si‑MALAT1 attenuates thymic cancer cell proliferation and promotes apoptosis via the miR‑145‑5p/HMGA2 pathway

Abstract

Metastasis-associated-lung-adenocarcinoma-transcript-1 (MALAT1) is a long non-coding RNA that is considered a potential tumor marker. The present study aimed to investigate the effect and mechanism of MALAT1 on cell proliferation and apoptosis in thymic cancer cells. IU-TAB-1, A549, HCT-116 and 293T cells were screened by reverse transcription-quantitative PCR to assess high-mobility group AT-hook 2 (HMGA2) expression in various types of cancer cells and were transfected with small interfering (si)RNA targeting MALAT1 (si-MALAT1). Cell proliferation was evaluated by Cell Counting Kit-8 assay. Cell apoptosis and cell cycle were examined using flow cytometry. The protein expression of cyclin D1, cyclin E, Bax, Bcl-2 and HMGA2 was determined by western blot analysis, while the associations between MALAT1 and microRNA (miR)-145-5p and between HMGA2 and miR-145-5p were determined by luciferase reporter assay. Among the four cell lines evaluated, IU-TAB-1 showed the highest expression of MALAT1; thus, IU-TAB-1 cells were selected for subsequent experiments. Compared with the findings in the control group, si-MALAT1 significantly decreased the cell proliferation of IU-TAB-1 cells, whereas the apoptosis levels and number of cells in G 2 phase were increased. The protein expression levels of cyclin D1, cyclin E, Bcl-2 and HMGA2 were significantly decreased in the si-MALAT1 group compared with those in the control group, while Bax levels were significantly increased. After treatment with si-MALAT1 in combination with miR-145-5p mimics or inhibitors, cell proliferation and apoptosis were respectively enhanced and inhibited in IU-TAB-1 cells. miR-145-5p inhibited the luciferase activity of IU-TAB-1 cells transfected with the MALAT1 or HMGA2 3′ untranslated region. In conclusion, si-MALAT1 significantly attenuated cell proliferation and apoptosis via the miR-145-5p/HMGA2 pathway in thymic cancer cells.

Locked Nucleic Acid Oligonucleotides Facilitate RNA•LNA-RNA Triple-Helix Formation and Reduce MALAT1 Levels

“…A nanocomplex carrying anti-MALAT1 siRNA crosses the blood-brain barrier to target glioblastoma multiforme tumor cells, resulting in a 2-5-fold decrease in MALAT1 levels, and induces increased sensitivity for temozolomide treatment [36]. In another report, an siMALAT1 inhibits cell proliferation and promotes apoptosis by enhancing the expression of miR-145-5p in thymic cancer cells [37]. A short 16-mer ASO gapmer with phosphorothioate-modified S-2 ′ -O-ethylene-2 ′ ,4 ′ -bridged nucleic acid targeted MALAT1 in an MMTV-PyMT carcinoma model, rendering slower tumor growth and reduced metastasis [11].…”

“…Although the MENβ triple helix is less studied than its counterpart in MALAT1, compounds like aurintricarboxylic acid, emodin, GW5074, mitoxantrone and rottlerin bind to the MENβ triple helix near the micromolar range, and the kinase inhibitor PIK-75 abolishes paraspeckles in the neuroblastoma cell line SH-SY5Y [30]. ASO therapeutics have been used to target and regulate the MALAT1 lncRNA in various cancer types [31][32][33][34][35][36][37][38][39][40][41][42][43][44][45]. A variety of ASOs, typically 16-20 nucleotides in length, have been designed, such as small interfering RNA (siRNA) [35][36][37]; gapmers with two to three locked nucleic acids (LNAs) [31,33,34,[38][39][40]; 2 ′ -O-methylethyl groups; 2 ′ -O,4 ′ -C-ethylene-bridged nucleic acid [41] or guanidine-bridged nucleic acid [42] at the end(s); PNA-DNA chimeras [43]; and the conjugation of ASO to single-wall carbon nanotubes [44], gold nanoparticles [32], TAT peptides [32], fatty acids [45] or membrane protein-binding aptamers [46] to improve delivery and biodistribution.…”

“…ASO therapeutics have been used to target and regulate the MALAT1 lncRNA in various cancer types [31][32][33][34][35][36][37][38][39][40][41][42][43][44][45]. A variety of ASOs, typically 16-20 nucleotides in length, have been designed, such as small interfering RNA (siRNA) [35][36][37]; gapmers with two to three locked nucleic acids (LNAs) [31,33,34,[38][39][40]; 2 ′ -O-methylethyl groups; 2 ′ -O,4 ′ -C-ethylene-bridged nucleic acid [41] or guanidine-bridged nucleic acid [42] at the end(s); PNA-DNA chimeras [43]; and the conjugation of ASO to single-wall carbon nanotubes [44], gold nanoparticles [32], TAT peptides [32], fatty acids [45] or membrane protein-binding aptamers [46] to improve delivery and biodistribution. Most ASO gapmers target unstructured regions of MALAT1, leading to RNase H-mediated knockdown from 2-50-fold [31,34,39,40].…”

Long Non-Coding RNAs in the Cell Fate Determination of Neoplastic Thymic Epithelial Cells

“…In this thymic tumor context, the downregulation of MALAT1 increased miR-145-5p expression and led to a reduction in cell proliferation and an increase in the apoptosis rate compared to that observed in the control. Additionally, the combination of MALAT1 silencing and miR-145-5p overexpression induces a synergistic effect, suggesting that MALAT1 may regulate the thymic cancer phenotype by inhibiting miR-145-5p (69). Recently, the expression of MALAT1 has been a focus in our studies where the relationship between lncRNA MALAT1 and METTL3, a methyltransferase enzyme that catalyzes the N6methyladenosine (m 6 A) modification, were described in the thymic carcinoma cell line, TC1889.…”

Non-Mutational Key Features in the Biology of Thymomas

“…The lncRNA MALAT1, acting as a miR-145-5p sponge, contributes to thymic cancer development, with its downregulation leading to decreased proliferation and increased apoptosis. The combination of MALAT1 silencing and miR-145-5p overexpression has a synergistic effect [ 99 ]. Iaiza et al, found that methylation and delocalization of MALAT1 through the methyltransferase METTL3 induces c-MYC expression in aggressive THs and TCs.…”