One ROCK is not like another

One ROCK is not like another he mammalian rho kinases, ROCKI and ROCKII, control distinct cytoskeletal functions from distinct locations, report Yoneda et al. on page 443. ROCKI is required for formation of actin stress fibers and cell adhesion, whereas ROCKII is needed for phagocytosis. The ROCK proteins are major effectors of the Rho signaling pathway, controlling cell adhesion, motility, and other actin-based functions. In kinase overexpression assays, ROCKI and ROCKII appear redundant, but several experiments, including mouse knockouts , hinted that the proteins have unique duties despite their structural similarity. While studying a signaling pathway that links integrins and cell surface proteoglycans to adhesion, Yoneda et al. saw that ROCKI but not ROCKII activity increased during adhesion. To learn how the proteins differ functionally, the team knocked down each ROCK gene independently using siRNA sequences that left the other gene unchanged. Cells lacking ROCKI formed few stress fibers or focal adhesions. ROCKII-depleted cells produced oversized stress fibers and adhesions, and showed problems with phagocytic uptake of fibronectin-coated beads. The PH domain is the most divergent region of the two ROCKs, and GFP-PH from each protein localized to distinct subcellular locations. The ROCKI PH domain was evenly distributed at membranes, whereas ROCKII PH concentrated in ruffles at the cell surface. Subsequent analysis showed that only ROCKII PH binds to PIP 3 lipids and may, therefore, be regulated by PI3-kinase. Although the ROCK proteins phosphorylate similar targets in vitro, Yoneda et al. think that subcellular targeting restricts the pair's functions. This is consistent with over-expression of either protein masking their differences. If the team is right, then what holds for real estate holds for the ROCKs: it's all about location, location, location. T Cells low in ROCKI (center) lack stress fibers. AD helps counteract energy leakage from severed axons, report Wang et al. on page 349. Recently, Araki et al. (Science. 305:1010–1013) showed that NAD protects axons from degeneration after injury, apparently by activating SIRT1, a nuclear deacetylase involved in aging. Now, Wang et al. show that NAD prevents degeneration independent of SIRT1 and works locally to protect membrane integrity. Axons degenerate when they are cut from their cell body. However, neurons from mice are protected from degeneration when they over-express either Nmnat1, which synthesizes NAD, or the Wld s fusion protein that contains Nmnat1. Wang et al. found that overexpression of Wld s or Nmnat1 prevented a decrease of NAD, …