Many studies have suggested that EIF4G2-dependent mRNAs were specifically involved in pro-oncogenic activities, such as cell proliferation, anti-apoptosis, tumor invasion, metastasis and angiogenesis [
6,
7,
24‐
28]. Therefore, EIF4G2 has been found to be associated with tumor development and treatments. Downregulation of EIF4G2 could induce reacquisition of chemosensitivity to paclitaxel in ovarian cancer [
29] and enhance cisplatin chemosensitivity in nonsmall cell lung cancer [
30]. Here, we first reported that EIF4G2 was abnormally enhanced in HCC tissues and that higher EIF4G2 was associated with some clinicopathological characteristics, such as T stage, TNM stage, recurrence, and poorer DFS of HCC patients. The OS results in our study were not significantly different, which might be because the number of our samples was too small (
n = 89) compared with the database (
n = 365). Further study revealed that EIF4G2 showed no difference between HBV+ HCC cases and HBV- HCC cases, demonstrating that EIF4G2 was not associated with HBV (Fig. S
1F). Besides, the positive correlation between EIF4G2 and PDL1 expression reflected that they might be jointly involved in the disease progression and immune escape of HCC, which deserves further study. Moreover, EIF4G2 strongly promoted HCC cell growth and metastasis and promoted HCC xenografts in nude mice. Mechanically, in our study, the results of transcriptional profiling demonstrated that EIF4G2 knockdown could obviously inhibit the MAPK signaling pathway. MAPKs in mammals mainly include three major subfamilies: JNK, p38 MAPK and ERK [
31,
32]. Here, we tested all three signaling pathways by Western blot assay to find out which one was implicated. As shown in Fig.
3b, both si-EIF4G2 groups caused p-ERK suppression in Huh7 and Hep3B cells. In contrast, p-p38 and p-JNK showed a higher expression in the si-EIF4G2 groups of Hep3B cells and showed the opposite trend in si-EIF4G2#1 versus si-EIF4G2#2 in Huh7 cells. Our data were consistent with other studies, in which ERK signaling was shown to be one of the most important pathways in cell proliferation and metastasis, and activation of the ERK signaling pathway is closely related to HCC prognosis and development, and is detectable in nearly half of early HCC patients and almost all patients with advanced HCC [
33,
34]. And the p38 MAPK and JNK signaling pathways play a role in cell apoptosis and proinflammatory responses [
35,
36]. Taken together, we speculated that EIF4G2 promoted HCC development through the ERK signaling pathway. Consistent with this, a study revealed that deletion of EIF4G2 caused decreased expression of MAP3K3 and SOS1, which were reported to be upstream of the ERK/MAPK signaling pathway [
37,
38]. While, in our study, there was no significant difference of MAP3K3 and SOS1, this might be because the cell lines used were different. On the other hand, we found the mRNA level of RASGRF1 and RAC2 were suppressed and the level of DUSP3 was increased in the downregulation of EIF4G2 according to the result of transcriptional profiling. These three molecules were all involved in the ERK/MAPK pathway. RASGRF1, like the SOS1 (mentioned above), is one of the Ras-specific guanine nucleotide exchange factors, which can convert Ras from inactive GDP-Ras form to GTP-Ras activate form, then activating the downstream ERK signaling [
39]. RAC2 is one of Rac GTPase, which can activate the Raf together with the Cdc42hs and RhoA, and then increasing ERK1/2 activity [
40]. While DUSP3 is one of the dual specific protein phosphatases, which can dephosphorylate and inactivate ERK1/2 [
41]. These data further suggested that knockdown of EIF4G2 inhibit the ERK pathway by regulating the upstream genes of the ERK/MAPK signaling pathway.
Analysis of GEPIA data showed that the level of EIF4G2 mRNA was not significantly different between HCC tissues and paracarcinoma tissues (Fig. S
1E), while the protein level of EIF4G2 was obviously different. The results reminded us of the regulatory mechanism of miRNAs. miRNAs participate in posttranscriptional regulation by binding to the 3’UTR of targeted mRNAs, preventing protein translation. Using some website databases containing TargetScan, miRCODE and starBase, we found that miR-144 was likely a new regulator to modulate EIF4G2 because there were several conserved binding sites between them. miR-144, a well-known tumor suppressor, has been found to be involved in the development of several cancers, including HCC. A comprehensive analysis of miR-144 in HCC revealed that many genes and signaling pathways were regulated by miR-144, including the Toll-like receptor pathway, p53 signaling pathway, and cell cycle-associated proteins [
42]. In addition, miR-144 could inhibit human hepatocellular carcinoma by regulating CCNB1 [
43], repress the mTOR-VEGF pathway by targeting SGK3 in HCC [
44], and reverse the chemoresistance of HCC cells by suppressing Nrf2 [
45]. In our work, EIF4G2 was found to be negatively regulated by miR-144, and the levels of miR-144 and EIF4G2 were inversely associated with each other in HCC samples. Consistent with other studies, we demonstrated that miR-144 suppressed HCC development in vitro and in vivo. Moreover, we discovered that re-expression of EIF4G2 could attenuate the inhibitory action of miR-144 on HCC.