Genes associated with bowel metastases in ovarian cancer

Abstract

Objective: This study is designed to identify genes and pathways that could promote metastasis to the bowel in high-grade serous ovarian cancer (OC) and evaluate their associations with clinical outcomes.

Methods: We performed RNA sequencing of OC primary tumors (PTs) and their corresponding bowel metastases (n = 21 discovery set; n = 18 replication set). Differentially expressed genes (DEGs) were those expressed at least 2-fold higher in bowel metastases (BMets) than PTs in at least 30% of patients (P < .05) with no increased expression in paired benign bowel tissue and were validated with quantitative reverse transcription PCR. Using an independent OC cohort (n = 333), associations between DEGs in PTs and surgical and clinical outcomes were performed. Immunohistochemistry and mouse xenograft studies were performed to confirm the role of LRRC15 in promoting metastasis.

Results: Among 27 DEGs in the discovery set, 21 were confirmed in the replication set: SFRP2, Col11A1, LRRC15, ADAM12, ADAMTS12, MFAP5, LUM, PLPP4, FAP, POSTN, GRP, MMP11, MMP13, C1QTNF3, EPYC, DIO2, KCNA1, NETO1, NTM, MYH13, and PVALB. Higher expression of more than half of the genes in the PT was associated with an increased requirement for bowel resection at primary surgery and an inability to achieve complete cytoreduction. Increased expression of LRRC15 in BMets was confirmed by immunohistochemistry and knockdown of LRRC15 significantly inhibited tumor progression in mice.

Conclusions: We identified 21 genes that are overexpressed in bowel metastases among patients with OC. Our findings will help select potential molecular targets for the prevention and treatment of malignant bowel obstruction in OC.

Keywords: Bowel metastasis; Differentially expressed genes; Extracellular matrix; Malignant bowel obstruction; Ovarian cancer.

Fig. 1.

Summary of patient populations used and the gene selection and validation process. A, Population cohorts of the study. In the discovery set, we identified 27 genes upregulated in BMets compared with PTs using whole-transcriptome RNAseq. Only genes that were not significantly upregulated in normal bowel compared with PT were included (normal bowel set). Expression of 22 of the 27 upregulated genes was verified in the technical validation set using a different approach (qRT-PCR). qRT-PCR was used to validate the genes in an independent set of 18 matched PTs-BMets (replication set); 21 of the 22 tested genes were validated. To investigate the importance of these upregulated genes, we evaluated both their gene expression in 333 PTs and the association between gene expression and surgical outcomes. B, Overall scheme for identifying and validating BMet-upregulated genes. C, Standardized RNAseq expression heat map of 27 genes selected for PCR validation.

Fig. 2.

Correlation between gene expression and need for bowel resection in the “primary tumor” ovarian cancer population. A, Scatterplot of t-statistics evaluating expression differences for patients with vs without bowel resection against patients with vs without RD0 debulking status. Genes with significantly different expression (P < .05) in both comparisons are red. B and C, Box plots showing differences in expression of FAP (B) and POSTN (C) between patients with and without bowel resection and RD0 debulking status (all t-test P < .001).

Fig. 3.

Expression analysis of BMet-associated proteins by Western blot and IHC analysis of LRRC15. A, Western blot of matched PTs and BMets with indicated antibodies. B, Densitometric analysis of the intensity of LRRC15 expression in PTs and BMets normalized to expression of control PCNA was used to determine higher (blue) or lower (red) level of expression in BMets compared with matched PTs. Lack of expression in both PTs and BMets is indicated in green. C, Expression level changes (BMet/PT) of specific proteins. D, Representative IHC analysis of LRRC15 expression in matched ovarian PTs and BMets showing low to moderate (0–1) and high [2,3] levels of LRRC15 staining. Small sections of tumors with 4 representative LRRC15 expression levels are shown. Scale bars represent approximately 100 μm. E, IHC scores in PTs and their paired BMets.

Fig. 4.

Inhibition of tumorigenesis and metastatic spread in LRRC15-knockdown xenografts. A, Western blot analysis showing downregulation of LRRC15 in sh-LRRC15-transfected compared with sh-NTC-transfected OVCAR5 cells. B and C, Representative photographs of nude mice with tumors that formed 27 days after intraperitoneal injection of OVCAR5 cells transduced with nontargeted sh-NTC (B) or sh-LRRC15 (day 39) (C). Arrows indicate large tumor nodules. D and E, Quantification of wet tumor weight (D) and ascites volumes (E) of sh-NTC and sh-LRRC15 xenografts. Data are presented as mean ± SEM. *P < .05.