Co-expression analysis reveals a group of genes potentially involved in regulation of plant response to iron-deficiency

Iron (Fe) is an essential element for plant growth and development. Iron deficiency results in abnormal metabolisms from respiration to photosynthesis. Exploration of Fe-deficient responsive genes and their networks is critically important to understand molecular mechanisms leading to the plant adaptation to soil Fe-limitation. Co-expression genes are a cluster of genes that have a similar expression pattern to execute relatively biological functions at a stage of development or under a certain environmental condition. They may share a common regulatory mechanism. In this study, we investigated Fe-starved-related co-expression genes from Arabidopsis. From the biological process GO annotation of TAIR (The Arabidopsis Information Resource), 180 iron-deficient responsive genes were detected. Using ATTED-II database, we generated six gene co-expression networks. Among these, two modules of PYE and IRT1 were successfully constructed. There are 30 co-expression genes that are incorporated in the two modules (12 in PYE-module and 18 in IRT1-module). Sixteen of the co-expression genes were well characterized. The remaining genes (14) are poorly or not functionally identified with iron stress. Validation of the 14 genes using real-time PCR showed differential expression under iron-deficiency. Most of the co-expression genes (23/30) could be validated in pye and fit mutant plants with iron-deficiency. We further identified iron-responsive cis-elements upstream of the co-expression genes and found that 22 out of 30 genes contain the iron-responsive motif IDE1. Furthermore, some auxin and ethylene-responsive elements were detected in the promoters of the co-expression genes. These results suggest that some of the genes can be also involved in iron stress response through the phytohormone-responsive pathways.     

Systematic proteomic analysis of human hepotacellular carcinoma cells reveals molecular pathways and networks involved in metastasis

Systematic proteomic studying of the mechanism of hepatocellular carcinoma (HCC) metastasis remains challenging. We performed comparative proteomic and pathway analysis of four human metastatic HCC cell lines to identify metastasis-associated proteins. These HCC cell lines had a similar genetic background but with an increasing potential of metastasis. Using a combination of two dimensional electrophoresis (2-DE) and MALDI-TOF mass spectrometry, a total of 125 proteins and their post-translational modification forms or isoforms were found to be differentially expressed in the cell lines. Among them, 29 were gradually up-regulated whereas 17 were down-regulated with increasing metastatic potential. Instead of a traditional single-gene readout, global bioinformatics analysis was carried out, which revealed that the glycolysis pathway was the most significantly enriched pathway. The heat shock proteins (HSPs) centered and NF-kappaB centered networks were also enriched in the result, which may imply the key function of inflaming on metastasis. Meanwhile, knockdown of HDGF, an up-regulated protein and a target of NF-kappaB, induced cell apoptosis in the metastatic HCC cells. This work provides a demonstration that a combination of bioinformatics and comparative proteomics can help in finding out potential biomarkers associated with HCC metastasis on the level of pathways.     

Signaling pathways involved in PDGF-evoked cellular responses in human RPE cells

We examined whether PDGF may directly stimulate the expression of VEGF by retinal pigment epithelial (RPE) cells in vitro, and the involvement of three signal transduction pathways in the regulation of PDGF-evoked cell proliferation, migration, and production of VEGF-A was investigated. PDGF stimulated the gene and protein expression of VEGF-A by RPE cells, and increased cell proliferation and chemotaxis. PDGF activated all signaling pathways investigated, as determined by increased phosphorylation levels of ERK1/2, p38, and Akt proteins. The three signaling pathways were involved in the mediation of PDGF-evoked cell proliferation, while p38 and PI3K mediated cell migration, and PI3K mediated secretion of VEGF-A. In addition to VEGF-A, the cells expressed mRNAs for various members of the VEGF family and for their receptors, including VEGF-B, -C, -D, flt-1, and KDR. The data indicate that PDGF selectively stimulates the expression of VEGF-A in RPE cells. PDGF evokes at least three signal transduction pathways which are differentially involved in various cellular responses.     

Proteomic analysis by SILAC and 2D-DIGE reveals radiation-induced endothelial response: four key pathways

Epidemiological data show that ionising radiation increases the risk of cardiovascular disease. The endothelium is one of the main targets of radiation-induced damage. Rapid radiation-induced alterations in the biological processes were investigated after exposure to a clinically relevant radiation dose (2.5 Gy gamma radiation). The changes in protein expression were determined using the human endothelial cell line EA.hy926 as a model. Two complementary proteomic approaches, SILAC (Stable Isotope Labelling with Amino acids in Cell culture) and 2D-DIGE (Two Dimensional Difference-in-Gel-Electrophoresis) were used. The proteomes of the endothelial cells were analysed 4h and 24h after irradiation. Differentially expressed proteins were identified and quantified by MALDI-TOF/TOF and LTQ Orbitrap tandem mass spectrometry. The deregulated proteins were mainly categorised in four key pathways: (i) glycolysis/gluconeogenesis and synthesis/degradation of ketone bodies, (ii) oxidative phosphorylation, (iii) Rho-mediated cell motility and (iv) non-homologous end joining. We suggest that these alterations facilitate the repair processes needed to overcome the stress caused by irradiation and are indicative of the vascular damage leading to radiation-induced cardio- and cerebrovascular impairment.     

Functional genomics reveals diverse cellular processes that modulate tumor cell response to oxaliplatin

Oxaliplatin is widely used to treat colorectal cancer, as both adjuvant therapy for resected disease and palliative treatment of metastatic disease. However, a significant number of patients experience serious side effects, including prolonged neurotoxicity, from oxaliplatin treatment creating an urgent need for biomarkers of oxaliplatin response or resistance to direct therapy to those most likely to benefit. As a first step to improve selection of patients for oxaliplatin-based chemotherapy, we have conducted an in vitro cell-based small interfering RNA (siRNA) screen of 500 genes aimed at identifying genes whose loss of expression alters tumor cell response to oxaliplatin. The siRNA screen identified twenty-seven genes, which when silenced, significantly altered colon tumor cell line sensitivity to oxaliplatin. Silencing of a group of putative resistance genes increased the extent of oxaliplatin-mediated DNA damage and inhibited cell-cycle progression in oxaliplatin-treated cells. The activity of several signaling nodes, including AKT1 and MEK1, was also altered. We used cDNA transfection to overexpress two genes (LTBR and TMEM30A) that were identified in the siRNA screen as mediators of oxaliplatin sensitivity. In both instances, overexpression conferred resistance to oxaliplatin. In summary, this study identified numerous putative predictive biomarkers of response to oxaliplatin that should be studied further in patient specimens for potential clinical application. Diverse gene networks seem to influence tumor survival in response to DNA damage by oxaliplatin. Finally, those genes whose loss of expression (or function) is related to oxaliplatin sensitivity may be promising therapeutic targets to increase patient response to oxaliplatin.