Cell cycle-dependence of HL-60 cell deformability

In this study, the role of cytoskeleton in HL-60 deformability during the cell cycle was investigated. G(1), S, and G(2)/M cell fractions were separated by centrifugal elutriation. Cell deformability was evaluated by pipette aspiration. Tested at the same aspiration pressures, S cells were found to be less deformable than G(1) cells. Moreover, HL-60 cells exhibited power-law fluid behavior. mu = mu(c)(gamma(m)/gamma(c))(-b), where mu is cytoplasmic viscosity, gamma(m) is mean shear rate, mu(c) is the characteristic viscosity at the characteristic shear rate gamma(c) and b is a material constant. At a given shear rate, S cells (mu(c) = 276 +/- 14 Pa . s, b = 0.51 +/- 0.03) were more viscous than G(1) cells (mu c = 197 +/- 25, b = 0.53 +/- 0.02). To evaluate the relative importance of different cytoskeletal components in these cell cycle-dependent properties, HL-60 cells were treated with 30 mu M dihydro-cytochalasin B (DHB) to disrupt F-actin or 100 mu M colchicine tb collapse microtubules. DHB dramatically softened both G(1) and S cells, which reduced the material constants mu(c) by similar to 65% and b by 20-30%. Colchicine had a limited effect on G(1) cells but significantly reduced mu(c) of S cells (similar to 25%), Thus, F-actin plays the predominate role in determining cell mechanical properties, but disruption of microtubules may also influence the behavior of proliferating cells in a cell cycle-dependent fashion.