Biosketch / Results /

Mark Philips

Professor, Department of Medicine;Professor, Department of Biochemistry and Molecular Pharmacology;Professor, Department of Cell Biology
Perlmutter Cancer Center

Contact Info

522 First Avenue
New York, NY 10016


Research Summary

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.

Research Interests

Processing and membrane targeting of GTPases.

Targeting RAS Membrane Association: Back to the Future for Anti-RAS Drug Discovery?
Cox, Adrienne D; Der, Channing J; Philips, Mark R
2015-04-20; 1078-0432,Clinical cancer research - id: 1532252, year: 2015 Editorial

The differential palmitoylation States of N-ras and h-ras determine their distinct Golgi subcompartment localizations
Lynch, Stephen J; Snitkin, Harriet; Gumper, Iwona; Philips, Mark R; Sabatini, David; Pellicer, Angel
2014-12-01; 0021-9541,Journal of cellular physiology - id: 1360222, year: 2015 Journal Article

K-Ras4A splice variant is widely expressed in cancer and uses a hybrid membrane-targeting motif
Tsai, Frederick D; Lopes, Mathew S; Zhou, Mo; Court, Helen; Ponce, Odis; Fiordalisi, James J; Gierut, Jessica J; Cox, Adrienne D; Haigis, Kevin M; Philips, Mark R
2015-01-26; 0027-8424,Proceedings of the National Academy of Sciences of the United States of America (PNAS) - id: 1441022, year: 2015 Journal Article

Metabolic labeling of ras with tritiated palmitate to monitor palmitoylation and depalmitoylation
Tsai, Frederick D; Wynne, Joseph P; Ahearn, Ian M; Philips, Mark R
2014-02-03; 1064-3745,Methods in molecular biology - id: 778262, year: 2014 Journal Article

Isoprenylcysteine carboxylmethyltransferase deficiency exacerbates KRAS-driven pancreatic neoplasia via Notch suppression
Court, Helen; Amoyel, Marc; Hackman, Michael; Lee, Kyoung Eun; Xu, Ruliang; Miller, George; Bar-Sagi, Dafna; Bach, Erika A; Bergo, Martin O; Philips, Mark R
2014-01-27; 0021-9738,Journal of clinical investigation - id: 761382, year: 2013 JOURNAL ARTICLE