Background
Long non-coding RNAs (lncRNAs) are referred to as the non-protein coding portion of the transcriptome with length of more than 200 nucleotides. They represent, together with small noncoding RNAs (< 200 nucleotides), the biggest part of the transcriptome, since only 1 to 3% of the transcriptome can code for protein synthesis [
1‐
3]. Long noncoding RNAs are involved in several biological processes including cell proliferation, cell differentiation, cell cycle progression, cell apoptosis and metastasis [
4‐
10]. Notably, they were identified as oncogenes or tumor suppressors, prognostic and diagnostic biomarkers and as therapeutic targets [
11‐
13]. For instance, Tang and colleagues reviewed the implication of lncRNAs in colorectal cancer progression and figured out their potential clinical applications as novel diagnostic and prognostic biomarkers and therapeutic targets [
14].
Long intergenic non-coding RNA 00511 (LINC00511) is a 2265-bp lncRNA mapped to chromosome 17q24.3 with five exons. Recent studies found that LINC00511 is overexpressed in various type of cancers including breast cancer, ovarian cancer, liver cancer, pancreatic cancer, lung cancer and glioma. LINC00511 is an oncogene which plays a negative regulatory role in cell proliferation, cell cycle progression, apoptosis, invasion, migration, metastasis and chemoresistance [
15‐
23]. Noteworthily, overexpression of LINC00511 was shown to be a predictor for cancer prognosis [
16,
18,
20,
22,
24‐
28]. However, the results of the studies were not consistent. For instance, the studies of Deng et al. [
27], Zhao et al. [
20] and Wang et al. [
18] showed no correlation between the expression level of LINC00511 and tumor size; in contrast the studies of Sun et al. [
22], Yu et al. [
25] and Zhang et al. [
26] demonstrated an association between LINC00511 expression and tumor size. Similarly, Lu et al. [
16] detected significant correlation between LINC00511 overexpression and lymph node metastasis in breast cancer, whereas the study conducted by Zhang et al. [
26] provided a contradictory result. In view of these contradictory outcomes, we conducted a systematic review and meta-analysis to evaluate the prognostic role of LINC00511 for cancer patients. Next, we validated our results by using The Cancer Genome Atlas (TCGA) and Genotype-Tissue Expression (GTEx) datasets.
Discussion
LINC00511, a newly identified lncRNA, has been reported to be upregulated and to have an oncogenic function in diverse cancers including lung cancer, breast cancer, pancreatic cancer, cervical cancer, liver cancer, ovarian cancer and glioma. Its underlying mechanisms of action include promotion of proliferation, tumorigenesis, cell cycle progression, invasion, migration, metastasis and chemoresistance and inhibition of apoptosis [
16‐
22,
24]. More importantly, upregulated LINC00511 has been associated with prognosis, suggesting that it can represent a biomarker for prognosis in cancer patients. However, there is still discrepancy regarding the relationship between LINC00511 expression and clinical outcomes. In the present study, a first-time, comprehensive meta-analysis on the prognostic value of LINC00511 in diverse human cancers is presented. Collectively, 14 eligible studies were systematically included.
The results obtained from this meta-analysis have shown that upregulated LINC00511 is strongly predictive of poor overall survival of cancer patients. Moreover, the combination of multivariate analysis of four relevant studies showed that LINC00511 may serve as an independent predictor of poor overall survival for cancer patients. The subgroup analysis revealed that elevated LINC00511 expression correlated with poor overall survival independently to the tumor type, sample size, cut-off value and the data extraction method. Nevertheless, some subgroup analysis results should be taken with caution, due to the small number of studies included. Subsequently, these findings were corroborated by the results of TCGA analysis. Additionally, it was found that patients with elevated LINC00511 expression were more prone to worse clinicopathological features including larger tumor size, advanced clinical tumor stage, lymph node metastasis, distant metastasis and disease recurrence. Besides, high LINC00511 expression was found to be associated with poor disease-free survival and progression-free survival.
Taken together, the above findings lead to the suggestion that LINC00511 could serve as a potential biomarker and functional regulator in human cancers. Molecular mechanisms investigations highlighted that LINC00511 exerts its oncogenic function mainly by modulating microRNAs functions [
42‐
44]. For instance, via its competing endogenous RNA activity on hsa-miR-29b-3p, LINC00511 induced the expression of VEGFA leading functionally to pancreatic ductal adenocarcinoma progression [
20]. Similarly, Lu et al. [
16] found that LINC00511 targeted the miR-185-3p/E2F1/Nanog axis in order to promote breast cancer tumorigenesis and stemness. In a recent study, LINC00511 was also found to foster the process of gastric cancer by targeting miR-625-5p/NFIX axis [
43]. These mechanistic studies revealed that LINC00511 could act at transcriptional and post-transcriptional level. Moreover, LINC00511 was found to interact with a variety of signaling pathways including JAK2/STAT3 [
45], Wnt/β-catenin [
46], and PTEN/AKT/FOXO1 [
47], in the pathogenesis of cancers.
LINC00511 has been demonstrated to be a poor predictor for both cancer recurrence and progression. These analogous outcomes imply that there might be similar LINC0511-dependent mechanisms underlying these two events. In particular, LINC00511 has been shown to induce radio-resistance in breast cancer resulting in recurrence and progression by regulating STXBP4 expression via miR-185 [
28]. Similarly, the silencing of LINC00511 in cervical cancer cells enhanced cancer drug paclitaxel’s sensitivity, suppressed cell viability, cell proliferation, migration and invasion, and promoted apoptosis, thereby preventing progression and recurrence [
24]. To achieve those functions, LINC00511 modulated the expression of related proteins, namely Bcl-2, Bax, cleaved caspase-3, metalloproteinases 2 and 9, multidrug resistance protein 1 (MRP1) and P-glycoprotein. The resistance to paclitaxel caused by LINC00511 was also found in breast cancer and is mediated via regulating miR-29c/CDK6 axis [
23]. Du et al. found, in glioblastoma multiforme (GBM), that high LINC00511 expression was correlated with recurrence, and ectopic LINC00511 enhanced GBM cells proliferation, EMT, migration and invasion by sponging miR-524-5p to indirectly regulate YB1/ZEB1 [
39].
A number of limitations should be addressed when considering the findings of the present study. Firstly, all the studies included in the meta-analysis have been conducted in China, narrowing the representativeness of the results. Secondly, there is a rather limited number of studies available on major cancers, such as lung neoplasms and brain neoplasms. Therefore, the results on subgroup analysis based on cancer types should be taken with cautions. Thus, more clinical studies would be necessary to better assess the relationship between LINC00511 expression and cancer patients’ clinical outcomes.
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