3-Hydroxy-3-methylglutaryl coenzyme A reductase inhibitors (statins) have been reported to reduce the risk of Alzheimer disease. We have shown previously that statins inhibit a ␤-amyloid (A␤)-mediated inflammatory response through mechanisms independent of cholesterol reduction. Specifically, statins exert anti-inflammatory actions through their ability to prevent the isoprenylation of members of the Rho family of small G-proteins, resulting in the functional inactivation of these G-proteins. We report that statin treatment of microglia results in perturbation of the cytoskeleton and morphological changes due to alteration in Rho family function. Statins also block A␤-stimulated phagocytosis through inhibition of Rac action. Paradoxically, the statin-mediated inactivation of G-protein function was associated with increased GTP loading of Rac and RhoA, and this effect was observed in myeloid lineage cells and other cell types. Statin treatment disrupted the interaction of Rac with its negative regulator the Rho guanine nucleotide dissociation inhibitor (RhoGDI), an interaction that is dependent on protein isoprenylation. We propose that lack of negative regulation accounts for the increased GTP loading. Isoprenylation of Rac is also required for efficient interaction with the plasma membrane, and we report that statin treatment dramatically reduces the capacity of Rac to interact with membranes. These results suggest a mechanism by which statins inhibit the actions of Rho GTPases and attenuate A␤-stimulated inflammation.

Nerve growth factor (NGF) acts through its receptor, TrkA, to elicit the neuronal differentiation of PC12 cells through the action of extracellular signal-regulated kinase 1 (ERK1) and ERK2. Upon NGF binding, TrkA translocates and concentrates in cholesterol-rich membrane microdomains or lipid rafts, facilitating formation of receptor-associated signaling complexes, activation of downstream signaling pathways, and internalization into endosomes. We have investigated the mechanisms responsible for the localization of TrkA within lipid rafts and its ability to activate ERK1 and ERK2. We report that NGF treatment results in the translocation of activated forms of TrkA to lipid rafts, and this localization is important for efficient activation of the ERKs. TrkA is recruited and retained within lipid rafts through its association with flotillin, an intrinsic constituent of these membrane microdomains, via the adapter protein, c-Cbl associated protein (CAP). Mutant forms of CAP that lack protein interaction domains block TrkA localization to lipid rafts and attenuate ERK activation. Importantly, suppression of endogenous CAP expression inhibited NGF-stimulated neurite outgrowth from primary dorsal root ganglion neurons. These data provide a mechanism for the lipid raft localization of TrkA and establish the importance of the CAP adaptor protein for NGF activation of the ERKs and neuronal differentiation.Nerve Growth factor (NGF) is responsible for the development and survival of sympathetic and sensory neurons (17,56) and plays an important role in neuronal plasticity in the central nervous system (11, 61). PC12 cells have been extensively employed to examine the mechanisms subserving the NGF-stimulated neuronal differentiation of these cells. A number of studies have demonstrated that the activation of the extracellular signal-regulated kinase (ERK) subfamily of mitogen-activated protein kinases (MAPKs) are responsible for directing the morphological and biochemical differentiation of these cells into a neuronal phenotype (12,22,33,34,42). NGF initiates its actions upon binding to its specific receptor, TrkA, which dimerizes and becomes autophosphorylated through its intrinsic tyrosine kinase activity. TrkA activation results in the association of a number of adapter proteins with the receptor, including those necessary for activation of the ERK MAPK cascade (28,55,69). NGF stimulates ERK activation via the recruitment and activation of the guanine nucleotide exchange factors SOS and C3G, which catalyze the exchange of GDP for GTP, activating the small G proteins Ras and Rap1, respectively. Ras and Rap1 then activate the MEK kinases, c-Raf and B-Raf, which in turn activate MEK-1 and -2. MEK-1 and -2 stimulate the activation of ERK1 and ERK2 (ERK1/2). NGF activation of the ERKs occurs predominately through a pathway involving the B-Raf isoform, with c-Raf playing a minor role (21). B-Raf is activated almost exclusively through Rap1 (70), leading to the prolonged stimulation of the ERKs due to the formation of a stable...

During times of stress, autophagy is a cellular process that enables cells to reclaim damaged components by a controlled recycling pathway. This mechanism for cellular catabolism is dysregulated in cancer with evidence indicating that cancer cells rely on autophagy in the hypoxic and nutrient-poor microenvironment of solid tumors. Mounting evidence suggests that autophagy plays a role in the resistance of tumors to standard-of-care therapies. There is therefore significant interest in the discovery of small molecules that can safely modulate autophagy. In this review we describe recent advances in the identification of new pharmacological compounds that modulate autophagy with a focus on their mode of action, value as probe compounds and validation as potential therapeutics.