Stress fiber strain recognition by the LIM protein testin is cryptic and mediated by RhoA

Mol Biol Cell. 2021 Aug 19;32(18):1758-1771. doi: 10.1091/mbc.E21-03-0156. Epub 2021 May 26.


The actin cytoskeleton is a key regulator of mechanical processes in cells. The family of LIM domain proteins have recently emerged as important mechanoresponsive cytoskeletal elements capable of sensing strain in the actin cytoskeleton. The mechanisms regulating this mechanosensitive behavior, however, remain poorly understood. Here we show that the LIM domain protein testin is peculiar in that despite the full-length protein primarily appearing diffuse in the cytoplasm, the C-terminal LIM domains alone recognize focal adhesions and strained actin, while the N-terminal domains alone recognize stress fibers. Phosphorylation mutations in the dimerization regions of testin, however, reveal its mechanosensitivity and cause it to relocate to focal adhesions and sites of strain in the actin cytoskeleton. Finally, we demonstrate that activated RhoA causes testin to adorn stress fibers and become mechanosensitive. Together, our data show that testin's mechanoresponse is regulated in cells and provide new insights into LIM domain protein recognition of the actin cytoskeleton's mechanical state.

Publication types

  • Research Support, U.S. Gov't, Non-P.H.S.
  • Video-Audio Media

MeSH terms

  • Actins / metabolism
  • Cells, Cultured
  • Cytoskeletal Proteins / genetics
  • Cytoskeletal Proteins / metabolism*
  • Fibroblasts / cytology
  • Fibroblasts / metabolism
  • Focal Adhesions / physiology
  • Humans
  • LIM Domain Proteins / metabolism
  • Mechanotransduction, Cellular / physiology
  • Protein Domains
  • RNA-Binding Proteins / genetics
  • RNA-Binding Proteins / metabolism*
  • Stress Fibers / physiology*
  • Traction
  • Tyrosine / genetics
  • rhoA GTP-Binding Protein / metabolism*


  • Actins
  • Cytoskeletal Proteins
  • LIM Domain Proteins
  • RNA-Binding Proteins
  • TES protein, human
  • RHOA protein, human
  • Tyrosine
  • rhoA GTP-Binding Protein