Abstract
BackgroundHeat shock factor 1 (HSF1) is the master regulator of the heat shock response and supports malignant cell transformation. Recent work has shown that HSF1 can access the promoters of heat shock proteins (HSPs) and allow HSP expression during mitosis. It also acts as a mitotic regulator, controlling chromosome segregation. In this study, we investigated whether the transactivation activity of HSF1 is required for the assembly of mitotic spindles.ResultsOur results showed that phosphorylation of HSF1 at serine 326 (S326) and its transactivation activity were increased during mitosis. Inhibition of the transactivation activity of HSF1 by KRIBB11 or CCT251263 during mitosis significantly increased the proportion of mitotic cells with abnormal spindles. It also hampered the reassembly of spindle microtubules after nocodazole treatment and washout by impeding the formation of chromosomal microtubule asters. Depletion of HSF1 led to defects in mitotic spindle assembly, subsequently attenuating cell proliferation and anchorage-independent cell growth (AIG). These HSF1 depletion-induced effects could be rescued by ectopically expressing wild-type HSF1 or a constitutively active mutant (∆202-316, caHSF1) but not the S326A or dominant negative (∆361-529, dnHSF1) mutants. In addition, overexpression of HSP70 partially reduced HSF1 depletion-induced spindle abnormalities. These results indicate that HSF1 may support cell proliferation and AIG by maintaining spindle integrity through its transactivation activity. Furthermore, inhibition of HSF1 transactivation activity by KRIBB11 or CCT251236 can enhance diverse anti-mitosis drug-induced spindle defects and cell death.ConclusionsThe increased transactivation activity of HSF1 during mitosis appears to be required for accurate assembly of mitotic spindles, thereby supporting cell viability and probably AIG. In addition, inhibition of the transactivation activity of HSF1 may enhance the mitotic errors and cell death induced by anti-mitosis drugs.
Highlights
Heat shock factor 1 (HSF1) is the master regulator of the heat shock response and supports malignant cell transformation
HSF1 did not show a distinct distribution in unstressed interphase CGL2 cells (Fig. 1a left panel), but faint staining was observed on the spindles of mitotic CGL2 cells (Fig. 1a right panel) using two different HSF1 antibodies (ADISPA-901 Enzo Life Sciences; sc-9144 Santa Cruz Technology)
Cells depleted of HSF1 (Fig. 1b. short hairpin RNA (shRNA) targeting HSF1 (sh-HSF1)) was stained with the HSF1-pS326 antibodies to check the specificity of the antibodies and the results showed that the spindle pole localization of phospho-HSF1 was diminished in the depleted cells, indicating that the antibodies are specific
Summary
Heat shock factor 1 (HSF1) is the master regulator of the heat shock response and supports malignant cell transformation. Recent work has shown that HSF1 can access the promoters of heat shock proteins (HSPs) and allow HSP expression during mitosis. It acts as a mitotic regulator, controlling chromosome segregation. Heat shock factor-1 (HSF1) is the master transcriptional regulator of the cellular responses to heat and a wide variety of other stresses [1]. In response to these stresses, the inactive monomer HSF1 forms a trimer and is hyperphosphorylated to become transcriptionally active. The functions of HSF1 that promote malignancy may extend beyond its well-known roles in protein quality control [10]
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