Platelets are essential to maintaining a pressurized vasculature. The
platelet's role is to sense vascular damage and to promote clot
formation and tissue repair. Secretion from their three granular stores
is essential to hemostasis and our goal is to understand the mechanisms
of this secretory process. In the resting platelet, hemostatic and
tissue repair-inducing components are stored in three types of membrane
bound granules. Upon stimulation, these granules are targeted to
specific sites on the platelet's plasma membrane where the granule
membranes fuse with the plasma membrane thus releasing the granule
contents. Our studies are designed to determine what platelet proteins
are involved in the steps leading to secretion. We are specifically
interested in how the activities of these proteins are controlled by the
signaling cascades that are initiated by external events such as
vascular damage.
As
part of these studies, we have also focused on a Ras-related ,small GTP
binding protein called ADP Ribosylation Factors 6 (Arf6). In our
groundbreaking studies, we have shown that Arf6 is critical for the
platelet cytoskeletal rearrangements needed for aggregation and clot
formation. This work is particularly exciting since it places Arf6 as a
central regulator of many of the steps that occur in activated
platelets.
NSF:
All membrane trafficking events are mediated by integral membrane
proteins (SNAREs) that span the two fusing bilayers and promote membrane
fusion. Once fusion is accomplished, the complex formed by the spent
SNAREs must be disassembled for recycling. Our group focuses on the
enzyme that disassembles all cellular SNARE complexes and is thus
essential to all membrane trafficking events. The N-ethylmaleimide
Sensitive Fusion protein (NSF) is a homo-hexamer whose subunits contain
three domains (an amino and two ATP binding domains). It is our
hypothesis that each domain of NSF is responsible for a distinct aspect
of the SNARE recycling process. Our laboratory uses structure-based
mutagenesis together with a battery of assays to determine what parts of
the NSF hexamer are responsible for the various processes required to
disassemble SNARE complexes.
Representative
Publications:
Chen,
D., Bernstein, A.M., Lemons, P.P., and Whiteheart, S.W., (2000)
Molecular Mechanisms of Platelet Exocytosis: Role of SNAP-23 and
Syntaxin 2 in Dense Core Granule Release. Blood, 95, 921.
Ren,
Q., Barber, H.K., Crawford, G.L., Karim, Z.A., Zhao, C., Choi, W., Wang,
C.C., Hong, W., and Whiteheart, S.W. (2007) Endobrevin/VAMP-8 is the
Primary v-SNARE Required for the Platelet Release Reaction. Molecular
Biology of the Cell 18, 24.
Choi,
W., Karim, Z. and Whiteheart, S.W. (2006) Arf6 Plays an Early Role in
Platelet Activation by Collagen and Convulxin. Blood 107, 3145.
Hanson, P.I. and Whiteheart, S.W. (2005) AAA ATPases: Have Engine Will
Work. Nature Reviews, Molecular Cell Biology, 6, 519.
May,
A.P., Misura, K.M.S., Whiteheart, S.W., and Weis, W.I. (1999) Crystal
Structure of the Amino-Terminal Domain of the N-ethylmaleimide Sensitive
Fusion Protein (NSF). Nature Cell Biology, 1, 175
Lenzen, C.U., Oppitz, D., Whiteheart, S.W., and Weis, W.I. (1998)
Crystal Structure of the Hexamerization Domain of N-Ethylmaleimide-Sensitive
Fusion Protein. Cell, 94, 525-536.
Current Publications:
Rutledge, T. W. and Whiteheart, S.W. (2004) Studies of Secretion Using
Permeabilized Platelets. Platelets and Megakaryocytes: Vol. 1
Functional Assays, Gibbins, J.M. and Mahaut-Smith, M.P. eds.,
Methods in Molecular Biology Vol. 272, p. 109.
Schraw, T.D., Crawford, G.L., Ren, Q., Choi, W., Thurmond, D. C., Pessin,
J. E., and Whiteheart, S.W. (2004) Platelets from Munc18c Heterozygous
Mice Exhibit Normal Stimulus-Induced Release. Thrombosis and
Haemostasis, 92, 829.
Schraw, T.D. and Whiteheart,
S.W. (2005)
The
development of a quantitative ELISA to detect human platelet factor 4.
Transfusion. 45, 717.
Hepp,
R., Puri, N., Hohenstein, A.C., Crawford, G.L., Whiteheart, S.W., and
Roche, P.A. (2005) Phosphorylation of SNAP-23 Regulates Exocytosis from
Mast Cells. Journal of Biological Chemistry, 280, 6610.
Choi,
W., Karim, Z. and Whiteheart, S.W. (2006) Arf6 Plays an Early Role in
Platelet Activation by Collagen and Convulxin. Blood 107, 3145.
Matveeva, E.A., Vanaman, T.C., Whiteheart, S.W., and Slevin, J.T. (2007)
Asymmetric Accumulation of Hippocampal 7S SNARE Complexes Occurs
Regardless of Kindling Paradigm. Epilepsy Research 73, 266.
Ren,
Q., Barber, H.K., Crawford, G.L., Karim, Z.A., Zhao, C., Choi, W., Wang,
C.C., Hong, W., and Whiteheart, S.W. (2007) Endobrevin/VAMP-8 is the
Primary v-SNARE Required for the Platelet Release Reaction. Molecular
Biology of the Cell 18, 24.
Zhao,
C., Slevin, J.T., and Whiteheart, S.W. (2007) Cellular Functions of NSF:
Not Just SNAPs and SNAREs. FEBS Letters 581, 2140.
