title: Substrate stiffness regulates filopodial activities in lung cancer cells.
abstract: Microenvironment stiffening plays a crucial role in tumorigenesis. While filopodia are generally thought to be one of the cellular mechanosensors for probing environmental stiffness, the effects of environmental stiffness on filopodial activities of cancer cells remain unclear. In this work, we investigated the filopodial activities of human lung adenocarcinoma cells CL1-5 cultured on substrates of tunable stiffness using a novel platform. The platform consists of an optical system called structured illumination nano-profilometry, which allows time-lapsed visualization of filopodial activities without fluorescence labeling. The culturing substrates were composed of polyvinyl chloride mixed with an environmentally friendly plasticizer to yield Young's modulus ranging from 20 to 60 kPa. Cell viability studies showed that the viability of cells cultured on the substrates was similar to those cultured on commonly used elastomers such as polydimethylsiloxane. Time-lapsed live cell images were acquired and the filopodial activities in response to substrates with varying degrees of stiffness were analyzed. Statistical analyses revealed that lung cancer cells cultured on softer substrates appeared to have longer filopodia, higher filopodial densities with respect to the cellular perimeter, and slower filopodial retraction rates. Nonetheless, the temporal analysis of filopodial activities revealed that whether a filopodium decides to extend or retract is purely a stochastic process without dependency on substrate stiffness. The discrepancy of the filopodial activities between lung cancer cells cultured on substrates with different degrees of stiffness vanished when the myosin II activities were inhibited by treating the cells with blebbistatin, which suggests that the filopodial activities are closely modulated by the adhesion strength of the cells. Our data quantitatively relate filopodial activities of lung cancer cells with environmental stiffness and should shed light on the understanding and treatment of cancer progression and metastasis.
authors.affiliation: Graduate Institute of Biomedical Electronics and Bioinformatics, National Taiwan University, Taipei, Taiwan.
authors.forename: Yu-Ren
authors.initials: YR
authors.lastname: Liou
authors.affiliation: Department of Electrical Engineering, National Taiwan University, Taipei, Taiwan.
authors.forename: Wen
authors.initials: W
authors.lastname: Torng
authors.affiliation: Graduate Institute of Biomedical Electronics and Bioinformatics, National Taiwan University, Taipei, Taiwan ; Research Center for Applied Sciences, Academia Sinica, Taipei, Taiwan.
authors.forename: Yu-Chiu
authors.initials: YC
authors.lastname: Kao
authors.affiliation: Graduate Institute of Biomedical Electronics and Bioinformatics, National Taiwan University, Taipei, Taiwan.
authors.forename: Kung-Bin
authors.initials: KB
authors.lastname: Sung
authors.affiliation: Research Center for Applied Sciences, Academia Sinica, Taipei, Taiwan ; Institute of Biophotonics, National Yang-Ming University, Taipei, Taiwan.
authors.forename: Chau-Hwang
authors.initials: CH
authors.lastname: Lee
authors.affiliation: Graduate Institute of Biomedical Electronics and Bioinformatics, National Taiwan University, Taipei, Taiwan ; Department of Electrical Engineering, National Taiwan University, Taipei, Taiwan ; Department of Rehabilitation, National Taiwan University Hospital, Taipei, Taiwan.
authors.forename: Po-Ling
authors.initials: PL
authors.lastname: Kuo
mesh_terms: D002448:Cell Adhesion / Q000187:drug effects; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects; D006576:Heterocyclic Compounds, 4 or More Rings / Q000494:pharmacology; D006801:Humans; D008175:Lung Neoplasms / Q000378:metabolism* / Q000473:pathology*; D011554:Pseudopodia / Q000378:metabolism*; D014407:Tumor Cells, Cultured
chemical_list: D006576:Heterocyclic Compounds, 4 or More Rings; C472645:blebbistatin