Apoptosis screening of human chromosome 21 proteins reveals novel cell death regulators

S-phase kinase-associated protein 2 knockdown blocks colorectal cancer growth via regulation of both p27 and p16 expression

The objective of this study was to determine the role and mechanism of S-phase kinase-associated protein 2 (Skp2) in colorectal cancer cell proliferation and survival both in vitro and in vivo. Adenoviral vector expressing Skp2 short hairpin RNA was transduced into SW480 cells. The effects of Skp2 on cell cycle and survival were assessed by Flow Cytometry. Cell proliferation was analyzed by MTT assay. The expression of cell cycle regulators p16 and p27 were measured by western blot. In vivo, human colorectal cancer was produced by xenograft of cancer cells in nude mouse. Tumor growth inhibitory rate was calculated to generate growth curve. Tumor growth was monitored by examining proliferating cell nuclear antigen expression, whereas tumor cell apoptosis was detected by TdT-mediated dUTP nick-end labeling (TUNEL) staining. Knockdown of Skp2 blocked SW480 tumor cell growth and induced cell apoptosis. Skp2 appeared to be very important for the progression of cell cycle at G1/S phase. In vivo, blockade of Skp2 expression inhibited tumor growth and induced tumor apoptosis. Mechanistically, Skp2 regulated the expression of both p27 and p16 both in vitro and in vivo. The conclusion that we derive from this study is that Skp2 regulates colorectal cancer cell growth by inhibiting the expression of cell cycle regulator p27 and p16.

Senescence in amniocytes and placentas from trisomy 21 pregnancies

OBJECTIVE

Senescence has been described as a stable cell proliferation arrest resulting from the progression of primary human fibroblasts through a finite number of population doublings in vitro. Accelerated telomere shortening was observed in pregnancies complicated by intrauterine growth restriction, in placentas of diabetic mothers and trisomy 21 amniocytes. We hypothesized that under conditions of stress, telomeres in placentas will be shorter and there will be more cells with the senescence phenotype.

METHODS

The two study groups included placental biopsies from 7 cases of trisomy 21 and amniocytes from 10 cases of trisomy 21. The control groups consisted of placental biopsies from 6 cases and amniocytes from 10 pregnancies with a normal karyotype. The samples were analyzed for the presence of senescent cells based on the number of fragments in each cell.

RESULTS

A significantly higher percentage of cells in the senescent state, based on a higher percentage of cells with more fragmentations, were found in the amniocytes (20.8%) and in trophoblasts (94.3%) from placentas with trisomy 21 compared to the control groups.

CONCLUSION

Among other genetic instability parameters, trisomy 21 amniocytes and trophoblasts express a higher prevalence of senescent cells than were previously reported.

Dissecting mitochondrial apoptosis pathways by gain-of-function cell culture screens

While more primitive organism such as Caenorhabditis elegans and Drosophila melanogaster feature a limited, and by now probably mostly known, array of basic cell death factors, the mammalian cell is replete with additional regulators of the cell's demise. This abundance of apoptosis mediators has made it imperative to set up a systematic inventory of mammalian cell death genes. Genetic screens in this biological system have recently uncovered the rich diversity of cell death signalling and have in particular highlighted mitochondria as an organelle loaded with apoptosis regulators. Many of the screens that have addressed this utilised the novel technique of RNA interference but some also looked at gain-of-functions with transfected cDNAs. Here we give an overview of the rationale for the latter approach, present the genes discovered by this strategy and in particular describe the involvement of mitochondria and their signalling pathways defined by those genes.

VEGF is essential for the growth and migration of human hepatocellular carcinoma cells

Vascular endothelial growth factor (VEGF) plays a crucial role in tumor angiogenesis. VEGF induces new vessel formation and tumor growth by inducing mitogenesis and chemotaxis of normal endothelial cells and increasing vascular permeability. However, little is known about VEGF function in the proliferation, survival or migration of hepatocellular carcinoma cells (HCC). In the present study, we have found that VEGF receptors are expressed in HCC line BEL7402 and human HCC specimens. Importantly, VEGF receptor expression correlates with the development of the carcinoma. By using a comprehensive approaches including TUNEL assay, transwell and wound healing assays, migration and invasion assays, adhesion assay, western blot and quantitative RT-PCR, we have shown that knockdown of VEGF165 expression by shRNA inhibits the proliferation, migration, survival and adhesion ability of BEL7402. Knockdown of VEGF165 decreased the expression of NF-κB p65 and PKCα while increased the expression of p53 signaling molecules, suggesting that VEGF functions in HCC proliferation and migration are mediated by P65, PKCα and/or p53.

Identification of transcription factor E3 (TFE3) as a receptor-independent activator of Gα16: gene regulation by nuclear Gα subunit and its activator

Receptor-independent G-protein regulators provide diverse mechanisms for signal input to G-protein-based signaling systems, revealing unexpected functional roles for G-proteins. As part of a broader effort to identify disease-specific regulators for heterotrimeric G-proteins, we screened for such proteins in cardiac hypertrophy using a yeast-based functional screen of mammalian cDNAs as a discovery platform. We report the identification of three transcription factors belonging to the same family, transcription factor E3 (TFE3), microphthalmia-associated transcription factor, and transcription factor EB, as novel receptor-independent activators of G-protein signaling selective for Gα(16). TFE3 and Gα(16) were both up-regulated in cardiac hypertrophy initiated by transverse aortic constriction. In protein interaction studies in vitro, TFE3 formed a complex with Gα(16) but not with Gα(i3) or Gα(s). Although increased expression of TFE3 in heterologous systems had no influence on receptor-mediated Gα(16) signaling at the plasma membrane, TFE3 actually translocated Gα(16) to the nucleus, leading to the induction of claudin 14 expression, a key component of membrane structure in cardiomyocytes. The induction of claudin 14 was dependent on both the accumulation and activation of Gα(16) by TFE3 in the nucleus. These findings indicate that TFE3 and Gα(16) are up-regulated under pathologic conditions and are involved in a novel mechanism of transcriptional regulation via the relocalization and activation of Gα(16).

High-throughput subcellular protein localization using transfected-cell arrays. Subcellular protein localization using cell arrays

Knowledge of protein localization within the cellular environment is critical for understanding the function of the protein and its regulatory networks. Protein localization data, however, have traditionally been accumulated from single or small-scale experiments. Transfected-cell arrays (TCAs) represent a robust alternative for the high-throughput analysis of gene/protein functions in mammalian cells. For protein localization studies, TCAs not only allow for the transfection and expression of over 1,000 genes in a single experiment but also make it feasible for simultaneous co-localization analyses of different subcellular compartments. In this chapter, we have described a protein co-localization protocol using transfected human cell arrays for a large set of cellular compartments, including the nucleus, ER, Golgi apparatus, mitochondrion, lysosome, peroxisome, and the microtubules, intermediate filaments and actin filaments. The application of these "organelle-co-localized cell arrays" facilitates the precise determination of the localizations of numerous recombinant proteins in a single experiment, making it currently the most efficient technique for high-throughput protein co-localization screening.

DLC-1 as a modulator of proliferation, apoptosis and migration in Burkitt's lymphoma cells

Deleted in liver cancer-1(DLC-1) gene expression is frequently down-regulated or deleted in many types of human cancer. To evaluate whether DLC-1 could be a therapeutic target for non-Hodgkin lymphoma (NHL), we examined the expressions of DLC-1 in Burkitt's lymphoma (BL) cell lines and tested the effects of DLC-1 on cellular growth and migration in BL cells. DLC-1 expression was not detectable in two human BL cell lines, Raji and Daudi, by reverse transcription-PCR. The transfer of DLC-1 into Raji and Daudi cell lines caused a significant inhibition in cell proliferation. This inhibitory effect on cell proliferation in BL cell lines was accompanied by induction of apoptosis. Furthermore, restoration of DLC-1 expression in BL cells had a significant inhibitory effect on migration. Our findings suggest that DLC-1 may play an important role in lymphoma by acting as a bona fide new tumor suppressor gene.