Cathepsin S (CTSS)

CTSS is a member of the peptidase C1 family, is a lysosomal cysteine protease that may participate in the degradation of antigenic proteins to peptides for presentation on MHC class II molecules. The encoded protein can function as an elastase over a broad pH range in alveolar macrophages.

Cathepsin S has been shown to be a significant prognostic factor for patients with type IV astrocytomas (glioblastoma multiforme) and its inhibition has shown improvement in survival time by mean average 5 months. This is because the cysteine enzyme can no longer act together with other proteases to break up the brain extracellular matrix. So the spread of the tumor is halted.