TACC3 deregulates the DNA damage response and confers sensitivity to radiation and PARP inhibition.

Deregulation of the transforming acidic coiled-coil protein 3 (TACC3), an important factor in the centrosome-microtubule system, has been linked to a variety of human cancer types. We have recently reported on the oncogenic potential of TACC3; however, the molecular mechanisms by which TACC3 mediates oncogenic function remain to be elucidated. In this study, we show that high levels of TACC3 lead to the accumulation of DNA double-strand breaks (DSBs) and disrupt the normal cellular response to DNA damage, at least in part, by negatively regulating the expression of ataxia telangiectasia mutated (ATM) and the subsequent DNA damage response (DDR) signaling cascade. Cells expressing high levels of TACC3 display defective checkpoints and DSB-mediated homologous recombination (HR) and non-homologous end joining (NHEJ) repair systems, leading to genomic instability. Importantly, high levels of TACC3 confer cellular sensitization to radiation and poly(ADP-ribose) polymerase (PARP) inhibition. Overall, our findings provide critical information regarding the mechanisms by which TACC3 contributes to genomic instability, potentially leading to cancer development, and suggest a novel prognostic, diagnostic and therapeutic strategy for the treatment of cancer types expressing high levels of TACC3.

Tankyrase-1 function at telomeres and during mitosis is regulated by Polo-like kinase-1-mediated phosphorylation.

Telomere length is critical for chromosome stability that affects cell proliferation and survival. Telomere elongation by telomerase is inhibited by the telomeric protein, TRF1. Tankyrase-1 (TNKS1) poly(ADP-ribosyl)ates TRF1 and releases TRF1 from telomeres, thereby allowing access of telomerase to the telomeres. TNKS1-mediated poly(ADP-ribosyl)ation also appears to be crucial for regulating the mitotic cell cycle. In searching for proteins that interact with polo-like kinase-1 (Plk1) by using complex proteomics, we identified TNKS1 as a novel Plk1-binding protein. Here, we report that Plk1 forms a complex with TNKS1 in vitro and in vivo, and phosphorylates TNKS1. Phosphorylation of TNKS1 by Plk1 appears to increase TNKS1 stability and telomeric poly(ADP-ribose) polymerase (PARP) activity. By contrast, targeted inhibition of Plk1 or mutation of phosphorylation sites decreased the stability and PARP activity of TNKS1, leading to distort mitotic spindle-pole assembly and telomeric ends. Taken together, our results provide evidence of a novel molecular mechanism in which phosphorylation of TNKS1 by Plk1 may help regulate mitotic spindle assembly and promote telomeric chromatin maintenance.

Mitotic catastrophe is the predominant response to histone acetyltransferase depletion.

Histone acetylation induces chromatin opening by perturbing higher-order chromatin compaction and folding, suggesting that histone acetylation and deacetylation dynamics are central to chromosome condensation or decondensation. The condensation of chromosomes during mitosis is an essential prerequisite for successful chromosome segregation. In this study, we depleted three representative histone acetyltransferases (HATs; p300, CBP, and P/CAF) using shRNAs to explore their role in regulating mitotic progression and chromosome segregation. We showed that HAT depletion severely interfered with the normal timing of mitotic progression, and it reduced condensin subunit levels. The predominant response to HAT depletion, in both human primary and cancer cells, was a mitotic catastrophe following aberrant mitotic arrest. Alternatively, adaptation to HAT depletion, particularly in cancer cells, led to multinucleation and aneuploidy. Interestingly, mitotic catastrophe induced by HAT depletion appeared to be coupled to the signaling process of H2AX phosphorylation and foci formation, independently of DNA double-strand breaks and DNA damage. Taken together, our results provide novel molecular evidence that HAT proteins maintain mitotic chromatin assembly and integrity as a cellular determinant of mitotic cell death.