Regulation of mitosis and taxane response by Daxx and Rassf1

Abstract

Current theories suggest that mitotic checkpoint proteins are essential for proper cellular response to taxanes, a widely-used family of chemotherapeutic compounds. We recently demonstrated that absence or depletion of protein Daxx increases cellular taxol (paclitaxel) resistance—a common trait of patients diagnosed with several malignancies, including breast cancer. Further investigation of Daxx-mediated taxol response revealed that Daxx is important for the proper timing of mitosis progression and cyclin B stability. Daxx interacts with mitotic checkpoint protein Rassf1 and partially co-localizes with this protein during mitosis. Rassf1/Daxx depletion or expression of Daxx binding domain of Rassf1 elevates cyclin B stability and increases taxol resistance in cells and mouse xenograft models. In breast cancer patients, we observed the inverse correlation between Daxx and clinical response to taxane-based chemotherapy. These data suggest that Daxx and Rassf1 define a mitotic stress checkpoint that enables cells to exit mitosis as micronucleated cells (and eventually die) when encountered with specific mitotic stress stimuli, including taxol. Surprisingly, depletion of Daxx or Rassf1 does not change activity of E3 ubiquitin ligase APC/C in in vitro settings, suggesting necessity of mitotic cellular environment for proper activation of this checkpoint. Daxx and Rassf1 may become useful predictive markers for the proper selection of patients for taxane chemotherapy.

USP7 and Daxx regulate mitosis progression and taxane sensitivity by affecting stability of Aurora-A kinase

“…We have previously shown that Daxx protein participates in mitosis regulation, thus affecting taxane resistance. 20,21 According to our model, 21 Daxx-deficient cells cannot resolve prometaphase/ metaphase transition as efficiently as control cells. This would explain the observation that, upon taxane treatment, cells with a low Daxx expression are protected from mitotic catastrophe/slippage and are able to complete mitosis and survive after taxane decay.…”

“…We previously demonstrated that Daxx depletion causes stabilization of cyclin B1, thus blocking cells transiently in mitosis. 21 To test whether Daxx and USP7 cooperate to maintain this block, we monitored the stability of cyclin B in HEp2 cells depleted by control or USP7 shRNAs (Supplementary Figure S1a). Cells were synchronized in mitosis by either Taxol or Nocodazole exposure.…”

“…15,16 Aurora-A kinase has been linked to taxane resistance; 17 it is amplified in breast cancer, 18 overexpressed in several tumors with poor prognosis and it is an emerging therapeutic target. 19 Previously, we identified a novel role of death domainassociated protein (Daxx) in taxane sensitivity 20 and mitotic progression, 21 in both experimental models and breast cancer patients. Daxx is a highly conserved and developmentally essential nuclear protein, 22,23 involved in numerous cellular processes, such as transcriptional regulation, 22 apoptosis 24 and carcinogenesis.…”

“…Daxx is a highly conserved and developmentally essential nuclear protein, 22,23 involved in numerous cellular processes, such as transcriptional regulation, 22 apoptosis 24 and carcinogenesis. 21,25,26 To further understand the mechanism of Daxx-based mitosis progression and taxane resistance, we employed proteomic approach to isolate the Daxx mitotic complex and characterize Daxx-interacting proteins. Here we report that ubiquitin (Ub)-specific processing protease-7 (USP7), 27 a deubiquitylating enzyme, is a Daxx-interacting protein in mitosis.…”

Germinal center kinases in immune regulation

“…It is interesting that both MST1 and Daxx have been observed to associate with mitotic checkpoint protein Rassf1. 44,45 In addition, Ferritin heavy chain (FTH1) may bind directly with Daxx to regulate apoptosis. 46 At this point, it remains unknown how Daxx mechanistically regulates the activity and cellular localization of MST1 and how MST1 and Daxx may interplay with Rassf1 and FTH1.…”