As a crucial constituent of the FA pathway, the activation of FANCD2 assumes the responsibility for rectifying interstrand crosslink (ICL) damage prompted by genotoxic stresses including ionizing radiation and DNA cross-linking agents, resolving DNA replication fork stalling, and upholding genomic stability[26]. While previous investigations have delineated the carcinogenic impact of FANCD2 in diverse solid malignancies, limited knowledge exists regarding its expression and functionality in pan-cancer. Our preceding research has unveiled that impeding the monoubiquitination process and the formation of nuclear foci of FANCD2 could heighten the susceptibility of non-small cell lung cancer (NSCLC) to cisplatin-induced DNA damage and apoptosis[27]. Building upon the anticipated role of FANCD2 in human malignancy, we have executed a comprehensive pan-cancer analysis aimed at characterizing the expression profile of FANCD2 across diverse cancer types, while delving further into its prognostic potential, genetic alterations, association with the cancer immune microenvironment, and regulatory network. This endeavor seeks to foster an enhanced comprehension of the latent attributes of FANCD2 in human cancers.
Based on our investigation utilizing the TCGA datasets, it was observed that the levels of FANCD2 expression in tumor tissues were notably elevated in comparison to their corresponding normal tissues. This trend was observed in various types of cancers, including BLCA, BRCA, CESC, CHOL, COAD, ESCA, GBM, HNSC, KICH, KIRC, KIRP, LIHC, LUAD, LUSC, PCPG, PRAD, READ, SARC, STAD, THCA, and UCEC. Previous research has suggested that the amplification of FANCD2 in esophageal squamous cell carcinoma leads to the emergence of a malignant nature, thereby promoting the progression of the tumor[28]. The heightened FANCD2 expression has been correlated with an enlarged tumor size, a highly aggressive tumor phenotype, and an unfavorable prognosis in cases of hepatocellular carcinoma[15]. Additionally, FANCD2 acts as an autonomous prognostic indicator for LUAD, exhibiting considerably elevated levels of expression in tumor tissues compared to their normal counterparts[29].The results obtained from CPTAC and HPA database further substantiate our findings. Additionally, we observed a significant increase in FANCD2 expression with the progression of the disease in the majority of analyzed cancers. These discoveries indicate the potential of utilizing FANCD2 as a diagnostic marker for specific types of tumors.
In our study, Cox regression analysis and Kaplan-Meier analysis demonstrated that high FANCD2 expression was associated with a poor prognosis in a variety of tumors, which was consistent with the previous studies. Research has demonstrated that FANCD2 possesses enhanced prognostic predicting efficacy in select malignancies. For instance, FANCD2 can serve as a biomarker for prognosticating the likelihood of recurrence and survival in patients with nonmuscle invasive bladder cancer[30]. Elevated FANCD2 expression acts as an independently unfavorable prognostic factor, exhibiting a positive correlation with tumor size and stage in spontaneous breast cancer[31]. These findings suggest that FANCD2 may serve as a novel prognostic indicator in clinical applications.
The tumor microenvironment (TME) encompasses immune cells, tumor cells, and stromal microenvironment[32].Among these components, tumor immune-infiltrating cells, constituting a significant portion of the TME, exhibit a close association with tumor progression, immune checkpoint inhibition, and immunotherapy[33–35]. In this study, we have examined the correlation between the expression of FANCD2 and the infiltration of immune-related cells, revealing a close relationship between the level of immune cell infiltration and FANCD2 expression across various cancer types. The maintenance of genomic stability is vital for cell survival and replication, as genomic instability may instigate cancer development, which escalates with the accumulation of DNA damage[36]. Notably, the DDR pathway, linked to tumor cells, greatly impacts immune surveillance, immune response, and immunogenicity[37]. The TME experiences perturbations due to augmented DNA damage and impaired repair[38]. Consequently, the DNA damage repair function of FANCD2 may contribute to safeguarding genomic stability by influencing immune-infiltrating cells.
TMB has the potential to serve as a comprehensive biomarker across various cancers, aiding in the guidance of immunotherapy interventions[39]. Additionally, MSI can be utilized as a prognostic indicator for diverse malignancies, as well as a predictive factor for chemotherapy response and resistance in a wide array of tumor types[19, 40]. It has been observed that tumors exhibiting elevated TMB and MSI display enhanced sensitivity to immunotherapy[41, 42]. Our investigation has revealed a significant positive correlation between FANCD2 expression and TMB in 12 tumors, as well as between FANCD2 expression and MSI in 8 tumors. Furthermore, the expression of FANCD2 showed significant correlations with various key immune checkpoint markers, such as CTLA4, HAVCR2, LAG3, PDCD1, PDCD1LG2, SIGLEC15, TIGIT, and CD274. These immune checkpoints operate as crucial mechanisms employed by tumors to evade immune responses[43]. Consequently, blockade of immune checkpoints hinders tumor immune evasion[44]. Immune checkpoint inhibitors (ICI) have emerged as remarkably effective in current cancer immunotherapy. By amalgamating these findings, we posit that FANCD2 could serve as a novel and efficacious target for anti-cancer immunotherapy, complementing the use of chemotherapeutic agents.
GO and KEGG enrichment analysis revealed that FANCD2-related genes are involved in numerous potential pathways, particularly in cell cycle and DDR pathways. The DDR process plays a significant role in cancer susceptibility, progression, and response to treatment[45]. The FA pathway, which is activated in response to DNA damage, can maintain genomic stability during the DDR to prevent cancer[46]. Additionally, the FA pathway plays a critical role in cell division and helps protect chromosomes during mitosis[47]. In the G2/M phase of the cell cycle, FANCD2/FANCI protein dimers interconnect with sister chromatids and ensure proper chromosomal separation. This independent function of FANCD2/FANCI is a crucial checkpoint for tumor cells as they disproportionately depend on the G2/M checkpoint to avoid mitotic disasters[48, 49]. These groundbreaking discoveries align with previous research on post-translational modifications of FANCD2, such as phosphorylation and ubiquitination, which also participate intricately in DNA damage repair[50], regulation of the cell cycle[51],apoptosis[52], and chromatin remodeling[53]. Moreover, these modifications are closely associated with cellular growth, differentiation, and the maintenance of normal physiological functions within an organism.
Based on an analysis conducted using the cBioPortal database, it has been observed that alterations in the FANCD2 gene are prevalent across various types of cancer. Among the 32 different cancer types examined, it was found that 11.92% of the BLCA population possessed mutations in the FANCD2 gene, representing the highest occurrence rate among all cancer types. This finding suggests the importance of emphasizing the clinical significance of FANCD2 gene mutations and the potential for targeted therapy in the context of BLCA. Furthermore, a comprehensive assessment was carried out to investigate the relationship between FANCD2 expression levels and disease-specific survival or progression-free intervals in cancer patients. The analysis demonstrated that, in general, FANCD2 could exhibit adverse effects on overall survival, disease-specific survival, or progression-free intervals in some cancer cases. DNA methylation, a prevailing form of epigenetic alteration, governs cellular essence by regulating gene manifestation and genetic equilibrium, whilst deviant DNA methylation has the potential to foster carcinogenesis[54].Through scrutinizing the epigenetic blueprint of FANCD2 in 33 malignancies, we have unearthed that abnormal levels of DNA methylation could potentially precipitate atypical expression of FANCD2 within tumors. This peculiar phenomenon may be attributed to two primary factors. Firstly, the overmethylation of promoter regions may instigate the suppression of tumor suppressor genes, thereby modulating diverse regulatory proteins and enzymes. Secondly, in the nascent stages of cancer progression, hypomethylation might facilitate genomic instability and cellular metamorphosis[55].
While we have examined data from various databases, it is important to acknowledge certain limitations in this study. Firstly, although bioinformatic analyses have offered valuable insights into the role of FANCD2 in pan-cancer, it is necessary to conduct further experiments to validate these findings. Secondly, even though our study has demonstrated a correlation between FANCD2 expression and immune activity as well as clinical survival in pan-cancer, we cannot definitively confirm whether FANCD2 directly impacts clinical survival through an immune pathway.
In conclusion, our comprehensive analysis of pan-cancer data has shed light on the potential involvement of FANCD2 in a wide range of cancer types. Based on our findings, we propose that FANCD2 holds promise as a novel diagnostic biomarker and therapeutic target for cancers such as lung, breast, liver, and colon cancer, among others. Moreover, our research advances the understanding of the role of FANCD2 in cancer immunotherapy, as we have observed significant associations between FANCD2, immune cells, and immune checkpoints. Moving forward, conducting further experiments and prospective studies on FANCD2 in diverse cancer types can provide valuable insights into its regulatory mechanisms and contribute to the development of targeted therapeutic strategies.