Filamin-A and Rheological Properties of Cultured
Melanoma Cells
Mark F. Coughlin 1*, Marina Puig-de-Morales 1, Predrag Bursac 1, Matthew Mellema 1, Emil Millet 1 and Jeffrey J. Fredberg 1
1 Harvard School of Public Health
* To whom correspondence should be addressed. E-mail: mcoughli{at}hsph.harvard.edu.
Submitted on February 19, 2005
Revised on April 25, 2005
Accepted on 15 November 2005
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Abstract |
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Here we report the rheological properties of cultured hsFLNa (filamin-A)-expressing (FIL+) and hsFLNa-deficient (FIL-) melanoma cells. Using magnetic twisting cytometry over a wide range of probing frequencies, and targeting either cortical or deeper cytoskeletal structures, we found that differences in stiffness of FIL+ versus FIL- cells were remarkably small. When probed through deep cytoskeletal structures FIL+ cells were at most 30% stiffer than FIL- cells, whereas when probed through more peripheral cytoskeletal structures FIL- cells were not different except at very high frequencies. The loss tangent, expressed as an effective cytoskeletal temperature, was systematically greater in FIL- than FIL+ cells, but these differences were small and showed that the FIL+ cells were only slightly closer to a solid-like state. To quantify cytoskeletal remodeling we measured spontaneous motions of beads bound to cortical cytoskeletal structures, and found no difference in FIL+ versus FIL- cells. Although mechanical differences between FIL+ and FIL- cells were evident both in cortical and deeper structures, these differences were far smaller than expected based on measurements of the rheology of purified actin-filamin solutions. These findings do not rule out an important contribution of filamin to the mechanical properties of the cortical cystoskeleton, but suggest that effects of filamin in the cortex are not exerted on the length scale of the probe used here. These findings would appear to rule out any important contribution of filamin to the bulk mechanical properties of the cytoplasm, however. Although filamin is present in the cytoplasm, it may be inactive, its mechanical effects may be small compared with other crosslinkers, or mechanical properties of the matrix may be dominated by an overriding role of cytoskeletal prestress.
Key Words:
Cytoskeletal Mechanics, Effective Cytoskeletal Temperature, Loss Modulus, Magnetic Twisting Cytometry, Soft Glassy Rheology, Storage Modulus
