PCSK6 and breast cancer: During the course of this study, we found that the full-length LOXL2 (fl-LOXL2, ~100-kDa) secreted from human embryonic kidney (HEK) cells and breast cancer cells (MDA-MB-231, MCF-7) undergoes proteolytic cleavage of the first two SRCR domains (SRCR1-SRCR2) to yield Δ1-2SRCR-LOXL2 (~60-kDa) by PACE4, a member of the proprotein convertase family of proteins, at 314Arg-315Phe-316Arg-317Lys↓318Ala (underlined, PACE4 recognition sequence, Figure 1 and Figure S2).