Yuanshen Mao1, Wenfeng Li1, YiMing Weng2, Bao Hua1, Xin Gu1, Chao Lu1, Bin Xu1, Huan Xu1, Zhong Wang1. 1. Department of Urology, Shanghai Ninth People's Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, China. 2. Reproductive Medical Center, Tongji Hospital, Tongji University School of Medicine, Shanghai, China.
Abstract
Accumulating data show that N6-methyladenosine (m6A) methyltransferase METTL3 and long noncoding RNA MALAT1 act pivotal roles in multiple malignancies including prostate cancer (PCa). However, the role and molecular mechanism underlying METTL3-mediated m6A modification of MALAT1 in PCa remain undocumented. The association of METTL3 and MALAT1 expression with clinicopathological characteristics and prognosis in patients with PCa was analyzed by quantitative real-time polymerase chain reaction (qRT-PCR), Western blot, and public The Cancer Genome Atlas (TCGA) dataset. The in vitro and in vivo experiments were executed to investigate the role of METTL3 in PCa. m6A dot blot, methylated RNA immunoprecipitation (MeRIP), RIP, and qRT-PCR assays were employed to observe METTL3-mediated m6A modification of MALAT1. The effects of METTL3 on MALAT1-mediated PI3K/AKT pathway were assessed by Western blot analysis. As a result, we found that METTL3 was significantly upregulated in PCa tissues and high expression of METTL3 was associated with Gleason score and tumor recurrence in patients with PCa. Knockdown of METTL3 markedly repressed growth and invasion of PCa cells in vitro and in vivo, whereas ectopic expression of METTL3 showed the opposite effects. Moreover, knockdown of METTL3 decreased the total m6A levels of PCa cells as well as the MALAT1 m6A levels, leading to reduced MALAT1 expression. Overexpression of MALAT1 reversed METTL3 knockdown-induced antitumor effects and PI3K/AKT signaling inactivation. MALAT1 harbored a positive correlation with METTL3 expression and tumor recurrence in PCa. In conclusion, our findings demonstrate that METTL3-mediated m6A modification of lncRNA MALAT1 promotes growth and invasion of PCa cells by activating PI3K/AKT signaling.
Accumulating data show that N6-methyladenosine (m6A) methyltransferase METTL3 and long noncoding RNA MALAT1 act pivotal roles in multiple malignancies including prostate cancer (PCa). However, the role and molecular mechanism underlying METTL3-mediated m6A modification of MALAT1 in PCa remain undocumented. The association of METTL3 and MALAT1 expression with clinicopathological characteristics and prognosis in patients with PCa was analyzed by quantitative real-time polymerase chain reaction (qRT-PCR), Western blot, and public The Cancer Genome Atlas (TCGA) dataset. The in vitro and in vivo experiments were executed to investigate the role of METTL3 in PCa. m6A dot blot, methylated RNA immunoprecipitation (MeRIP), RIP, and qRT-PCR assays were employed to observe METTL3-mediated m6A modification of MALAT1. The effects of METTL3 on MALAT1-mediated PI3K/AKT pathway were assessed by Western blot analysis. As a result, we found that METTL3 was significantly upregulated in PCa tissues and high expression of METTL3 was associated with Gleason score and tumor recurrence in patients with PCa. Knockdown of METTL3 markedly repressed growth and invasion of PCa cells in vitro and in vivo, whereas ectopic expression of METTL3 showed the opposite effects. Moreover, knockdown of METTL3 decreased the total m6A levels of PCa cells as well as the MALAT1 m6A levels, leading to reduced MALAT1 expression. Overexpression of MALAT1 reversed METTL3 knockdown-induced antitumor effects and PI3K/AKT signaling inactivation. MALAT1 harbored a positive correlation with METTL3 expression and tumor recurrence in PCa. In conclusion, our findings demonstrate that METTL3-mediated m6A modification of lncRNA MALAT1 promotes growth and invasion of PCa cells by activating PI3K/AKT signaling.
Entities:
Keywords:
MALAT1; METTL3; growth; m6A; prostate cancer
Prostate cancer (PCa) is the most common malignancy in men and constructs the second
leading cause of cancer-related death in men worldwide
. Despite the great advances made in cancer therapy, advanced patients with
PCa still possess the poor prognosis ascribed to the tumor invasiveness and metastasis
. Epigenetic regulations including RNA modifications and dysregulation of
noncoding RNA are implicated in gene expression and cancer progression
. Therefore, comprehensive observations of the molecular mechanisms underlying
PCa progression are essential for the effective therapeutic strategies.N6-methyladenosine (m
A), one of the most abundant mRNA modifications, is catalyzed by the
methyltransferase complex including methyltransferase-like 3/14 (METTL3/14), and
dynamically reversed by demethylase fat mass and obesity associated (FTO) and ALKBH5
. Increasing data uncover that METTL3 acts a critical role in cancer
progression and treatment
. METTL3 facilitates cancer growth and metastasis by promoting
m6A-dependent pri-miR221/222/1246 maturation[6,7], mediates m6A
modification of HDGF/SPHK2/SOX2 contributing to cancer progression and poor
prognosis[8-10], and
regulates oncogene translation and immune responses in cancer[11,12]. STM2457, a
potent and selective inhibitor of METTL3, provides a novel strategy against acute
myeloid leukemia
.Metastasis-associated lung adenocarcinoma transcript 1 (MALAT1) as a long noncoding
RNA (lncRNA) acts a multi-functional role in cancer. It has been reported that
MALAT1 promotes cancer cell growth, invasion, and metastasis and regulates
chemoresistance by sponging miR-3064-5p/-613/-204/-27a-5p[14-17], binding to splicing factor
proline and glutamine rich (SFPQ)
and impairing β-catenin degradation
. MALAT-1 facilitates PCa progression and represents a potential therapeutic target
. Targeting MALAT1 by nanocomplex carrying siRNA sensitizes glioblastoma to temozolomide
.Recent studies reveal that METTL3/SNHG1/miR-140-3p axis exerts prognostic and
immunological roles in non-small-cell lung cancer (NSCLC)
, and METTL3-mediated lncRNA FOXD2-AS1 and ABHD11-AS1 aggravate the
tumorigenesis of cervical cancer
and the Warburg effect of NSCLC
. However, the role and molecular mechanism underlying METTL3-mediated MALAT1
in PCa remain undocumented. We herein found that METTL3-mediated m
A modification of lncRNA MALAT1 promoted proliferation and invasion of PCa
cells by activating PI3K/AKT signaling, and might provide a therapeutic target for
PCa.
Methods
Clinical Samples
In all, 484 cases of non-paired PCa tissue samples and 52 pair-matched samples
were collected from The Cancer Genome Atlas (TCGA) database (http://xena.ucsc.edu/getting-started/). Ten pairs of PCa
samples, used for polymerase chain reaction (PCR) and Western blot assays were
preserved in liquid nitrogen and frozen at −80°C. Our study protocol was
approved by the Ethics Committee of Shanghai Ninth People’s Hospital.
RNA Extraction and Real-Time Quantitative PCR
Total RNA was collected by using a RNA extraction kit (QIAGEN, Dusseldorf,
Germany), and cDNA was synthesized by using a reverse transcription kit
(Promega, Madison, USA) according to the manufacturer’s instructions. PCR assay
was performed using the SYBR Green Master Mix. After the reactions were
finished, the relative expression levels of METTL3 and MALAT1 were calculated
using the 2−ΔΔCt. The primer sequences used were shown in Supplementary Table S1.
Western Blot
PCa tissue samples and DU145 and 22RV1 cells were lysed by RIPA
(radio-immunoprecipitation assay) buffer (P0013B; Beyotime, Shanghai, China).
The supernatants were resolved in SDS-PAGE and transferred onto polyvinylidene
fluoride (PVDF) membranes (IPVH00010; Millipore, Billerica, MA, USA), incubated
with anti-METTL3 (DF12020; Affinity, Changzhou, China), anti-PI3K (AF6241,
Affinity), anti-AKT (60203-2-Ig; Proteintech, Wuhan, China), anti-p-AKT
(66444-1-Ig; Proteintech), and anti-glyceraldehyde-3-phosphate dehydrogenase
(GAPDH; AB-P-R 001; Hangzhou, China) overnight at 4°C. Protein bands were
scanned by enhanced chemiluminescence (ECL).
Plasmid, shRNA, and Cell Transfection
METTL3 plasmid vector, lentivirus-mediated shRNA targeting METTL3 (sh-METTL3,
5′-GCAAGAATTCTGTGACTATGG-3′), and MALAT1 plasmids were purchased from GenePharma
(Shanghai, China). The negative vector (Vector) and sh-NC were regarded as the
control groups. DU145 and 22RV1 cells were planted in six-well plates 24 h prior
to sh-METTL3, METTL3 plasmids, and MALAT1 plasmids transfection with 50% to 60%
confluence, and then mixed with Lipofectamine 2000 (Invitrogen, Carlsbad, CA,
USA) according to the manufacture instructions.
Cell Culture, MTT, EdU, Transwell Assays, and Immunohistochemistry
Analysis
These assays were performed as previously reported
.
RNA Immunoprecipitation
Magna RIPTM RNA-Binding Protein Immunoprecipitation Kit (Millipore) was used.
DU145 and 22RV1 cells were lysed in RNA immunoprecipitation (RIP) lysis buffer,
and then cell extracts were incubated with magnetic beads labeled with the
antibodies of Argonaute2 (Ago2; Millipore), METTL3 (Affinity), and
Immunoglobulin G (IgG; Millipore). RNAs that were pulled-down were extracted
using Trizol reagent (Invitrogen). RNA expression was determined by real-time
quantitative PCR (RT-qPCR).
Methylated RNA Immunoprecipitation Assay
Methylated RNA immunoprecipitation (MeRIP) assay was performed according to the
MeRIP Kit (BersinBio, Guangzhou, China) was used. Briefly, RNA was broken into
about 300 bp fragments, and 50 μl was separated as input. The remaining samples
were divided into two groups and incubated with m6A (A-1801-020;
Epigentek, Wuhan, China) and IgG antibodies, respectively. The enriched RNA was
extracted after immunoprecipitation, and qPCR was used for subsequent
experimental analysis after RNA reverse transcription.
In Vivo Tumorigenesis Assay
The female Balb/C-nu/nu nude mice (6–8 weeks old, 18–20 g) were purchased from
the Shanghai Laboratory Animal Central. DU145 cells (2 × 106) transfected with
the stable transfection of sh-METTL3 lentivirus or sh-NC were resuspended in 200
μl of sterile PBS and injected subcutaneously into the right flanks of mice.
After 5 weeks, the mice were killed, and the tumor volume and weight were
calculated. The animal experiments were approved by the Ethics Committee of
Shanghai Ninth People’s Hospital.
Statistical Analysis
Statistical analyses were processed with GraphPad Prism 7 (La Jolla, CA, USA).
The values are expressed as the mean ± standard deviation. Chi-square, Student’s
t test, and analysis of variance were used for comparisons
between groups. Kaplan–Meier analysis was used to analyze the correlation of
METTL3 or MALAT1 with PCa. A Cox proportional hazard model was used to estimate
the risk of METTL3 or MALAT1 in PCa. Pearson correlation analysis was used to
analyze the correlation of METTL3 and MALAT1. P < 0.05 was
considered statistically significant.
Results
The Upregulation of METTL3 Indicates Tumor Recurrence in Patients With
PCa
The RNA expression levels of METTL3 in PCa tissue samples were assessed by TCGA
cohort, which indicated that METTL3 was upregulated in both 52 pare-matched PCa
tissue samples and 484 non-pairs of PCa samples as compared with adjacent normal
tissues (Fig. 1A). The
upregulation of METTL3 in PCa was further validated in our cohort by qRT-PCR
(Fig. 1B) and
Western blot assays (Fig.
1C). Then, according to the survival time, survival status, and
METTL3 expression levels, we acquired the cutoff value of METTL3 (9.723) in PCa
patients from TCGA cohort by a Cutoff Finder and divided the patients into
METTL3-high group (n = 278) and METTL3-low group
(n = 116). It was shown that elevation of METTL3 expression
was associated with Gleason score (P < 0.001) in PCa
patients from TCGA cohort (Supplementary Table S2). Kaplan–Meier analysis revealed that the
PCa patients with METTL3-high expression harbored higher tumor recurrence as
compared with those with METTL3-low expression (Fig. 1D), but had no difference in
overall survival (Fig. S1). Subsequently, multivariate Cox regression analysis
unveiled that METTL3 high expression was not an independent risk factor for
tumor recurrence in patients with PCa from TCGA cohort (Supplementary Table S3).
Figure 1.
Upregulation of METTL3 is associated with tumor recurrence in patients
with PCa. (A) TCGA analysis of the expression levels of METTL3 in 52
pair-matched and 484 non-paired PCa tissue samples. (B, C) qRT-PCR and
Western blot analysis of the expression levels of METTL3 in 10
pair-matched PCa tissue samples. (D) TCGA cohort analysis of the
association of METTL3 with the prognosis in PCa with patients. PCa:
prostate cancer; qRT-PCR: quantitative real-time polymerase chain
reaction.
Upregulation of METTL3 is associated with tumor recurrence in patients
with PCa. (A) TCGA analysis of the expression levels of METTL3 in 52
pair-matched and 484 non-paired PCa tissue samples. (B, C) qRT-PCR and
Western blot analysis of the expression levels of METTL3 in 10
pair-matched PCa tissue samples. (D) TCGA cohort analysis of the
association of METTL3 with the prognosis in PCa with patients. PCa:
prostate cancer; qRT-PCR: quantitative real-time polymerase chain
reaction.
Knockdown of METTL3 Dampens PCa Cell Growth and Invasion
The transfection levels of lentivirus-mediated sh-METTL3 were determined by
qRT-PCR and Western blot assays, which indicated that the METTL3 expression
levels were markedly decreased in DU145 and 22RV1 cell liens after transfection
with sh-METTL3 for 48 h (Fig.
2A). Cell proliferation and DNA synthesis were assessed by MTT and
EdU assays, which indicated that knockdown of METTL3 repressed cell
proliferation activity (Fig.
2B) and DNA synthesis (Fig. 2C) in DU145 and 22RV1 cells.
Transwell was used to evaluate cell invasive capabilities, indicating that
inhibition of METTL3 prohibited cell invasive potential in DU145 and 22RV1 cells
(Fig. 2D).
Figure 2.
Knockdown of METTL3 suppresses the proliferation and invasion of PCa
cells. (A) qRT-PCR and Western blot analysis of the transfection
efficiency of sh-METTL3 in DU145 and 22RV1 cells. (B) MTT analysis of
the cell proliferation activities after transfection of sh-METTL3 into
DU145 and 22RV1 cells. (C) Colony formation analysis of the cell colony
abilities after transfection of sh-METTL3 into DU145 and 22RV1 cells.
(D) Transwell analysis of the cell invasion capabilities after
transfection of sh-METTL3 into DU145 and 22RV1 cells. Data are the means
± SEM of three experiments. qRT-PCR: quantitative real-time polymerase
chain reaction. *P < 0.05; **P <
0.01; ***P < 0.001.
Knockdown of METTL3 suppresses the proliferation and invasion of PCa
cells. (A) qRT-PCR and Western blot analysis of the transfection
efficiency of sh-METTL3 in DU145 and 22RV1 cells. (B) MTT analysis of
the cell proliferation activities after transfection of sh-METTL3 into
DU145 and 22RV1 cells. (C) Colony formation analysis of the cell colony
abilities after transfection of sh-METTL3 into DU145 and 22RV1 cells.
(D) Transwell analysis of the cell invasion capabilities after
transfection of sh-METTL3 into DU145 and 22RV1 cells. Data are the means
± SEM of three experiments. qRT-PCR: quantitative real-time polymerase
chain reaction. *P < 0.05; **P <
0.01; ***P < 0.001.
Overexpression of METTL3 Promotes PCa Cell Growth and Invasion
The transfection levels of METTL3 plasmids were defined by qRT-PCR and Western
blot assays, which showed that the METTL3 expression levels were dramatically
increased in DU145 and 22RV1 cells after transfection with METTL3 plasmids for
48 h (Fig. 3A). Cell
proliferation and DNA synthesis were estimated by MTT and EdU assays, which
indicated that METTL3 overexpression enhanced cell proliferation activity (Fig. 3B) and DNA
synthesis (Fig. 3C) in
DU145 and 22RV1 cells. Transwell was used to evaluate cell invasive
capabilities, implying that overexpression of METTL3 drove cell invasive
potential in DU145 and 22RV1 cells (Fig. 3D).
Figure 3.
Overexpression of METTL3 promotes the proliferation and invasion of PCa
cells. (A) qRT-PCR and Western blot analysis of the transfection
efficiency of METTL3 plasmids in DU145 and 22RV1 cells. (B) MTT analysis
of the cell proliferation activities after transfection of METTL3
plasmids into DU145 and 22RV1 cells. (C) Colony formation analysis of
the cell colony abilities after transfection of METTL3 plasmids into
DU145 and 22RV1 cells. (D) Transwell analysis of the cell invasion
capabilities after transfection of METTL3 plasmids into DU145 and 22RV1
cells. Data are the means ± SEM of three experiments. qRT-PCR:
quantitative real-time polymerase chain reaction. *P
< 0.05; **P < 0.01; ***P <
0.001.
Overexpression of METTL3 promotes the proliferation and invasion of PCa
cells. (A) qRT-PCR and Western blot analysis of the transfection
efficiency of METTL3 plasmids in DU145 and 22RV1 cells. (B) MTT analysis
of the cell proliferation activities after transfection of METTL3
plasmids into DU145 and 22RV1 cells. (C) Colony formation analysis of
the cell colony abilities after transfection of METTL3 plasmids into
DU145 and 22RV1 cells. (D) Transwell analysis of the cell invasion
capabilities after transfection of METTL3 plasmids into DU145 and 22RV1
cells. Data are the means ± SEM of three experiments. qRT-PCR:
quantitative real-time polymerase chain reaction. *P
< 0.05; **P < 0.01; ***P <
0.001.
LncRNA MALAT1 is an m6A Target of METTL3 in PCa Cells
We identified the binding RNAs of METTL3 by using starbase3.0 (https://starbase.sysu.edu.cn) and found that METTL3 had the most
binding sites with lncRNA MALAT1. We proposed that METTL3 might mediate the
m6A modification of MALAT1. The m6A dot blot showed
that knockdown of METTL3 reduced the whole m6A levels in DU145 and
22RV1 cells (Fig. 4A).
MeRIP and qRT-PCR further verified that knockdown of METTL3 decreased the
m6A levels of MALAT1 (Fig. 4B) as well as its mRNA levels
(Fig. 4C) in DU145
and 22RV1 cells. Furthermore, we conducted RIP assay for METTL3-specific binding
with MALAT1 in DU145 and 22RV1 cells and investigated the endogenous levels of
MALAT1 pulled-down from METTL3-expressed cells by qRT-PCR analysis, which
indicated that MALAT1 was obviously enriched in the METTL3 pellet compared with
those in the IgG control (Fig.
4D).
Figure 4.
LncRNA MALAT1 is identified as an m6A target of METTL3 in PCa
cells. (A) m6A dot blot analysis of the effects of METTL3
knockdown on the total m6A levels in DU145 and 22RV1 cells.
(B) Schematic analysis of the binding sites between m6A and
MALAT1 and MeRIP analysis of the effects of METTL3 knockdown on the
m6A levels of MALAT1 in DU145 and 22RV1 cells. (C)
qRT-PCR analysis of the effects of METTL3 knockdown on the mRNA levels
of MALAT1 in DU145 and 22RV1 cells. (D) RIP for METTL3 was conducted to
measure the endogenous expression of MALAT1 in DU145 and 22RV1 cells.
Data are the means ± SEM of three experiments. qRT-PCR: quantitative
real-time polymerase chain reaction; RIP: RNA immunoprecipitation.
****P < 0.0001.
LncRNA MALAT1 is identified as an m6A target of METTL3 in PCa
cells. (A) m6A dot blot analysis of the effects of METTL3
knockdown on the total m6A levels in DU145 and 22RV1 cells.
(B) Schematic analysis of the binding sites between m6A and
MALAT1 and MeRIP analysis of the effects of METTL3 knockdown on the
m6A levels of MALAT1 in DU145 and 22RV1 cells. (C)
qRT-PCR analysis of the effects of METTL3 knockdown on the mRNA levels
of MALAT1 in DU145 and 22RV1 cells. (D) RIP for METTL3 was conducted to
measure the endogenous expression of MALAT1 in DU145 and 22RV1 cells.
Data are the means ± SEM of three experiments. qRT-PCR: quantitative
real-time polymerase chain reaction; RIP: RNA immunoprecipitation.
****P < 0.0001.
The Upregulation of MALAT1 Indicates Tumor Recurrence in Patients With
PCa
The expression of MALAT1 in PCa tissue samples was estimated by TCGA cohort,
which indicated that MALAT1 expression was significantly increased in both 51
pare-matched PCa tissue samples and 481 non-pairs of PCa samples as compared
with adjacent normal tissues (Fig. 5A). The expression of MALAT1 was elevated in PCa with Gleason
(≥8) relative to those with Gleason (= 7) (Fig. 5B). The upregulation of MALAT1 was
further validated in 10 pairs of PCa tissue samples by qRT-PCR analysis (Fig. 5C). Pearson
correlation analysis showed that METTL3 had a positive correlation with MALAT1
expression in PCa (Fig.
5D). We obtained the cutoff value of MALAT1 (11.96) in PCa patients
and divided the patients from TCGA cohort into MALAT1-high group
(n = 169) and MALAT1-low group (n = 122).
Then, high expression of MALAT1 was associated with Gleason score
(P = 0.007) and lymph node metastasis (P =
0.017) in PCa patients from TCGA cohort (Supplementary Table S4). Kaplan–Meier analysis revealed that the
PCa patients with MALAT1-high expression possessed higher tumor recurrence as
compared with those with MALAT1-low expression (Fig. 5E), but had no difference in
overall survival (Fig. S2). Multivariate Cox regression analysis unveiled that
MALAT1 high expression was not an independent risk factor for overall survival
and tumor recurrence in patients with PCa from TCGA cohort (Supplementary Tables S5 and S6).
Figure 5.
Upregulation of MALAT1 is associated with tumor recurrence in patients
with PCa. (A) TCGA analysis of the expression levels of MALAT1 in 51
pair-matched and 481 non-paired PCa tissue samples. (B) TCGA analysis of
the expression levels of MALAT1 in patients with diverse Gleason
scorings. (C) qRT-PCR analysis of the expression levels of MALAT1 in 10
pairs of PCa tissue samples. (D) Pearson correlation analysis of the
correlation of METTL3 with MALAT1 in PCa tissue samples. (E) TCGA cohort
analysis of the association of MALAT1 with the prognosis in PCa with
patients. PCa: prostate cancer; qRT-PCR: quantitative real-time
polymerase chain reaction.
Upregulation of MALAT1 is associated with tumor recurrence in patients
with PCa. (A) TCGA analysis of the expression levels of MALAT1 in 51
pair-matched and 481 non-paired PCa tissue samples. (B) TCGA analysis of
the expression levels of MALAT1 in patients with diverse Gleason
scorings. (C) qRT-PCR analysis of the expression levels of MALAT1 in 10
pairs of PCa tissue samples. (D) Pearson correlation analysis of the
correlation of METTL3 with MALAT1 in PCa tissue samples. (E) TCGA cohort
analysis of the association of MALAT1 with the prognosis in PCa with
patients. PCa: prostate cancer; qRT-PCR: quantitative real-time
polymerase chain reaction.
MALAT1 Abrogates METTL3 Knockdown-Induce Antitumor Effect and PI3K/AKT
Inactivation
To further assess the regulation of METTL3 on MALAT1 in PCa cells, we constructed
MALAT1-overexpressed DU145 and 22RV1 cells, indicated by qRT-PCR analysis (Fig. 6A). We
co-transfected MALAT1 plasmids and sh-METTL3 lentiviruses into DU145 and 22RV1
cells and found that MALAT1 overexpression could reverse METTL3
knockdown-induced inhibitory effects on cell proliferation, invasion and DNA
synthesis in DU145 and 22RV1 cells (Fig. 6B–D). Moreover, Western blot analysis
displayed that knockdown of METTL3 could markedly repress the phosphorylated
PI3K/AKT activities rather than the total PI3K/AKT expression, and
overexpression of MALAT1 could reverse METTL3 knockdown-caused PI3K/AKT
inactivation in DU145 and 22RV1 cells (Fig. 6E).
Figure 6.
Overexpression of MALAT1 abolishes METTL3 knockdown-induced antitumor
effect and PI2K/AKT signaling inactivation. (A) qRT-PCR analysis of the
transfection efficiency of MALAT1 plasmids in DU145 and 22RV1 cells. (B)
MTT analysis of the cell proliferation activities after co-transfection
with MALAT1 plasmids and sh-METTL3 into DU145 and 22RV1 cells. (C)
Transwell analysis of the cell invasion capabilities after
co-transfection with MALAT1 plasmids and sh-METTL3 into DU145 and 22RV1
cells. (D) EdU analysis of the DNA synthesis after co-transfection with
MALAT1 plasmids and sh-METTL3 into DU145 and 22RV1 cells. (E) Western
blot analysis of the PI3K/AKT signaling activities after co-transfection
with MALAT1 plasmids and sh-METTL3 into DU145 and 22RV1 cells. Data are
the means ± SEM of three experiments. qRT-PCR: quantitative real-time
polymerase chain reaction. *P < 0.05;
**P < 0.01; ***P < 0.001;
****P < 0.0001.
Overexpression of MALAT1 abolishes METTL3 knockdown-induced antitumor
effect and PI2K/AKT signaling inactivation. (A) qRT-PCR analysis of the
transfection efficiency of MALAT1 plasmids in DU145 and 22RV1 cells. (B)
MTT analysis of the cell proliferation activities after co-transfection
with MALAT1 plasmids and sh-METTL3 into DU145 and 22RV1 cells. (C)
Transwell analysis of the cell invasion capabilities after
co-transfection with MALAT1 plasmids and sh-METTL3 into DU145 and 22RV1
cells. (D) EdU analysis of the DNA synthesis after co-transfection with
MALAT1 plasmids and sh-METTL3 into DU145 and 22RV1 cells. (E) Western
blot analysis of the PI3K/AKT signaling activities after co-transfection
with MALAT1 plasmids and sh-METTL3 into DU145 and 22RV1 cells. Data are
the means ± SEM of three experiments. qRT-PCR: quantitative real-time
polymerase chain reaction. *P < 0.05;
**P < 0.01; ***P < 0.001;
****P < 0.0001.
Knockdown of METTL3 Suppresses In Vivo Tumorigenesis
To decipher whether METTL3 affects in vivo tumor growth, we
constructed a sh-METTL3 or sh-NC stably transfected DU145 cells, and then
subcutaneously injected into the flank of nude mice. After investigations for 5
weeks, it was found that the tumor volumes of sh-METTL3-transfected group were
smaller than the sh-NC group (Fig. 7A). The curve for tumor growth implied that the tumors in
sh-METTL3 transfected group showed a decrease in a time-dependent manner (Fig. 7B), and the volume
and weight of xenograft tumors were markedly weakened in sh-METTL3 transfected
group as compared with the sh-NC group (Fig. 7C, D). Further analyses of qRT-PCR
and immunohistochemistry (IHC) showed that knockdown of METTL3 reduced the
expression of MALAT1 (Fig.
7E) and inhibited the activation of p-PI3K and p-AKT (Fig. 7F, G) in xenograft
tumor tissues.
Figure 7.
Knockdown of METTL3 represses in vivo tumorigenesis. (A)
Comparison of the tumor size between sh-METTL3 and sh-NC transfected
groups. (B) A growth curve analysis of the tumor alterations in
sh-METTL3 and sh-NC transfected groups. (C, D) Comparison of the tumor
volume and weight between sh-METTL3 and sh-NC transfected groups. (E)
qRT-PCR analysis of the expression of MALAT1 between sh-METTL3 and sh-NC
transfected groups. (F, G) IHC analysis of the activities of p-PI3K and
p-AKT between sh-METTL3 and sh-NC transfected groups. Data are the means
± SEM of five experiments. IHC: immunohistochemistry; qRT-PCR:
quantitative real-time polymerase chain reaction.
Knockdown of METTL3 represses in vivo tumorigenesis. (A)
Comparison of the tumor size between sh-METTL3 and sh-NC transfected
groups. (B) A growth curve analysis of the tumor alterations in
sh-METTL3 and sh-NC transfected groups. (C, D) Comparison of the tumor
volume and weight between sh-METTL3 and sh-NC transfected groups. (E)
qRT-PCR analysis of the expression of MALAT1 between sh-METTL3 and sh-NC
transfected groups. (F, G) IHC analysis of the activities of p-PI3K and
p-AKT between sh-METTL3 and sh-NC transfected groups. Data are the means
± SEM of five experiments. IHC: immunohistochemistry; qRT-PCR:
quantitative real-time polymerase chain reaction.
Discussion
Accumulating studies indicate that m6A methylation modification is
essential to maintain cancer growth and metastasis[8,25]. METTL3 is upregulated in
bladder cancer
, cervical cancer
, colorectal cancer (CRC)
, oral squamous cell carcinoma
, and associated with lymph node metastasis and poor prognosis[6,26]–
. METTL3 expression is also elevated in metastatic PCa and correlated with
malignant progression and poor prognosis in PCa
. However, METTL3 is downregulated in papillary thyroid cancer (PTC),
restrains tumor growth, and indicates favorable prognosis in patients with PTC
. In the present study, we found that METTL3 was upregulated in PCa and
associated with Gleason score and tumor recurrence in patients with PCa, suggesting
that METTL3 may be a potential prognostic factor in PCa.Previous studies showed that, on one hand, METTL3 acts as an oncogene in multiple malignancies
–[10,26]–
. On the other hand, METTL3 functions as a tumor suppressor in renal cell carcinoma
and enhances cisplatin chemosensitivity of cervical cancer by downregulation
of RAGE
. In PCa tissues, METTL3-mediated m6A modification of KIF3C and MYC
facilitates PCa progression[33,34] and inhibition of METTL3 impairs invasion and metastasis of PCa
. In consistence with these studies[33-35], we herein found that
knockdown of METTL3 suppressed PCa cell proliferation and invasion in
vitro and in vivo, whereas overexpression of METTL3
had the opposite effects, indicating that METTL3 may be an oncogenic factor in
PCa.Mechanistical investigations unveil that METTL3 can mediate m6A
modification of noncoding RNAs including miRNA[6,7] and lncRNA[22-24] involved in cancer
progression. MALAT1 has been verified as a crucial tumorigenic factor in
PCa[14-20], and METTL3-mediated
m6A modification of MALAT1 promotes growth and metastasis in NSCLC
and glioma
. We herein found that knockdown of METTL3 reduced the m6A
modification level of MALAT1, which reversed METTL3 knockdown-induced antitumor
effects and indicated tumor recurrence in PCa. These findings suggested that
METTL3-mediated m6A modification of MALAT1 promoted PCa growth.In addition, MALAT1 facilitates cell proliferation, invasion, and cisplatin
resistance by activating PI3K/AKT pathway in gastric cancer and
cholangiocarcinoma[38-40].
MALAT1/miR-146a/PI3K/AKT pathway repress cell apoptosis and autophagy in
hepatocellular carcinoma (HCC)
and MALAT1/miR-26a/26b/FUT4/PI3K/AKT pathway promotes CRC invasion and metastasis
. METTL3 promotes retinoblastoma growth and endothelial progenitor cell
angiogenesis by PI3K/AKT pathway[43,44]. We herein found that MALAT1
promoted the activation of PI3K/AKT signaling and abrogated METTL3 knockdown-induced
PI3K/AKT signaling inactivation in PCa cells.In conclusion, our findings demonstrate that METTL3 upregulation is associated with
Gleason scoring and tumor recurrence in patients with PCa and METTL3-mediated
m6A modification of lncRNA MALAT1 promotes PCa tumorigenesis by
activation of PI3K/AKT signaling. Our present study may provide potential
therapeutic strategies for treatment of PCa.Click here for additional data file.Supplemental material, sj-docx-1-cll-10.1177_09636897221122997 for
METTL3-Mediated m6A Modification of lncRNA MALAT1 Facilitates Prostate Cancer
Growth by Activation of PI3K/AKT Signaling by Yuanshen Mao, Wenfeng Li, YiMing
Weng, Bao Hua, Xin Gu, Chao Lu, Bin Xu, Huan Xu and Zhong Wang in Cell
TransplantationClick here for additional data file.Supplemental material, sj-tif-2-cll-10.1177_09636897221122997 for METTL3-Mediated
m6A Modification of lncRNA MALAT1 Facilitates Prostate Cancer Growth by
Activation of PI3K/AKT Signaling by Yuanshen Mao, Wenfeng Li, YiMing Weng, Bao
Hua, Xin Gu, Chao Lu, Bin Xu, Huan Xu and Zhong Wang in Cell TransplantationClick here for additional data file.Supplemental material, sj-tif-3-cll-10.1177_09636897221122997 for METTL3-Mediated
m6A Modification of lncRNA MALAT1 Facilitates Prostate Cancer Growth by
Activation of PI3K/AKT Signaling by Yuanshen Mao, Wenfeng Li, YiMing Weng, Bao
Hua, Xin Gu, Chao Lu, Bin Xu, Huan Xu and Zhong Wang in Cell Transplantation