CTSK and neuroblastoma: In the experimental part of our study (Fig. 1a), human neuroblastoma SH-SY5Y cell lysates were treated separately with recombinant human cathepsins K, V, L, S, F, and B. Cleavage sites from the endoproteolytic activity of these cathepsins were determined by N-terminal combined fractional diagonal chromatography (COFRADIC)21.