Although ISLR was discovered as early as 1997, it has not been fully studied in tumors. Some studies have reported that ISLR plays an important role in tumor progression in CAFs, such as colorectal cancer, pancreatic cancer, and malignant pleural stromal tumors[7, 23, 24]. This means that ISLR may play a role in the TME, which is one of the reasons why we conducted this research on the role of ISLR in pan-cancer and tumor immunity.
Based on the combined results of TCGA and GTEx data, we found that the ISLR gene was highly expressed in 11 tumors (GBM, GBMLGG (glioma), LGG, STES (stomach and esophageal carcinoma), STAD, HNSC, WT (high-risk wilms tumor), THCA, PAAD, LAML, CHOL) and is expressed at low levels in 18 cancers (UCEC, CESC, ESCA, KIRP, KIPAN (pan-kidney cohort), COAD, COADREAD, PRAD, KIRC, LUSC, LIHC, SKCM, BLCA, OV, UCS, ALL (acute lymphoblastic leukemia), ACC, KICH). In addition, we found that ISLR expression was correlated with the overall staging of tumors such as BLCA, BRCA, COAD, ESCA, KIRC, KIRP, STAD, and TGCT. The results showed that the expression of ISLR had a greater relationship with the grades of gastrointestinal tumors and urinary system tumors. We then analyzed the relationship between ISLR expression and patient prognosis and found that the high expression of ISLR in STAD, OV, KIRC, KIRP, and BLCA would lead to poor OS. In contrast, the low expression of ISLR in UCEC, HNSC, and CESC caused the OS of the patient to be poor. The prognostic results of ISLR in STAD, UCSC, and CESC were consistent with the results of expression differences. The inconsistency between the remaining tumor prognosis results and the differential expression results may be related to other biological factors, such as epigenetics or limited sample data. The specific reasons for this are still awaiting further study. In addition, we found that ISLR also affects the prognosis of RFS, DFS, DSS, and PFS in pan-cancer. The results indicated that the high expression of ISLR not only caused the poor prognosis of STAD patients with OS, but also caused the poor prognosis of STAD patients with RFS and DSS. Similarly, high expression of ISLR can lead to poor prognosis of OV patients with RFS, poor prognosis of KIRP patients with DSS, and poor prognosis of KIRC patients with DSS and PFS. In addition, the low expression of ISLR not only affects the poor prognosis of UCEC patients with OS, but also leads to poor prognosis in patients with RFS and DFS. Although the high expression of ISLR leads to a better prognosis for OS in patients with HNSC, it leads to a poor prognosis for RFS. This may be due to its small size. Although ISLR expression was not correlated with OS prognosis in ESCA, PAAD, and THCA patients, it affected the prognosis of RFS and DFS in PAAD and THCA patients, and also had a significant correlation with RFS and DSS in ESCA patients. These results indicate that the ISLR is expected to become a potential prognostic marker for a variety of cancers.
The TME plays a key role in regulating tumor progression and regulating immunotherapy[25, 26]. Therapies targeting TME, including immunotherapy, anti-angiogenic drugs, and treatments for cancer-related fibroblasts and extracellular matrix, have great potential in the future[27]. We found that ISLR affected the tumor immunity. We used TCGA data for analysis and found that ISLR expression was directly proportional to the stromal scores of BLCA, CHOL, COAD, READ, GBM, KICH, KIRP, LIHC, LUAD, LUSC, PAAD, PRAD, SKCM, STAD, and THYM. ISLR expression in THYM is directly proportional to the stromal score and inversely proportional to the immune score. ISLR expression is directly proportional to ACC, BRCA, CESC, ESCA, HNSC, KIRC, LGG, MESO, OV, TGCT, UCEC, and UVM stromal scores. In addition, based on the relationship between immune cell infiltration and prognosis, combined with the correlation between ISLR expression and immune cell infiltration, we conclude that ISLR expression can affect the prognosis of patients by affecting the amount of immune cell infiltration. In BLCA, GBM, STAD, and KIRP, high expression of ISLR causes high infiltration of immune cells, and the high infiltration of immune cells will cause poor prognosis in patients. In CESC, HNSC, LUAD, OV, SKCM, UVM, high expression of ISLR causes high infiltration of immune cells, and the low infiltration of immune cells can cause poor prognosis. In LGG, low ISLR expression is directly proportional to high immune cell infiltration, and high immune cell infiltration can cause poor prognosis. In MESO, high expression of ISLR is directly proportional to low immune cell infiltration, and low immune cell infiltration will cause poor prognosis. Subsequently, we found that ISLR may affect the conversion of immune cell subtypes. To further verify the role of ISLR in immunity, we analyzed the role of ISLR in pan-cancer and immune genes and found that ISLR is significantly correlated with a variety of immune genes and immune checkpoints.
Some studies have shown that TMB is related to the clinical response of immune checkpoints to block immunotherapy in certain tumors. It is also believed that TMB can independently predict the response to anti-PD-1 therapy in a variety of tumors[28–30]. MSI refers to the mutation of mismatch repair (MMR) gene, which causes changes in DNA repetitive sequences (microsatellites) and affects tumor progression. MSI status can aggravate or alleviate the resistance of immune checkpoint inhibitors in patients by changing the TME in tumors[31]. Our results showed that ISLR has a certain correlation with TMB and MSI in some tumors. Combining the correlation between ISLR and immune genes, we hypothesized that the expression of ISLR had a significant impact on immunotherapy. This conclusion has been verified in patients with melanoma. Higher expression of ISLR leads to poor immunotherapy effects. Finally, our enrichment analysis proved that ISLR may affect the pathogenesis or prognosis of tumors by playing a role in a variety of common cancer pathways and immune-related pathways.
In conclusion, this ISLR pan-cancer analysis found that ISLR has high or low expression in most tumors compared to normal tissues and is different from multiple prognostic types. The impact of ISLR on each tumor is different, and its impact on prognosis may be related to TMB, MSI, and immune cell infiltration in some tumors. These results may help clarify the causes of tumor occurrence and development and provide new research ideas and directions for solving the drug resistance of tumor immunotherapy. However, the specific impact mechanism of ISLR on tumors is still waiting for us to further study.