Long noncoding RNAs as putative biomarkers for prostate cancer detection

Abstract

Prostate cancer is one of the leading causes of mortality among US males. There is an urgent unmet need to develop sensitive and specific biomarkers for the early detection of prostate cancer to reduce overtreatment and accompanying morbidity. We identified a group of differentially expressed long noncoding RNAs in prostate cancer cell lines and patient samples and further characterized six long noncoding RNAs (AK024556, XLOC_007697, LOC100287482, XLOC_005327, XLOC_008559, and XLOC_009911) in prostatic adenocarcinoma tissue samples (Gleason score >6.0) and compared them with matched normal (healthy) tissues. Interestingly, these markers were also successfully detected in patient urine samples and were found to be up-regulated when compared with normal (healthy) urine. AK024556 (SPRY4-IT1) was highly up-regulated in human prostate cancer cell line PC3 but not in LNCaP, and siRNA knockdown of SPRY4-IT1 in PC3 cells inhibited cell proliferation and invasion and increased cell apoptosis. Chromogenic in situ hybridization assay was developed to detect long noncoding RNAs in primary prostatic adenocarcinoma tissue samples, paving the way for clinical diagnostics. We believe that these results will set the stage for more extensive studies to develop novel long noncoding RNA-based diagnostic assays for early prostate cancer detection and will help to distinguish benign prostate cancer from precancerous lesions.

Figure 1

Screening of prostate cancer–related long noncoding RNA (lncRNA) expression using microarrays. Alterations in lncRNA expression profiles between prostatic epithelial cells and PC3 cells (NCode human noncoding RNA microarray; Life Technologies) (A) and prostatic epithelial cells, LNCaP, and PC3 cells (SurePrint G3 human lncRNA microarray; Agilent Technologies) (B). Hierarchical clustering reveals distinguishable lncRNA expression profiles. Red indicates high relative expression and green indicates low relative expression. Numbers represent replicates.

Figure 2

Expression of the long noncoding RNAs (lncRNAs) XLOC_007697 (A), LOC100287482 (B), and SPRY4-IT1 (C) as measured by qPCR. The relative expression levels in five prostate cancer cell lines (PPC1, 22Rv1, DU-145, LNCaP, and PC3) and additional two prostatic epithelial cells (Prostate Epi 2 and Prostate Epi 3) are compared with the expression in prostatic epithelial cells (Prostate Epi 1). The Ct value of each lncRNA was normalized to the Ct value of GAPDH, and the relative expression was calculated by comparing with prostatic epithelial cells by calculating the ΔΔCt method. Data are expressed as means ± SD from three biological replicates for each cell line (A–C).

Figure 3

Expression of SPRY4-IT1 by RNA–fluorescence in situ hybridization staining of prostatic epithelial LNCaP and PC3 cells. SPRY4-IT1 staining is in green (fluorescein isothiocyanate) and nuclei are stained in blue (DAPI).

Figure 4

Differential expression of the long noncoding RNAs (lncRNAs) in human prostatic adenocarcinoma. A: Heat map shows differential lncRNA expression between pooled prostate tumor samples and pooled adjacent normal tissues. Each column represents the mean normalized signal intensity values of two technical replicates from pooled normal and pooled tumor samples. B: Five lncRNAs (XLOC_009911, XLOC_008559, XLOC_005327, XLOC_007697, and LOC100287482) were selected on the basis of the microarray results. The expression levels were measured in prostate tumor samples (T) and matched normal tissues (N) by qPCR. ΔCt was calculated by subtracting the Ct value of GAPDH from the Ct value of lncRNA. Graph shows the ΔCt values of lncRNA. The lines inside the boxes denote the medians. ^∗P ≤ 0.05, Student's t-test.

Figure 5

Detection of long noncoding RNAs (lncRNAs) up-regulated in urine samples in prostate cancer. Expression of six lncRNAs (SPRY4-IT1, XLOC_007697, LOC100287482, XLOC_009911, XLOC_008559, and XLOC_005327) was measured by qPCR in 14 normal and 13 prostate cancer patients. ΔCt was calculated by subtracting the Ct value of GAPDH from the Ct value of lncRNA. The lines inside the boxes denote the medians. The expression of all six lncRNAs was significantly higher in prostate cancer patients. ^∗P ≤ 0.05, ^∗∗P ≤ 0.01, Student's t-test. N, normal patient; T, prostate cancer patient.

Figure 6

Differential expression of AK024556 (SPRY4-IT1) in human prostatic adenocarcinoma. A: The expression level of SPRY4-IT1 was measured by qPCR in 18 paired prostate tumor and normal samples. ΔCt was calculated by subtracting the Ct value of GAPDH from the Ct value of long noncoding RNA. B: The expression level of SPRY4-IT1 in patient samples measured by droplet digital PCR (ddPCR). The lines inside the boxes denote the medians. ^∗P ≤ 0.05, ^∗∗∗P ≤ 0.001, Student's t-test.

Figure 7

RNA–chromogenic in situ hybridization (CISH) analysis of SPRY4-IT1. A: RNA-CISH staining of SPRY4-IT1 in tumor samples and matched normal tissues [formalin-fixed, paraffin-embedded (FFPE) samples]. Expression was visualized using alkaline phosphatase-labeled probes. B: qPCR of SPRY-IT1 expression in tumor and matched tissue samples (FFPE samples in A). C: RNA-CISH staining of SPRY4-IT1 expression in human prostate cancer tissue array. Tissue samples include normal prostate, adjacent normal, and prostate cancer samples indicated by Gleason scores: 6 (3 + 3), 7 (3 + 4 and 4 + 3), 8 (4 + 4), 9 (5 + 4 and 4 + 5), and 10 (5 + 5). Expression is visualized using alkaline phosphatase-labeled probes. Scale bar = 100 μm (A). N, normal patient; T, prostate cancer patient.

Figure 8

SPRY4-IT1 knockdown effect on PC3 cells. PC3 cells were treated with siRNA duplexes to SPRY4-IT1 or with a scramble control siRNA (Scr siRNA) at either 100 or 200 nmol/L. The amount of SPRY4-IT1 transcript was analyzed by quantitative real-time PCR at 48 hours after transfection. A: Relative RNA expression was determined using GAPDH control to untransfected cells. B: Loss of SPRY4-IT1 affects PC3 cell viability by MTT assay. C: A significant decrease in the viability of PC3 cells was observed after 48 hours of SPRY4-IT1 siRNA transfection. Knockdown of SPRY4-IT1 resulted in suppressing PC3 cells invasion. PC3 cell invasion after 48 hours transfection with siRNA. D: Staining of PC3 cells (crystal violet) after 48 hours transfection with SPRY4-IT1 siRNA to show the decrease of cell invasion. E: Apoptosis measured by caspase 3/7 activity in PC3 cells 48 hours after transfection with SPRY4-IT1 siRNA. Results are expressed as means ± SD of three experiments and are presented as a bar graph after normalizing to the untransfected control. ^∗∗∗P ≤ 0.001 compared with the untransfected control.