CDCA7 is a member of the cell division cycle associated family of genes, located on chromosome 2q31, encodes a 47 kDa nuclear protein consisting of 371 amino acids [4, 5] and is involved in embryonic development . It was found that CDCA7 was expressed in many human tissues including small intestine, thymus, colon, bone marrow, lymph node, spleen, and peripheral leukocytes . And previous researches have reported its close correlation to malignant tumors. It was reported that CDCA7 was markedly upregulated in triple-negative breast cancer (TNBC), the most aggressive subtype of breast cancer, and relevant to tumor proliferation and metastatic relapse status, and predicted poor prognosis . Wang etc. discovered that CDCA7 was preferentially elevated in lung adenocarcinoma (LUAD) and overexpression of CDCA7 could enhance cell proliferation in LUAD through G1 phase promotion . And CDCA7 was essential for invasion and migration of lymphoma cells . However, no data up to date was reported about the expression level and potential function of CDCA7 in ccRCC.
In our study, we carried out a systematic analysis on CDCA7 in ccRCC by analyzing the RNA sequence data downloaded from TCGA database. Comparing to the expression level of CDCA7 in normal kidney tissues, we found CDCA7 was elevated in ccRCC tissues. The enrolled ccRCC patients from TCGA was divided into a high- and low-expression group according to the median CDCA7 expression value of all the patients. And we discovered that patients in the low-expression group had longer OS than those in high. Meantime, higher expression of CDCA7 was significantly associated with higher disease grade, stage, T and M period. Then we conducted univariate and multivariate Cox regression analysis on CDCA7 and found that CDCA7 could serve as an independent prognostic factor of ccRCC. Moreover, to help clinicians predict the prognosis of ccRCC patients, we constructed a predictive nomogram based on the CDCA7 expression level and relative clinicopathological parameters.
Gene Set Enrichment Analysis (GSEA) is a computational method utilized to evaluate whether a prior defined set of genes display statistically significant, consistent differences between two biological states . To explore possible signaling pathways and mechanisms CDCA7 could functioned through, we conducted GSEA analysis and discovered signal pathways CDCA7 might be involved in including apoptosis pathway, cell cycle pathway, JAK-STAT pathway, NOD like receptor pathway, P53 pathway, T cell receptor pathway and toll like receptor pathway. Previous researches indicated that down-expression of A100A4 could reduce cell growth of RCC via NF-kB-dependent MMP-2 and bcl-2 Pathway . Fang etc. discovered that simvastatin could lead to the inhibition of cell growth of RCC via AKT/mTOR, ERK and JAK2/STAT3 pathway . It was also reported that Tropomyosin-1, a widely expressed actin-binding protein, could promotes cancer cell apoptosis via the p53-mediated mitochondrial pathway in ccRCC , and the MDM2 inhibitor MI-319 could induce RCC cell apoptosis mainly dependent on p53 overexpression .
Then we constructed the PPI network of CDCA7 to explore potential protein-protein interaction. It showed that ten genes were significantly functional associated with CDCA7, including SLBP, GINS2, HELLS, UHRF1, MCM2, MCM4, MCM5, NASP, TYMS, and CDC6. Researchers have discovered the important roles of these genes in physiological process and tumor progression. For instance, SLBP (Stem-loop-binding protein) is evolutionarily conserved and involved in the processing, translation, and degradation of canonical histones mRNAs including H1, H2A, H2B, H3, and H4 . With regard to GINS2, it was reported that GINS2 could promote cancer cell proliferation, migration and invasion of non-small-cell lung cancer (NSCLC) via facilitating epithelial-to-mesenchymal transition and modulating PI3K/Akt and MEK/ERK signal pathway . Previous reports revealed that mutations in CDCA7 and HELLS respectively cause immunodeficiency, centromeric instability, and facial anomalies (ICF) syndrome types 3 and 4, that encode a CXXC-type zinc finger protein and an SNF2 family chromatin remodeler . And the ZBTB24-CDCA7 axis could facilitate DNA methylation by regulating HELLS enrichment at centromeric satellite repeats . As to the minichromosome maintenance (MCM) proteins family, they were mainly involved in the initiation and elongation of DNA replication  and the formation of the pre-replicative complex (preRC), the replication fork and the initial steps of DNA synthesis . MCM2, MCM4, and MCM5 served as essential components of a hexameric, ring-shaped complex that acted as one of the pre-replication factors and were related to the chromatin and the proteins of the origin recognition complex at the M-G1 transition . The important roles of these genes in the PPI network of CDCA7 all indicated the possible essential functions of CDCA7.
We also discovered the association of CDCA7 with immunity. CDCA7 was in close connection with the immune infiltration including B cell infiltration, CD4+ T cell infiltration, CD8+ T cell infiltration, neutrophil infiltration, macrophage infiltration, and dendritic cell infiltration. Moreover, CDCA7 was significantly correlated to tumor-related immunosuppressive molecules including PDCD1, CD274, CTLA4, BTLA and LAG3. PDCD1 (programmed cell death 1), CTLA-4 (cytotoxic T-lymphocyte-associated antigen 4) and BTLA (B and T lymphocyte attenuator) are members of immunoglobulin-related receptors family associated with various aspects of T cell immune regulation . PDCD1 (PD-1, CD279) and CD274 (PD-L1) axis has been discovered as a worthy therapeutic target for its important role not only in physiological immune homoeostasis, but also in the way through which cancer cells evade the immune system . Overexpression of PD-1 and PD-L1 in tumors is closely correlated with poor disease outcome in some human cancers . The research of PD-1 or PD-L1 inhibitors have greatly promoted the development of the treatment of cancer . As to CTLA4, it is a transmembrane receptor with inhibitory function expressed by T lymphocytes. CTLA4 could inhibit costimulation through competing for CD28 ligands . In addition to CTLA4 and PD1, BTLA is also an immune checkpoint related to suppressing immune responses , containing two immunoreceptor tyrosine-based inhibitory motifs in its cytoplasmic region. BTLA could modulate T cell responses and attenuate B cell function to paly its inhibitory roles in multiple diseases [38, 39]. Lymphocyte Activation Gene-3 (LAG3, CD223) served as another potential cancer immunotherapeutic target. It could inhibit T cells function and mediate a state of exhaustion in combination with PD1 . The association of CDCA7 with these tumor-related immunosuppressive molecules suggested its important potential functions in human immunity.
To conclude, our study elucidated that CDCA7 could act as a favorable prognostic factor for ccRCC. Moreover, apoptosis pathway, cell cycle pathway, JAK-STAT pathway, NOD like receptor pathway, P53 pathway, T cell receptor pathway and toll like receptor pathway might be the primary pathways regulated by CDCA7. Furthermore, CDCA7 could serve as an independent prognostic factor for ccRCC and it was closely related to immunity. And advanced researches were required to verify our findings in vivo and in vitro.