Spotlight: The use of RNAscope to identify an association of KCNJ14 mRNA with tumour progression and immunosuppression
RNAscope biomarker analysis for CRC
Introduction
Colorectal carcinoma (CRC) is one of the major causes of cancer mortality but there are a lack of reliable biomarkers to predict tumour progression and prognosis. KCNJ14 is a member of the inwardly rectifying potassium channel family that has recently been implicated in tumour progression and immune suppression. Using RNAscope on CRC tissue microarrays (TMAs) the authors assessed the associations between KCNJ14 mRNA expression and clinicopathological features, tumour-infiltrating cells and patient outcomes.
Main Points
- In the absence of a reliable immunohistochemistry (IHC) antibody, RNAscope was used to determine levels of KCNJ14 mRNA in TMAs made from 259 CRCs.
- The TMAs were also labelled via IHC for tumour-infiltrating CD4+, CD8+ and FOXP3+ T cells.
- Single-cell RNA sequencing (scRNAseq) analysis was also performed to confirm the cell type in which KCNJ14 was expressed.
- RNAscope showed varying levels of KCNJ14 expression in tumour cells but no signal was found in the normal mucosa, as confirmed by scRNAseq.
- Compared with low KCNJ14 expressing CRCs, high expressing CRCs exhibited significantly higher frequencies of lymphatic and venous invasion, lymph node metastasis and advanced tumour stages, suggesting KCNJ14 has a role in tumour progression, although there was no difference in overall survival.
- High-expressing KCNJ14 CRCs had reduced numbers of CD4+ and CD8+ T cells, indicating suppressed immune activation, supporting the notion that KCNJ14 may contribute to the development of an immunosuppressive tumour microenvironment (TME). This may serve as a potential biological indicator of resistance to immunotherapy.
- In contrast, no significant association was found between KCNJ14 expression and infiltration of FOXP3+ cells, suggesting that KCNJ14-mediated immunosuppression is likely independent of Treg involvement. Previous studies have shown that high KCNJ14 expression is associated with activation of the mTOR pathway, VEGF and NOD-like receptor signaling, and increased expression of immune checkpoint molecules such as PD-L1 and CTLA-4. These pathways may contribute to the immunosuppressive phenotype observed in the TME.
Conclusion
The study found that high KCNJ14 expression is associated with reduced infiltration of CD4+ and CD8+ T cells and may contribute to tumour progression and the establishment of an immunosuppressive TME. KCNJ14 may serve as a clinically relevant biomarker for immunotherapy resistance and may be a potential therapeutic target.
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