Mammalian Hsp22 is a heat-inducible small heat-shock protein with chaperone-like activity

Abstract

A newly identified 22 kDa protein that interacts with Hsp27 (heat-shock protein 27) was shown to possess the characteristic alpha-crystallin domain, hence named Hsp22, and categorized as a member of the sHsp (small Hsp) family. Independent studies from different laboratories reported the protein with different names such as Hsp22, H11 kinase, E2IG1 and HspB8. We have identified, on the basis of the nucleotide sequence analysis, putative heat-shock factor 1 binding sites upstream of the Hsp22 translation start site. We demonstrate that indeed Hsp22 is heat-inducible. We show, in vitro, chaperone-like activity of Hsp22 in preventing dithiothreitol-induced aggregation of insulin and thermal aggregation of citrate synthase. We have cloned rat Hsp22, overexpressed and purified the protein to homogeneity and studied its structural and functional aspects. We find that Hsp22 fragments on storage. MS analysis of fragments suggests that the fragmentation might be due to the presence of labile peptide bonds. We have established conditions to improve its stability. Far-UV CD indicates a randomly coiled structure for Hsp22. Quaternary structure analyses by glycerol density-gradient centrifugation and gel filtration chromatography show that Hsp22 exists as a monomer in vitro, unlike other members of the sHsp family. Hsp22 exhibits significantly exposed hydrophobic surfaces as reported by bis-8-anilinonaphthalene-l-sulphonic acid fluorescence. We find that the chaperone-like activity is temperature dependent. Thus Hsp22 appears to be a true member of the sHsp family, which exists as a monomer in vitro and exhibits chaperone-like activity.

Induction of Hsp22 (HspB8) by estrogen and the metalloestrogen cadmium in estrogen receptor– positive breast cancer cells

“…Whatever the actual function of Hsp22 in breast cancer cells is, it might be accomplished by these HMMCs. For example, HMMC formation might be involved in the chaperone-like activity that has been reported for Hsp22 (Chowdary et al 2004;Kim et al 2004;Carra et al 2005). Apparently, Hsp22 and Hsp27 were, in part, components of distinct complex populations.…”

“…Similarly extended 5Ј-(G/A)GGTCA-3Ј sites were shown to represent common response elements for nuclear receptors with P boxes homologous to that of the ER, including RXRs (Kato et al 1995). In addition, the proximal promoter contains the common promoter elements CAAT box and TATA box, and 2 perfect palindromic putative heat shock elements (consensus sequence 5Ј-GAANNTTC-3Ј) that could account for the heat inducibility reported for Hsp22 (Chowdary et al 2004).…”

Stress under the dam: meeting report of the Fourth International Workshop on the Molecular Biology of Stress Responses

“…The flexible C-terminus of IbpB that is essential for chaperone activity and temperature-dependent regulation of its oligomeric status was found to be highly susceptible to limited proteolysis. This is particularly interesting and may relate to the recently reported sensitivity and cleavage of the flexible N-terminal end of mammalian Hsp22 (Chowdary et al 2004). Why small Hsps from diverse organisms can act as monomers while others are found as dimers, trimers, or very large oligomers and how this relates to chaperone activity remains an intriguing problem of structural biology and evolution.…”

Abnormal interaction of motor neuropathy-associated mutant HspB8 (Hsp22) forms with the RNA helicase Ddx20 (gemin3)

“…The approximate positions of the marker proteins β-lactoglobulin B (∼5.1), phycocyanin (∼4.6), and glucose oxidase (∼4.2) are indicated HspB1, HspB2, HspB5, HspB6, and HspB7 (Sun et al 2004;Fontaine et al 2005), although oligomeric forms could not be detected using recombinant HspB8 (Chowdary et al 2004;Kim et al 2004). However, in extracts of cardiac and breast cancer cells, recruitment of HspB8 into highmolecular-mass material was reported, even though the nature of this material is not known (Fontaine et al 2005;Sun et al 2007).…”