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

Microtubule-interfering cancer drugs such as paclitaxel (PTX) often cause chemoresistance and severe side effects, including neurotoxicity. To explore potentially novel antineoplastic molecular targets, we investigated the cellular response of breast carcinoma cells to short hairpin(sh)RNA-mediated depletion of the centrosomal protein transforming acidic coiled coil (TACC) 3, an Aurora A kinase target expressed during mitosis. Unlike PTX, knockdown of TACC3 did not trigger a cell death response, but instead resulted in a progressive loss of the pro-apoptotic Bcl-2 protein Bim that links microtubule integrity to spindle poison-induced cell death. Interestingly, TACC3-depleted cells arrested in G1 through a cellular senescence program characterized by the upregulation of nuclear p21(WAF), downregulation of the retinoblastoma protein and extracellular signal-regulated kinase 1/2, formation of HP1γ (phospho-Ser83)-positive senescence-associated heterochromatic foci and increased senescence-associated ß-galactosidase activity. Remarkably, the onset of senescence following TACC3 knockdown was strongly accelerated in the presence of non-toxic PTX concentrations. Thus, we conclude that mitotic spindle stress is a major trigger of premature senescence and propose that the combined targeting of the centrosomal Aurora A-TACC3 axis together with drugs interfering with microtubule dynamics may efficiently improve the chemosensitivity of cancer cells.

Odorant-stimulated phosphoinositide signaling in mammalian olfactory receptor neurons.

Recent evidence has revived interest in the idea that phosphoinositides (PIs) may play a role in signal transduction in mammalian olfactory receptor neurons (ORNs). To provide direct evidence that odorants indeed activate PI signaling in ORNs, we used adenoviral vectors carrying two different fluorescently tagged probes, the pleckstrin homology (PH) domains of phospholipase C delta 1 (PLC delta 1) and the general receptor of phosphoinositides (GRP1), to monitor PI activity in the dendritic knobs of ORNs in vivo. Odorants mobilized PI(4,5)P(2)/IP(3) and PI(3,4,5)P(3), the substrates and products of PLC and PI3K. We then measured odorant activation of PLC and PI3K in olfactory ciliary-enriched membranes in vitro using a phospholipid overlay assay and ELISAs. Odorants activated both PLC and PI3K in the olfactory cilia within 2s of odorant stimulation. Odorant-dependent activation of PLC and PI3K in the olfactory epithelium could be blocked by enzyme-specific inhibitors. Odorants activated PLC and PI3K with partially overlapping specificity. These results provide direct evidence that odorants indeed activate PI signaling in mammalian ORNs in a manner that is consistent with the idea that PI signaling plays a role in olfactory transduction.