In order to gather the most complete representation of the human protein–protein interaction network, we integrate information from five resources: the Human Protein Reference Database (HPRD) (33), BioGRID (34), IntAct (35), the Molecular INTeraction database (MINT) (36) and the Database of Interacting Proteins (DIP) (37). We only consider primary data on interactions between human proteins, i.e. putative interactions inferred from orthology relationships are discarded. The resulting non-redundant network is composed of 68 498 interactions among 11 988 proteins, derived from 19 886 independent literature reports (Table 1). Overall, we find 4621 human proteins that interact with cancer proteins. To provide a complete view of the network of cancer proteins, NCG also allows retrieving information on the systems-level properties for all these primary interactors. Table 1.Integration of protein–protein interaction dataDatabaseVersionProteinsInteractionsIndependent reportsHPRD (33)1 September 2007869734 93817 770BioGRID (34)1 February 2009716323 5888815IntAct (35)23 January 2009706622 1191374MINT (36)5 February 2009515112 6531210DIP (37)26 January 200911081326739NCG21 June 200911 98868 49819 886Data from five different sources are integrated in NCG. To derive a non-redundant version of the network, proteins are counted as number of non-redundant Entrez IDs.
