Nuclear translocation of the phosphoprotein Hop (Hsp70/Hsp90 organizing protein) occurs under heat shock, and its proposed nuclear localization signal is involved in Hsp90 binding

Abstract

The Hsp70-Hsp90 complex is implicated in the folding and regulation of numerous signaling proteins, and Hop, the Hsp70-Hsp90 Organizing Protein, facilitates the association of this multichaperone machinery. Phosphatase treatment of mouse cell extracts reduced the number of Hop isoforms compared to untreated extracts, providing the first direct evidence that Hop was phosphorylated in vivo. Furthermore, surface plasmon resonance (SPR) spectroscopy showed that a cdc2 kinase phosphorylation mimic of Hop had reduced affinity for Hsp90 binding. Hop was predominantly cytoplasmic, but translocated to the nucleus in response to heat shock. A putative bipartite nuclear localization signal (NLS) has been identified within the Hsp90-binding domain of Hop. Although substitution of residues within the major arm of this proposed NLS abolished Hop-Hsp90 interaction as determined by SPR, this was not sufficient to prevent the nuclear accumulation of Hop under leptomycin-B treatment and heat shock conditions. These results showed for the first time that the subcellular localization of Hop was stress regulated and that the major arm of the putative NLS was not directly important for nuclear translocation but was critical for Hop-Hsp90 association in vitro. We propose a model in which the association of Hop with Hsp90 and the phosphorylated status of Hop both play a role in the mechanism of nucleo-cytoplasmic shuttling of Hop.

RNAi knockdown of Hop (Hsp70/Hsp90 organising protein) decreases invasion via MMP-2 down regulation

“…There is evidence to suggest that localisation of Hop may be due to phosphorylation. Hop can be phosphorylated by cell cycle kinases, phosphorylation by cdc2 (cell division cycle 2) kinase promotes cytoplasmic retention, whereas phosphorylation by casein kinase II (CKII) promotes nuclear Hop, suggesting that Hop might move between the cytoplasm and the nucleus under certain cell cycle conditions [40,41]. The nuclear accumulation of Hop is primarily stress regulated and CKII phosphorylation has been shown not to disrupt Hop-Hsp90 binding [36].…”

Neuroproteomics: A Biochemical Means To Discriminate the Extent and Modality of Brain Injury

“…Before receiving a protein from HSP70, HSP90 must complex with dephosphorylated stress-induced phosphoprotein 1 (STIP1; Daniel et al, 2008). In the 30-min MCAO group, increased HSP70 was accompanied by a proportional increase in dephosphorylated STIP1 and an increase in HSP90, signifying upregulated and fully functional chaperone activity.…”

Nuclear Tau, a Key Player in Neuronal DNA Protection

“…Interestingly, oxidative stress and hyperthermia quickly induce nuclear translocation of molecular chaperones (38,39) as well as proteins involved in the etiopathology of neurodegenerative diseases, such as ␣-synuclein (40), the amyloid precursor protein C-terminal fragment (41) or amyloid precursor protein partner Fe65 (42) and ataxin-3 (43).…”