Does endogenously expressed DAPase in human cells degrade proteins that are expressed in cell culture?
FAQ ID -527

DAPase (dipeptidyl aminopeptidase I = Cathepsin C), even though endogenously expressed in human tissues and cells, will have only a negligible effect on the degradation of proteins expressed in cell culture. The reason for this is the low level of endogenous DAPase compared to the much higher level of typically overexpressed recombinant protein. However, it is always worthwhile to run a time-course expression experiment to check for possible protein degradation, since proteases and peptidases tend to degrade proteins over time.