Gary Thomas

Senior Scientist -Vollum Institute

Associate Professor - Cell and Developmental Biology

The Thomas lab studies the cellular machinery that directs the sorting of membrane proteins in the secretory pathway. The regulation of membrane and protein traffic between secretory pathway compartments requires the orchestrated interaction of many components, including small molecules, lipid, cytosolic and membrane proteins, and cytoskeletal elements. Thomas and his associates focus on the proprotein convertase furin, which provides an excellent model for study of the regulation of protein traffic, mechanisms of proenzyme activation, and development of proteinase inhibitors as anti-infective agents.

Furin is localized to the trans-Golgi network (TGN) and cycles between the proprotein processing compartment, the cell surface, and the early endosome system. TGN localization requires phosphorylation of the furin cytosolic domain (cd) by casein kinase II. Movement of furin between endosomes and the TGN is regulated by dephosphorylation of the furin-cd by a tautomycin-sensitive furin phosphatase. The phosphorylation-dependent trafficking of furin suggests that formation of furin-containing processing compartments is regulated by signal transduction pathways.

The Thomas lab has identified several sorting proteins that regulate protein traffic in the TGN/endosomal system. Localization of furin to the TGN is directed by the sorting protein PACS-1 (phosphofurin acidic cluster sorting protein). PACS-1 mediates TGN localization of furin by connecting the phosphorylated endoprotease to the clathrin sorting machinery. The presence of PACS binding motifs on a large number of membrane proteins suggests a broad and important role for this protein family in the organization of the secretory pathway.

Thomas and associates found that the cytoskeletal protein ABP-280 transiently tethers furin to the cell surface and directs the rate of internalization of endoprotease into endosomal compartments. This is the first demonstration of an identified component of the cytoskeleton that regulates the sorting of an itinerant TGN/endosomal membrane protein. The researchers are currently studying how signaling systems direct PACS-1 and ABP-280 in sorting furin.

The Thomas lab has also shown that activation of the furin zymogen requires a coordinated set of autoproteolytic cleavages within its N-terminal propeptide. These cleavages occur during sequential exposure of the enzyme to the microenvironments of the endoplasmic reticulum and the TGN/endosomal systems. How the propeptide mediates the folding and compartment-specific activation of furin is currently being studied.

The central role of furin in the activation of numerous bacterial and viral pathogens makes the endoprotease a strategic target for novel therapeutics. Recent studies in the Thomas lab have determined that an engineered variant of

Crump, C.M. Xiang, Y. Thomas, L. Gu, F, Austin, C., Tooze, S.A. and Thomas G. (2001) PACS-1 binding to adaptors is required for acidic cluster motif-mediated protein traffic. EMBO J. 20:2191-2201.

Xiang, Y., Molloy, S.S., Thomas, L., and Thomas, G. (2000) The PC6B cytosolic domain contains two acidic clusters that direct sorting to distinct TGN/endosomal compartments. Mol. Biol. Cell 11:1257-1273.

Piguet, V., Wan, L., Borel, C., Mangasarian, A., Demaurex, N., Thomas, G., and Trono, D. (2000) HIV-1 Nef protein binds to the cellular protein PACS-1 to downregulate class I major histocompatibility complexes. Nature Cell Biol. 2:163-167.

Jean. F., Thomas, L., Molloy, S.S., Liu, G., Jarvis, M.A., Nelson, J.A., and Thomas, G. (2000) A protein-based therapeutic for human cyto-megalovirus infection. Proc. Natl. Acad. Sci. USA 97:2864-2869.

Molloy, S.S., Anderson, E.D., Jean, F., and Thomas, G. (1999) Bi-cycling the furin pathway: from TGN localization to pathogen activation and embryogenesis. Trends Cell Biol. 9:28-35.

Molloy, S.S., Thomas, L., Kamibayashi, C., Mumby, M.C., and Thomas,G. (1998) Regulation of endosome sorting by a specific PP2A isoform. J. Cell. Biol. 142:1399-1411.

Wan, L., Molloy S.S., Thomas, L., Liu, G., Xiang, Y., Rybak, S.L., and Thomas, G. (1998) PACS-1 defines a novel gene family of cytosolic sorting proteins required for trans-Golgi network localization. Cell 94:205-216.

To contact Dr. Thomas directly: thomasg@ohsu.edu