The serine-threonine kinase gene AURORA-A is commonly amplified in epithelial malignancies. Here we show that elevated Aurora-A expression at levels that reflect cancer-associated gene amplification overrides the checkpoint mechanism that monitors mitotic spindle assembly, inducing resistance to the chemotherapeutic agent paclitaxel (Taxol). Cells overexpressing Aurora-A inappropriately enter anaphase despite defective spindle formation, and the persistence of Mad2 at the kinetochores, marking continued activation of the spindle assembly checkpoint. Mitosis is subsequently arrested by failure to complete cytokinesis, resulting in multinucleation. This abnormality is relieved by an inhibitory mutant of BUB1, linking the mitotic abnormalities provoked by Aurora-A overexpression to spindle checkpoint activity. Consistent with this conclusion, elevated Aurora-A expression causes resistance to apoptosis induced by Taxol in a human cancer cell line.

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SummaryBulk nuclear export of messenger ribonucleoproteins (mRNPs) through nuclear pore complexes (NPCs) is mediated by NXF1. It binds mRNPs through adaptor proteins such as ALY [1, 2] and SR splicing factors [3] and mediates translocation through the central NPC transport channel via transient interactions with FG nucleoporins [4–10]. Here, we show that mammalian cells require GANP (germinal center-associated nuclear protein) for efficient mRNP nuclear export and for efficient recruitment of NXF1 to NPCs. Separate regions of GANP show local homology to FG nucleoporins, the yeast mRNA export factor Sac3p, and the mammalian MCM3 acetyltransferase. GANP interacts with both NXF1 and NPCs and partitions between NPCs and the nuclear interior. GANP depletion inhibits mRNA export, with retention of mRNPs and NXF1 in punctate foci within the nucleus. The GANP N-terminal region that contains FG motifs interacts with the NXF1 FG-binding domain. Overexpression of this GANP fragment leads to nuclear accumulation of both poly(A)+RNA and NXF1. Treatment with transcription inhibitors redistributes GANP from NPCs into foci throughout the nucleus. These results establish GANP as an integral component of the mammalian mRNA export machinery and suggest a model whereby GANP facilitates the transfer of NXF1-containing mRNPs to NPCs.

Telomeres, a validated biomarker of aging, comprise multiple nucleotide repeats capping chromosomes that shorten with each cell cycle until a critical length is achieved, precipitating cell senescence. Only two previous studies focused on the effect of aging in ''normal'' liver tissue, but these studies were compromised by small sample size, limited age range, tissue derived from individuals with an increased risk of senescence, and the use of liver homogenates. We developed a robust large-volume, four-color quantitative fluorescent in situ hybridization technique to measure telomere length in large numbers of hepatocytes, Kupffer cells, hepatic stellate cells, CD4-positive and CD8-positive lymphocytes, and cholangiocytes. Following validation against the gold standard (Southern blotting), the technique was applied to normal archived paraffin-embedded liver tissue obtained following reperfusion of implanted donor liver. We studied 73 highly selected donors aged 5-79 years with a short medical illness preceding death and no history of liver disease, reperfusion injury, or steatosis and normal graft function 1-year posttransplantation. Cholangiocytes had significantly longer telomeres compared with all other intrahepatic lineages over a wide age range (P < 0.05). Age-related telomere attrition was restricted to sinusoidal cells (i.e., Kupffer cells [P 5 0.0054] and stellate cells [P 5 0.0001]). Cholangiocytes and hepatocytes showed no age-related telomere shortening. Conclusion: In normal liver and over a broad age range, cholangiocytes have longer telomeres than all other intrahepatic lineages. Age-related telomere length decline is restricted to Kupffer cells and stellate cells. (HEPATOLOGY 2012;56:1510-1520