Identification of AF-6 and Canoe as putative targets for Ras

Ras (Ha-Ras, Ki-Ras, N-Ras) is implicated in the regulation of various cell functions such as gene expression and cell proliferation downstream from specific extracellular signals. Here, we partially purified a Ras-interacting protein with molecular mass of about 180 kDa (p180) from bovine brain membrane extract by glutathione S-transferase (GST)-Ha-Ras affinity column chromatography. This protein bound to the GTPγS (guanosine 5'-(3-O- thio)triphosphate, a nonhydrolyzable GTP analog)-GST-Ha-Ras affinity column but not to those containing GDP·GST-Ha-Ras or GTPγS·GST-Ha-Ras with a mutation in the effector domain (Ha-Ras(A38)). The amino acid sequences of the peptides derived from p180 were almost identical to those of human AF-6 that is identified as the fusion partner of the ALL-1 protein. The ALL-1/AF- 6 chimeric protein is the critical product of the t (6:11) abnormality associated with some human leukemia. AF-6 has a GLGF/Dlg homology repeat (DHR) motif and shows a high degree of sequence similarity with Drosophila Canoe, which is assumed to function downstream from Notch in a common developmental pathway. The recombinant N-terminal domain of AF-6 and Canoe specifically interacted with GTPγS·GST-Ha-Ras. The known Ras target c-Raf- 1 inhibited the interaction of AF-6 with GTPγS·GST-Ha-Ras. These results indicate that AF-6 and Canoe are putative targets for Ras.