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New York, NY 10016
Our laboratory is primarily interested in the cell biology of GTPases. GTPases are ubiquitous elements of signaling pathways, including those regulating cell growth and differentiation. Virtually all cellular processes utilize GTPases as regulatory elements including processes that control the immune response. Thus, although our work has immediate relevance to cancer, insights from our studies may be relevant to a wide variety of human diseases including inflammatory and autoimmune disorders.
The protooncogene ras and closely related GTPases are among a class of proteins that are synthesized as soluble molecules in the cytosol and are then targeted to membranes by a series of posttranslational modifications of a C-terminal CAAX sequence that includes prenylation, proteolysis, and carboxyl methylation. Of these modifications, only carboxyl methylation is reversible and may therefore have a signaling function. We therefore focused on the enzyme that catalyzes this modification, prenylcysteine carboxyl methyltransferase, and recently cloned its gene.
Prenylcysteine carboxyl methyltransferase proved to be a multiple membrane spanning protein that is expressed in ER and Golgi but not plasma membrane (see figure). This observation was surprising since it implied that ras, synthesized in the cytosol and destined for the plasma membrane, must make a detour to the ER to complete processing. The ER processing of ras led us to hypothesize that ras is transported to plasma membrane via the vesicular transport system. Using green fluorescent protein-tagged ras proteins we showed that this model is correct. We also showed that carboxyl methylation is required for vesicular transport of ras. We hope to exploit this previously unappreciated aspect of ras biology to develop novel anticancer therapies.
In more recent work we have tested the hypothesis that intracellular ras can be activated and regulate signaling pathways and proved it correct. We accomplished this by developing a novel fluorescent probe that reports when and where Ras becomes activated in living cells. We consider our probe for activated ras a prototyped of a class of molecules that can serve as fluorescent reporters of signaling events in living cells and thereby elucidate many previously inaccessible aspects of signal transduction.
ERK1/2-induced phosphorylation of R-Ras GTPases stimulates their oncogenic potential
Fremin, C; Guegan, J-P; Plutoni, C; Mahaffey, J; Philips, M R; Emery, G; Meloche, S. ERK1/2-induced phosphorylation of R-Ras GTPases stimulates their oncogenic potential. Oncogene. 2016 Oct 27;35(43):5692-5698 (2317622)
VPS35 binds farnesylated N-Ras in the cytosol to regulate N-Ras trafficking
Zhou, Mo; Wiener, Heidi; Su, Wenjuan; Zhou, Yong; Liot, Caroline; Ahearn, Ian; Hancock, John F; Philips, Mark R. VPS35 binds farnesylated N-Ras in the cytosol to regulate N-Ras trafficking. Journal of cell biology. 2016 Aug 15;214(4):445-458 (2213572)
Rap1 and its effector riam are required for lymphocyte trafficking
Su, Wenjuan; Wynne, Joseph; Pinheiro, Elaine M; Strazza, Marianne; Mor, Adam; Montenont, Emilie; Berger, Jeffrey; Paul, David S; Bergmeier, Wolfgang; Gertler, Frank B; Philips, Mark R. Rap1 and its effector riam are required for lymphocyte trafficking. Blood. 2015 Dec 17;126(25):2695-2703 (1761692)
p27kip1 controls H-Ras/MAPK activation and cell cycle entry via modulation of MT stability
Fabris, Linda; Berton, Stefania; Pellizzari, Ilenia; Segatto, Ilenia; D'Andrea, Sara; Armenia, Joshua; Bomben, Riccardo; Schiappacassi, Monica; Gattei, Valter; Philips, Mark R; Vecchione, Andrea; Belletti, Barbara; Baldassarre, Gustavo. p27kip1 controls H-Ras/MAPK activation and cell cycle entry via modulation of MT stability. Proceedings of the National Academy of Sciences of the United States of America (PNAS). 2015 Nov 10;112(45):13916-13921 (1817572)
Seeing is believing: Ras dimers observed in live cells
Philips, Mark R; Der, Channing J. Seeing is believing: Ras dimers observed in live cells. Proceedings of the National Academy of Sciences of the United States of America (PNAS). 2015 Aug 11;112(32):9793-9794 (1698672)