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During ageing of primary mouse embryonic fibroblasts, cyclin D1 (green) relocalizes from the nucleus (blue) to the cytosol(the actin cytoskeleton is shown in red).p877
The RhoGTPases Rac and Rho are important for orchestrating cytoskeletal dynamics during cell migration and crosstalk to antagonize each others' activities. The discovery of a Rac GTPase activating protein (GAP) that is regulated by Rho and Rho kinase (ROCK) provides a new basis for this crosstalk.
Actin filament branch initiation by the Arp2/3 complex requires that the Arp2 and Arp3 subunits are loaded with ATP. However, whether ATP hydrolysis is required for branch initiation or subsequent debranching is controversial. New analysis of budding yeast Arp2/3 mutants suggests that debranching, not branching, depends on ATP hydrolysis.
Gleevec inhibits the oncogenic BCR–ABL tyrosine kinase in chronic myelogenous leukaemia and thus safely and effectively suppresses this human cancer. Gleevec also inhibits the normal cellular ABL, a downstream effector of the Eph-receptors, which mediate repulsive cell–cell interactions to regulate axon guidance, angiogenesis and epithelial homeostasis. New work shows that Eph-dependent tumour suppression requires ABL and is blocked by Gleevec, thus cautioning against the indiscriminate use of this drug in cancer therapy.
Ubiquitin, best known as a degradation signal, is also a protein-sorting tag on endocytic cargoes and a regulatory switch on endocytic adaptor proteins. Parkin, a ubiquitin ligase whose mutations are associated with Parkinson's disease, has now been shown to control EGF-receptor internalization and Akt signalling by ubiquitination of the endocytic scaffold protein Eps15.
RING-finger ubiquitin ligases elicit ubiquitination of their substrates, which is balanced by their self-ubiquitination. New insights into regulating the switch between these two modes are illustrated by the role of the adaptor protein Daxx (death domain-associated protein) in regulating the deubiquitinating enzyme HAUSP which, in turn, directs the ligase activity of Mdm2.
