Caspase-3 is a cysteine protease predominately known for its role in apoptosis. However, emerging evidence is highlighting alternative roles of caspase-3 in cell cycle, differentiation and migration. Genome sequencing projects have revealed the genomic landscape of human colorectal cancer (CRC), with recurrent heterozygous caspase-3 deletions in ~10% of patients. However, the contribution of caspase-3 loss to CRC development is unclear.
To investigate whether CASP3 loss contributed to intestinal tumour growth, we generated CASP3 knockout CRISPR clones for five CRC cell lines. Cells were examined for growth, proliferation and clonogenic potential. The ApcMin mouse model of intestinal tumourigenesis was used to assess the effects of caspase-3 loss on tumour development in vivo, and gene expression profiles were determined using RNA sequencing. A cohort of 662 patients with CRC was analysed for association of CASP3 gene deletion with clinico-molecular features and disease outcome.
In comparison to wild-type CRC cell lines, cell lines with heterozygous knockout of CASP3 exhibited increased cell viability, proliferation and clonogenic potential. Consistent with these findings, we observed a significant increase in the incidence and volume of colonic polyps in ApcMin/-Casp3+/- mice as compared with ApcMin/-Casp3+/+ mice, and overall survival of aging ApcMin/-Casp3+/- mice was significantly decreased. Furthermore, ApcMin/-Casp3+/- mice exhibited increased numbers of aberrant crypt foci. RNA sequencing of mouse colonic polyps identified upregulation of genes related to the TCA cycle and steroid biosynthesis and downregulation of genes related to various signalling pathways. Heterozygous CASP3 gene deletion in CRC patients was associated with overall survival, late-stage disease and poor differentiation. Further studies to elucidate the functional role and molecular interactions of caspase-3 in tumour development are warranted.