Migrating cells do not proliferate and vice versa, but the mechanism involved remains unknown. Ghosh et al. reveal how this cellular decision is made by showing that a Gαi–GIV molecular complex interacts with EGF receptor and programs growth factor signaling, triggering migration when assembled and favoring mitosis when assembly is prevented.

Although several non-receptor activators of heterotrimeric G proteins have been identified, the structural features of G proteins that determine their interaction with such activators and the subsequent biological effects are poorly understood. Here we investigated the structural determinants in G␣ i3 necessary for its regulation by GIV/girdin, a guanine-nucleotide exchange factor (GEF) that activates G␣ i subunits. Using G protein activity and in vitro pulldown assays we demonstrate that G␣ i3 is a better substrate for GIV than the highly homologous G␣ o . We identified Trp-258 in the G␣ i subunit as a novel structural determinant for GIV binding by comparing GIV binding to G␣ i3 /G␣ o chimeras. Mutation of Trp-258 to the corresponding Phe in G␣ o decreased GIV binding in vitro and in cultured cells but did not perturb interaction with other G␣-binding partners, i.e. G␤␥, AGS3 (a guanine nucleotide dissociation inhibitor), GAIP/ RGS19 (a GTPase-activating protein), and LPAR1 (a G proteincoupled receptor). Activation of G␣ i3 by GIV was also dramatically reduced when Trp-258 was replaced with Tyr, Leu, Ser, His, Asp, or Ala, highlighting that Trp is required for maximal activation. Moreover, when mutant G␣ i3 W258F was expressed in HeLa cells they failed to undergo cell migration and to enhance Akt signaling after growth factor or G protein-coupled receptor stimulation. Thus activation of G␣ i3 by GIV is essential for biological functions associated with G␣ i3 activation. In conclusion, we have discovered a novel structural determinant on G␣ i that plays a key role in defining the selectivity and efficiency of the GEF activity of GIV on G␣ i and that represents an attractive target site for designing small molecules to disrupt the G␣ i -GIV interface for therapeutic purposes.

This work introduces a nonreceptor GEF for Gαi subunits as a regulator of autophagy. The authors reveal how growth factors reversibly regulate autophagy by a unique mechanism that involves reversible regulation of Gαi3 activity by AGS3, a GDI, and GIV, a GEF, during initiation and reversal of autophagy, respectively.

GIV (Gα-interacting vesicle-associated protein; also known as Girdin), enhances Akt activation downstream of multiple growth factor– and G-protein–coupled receptors to trigger cell migration and cancer invasion. Here we demonstrate that GIV is a tyrosine phosphoprotein that directly binds to and activates phosphoinositide 3-kinase (PI3K). Upon ligand stimulation of various receptors, GIV was phosphorylated at Tyr1764 and Tyr1798 by both receptor and non-receptor tyrosine kinases. These phosphorylation events enabled direct binding of GIV to the N- and C-terminal SH2 domains of p85α, a regulatory subunit of PI3K, stabilized receptor association with PI3K, and enhanced PI3K activity at the plasma membrane to trigger cell migration. Tyrosine phosphorylation of GIV and its association with p85α increased during metastatic progression of a breast carcinoma. These results suggest a mechanism by which multiple receptors activate PI3K through tyrosine phosphorylation of GIV, thereby making the GIVPI3K interaction a potential therapeutic target within the PI3K-Akt pathway.

The zebrafish is emerging as a model organism for the safety assessment and hazard ranking of engineered nanomaterials. In this Communication, the implementation of a roboticized high‐throughput screening (HTS) platform with automated image analysis is demonstrated to assess the impact of dissolvable oxide nanoparticles on embryo hatching. It is further demonstrated that this hatching interference is mechanistically linked to an effect on the metalloprotease, ZHE 1, which is responsible for degradation of the chorionic membrane. The data indicate that 4 of 24 metal oxide nanoparticles (CuO, ZnO, Cr2O3, and NiO) could interfere with embryo hatching by a chelator‐sensitive mechanism that involves ligation of critical histidines in the ZHE1 center by the shed metal ions. A recombinant ZHE1 enzymatic assay is established to demonstrate that the dialysates from the same materials responsible for hatching interference also inhibit ZHE1 activity in a dose‐dependent fashion. A peptide‐based BLAST search identifies several additional aquatic species that express enzymes with homologous histidine‐based catalytic centers, suggesting that the ZHE1 mechanistic paradigm could be used to predict the toxicity of a large number of oxide nanoparticles that pose a hazard to aquatic species.