No abstract

We previously reported that the activation of prostaglandin E receptor EP3 subtype caused neurite retraction via small GTPase Rho in the EP3B receptor-expressing PC12 cells (Katoh, H., Negishi, M., and Ichikawa, A. (1996) J. Biol. Chem. 271, 29780 -29784). However, a potential downstream effector of Rho that induces neurite retraction was not identified. Here we examined the morphological effect of p160 RhoA-binding kinase ROK␣, a target for RhoA recently identified, on the nerve growth factor-differentiated PC12 cells. Microinjection of the catalytic domain of ROK␣ rapidly induced neurite retraction similar to that induced by microinjection of a constitutively active Rho, Rho V14 , whereas microinjection of the kinase-deficient catalytic domain of ROK␣ did not induce neurite retraction. This morphological change was observed even though C3 exoenzyme, which was known to inactivate Rho, had been preinjected. On the other hand, microinjection of the Rho-binding domain or the pleckstrin homology domain of ROK␣ inhibited the EP3 receptor-induced neurite retraction. These results demonstrate that ROK␣ induces neurite retraction acting downstream of Rho in neuronal cells.Rho, a member of the Ras superfamily of small GTPases, is implicated in various cellular morphological functions, such as formation of stress fibers and focal adhesion (1), cell motility (2), cytokinesis (3), cell aggregation (4), and smooth muscle contraction (5). When cells are activated by extracellular stimuli, inactive GDP-bound Rho is converted to active GTP-bound Rho. Once activated, Rho probably interacts with its specific targets, leading to a variety of biological functions (6). Recently, several target proteins that interact only with GTP-bound Rho have been identified, including p128 protein kinase N (7, 8), p160 RhoA-binding kinase ROK␣ (9) also known as its bovine counterpart Rho-kinase (10) or its mouse counterpart ROCK-II (11), rhophilin (7), rhotekin (12), and p140mDia (13). Among them, ROK␣ has been reported to be involved in several functions of Rho: the regulation of myosin phosphorylation (14, 15), the formation of stress fibers and focal adhesions (16,17), and probably the regulation of cytokinesis (18).Rho has also been implicated in the control of neuronal cell morphologies. The activation of a certain heterotrimeric GTPbinding protein (G-protein)-coupled receptor, 1 such as lysophosphatidic acid and thrombin receptors, caused the rapid retraction of extended neurites in several neuronal cell lines (19 -21). Clostridium botulinum C3 exoenzyme, which specifically ADP-ribosylates Rho and suppresses the actions of Rho (22, 23), inhibits the receptor-mediated neurite retraction (24, 25), indicating that Rho activity is required for this morphological change. Although this effect appears to be induced by the contractility of the actin-based cytoskeleton (24, 26), a downstream effector of Rho that induces neurite retraction has not yet been identified.We previously reported that the activation of prostaglandin EP3 receptor caused Rho...

The Rho family of small GTPases has been implicated in cytoskeletal reorganization and subsequent morphological changes in various cell types. Among them, Rac and Cdc42 have been shown to be involved in neurite outgrowth in neuronal cells. In this study, we examined the role of RhoG, another member of Rho family GTPases, in nerve growth factor (NGF)-induced neurite outgrowth in PC12 cells. Expression of wild-type RhoG in PC12 cells induced neurite outgrowth in the absence of NGF, and the morphology of wild-type RhoGexpressing cells was similar to that of NGF-differentiated cells. Constitutively active RhoG-transfected cells extended short neurites but developed large lamellipodial or filopodial structures at the tips of neurites. RhoGinduced neurite outgrowth was inhibited by coexpression with dominant-negative Rac1 or Cdc42. In addition, expression of constitutively active RhoG elevated endogenous Rac1 and Cdc42 activities. We also found that the NGF-induced neurite outgrowth was enhanced by expression of wild-type RhoG whereas expression of dominant-negative RhoG suppressed the neurite outgrowth. Furthermore, constitutively active Ras-induced neurite outgrowth was also suppressed by dominant-negative RhoG. Taken together, these results suggest that RhoG is a key regulator in NGF-induced neurite outgrowth, acting downstream of Ras and upstream of Rac1 and Cdc42 in PC12 cells.

Neurite outgrowth of PC12 cells is induced by nerve growth factor (NGF) but not by epidermal growth factor (EGF).

A new miniature multiturn time-of-flight (TOF) analyzer "MULTUM-S II" has been designed and constructed. This instrument consists of an electron ionization source, the multiturn TOF ion optics, a detector, vacuum system, and electronic circuits. The multiturn TOF analyzer consists of four electrostatic toroidal sectors and two additional electric toroidal sectors for the purpose of ion injection/ejection. The size and weight of the system is less than 50 cm × 57 cm × 30 cm and 35 kg (including vacuum pumps and electronic circuits). The multiturn TOF analyzer is capable of high mass resolution because of its infinite flight path utilizing perfect space and time focused closed flight orbit. To evaluate the resolution in MULTUM-S II, separation of pyridine (¹²C₅H₅N) and the isotopic component of benzene (¹³C¹²C₅H₆) was performed at a mass resolution of about 20,000. Another performance characteristic of the MULTUM-S II was demonstrated by the separation of the greenhouse gas doublet CO₂ and N₂O (Δm = 0.0113 Da). While the mass difference is a mere 0.01 Da, the instrument could easily separate the two peaks at a calculated mass resolution of 31,600. The MULTUM-S II offers high mass resolution mass spectrometry in a miniaturized/portable enclosure.