Rad is the prototypic member of a new class of Ras-related GTPases. Purification of the GTPase-activating protein (GAP) for Rad revealed nm23, a putative tumor metastasis suppressor and a development gene in Drosophila. Antibodies against nm23 depleted Rad-GAP activity from human skeletal muscle cytosol, and bacterially expressed nm23 reconstituted the activity. The GAP activity of nm23 was specific for Rad, was absent with the S105N putative dominant negative mutant of Rad, and was reduced with mutations of nm23. In the presence of ATP, GDP⅐Rad was also reconverted to GTP⅐Rad by the nucleoside diphosphate (NDP) kinase activity of nm23. Simultaneously, Rad regulated nm23 by enhancing its NDP kinase activity and decreasing its autophosphorylation. Melanoma cells transfected with wild-type Rad, but not the S105N-Rad, showed enhanced DNA synthesis in response to serum; this effect was lost with coexpression of nm23. Thus, the interaction of nm23 and Rad provides a potential novel mechanism for bidirectional, bimolecular regulation in which nm23 stimulates both GTP hydrolysis and GTP loading of Rad whereas Rad regulates activity of nm23. This interaction may play important roles in the effects of Rad on glucose metabolism and the effects of nm23 on tumor metastasis and developmental regulation. Ras-related GTP-binding proteins are a superfamily consisting of many members that play important roles in cell proliferation and differentiation (1), intracellular vesicular trafficking (2), cytoskeletal rearrangement (3), cell cycle regulation (4), and glucose transport into cells (5, 6). These GTPases cycle between GTP-bound (active) and GDP-bound states (inactive) in a controlled manner, stimulated by interaction with GTPaseactivating proteins (GAPs) present in the cytoplasm of the cells (7,8). Conversely, the reloading of the GTPases is made possible by the action of guanine nucleotide exchange factors (GEFs), which facilitates the exchange of free GTP for G protein-bound GDP (7), or is slowed by the presence of GDP dissociation inhibitors (9).Rad is the prototype of a new subfamily of Ras-related GTPases, which are of molecular mass 33-35 kDa and lack typical prenylation motifs at the C terminus. It was initially identified by subtraction cloning and is overexpressed in skeletal muscle of a subset of humans with type 2 diabetes (10). Overexpression of Rad in 3T3-L1 adipocytes and C2C12 myocytes causes a marked reduction in glucose uptake in response to insulin stimulation, suggesting that it contributes to the insulin resistance of diabetes (6). Rad also interacts with calmodulin and calmodulin kinase II (11) and ␤-tropomyosin (12). These interactions are enhanced by an increase in the calcium influx and favor the GDP-bound form of Rad. The other two members of Rad family are Gem͞Kir and Rem. Gem͞Kir was identified in activated T lymphocytes (13) and v-abl transformed pre-B cells (14). Rem was cloned as a PCR product by using primers derived from conserved regions of Rad and Gem͞Kir, is expressed in heart, lung, and oth...

Compared with the parent cell line, we did observe a dose-dependent decrease in growth factor-stimulated motility and a decrease in metastatic potential in two clones with four-and eighffold elevated nm23-H1 expression, whereas the proliferative activities were similar. We conclude that the decreased metastatic potential might be related to down-regulation of growth factor-stimulated motility.

In patients with advanced/metastatic cancer, brivanib demonstrates promising antiangiogenic and antitumor activity and manageable toxicity at doses ≤800 mg orally q.d., the recommended phase II study dose.

Mammalian cells express several isoforms of beta-thymosin, a major actin monomer sequestering factor, including thymosins beta4, beta10, and beta15. Differences in actin-binding properties of different beta-thymosin family members have not been investigated. We find that thymosin beta15 binds actin with a 2.4-fold higher affinity than does thymosin beta4. Mutational analysis was performed to determine the amino acid differences in thymosin beta15 that specify its increased actin-affinity. Previous work with thymosin beta4 identified an alpha-helical domain, as well as a conserved central motif, as crucial for actin binding. Mutational analysis confirms that these domains are also vital for actin binding in thymosin beta15, but that differences in these domains are not responsible for the variation in actin-binding properties between thymosins beta4 and beta15. Truncation of the unique C-terminal residues in thymosin beta15 inhibits actin binding, suggesting that this domain also has an important role in mediating actin-binding affinity. Replacement of the 10 C-terminal amino acids of thymosin beta15 with those of thymosin beta4 did, however, reduce the actin-binding affinity of the hybrid relative to thymosin beta15. Similarly, replacement of the thymosin beta4 C-terminal amino acids with those of thymosin beta15 led to increased actin binding. We conclude that functional differences between closely related beta-thymosin family members are, in part, specified by the C-terminal variability between these isoforms. Such differences may have consequences for situations where beta-thymosins are differentially expressed as in embryonic development and in cancer.