NCALD affects drug resistance and prognosis by acting as a ceRNA of CX3CL1 in ovarian cancer

Drug resistance, an impenetrable barrier in the treatment of ovarian cancer (OC), is often associated with poor outcomes. Hence, it is urgent to discover new factors controlling drug resistance and survival. The association between neurocalcin delta (NCALD) and cancer drug resistance is poorly understood. Here, we reveal that NCALD messenger RNA expression, probably regulated by DNA methylation and microRNAs, was significantly downregulated in at least three independent microarrays covering 633 ovarian carcinomas and 16 normal controls, which includes the Cancer Genome Atlas (TCGA) ovarian cohort. In the sub-groups of the TCGA cohort, NCALD was suppressed in 90 platinum-resistant tissues vs in 197 sensitive tissues. It is consistent with the quantitative reverse transcription polymerase chain reaction results revealing gene downregulation in carboplatin-resistant SKOV3 and HeyA8 OC cells as compared with that in controls. Low expression of NCALD predicted poor overall survival (OS) in sub-groups of 1656 patients, progression-free survival (PFS) in 1435 patients, and post-progression survival (PPS) in 782 patients according to Kaplan-Meier plotter covering 1815 OC patients. Comprehensive bioinformatic analyses strongly implicated NCALD in the regulation of drug resistance, probably via competing for endogenous RNA (ceRNA) interactions with CX3CL1 and tumor immune-microenvironment. NCALD acted as a ceRNA for CX3CL1 in 21 different cancers includes OC according to Starbase. These two genes negatively correlated with tumor purity and positively correlated with infiltration levels of neutrophils and dendritic cells in OC. The combined low expression of NCALD and CX3CL1 showed better prognosis potential for OS, PFS, and PPS in the 1815 OC patients than any of the individually tested genes. In summary, NCALD acts as a ceRNA for CX3CL1, and its downregulation may affect drug resistance and prognosis in OC. Thus, NCALD could be a new therapeutic target for anticancer therapy and a new biomarker for survival prediction in OC.