Enzyme Helps Cancer Cells Avoid Genetic Instability

Cells that have a mutant gene, BRCA1, also reduce output of the protein 53BP1.  That protein helps promote non-homologous end joining, a DNA repair mechansim which is very error prone.  So by cutting back, the mutated cell is more likely to remain viable.  The protease (an enzyme that destroys proteins) cathepsin-L is employed to reduce the 53BP1.