Identification of serum EVs
EV is a small membrane capsule containing proteins and nucleic acids, such as miRNAs [26, 27]. There are a large number of deregulated miRNAs in patients with NSCLC, and serum EV-shuttled miRNAs can be used as tumor biomarkers of NSCLC [28, 29]. In order to study the relationship between miRNAs in serum EVs of NSCLC patients with and prognosis, we first isolated the serum EVs from NSCLC patients and healthy people by ultracentrifugation, and then characterized the isolated EVs by TEM and NTA. The results showed that the isolated EVs had a bilayer membrane structure (Fig. 1A), and the size distribution was about 100 nm in diameter (Fig. 1B). Western blot analysis showed that specific EV marker proteins (CD9 and CD63) were present in the part enriched with EVs, but not in the negative control. On the other hand, calnexin was not present in the part enriched with EVs (Fig. 1C). Briefly, EVs were successfully isolated.
Low expression of miR-126-5p and miR-34c-3p in serum EVs of NSCLC patients
The results of database prediction showed that miR-126-5p and miR-34c-3p were lowly expressed in NSCLC patients (Fig. 2A-D). RT-qPCR showed that miR-126-5p and miR-34c-3p in the obtained serum EVs in NSCLC patients was much lower than that in the normal people (p < 0.01, Fig. 2E). These results unveiled the low expression of miR-126-5p and miR-34c-3p in serum EVs of NSCLC patients.
Low miR-126-5p and miR-34c-3p in serum EVs are associated with poor prognosis
Next, we analyzed the relationship between miR-126-5p/miR-34c-3p and the prognosis of NSCLC patients. According to the pathological characteristics [age, gender, tumor size, clinical stage and lymph node metastasis (LNM)], 85 patients with NSCLC were allocated into two groups. As shown in Fig. 3A-E, the low expression of miR-126-5p and miR-34c-3p in serum EVs was not related to age, gender and tumor size, but related to clinical stage and positive LNM (p < 0.05). The database predicted that NSCLC patients with low miR-126 expression had shorter survival time (Fig. 3F). According to the median expression of miR-126-5p and miR-34c-3p, NSCLC patients were divided into miR-126-5p or miR-34c-3p high expression group and low expression group. By tracking the survival time of these NSCLC patients, we generated the survival curves. Patients with low expression of miR-126-5p or miR-34c-3p in serum EVs had shorter survival time (p < 0.01, Fig. 3G). The diagnostic efficacy of miR-126-5p and miR-34c-3p in serum EVs for NSCLC was analyzed by receiver operating characteristic (ROC) curve. The area under the ROC curve was 0.7916 (sensitivity: 0.7412; specificity: 0.7273) and 0.7807 (sensitivity: 0.7412; specificity: 0.8182), respectively (Fig. 3H). In conclusion, miR-126-5p and miR-34c-3p in serum EVs may be diagnostic markers in NSCLC patients and are related to the prognosis.
CDK6 and LYPLA1 are downstream targets of miR-126-5p and miR-34c-3p
In an attempt to explore the downstream of miR-126-5p and miR-34c-3p, we predicted the common target genes through Targetscan and Starbase databases, and finally got 151 target genes (Fig. 4A). The predicted results showed that CDK6 and LYPLA1 were highly expressed in NSCLC (Fig. 4B-C), which was also verified by the literatures [30, 31]. The binding sites of miR-126-5p/miR-34c-3p with CDK6 and LYPLA1 obtained from Targetscan database (Fig. 4D) and dual-luciferase assay (p < 0.01, Fig. 4E) confirmed the binding relations. RT-qPCR showed that CDK6 and LYPLA1 were highly expressed in NSCLC patients (p < 0.01, Fig. 4F), and negatively correlated with miR-126-5p/miR-34c-3p expression in serum EVs of NSCLC patients (p < 0.01, Fig. 4G). In conclusion, CDK6 and LYPLA1 are common targets of miR-126-5p and miR-34c-3p.
Serum levels of CDK6 and LYPLA1 are associated with poor prognosis in NSCLC patients
Next, the relation between CDK6 and LYPLA1 in serum of NSCLC patients and prognosis was analyzed. As shown in Fig. 5A-E, the high expression of CDK6 and LYPLA1 in serum was only associated with clinical stage and LNM (p < 0.01). The database predicted that patients with high expression of CDK6 and LYPLA1 had shorter survival time (Fig. 5F). According to the median expression of CDK6 and LYPLA1, NSCLC patients were allocated into two groups, and the survival curves of the two groups were generated. Patients with high expression of CDK6 and LYPLA1 in serum had shorter survival time (p < 0.01, Fig. 5G). In addition, ROC curve showed that CDK6 and LYPLA1 had good diagnostic efficacy for NSCLC patients (CDK6: area under the curve: 0.8061, sensitivity: 0.8118, specificity: 0.8788; LYPLA1: area under the curve: 0.7594, sensitivity: 0.6824, specificity: 0.7879) (Fig. 5H). In conclusion, CDK6 and LYPLA1 in serum can be used as diagnostic markers of NSCLC and are associated with poor prognosis.