Formation of nuclear HSF1 granules varies depending on stress stimuli

In concert with the stress-induced activation of human heat shock factor 1 (HSF1), the factor becomes inducibly phosphorylated and accumulates into nu clear granules. To date, these processes are not fully understood. Here, we show that although stress caused by the proteasome inhibitors MG132 and cl asto-lactacystine beta-lactone induces the expression of Hsp70, the formati on of HSF1 granules is affected differently in comparison to heat shock. Fu rthermore, proteasome inhibition increases serine phosphorylation on HSF1, but to a lesser extent than heat stress. Our results suggest that, dependin g on the type of stress stimulus, the multiple events associated with HSF1 activation might be affected differently.