Heterogeneous expression and role of receptor tyrosine kinase-like orphan receptor 2 (ROR2) in small cell lung cancer

The present study investigated the expression and role of ROR2 in small cell lung cancer (SCLC). To examine the expression of ROR2, 27 surgically resected SCLC tissue samples were immunostained for ROR2. Sixteen tissue samples were positive and some showed intratumor heterogeneity in staining intensity. The heterogeneity of ROR2 expression was also observed in tumor tissues from a PDX model of SCLC, in which there were cells with high ROR2 expression (ROR2^high cells) and without its expression (ROR2^low cells). These cells were subjected to a RNA sequence analysis. GSEA was performed and the results obtained revealed the enrichment of molecules such as G2M checkpoint, mitotic spindle, and E2F targets in ROR2^high cells. The rate of EdU incorporation was significantly higher in ROR2^high cells than ROR2^low cells from the PDX model and the SCLC cell lines. Cell proliferation was suppressed in ROR2 KO SBC3 cells in vitro and in vivo. Comparisons of down-regulated differentially expressed genes in ROR2 KO SBC3 cells with up-regulated DEG in ROR2^high cells from the PDX model revealed 135 common genes. After a Metascape analysis of these genes, we focused on Aurora kinases. In SCLC cell lines, the knockdown of ROR2 suppressed Aurora kinases. Therefore, ROR2 appears to regulate the cell cycle through Aurora kinases. The present results reveal a role for ROR2 in SCLC and afford a candidate system (ROR2-Aurora kinase) accompanying tumor heterogeneity in SCLC.