Inverted formin 2 in focal adhesions promotes dorsal stress fiber and fibrillar adhesion formation to drive extracellular matrix assembly

Proc Natl Acad Sci U S A. 2015 May 12;112(19):E2447-56. doi: 10.1073/pnas.1505035112. Epub 2015 Apr 27.


Actin filaments and integrin-based focal adhesions (FAs) form integrated systems that mediate dynamic cell interactions with their environment or other cells during migration, the immune response, and tissue morphogenesis. How adhesion-associated actin structures obtain their functional specificity is unclear. Here we show that the formin-family actin nucleator, inverted formin 2 (INF2), localizes specifically to FAs and dorsal stress fibers (SFs) in fibroblasts. High-resolution fluorescence microscopy and manipulation of INF2 levels in cells indicate that INF2 plays a critical role at the SF-FA junction by promoting actin polymerization via free barbed end generation and centripetal elongation of an FA-associated actin bundle to form dorsal SF. INF2 assembles into FAs during maturation rather than during their initial generation, and once there, acts to promote rapid FA elongation and maturation into tensin-containing fibrillar FAs in the cell center. We show that INF2 is required for fibroblasts to organize fibronectin into matrix fibers and ultimately 3D matrices. Collectively our results indicate an important role for the formin INF2 in specifying the function of fibrillar FAs through its ability to generate dorsal SFs. Thus, dorsal SFs and fibrillar FAs form a specific class of integrated adhesion-associated actin structure in fibroblasts that mediates generation and remodeling of ECM.

Keywords: INF2; actin; fluorescence microscopy; integrin.

Publication types

  • Research Support, N.I.H., Intramural
  • Retracted Publication

MeSH terms

  • Actins / metabolism
  • Animals
  • Cell Adhesion
  • Cytoskeleton / metabolism
  • Extracellular Matrix / metabolism*
  • Fibroblasts / metabolism
  • Fibronectins / metabolism
  • Focal Adhesions / metabolism*
  • Formins
  • Green Fluorescent Proteins / metabolism
  • Humans
  • Integrins / metabolism
  • Mice
  • Microfilament Proteins / metabolism*
  • Microscopy, Confocal
  • Microscopy, Fluorescence
  • Protein Isoforms
  • Pseudopodia / metabolism
  • RNA, Small Interfering / metabolism
  • Stress Fibers / metabolism*


  • Actins
  • Fibronectins
  • Formins
  • INF2 protein, human
  • INF2 protein, mouse
  • Integrins
  • Microfilament Proteins
  • Protein Isoforms
  • RNA, Small Interfering
  • Green Fluorescent Proteins