Membrane targeting of p21-activated kinase 1 (PAK1) induces neurite outgrowth from PC12 cells
Related Experiment Videos
R H Daniels1, P S Hall, G M Bokoch
1Departments of Immunology and Cell Biology, The Scripps Research Institute, 10550 North Torrey Pines Rd, La Jolla, CA 92037, USA.
Abstract:
Rho-family GTPases regulate cytoskeletal dynamics in various cell types. p21-activated kinase 1 (PAK1) is one of the downstream effectors of Rac and Cdc42 which has been implicated as a mediator of polarized cytoskeletal changes in fibroblasts. We show here that the extension of neurites induced by nerve growth factor (NGF) in the neuronal cell line PC12 is inhibited by dominant-negative Rac2 and Cdc42, indicating that these GTPases are required components of the NGF signaling pathway. While cytoplasmically expressed PAK1 constructs do not cause efficient neurite outgrowth from PC12 cells, targeting of these constructs to the plasma membrane via a C-terminal isoprenylation sequence induced PC12 cells to extend neurites similar to those stimulated by NGF. This effect was independent of PAK1 ser/thr kinase activity but was dependent on structural domains within both the N- and C-terminal portions of the molecule. Using these regions of PAK1 as dominant-negative inhibitors, we were able to effectively inhibit normal neurite outgrowth stimulated by NGF. Taken together with the requirement for Rac and Cdc42 in neurite outgrowth, these data suggest that PAK(s) may be acting downstream of these GTPases in a signaling system which drives polarized outgrowth of the actin cytoskeleton in the developing neurite.
Insights
Nerve growth factor (NGF) signaling in PC12 cells requires Rac and Cdc42 GTPases for neurite outgrowth. PAK1, when localized to the plasma membrane, promotes neurite extension independently of its kinase activity.
Area of Science:
- Cell biology
- Neuroscience
- Molecular signaling
Background:
- Rho-family GTPases are key regulators of cytoskeletal dynamics.
- p21-activated kinase 1 (PAK1) is a downstream effector of Rac and Cdc42, involved in cytoskeletal organization.
- Neurite outgrowth is a critical process in neuronal development.
Purpose of the Study:
- To investigate the role of Rac and Cdc42 GTPases in NGF-induced neurite outgrowth in PC12 cells.
- To determine the involvement of PAK1 in NGF signaling and neurite extension.
- To elucidate the signaling pathway mediating polarized actin cytoskeleton outgrowth.
Main Methods:
- Utilized dominant-negative Rac2 and Cdc42 to inhibit GTPase activity.
- Expressed cytoplasmically-localized and plasma membrane-targeted PAK1 constructs in PC12 cells.
- Assessed neurite outgrowth in response to NGF and PAK1 expression.
- Employed PAK1 structural domains as dominant-negative inhibitors.
Main Results:
- Dominant-negative Rac2 and Cdc42 inhibited NGF-induced neurite outgrowth, confirming their necessity.
- Targeting PAK1 to the plasma membrane induced significant neurite extension, mimicking NGF effects.
- PAK1-induced neurite outgrowth was independent of its kinase activity but reliant on N- and C-terminal domains.
- PAK1 N- and C-terminal domains acted as dominant-negative inhibitors of NGF-stimulated neurite outgrowth.
Conclusions:
- Rac and Cdc42 GTPases are essential for NGF-mediated neurite outgrowth in PC12 cells.
- PAK1, particularly when localized to the plasma membrane, plays a crucial role in promoting neurite extension.
- PAK1 likely functions downstream of Rac and Cdc42 in a signaling cascade that drives polarized actin cytoskeleton outgrowth during neurite development.