Gilbert C. White, II, MD

Thrombosis, Hemostasis and Vascular Biology

The overall goal of the White lab is to understand the signaling pathways that mediate the hemostatic responses of blood platelets. Understanding these responses at a molecular level permits the development of methods to selectively and precisely manipulate those pathways, thereby controlling vascular diseases like heart attacks and strokes. A current focus is the role of rap1b, a low molecular weight GTP binding protein member of the ras superfamily, which is present in high concentrations in platelets and plays a role in the activation in platelets, including platelet aggregation, the integrin-mediated interaction of one platelet with another to form a platelet hemostatic plug. Rap1b also plays a role in the inhibition of platelets by cyclic AMP. Thus, rap1b appears to be positioned as a unique and critical bi-directional modulator of platelet activation. Using knock-out and transgenic mice combined with proteomic and genetic approaches like yeast two-hybrid screening, we are exploring the pathway(s) by which rap1b and other proteins mediate signals from G-protein coupled receptors such as P2Y12 to integrins like αIIbβ3 that mediate platelet aggregation. We are also exploring the pathway(s) that link cyclic AMP and rap1b. Understanding the rap1b-dependent pathways that are involved in mediating platelet responses will provide new ways to control platelet in vascular diseases.

Montage of platelet responses. Starting with the upper left panel, platelet low molecular weight G proteins rac and rho are involved in cytoskeletal rearrangements; rap1b knockout platelets (-/-) have an impaired response to collagen; signal transduction pathway from P2Y12 to aIIbb3 integrin; GDP/GTP exchange cycle for rap1b

• NIH: T32 (NHLBI) “Research Training in Transfusion Medicine”, 2008-2013
• NIH: UL1 (NCRR), “Clinical and Translational Science Award”, Co-PI, 2010-2015
• NIH: C06 (NCRR), “Initiative in Stem Cell Biology”, 2010-2015 

• Awasthi, A., Samarakoon, A., Chu, H., Kamalakannan, R., Quilliam, L.A., Chrzanowska-Wodnicka, M., White, II, G.C. and Malarkannan, S. Rap1b facilitates NK cell functions via IQGAP1-mediated signalosomes. J Exp Med 207:1923-1938, 2010.
• Carbo, C., Duerschmied, D., George, T., Hattori, H., Sakai, J., Cifuni, S.M., White, II, G.C., Chrzanowska-Wodnicka, M., Luo, H.R. and Wagner, D.D. Integrin-dependent role of CalDAG-GEFI in neutrophil chemotaxis, J. Leukocyte Biol. 88:313-319, 2010
• Wang, Z., Holly, S.P., Larson, M.K., Lui, J., Yuan, W., Chrzanowska-Wodnicka, M., White, II, G.C. and Parise, L.V., Rap1b is critical for GPVI- but not ADP receptor-mediated α2β1 activation. J. Thrombos. Haemostas 7:693-700, 2009
• Kempton, C.L. and White, II, G.C. How we treat a hemophilia A patient with a factor VIII inhibitor. Blood 113:11-17, 2009.
• White, II, G.C., Prediction of inhibitors in hemophilia. J. Thrombos. Haemostas. 6:2045-2047, 2008.
• Chrzanowska-Wodnicka, M., Kraus, A.E., Gale, D., White, II, G.C. and van Sluys, J., Defective angiogenesis, endothelial migration, proliferation, and MAPK signaling in rap1b-deficient mice (commentary paper). Blood 111:2647-2656, 2008.
• Chen, Y., Yu, M., Podd, A., Wen, R., Chrzanowska-Wodnicka, M., White, II, G.C. and Wang, D., A critical role of rap1b in B cell trafficking and marginal zone B cell development. Blood 111:4627-4636, 2008
• Chu, H., Awasthi, A., White, II, G.C., Chrzanowski-Wodnicka, M. and Malarkannan, S., Rap1b-regulates B cell development, homing, and T cell-dependent humoral immunity, J. Immunol. 181:3373-3383, 2008
• Ferro, E., Magrini, D., Guazzi, P., Fischer, T.H., Pistolesi, S., Pogni, R., White, II, G.C. and Trabalzini, L., G-protein binding features and regulation of the RalGDS family member, RGL2. Biochem. J. 415:145-154, 2008
• Chzanowska-Wodnicka M, Smyth SS, Schoenwaelder SM, Fischer TH, White II GC. Rap1b is required for normal platelet function and hemostasis in mice. J Clin Invest 115:680-7, 2005.
• Fang J, Hodivala-Dilke K, Johnson BD, Hynes RO, White II GC, Wilcox DA. Therapeutic expression of the platelet-specific integrin, αIIbβ3, in a murine model for Glanzmann thrombasthenia. Blood 106:2671-9, 2005.
• White II GC, Kempton CL, Grinsley A, Nielsen B, Roberts HR. Cellular immune responses in hemophilia. Why do inhibitors develop in some but not all hemophiliacs? J Thrombos Haemostas 3:1676-81, 2005.
• Gidwitz S, Temple B, White II GC. Mutations in and near the second calcium-binding domain of integrin αIIb affect the structure and function of integrin αIIbβ3. Biochem J 379:449-59, 2004.
• Fischer TH, Brittain J, Trabalzini L, Banes AJ, White II GC, Smith CJ, Nichols TC. The ras-binding domain of ral GDS-like protein–2 as a ras inhibitor in smooth muscle cells. Biochem Biophys Res Commun 305:934-40, 2003.
• Powell JS, Ragni MV, White II GC, Lusher JM, Hillman-Wiseman C, Moon TE, Cole V, Ramanathan-Girish S, Roehl H, Sajjadi N, Jolly DJ, Hurst D. Phase 1 trial of FVIII gene transfer for severe hemophilia A using a retroviral construct administered by peripheral intravenous infusion. Blood 102:2038-45, 2003.
• Zhang B, Cunningham MA, Nichols WC, Bernat JA, Seligsohn U, Pipe SW, McVey JH, Schulte-Overberg U, de Bosch NB, Ruiz-Saez A, White II GC, Tuddenham EG, Kaufman RJ, Ginsburg D. Bleeding due to disruption of a cargo-specific ER-to-Golgi transport complex. Nat Genet 34:220-5, 2003.
• Rick ME, Moll S, Taylor MA, Krizek DM, White II GC, Aronson DL. Clinical use of a rapid collagen binding assay for von Willebrand factor cleaving protease in patients with thrombotic thrombocytopenic purpura. Thromb Haemost 88:595-604, 2002.
• Bertoni A, Tadokoro S, Eto K, Pampori N, Parise LV, White II GC, Shattil SJ. Relationships between Rap1b, affinity modulation of integrin αIIbβ3, and the actin cytoskeleton. J Biol Chem 277:25715-21, 2002.
• Wilcox DA, Olsen JC, Ishizawa L, Bray PF, French DL, Steeber DA, Bell WR, Griffith M, White II GC. Megakaryocyte-targeted synthesis of the integrin β3-subunit results in the phenotypic correction of Glanzmann thrombasthenia. Blood. 95:3645-3651, 2001.
• Gidwitz S, Lyman S, White II GC. Expression and function of calcium binding domain chimeras of the integrins αIIb and α5. J Biol Chem. 275:6680-6688, 2000.
• Wilcox DA, Olsen JC, Ishizawa L, Griffith M, White II GC. Integrin alphaIIb promoter-targeted expression of gene products in megakaryocytes derived from retrovirus-transduced human hematopoietic cells. Proc Natl Acad Sci U S A. 96:9654-9659, 1999.
• Nichols WC, Terry VH, Wheatley MA, Yang A, Zivelin A, Ciavarella N, Stefanile C, Matsushita T, Saito H, de Bosch NB, Ruiz-Saez A, Torres A, Thompson AR, Feinstein DI, White II GC, Negrier C, Vinciguerra C, Aktan M, Kaufman RJ, Ginsburg D, and Seligsohn U. ERGIC-53 gene structure and mutation analysis in 19 combined factors V and VIII deficiency families. Blood 93(7):2261-2266, 1999.
• Michael NL, Nelson JA, KewalRamani VN, Chang G, O'Brien SJ, Mascola JR, Volsky B, Louder M, White II GC, Littman DR, Swanstrom R,and O'Brien TR. Exclusive and persistent use of the entry coreceptor CXCR4 by human immunodeficiency virus type 1 from a subject homozygous for CCR5 delta32. J Virol 72(7):6040-6047, 1998.
• Thomas JW, Ellis B, Boerner RJ, Knight WB, White II GC and Schaller MD. SH2- and SH3-mediated interactions between FAK and Src. J Biol Chem 273:577-583, 1998.
• White II GC, Fischer T and Duffy CM: Rap1b association with the platelet cytoskeleton occurs in the absence of glycoproteins IIb/IIIa. Thrombos Haemostas 79:832-836, 1998.
• Lyman S, Gilmore A, Burridge KW, Gidwitz S and White II GC: Integrin-mediated activation of focal adhesion kinase is independent of focal adhesion formation or integrin activation. Studies with activated and inactivated β3 cytoplasmic domain mutants. J Biol Chem 272:22538-22547, 1997
• Peterson SN, Trabalzini L, Brtva TR, Fischer TH, Altschuler DL, Martelli P, Lapetina EG, Der CJ and White II GC. Identification of a novel ralGDS-like protein as a candidate effector for ras and rap1. J. Biol. Chem., J Biol Chem 271:29903-29908, 1996
• Fischer,TH, Gatling MN, McCormick F, Duffy CM and White II GC. Incorporation of rap1B into the platelet cytoskeleton is dependent on thrombin activation and extracellular calcium. J Biol Chem 269:17257- 17261, 1994.
• White II GC, Crawford N and Fischer TH. Cytoskeletal interactions of rap 1B in platelets. Adv. Exp Med Biol 344:187-194, 1993.
• Fischer TH, Gatling MN, Lacal JC and White II GC.Rap1B, a cAMP-dependent protein kinase substrate, associates with the platelet cytoskeleton. J. Biol Chem 265:19405-19408, 1991.
• Fischer TH, Collins JH, Gatling MN and White II GC. The localization of the cAMP-dependent protein kinase phosphorylation site in the platelet ras protein, rap1B. FEBS Letters 283:173-176, 1991.