Differential Contributions of Nonmuscle Myosin II Isoforms and Functional Domains to Stress Fiber Mechanics.
While is widely acknowledged that nonmuscle myosin II (NMMII) enables stress fibers (SFs) to generate traction forces against the extracellular matrix, little is known about how specific NMMII isoforms and functional domains contribute to SF mechanics. Here we combine biophotonic and genetic approaches to address these open questions. First, we suppress the NMMII isoforms MIIA and MIIB and apply femtosecond laser nanosurgery to ablate and investigate the viscoelastic retraction of individual SFs. SF retraction dynamics associated with MIIA and MIIB suppression qualitatively phenocopy our earlier measurements in the setting of Rho kinase (ROCK) and myosin light chain kinase (MLCK) inhibition, respectively. Furthermore, fluorescence imaging and photobleaching recovery reveal that MIIA and MIIB are enriched in and more stably localize to ROCK- and MLCK-controlled central and peripheral SFs, respectively. Additional domain-mapping studies surprisingly reveal that deletion of the head domain speeds SF retraction, which we ascribe to reduced drag from actomyosin crosslinking and frictional losses. We propose a model in which ROCK/MIIA and MLCK/MIIB functionally regulate common pools of SFs, with MIIA crosslinking and motor functions jointly contributing to SF retraction dynamics and cellular traction forces.
Department of Bioengineering, University of California, Berkeley, Berkeley, CA 94720.
Ching-Wei
CW
Chang
Department of Bioengineering, University of California, Berkeley, Berkeley, CA 94720.
Sanjay
S
Kumar
D000595:Amino Acid Sequence; D055119:Elastic Modulus / Q000502:physiology; D006801:Humans; D020409:Molecular Motor Proteins / Q000737:chemistry / Q000502:physiology; D008969:Molecular Sequence Data; D018482:Muscle, Skeletal / Q000737:chemistry / Q000502:physiology; D024462:Myosin Type II / Q000737:chemistry* / Q000502:physiology*; D009219:Myosin-Light-Chain Kinase / Q000737:chemistry / Q000502:physiology*; D020033:Protein Isoforms / Q000737:chemistry / Q000502:physiology; D017434:Protein Structure, Tertiary; D022502:Stress Fibers / Q000737:chemistry* / Q000502:physiology*; D013314:Stress, Mechanical; D013329:Structure-Activity Relationship; D014783:Viscosity; D054460:rho-Associated Kinases / Q000737:chemistry / Q000502:physiology*
D020409:Molecular Motor Proteins; D020033:Protein Isoforms; D054460:rho-Associated Kinases; D009219:Myosin-Light-Chain Kinase; D024462:Myosin Type II