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Structure and Function of Integrins

D. Calderwood, F.-L. Chou, C. Feral, Y. Fujioka, A. Glading, L. Goldfinger, J. Han, K. Kimbara, J. Krueger, J. Lin, S. Lizano, S. Liu, T. Nakamoto, N. Nishiya, B. Ratnikov, J.-C. Shieh, M. Ginsberg

The development and functioning of multicellular animals depend on integrins. These adhesion receptors link to the actin cytoskeleton, resulting in transmission of biochemical signals and of force during cell migration and interactions with the extracellular matrix. One class of integrin-cytoskeletal connections is formed by the filamins, parallel dimers that anchor integrins to the cortical actin cytoskeleton; another is mediated by antiparallel dimers of talin or a-actinin.

To examine the biological significance of different linkages, we assessed the effect of switching the cytoskeletal class selectivity of integrin b cytoplasmic domains. We found that the b₇ integrin tail, which binds strongly to filamin, supports less migration, assembly of fibronectin matrix, and formation of focal adhesions than either the b_1D tail, which binds strongly to talin, or the b_1A tail, which binds to both filamin and talin with modest affinity. To specifically probe the role of filamin binding in integrin function, we mapped the filamin-binding site in the integrin tails and identified conserved (isoleucine-valine) substitutions that led to selective loss of filamin binding to the b₇ tail and gain of filamin binding to the b_1A tail. Loss of filamin binding to the b₇ tail resulted in dramatic enhancement of cell migration and an increase in transient membrane protrusions. Conversely, the gain of filamin binding to the b_1A tail strongly suppressed cell migration and membrane protrusion. These changes in filamin binding did not alter assembly of a fibronectin matrix or formation of focal adhesions. Thus, tight filamin binding restricts integrin-dependent cell migration by inhibiting transient membrane protrusion and cell polarization.

The ERK 1/2 MAP kinase pathway controls cell growth and survival and modulates integrin function. We found that PEA-15, a protein variably expressed in multiple cell types, blocks ERK-dependent transcription and proliferation by binding ERKs and preventing their localization in the nucleus. Anchoring of ERK in the cytoplasm by PEA-15 requires the presence of a nuclear export sequence in the protein. Genetic deletion of PEA-15 results in increased ERK nuclear localization, with consequent increased cFos transcription and cell proliferation. Thus, PEA-15 redirects the biological outcomes of the ERK MAP kinase pathway. These results support a new model for regulation of MAP kinase signaling by proteins that enforce sequestration of MAP kinases in specific cellular locations.

PUBLICATIONS

Calderwood, D.A., Huttenlocher, A., Kiosses, W.B., Schwartz, M.A., Ginsberg, M.H. Increased filamin binding to integrin b cytoplasmic domains inhibits cell migration. Nat. Cell Biol. 3:1060, 2001.

Formstecher, E., Ramos, J.W., Fauquet, M., Calderwood, D.A., Hsieh, J.C., Canton, B., Nguyen, X.T., Barnier, J.V., Camonis, J., Ginsberg, M.H., Chneiweiss, H. PEA-15 mediates cytoplasmic sequestration of ERK MAP kinase. Dev. Cell 1:239 2001.

Han, J., Liu, S., Rose, D.M., Schlaepfer, D.D., McDonald, H., Ginsberg, M.H. Phosphorylation of the integrin a₄ cytoplasmic domain regulates paxillin binding. J. Biol. Chem. 276:40903, 2001.

Hughes, P.E., Oertli, B., Han, J., Ginsberg, M.H. R-Ras regulation of integrin function. Methods Enzymol. 333:163, 2001.

Liu, S., Kiosses, W., Rose, D.M., Slepak, M., Salgia, R., Griffin, J.D., Turner, C.E., Schwartz, M.A., Ginsberg, M.H. A fragment of paxillin binds the a₄ integrin cytoplasmic domain (tail) and selectively inhibits a₄-mediated cell migration. J. Biol. Chem. 277:20887, 2002.

Liu, S., Slepak, M., Ginsberg, M.H. Binding of paxillin to the a₉ integrin cytoplasmic domain inhibits cell spreading. J. Biol. Chem. 276:37086, 2001.

Rose, D.M., Grabovsky, V., Alon, R., Ginsberg, M.H. The affinity of integrin a₄b₁ governs lymphocyte migration. J. Immunol. 167:2824, 2001.

Woodside, D.G., Liu, S., Ginsberg, M.H. Integrin activation. Thromb. Haemost. 86:316, 2001.

Woodside, D.G., Obergfell, T.D., Leng, L., Wilsbacher, J.L., Miranti, C.K., Brugge, J.S., Shattil, S.J., Ginsberg, M.H. Activation of Syk protein tyrosine kinase through interaction with integrin b cytoplasmic domains. Curr. Biol. 11:1799, 2001.

Woodside, D.G., Shattil, S.J., Ginsberg, M.H. The T cell receptor SLAPs integrins together. Nat. Immunol. 2:904, 2001.

Yan, B., Calderwood, D.A., Yaspan, B., Ginsberg, M.H. Calpain cleavage promotes talin binding to the b₃ integrin cytoplasmic domain. J. Biol. Chem. 276:28164, 2001.