Targeting of Heat Shock Protein HSPA6 (HSP70B′) to the Periphery of Nuclear Speckles is Disrupted by a Transcription Inhibitor Following Thermal Stress in Human Neuronal Cells

Abstract

Heat shock proteins (Hsps) are a set of highly conserved proteins involved in cellular repair and protective mechanisms. The intracellular localization of inducible members of the HSPA (HSP70) family can be used as an index to identify stress-sensitive sites in differentiated human neuronal cells. Following thermal stress, the little studied HSPA6 (HSP70B') was targeted to the periphery of nuclear speckles (perispeckles) that are sites of transcription factories. Triptolide, a fast-acting transcription inhibitor, knocked down levels of the large subunit of RNA polymerase II, RPB1, during the time-frame when HSPA6 associated with perispeckles. Administration of triptolide to heat shocked human neuronal SH-SY5Y cells, disrupted HSPA6 localization to perispeckles, suggesting the involvement of HSPA6 in transcriptional recovery after stress. The HSPA6 gene is present in the human genome but is not found in the genomes of the mouse and rat. Hence current animal models of neurodegenerative diseases lack a member of the HSPA family that exhibits the feature of stress-induced targeting to perispeckles.

Olfactory experience primes the heat shock transcription factor HSF-1 to enhance the expression of molecular chaperones in C. elegans

“…6, D to F). Consistent with previous reports (46, 56–58), pol II appeared to cluster in discrete nuclear regions even before 2AA exposure or heat shock (Fig. 6, D to F).…”

Olfactory learning primes the heat shock transcription factor HSF-1 to enhance the expression of molecular chaperone genes inC. elegans

“…3E, F). Consistent with previous reports (40,(50)(51)(52), Pol II appeared to cluster in discrete nuclear regions even prior to 2AA exposure or heat shock (Fig. 3E), and the few HSF-1 nuclear bodies/nucleus present in control water-trained animals also co-localized with Pol II (0.09 HSF-1 nuclear bodies/nucleus co-localized with Pol II in control animals;…”

“…We conclude from these studies that olfactory training on aversive signals such as 2AA was priming HSF-1 by pre-emptively concentrating it at nuclear loci in close proximity to RNA polymerase II. Although we do not yet understand the cellular mechanisms by which this occurred the ability of the serotonin-based learning circuitry to induce the co-localization of HSF-1 with Pol II in somatic nuclei could conceivably result in an enhanced transcriptional response upon actual encounter with the pathogen (40,41,48,(50)(51)(52).…”

“…In summary, our data provide a mechanism whereby 5-HT release and HSF-1 activation cooperate to elicit behavioral avoidance and transcription of cytoprotective chaperones. Remarkably, 5-HT-dependent learning pre-emptively promotes HSF-1 concentration at nuclear regions close to RNA polymerase II required for the active transcription of hsp genes, potentially allowing animals to enhance chaperone expression in the event that they encountered the actual stressor (40,41,48,(50)(51)(52). The exact mechanism by which 5-HT-dependent learning induces HSF-1 is localized to these regions and the nature of the genomic regions in the vicinity (54,55) remain to be investigated.…”

Differential Targeting of Hsp70 Heat Shock Proteins HSPA6 and HSPA1A with Components of a Protein Disaggregation/Refolding Machine in Differentiated Human Neuronal Cells following Thermal Stress

“…HSPA6 (Hsp70B') is an inducible member that has received little attention compared to the more widely studied HSPA1A (Hsp70-1). HSPA6 has been investigated in cultured human neuronal cells (Chow and Brown, 2007; Chow et al, 2010; Khalouei et al, 2014a,b; Deane and Brown, 2016, 2017; Shorbagi and Brown, 2016; Becirovic and Brown, 2017), and in human cancer cell lines (Noonan et al, 2007, 2008). Interestingly, the HSPA6 gene is found in the human genome but not in mouse and rat, hence it is absent in current animal models of neurodegenerative diseases (Noonan et al, 2007; Deane and Brown, 2016, 2017).…”