Expression alterations induced by restoration of AXIN1 expression in SNU449 hepatocellular carcinoma cells

Aberrant activation of Wnt/ß-catenin signaling is observed in numerous cancers. In hepatocellular carcinoma activating mutations in CTNNB1 (20-25%) or loss of function mutations in AXIN1 (10%), AXIN2 (2%) and APC (1-2%) are observed. All these mutations lead to aberrant stabilization of ß-catenin, which constitutively activates downstream Wnt/ß-catenin target genes and triggers a genetic program resulting in tumor formation. However, in relation to AXIN1 mutations some reports have challenged whether these indeed result in tumor growth by enhancing ß-catenin signaling (e.g. PMID: 16964294, 29525529). Several alternative pathways have also been linked to AXIN1 (ENSG00000103126), such as TGFß, SAPK/JNK, p53, YAP/TAZ and c-myc. To identify which one of these or other unknown signaling routes are linked to AXIN1, using CRISPR-Cas9 genome editing, we have successfully repaired the homozygous p.R712* AXIN1 mutation present in the SNU449 hepatocellular carcinoma cell line. Next, using RNA sequencing the RNA expression patterns of 3 independent repaired clones were compared with 3 clones retaining the AXIN1 mutation. Surprisingly, only 5 genes were significantly altered in the repaired clones, among which AXIN2, a well-established ß-catenin target gene. Thus, this analysis leads to the surprising observation that a commonly observed mutation in a hepatocellular tumor suppressor gene, is associated with minimal alterations in gene expression, at least in the SNU449 cell line. Overall design: Comparison of 3 independent repaired SNU449 clones with 3 clones retaining the AXIN1 mutation