Characterization of cellular dielectrophoretic (DEP) behaviors, when cells are exposed to an alternating current (AC) electric field of varying frequency, is fundamentally important to many applications using dielectrophoresis. However, to date, that characterization has been performed with monotonically increasing or decreasing frequency, not with successive increases and decreases, even though cells might behave differently with those frequency modulations due to the nonlinear cellular electrodynamic responses reported in previous works. In this report, we present a method to trace the behaviors of numerous cells simultaneously at the single-cell level in a simple, robust manner using dielectrophoretic tweezers-based force spectroscopy. Using this method, the behaviors of more than 150 cells were traced in a single environment at the same time, while a modulated DEP force acted upon them, resulting in characterization of nonlinear DEP cellular behaviors and generation of different cross-over frequencies in living cells by modulating the DEP force. This study demonstrated that living cells can have non-linear di-polarized responses depending on the modulation direction of the applied frequency as well as providing a simple and reliable platform from which to measure a cellular cross-over frequency and characterize its nonlinear property.
Interferon (IFN)-β and/or tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) secreted by adipose tissue-derived mesenchymal stem cells (ASCs) have been proposed as key mechanistic factors in anti-cancer efficacy in lung cancer and breast cancer cells, where they act through paracrine signaling. We hypothesized that IFN-β and TRAIL produced by ASCs suppress proliferation of hepatocellular carcinoma cells (HCCs). The present study evaluated the anti-cancer effects of ASCs on HCCs in vitro. We found that indirect co-culture with ASCs diminished growth of Huh7 hepatocellular carcinoma cells with increased protein levels of p53/p21 and phosphorylated STAT1 (pSTAT1), without apoptosis. Treatment with ASC-conditioned medium (ASC-CM) also decreased growth of Huh7 cells through elevated p53/p21 and pSTAT1 signaling. ASC-CM-mediated inhibition of cell growth was neutralized in Huh7 cells treated with anti-IFN-β antibody compared to that in ASC-CM-treated Huh7 cells incubated with an anti-TRAIL antibody. Treatment with JAK1/JAK2 inhibitors recovered inhibition of growth in Huh7 cells incubated in ASC-CM or IFN-β via down-regulation of pSTAT1/p53/p21. However, treatment of IFN-β resulted in no alterations in resistance of Huh7 cells to TRAIL. Our findings suggest that ASCs decrease growth through activated STAT1-mediated p53/p21 by IFN-β, but not TRAIL, in Huh7 cells.
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