(271a) Focal Adhesion Architecture and Composition Regulate Cell Adhesion and Traction Generation Independent of Integrin Class

Integrins are a class of
heterodimeric transmembrane proteins that mediate attachment to the
extracellular matrix (ECM) and serve as templates for focal adhesions (FAs),
sophisticated protein complexes that regulate mechanical and chemical signals.
At present, the mechanisms by which specific focal adhesion architectures
affect traction generation and cellular adhesion remain poorly understood. Here,
we use Förster resonance energy transfer (FRET)-based molecular tension sensors
(MTSs) to measure the distribution of mechanical forces exerted by individual
integrin heterodimers in living cells at the single-molecule level. We
engineered two MTS variants: MTS_low, to
probe a low force range (0-8 pN), and MTS_int, for examining intermediate forces (8-12
pN). We find the majority of bound integrins bear forces <12 pN and that integrins
within defined adhesion complexes exert tractions that fall into distinct subpopulations.
Using integrin knock-out lines rescued with specific integrin classes, we find that
the single-molecule force distributions remain remarkably similar, indicating
that these subpopulations are not primarily determined by the integrin class. Furthermore,
we find that although integrin linkages bearing more than 6 pN are actin
mediated, they are not required to support cell adhesion. In ongoing work, we investigate
how perturbations to FA architecture and composition alter traction on the
molecular and cellular levels.