Systematic mapping of protein-protein interactions, or 'interactome' mapping, was initiated in model organisms, starting with defined biological processes and then expanding to the scale of the proteome. Although far from complete, such maps have revealed global topological and dynamic features of interactome networks that relate to known biological properties, suggesting that a human interactome map will provide insight into development and disease mechanisms at a systems level. Here we describe an initial version of a proteome-scale map of human binary protein-protein interactions. Using a stringent, high-throughput yeast two-hybrid system, we tested pairwise interactions among the products of approximately 8,100 currently available Gateway-cloned open reading frames and detected approximately 2,800 interactions. This data set, called CCSB-HI1, has a verification rate of approximately 78% as revealed by an independent co-affinity purification assay, and correlates significantly with other biological attributes. The CCSB-HI1 data set increases by approximately 70% the set of available binary interactions within the tested space and reveals more than 300 new connections to over 100 disease-associated proteins. This work represents an important step towards a systematic and comprehensive human interactome project.

Several attempts have been made to systematically map protein-protein interaction, or 'interactome', networks. However, it remains difficult to assess the quality and coverage of existing data sets. Here we describe a framework that uses an empirically-based approach to rigorously dissect quality parameters of currently available human interactome maps. Our results indicate that high-throughput yeast two-hybrid (HT-Y2H) interactions for human proteins are more precise than literature-curated interactions supported by a single publication, suggesting that HT-Y2H is suitable to map a significant portion of the human interactome. We estimate that the human interactome contains approximately 130,000 binary interactions, most of which remain to be mapped. Similar to estimates of DNA sequence data quality and genome size early in the Human Genome Project, estimates of protein interaction data quality and interactome size are crucial to establish the magnitude of the task of comprehensive human interactome mapping and to elucidate a path toward this goal.

To characterize the function of a novel Src homology 3 (SH3) adapter protein termed NESH, we have established transfectants stably expressing NESH. We observed that every clone of NESH transfectants caused a marked reduction in motility, although the clones exhibited no significant differences in intrinsic cell growth compared with the control cells in vitro. The NESH transfectants also exhibited significant reduction in tumor metastatic potential in vivo. We found that NESH expression is frequently lost in invasive cancer cell lines despite its ubiquitous expression in normal tissues. The SH3 domain of NESH seems to interact with p21-activated kinase (PAK), which is involved in regulation of cell motility. Furthermore, a significant decrease in PAK phosphorylation at (402)Thr was found in NESH transfectants. Taken together, these results suggest that NESH inhibits ectopic metastasis of tumor cells as well as cell migration through interaction with intracellular molecules such as PAK that are essential for cell motility.

Abl interactor (Abi) was identified as an Abl tyrosine kinase-binding protein and subsequently shown to be a component of the macromolecular Abi/WAVE complex, which is a key regulator of Rac-dependent actin polymerization. Previous studies showed that Abi-1 promotes c-Abl-mediated phosphorylation of Mammalian Enabled (Mena) and WAVE2. In addition to Abi-1, mammals possess Abi-2 and NESH (Abi-3). In this study, we compared the three Abi proteins in terms of the promotion of c-Abl-mediated phosphorylation and the formation of Abi/WAVE complex. Although Abi-2, like Abi-1, promoted the c-Abl-mediated phosphorylation of Mena and WAVE2, NESH (Abi-3) had no such effect. This difference was likely due to their binding abilities as to c-Abl. Immunoprecipitation revealed that NESH (Abi-3) is present in the Abi/WAVE complex. Our results suggest that NESH (Abi-3), like Abi-1 and Abi-2, is a component of the Abi/WAVE complex, but likely plays a different role in the regulation of c-Abl.

To characterize the function of a novel Src homology 3 (SH3) adapter protein termed NESH, we have established transfectants stably expressing NESH. We observed that every clone of NESH transfectants caused a marked reduction in motility, although the clones exhibited no significant differences in intrinsic cell growth compared with the control cells in vitro. The NESH transfectants also exhibited significant reduction in tumor metastatic potential in vivo. We found that NESH expression is frequently lost in invasive cancer cell lines despite its ubiquitous expression in normal tissues. The SH3 domain of NESH seems to interact with p21-activated kinase (PAK), which is involved in regulation of cell motility. Furthermore, a significant decrease in PAK phosphorylation at (402)Thr was found in NESH transfectants. Taken together, these results suggest that NESH inhibits ectopic metastasis of tumor cells as well as cell migration through interaction with intracellular molecules such as PAK that are essential for cell motility.