Detection of novel paraja ring finger 2-fer tyrosine kinase mRNA chimeras is associated with poor postoperative prognosis in non-small cell lung cancer

Abstract

Previously, we reported that the overexpression of fer tyrosine kinase (FER), a non-receptor tyrosine kinase, is correlated with poor postoperative prognosis and cancer-cell survival in non-small cell lung cancer (NSCLC). In the present study, we further analyzed FER-overexpressed NSCLC cases and identified various patterns of chimeric mRNAs, composed of paraja ring finger 2 (PJA2) and FER. We detected no genomic rearrangements between PJA2 and FER and attributed these chimeric mRNAs to alterations at the transcriptome level: i.e., trans-splicing. Several chimeric patterns were detected concurrently in each patient, and the pattern sets varied among patients, although the pattern in which PJA2 exon 1 was fused to FER exon 3 (designated as Pe1-Fe3 mRNA) was detected constantly. Therefore, in a wide screening for PJA2-FER mRNAs in NSCLC, we focused on this chimeric pattern as a representative chimera. In analyses of 167 NSCLC samples, Pe1-Fe3 mRNA was identified in about 10% of the patients, and the presence of chimeric mRNA was significantly correlated with a high expression level of parental FER mRNA. Furthermore, we found that the detection of Pe1-Fe3 mRNA was correlated with poor postoperative survival periods in NSCLC, consistent with a previous finding in which FER overexpression was correlated with poor postoperative prognosis in NSCLC. This report is the first to suggest a correlation between chimeric mRNA and the expression level of parental mRNA. Furthermore, our findings may be clinically beneficial, suggesting that PJA2-FER mRNAs might serve as a novel prognostic biomarker in NSCLC.

Figure 1

Identification of chimeric PJA2‐FER mRNAs. (a) Sequence chromatogram showing exon 1 of PJA2 mRNA fused to exon 3 of FER mRNA. (b) RT‐PCR to detect chimeric PJA2‐FER mRNAs. An image of the RT‐PCR products on an agarose gel and a schema of the corresponding PJA2‐FER mRNAs are shown. The red arrows represent the primers used to detect PJA2‐FER mRNAs. The number indicates the exon number, and the exons from PJA2 and FER are shown in blue and red, respectively. Marker, 1000‐bp DNA ladder. (c) Wide screening for Pe1‐Fe3 mRNA in non‐small cell lung cancer (NSCLC) samples. A representative image of the RT‐PCR products on an agarose gel is shown. The red arrows represent the primers used to detect Pe1‐Fe3 mRNA. The number indicates the exon number, and the exons from PJA2 and FER are shown in blue and red, respectively. Marker, 100‐bp DNA ladder.

Figure 2

Expression levels of PJA2 and FER mRNA. (a) Expression level of PJA2 mRNA and FER mRNA in several normal human tissues. The error bars indicate the standard deviations. (b) Comparison of the expression levels between PJA2 mRNA and FER mRNA in NSCLC cases. Each circle indicates data obtained from each specimen. Data for PJA2 mRNA and FER mRNA are shown in blue and red, respectively. The bars indicate the median values. (c) Comparison of the FER mRNA expression level between Pe1‐Fe3 mRNA‐positive cases and Pe1‐Fe3 mRNA‐negative cases. Each circle indicates data obtained from each specimen. The bars indicate the median values.

Figure 3

Correlation between the detection of PJA2‐FER mRNA and the postoperative prognosis of non‐small cell lung cancer (NSCLC) patients. Kaplan–Meier analyses of the progression‐free and overall survival periods among 167 curatively resected NSCLC patients are shown stratified according to the detection of Pe1‐Fe3 mRNA.