Targeting the INCENP IN-box–Aurora B interaction to inhibit CPC activity in vivo

The chromosome passenger complex (CPC) is an essential regulator of mitosis and cytokinesis. The CPC consists of Aurora B kinase, inner centromere protein (INCENP), and the targeting subunits survivin and borealin/Dasra B. INCENP is a scaffolding subunit for the CPC and activates Aurora B via its conserved IN-box domain. We show that overexpression of soluble IN-box in HeLa cells affects endogenous CPC localization and produces a significant increase in multinucleated and micronucleated cells consistent with CPC loss of function. The dominant-negative effect of soluble IN-box expression depends on residues corresponding to hINCENP W845 and/or F881, suggesting that these are essential for Aurora B binding in vivo. We then screened a targeted library of small (five to nine residues long) circular peptide (CP) IN-box fragments generated using split intein circular ligation of proteins and peptides (SICLOPPS) methodology. We identified a number of CPs that caused modest but reproducible increases in rates of multinucleated and micronucleated cells. Our results provide proof of concept that inhibition of the Aurora B–IN-box interaction is a viable strategy for interfering with CPC function in vivo.     

Gene expression signature of human HepG2 cell line

Hepatocellular carcinoma (HCC) is the fifth most common cancer worldwide and is associated with various clinico-pathological characteristics such as genetic mutations and viral infections. Therefore, numerous laboratories look out for identifying always new putative markers for the improvement of HCC diagnosis/prognosis. Many molecular profiling studies investigated gene expression changes related to HCC. HepG2 represents a pure cell line of human liver carcinoma, often used as HCC model due to the absence of viral infection. In this study we compare gene expression profiles associated with HepG2 (as HCC model) and normal hepatocyte cells by microarray technology. Hierarchical cluster analysis of genes evidenced that 2646 genes significantly down-regulated in HepG2 cells compared to hepatocytes whereas a further 3586 genes significantly up-regulated. By using the Ingenuity Pathway Analysis (IPA) program, we have classified the genes that were differently expressed and studied the functional networks correlating these genes in the complete human interactome. Moreover, to confirm the differentially expressed genes as well as the reliability of our microarray data, we performed a quantitative Real time RT-PCR analysis on 9 up-regulated and 11 down-regulated genes, respectively. In conclusion this work i) provides a gene signature of human hepatoma cells showing genes that change their expression as a consequence of liver cancer in the absence of any genetic mutations or viral infection, ii) evidences new differently expressed genes found in our signature compared to previous published studies and iii) suggests some genes on which to focus future studies to understand if they can be used to improve the HCC prognosis/diagnosis.     

EVI5 protein associates with the INCENP-aurora B kinase-survivin chromosomal passenger complex and is involved in the completion of cytokinesis

EVI5 has been shown to be a novel centrosomal protein in interphase cells. In this report, we demonstrate using immunofluorescence microscopy that EVI5 has a dynamic distribution during mitosis, being associated with the mitotic spindle through anaphase and remaining within the midzone and midbody until completion of cytokinesis. Knockdown of EVI5 using siRNA results in a multinucleate phenotype, which is consistent with an essential role for this protein in the completion of cytokinesis. The EVI5 protein also undergoes posttranslational modifications during the cell cycle, which involve phosphorylation in early mitosis and proteolytic cleavage during late mitosis and cytokinesis. Since the subcellular distribution of the EVI5 protein was similar to that characteristic of chromosomal passenger proteins during the terminal stages of cytokinesis, we used immunoprecipitation and GST pull-down approaches to demonstrate that EVI5 is associated with the aurora B kinase protein complex (INCENP, aurora B kinase and survivin). Together, these data provide evidence that EVI5 is an essential component of the protein machinery facilitating the final stages of cell septation at the end of mitosis.