TACC3 depletion sensitizes to paclitaxel-induced cell death and overrides p21WAF-mediated cell cycle arrest

Abstract

Regulators of the mitotic spindle apparatus are attractive cellular targets for antitumor therapy. The centrosomal protein transforming acidic coiled coil (TACC) 3 is required for spindle assembly and proper chromosome segregation. In this study, we employed an inducible RNA interference approach to downregulate TACC3 expression. We show that TACC3 knock-down in NIH3T3 fibroblasts caused aneuploidy, but failed to overtly impair mitotic progression. TACC3 depletion rather triggered a postmitotic p53-p21 WAF pathway and led to a reversible cell cycle arrest. Similar effects were induced by low concentrations of paclitaxel, a spindle poison used in antitumor therapy. Interestingly, however, and unlike in TACC3-proficient cells, paclitaxel was able to induce strong polyploidy and subsequent apoptosis in TACC3-depleted cells. Even though paclitaxel treatment was associated with the activation of the survival kinase Akt and an antiapoptotic expression of cytoplasmic p21 WAF and cyclin D1, this inhibition of cell death was abrogated by depletion of TACC3. Thus, our data identify TACC3 as a potential target to overcome p21 WAF -associated protection of transformed cells against paclitaxel-induced cell death.

The Transforming Acidic Coiled Coil 3 Protein Is Essential for Spindle-dependent Chromosome Alignment and Mitotic Survival

“…Our studies of TACC3 depletion in murine cells confirm the importance of p21 WAF in preventing severe mitotic abnormalities (23). The p53/ p21 WAF -and retinoblastoma-dependent G 1 checkpoint is compromised in HeLa cells (46), whereas both are functional in the HCT116 cells.…”

“…The critical and gene dosage-dependent function of TACC3 in development is further underlined by the impaired chondrocyte differentiation and skeletal malformations in homozygous mutant mice carrying a hypomorphic TACC3 allele (22). Moreover, in the absence of TACC3, murine NIH3T3 fibroblasts enter a G 1 and G 2 cell cycle arrest (23).…”

The centrosomal protein TACC3 controls paclitaxel sensitivity by modulating a premature senescence program

“…Accordingly, the p53 target gene p21 WAF , a cyclin-dependent kinase inhibitor, was efficiently induced upon TACC3 depletion, whereas expression of the p53-independent cyclin-dependent kinase inhibitor, p27 KIP , remained unchanged (Supplementary Figure 3a). Furthermore, TACC3 depletion correlated with increased levels of cyclin D1 (Supplementary Figure 3a), which was predominantly confined to the cytoplasm (Schneider et al, 2008 and data not shown) and which is consistent with its function in G 1 arrest and senescence (Kortlever et al, 2006). In contrast, protein levels of the G 2 /Massociated cyclins A and B1 were strongly reduced upon prolonged TACC3 depletion (Supplementary Figure 3a), thus excluding a major contribution of the G 2 checkpoint in the post-mitotic arrest caused by TACC3 depletion.…”

“…We have recently shown that TACC3 depletion sensitizes NIH3T3 fibroblasts to PTX-induced cell death, indicating that spindle poisons and downregulation of TACC3 elicit similar signaling pathways in cellular stress responses (Schneider et al, 2008). Indeed, the onset of senescence of two independent TACC3 shRNA-expressing MCF-7 clones could be strongly …”

“…Moreover, we have recently shown that the cellular outcome of mitotic stress induced by TACC3 depletion is decisively determined by the status of the post-mitotic G 1 checkpoint. Whereas TACC3-deficient murine fibroblasts with functional post-mitotic checkpoints enter a reversible G 1 and G 2 arrest, checkpointcompromised cells rapidly succumb to mitotic cell death and polyploidization (Schneider et al, 2007(Schneider et al, , 2008. Given that centrosomal localization of human TACC3 requires its phosphorylation by Aurora A kinase at Ser558 (LeRoy et al, 2007) and because pharmacological inhibition of Aurora A kinase induces premature senescence (Huck et al, 2010), we explored here (i) whether senescence is the prevailing outcome of TACC3 reduction in G 1 checkpoint-proficient transformed and non-transformed breast epithelial cells and (ii) to which extent their chemosensitivity against PTX can be modulated by targeting TACC3 expression.…”