3.1 Screening of 3′-tRFArg in GC
Through high-throughput sequencing of GC tissues and their matched paracancerous tissues, tsRNAs differentially expressed in GC were identified. Based on the sequencing results, we screened three low-expressed tsRNAs and validated them in the serum of 24 GC patients by qRT-PCR and found that only 3′-tRFArg exhibited significant differences (Fig. 1a). Subsequently, we collected 20 pairs of GC tissues and their adjacent paracancerous tissues. Consistently, the expression level of 3′-tRFArg was significantly lower in GC tissues compared to matched paracancerous tissues (Fig. 1b). Furthermore, correlation analysis of GC tissues and corresponding patient serum samples revealed that patients with lower serum levels of 3′-tRFArg also exhibited lower expression in paired GC tissues (Fig. 1c). Therefore, we selected 3′-tRFArg for an in-depth study.
Fig. 1 Expression of tsRNAs in GC and screening of 3′-tRFArg. a Relative expression of three low-expressed tsRNAs in the serum of 24 GC patients; b Expression levels of 3′-tRFArg in 20 pairs of GC tissues and their adjacent non-cancerous tissues; c Pearson correlation analysis of the expression levels of 3′-tRFArg in 20 pairs of GC tissues and corresponding patient serum samples. *P < 0.05, **P < 0.01, ***P < 0.001, ****P < 0.0001
3.2 3′-tRFArg is a sort of tRFs
As shown in the human genome build (GRCh37/hg19) in the UCSC Genome Browser database (http://genome-asia.ucsc.edu/biomarker.html), 3′-tRFArg is located on chromosome 7, with coordinates ranging from 139,025,486 to 139,025,518 (Fig. 2a). Based on the basic information in MINTbase v2.0 (http://cm.jefferson.edu/MINTbase/), 3′-tRFArg is identified as a 33bp 3'-tRF fragment (CAGGGATTGTGGGTTCGAGTCCCATCTGGGGTGCCA) (Fig. 2b), with the cleavage site located on the anticodon stem of tRNA-Arg-CCT-4-1 (http://gtrnadb.ucsc.edu/genomes/eukaryota/Hsapi19/genes/tRNA-Arg-CCT-4-1.html) (Fig. 2c). Accordingly, we named it 3′-tRFArg (Lyons et al. 2016). Upon agarose gel electrophoresis, we observed a clear, single band of approximately 75 bp, which confirmed the integrity and accuracy of the qRT-PCR product (Fig. 2d). Meanwhile, Sanger sequencing of the product was consistent with the designed sequence (Fig. 2e).
Fig. 2 3′-tRFArg is a sort of tRFs. a UCSC Genome Browser database showed that 3′-tRFArg is located on chromosome 7, with coordinates of 139,025,486-139,025,518; b According to MINTbase v2.0, 3′-tRFArg is a 3'-tRF (5'-CAGGGATTGTGGGTTCGAGTCCCATCTGGGGTGCCA-3'); c The cleavage site of 3′-tRFArg is located on the Anticodon stem of tRNA-Arg-CCT-4-1; d Agarose gel electrophoresis showed that the RT-qPCR product of 3′-tRFArg has a single band of approximately 75bp; e Sanger sequencing of the qRT-PCR product confirmed its consistency with the designed sequence
3.3 Methodological evaluation of 3′-tRFArg
We analyzed the molecular properties of 3′-tRFArg in order to determine whether the method for estimating the expression level is suitable for clinical use. Firstly, the stability of 3′-tRFArg was tested using mixed serum samples, showing good performance with a coefficient of variation (CV) of 1.85 in the intra-assay and 2.47 in the inter-assay (Table 1). Subsequently, the mixed serum samples were left at room temperature for 0, 6, 12, 18, and 24 hours with repeated freeze-thaw cycles (0, 1, 3, 5, and 10 times). Despite the change in external conditions, there was no significant difference between the expression levels of 3′-tRFArg (P > 0.05), which demonstrated its stability and good resistance to interference (Fig. 3a, b). Gradient dilution experiments showed that 3′-tRFArg exhibited good linearity, ensuring the reproducibility of the measurements (Fig. 3c, d). The qRT-PCR results revealed smooth amplification curves and single-peak melting curves for 3′-tRFArg (Fig. 3e, f).
Fig. 3 Methodological evaluation of 3′-tRFArg. a, b Room temperature placement and repeated freeze-thaw experiments showed no significant change in the expression level of 3′-tRFArg; c, d Gradient dilution assays demonstrated good linearity; e, f 3′-tRFArg exhibited smooth amplification curves and single-peak melting curves, with the red line representing 3′-tRFArg and the blue line representing RNU6B
Table 1 The intra-assay CV and the inter-assay CV of 3′-tRFArg
|
3′-tRFArg
|
U6
|
Intra assay CV, %
|
1.85
|
2.08
|
Inter assay CV, %
|
2.47
|
2.82
|
Abbreviations: CV, coefficient of variation
3.4 Clinical role and prognostic value of the serum 3′-tRFArg expression
A serum sample analysis of 129 GC patients, 52 gastritis patients, and 120 healthy donors explored the utility of 3′-tRFArg as a GC biomarker in clinical practice. The results showed that the expression level of 3′-tRFArg in the serum of GC patients was considerably lower than that in healthy donors and gastritis patients (P < 0.05), while there was no significant difference in expression level between gastritis patients and healthy donors (Fig. 4a). To further explore the correlation between the expression level of 3′-tRFArg and clinicopathological features, the 129 GC patients were split into two groups based on the median expression level: a relatively high expression group (expression level >0.494479171, n=64) and a relatively low expression group (expression level ≤0.494479171, n=65). The analysis of the correlation of serum 3′-tRFArg expression and clinicopathological parameters was conducted using Chi-square tests (Table 2). The results showed that the expression level of 3′-tRFArg was significantly associated with tumor differentiation, T stage, lymph node metastasis, TNM stage, and neural/vascular invasion (Fig. 4b-e), with no significant differences observed in terms of gender, age, tumor size, Lauren classification, C-erbB-2, and MMR. Different TNM stages significantly differed in 3′-tRFArg expression levels in the serum of GC patients: patients with stage I-IV GC showed significantly lower expression levels than healthy donors, with the lowest expression levels observed in stage III-IV patients, followed by stage I-II patients (Fig. 4f). As shown in Fig. 4d, patients with neural/vascular invasion have a lower serum concentration of 3′-tRFArg than those without invasion, suggesting that 3′-tRFArg could facilitate the diagnosis of malignant progression. By following 40 GC patients after surgery, we investigated the correlation between serum expression levels and prognosis. Our findings indicated that serum expression levels had increased notably after surgery, approaching normal levels (Fig. 4g). According to a Kaplan-Meier analysis, patients with low expression showed a significantly worse prognosis than those with high expression (P < 0.05) (Fig. 4h). The findings suggest that 3′-tRFArg may be useful as a diagnostic biomarker for GC, assisting in the clinical dynamic monitoring of tumor progression
Fig. 4 Clinical value and prognostic effect of serum 3′-tRFArg in GC. a Expression levels of 3′-tRFArg in serum samples from GC patients (n=129), gastritis patients (n=52), and healthy donors (n=120); b Expression levels of 3′-tRFArg in serum samples from GC patients with high differentiation (n=59) and low differentiation (n=70); c Expression levels of 3′-tRFArg in serum samples from GC patients at different stages of tumor invasion depth and healthy donors (T1–T2: n=81, T3–T4: n=48, healthy donors: n=120); d Expression levels of 3′-tRFArg in serum samples from GC patients with (n=66) or without (n=63) neural/vascular invasion; e Expression levels of 3′-tRFArg in serum samples from GC patients with (n=98) or without (n=31) lymph node metastasis; f Expression levels of 3′-tRFArg in serum samples from GC patients at stages I–II (n=76), stages III–IV (n=53), and healthy donors (n=120); g Changes in serum 3′-tRFArg expression levels before and after surgery in 40 GC patients; h Kaplan-Meier curve analysis of the relationship between 3′-tRFArg expression levels and survival rates in GC patients. *P<0.05 **P<0.01 ***P<0.001 ****P<0.0001
Table 2 Clinical pathological analysis of 3′-tRFArg
Parameter
|
|
No. of patients
|
3′-tRFArg(low)
|
3′-tRFArg(high)
|
P-value
|
Sex
|
male
|
85
|
43
|
42
|
0.758
|
|
female
|
44
|
21
|
23
|
Age(year)
|
<60
|
33
|
12
|
21
|
0.078
|
|
≥60
|
96
|
52
|
44
|
Tumor size
|
<5
|
91
|
46
|
45
|
0.742
|
|
≥5
|
38
|
18
|
20
|
Differentiation grade
|
Well-moderate
|
59
|
21
|
38
|
0.003
|
|
Poor-undifferentiation
|
70
|
43
|
21
|
T stage
|
T1-T2
|
81
|
31
|
50
|
0.001
|
|
T3-T4
|
48
|
33
|
15
|
Lymph node status
|
Positive
|
98
|
56
|
42
|
0.002
|
|
Negative
|
31
|
8
|
23
|
TNM stage
|
Ⅰ-Ⅱ
|
76
|
25
|
51
|
<0.001
|
|
Ⅲ-Ⅳ
|
53
|
39
|
14
|
Nerve/vascular invasion
|
Positive
|
66
|
42
|
24
|
0.001
|
|
Negative
|
63
|
22
|
41
|
|
Intestinal type
|
60
|
32
|
28
|
|
Lauren classifcation
|
Mixed type
|
45
|
20
|
25
|
0.665
|
|
Difuse type
|
24
|
12
|
12
|
|
C-erbB-2
|
Positive
|
22
|
11
|
11
|
0.968
|
|
Negative
|
107
|
53
|
54
|
|
MMR
|
dMMR
|
119
|
57
|
62
|
0.179
|
|
pMMR
|
10
|
7
|
3
|
|
Abbreviations: MLH1, PMS2, MSH2, and MSH6 were all positive for pMMR (normal expression), and 1 or more negative for dMMR (deletion)
3.5 Evaluation of the diagnostic efficacy of serum 3′-tRFArg for GC
Given the limitations of commonly used GC diagnostic markers such as CEA, CA199, and CA724, we explored the diagnostic value of 3′-tRFArg as a potential biomarker for GC. An analysis of ROC curves was performed to evaluate the expression levels of 3′-tRFArg, CEA, CA199, and CA724 in 129 GC patients and 120 healthy individuals., comprehensively analyzing the diagnostic efficacy of each biomarker. 3′-tRFArg had an AUC of 0.808 (95% confidence interval (CI) 0.752-0.863), which was higher than that of CEA (0.747, 95% CI 0.686–0.808), CA199 (0.683, 95% CI 0.616–0.750), and CA724 (0.759, 95% CI 0.699–0.818) (Fig. 5a). Subsequently, 3′-tRFArg was combined with CEA, CA199, and CA724 for diagnosis and with all three and four biomarkers together. Based on Fig. 4b, combined diagnosis had a higher AUC than any single biomarker. When the four markers were combined, the AUC reached the highest value (0.856) (95% CI:0.808-0.903) (Fig. 5c). A combination and a single diagnostic model were investigated for their ability to differentiate GC patients from healthy donors based on the sensitivity (SEN), overall accuracy (ACCU), positive predictive value (PPV), and negative predictive value (NPV). With a cutoff point of 1.093635 and a Youden index of 0.566, 3′-tRFArg showed higher SEN (79%), ACCU (81%), PPV (83%), and NPV (79%) compared to CEA, CA199, and CA724 (Table 3). These analyses indicate that 3′-tRFArg may be useful as a biomarker for GC, and its diagnostic efficacy can be enhanced in combination with other tumor markers.
The lack of highly sensitive biomarkers in the clinic often leads to GC patients being diagnosed at an advanced stage, missing the opportunity for an early cure. For the evaluation, we collected information from 76 early-stage GC patients (stage I and II) and 120 healthy donors. The ROC curve showed that the AUC of 3′-tRFArg was 0.785 (95% CI 0.718–0.852), superior to that of CEA (0.744, 95% CI 0.675–0.814), CA199 (0.663, 95% CI 0.582–0.745), and CA724 (0.763, 95% CI 0.694–0.832) (Fig. 5d). Moreover, with a cut-off point of 1.093635 and a Youden index of 0.549, 3′-tRFArg had SEN of 72%, ACCU of 79%, PPV of 72%, and NPV of 83%, which were all higher than those of CEA, CA199, and CA724 (Table 4). The combined diagnosis had a higher AUC than any single biomarker in identifying early-stage GC patients from healthy donors (Fig. 5e). When all four biomarkers were combined, the AUC reached the highest value of 0.839 (95% CI 0.782–0.895) (Fig. 5f).
In our analysis of serum 3′-tRFArg levels, we found differences between patients with GC and those with gastritis. In light of the fact that the symptoms of GC are similar to gastritis in the early stages, the ability of serum 3′-tRFArg to distinguish between early-stage GC patients and gastritis patients is of great significance. We performed ROC analysis of the expression levels of serum 3′-tRFArg and conventional biomarkers in 129 patients with GC and 50 patients with gastritis. The AUC of 3′-tRFArg was 0.784 (95% CI 0.713–0.855), higher than that of CEA (0.659, 95% CI 0.576–0.742), CA199 (0.660, 95% CI 0.576–0.743), and CA724 (0.734, 95% CI 0.658–0.810) (Fig. 5g). The AUC increased when 3′-tRFArg was diagnosed in combination with other markers (Fig. 5h). The AUC reached a maximum value of 0.858 when the four biomarkers were combined (Fig. 5i), and the SEN increased to 96% (Table 5). These findings indicate that serum 3′-tRFArg expression levels can differentiate between GC patients and gastritis patients, and its diagnostic value is further enhanced when used in conjunction with other tumor markers.
Fig. 5 Diagnostic value of serum 3′-tRFArg for GC. a-c Diagnostic efficacy of 3′-tRFArg, CEA, CA199, and CA724 in distinguishing GC patients from healthy donors; d-f Diagnostic value of 3′-tRFArg, CEA, CA199, and CA724 in distinguishing early-stage GC patients from healthy donors as determined by ROC analysis; g-i Ability of 3′-tRFArg, CEA, CA199, and CA724 to distinguish between GC patients and gastritis patients as determined by ROC analysis. *P<0.05**P<0.01***P<0.001****P<0.0001
Table 3 Diagnostic performance of 3′-tRFArg, CEA, CA199, and CA724 in distinguishing GC patients from healthy controls
|
SEN
|
SPE
|
ACCU
|
PPV
|
NPV
|
3′-tRFArg
|
0.79(102/129)
|
0.83(99/120)
|
0.81(201/249)
|
0.83(102/123)
|
0.79(99/126)
|
CEA
|
0.52(67/129)
|
0.82(98/120)
|
0.66(165/249)
|
0.75(67/89)
|
0.61(98/160)
|
CA199
|
0.43(56/129)
|
0.88(105/120)
|
0.65(161/249)
|
0.79(56/71)
|
0.59(105/178)
|
CA724
|
0.51(66/129)
|
0.86(103/120)
|
0.68(169/249)
|
0.80(66/83)
|
0.62(103/166)
|
3′-tRFArg+CEA
|
0.90(116/129)
|
0.67(80/120)
|
0.79(196/249)
|
0.74(116/156)
|
0.86(80/93)
|
3′-tRFArg+CA199
|
0.85(110/129)
|
0.72(86/120)
|
0.79(196/249)
|
0.76(110/144)
|
0.82(86/105)
|
3′-tRFArg+CA724
|
0.91(117/129)
|
0.69(83/120)
|
0.80(200/249)
|
0.76(117/154)
|
0.87(83/95)
|
3′-tRFArg+CEA+CA199
|
0.93(120/129)
|
0.59(71/120)
|
0.77(191/249)
|
0.71(120/169)
|
0.89(71/80)
|
3′-tRFArg+CEA+CA724
|
0.95(122/129)
|
0.55(66/120)
|
0.76(188/249)
|
0.69(122/176)
|
0.90(66/73)
|
3′-tRFArg+CA199+CA724
|
0.92(119/129)
|
0.61(73/120)
|
0.77(192/249)
|
0.72(119/166)
|
0.88(73/83)
|
3′-tRFArg+CEA+CA199+CA724
|
0.96(124/129)
|
0.49(59/120)
|
0.73(183/249)
|
0.67(124/185)
|
0.92(59/64)
|
Abbreviations: SEN, sensitivity; SPE, specificity; ACCU, overall accuracy; PPV, positive predictive value; NPV, negative predictive value
Table 4 Diagnostic performance of 3′-tRFArg, CEA, CA199, and CA724 in distinguishing early-stage GC patients from healthy controls
|
SEN
|
SPE
|
ACCU
|
PPV
|
NPV
|
3′-tRFArg
|
0.72(55/76)
|
0.83(99/120)
|
0.79(154/196)
|
0.72(55/76)
|
0.83(99/120)
|
CEA
|
0.50(38/76)
|
0.82(98/120)
|
0.69(136/196)
|
0.63(38/60)
|
0.72(98/136)
|
CA199
|
0.37(28/76)
|
0.88(105/120)
|
0.68 133/196
|
0.65 28/43
|
0.69(105/153)
|
CA724
|
0.46(35/76)
|
0.86(103/120)
|
0.70(138/196)
|
0.67(35/52)
|
0.72(103/144)
|
3′-tRFArg+CEA
|
0.87(66/76)
|
0.67(80/120)
|
0.74(146/196)
|
0.62(66/106)
|
0.89(80/90)
|
3′-tRFArg+CA199
|
0.80(61/76)
|
0.72(86/120)
|
0.75(147/196)
|
0.64(61/95)
|
0.85(86/101)
|
3′-tRFArg+CA724
|
0.86(65/76)
|
0.69(83/120)
|
0.76(148/196)
|
0.64(65/102)
|
0.88(83/94)
|
3′-tRFArg+CEA+CA199
|
0.91(69/76)
|
0.59(71/120)
|
0.71(140/196)
|
0.58(69/118)
|
0.91(71/78)
|
3′-tRFArg+CEA+CA724
|
0.92(70/76)
|
0.55(66/120)
|
0.69(136/196)
|
0.56(70/124)
|
0.92(66/72)
|
3′-tRFArg+CA199+CA724
|
0.88(67/76)
|
0.61(73/120)
|
0.71(140/196)
|
0.59(67/114)
|
0.89(73/82)
|
3′-tRFArg+CEA+CA199+CA724
|
0.95(72/76)
|
0.49(59/120)
|
0.67(131/196)
|
0.54(72/133)
|
0.94(59/63)
|
Abbreviations: SEN, sensitivity; SPE, specificity; ACCU, overall accuracy; PPV, positive predictive value; NPV, negative predictive value
Table 5 Diagnostic performance of 3′-tRFArg, CEA, CA199, and CA724 in distinguishing GC patients from gastritis patients
|
SEN
|
SPE
|
ACCU
|
PPV
|
NPV
|
3′-tRFArg
|
0.80(103/129)
|
0.67(35/52)
|
0.76(138/181)
|
0.86(103/120)
|
0.57(35/61)
|
CEA
|
0.52(67/129)
|
0.79(41/52)
|
0.60(108/181)
|
0.86(67/78)
|
0.40(41/103)
|
CA199
|
0.43(56/129)
|
0.88(46/52)
|
0.56(102/181)
|
0.90(56/62)
|
0.39(46/119)
|
CA724
|
0.51(66/129)
|
0.79(41/52)
|
0.59(107/181)
|
0.86(66/77)
|
0.39(41/104)
|
3′-tRFArg+CEA
|
0.91(117/129)
|
0.54(28/52)
|
0.80(145/181)
|
0.83(117/141)
|
0.70(28/40)
|
3′-tRFArg+CA199
|
0.85(110/129)
|
0.58(30/52)
|
0.77(140/181)
|
0.83(110/132)
|
0.61(30/49)
|
3′-tRFArg+CA724
|
0.91(118/129)
|
0.54(28/52)
|
0.81(146/181)
|
0.83(118/142)
|
0.72(28/39)
|
3′-tRFArg+CEA+CA199
|
0.93(120/129)
|
0.46(24/52)
|
0.80(144/181)
|
0.81(120/148)
|
0.73(24/33)
|
3′-tRFArg+CEA+CA724
|
0.95(123/129)
|
0.42(22/52)
|
0.80(145/181)
|
0.80(123/153)
|
0.79(22/28)
|
3′-tRFArg+CA199+CA724
|
0.92(119/129)
|
0.44(23/52)
|
0.78(142/181)
|
0.80(119/148)
|
0.70(23/33)
|
3′-tRFArg+CEA+CA199+CA724
|
0.96(124/129)
|
0.35(18/52)
|
0.78(142/181)
|
0.78(124/158)
|
0.78(18/23)
|
Abbreviations: SEN, sensitivity; SPE, specificity; ACCU, overall accuracy; PPV, positive predictive value; NPV, negative predictive value
3.6 Prediction of downstream target genes of 3′-tRFArg
The downstream target genes of 3′-tRFArg were predicted. Utilizing bioinformatics databases, we conducted an analysis to anticipate the binding of 3′-tRFArg with its target genes. As illustrated in Fig. 6a, an overlap of 537 potential target genes was observed between the miRanda and TargetScan prediction tools, suggesting a high likelihood of interaction with 3′-tRFArg. An analysis of the connection network identified 80 target genes associated with 3′-tRFArg (Fig. 6b). Subsequent enrichment analysis of Kyoto Encyclopedia of Genes and Genomes (KEGG) signaling pathways highlighted significant enrichment in amino sugar and nucleotide sugar metabolism, the Hippo signaling pathway, and central carbon metabolism in cancer (Fig. 6c). Gene Ontology (GO) functional enrichment analysis of these target genes indicated potential involvement in energy metabolism, transcriptional regulation, and cellular signal transduction (Fig. 6d). Further exploration is essential to elucidate the underlying regulatory mechanisms of 3′-tRFArg in GC.
Fig. 6 Prediction of the downstream regulation mechanism of 3′-tRFArg. a Venn diagram evaluating the overlapping genes predicted by the miRanda and TargetScan databases; b Potential target genes of 3′-tRFArg; c Enrichment analysis of potential target genes in the Kyoto Encyclopedia of Genes and Genomes; d Functional enrichment analysis of potential target genes in Gene Ontology.