Signaling pathways that contribute to cell death/survival influence diseases including cancer and many neurodegenerative conditions. Elaborating signal transduction mechanisms that regulate these processes are thus important for understanding basic biology and for therapeutic intervention. Neurotrophins potently stimulate neuronal survival in part by activating the small GTP-binding protein Ras, which functions by translating neurotrophin-initiated signals into multiple signaling pathways, including PI-3 kinase/Akt and MEK/ERK, to promote survival. In the initial funding period it was proposed that a novel, and evolutionarily conserved group of Ras-related GTPases, including two mammalian proteins (Rit and Rin) and a single Drosophila ortholog (Ric), play critical roles in regulating apoptotic signaling. From this work, it is now clear that both Rit and Ric promote neuronal survival in a manner distinct from that of Ras. The original hypothesis is now expanded to address how these anti-apoptotic signaling cascades are regulated. The central hypothesis of this proposal is that the Rit GTPase functions as a molecular switch in neurons, responding to both apoptotic stresses and neurotrophin-initiated signals, to activate a distinct pro-survival signaling cascade that relies upon p38 MAP kinase signaling.
Three specific aims are proposed:
Aim 1 will characterize the ability of activated Rit to promote neuronal survival. In particular, we will assess the ability of Rit signaling to protect neurons from trophic factor-withdrawal mediated apoptosis. Using primary neurons from two transgenic mouse models either expressing activated Rit specifically in neurons or a homozygous Rit knockout mouse (developed during the previous period) it is now possible to analyze these critical issues. In addition, microarray analysis will be used to catalog the neuronal transcriptional program regulated by Rit signaling.
Aim 2 will determine the regulatory mechanism that couples NGF-stimulated TrkA to Rit activation and the nature of Rit-dependent regulation of the p38 MAP kinase cascade.
Aim 3 will explore the critical signaling pathways utilized for Rit anti-apoptotic signaling. In particular, Rit-mediated activation of both the p38- MSK1/2 kinase cascade and CREB transcriptional pathways appear to play central roles and will be tested using a combination of both cell model systems and primary neurons. Importantly, data developed since the previous review suggests that a second novel Rit-p38-HSP27-MK2 pathway may stimulate AKT signaling to afford neuronal protection. In summary, these studies will establish a role for Rit in neuronal survival. Regulation of this novel Ras-related G-protein may have a pronounced impact on neuronal physiology and would make Rit and its effectors, potential targets for the development of new therapeutic strategies.

Public Health Relevance

The death of neurons causes or contributes to various neurodegenerative disorders including stroke, epilepsy, Parkinson's disease, Huntington's disease, and Alzheimer's disease. Importantly, we have discovered a protein that promotes neuronal survival, protecting neurons from potentially lethal stimuli. Understanding the mechanism that foster neuronal survival is of fundamental importance to the development of treatment strategies for these disorders. Thus, the goal of this research is to speed progress toward therapeutic exploitation of this protein in neurodegenerative disease.

National Institute of Health (NIH)
National Institute of Neurological Disorders and Stroke (NINDS)
Research Project (R01)
Project #
Application #
Study Section
Neural Oxidative Metabolism and Death Study Section (NOMD)
Program Officer
Mamounas, Laura
Project Start
Project End
Budget Start
Budget End
Support Year
Fiscal Year
Total Cost
Indirect Cost
University of Kentucky
Schools of Medicine
United States
Zip Code
Andres, Douglas A; Shi, Geng-Xian; Bruun, Donald et al. (2008) Rit signaling contributes to interferon-gamma-induced dendritic retraction via p38 mitogen-activated protein kinase activation. J Neurochem 107:1436-47
Rudolph, Jennifer L; Shi, Geng-Xian; Erdogan, Eda et al. (2007) Rit mutants confirm role of MEK/ERK signaling in neuronal differentiation and reveal novel Par6 interaction. Biochim Biophys Acta 1773:1793-800
Lein, Pamela J; Guo, Xin; Shi, Geng-Xian et al. (2007) The novel GTPase Rit differentially regulates axonal and dendritic growth. J Neurosci 27:4725-36
Shi, Geng-Xian; Rehmann, Holger; Andres, Douglas A (2006) A novel cyclic AMP-dependent Epac-Rit signaling pathway contributes to PACAP38-mediated neuronal differentiation. Mol Cell Biol 26:9136-47
Harrison, Susan M W; Rudolph, Jennifer L; Spencer, Michael L et al. (2005) Activated RIC, a small GTPase, genetically interacts with the Ras pathway and calmodulin during Drosophila development. Dev Dyn 232:817-26
Shi, Geng-Xian; Andres, Douglas A (2005) Rit contributes to nerve growth factor-induced neuronal differentiation via activation of B-Raf-extracellular signal-regulated kinase and p38 mitogen-activated protein kinase cascades. Mol Cell Biol 25:830-46
Shi, Geng-Xian; Han, Jiahuai; Andres, Douglas A (2005) Rin GTPase couples nerve growth factor signaling to p38 and b-Raf/ERK pathways to promote neuronal differentiation. J Biol Chem 280:37599-609