A PDZ domain protein interacts with the C-terminal tail of the insulin-like growth factor-1 receptor but not with the insulin receptor.

In this study, we report on the isolation of a PDZ domain protein, here designated as IIP-1, insulin-like growth factor-1 (IGF-1) receptor-interacting protein-1, which binds to the IGF-1 receptor, but not to the related insulin receptor, and which is involved in the regulation of cell motility. The interaction between the IGF-1 receptor and IIP-1 as well as a splice variant IIP-1/p26 was demonstrated in the yeast two-hybrid system. Using co-precipitation experiments, we confirmed the interaction in transfected cells as well as in vitro. Analysis of deletion mutants indicates that the PDZ domain of IIP-1 mediates interaction with the C-terminal tail of the IGF-1 receptor (serine-threonine-cysteine). This finding demonstrates that the C terminus of the IGF-1 receptor acts as novel PDZ domain binding site. Immunofluorescence analysis revealed an overlapping localization of IIP-1 and the IGF-1 receptor in the breast cancer cell line MCF-7. A functional connection between IIP-1 and the IGF-1 receptor is further supported by the finding that the level of expression of IIP-1 and the IGF-1 receptor strongly correlates in different normal and cancer cells. Furthermore, overexpression of IIP-1 resulted in an attenuation of migration of MCF-7 cells, which is one of the biological activities mediated by the IGF-1 signaling system.

Negative regulation of Ros receptor tyrosine kinase signaling. An epithelial function of the SH2 domain protein tyrosine phosphatase SHP-1.

Male "viable motheaten" (me(v)) mice, with a naturally occurring mutation in the gene of the SH2 domain protein tyrosine phosphatase SHP-1, are sterile. Known defects in sperm maturation in these mice correlate with an impaired differentiation of the epididymis, which has similarities to the phenotype of mice with a targeted inactivation of the Ros receptor tyrosine kinase. Ros and SHP-1 are coexpressed in epididymal epithelium, and elevated phosphorylation of Ros in the epididymis of me(v) mice suggests that Ros signaling is under control of SHP-1 in vivo. Phosphorylated Ros strongly and directly associates with SHP-1 in yeast two-hybrid, glutathione S-transferase pull-down, and coimmunoprecipitation experiments. Strong binding of SHP-1 to Ros is selective compared to six other receptor tyrosine kinases. The interaction is mediated by the SHP-1 NH(2)-terminal SH2 domain and Ros phosphotyrosine 2267. Overexpression of SHP-1 results in Ros dephosphorylation and effectively downregulates Ros-dependent proliferation and transformation. We propose that SHP-1 is an important downstream regulator of Ros signaling.

Interaction of the Grb7 adapter protein with Rnd1, a new member of the Rho family.

Grb7 is a member of a family of molecular adapters which are able to contribute positively but also negatively to signal transduction and whose precise roles remain obscure. Rnd1 is a member of the Rho family, but, as opposed to usual GTPases, it is constitutively bound to GTP. We show here that Rnd1 and Grb7 interact, in two-hybrid assays, in vitro, and in pull-down experiments performed with SK-BR3, a breast cancer cell line that overexpresses Grb7. This interaction involves switch II loop of Rnd1, a region crucial for guanine nucleotide exchange in all GTPases, and a Grb7 SH2 domain, a region crucial for Grb7 interaction with several activated receptors. The contribution of the interaction between Rnd1 and Grb7 to their respective functions and properties is discussed.