In this work, atomic force microscopy (AFM) based techniques (imaging and measurements of cell stiffness) and fluorescence staining were used to monitor apoptosis in larynx carcinoma HEp2 cells. HEp2 were exposed to TRAIL (TNF-related apoptosis inducing ligand), Actinomycin-D (a chemotherapeutic drug) or to a simultaneous action of these agents. For incubation with TRAIL,  an increase in the stiffness of the cells was observed and correlated with the rearrangement of cell cytoskeleton, particularly actin fibers. However, the detection of apoptotic cells using fluorescence markers revealed the resistance of HEp2 cells to TRAIL-mediated apoptosis. Most probably, TRAIL initiates apoptosis in HEp2 cells, but the apoptosis process was terminated by anti-apoptotic agents. Unblocking of apoptosis by sensitization of HEp2 cells with a chemoterapeutic drug Actinomycin-D is related to the depolymerization of F-actin with the decrease in the cell stifness. Most probably, the depolymerization of actin results from downregulation of Rho protein, which in turn is accompanied by a lower activity of Bcl-2 and in consequence releases the intrinsic apoptotic channel. The presented results reveal a promising application of nanoindentaion spectroscopy with AFM tip as a novel tool for monitoring the apoptosis inhibition processes.

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