ABSTRACT
Filopodia are actin-dependent finger-like structures that protrude from the plasma membrane. Actin filament barbed-end-binding proteins localized to filopodial tips are key to filopodial assembly. Two classes of barbed-end-binding proteins are formins and Ena/VASP proteins, and both classes have been localized to filopodial tips in specific cellular contexts. Here, we examine the filopodial roles of the FMNL formins and Ena/VASP proteins in U2OS cells. FMNL3 suppression reduces filopodial assembly by 90%, and FMNL3 is enriched at >95% of filopodial tips. Suppression of VASP or Mena (also known as ENAH) reduces filopodial assembly by >75%. However, VASP and Mena do not display consistent filopodial tip localization, but are enriched in focal adhesions (FAs). Interestingly, >85% of FMNL3-containing filopodia are associated with FAs. Two situations increase Ena/VASP filopodial localization: (1) expression of myosin-X, and (2) actively spreading cells. In spreading cells, filopodia often mark sites of nascent adhesions. Interestingly, VASP suppression in spreading cells causes a significant increase in adhesion assembly at filopodial tips. This work demonstrates that, in U2OS cells, Ena/VASP proteins play roles in filopodia beyond those at filopodial tips.
This article has an associated First Person interview with the first author of the paper.
Footnotes
Competing interests
The authors declare no competing or financial interests.
Author contributions
Conceptualization: L.E.Y., H.N.H.; Methodology: L.E.Y., H.N.H.; Validation: L.E.Y.; Formal analysis: L.E.Y.; Investigation: L.E.Y., C.J.L.; Writing - original draft: L.E.Y., H.N.H.; Writing - review & editing: L.E.Y., H.N.H.; Visualization: L.E.Y.; Supervision: H.N.H.; Project administration: H.N.H.; Funding acquisition: H.N.H.
Funding
This work was supported by National Institutes of Health (NIH R01 GM109965 and NIH R35 GM122545 to H.N.H., as well as NIH P20 GM113132. Deposited in PMC for release after 12 months.
Supplementary information
Supplementary information available online at http://jcs.biologists.org/lookup/doi/10.1242/jcs.220814.supplemental
- Received May 24, 2018.
- Accepted September 25, 2018.
- © 2018. Published by The Company of Biologists Ltd
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