Effect of N-Wasp knockout on tumour burden and survival in murine models of intestinal tumorigenesis and its potential as a prognostic biomarker in human colorectal cancer

Abstract Background APC loss is a common initiating event in colorectal cancer but additional mutations are required for progression along the adenoma–carcinoma pathway. The Neural Wiskott–Aldrich syndrome protein (N-WASP) is crucial for invasion in a variety of cancers. Its role in colorectal cancer has not been investigated; however, it is implicated in Wnt signalling (the pathway affected when APC function is lost). The aim of this project was to investigate the role of N-WASP in intestinal tumorigenesis and its potential as a prognostic biomarker. Methods The effect of N-Wasp knockout (N-Waspfl/fl) on survival and tumour burden was investigated using two established murine models of intestinal tumorigenesis (Apcfl/+ and Apcfl/+ KrasG12D/+). Immunohistochemistry for N-WASP was performed on two human tissue microarrays—namely, colorectal cancers with linked clinicopathological data and long-term follow-up, and early cancers diagnosed via bowel screening. N-WASP expression was assessed by weighted histoscore, and correlation with survival was tested. Findings N-Wasp knockout decreased survival in the Apcfl/+ model (median survival 143 days [IQR 127·3–167·0] vs 269 [228·8–304·5], p vs 8 [4·34], p 2 [SD 0·238] vs 1·547 [0·609], p=0·0317), there was no difference in mean size of the largest tumour. There was no effect of N-Wasp knockout on survival or small intestinal tumour burden in the Apcfl/+ KrasG12D/+ model. However, they developed fewer colonic tumours (mean 16·8 [SD 10·2] vs 35·4 [11·5], p=0·0018). In the human tissue microarray studies, there was no difference in overall or cancer-specific survival between tumours with high and low N-WASP expression. Interpretation We found that loss of N-Wasp promotes early tumorigenesis in Apc-deficient intestinal epithelium in mice. N-WASP stabilises epithelial cell–cell junctions and might be a regulator of Wnt signalling. Further research is required to ascertain whether either of these roles explains the effects seen here and whether it promotes invasion and metastasis in more advanced intestinal cancers, as seen in other tissues. Funding Funded by a Medical Research Council grant via the Scottish Clinical Pharmacology and Pathology Programme (SCP3).