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SHARPIN is an endogenous inhibitor of β1-integrin activation

Abstract

Regulated activation of integrins is critical for cell adhesion, motility and tissue homeostasis. Talin and kindlins activate β1-integrins, but the counteracting inhibiting mechanisms are poorly defined. We identified SHARPIN as an important inactivator of β1-integrins in an RNAi screen. SHARPIN inhibited β1-integrin functions in human cancer cells and primary leukocytes. Fibroblasts, leukocytes and keratinocytes from SHARPIN-deficient mice exhibited increased β1-integrin activity, which was fully rescued by re-expression of SHARPIN. We found that SHARPIN directly binds to a conserved cytoplasmic region of integrin α-subunits and inhibits recruitment of talin and kindlin to the integrin. Therefore, SHARPIN inhibits the critical switching of β1-integrins from inactive to active conformations.

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Figure 1: SHARPIN is an inhibitor of β1-integrin activity.
Figure 2: SHARPIN interacts with the conserved membrane proximal segment of integrin α-tails.
Figure 3: SHARPIN co-localizes with inactive β1-integrins in membrane ruffles and associates with them in cells.
Figure 4: SHARPIN directly interacts with β1-integrins in cells and inhibits recruitment of talin and kindlin to β1-integrins.
Figure 5: SHARPIN inhibits β1-integrin activity in primary human leukocytes.
Figure 6: Loss of SHARPIN correlates with increased β1-integrin activity in vivo.

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Acknowledgements

We thank H. Marttila, J. Siivonen, L. Lahtinen, R. Kaukonen, E. Väänänen, K. Silva and A. Arola for technical assistance. P.R. Elliot is acknowledged for the recombinant talin 1–400 protein. R. Fässler, M. Ginsberg, J. Norman and S. Lee are acknowledged for the plasmids. This study has been supported by the Academy of Finland, EU-FP06 project ENLIGHT, a European Research Council Starting Grant, the Sigrid Juselius Foundation, the European Molecular Biology Organization (EMBO) Young Investigator Programme and Finnish Cancer Organizations. J.P. and E.M., Academy of Finland postdoc grant; T.P., Turku Graduate School of Biomedical Sciences; S.V., Alexander von Humbold foundation and an EMBO long-term fellowship. C.S.P. and J.P.S were supported by the National Institutes of Health (T32 DK07449-28 to C.S.P. and AR49288 to J.P.S.).

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J.K.R. and O.K. developed cell spot microarrays, J.K.R. and T.P. carried out the screen. J.K.R., J.P., P.L., S.V. and J.I. carried out the experiments. E.M. immortalized the MEFs. M.P. carried out the FRET-FLIM, C.S.P, T.D. and J.P.S. contributed to the mouse data, J.A.A. and M.J.H. contributed to the legs together integrin experiments and M.S. contributed to the leukocyte work. J.P., J.I. and M.S. wrote the manuscript.

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Correspondence to Johanna Ivaska.

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Rantala, J., Pouwels, J., Pellinen, T. et al. SHARPIN is an endogenous inhibitor of β1-integrin activation. Nat Cell Biol 13, 1315–1324 (2011). https://doi.org/10.1038/ncb2340

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