SUNDAY, DECEMBER 4- Late Abstracts 1 - Molecular Biology of the ...

SUNDAY
2047
The Scar/WAVE complex is necessary for proper regulation of traction stresses during
amoeboid motility.
E. E. Bastounis 1 , R. Meili 2 , B. Alonso Latorre 2 , J-C. del Alamo 2 , J. Lasheras 2 , R. Firtel 2 ;
1 Bioengineering, University of California, San Diego, San Diego, CA, 2 University of California,
San Diego
Chemotaxis, or directed cell migration, is involved in a broad spectrum of biological phenomena,
ranging from the metastatic spreading of cancer to the active migration of neutrophils during
wound healing or in response to bacterial infection. Chemotaxis requires a tightly regulated,
spatiotemporal coordination of underlying biochemical processes. SCAR/WAVE-mediated
dendritic F-actin polymerization at the cell’s leading edge plays a key role in cell migration. Our
study identifies a mechanical and biochemical role for the SCAR/WAVE complex in modulating
the traction stresses that drive cell movement. We demonstrate that the traction stresses of
wild-type Dictyostelium cells or cells lacking the SCAR/WAVE complex protein PIR121 (pirA-) or
SCAR (scrA-) exert stresses of different strength that correlate with their levels of F-actin. By
processing the time records of the cell length and the strain energy exerted by the cells on their
substrate, we show that wild-type cells migrate by repeating a specific set of mechanical steps
(motility cycle), whereby the cell length (L) and the strain energy exerted by the cells on their
substrate (Us) vary periodically. Our analysis also revealed that scrA- cells exhibit an altered
motility cycle with a longer period (T=160s) and a lower migration velocity (V =6μm/min)
compared to those of wild-type cells (T=80s, V =13μm/min). In marked contrast to these strains,
pirA- cells, although they have a higher F-actin content, migrate as slowly as scrA- cells but their
migration occurs in a seemingly random manner in that they lack the periodic changes in
traction stresses that are observed for the other two strains. Finally, by quantifying the level of
F-actin in the leading edge in combination with the traction stresses, we demonstrated that the
level of leading edge, SCAR/WAVE complex-mediated F-actin polymerizations is critical for the
level and spatiotemporal control of the traction stresses, cell-substrate interactions, and the
motility cycle.
2048
Self-Generated EGF Gradients Guide Epithelial Cell Migration.
D. Irimia 1 , A. J. Aranyosi 1 , B. Kulemann 1 , S. Thayer 1 , M. Toner 1 , O. Illiopoulos 1 , C. Scherber 1 ;
1 BioMEMS Resource Center, Massachusetts General Hospital/Harvard Medical School, Boston,
MA
Migrating epithelial cells can contribute to wound healing processes, or can trigger lethal
complications during cancer through invasion and distant metastasis. During their migration,
cells must be able to orient accurately and it is generally assumed that gradients of chemokines
or growth factors are required to guide epithelial cells towards their target location.
Unexpectedly, we uncovered a novel strategy for epithelial cell orientation during migration that
does not require pre-existent chemical gradients. Using microscale engineering techniques, we
demonstrate that the strategy is dependent on the competition between epidermal growth factor
(EGF) uptake by the cells and the restricted diffusion of EGF from surrounding
microenvironment. Both normal and malignant epithelial cells are capable of EGF uptake and
can use this strategy when placed in confined environment. The strategy has some surprising
consequences for epithelial cells, like the ability to efficiently disperse through channels, or to
navigate along the shortest path to exit from various microscopic mazes. Inhibition of EGFreceptor
but not the inhibition of chemokine receptors, reduces the ability of the cells to orient,
without altering their velocity of migration. Better understanding of the epithelial cells guidance
strategy by EGF uptake-dependent self-generated gradients could lead to approaches for