Research reportThe distribution and localization of hsp110 in brain
Introduction
Hsp70 is perhaps the best studied of the major heat shock proteins and has been shown to play essential roles in a variety of cellular activities including the folding of nascent polypeptides, protein translocation across intracellular membranes, and regulation of the activities of steroid hormone receptors and kinases. Because of its involvement in numerous cellular processes and the role of it, as well as other heat shock proteins, in protecting cells from stressful environments, the expression of hsp70 family members in tissues of a variety of organisms has been investigated [4]. Most notably, the expression of hsp70 in the critical organs, heart and brain, has been extensively studied and characterized [3], [6], [14], [15]. Studies in brain have suggested a relationship between hsp70 expression and sensitivity of particular brain regions to ischemia/reperfusion injuries [9], [22], [2] as well as pathological conditions such as Alzheimer’s [20].
While a potential function for hsp70 in the pathophysiology of brain is likely to be highly important, recent studies have indicated that another heat shock protein, hsp110, is also a major brain protein. Hsp110 and its family members have only been recently cloned and have been shown to be distant relatives of the hsp70 family. While three hsp110 family members have been identified in mouse, hsp110 is the principal representative in most tissues. In addition, studies have shown that hsp110 is significantly more strongly expressed in brain than in other tissues [11], [18], [25], [26]. Indeed, the expression of hsp110 in mouse brain in the absence of stress is comparable to its expression in heat shocked Chinese hamster cells, using conditions for optimal hsp expression [11], [18]. Curiously, hsp110 has not been examined until recently and these recent studies have begun to unravel the molecular chaperoning properties of hsp110. It has been shown to be a highly efficient molecular chaperone and to recognize and sustain denatured protein in a soluble, refoldable state [18]. Moreover, hsp110 appears to be considerably more efficient in performing this function than is hsc70 (the constituitive form of this hsp family). At the same time hsp110 exhibits different ATP binding properties compared to hsc70, suggesting important differences between these two chaperones in their regulatory properties of peptide binding [19].
The present study presents an analysis of hsp110 expression in brain. Regional and cellular localization of hsp110 in brain using Northern and Western blot, and immunohistochemical analyses demonstrates that there is a significant variation in the regional expression of this major heat shock protein. Specifically, expression in the granule cells of the cerebellum is several fold lower than is its expression in the other neurons of the brain. A potential connection between expression of hsp110 and the pathophysiology accompanying chronic alcohol syndrome and heat stroke is suggested.
Section snippets
Materials and methods
A Poly A+ Northern blot containing 15 regions of human brain was obtained from Clontech Corp. (Clontech RNA Master BlotTM). The blot was hybridized with a 0.94 kb (nucleotides 1669–2610) hsp110 cDNA probe in hybridization buffer from Clontech Corp. After 16 h of hybridization at 65°C, the blot was washed four times in a wash buffer (2× SSC, 0.1% SDS), each for 20 min. The blot was exposed to Kodak XAR X-ray film for 16 h at −70°C. The blot was normalized at the company to the expression of
Results
Fig. 1A shows a Northern (dot) blot analysis of several regions of human brain, probed for hsp110 message. While notable variability of hsp110 message expression from region to region of human brain is evident, the absence (i.e. very low expression) of hsp110 in the cerebellum is obvious. The spinal cord expression of hsp110 mRNA was also somewhat reduced relative to other brain regions, but not to the extent of the cerebellum.
Hsp110 protein expression was also examined using a Western blot
Discussion
We have previously examined several murine tissues and demonstrated that hsp110 is most highly expressed in brain. Moreover, this level of natural expression (i.e. in the absence of heat shock) is comparable in quantity to the expression obtained in heat shocked CHO cells [11]. This high degree of expression argues for an important role for this major stress protein in this highly complex and sensitive tissue. With the hope that a more detailed analysis of hsp110 expression in brain might
Acknowledgements
We appreciate the assistance of Dr. T. Szczesny in the preparation of the figures. We also appreciate the expert comments of Dr. Elizabeth Repasky and Dr. Xiang Wang as well as the insight of Dr. Hyun Ju Oh in suggesting the present study. This work was supported in part by PHS grant GM45994.
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