== The x-axis contains 459 kinase genes and the y-axis contains GO-BP classes. functional associations of individual cancer associated kinase genes. In summary, we report here a systematic classification of kinases based on the bioinformatic analysis of their expression in human tissues and diseases, AZD3759 as well as grouping of tissues and tumor types according to the similarity of their kinome transcription. == Introduction == Much of our knowledge around the functions of genes, both in health and disease, is derived from molecular biological experiments with specific model systems, which often provide a biased and context-specific view of gene functions. Inin vivoin human tissues, gene function often varies from one organ to another as well as across different disease says. The 518 human kinases represent an intensively studied class of proteins which may regulate the activity of up to a third of all human proteins by phosphorylation[1]. Because of their central role in cell signalling, kinases are important targets for drug development, particularly in cancer[2],[3],[4],[5]. The role of kinase genes in cancer has been systematically studied at AZD3759 the genomic DNA level. For example, a recent cancer gene census[6]lists 33 kinases that may undergo genetic alterations in cancer. Numerous reports have also been published around Rabbit polyclonal to HAtag the differential expression of kinase genes and proteins in specific types of cancers, but these results are highly biased towards the most commonly studied kinase genes and towards common cancer forms. Furthermore, published data are often contradictory, precluding an assessment of the overall importance of kinases across different diseases. Kinase genes are known to be strongly regulated at the protein level, but transcriptional level regulation has not been comprehensively studied. Meta-analyses of large publicly available microarray data sources, such as GeneExpressionOmnibus[7]and ArrayExpress[8]have been shown to facilitate the analysis gene expression across healthy and disease says[9],[10],[11]. However, due to the variability of microarray platforms from one study to another, most investigators have analyzed each of the multiple datasets separately[12],[13],[14],[15],[16],[17], focusing on e.g. cancer-normal comparisons within a tissue type. We reasoned that a direct systematic comparison of kinase gene expression levels across all cells, tissues and disease says would be more informative. We have previously developed and reported a methodology for integrating very large quantities of human expression data into a unified format in order to AZD3759 create a comprehensive reference database of the human transcriptome, GeneSapiens[18]. Here, we made use of this methodology in order to perform the first systematic study of kinase gene expression levels and co-expression networks across thousands of healthy and malignant tissues. == Results == == Definition of the transcriptional activity of kinase genes == The analysis focused on 459 genes encoding proteins with protein kinase activity (Table S1) for which sufficient expression data were available in the GeneSapiens database[18]. Expression levels of kinases were first analyzed across 55 major tumor types (n = 4078 samples) and 44 healthy tissues (n = 1603 samples) (Table S2). Expression of kinase genes across these 99 tissue types was first analyzed in a binary fashion, defining those tissues and tumor types where each kinase gene was transcriptionally active. Previously such binary level analysis has been shown to be a useful method to reduce noise[19],[20]. A kinase gene was defined to be transcriptionally active in a tissue if its median expression in the tissue was more than the predefined background expression level (Physique S1) across all healthy tissue types. We defined the background gene expression activity for each kinase across the 1603 samples representing the healthy human transcriptome (seemethodssection andFigure S1). Any kinase gene whose expression levels in healthy or tumor tissues exceeding this range were nominated as.