VIMENTIN AND CYTOKERATIN INTERMEDIATE FILAMENTS IN THE MECHANOBIOLOGY AND MALIGNANT BEHAVIORS OF CHORDOMA CELLS
Hsieh, Adam H
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Chordoma, an aggressive tumor derived from notochordal remnants, is difficult to treat due to its proximity to the spinal cord and brain stem and its resistance to conventional treatments, such as radiation and chemotherapy. The development of effective treatments requires research at the molecular level, which presumably due to its rare diagnosis, is lacking for chordoma. Recent studies have identified potential targets for systemic therapy; however, there are currently no drugs approved by the Food and Drug Administration (FDA) to treat chordoma. One promising approach is to target the cytoskeleton, in order to stall progression and sensitize cells to chemotherapeutics. Similar to other cancers, chordoma cells co-express vimentin and cytokeratin intermediate filaments (IFs), which have both been found to play roles in cell mechanical properties and behaviors and their expression has been associated with cancer metastasis, chemoresistance, and poor prognosis. Therefore, we investigated the functional roles of vimentin and cytokeratin IFs in chordoma cells using RNA interference (RNAi). First, we examined whether cytoskeletal disruption by siRNA-mediated silencing of vimentin or cytokeratin-8 altered the chordoma phenotype. We determined that the vacuolated cytoplasm, a distinguishing feature of chordoma, was dependent on cytokeratin-8 IFs. Next, we examined the effects of vimentin and cytokeratin-8 knockdown on chordoma cell mechanics. We found that chordoma cell stiffness, traction forces, and mechanosensitivity to substrate stiffness were all dependent on vimentin IFs. These results suggest that vimentin, rather than cytokeratin, IFs play a predominant role in chordoma cell mechanobiology. Finally, we analyzed the roles of vimentin and cytokeratin-8 IFs in cellular behaviors associated with cancer progression. We demonstrated that chordoma cell invasion and expression of the biomarker sonic hedgehog were dependent on vimentin. Further, we found that decreasing vimentin expression in chordoma cells may increase their sensitivity to chemotherapeutics. Because mechanical cues are important determinants of cell function, we hypothesize this correlation is in part due to the newly discovered role of vimentin IFs in chordoma cell mechanobiology. These results elucidate novel roles of vimentin and cytokeratin-8 IFs in chordoma cells, which may assist in the development of effective treatments for chordoma.