Open Access

Downregulation of fascin induces collective cell migration in triple‑negative breast cancer

  • Authors:
    • Yumiko Yamamoto
    • Yoshihiro Hayashi
    • Hideyuki Sakaki
    • Ichiro Murakami
  • View Affiliations

  • Published online on: June 14, 2023     https://doi.org/10.3892/or.2023.8587
  • Article Number: 150
  • Copyright: © Yamamoto et al. This is an open access article distributed under the terms of Creative Commons Attribution License.

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Abstract

Breast cancer (BC) is one of the most common types of cancer affecting female patients. Triple‑negative BC (TNBC) is an aggressive subtype. Fascin, an actin‑bundling protein, serves a significant role in cancer metastasis. Fascin overexpression is associated with poor prognosis of BC. To confirm the relationship between fascin expression and BC malignancy, the present study reviewed clinical data from 100 Japanese patients with BC and performed fresh immunohistochemical fascin examination of tissue samples. Statistical analyses showed metastasis or recurrence in 11 of 100 patients and a significant association between high fascin expression and poor prognosis. The TNBC subtype was also associated with high fascin expression. However, a few cases developed poor prognosis regardless of negative or slightly positive fascin expression. The present study established fascin knockdown (FKD) MDA‑MB‑231, a TNBC cell line, and investigated morphological effects of fascin on TNBC cells. FKD cells exhibited cell‑cell connections and bulbous nodules of various sizes on the cell surface. Conversely, non‑FKD MDA‑MB‑231 cells exhibited loose cell‑cell connections with numerous filopodia on the cell surface. Filopodia, actin‑rich plasma membrane protrusions, are composed of fascin and control cell‑cell interaction, migration and wound healing. Cancer metastasis is conventionally classified into two mechanisms: single and collective cell migration. Fascin increases cancer metastasis by single cell migration via filopodia on the cell surface. However, the present study suggested that following FKD, TNBC cells lost filopodia and exhibited collective cell migration.

Introduction

Breast cancer (BC) is one of the most common types of cancer affecting women (13) and the number of patients diagnosed with BC remains high worldwide as indicated in the WHO data up to 2016 (1). In Japan, BC is the most frequently diagnosed cancer in women (4). However, recent reports present that mortality rates of BC tend to decrease especially in developed countries (1,2), which could be attributed to the progress of diagnostic methods and therapies for BC (15). Despite advances in BC research and treatment, due to the lack of therapeutic targets, triple-negative BC (TNBC) is regarded as an aggressive subtype with a poor prognosis and its clinical outcome remain, unsatisfactory (1,6,7).

Fascin, an actin-bundling protein, serves a significant role in the regulation of cell adhesion, migration, and invasion (815). Fascin is strongly upregulated in several types of human carcinoma and sarcoma (812,14). Fascin overexpression is associated with higher grade of BC and its expression commonly predicts an aggressive clinical course in patients (7,10,13,16,17). Filopodia, bundles of actin, are fibrous protrusions on the cell membrane. They are also essential in processes of cell proliferation, including adhesion, migration and the formation of cell-cell contacts. Filopodia allow cells to migrate to the surrounding tissue through the extracellular matrix by interacting with various types of intercellular adhesive structure such as tight junctions, adherens junctions containing cadherin and desmosomes (18).

The present study reviewed clinical data from 100 patients diagnosed with BC in 2015. Fresh immunohistochemical assessment of fascin in tissue samples was performed to examine the association between BC malignancy with fascin expression and TNBC subtype. The present study aimed to investigate the association between fascin and BC invasion by morphological observation of cytoplasm and the cell surface. Fascin knockdown (FKD) was induced in MDA-MB-231, a TNBC cell line, to detect morphological effects of fascin on TNBC cells.

Materials and methods

Clinical data of patients with BC

Clinical data were reviewed from 100 consecutive patients who had been diagnosed with early-stage BC at Kochi University Hospital, Nankoku, Japan, from January to December 2015. The study was reviewed and approved by the Ethic Committee for Clinical Research of the School of Medicine, Kochi University (approval no. 2020-123; 4th December 2020). Written consent to participate was obtained from all patients. All 100 patients had undergone surgical treatment and completed follow-up for >5 years at the hospital. All tissues obtained during surgery had been embedded in paraffin blocks following formalin fixation for preservation. The immunohistochemical evaluation of estrogen receptor (ER), progesterone receptor (PR) and human epidermal growth factor receptor 2 (HER2) were also reviewed from clinical pathology reports at the time of initial diagnoses.

Fascin immunohistochemical evaluation

A total of 11 tissue samples from patients with metastasis or recurrence during 5-year follow-up were cut into 4 µm thick slices and heat-treated at 95°C for 30 min with ULTRA cell conditioning 1 retrieval solution (Ventana Automated Systems). Immunohistochemical examination was performed using a Ventana automated system with anti-fascin-1 mouse monoclonal antibody (1:100; cat. no. M3567; Dako, Agilent Technologies, Inc.). Another set of 17 consecutive tissue samples from patients without metastasis or recurrence underwent the same procedure as a control group. To evaluate immunohistochemical expression of fascin, the Allred scoring system was used (13,14). Briefly, the proportion of stained cells was categorized as negative (0), <1 (1), 1–10 (2), 11–33 (3), 34–66 (4) and >66% (5) positive. The intensity of the most predominantly stained area was categorized as no (0), weak (1), intermediate (2), or strong (3) staining (Fig. 1). Allred score (0–8 points) was calculated by adding the proportion and intensity values. Independent evaluation of immunostaining was performed by two expert pathologists (YH, IM).

FKD MDA-MB-231 cells

Human TNBC MDA-MB-231 cells (American Type Culture Collection), were cultured at 37°C for 24 h with 5% CO2 in DMEM (Sigma-Akdrech, Merck KGaA) with 10% fetal bovine serum (Biosera France SAS). Following recombination of the short hairpin RNA (shRNA) against fascin, the pLKO.1-puro plasmid vector (1 µg/µl; Clone ID: NM_003088.2-1699s1c; Sigma-Aldrich, Merck KGaA), containing the puromycin-resistance gene, was transfected into MDA-MB-231 cells with FuGene®6 Transfection Reagent (Roche Diagnostics) at 37°C for 24 h, according to the manufacturer's instructions. Cells were incubated at 37°C with 2.2 µg/ml puromycin (Sigma-Akdrech, Merck KGaA) for 2 weeks. Puromycin-resistant colonies (~20) were obtained and cultured with the medium containing puromycin (2.2 µg/ml) in 100 mm-diameter dishes. When the cell confluency reached 80%, dishes were provided to carry out western blot analysis and to gain FKD MDA-MB-231 cells, respectively. Transfection of the pLKO.1-puro plasmid vector without shRNA against fascin was used to generate non-FKD MDA-MB-231 cells.

Immunocytochemical and phalloidin staining of MDA-MB-231 cells

For immunocytochemical staining, non-FKD and FKD MDA-MB-231 cells were incubated with anti-fascin-1 mouse monoclonal antibody (1:100; cat. no. M3567; Dako, Agilent Technologies, Inc.) at 4°C overnight reacted with fluorescein isothiocyanate (FITC)-labeled anti-mouse IgG antibody (1:200; cat. no. F-2761; Molecular Probes, Thermo Scientific, Inc.) at room temperature for 1 h and nuclei were stained with DAPI (Sigma-Akdrech, Merck KGaA). For phalloidin staining, cells (2×104/well) were cultured at 37°C for 24 h on a slide chamber (AGC Techno Co., Ltd), fixed with 100% acetone at −20°C for 20 min and stained with FITC-labeled phalloidin (Sigma-Akdrech, Merck KGaA) to bind actin filaments, according to the manufacturer's instructions. Fluorescence microscopy was performed using an Olympus BX53 (Olympus Corporation; magnification ×200) with cellSens standard (ver.1.12, Olympus Corporation).

Western blot analysis

Concentration of samples lysed in RIPA Buffer (Fujifilm Wako Pure Chemical Corp) was measured by Pierce BCA Protein Assay Kit (cat. no. 23227; Thermo Fisher Scientific, Inc.). 20 µg/lane samples were prepared for SDS-PAGE separation (10% SDS-PAGE Gel; Bio-Rad Laboratories, Inc.) and transferred to polyvinylidene difluoride membranes using the Trans-Blot Turbo Transfer System (Bio-Rad Laboratories, Inc.). Membranes were blocked with Blocking One (cat. no. 03953-93; Nacalai Tesque, Inc.) at room temperature for 1 h, and incubated at 4°C overnight with following antibodies: anti-fascin-1 mouse monoclonal (1:500; cat. no. M3567; Dako, Agilent Technologies, Inc.), E-cadherin mouse monoclonal (1:500; cat. no. M3612; Dako, Agilent Technologies, Inc.), Snail1 rabbit polyclonal antibody (1:200; cat. no. Ap205Aa; Adgent, Inc.), and GAPDH mouse monoclonal antibody (1:2000; cat. no. 20035; ProMab Biotechnologies, Inc.). Then, the membranes were incubated at room temperature for 1 h with either of following secondary antibodies: HRP-labeled anti-mouse polyclonal antibody (1:2000; cat. no. P0447; Dako, Agilent Technologies, Inc.) or anti-rabbit polyclonal antibody (1:2000; cat. no. P0399; Dako, Agilent Technologies, Inc.). Bands were visualized by ECL Prime Western Blotting Detection Reagents (Amersham, Cytiva) and observed using LAS-4000 Lumino-Image Analyzer (FUJIFILM Wako Pure Chemical Corporation). ImageJ (version no. 1.53; National Institutes of Health) was used for analysis.

Wound healing assay

Trypsinized 2×104/ml parent, non-FKD and FKD cells were counted with SKC, Inc. C-Chip Disposable (Thermo Fisher Scientific), disposable hemocytometer, seeded onto a 35 mm-diameter dish and cultured at 37°C for 48 h. When the cell confluence reached 90%, a scratch was made through the center of the cell layer using a 20-µl pipette tip. The cells were incubated using 10% FBS at 37°C for 20 h. Phase-contrast microscopy was performed at 0, 12, 16 and 20 h on 50 spots, which were randomly marked on 35-mm dishes containing each cell (Olympus Corporation, CKX41, original magnification ×200). To investigate cell migration ratio, the area of each scratch without cell migration was measured in the same size dimension with the same magnification, using ImageJ software, ver.1.53. The mean migration of 50 spots in each cell sheet was examined. Then, the mean value at 0 h was defined as 1.0 and relative cell migration ratio was detected at each time of each cell.

Correlative light and electron microscopy (CLEM)

As aforementioned, a scratch was made using a 20-µl pipette tip on a layer of non-FKD and FKD cells (2×104/well each) seeded onto the slide chambers (AGC Techno Co., Ltd). Immunocytochemical staining with anti-fascin-1 mouse monoclonal antibody and FITC-labeled anti-mouse IgG antibody was performed as aforementioned. Following immunofluorescence microscopy, cells were fixed with 2.5% glutaraldehyde and 1% osmic acid at 4°C for 6 h and 1h, respectively. Then, cells were stained with 1% phosphotungstic acid at room temperature for 10 min and low-vacuum scanning electron microscopy (LV-SEM) was performed. Finally, images of immunofluorescence and LV-SEM were superimposed using ImageJ software, ver.1.53.

Hematoxylin-eosin (HE) and immunohistochemical stain of non-FKD and FKD MDA-MB-231 cells cultured in Cellmatrix®

A total of 1×104/ml non-FKD and FKD MDA-MB-231 cells were counted as aforementioned and Cellmatrix (Nitta Gelatin Inc.) was prepared according to the manufacturer's instructions. Subsequently, each group of cells and 500 µl Cellmatrix® were poured into a 35-mm-diameter dish (coated with Cellmatrix at 37°C for 30 min), covered with 200 µl DMEM and cultured at 37°C for 10 days. The gels were fixed in 20% buffered formaldehyde at room temperature overnight and embedded in paraffin. Following HE stain (Mayer's hematoxylin and 1% eosin staining at room temperature for 10 and 5 min, respectively), immunohistochemical staining for E-cadherin, Snail1 and vimentin was performed as follows. 4 µm-thick tissue samples were immersed in 0.01 M citrate buffer (pH 7.0) for antigen retrieval (98°C, 30 min). Sections were immersed in 0.3% hydrogen peroxide/methanol at room temperature for 10 min to remove endogenous peroxidase. Then, the sections were blocked using Blocking One (cat. no. 03953-93; Nacalai Tesque, Inc.) at room temperature for 1 h and incubated at 4°C overnight with following antibodies: anti-E-cadherin mouse monoclonal antibody (1:100; cat. no. M3612; Dako, Agilent Technologies, Inc.), Snail1 rabbit polyclonal antibody (1:100; cat. no. Ap2054a; Adbent, Inc.) and vimentin mouse monoclonal antibody (1:200; cat. no. M725; Dako, Agilent Technologies, Inc.). After washing with PBS, sections were incubated in N-Histofine Simple Stain MAX PO (MULTI; cat. no. 424151; Nichirei Biosciences Inc.) at room temperature for 1 h and washed again with PBS. Finally, the sections were immersed in DAB substrate solution (tablet/15 ml distilled water; SIGMAFAST 3,3′-Diaminobenzin tablets; D4418; Sigma-Aldrich, Merck KGaA) and the nucleus was stained with Mayer Hematoxylin at room temperature for 1 min. Optical microscope images were performed using an Olympus BX53 with cellSens (Olympus Corporation). An additional set of gels was fixed in 2.5% glutaraldehyde at 4°C for 6 h for LV-SEM.

Spheroids of non-FKD and FKD MDA-MB-231 cells

A total of 1×104/well parent, non-FKD and FKD MDA-MB-231 cells were counted as aforementioned and seeded onto PrimeSurface® (Sumitomo Bakelite Co., Ltd.), 96-well plate with ultra-low adhesion round bottom dishes. Following incubation at 37°C with 5% CO2 for 5 days, multicellular spheroids were generated. As aforementioned, fixation of the samples, HE and immunohistochemical staining of fascin and E-cadherin for microscopy (Olympus BX53), and LV-SEM were completed. A total of 10 spheroids was collected in a 35-mm-diameter dish (coated with Cellmatrix at 37°C for 30 min) with 500 µl Cellmatrix, covered with 200 µl DMEM and cultured at 37°C for 3 days. After fixation in 20% buffered formaldehyde at room temperature for 6 h, the samples were observed under stereoscopic microscope MZ16FA (Leica Microsystems Tokyo, Japan, original magnification ×200).

Immunohistochemistry of non-FKD and FKD MDA-MB-231

Immunohistochemical and immunofluorescent analyses were performed as previously described (9). The antibodies and chemical agents are shown in Table I.

Table I.

Reagents and suppliers.

Table I.

Reagents and suppliers.

ReagentSupplierDilution
Anti-fascin-1 mouse monoclonal antibodyDako (Agilent Technologies, Inc.)1:100
Anti-vimentin mouse monoclonal antibodyDako (Agilent Technologies, Inc.)1:200
Anti-E-cadherin mouse monoclonal antibodyDako (Agilent Technologies, Inc.)1:100
Anti-Snail1 rabbit polyclonal antibodyAbgent, Inc.1:100
Anti-GAPDH mouse monoclonal antibodyProMab Biotechnologies, Inc.1:2,000
Biotinylated goat anti-rabbit IgG antibodyAbcam1:200
Biotinylated rabbit anti-mouse IgG antibodyDako (Agilent Technologies, Inc.)1:200
FITC-labeled streptavidinDako (Agilent Technologies, Inc.)1:200
Texas Red-labeled anti-rabbit IgG antibodyMolecular Probes (Thermo Fisher Scientific, Inc.)1:200
N-Histofine Simple Stain MAX PO (MULTI)Nichirei Biosciences Inc.Ready to use
DABSigma Aldrich (Merck KGaA)Tablet/15 ml distilled water
LV-SEM

Samples containing cells or spheroids were fixed using 2.5% glutaraldehyde in 0.1M phosphate buffer (PB, pH 7.4) at 4°C for 4 h and postfixed with 1% osmium tetroxide in PB at 4°C for 1 h. Then, each block was washed with distilled water for 30 min and stained with 1% phosphotungstic acid solution at room temperature for 10 min. Following a final wash with distilled water for 30 min, the block was dried on an electrically conductive tape (Nisshin EM Co., Ltd.) and observed using a Miniscope® TM3030 (Hitachi Ltd.).

Statistical analysis

χ2 test was performed to detect the association between a TNBC subtype and the incidence of metastasis or recurrence. Cochran-Armitage test was performed to detect the relationship between the Allred score and the incidence of metastasis or recurrence. χ2 test was performed to analyze the relationship between E-cadherin expression in FKD and non-FKD cells, and Snail1 expression as well. Tukey-Kramer test was used to compare the mean values of cell migration ratios in wound healing assay. Two-side test was applied for all analyses except Cochran-Armitage test. JMP (ver. 14.3.0, SAS Institute inc.) was used for statistical analyses.

Results

Clinical data of patients with BC patients

A total of 11 out of 100 consecutive patients with BC developed metastasis or recurrence within five years (Table II). Fresh fascin immunostaining was performed on tissue samples from these patients as well as 17 patients without metastasis or recurrence. χ2 test result showed a significant association between TNBC subtype and the incidence of metastasis or recurrence (P<0.05, Table II). Cochran-Armitage test showed a significant association between the Allred score of fascin and the incidence of metastasis or recurrence (P<0.05, Table II). However, Cases #2 and #6 developed poor prognosis regardless of negative or slightly positive fascin expression (0 and 2, respectively). Cases #14 and #22 did not develop metastasis or recurrence during follow-up periods, although they showed high Allred scores (6 and 8, respectively).

Table II.

Clinical data of patients with breast cancer.

Table II.

Clinical data of patients with breast cancer.

Hormone receptor statusFascin expression
CaseAge, yearsMetastasis or recurrence

ERPgRHER2ProportionIntensityAllred score
  171+---538
  257+++-000
  363+++-213
  442+++-516
  565++--213
  651+---112
  765+---336
  874+++-314
  953+++-213
1074++--224
1177+---314
1260-++-000
1364-++-000
1459-+--426
1540-++-213
1658-++-000
1771-++-000
1859-+--000
1969-++-000
2085-++-000
2157-++-213
2271----538
2360-++-000
2469-++-224
2565-++-000
2664-++-000
2761-++-000
2840-++-224

[i] -, negative; +, positive; ER, estrogen receptor; PgR, progesterone receptor; HER2, human epidermal growth factor receptor 2.

Establishment of FKD MDA-MB-231 cells

The expression of fascin (green) was strongly positive in non-FKD cells and effectively suppressed in FKD cells (Fig. 2A). Numerous filopodia, including actin filaments (arrows), were observed on the membrane of non-FKD cells, however, these filopodia were decreased and actin positive granules (arrowheads) were observed on the membrane of FKD cells. Fascin was strongly positive in non-FKD cells and was suppressed in FKD cells (Fig. 2B). Snail1 expression was also decreased in FKD cells. By contrast, E-cadherin expression increased in FKD cells.

2D LV-SEM were performed following 3 day cultivation of non-FKD and FKD MDA-MB-231 cells. Non-FKD cells exhibited loose cell-cell connections (Fig. 3A), however, bundles of extremely thin microfibrils on the cell surface were observed (arrows; Fig. 3B). FKD cells exhibited cell-cell adhesion (Fig. 3C) and granular nodules of various sizes were observed on the cell surface (arrowheads; Fig. 3D).

Wound healing assay

Following 20 h incubation, the mean scratch areas in parent and non-FKD cell sheets decreased notably due to the cell migration, however, the mean scratch area in FKD cell sheets decreased only slightly (Fig. 4A and B). FKD cell migration showed a statistical difference from parent and non-FKD cells (Tukey-Kramer test, P<0.01).

In 2D LV-SEM observation, non-FKD cell sheet exhibited loose cell-cell connections (Fig. 5A), whereas the cells of FKD cell sheet were observed as groups with tight cell-cell connections (Fig. 5B). Bundles of extremely thin microfibrils (filopodia) existed on the surface of leading migratory non-FKD cells (Fig. 5C). By contrast, globular-shaped lamps of different sizes were observed on the surface of FKD cells (Fig. 5D).

Correlative light and electron microscopy (CLEM)

Fascin expression (green; Fig. 6) was strongly positive in non-FKD cells, which exhibited thin filopodia on the cell membrane (arrows). Meanwhile, fascin expression was effectively suppressed in FKD cells, and globular-shaped lamps were observed on the cell membrane (arrowheads). In LV-SEM, numerous lamps were recognized as whitish spots on the surface of FKD cells (arrowheads). Thus, fascin-positive spots observed by optical microscope were demonstrated to locate at the whitish spots in the bulbous-shaped protrusions on the FKD cell surface in LV-SEM.

HE and immunohistochemical study

Non-FKD and FKD cells were cultured in Cellmatrix® for 10 days. Following HE staining, non-FKD cells were observed to have loose cell-cell adhesions, whereas clusters with cell-cell connections were observed in FKD cells (Fig. 7). E-cadherin immunohistochemical staining was negative in non-FKD cells but positive in FKD cells. Snail1 expression (red) was observed in the nucleus of non-FKD cells but was decreased in FKD cells; however, vimentin was strongly positive in both cell lines (green). E-cadherin expression was significantly different between non-FKD and FKD cells, and Snail1 expression as well (P<0.01).

3D LV-SEM observation

Numerous thin cell protrusions (filopodia) were observed on the surface of non-FKD cells (Fig. 8). These cells exhibited loose cell-cell adhesions. By contrast, bulbous-shaped protrusions of varied sizes were detected on the surface of FKD cells, which exhibited partial cell-cell adhesions.

Spheroid cell culture

Densely aggregated tumor cells with irregularly shaped nuclei were observed in both non-FKD and FKD cells (Fig. 9). Fascin expression was strongly positive in non-FKD cells. Arrows indicate E-cadherin positive-stained membranes observed in FKD cells.

In 3D LV-SEM observation, non-FKD spheroid cells gathered densely forming a spherical spheroid block, by contrast, cells of the FKD spheroid gathered sporadically and eventually formed an irregularly shaped spheroid block (Fig. 10). There were numerous cell protrusions (filopodia) on the surface of non-FKD spheroid cells, in contrast, globular-shaped protrusions of varied sizes were observed on the surface of FKD spheroid cells. The morphological appearances of parent cells were similar to non-FKD cells.

In stereoscopic microscope observation, homogeneous filamentous cells were observed infiltrating into the surrounding gel from the non-FKD spheroid (Fig. 11A), while irregular heterogeneous fascicular cell invasion into the gel was observed from the FKD spheroid (Fig. 11B). HE staining revealed fibrous spindle-shaped tumor cells invading the surrounding gel from the non-FKD spheroid (Fig. 11C), while clusters of tumor cells (arrows; Fig. 11D) originating from the FKD spheroid were observed invading the gel.

Discussion

BC is the most frequently diagnosed cancer in female patients. Treatment of BC has improved, however the mortality of BC remains high among cancer-associated death in female patients (13). In the present study, during 5-year follow-ups, metastasis or recurrence occurred in 11 out of 100 consecutive Japanese patients diagnosed with early-stage BC at Kochi University Hospital, Japan, in 2015. In the United States, similarly, it is reported that nearly 12% of patients with BC develop metastasis or recurrence (19). However, rising rates of BC incidence and mortality in underdeveloped countries have been reported (1,20). Different factors, such as diet, alcohol, smoking, contraceptive pills and physical exercise may affect prognosis of BC (2). When BC is detected and treated at the earlier stages, more favorable prognosis can be achieved, as with other types of cancer (3,21).

Fascin is an actin-bundling protein. Fascin composes filopodia, slender bundled actin containing plasma membrane protrusions, which serve an important role in cellular processes such as cell adhesion, migration, wound healing, and the formation of cell-cell contacts by stimulating migration at the leading edge of cells (22,23). Recent studies have shown that fascin also localizes to invadopodia, actin-rich protrusions of the plasma membrane at the adherent cell surface, which facilitate extracellular matrix invasion (24,25). Lamb and Tootle (23) suggested that fascin may serve multiple functions to control cell migration; decreased fascin and prostaglandin expression induces delayed migration of border cells and elongated cell clusters (26). Higher fascin expression is associated with poorer prognosis in numerous types of cancer and sarcoma. Thus, fascin is considered to be key for cancer progression (7,10,13,16,17). The present study investigated the association between fascin and BC cell invasion via morphological observation of the cytoplasm and the cell surface. Previous studies have investigated the mechanism of how fascin increases cell migration and invasiveness to uncover an effective treatment for malignant tumors, including BC, by targeting fascin (17,27,28). Accordingly, at the annual meeting of the American Society of Clinical Oncology, 2021, Novita Pharmaceuticals presented Phase 1A results of fascin inhibitor NP-G2-044 in patients with advanced and metastatic solid tumor, which was shown to be safe and effective (29).

Despite advances in research, diagnosis and treatment of BC, TNBC is an aggressive subtype with a high rate of metastasis or recurrence (1,6,7). Esnakula et al (7) confirmed a strong association between TNBC and fascin. Wang et al (10) suggested that fascin may be used as a novel diagnostic marker of TNBC. The present results similarly suggested that fascin may serve as an index to evaluate malignancy of early-stage BC and there was a significant association between TNBC subtype and the incidence of metastasis or recurrence. Patients who developed metastasis with negative or slightly positive fascin expression were also included in the present study. Hence, to examine how TNBC cells migrate following downregulation of fascin, the present study established FKD and non-FKD MDA-MB-231 cells and performed wound healing assay, spheroid cell cultures, and 2D and 3D LV-SEM.

MDA-MB-231, a cell line isolated from a patient with invasive ductal BC, is characterized by negative ER, PR and E-cadherin expression and p53 mutation (30). The cells also lack growth factor receptor HER2 and represent a good model of TNBC (30). Hoa et al (31) knocked down fascin in human U251 glioma cells and confirmed that these cells lost microvilli and altered the glioma morphology. The present study successfully established FKD and non-FKD TNBC cells using MDA-MB-231.

The wound healing assay may be performed under various circumstances, such as mechanical, thermal or chemical damage, however, it is a 2D approach and its utility is limited to the observation of cells migrating as a collective epithelial sheet (32). Therefore, the wound healing assay does not simulate the natural environment where cells exist with cell-cell and cell-extracellular matrix interactions. A more ideal in vitro cell model that facilitates observation of migration of malignant cells is 3D spheroid cell culture. Compared with 2D monolayer culture, such as wound healing assay, spheroid cell cultures more accurately reflect the microenvironment in vivo (32).

LV-SEM in the present study demonstrated that FKD morphologically modified the surface of TNBC cells. When fascin was knocked down, cells lost filopodia, which are key for cell migration into the surrounding microenvironment. FKD cells developed granular lamps of various sizes that facilitated cell-cell connection. The spheroid culture showed that following FKD, tumor cells developed clusters and migrated into the surrounding gel. Fox et al (26) demonstrated that fascin promotes single cell migration; the present findings suggested that suppression of fascin induced collective migration of TNBC cells. The wound healing assay indicated that cell migration ability was impaired due to FKD, however, 3D spheroid cell culture suggested that modification of the surface of tumor cells facilitated collective cell migration. These results indicated that TNBC cells maintained the ability to migrate following FKD via collective cell migration.

Cancer metastasis is a radical progression of malignant cells that migrate into the surrounding microenvironment and its mechanism is generally classified as single or collective cell migration (15,33). Single cell migration has been studied widely, primarily using 2D cell cultivation methods that do not reflect the in vivo environment (3336). The theory of collective cell migration is relatively new. 3D methods, such as a spheroid cell culture used in the present study, facilitate analysis of collective cell migration, which is considered to be a primary mechanism of cancer metastasis (3336). However, cell migration process does not occur only at the single focal adhesion level, but it is also affected by the integration with surrounding cells (36). Thus, it is indispensable to observe the mechanism of different migration patterns. The present study performed the classic 2D wound healing assay and modern 3D spheroid cell culture, which indicated that MDA-MB-231 cells exhibited collective migration following FKD.

Certain patients did not develop metastasis or recurrence despite strong positive fascin expression. The Allred scores of Cases #14 and #22 were 6 and 8, respectively. These patients may have exhibited more favorable prognosis because the cancer subtype was not TNBC. These patients had detected breast tumors by self-exam, had an immediate consultation with a specialist and underwent surgery within two months of self-exam. Regular breast self-exam can detect cancer at an early stage, allowing more effective and less invasive treatment and leading to a more favorable prognosis (3,21).

The present study performed CLEM, one of the most advanced methods to observe cells morphologically and understand the dynamics of organelles. Recently, CLEM has achieved insights into cell biology by making it possible to observe the same area as an optical microscope with an electron microscope (3739). Here, CLEM demonstrated fascin-positive spots observed by optical microscope located at the whitish spots in the bulbous-shaped protrusions on the FKD cell surface in LV-SEM.

The present study demonstrated collective migration of TNBC cells by 3D LV-SEM. TNBC cells may migrate into the surrounding microenvironment through collective migration in FKD cells that lack filopodia on the cell surface.

Acknowledgements

The authors would like to thank Dr Nobuaki Yamanaka, Dr Kazuho Honda, and Mr. Takeshi Kamimura (The LVSEM Study Group of Renal Biopsy, Tokyo, Japan) for technical assistance of the LVSEM equipment.

Funding

The present study was supported by grant research No. 006 of the LVSEM Study Group of Renal Biopsy from the LVSEM Study Group of Renal Biopsy and Hitachi High-Tech.

Availability of data and materials

The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.

Authors' contributions

YY and YH conceived the study and performed experiments. YH and IM evaluated Allred score of fascin expression. YY and HS performed statistical analysis. YY wrote the manuscript. IM supervised the study. YY and YH confirm the authenticity of all the raw data. All authors have read and approved the final manuscript.

Ethics approval and consent to participate

The present study was reviewed and approved by the Ethic Committee for Clinical Research of the School of Medicine, Kochi University (approval no. 2020-123). Written consent to participate was obtained from all patients.

Patient consent for publication

Not applicable.

Competing interests

The authors declare that they have no competing interests.

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August-2023
Volume 50 Issue 2

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Spandidos Publications style
Yamamoto Y, Hayashi Y, Sakaki H and Murakami I: Downregulation of fascin induces collective cell migration in triple‑negative breast cancer. Oncol Rep 50: 150, 2023
APA
Yamamoto, Y., Hayashi, Y., Sakaki, H., & Murakami, I. (2023). Downregulation of fascin induces collective cell migration in triple‑negative breast cancer. Oncology Reports, 50, 150. https://doi.org/10.3892/or.2023.8587
MLA
Yamamoto, Y., Hayashi, Y., Sakaki, H., Murakami, I."Downregulation of fascin induces collective cell migration in triple‑negative breast cancer". Oncology Reports 50.2 (2023): 150.
Chicago
Yamamoto, Y., Hayashi, Y., Sakaki, H., Murakami, I."Downregulation of fascin induces collective cell migration in triple‑negative breast cancer". Oncology Reports 50, no. 2 (2023): 150. https://doi.org/10.3892/or.2023.8587