CTSD and melanoma: However, previous studies indicated a role for CTSB in tumor progression.52 The increased expression of CTSB was related to the invasion and proliferation of melanoma cells,9 and CTSB decreased dramatically after serum-deprivation-induced apoptosis, whereas CTSD increased, suggesting a balance between CTSB and CTSD.53 In the current study, we showed that lysosomal ceramide-activated CTSB induced caspase activation through XIAP degradation because an inhibitor of CTSB CA-074 Me was effective in blocking the apoptotic pathway.