ARID1B mutation is associated with Chromatin damage and ICIs response in NSCLC Patients
According to our previous study, NSCLC patients with ARID1B mutations treated with ICIs trends had better OS compared to WT group. We therefore used both TCGA as well as AACR GENIE databases to investigate the mutation status of ARID1B gene. According to our exploration of TCGA LUAD, LUSC datasets and AACR GENIE project datasets, we identified a mutation frequency of 5.7% for ARID1B gene in NSCLC patients of TCGA databases (Figure. 1a) and 4.4%in NSCLC patients of AACR GENIE project (Supplementary Figure. 1). The mutation type including missence, inframe, splice and fusion. Also, we identified some PTM location site, including phosphorylation, acetylation, ubiquitination, methylation and sumoylation. The mutations are evenly distributed across various exons of the entire gene, without the presence of hotspot mutations(Figure. 1a). The gene mutation rates of ARID1B in these two datasets are 6%(67/1053) and 5%(78/1636), respectively. Additionally, we observed a relationship between ARID1B mutation and smoking status, with a higher prevalence of ARID1B mutation in smoking patients, which indicated the tobacco exposure may significantly impact mutations of ARID1B gene(Figure. 1b). Furthermore, we found a correlation between ARID1B alteration(any form of non-synonymous mutation in ARID1B, classifies the patient as belonging to the ARID1B-altered group.) and bone metastasis in NSCLC patients, with a lower incidence of bone metastasis observed in patients with ARID1B mutation (Figure. 1c).
Analyzing the prognosis of nearly 3,000 NSCLC patients(1,053 patients from TCGA LUAD and LUSC datasets and 2,004 patients from the AACR GENIE project), we determined that ARID1B mutation was not associated with prognosis in patients who did not receive ICIs (Figure. 1d, e). However, in a subsequent prognosis analysis of 1661 cancer patients who underwent ICIs therapy, we discovered that patients with ARID1B mutation exhibited better outcomes following ICIs treatment, the median overall survival time for altered group is 44 months compared to 18 months for non-altered group(Figure. 1f). The prognosis analysis of 350 NSCLC patients who underwent ICIs therapy, we also discovered that patients with ARID1B mutation exhibited better outcomes following ICIs treatment ,the median progress free survival time is 22.43 months for altered group compared to 3.77 months for non-altered group (Figure. 1g). This result suggests a predictive value for ARID1B in ICIs response in NSCLC patients. Moreover, consistent with our previous findings, mutated patients demonstrated higher mutation counts and TMB (Figure. 1h, i).
To explore the role of ARID1B mutation in the regulation of response to ICIs, we first examined the pathway enrichment analysis of differentially expressed genes between mutated and non-mutated patients and it revealed that significant enrichment in pathways related to chromatin, DNA assembly and stability, and immune response (Figure. 1j). GSEA enrichment analysis indicated downregulation of numerous chromatin and DNA assembly/stability-related pathways associated with ARID1B mutation (Figure. 1k).
ARID1B Mutation leads to impaired DNA Damage Response and DNA Repair
To explore the role of ARID1B and DNA damage response genes, we first mined the TCGA database and found a positive correlation between ARID1B expression and genes for DNA damage response and DNA repair, such as ATM, CHEK1, CHEK2, H2AFX, KU70, and KU80(Fig. 2a-f).
Next, we want to know whether ARID1B respond to DNA damage. We induced DNA damage in SK-MES1 and H2030 lung cancer cells, which are ARID1B wild type cells, with etoposide, a known DNA-damaging agent. As shown in Fig. 2, we observed DNA damage induced by etoposide in SK-MES1 and H2030 cells, as evidenced by upregulation of phosphorylated γ-H2AX, a phosphorylated histone protein, which is a marker of DNA DSBs, as well as phosphorylated CHK1, CHK2, ATM, markers of DNA damage (Fig. 2g). Since in eukaryotic organism, non-homologous end joining (NHEJ) is one of the major DNA damage repair mechanisms, we further measured the expression of KU70 and KU80, which are involved in the NHEJ pathway, by immunoblotting. The DNA damage induced by etoposide led to the upregulation of KU70 and KU80 (Fig. 2h).
Since most ARID1B gene mutations are loss of function mutations, and to further elucidate the role of ARID1B in DNA damage response, we knocked down the ARID1B gene in SK-MES1 and H2030 cells using siRNA and subsequently induced DNA damage with etoposide. We observed that si-ARID1B alone did not change the expression of the DNA damage markers, but ARID1B knockdown cells showed enhanced DNA damage when treated with etoposide, resulting in increased levels of phosphorylated CHK1, CHK2, ATM, and γH2AX (Fig. 2i). Similar results were obtained using lentiviral-mediated ARID1B knockdown (Fig. 2j).
Furthermore, DNA repair pathways were up-regulated in ARID1B-knockdown cells, as evidenced with increased KU70 and KU80 expression (Fig. 2k, l)
We also confirmed the impact of loss function of ARID1B on DNA damage, with immunofluorescence experiments and the results demonstrated that SK-MES1 and H2030 cells with ARID1B gene knockdown exhibited increased upregulation of the γ-H2AX upon etoposide induction (Fig. 3a, b).
These findings suggest that ARID1B is associated with DNA damage response and modulates DNA repair pathways, highlighting its potential role in maintaining genome stability and influencing the cellular response to DNA damage.
Furthermore, comet assays were employed to assess DNA damage levels. Consistent with our findings, DNA damage was observed when SK-MES1 and H2030 cells treated with etoposide and comet assays revealed that ARID1B knockdown in SK-MES1 and H2030 cells resulted in an increased tail length, indicating enhanced DNA damage upon etoposide treatment (Fig. 3c). The statistical analysis of our Figure. 3c results demonstrated that in both the H2030 and SK-MES1 cell lines, the longest comet tail length was observed when ARID1B was knocked down and the cells were treated with etoposide. The next longest comet tails were observed when normal cells were treated with etoposide. However, when ARID1B was solely knocked down without etoposide treatment, the changes were not significant.
ARID1B is related to cell Chromatin accessibility
The DNA damage response (DDR) occurs in the context of chromatin, and architectural features of chromatin have played significant role in DNA damage signaling and repair. DNA break induced chromatin remodeling affects repair factor access and choice. Chromatin relaxation followed by condensation represent the initial effects of DSBs, which are necessary for both DSB damage and repair DNA damage accumulation may be impacted by altered chromatin and chromosome structures. Since SWI/SNF chromatin remodeling complexes uses the energy of ATP to change the structure of DNA, playing key roles in DNA regulation and repair. To determine whether ARID1B is responsible for the abnormal compaction of chromatin structures in associated DNA damage, micrococcal nuclease digestion assay was then carried out on both cell lines to determine whether ARID1B expression would alter the chromatin conformation. Larger diffuse DNA fragments can be seen in the chromatin of ARID1B knocking down cells following the addition of MNase and the DNA fragment is more degraded than the control group, which indicated that the chromatin structure is looser in ARID1B knockdown cells. These results demonstrate that reduced ARID1B gene expression increased the accumulation of DNA damage during DNA damage and exhibited increased chromatin accessibility (Fig. 3d, e).
Collectively, these findings provide further evidence that ARID1B knockdown enhances DNA damage in SK-MES1 and H2030 cells, as demonstrated by increased γH2AX levels, prolonged comet tail length, and enhanced chromatin accessibility. These results suggest a crucial role for ARID1B in maintaining DNA integrity and highlight its involvement in DNA damage response pathways.
ARID1B Expression Correlates with Immune Suppression in NSCLC
To determine whether ARID1B deficiency alter immune microenvironment, we collected data from TCGA and analyzed 25 immune-related pathways. Using gene set variation analysis (GSVA), we scored each tumor sample to represent its immune microenvironment. Based on ARID1B gene expression levels, we divided the samples into high and low expression groups, using a TPM value of 30 as the cutoff, with values above 30 indicating high expression and values below indicating low expression. Our analysis revealed that the ARID1B high-expression group exhibited a significantly lower immune score compared to the ARID1B low-expression group, indicating a state of immune suppression (Fig. 4a).
To validate this observation, we utilized the single-sample gene set enrichment analysis (ssGSEA) method to assess tumor immune cell infiltration. Consistently, we found that patients with high ARID1B expression showed reduced levels of immune cell infiltration compared to the low-expression group (Fig. 4b).
Furthermore, we employed five additional methods, including CIBERSORT (Fig. 4c), EPIC (Fig. 4d), MCPcounter (Fig. 4e), IPS (Fig. 4f), and QUANTISEQ (Fig. 4g), to evaluate immune infiltration in the tumor microenvironment. Correlation analysis between their results and ARID1B expression revealed a negative correlation between ARID1B expression and the majority of immune-related cells or functions. In our CIBERSORT analysis, we observed a negative correlation between the infiltration of CD8 + T cells in NSCLC and the expression of ARID1B (Fig. 4c). The results of the other four immune infiltration methods were consistent with CIBERSORT, but did not reach statistical significance. The EPIC analysis (Fig. 4d) and MCPcounter analysis (Fig. 4e) revealed a positive correlation between ARID1B and tumor-associated fibroblasts. Similarly, the IPS analysis(Fig. 4f) showed a negative correlation between ARID1B expression and tumor immunogenicity.
Taken together, our findings consistently demonstrate that high expression of ARID1B in NSCLC is associated with immune suppression, as evidenced by lower immune scores, reduced immune cell infiltration, and negative correlations with multiple immune-related cell types and functions. These results suggest that ARID1B may play a critical role in modulating the immune landscape of NSCLC tumors.
ARID1B regulates the immune microenvironment through cGAS-STING Pathway
The gene set enrichment analysis (GSEA) of differentially expressed genes revealed significant changes in multiple immune-related pathways following ARID1B mutation (Fig. 5a). Furthermore, we investigated the relationship between ARID1B and the cGAS-STING pathway. We found that ARID1B positively correlated with CGAS(Fig. 5b), TBK1 (Fig. 5d), and IRF3 (Fig. 5e), but showed no association with STING1(Fig. 5c) expression.
To validate these findings, we performed Western blot analysis. We observed that induction of cellular damage led to an upregulation of the cGAS-STING pathway (Fig. 5f). Interestingly, cells with ARID1B knockdown showed enhanced upregulation of the cGAS-STING pathway upon damage induction (Fig. 5g).
Collectively, our results demonstrate that ARID1B mutation alters immune-related pathways, as evidenced by significant changes in their enrichment. Additionally, we identified associations between ARID1B and key components of the cGAS-STING pathway. The induction of cellular damage resulted in the upregulation of the cGAS-STING pathway, and cells with ARID1B knockdown exhibited an augmented response in the pathway upon damage induction. These findings suggest that ARID1B plays a role in modulating the cGAS-STING pathway in NSCLC.