PENK and neuroblastoma: The known CTSV and CTSL pro-neuropeptide substrates PENK and NPY were co-expressed with CTSV and CTSL, consistent with participation of CTSV in processing these precursors in human neuroblastoma cells (Funkelstein et al., 2012), and participation of CTSL for production of these neuropeptides in mouse brain shown by cathepsin L gene knockout (Yasothornsrikul et al., 2003; Funkelstein et al., 2008a,b; Minokadeh et al., 2010; Beinfeld et al., 2009).