

alphaB-Crystallin, originally described as a structural lens protein, is now known to be a member of the small heat shock protein family and is expressed in a number of nonlens tissues. This highly conserved 20 kDa protein aggregates with homologous proteins, including alphaA-crystallin and the small heat shock protein HSP28, to form large heteromeric complexes. Recently, Roquemore et al. (1992) have established that both phosphorylated and unphosphorylated forms of lens alphaB-crystallin are modified with O-linked N-acetylglucosamine, a dynamic posttranslational modification abundant on nuclear and cytoplasmic proteins. In this paper, we have identified the major site of O-GlcNAcylation on lens alphaB as Thr 170. We have further shown that this modification is not restricted to lens alphaB-crystallin but occurs on alphaB isolated from rat heart tissue and human astroglioma cells. Two-dimensional electrophoresis of rat heart alphaB-crystallin revealed two O-GlcNAcylated forms with mobilities corresponding to the unphosphorylated form (alphaB2) and an unidentified, slightly more acidic form. Phosphorylated alphaB-crystallin (alphaB1) was not detected in the rat heart preparation. The major O-GlcNAcylation site on alphaB-crystallins from rat heart also appears to be at Thr 170. Metabolic pulse-chase labeling studies of U373-MG astroglioma cells indicated that turnover of the carbohydrate on alphaB-crystallin is not static but proceeds many-fold more rapidly than turnover of the protein backbone itself, consistent with a regulatory role for O-GlcNAc on this small heat shock protein.

Characterization of a polymorphic heat shock protein 70 gene in swine outside the SLA major histocompatibility complex

To characterize a hitherto unidentified swine Hsp70 gene, a cDNA library was prepared from total RNA isolated from swine lymphocytes and heat-shocked at 42 degrees C for 2 h. One positive clone with a 2.6 kb insert was found. Its sequencing revealed a maximum homology with the human inducible Hsp70B' gene. The genomic polymorphism of this insert was investigated by restriction fragment length polymorphism (RFLP) in an informative family for the major histocompatibility complex SLA. Digestion with PvuII generated 8 bands which were common to both parents, and for the male two extra bands at 0.69 and 0.64 kb. After digestion with PstI, there was also an extra band at 1.6 kb for the male in addition to the seven bands common to both parents. The eleven offsprings' RFLP patterns exhibited all the common parental bands, but four piglets displayed the male's specific bands in addition. All the polymorphic bands belonged to the same locus and segregated independently of SLA. Restriction mapping of the Hsp70 gene indicated the absence of introns, and showed that the polymorphic PstI site was located upstream of the gene's 5' coding region, and the PvuII site inside its coding region.

Expression, synthesis, and phosphorylation of HSP28 family during development and decay of thermotolerance in CHO plateau-phase cells

We investigated a correlation between development of thermotolerance and expression, synthesis, or phosphorylation of HSP28 family in CHO plateau phase cells. After heating at 45.5 degrees C for 10 min, thermotolerance developed rapidly and reached its maximum 12-18 hr after heat shock. This acquired thermal resistance was maintained for 72 hr and then gradually decayed. In parallel, the levels of three 28 kDa heat shock proteins, HSP28a along with its two phosphorylated isoforms (HSP28b,c), increased and reached their maximum 24-48 hr after heat shock. The levels of these polypeptides, except HSP28c, remained elevated for 72 hr and then decreased. The level of HSP28 mRNA increased rapidly and reached its maximum 12 hr after heat shock. However, unlike thermotolerance and the levels of HSP28 family proteins, the level of HSP28 mRNA decreased rapidly within 72 hr. These results demonstrate a correlation between the amount of intracellular HSP28 family proteins and development and decay of thermotolerance.