ESCA is a common malignant tumor with high invasiveness. Although the pathogenesis of ESCA is still unclear, it is known to be associated with chemical stimulation, genetic factors, and other esophageal diseases. Studies have shown that the biological characteristics of ESCA are closely related to autophagy. In the early stage of ESCA, autophagy can activate anti-tumor cells and micro-environment to inhibit the development of ESCA [16]. However, in the middle and later stages of ESCA, autophagy can be used as a promoter of tumor development, by clearing abnormal mitochondria and providing energy for tumor cells, and then promote the proliferation and metastasis of tumor cells [17]. Whelan et al. have also demonstrated that autophagy can promote the metastasis of ESCA by mediating the mechanism of epithelial-mesenchymal transition (EMT) [18]. In addition, it has been proved that autophagy inhibitors can inhibit the development of ESCA and improve the prognosis of patients [19]. Interestingly, anesthetics can also inhibit tumor growth by regulating autophagy. So et al. found that midazolam can induce apoptosis of Leydig tumor cells by regulating autophagy [20]. Zhang et al. also found that ropivacaine can inhibit the growth of melanoma [21]. Since these autophagy inhibitors have not been widely used in clinical treatment, their safety and potential molecular mechanisms related to ESCA are unclear. Therefore, it is very beneficial for patients to explore the potential autophagy mechanism of ESCA and to find more effective targets for diagnosis and treatment. However, most studies tend to evaluate the role of ARGs in ESCA. So far, there is no study on the diagnostic and prognostic value of autophagy-related lncRNAs in ESCA. Therefore, it is necessary to elucidate the potential molecular mechanism of autophagy-related lncRNAs in ESCA and identify new therapeutic targets.
In this study, we divided ESCA patients into high- and low-risk groups, and then performed KEGG analysis with GSEA on the genes of patients in the high- and low-risk groups. The final results showed that the genes in the high-risk group were enriched in the protein export and spliceosome KEGG pathways, compared with the low-risk group.
The spliceosome has been shown to be associated with the occurrence of cancer, and is also closely related to the autophagy process in cancer [1]. The spliceosome is a multi-component complex formed during the splicing of RNA, and has an important role in regulating genetic activities [22]. Under normal physiological conditions, the spliceosome removes introns and exon junctions by splicing precursor mRNA, which is transformed into mature mRNA and finally translated by ribosomes into proteins that perform various functions and activities essential to life. During tumor formation, abnormal RNA splicing at the transcript level often promotes the occurrence of cancer [23]. High expression of SF3B4, a component of the splicing complex, is significantly correlated with shorter OS in patients with ESCA [24]. Similarly, bioinformatics studies have shown that the occurrence of ESCA is related to the spliceosome [25]. Interestingly, the spliceosome is also closely related to autophagy [26-28]. Quidville et al. showed that SNRPE was overexpressed in lung and breast cancer, and knocking down SNRPE could cause cancer cell death through autophagy [29]. Therefore, we speculate that the spliceosome could affect the progress of ESCA by regulating the expression of autophagy genes in ESCA.
In this study, we identified seven lncRNAs and 33 mRNAs by analyzing autophagy-related lncRNAs in ESCA and constructing a co-expression network. These genes were closely related to autophagy in ESCA. ULK1 is a serine/threonine protein kinase that initiates autophagy and regulates autophagy through mTORC1 and AMPK. It has been shown to regulate the growth of cancer cells through autophagy in a variety of cancers [30]. In colon cancer, Liu et al. blocked the autophagy of cancer cells by knocking down the expression of ULK1, thereby promoting cell apoptosis and inhibiting the growth of colon cancer [31]. ULK1 has a similar role in prostate cancer [32]. Jiang et al. found that ULK1 was highly expressed in ESCA patients compared with normal samples through bioinformatics analysis [33]. Moreover, high expression of ULK1 was significantly correlated with shorter OS. Functional experiments showed that after inhibiting the expression of ULK1, the proliferation of ESCA cells decreased and apoptosis increased [33]. MAPK8, also known as JNK, is a member of the protein kinase family that participates in processes including cell proliferation, autophagy, and transcriptional regulation. MAPK8 can activate autophagy in lung cancer, bladder cancer, and prostate cancer cells. He et al. showed that activating MAPK8 could induce autophagy and reduce apoptosis of cancer cells [34]. Bao et al. found low expression of MAPK8 in ESCA, and showed that overexpression of MAPK8 could inhibit the proliferation and migration of cancer cells and was related to poor prognosis in ESCA patients [35]. CAPN10 is highly expressed in ESCA. Chan et al. found that knockdown of CAPN10 decreased proliferation of ESCA cells and increased apoptosis, which was significantly related to poor prognosis. However, the autophagy mechanism of CAPN10 in ESCA has not been reported. In addition, ULK1, MAPK8, and CAPN10 have roles involving the spliceosome in cancer or other diseases. In breast cancer, abnormal splicing of ULK1 leads to an increase in autophagy and promotes the growth of breast cancer cells [36]. ULK1 and MAPK8 have a similar role in retinitis pigmentosa [37]. Abnormal splicing of CAPN10 leads to ovarian cancer [38].
ZFAS1 is a new tumor-related lncRNA that is abnormally expressed in multiple tumors [39]. ZFAS1 is highly expressed in colon cancer and can inhibit tumor proliferation and promote cancer cell apoptosis by regulating downstream target genes [40]. ZFAS1 is also a sarcoplasmic reticulum Ca2+-ATPase2a (SERCA2a) inhibitor; it induces mitochondrial-mediated cardiomyocyte apoptosis by inhibiting SERCA2a [41]. The expression of ZFAS1 is upregulated in ESCC, and its silencing can inhibit the proliferation, migration, and invasion of ESCC cells [42]. However, the autophagy mechanism mediated by ZFAS1 in ESCA remains unclear. There have been few reports on RAB11B-AS1; at present, little is known about this lncRNA except that its expression is increased in breast cancer and lung cancer [43, 44]. Overexpression of RAB11B-AS1 has been shown to promote the proliferation and metastasis of breast cancer and lung cancer cells; however, it had the opposite effect on osteosarcoma [45].
In this study, we found that the pathogenesis of patients in the high-risk group may be related to the spliceosome, in contrast to those in the low-risk group. Survival analysis showed that a total of seven lncRNAs were closely related to the prognosis of patients with ESCA. Furthermore, the results of the multivariate Cox analysis showed that the combination of RAB11B-AS1, AC093582.1, ZFAS1, AC012467.2, AC079684.2, AC092687.3, and AC083799.1 could identify high-risk ESCA patients; thus, they represent a novel multi-gene signature for potential clinical use in ESCA. However, the role of these seven lncRNAs in the autophagy mechanism of ESCA has not been determined, and there have been no reports about the role of the spliceosome. Therefore, we will investigate this in future research.