RMI2 plays crucial roles in growth and metastasis of lung cancer

Lung cancer is the most commonly diagnosed cancer and the leading cause of cancer death in the world, but its therapeutic targets are still being explored.Genome instability as a key hallmark of cancer not only contributes to cancer initiation and progression, 1 but also creates vulnerabilities that are relatively specific to cancer cells, which may be potential therapeutic targets for cancer patients.During DNA Double-Strand Breaks (DSBs) repair, BTR (BLM-Topo IIIα-RMI1/RMI2) complex promotes the dissolution of double Holliday junctions to form non-crossover products and is often considered as a tumor suppressor. 2 However, the function of each individual component of this BTR complex in cancer remains largely unknown.Using the GEPIA tool based on TCGA and GTEx databases, we found that the mRNA levels of BLM, RMI1, and RMI2 were simultaneously increased in multiple cancer types, while TOP3A was not altered in the tested cancer types.Notably, RMI2, but neither BLM nor RMI1, was up-regulated in Adrenocortical carcinoma (ACC), Kidney Chromophobe (KICH), Liver hepatocellular carcinoma (LIHC), Lung adenocarcinoma (LUAD) and Thyroid carcinoma (THCA) (Supplementary Fig. S1a).Furthermore, the mRNA levels of RMI2 were up-regulated in other cancer types (21 out of 33 cancer types), including breast invasive carcinoma (BRCA), ovarian serous cystadenocarcinoma (OV), pancreatic adenocarcinoma (PAAD), uterine Corpus Endometrial Carcinoma (UCEC) and so on.Kaplan-Meier plotter revealed that high mRNA levels of RMI2 were correlated with poor prognoses in BRCA, LIHC, LUAD, OV, PAAD, UCEC (Supplementary Fig. S1b,c).Moreover, using a LUAD tumor tissue microarray, RMI2 was also higher by immunohistochemistry (IHC) in lung tumor tissues compared to normal lung tissues, and high RMI2 protein levels were significantly associated with poor outcomes in LUAD patients (Fig. 1a,b).To investigate the functions of RMI2 in lung cancer, A549 and NCI-H1975 cells were utilized to generate stable cells with knockdown of RMI2, as RMI2 was higher in lung cancer cell lines compared to BEAS-2B, a lung normal bronchial epithelial cell line (Supplementary Fig. S2a,b).Cell viability and colony formation, as well as tumor growth in the xenograft mouse model, were decreased by knocking down RMI2 in both A549 and NCI-H1975 cells (Fig. 1c and Supplementary Fig. S2c-e).Such a function of RMI2 on tumor growth depends on BTR complex, as the inhibition on colony formation by knocking down endogenous RMI2 in these cells was completely rescued by re-introducing wild type RMI2, but not its mutants of RMI2-K24A and RMI2-W135A, which are well-known to abolish the interaction of RMI2 with RMI1, TOP3A and/or BLM 3 (Fig. 1d).Consistently, γH2AX, a marker for DSBs, and apoptosis were substantially increased by knocking down RMI2 (Fig. 1e, f and Supplementary Fig. S2f,g).These results illustrate that RMI2 is