The effects of ARID1A mutations on colorectal cancer and associations with PD-L1 expression by stromal cells

Abstract

Background: ARID1A is a component of the SWI/SNF complex, which controls the accessibility of proteins to DNA. ARID1A mutations are frequently observed in colorectal cancers (CRCs) and have been reported to be associated with high mutational burden and tumor PD-L1 expression in vitro.

Aim: To clarify the role of ARID1A mutation in CRC.

Method and results: We used next generation sequencing (NGS) and immunohistochemistry on clinically obtained samples. A total of 201 CRC tissues from Niigata University and Niigata Center Hospital were processed by NGS using the CANCERPLEX panel. Immunohistochemistry for ARID1A, PD-L1, MLH1, and MSH2 was performed on 66 propensity-matched (33 microsatellite instability-high [MSI-H] and 33 microsatellite-stable [MSS]) cases among 499 cases from Kyushu University. TCGA data were downloaded from cBioPortal. NGS showed significantly more mutations in ARID1A mutated CRCs (p = 0.01), and the trend was stronger for right-sided CRCs than left-sided. TCGA data confirmed these findings (p < 0.01). BRAF V600E and ATM mutations were also found at higher frequencies. Immunohistochemistry showed that 30% of MSI-H CRCs had ARID1A loss, while this was true in only 6% of MSS CRCs. In both MSI-H and MSS, PD-L1 expression by stromal cells was enhanced in the ARID1A-mutant groups (90% vs 39% in MSI-H, 100% vs 26% in MSS).

Conclusion: We found a higher mutational burden in ARID1A-mutant CRCs, and IHC study showed that ARID1A loss was correlated with high PD-L1 expression in stromal cells regardless of MSI status. These data support the idea that mutant ARID1A is a potential biomarker for CRCs.

Keywords: ARID1A; PD-L1; colorectal cancer; microsatellite instability.

FIGURE 1

Immunohistochemical staining for MLH1, MSH2, AT‐rich interaction domain 1A(ARID1A), and programmed death‐ligand 1 (PD‐L1). (A) Negative MLH1 staining in the nuclei of tumor cells. (B) Positive MSH2 staining in the nuclei of both tumor and stromal cells. (C) Positive MLH1 staining in the nuclei of both cells. (D) Negative MSH2 staining in the nuclei of tumor cells. (E) Diffuse positive ARID1A staining in the nuclei of both cells. (F) Focal negative ARID1A staining in the nuclei of tumor cells. There are two separate regions, ARID1A‐negative on the right and ‐positive on the left. (G) High‐power magnification of (E), note that the nuclei of stromal cells in the ARID1A‐negative area are positive for ARID1A staining. (H) Diffuse negative ARID1A staining in the nuclei of tumor cells. (I) Positive membrane staining of PD‐L1 on the cytoplasm of tumor and stromal cells. (J) Positive membrane staining of PD‐L1 on the cytoplasm of stromal cells. (K) Negative PD‐L1 staining in both cells

FIGURE 2

The number of mutations in the (A) next generation sequencing (NGS) and (B) The Cancer Genome Atlas (TCGA) cohort, as well as in the NGS cohort divided by (C) right‐ and (D) left‐sided disease. The graphs display the means and standard deviations (SD), minimum score and maximum score for each group. *Statistically significant difference between the ARID1A‐mutant and wild‐type groups (p < 0.05)