Probing Mechanobiological Role of Filamin a in Migration and Invasion
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Ketebo et al. Nano Convergence (2021) 8:19 https://doi.org/10.1186/s40580-021-00267-6 FULL PAPER Open Access Probing mechanobiological role of flamin A in migration and invasion of human U87 glioblastoma cells using submicron soft pillars Abdurazak Aman Ketebo1, Chanyong Park1, Jaewon Kim1, Myeongjun Jun1 and Sungsu Park1,2,3,4* Abstract Filamin A (FLNa) belongs to an actin-binding protein family in binding and cross-linking actin flaments into a three- dimensional structure. However, little attention has been given to its mechanobiological role in cancer cells. Here, we quantitatively investigated the role of FLNa by analyzing the following parameters in negative control (NC) and FLNa- knockdown (KD) U87 glioma cells using submicron pillars (900 nm diameter and 2 μm height): traction force (TF), rigidity sensing ability, cell aspect ratio, migration speed, and invasiveness. During the initial phase of cell adhesion (< 1 h), FLNa-KD cells polarized more slowly than did NC cells, which can be explained by the loss of rigidity sensing in FLNa-KD cells. The higher motility of FLNa-KD cells relative to NC cells can be explained by the high TF exerted by FLNa-KD cells when compared to NC cells, while the higher invasiveness of FLNa-KD cells relative to NC cells can be explained by a greater number of flopodia in FLNa-KD cells than in NC cells. Our results suggest that FLNa plays important roles in suppressing motility and invasiveness of U87 cells. Keywords: Filamin A, Traction force, Rigidity sensing, Cell adhesion, Motility, Filopodia 1 Introduction and survive in ECM with variable stifness are largely Metastatic cells are highly motile and undergo cell mor- unknown. Understanding these mechanisms ultimately phology changes that facilitate penetration through the requires technology that can accurately quantify the TFs three-dimensional (3D) structures of the extracellular and rigidity sensing ability of cancer cells. matrix (ECM). During invasion, metastatic cells form thin TF microscopy that uses micron or submicron pil- cellular protrusions called flopodia [1, 2] in the direction lars [7–9] made of the elastomeric polymer polydi- of movement to form focal adhesions (FAs) [3]. Filopodia methylsiloxane (PDMS) can be used to quantify TFs and play an important role in cell migration by sensing and rigidity sensing of cells (Fig. 1). Tangential tension by a forming initial contact with ECM. Te primary function cell defects the pillar. Te degree of defection and the of FA is to transmit traction forces (TFs) through actin bending stifness of the pillar are used to quantify TFs flaments and attach cells to the ECM [4]. In addition, exerted by the cell [10]. Recent studies [11] showed that metastatic cells must be able to attach and survive in dif- cells sense the rigidity of ECM by producing local con- ferent or secondary sites with ECM of variable stifness tractions through actin-myosin interactions. Tese local [5, 6]. However, the physical mechanisms by which meta- contractions can be detected by observing the defection static cancer cells move through 3D structures of ECM of two neighboring pillars towards each other (Fig. 1A). TF microscopy showed that cancerous cells generated higher TFs than non-cancerous cells [12]. However, it has *Correspondence: [email protected] not been determined whether mutations in cancer cells 4 School of Mechanical Engineering, Sungkyunkwan University (SKKU), 2066 Seobu-ro, 16419 Suwon, Korea that increase metastasis, motility and invasion can also Full list of author information is available at the end of the article increase TFs. © The Author(s) 2021. This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http:// creat iveco mmons. org/ licen ses/ by/4. 0/. Ketebo et al. Nano Convergence (2021) 8:19 Page 2 of 9 Fig. 1 A Schematic describing traction forces (TFs) and rigidity sensing in a cell. F, D, L and E represent TF, the diameter, length, and Young’s modulus of PDMS, respectively. ∆x; the displacement of the pillar. B Schematic and AFM (2D and 3D) topographical images of the pillar arrays. The AFM image of the pillar array was taken in ambient conditions in a contact mode. It shows that the diameter of pillars and center-to-center (c-t-c) distance between pillars are 900 nm and 1.8 μm respectively Filamin A (FLNa) is a V-shaped actin-binding protein that mechanobiological results can be used as biomarkers that is abundantly expressed in human cells (Fig. 1A). for cancer metastasis. It binds and cross-links cortical actin flaments into a 3D structure [13] and mediates the conversion of 2 Experimental mechanical forces into biochemical signals [14]. It also 2.1 Cell culture and transfection links integrins to the actin flaments [15, 16]. Tus, it Te Uppsala 87 malignant glioma (U87) cell line was pur- integrates the cellular architecture and signaling that chased from American Type Culture Collection (ATCC, are essential for cell locomotion and development Manassas, VA). Cells were incubated in Gibco 1× mini- [17]. FLNa expression or suppression may facilitate mum essential medium (Termo Fisher Scientifc) con- or inhibit cancer invasion depending on the cell type, taining 10 % fetal bovine serum (FBS) (Gibco®, Termo FLNa expression levels, and FLNa’s interactions with Fisher Scientifc) and 100 units/ml penicillin (Sigma- other proteins. For example, the migration speed of Aldrich) under humid conditions at 37˚C in 5 % CO2. FLNa-defcient melanoma and breast cancer cells were Cells were transfected with either AccuTarget™ FLNa signifcantly lower than wild type cells [18]. In contrast, small interfering RNA (siRNA) oligonucleotide (target FLNa-knockdown (FLNa-KD) increased the frequency sequence: 5’-AAG ATG GAT TGC CAG GAG TG-3’) or of multifocal tumors of glioma cell lines in immuno- AccuTarget™ negative control (NC) siRNA from Bioneer defcient mice, and it increased the migration speeds Co. (Daejeon, Korea) according to the manufacturer’s of other glioma cell lines (A172 and LN-229) in vitro instructions. [19]. Te contradictory results from these studies show that the role of FLNa in cancer metastasis and invasion 2.2 Western blot analysis remains elusive [20]. Te total extract of NC and FLNa-KD cells was prepared Here, we evaluated the role of FLNa in cancer inva- using radioimmunoprecipitation assay bufer (LPS solu- sion by measuring TFs and rigidity sensing of negative tion, Daejeon, Korea) and protease inhibitor cocktail control (NC) and FLNa-KD glioma (U87) cells. We used (Roche). Anti-FLNa antibody from rabbit (Abcam) and submicron pillars (diameter, 900 nm; height, 2 μm; and anti-rabbit antibody conjugated with horseradish peroxi- center-to-center (c-t-c) distance between pillars, 1.8 μm; dase were used as primary and secondary antibodies to bending stifness, k = 24.2 nN/µm) (Fig. 1B). Te migra- visualize FLNa. Glyceraldehyde 3-phosphate dehydroge- tory and invasive behaviors of these cells were studied in nase (GAPDH) was used as control. Te image of the blot conventional motility and invasion assays to demonstrate was captured using a chemiluminescent imaging system Ketebo et al. Nano Convergence (2021) 8:19 Page 3 of 9 (Atto, Daejeon, Korea) and analyzed using ImageJ (NIH, initial phase of spreading (< 30 min) at the leading edges Bethesda, MD). (an area of 34.5 µm2) of the boundary of the cell as a measure of local contractions [24]. γ is calculated as the 2.3 Pillar fabrication sum of the force vectors of pillars divided by the sum Photolithography with reactive ion etching (RIE) was of their magnitudes. For this purpose, cell images taken used to fabricate a mold of linearly arranged arrays of within 30 min of cell substrate contact were used for γ holes (900 nm, diameter; 2 μm, depth; and 1.8 μm, c-t-c calculation. Average γ values of each type of cells were distance between holes) over 5-inch silicon wafers. obtained by calculating ffty frames of six diferent cells. PDMS Sylgrad® 184 silicon elastomeric base (Dow Corn- ing Co.) [21] was mixed with its curing agent at either 2.6 Fluorescent imaging of F‑actin a 5:1 or 10:1 (w/w) ratio to obtain PDMS elastic mod- Cells were incubated on fbronectin-coated pillars in an ules of 4 and 2 MPa [22] and the mixture was degassed incubator containing 5 % CO2 at 37 °C for 1 and 6 h. Te for 15 min. Next, the degassed mixture was spin-coated cells were washed with phosphate-bufered saline (PBS) over the mold at 500 rpm for 10 s and subsequently at (pH 7.4) and fxed with 4 % paraformaldehyde in PBS at 1,800 rpm for 30 s before being degassed for 30 min to room temperature (RT) for 10 min. Cells were permea- remove any trapped bubbles from the coated layer. Te bilized with 0.5 % triton X-100 in PBS at RT for 5 min. coated mold was cured at 80 °C for 4 h. Next, the PDMS F-actin was frst stained with rhodamine phalloidin (RP) layer was peeled of from the mold.