HSP70 colocalizes with PLK1 at the centrosome and disturbs spindle dynamics in cells arrested in mitosis by arsenic trioxide

Heat shock protein 70 (HSP70) has been shown to be a substrate of Polo-like kinase 1 (PLK1), and it prevents cells arrested in mitosis by arsenic trioxide (ATO) from dying. Here, we report that HSP70 participates in ATO-induced spindle elongation, which interferes with mitosis progression. Our results demonstrate that HSP70 and PLK1 colocalize at the centrosome in ATO-arrested mitotic cells. HSP70 located at the centrosome was found to be phosphorylated by PLK1 at Ser⁶³¹ and Ser⁶³³. Moreover, unlike wild-type HSP70 (HSP70^wt) and its phosphomimetic mutant (HSP70^SS631,633DD) , a phosphorylation-resistant mutant of HSP70 (HSP70^SS631,633AA) failed to localize at the centrosome. ATO-induced spindle elongation was abolished in cells overexpressing HSP70^SS631,633AA. Conversely, mitotic spindles in cells ectopically expressing HSP70^SS631,633DD were more resistant to nocodazole-induced depolymerization than in those expressing HSP70^wt or HSP70^SS631,633AA. In addition, inhibition of PLK1 significantly reduced HSP70 phosphorylation and induced early onset of apoptosis in ATO-arrested mitotic cells. Taken together, our results indicate that PLK1-mediated phosphorylation and centrosomal localization of HSP70 may interfere with spindle dynamics and prevent apoptosis of ATO-arrested mitotic cells.