The human thyroid carcinoma cell lines, CAL-62 and SW579, were obtained from The Cell Bank of Type Culture Collection of The Chinese Academy of Sciences. The immortalized normal human thyroid follicular epithelial cell line, Nthy-ori3-1, was purchased from CoBioer Biosciences Co., Ltd. (cat. no. CBP61205). HUVECs were purchased from Shanghai Zhong Qiao Xin Zhou Biotechnology Co., Ltd. HUVECs, CAL-62 and SW579 cells were cultured in DMEM supplemented with 1% penicillin/streptomycin and 10% FBS, at 37°C (5% CO₂) in a humidified atmosphere. Nthy-ori3-1 cells were maintained in RPMI-1640 with 10% FBS and 1% penicillin/streptomycin.

293T cells (The Cell Bank of Type Culture Collection of The Chinese Academy of Sciences) were transfected with 1 µg pLKO.1-LGMN, 0.5 µg pVSVG (Addgene, Inc.) and 0.5 µg pPAX2 (Addgene, Inc.) plasmids, and the resulting 2nd generation lentiviruses were collected after 36–48 h of transfection. The viruses (MOI=4) were used to infect CAL-62 and SW579 cells. Following incubation for 24 h, cells were cultured in the presence of 2 µg/ml puromycin for 1 week to obtain resistant cells. Puromycin (1 µg/ml) were used for maintenance. The short hairpin RNA (shRNA) sequences used were as follows: Sh-negative control (NC), 5′-AUUCGGUUCAAGGUCCAUUGGG-3′; sh-LGMN-1, 5′-CCUGCCGGAUAACAUCAAU-3′; and sh-LGMN-2, 5′-CGUGGAAGAUCUGACUAAA-3′.

Autophagy-related gene 3 (ATG3) cDNA (Genscript Biotech) or LGMN (Genscript Biotech) was subcloned into the pcDNA3.1 vector (Addgene, Inc.), 1 µg pcDNA3.1-ATG3 or pcDNA3.1-LGMN vector was used to transfect CAL-62 and SW579 cells with Lipofectamine^® 2000 (Thermo Fisher Scientific, Inc.) at room temperature. Following transfection for 24 h, the cells were harvested for further analysis. NC mimic (50 µM), miR-495 mimic (50 µM), NC inhibitor (50 µM), miR-495 inhibitor (50 µM) were transfected into CAL-62 and SW579 cells with Lipofectamine^® RNAiMAX (Thermo Fisher Scientific, Inc.) at room temperature. The interval transfection and subsequent experiments was 48 h. NC mimic, 5′-CAUUCAUCCAUCAAUCGGGCAGGCCUU−3′; miR-495 mimic, 5′-UUACCGAUCCAAUUUCCGGACGGUUAC−3′; NC inhibitor, 5′-UUCAGGCAAUCCAAAUGCAGG−3′; and miR-495 inhibitor, 5′-AAUGGGACUUCCAUCGGAAUCCU-3′.

A total of 2×10⁴ cells were seeded into each well of a 6-well plate, and cultured for ~1 week. Following colony formation, the cells were stained with 0.5% crystal violet at room temperature for 1–2 h.

CAL-62 and SW579 cells were seeded into the upper chambers of Matrigel-precoated inserts (BD Biosciences), at a density of 1×10⁵ cells in 250 µl serum-free medium. In addition, 300 µl medium supplemented with 20% FBS was added to the bottom chamber as a chemoattractant. Following incubation at 37°C for 24 h, invasive cells were stained with 0.05% crystal violet solution at room temperature for 1–2 h. A light microscope (CKX53; Olympus Corporation) was used to observe migratory cells in lower chamber (magnification, ×100).

CAL-62 and SW579 cells were seeded into 96-well plates at a density of 1×10³ cells/well. The cells were then transfected with the indicated oligonucleotides and incubated for different lengths of time. Subsequently, the cells were incubated with 10 µl CCK-8 reagent (Vazyme Biotech Co., Ltd.) for 3 h at 37°C (5% CO₂), after which the absorbance of each well was determined at a wavelength of 450 nm.

Total protein were extracted by RIPA buffer (Beijing Solarbio Science & Technology Co. Ltd.) from CAL-62 and SW579 cells. Protein concentration was determined by bicinchoninic acid (BCA) method and ~50 µg/lane of protein was separated by 10% SDS-PAGE, prior to transfer onto PVDF membranes. Following blocking with 5% non-fat milk at room temperature for 1 h, the membranes were incubated with primary antibodies overnight at 4°C. The following primary antibodies were used: Anti-ATG3 (cat. no. PA5-17018; 1:1,000; Thermo Fisher Scientific, Inc.), anti-p62 (cat. no. ab155686; 1:1,000; Abcam) and anti-GAPDH (cat. no. 8884; 1:2,000; Cell Signaling Technology, Inc.). The membranes were then incubated with the following secondary antibodies at room temperature for 1 h: Anti-mouse HRP-conjugated IgG (cat. no. 7076; 1:3,000) or anti-rabbit HRP-conjugated IgG (cat. no. 7074; dilution, 1:3,000) (both Cell Signaling Technology, Inc.). Enhanced chemiluminescent (ECL) reagent (ThermoFisher Scientific Inc.) was used to probe protein bands, which was visualized by ChemiDoc™ MP and Image Lab v.4.1 software (Bio-Rad Laboratories, Inc.).

The gene expression data from thyroid carcinoma samples, including 512 tumor and 337 normal tissues, were downloaded from TCGA (https://tcga.xenahubs.net). Comparisons between the expression levels of LGMN were conducted using Student's t-test (unpaired, two-tailed).

Growth factor-reduced Matrigel was used to coat 24-well plates at 37°C for 4–5 h. Subsequently, HUVECs at a density of 3×10³ cells/well were seeded into the coated plates in conditioned medium (Ham's F-12K + 0.1 mg/ml Heparin + 0.03–0.05 mg/ml ECGs + 10% FBS + 1% P/S). Tube formation was observed under a light microscope (magnification, ×200).

Total RNA was extracted from CAL-62 and SW579 cells using TRIzol^® reagent (Invitrogen; Thermo Fisher Scientific, Inc.). A total of 1 µg RNA was reverse transcribed into cDNA using the PrimeScript RT reagent kit (Takara Bio, Inc.) according to the manufacturer's instructions. qPCR was carried out with SYBR Green kit (Roche Applied Science) to determine relative gene expression, and quantified using the 2^−ΔΔCq method (27). The following thermocycling conditions were used: Initial denaturation at 95°C for 5 min, followed by 40 cycles of 95°C for 30 sec, 60°C for 30 sec and 72°C for 30 sec. The primer sequences used were as follows: LGMN forward, 5′-GTTGAGAGGCGATGCAGAAG-3′ and reverse, 5′-GCAGGTGGTTCATCATGGAC-3′; ATG3 forward, 5′-CAATGGGCTACAGGGGAAGA-3′ and reverse, 5′-ATCCGCCATCACCATCATCT-3′; p62 forward, 5′-CACAGAGGAGAAGAGCAGCT-3′ and reverse, 5′-TGGAGTTCACCTGTAGACGG-3′; miR-495 forward, 5′-ACCTGAAAAGAAGTTGCCCA-3′ and reverse, 5′-GCACCATGTTTGTTTCGTCAC−3′; and β-actin forward, 5′-ACTCTTCCAGCCTTCCTTCC-3′ and reverse, 5′-CGTACAGGTCTTTGCGGATG-3′.

GraphPad Prism 8.0 software (GraphPad Software, Inc.) was used to compare the differences between two groups, using unpaired Student's t-test. The differences among multiple groups were assessed using one-way ANOVA followed by Tukey's post hoc test. The data are expressed as the mean ± SD, and P<0.05 was considered to indicate a statistically significant difference.

To investigate the tumorigenic role of LGMN in thyroid carcinoma, the shRNA gene knockdown approach was employed. shRNAs against LGMN were synthesized, and RT-qPCR analysis was used to confirm knockdown efficiency (Fig. 1A). LGMN-knockdown notably impaired CAL-62 and SW579 cell proliferation (Fig. 1B). Similarly, LGMN-knockdown decreased the invasive capacity of both cell lines (Fig. 1C and D). Furthermore, a tube formation assay was conducted to evaluate the tube formation ability of HUVECs treated with conditioned medium from thyroid carcinoma cells. The results showed that LGMN-knockdown attenuated the tube formation ability of HUVECs compared with the sh-NC group (Fig. 1E and F). These findings suggested that LGMN depletion inhibited the tumor phenotype of thyroid carcinoma cells.

To investigate the potential effect of pseudogene LGMN on thyroid carcinoma, clinical TCGA datasets of thyroid carcinoma samples were obtained and analyzed using bioinformatics approaches. Bioinformatics analysis revealed that LGMN was significantly upregulated in thyroid carcinoma tissues compared with normal tissues (Fig. 2A). Furthermore, the overall survival (OS) rate was evaluated in the high- and low-LGMN expression groups. The results showed that the OS rate was higher in patients in the low-LGMN group compared with those in the high-LGMN group (Fig. 2B). Additionally, the analysis indicated that higher LGMN expression levels were associated with higher grades of thyroid carcinoma (Fig. 2C). Subsequently, RT-qPCR analysis was performed to detect the expression levels of LGMN in the normal thyroid epithelial cell line (Nthy-ori3-1) and thyroid carcinoma CAL-62 and SW579 cells. The results demonstrated that LGMN was significantly upregulated in thyroid carcinoma cell lines (Fig. 2D). The aforementioned findings suggested that LGMN promoted the development of thyroid carcinoma.

miRNAs have been reported to act as interacting factors for pseudogenes in various cancer types (28,29). A study reported that miR-495 could sponge LGMN in glioblastoma (14). Herein, RT-qPCR analysis was performed to determine the expression levels of miR-495 in CAL-62 and SW579 cells transfected with sh-NC, sh-LGMN-1 or sh-LGMN-2. The results revealed that miR-495 was significantly upregulated following LGMN-knockdown (Fig. 3A). In addition, following LGMN-overexpression in CAL-62 and SW579 cells, RT-qPCR showed that miR-495 levels were downregulated in a dose-dependent manner (Fig. 3B). Moreover, miR-495 expression levels were lower in thyroid carcinoma CAL-62 and SW579 cells compared with normal thyroid epithelial cells (Nthy-ori3-1) (Fig. 3C). miR-495 levels were upregulated in miR-495 mimic-transfected, and downregulated in miR-495 inhibitor-transfected CAL-62 cells (Fig. 3D). In order to determine whether miR-495 acts as key mediator for LGMN-regulated tumorigenesis, a colony formation assay was conducted to demonstrated that LGMN overexpression increased the number of CAL-62-cell colonies compared with the control, which was attenuated by miR-495 mimic transfection (Fig. 3E).

Subsequently, the present study aimed to identify the potential downstream effectors of miR-495. A previous report revealed that miR-495 attenuated ATG3 expression and promoted that of p62 (30). Therefore, western blot analysis was conducted to determine whether miR-495 could regulate the protein expression levels of ATG3 and p62 in thyroid carcinoma. To investigate whether miR-495 had a role in regulating autophagy in both CAL-62 and SW579 cells, western blotting was conducted in both cell lines using mimic or inhibitor. The results demonstrated that transfection with miR-495 mimics markedly reduced ATG3 and promoted p62 expression in CAL-62 cells, while the miR-495 inhibitor exerted opposing effects in SW579 cells (Fig. 3F-J). Furthermore, LGMN overexpression increased ATG3, and suppressed p62 expression in SW579 cells (Fig. 3K-M). Collectively, these results indicated that miR-495 was modulated by LGMN to regulate autophagy signaling.

Since the miR-495/autophagy axis may act as an effector of LGMN-mediated thyroid carcinoma progression, the current study aimed to further investigate the role of autophagy in the LGMN-modulated thyroid carcinoma phenotype. Firstly, the expression level of ATG3 was evaluated in CAL-62 and SW579 cells transfected with or without an ATG3 overexpression plasmid (Fig. 4A). CCK-8 and Transwell assays showed that LGMN-knockdown attenuated cellular proliferation and invasiveness, respectively, whereas ATG3 overexpression rescued the effects of LGMN silencing, to a certain degree (Fig. 4B-D). In addition, impaired tube formation ability was observed in HUVECs transfected with sh-LGMN, which was reversed by ATG3 overexpression (Fig. 4E and F). Overall, the results indicate that autophagy serves a critical role in LGMN/miR-495-regulated thyroid carcinoma progression.