MiRNAs are currently well defined as small regulatory molecules whose significant role is in post-transcriptional regulation of their target genes and play different crucial roles in physiological and pathological cellular processes (14). To date, the expression profile and dysregulation of microRNAs has been studied in more than a dozen disease, particularly various types of human cancer (15–17). Since the aberrant expression of serum miRNAs in cancer was for the first time described (18), their role in tumorigenesis has been highly regarded by researchers. Importantly, miRNAs are effective as biomarkers in classifying and tracing the source tissue of unknown primary and poorly differentiated cancers (19, 20). These findings emphasize the diagnostic value of miRNAs in cancers and also suggest their therapeutic role.
To the best of our knowledge, this study is the first report on the assessment of serum miR-22, miR-122, miR-217, and miR-367 in ALL and the use of combine miR-217 and miR-367 as biomarkers in this disease. Specifically, we found that the levels of miR-22, miR-122, and 367 were upregulated in ALL patients compared with controls, and additionally, miR-217 was markedly reduced. The analysis of ROC data revealed that serum miR-217 and miR-367 alone could be effective as a biomarker for early detection of ALL, while miR-22 has approximate discriminatory power that requires further investigation. Moreover, the combination of miR-217 and miR-367 further increased the diagnostic value and could distinguish newly diagnosed ALL patients from healthy controls.
Previous studies have examined the different roles of these miRNAs in various cancers. They have been described as double-faced molecules that can act as both a tumor suppressor and an oncogene. Bar N et al. demonstrated that overexpression of miR-22 can affect the tumor suppressor, i.e., PTEN and its downstream pathways PI3/AKT, thus inhibit AKT proliferative and anti-apoptotic activity (21). Another study by Song et al. reported that miR-22 is a crucial regulator for hematopoiesis maintenance, and it was found to be upregulated in myelodysplastic syndrome and leukemia associated with a poor prognosis. In this study, the TET-2 gene was mentioned as a target of miR-22, which its deletion is involved in hematologic malignancy (22). Given that PTEN activity is lost in many types of cancer, leading to increased cell survival and cell cycle progression (23), as well as the relationship between TET-2 and hematopoietic cell proliferation (24), it seems that miR-22 upregulation may lead to ALL due to its effect on these genes. Conversely, miR-22 was mentioned as a tumor suppressor in a study on acute myeloid leukemia (AML), which affects the MYC pathways (25). Due to the various functions of miRNAs in different tissues, a discrepancy in the results is conceivable. Furthermore, we found that the expression level of miR-22 was not significantly related to the patient's sex and laboratory information but was higher in the adult group, which could be related to the severity of ALL in adults. In a similar study on AML, a relationship between miR-22 and sex, platelet count, and disease subtypes was not reported, whereas a significant relationship was found with white blood cells and cytogenetic (26).
Similar to the results of our study, Manfe et al. mentioned miR-122 as an oncogene that enhances the anti-apoptotic pathway of AKT / P53 and represses chemotherapy-induced cytotoxicity in cutaneous T-cell lymphoma (27). Fornari et al. also evaluated the association between miR-122 and apoptosis and identified cyclin G1 as a target of miR-122 (28). By contrast, Yang et al. demonstrated that expression of miR-122 in AML patients was significantly lower than in the healthy group, and it may function as a tumor suppressor. Moreover, they showed that the induction of miR-122 could inhibit cell proliferation in both HL60 and K562 cell lines of AML compared to the control cell line (29). Consistent with the data of Zhang et al. on gastric cancer, in the present study, no significant relationship was observed between miR-122 expression levels and laboratory or demographic findings of patients (30).
According to the present study results, a marked downregulation of miR-217 was observed that confirmed the tumor suppressor action of miR-217. Moreover, we found a significant difference in the expression level of miR-217 in the post-treatment group compared to before treatment, which may be due to the effects of the treatment process. Our results are consistent with a previous study that demonstrated that the expression of miR-217 is decreased in colorectal cancer with the effect of the MAPK pathway, which regulates tumor growth and increases apoptosis (31). Other studies have identified AKT3 (32), Runx2 (33), E2F3 (34), and KRAS (35) as targets of miR-217. The interaction of miR-217 and these genes appear to be involved in pathogenicity in ALL. By contrast, in the study by Yebenes et al., miR-217 was mentioned as an oncogene that increases specifically in the germinal center of lymph nodes. According to this study, miR-217 reduces the expression of genes that respond to DNA damage and its repair and stabilizes the BCL-6 expression (36). Although the ROC analysis in a present study showed that miR-217 is favorable as a biomarker for diagnosing and following up the patients with ALL, it could be more potent in diagnosing. In line with these results, in a study by Yan et al., the ROC analysis revealed that miR-217 could consider as a promising biomarker with high sensitivity and specificity in AML (37).
In the previous study, miR-367 has been identified as a regulator of embryonic stem cell self-renewality and pluripotency, which induces the trait of being stemness in the cancer cell and contributes to the progression and spread of cancer (38). Consistent with the present study's data, Kaid et al. showed that miR-367 plays an oncogenic role in medulloblastoma cells by affecting OCT4 transcription factor, leading to poor survival and poor prognosis (39). In another similar study, miR-367 was mentioned as an oncogene that targets tumor suppressor KLF4. It could be blocked at both mRNA and protein levels and its subsequent pathways, BAX and caspase-3, leading to suppress apoptosis (40). Most studies indicated that miR-367 acts primarily as an oncogene. However, contrary to the present study's findings, it was shown that the expression of miR-367 was significantly reduced in gastric cancer tissues (41) and oral carcinoma cells (42).
According to the results of ROC analysis and based on the sensitivity, specificity, and Yuden index, we found that among the studied miRNAs, miR-217 and miR-367 have a more desirable ability to diagnose ALL, and a combination of these two miRNAs could reach a higher sensitivity and specificity. The limitations of our study were; limited access to newly diagnosed ALL patients, small sample sizes, and lack of access to patients' follow-up samples after the treatment process, which was due to the patient's death or referral to out-of-reach medical centers.