The involvement of Ral and its downstream molecules in receptor-mediated endocytosis was examined. Expression of either Ral G23V or Ral S28N , which are known to be constitutively active and dominantnegative forms, respectively, in A431 cells blocked internalization of epidermal growth factor (EGF). Stable expression of Ral G23V or Ral S28N in CHO-IR cells also inhibited internalization of insulin. Internalization of EGF and insulin was not affected by fulllength RalBP1 which is an effector protein of Ral, but was inhibited by its C-terminal region which binds directly to Ral and POB1. POB1 is a binding protein of RalBP1 and has the Eps15 homology (EH) domain. Deletion mutants of POB1 inhibited internalization of EGF and insulin. However, internalization of transferrin was unaffected by Ral, RalBP1, POB1 and their mutants. Epsin and Eps15 have been reported to be involved in the regulation of endocytosis of the receptors for EGF and transferrin. The EH domain of POB1 bound directly to Epsin and Eps15. Taken together with the observation that EGF and insulin activate Ral, these results suggest that Ral, RalBP1 and POB1 transmit the signal from the receptors to Epsin and Eps15, thereby regulating ligand-dependent receptormediated endocytosis.

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When Axin, a negative regulator of the Wnt signaling pathway, was expressed in COS cells, it coeluted with glycogen synthase kinase-3b (GSK-3b), b-catenin, and adenomatous polyposis coli protein (APC) in a high molecular weight fraction on gel ®ltration column chromatography. In this fraction, GSK-3b, b-catenin, and APC were co-precipitated with Axin. Although bcatenin was detected in the high molecular weight fraction in L cells on gel ®ltration column chromatography, addition of conditioned medium expressing Wnt3a to the cells increased b-catenin in the low molecular weight fraction. However, Wnt-3a-dependent accumulation of b-catenin was greatly inhibited in L cells stably expressing Axin. Axin also suppressed Wnt-3a-dependent activation of Tcf-4 which binds to b-catenin and acts as a transcription factor. These results suggest that Axin forms a complex with GSK-3b, b-catenin, and APC, resulting in the stimulation of the degradation of bcatenin and that Wnt-3a induces the dissociation of bcatenin from the Axin complex and accumulates bcatenin.

Secondary ion mass spectrometry measurements show that Earth's representative lower mantle minerals synthesized in a natural peridotitic composition can dissolve considerable amounts of hydrogen. Both MgSiO3-rich perovskite and magnesiowüstite contain about 0.2 weight percent (wt%) H2O, and CaSiO3-rich perovskite contains about 0.4 wt% H2O. The OH absorption bands in Mg-perovskite and magnesiowüstite were also confirmed with the use of infrared microspectroscopic measurements. Earth's lower mantle may store about five times more H2O than the oceans.