Proteotoxic stress results in an accumulation of misfolded proteins which tend to form insoluble protein aggregates. Histone deacetylase 6 (HDAC6) binds to ubiquitinated protein aggregates to regulate their degradation (Boyault C et al. 2006). HDAC6 was also found to interact with HSP90 and to regulate HSP90 chaperone complex activity via deacetylation of HSP90 (Kovacs JJ et al. 2005; Boyault C et al. 2007). Binding of HDAC6 to polyubiquitinted proteins triggers the dissociation of the HDAC6:HSP90:HSF1 complex resulting in the activation of HSF1 (Boyault C et al. 2007).
In the absence of stress HSF1 is predominantly monomeric and is thought to be repressed in its inactive monomeric state by the following mechanisms: