Intracellular and extracellular human lysyl oxidase‐like 2 in metastatic breast cancer cells

Abstract

Human lysyl oxidase‐like 2 (HLOXL2) is highly up‐regulated in metastatic breast cancer cells and tissues. Native and recombinant HLOXL2s (rHLOXL2s) are soluble and mostly secreted into the media, but also found in cytosol and nucleus. Secreted HLOXL2 (~100 kDa) was confirmed for the presence of glycosylation, proteolysis, and formation of lysine tyrosylquinone cofactor. The fourth SRCR and catalytic domains of HLOXL2 are in communication to achieve optimal activity, and N‐glycosylation at Asn455 and Asn644 is essential for protein secretion. MCF‐7 cells stably expressing rHLOXL2s show higher proliferation and invasiveness in vitro, but do not exhibit characteristic metastasis molecular markers. Addition of β‐Aminopropionitrile, the specific inhibitor of HLOXL2, significantly abolished proliferation and invasiveness, as in the case for MDA‐MB‐231. Intracellular HLOXL2 (~80 kDa) is unglycosylated, but catalytically competent. Wild type MCF‐7 cells can uptake the purified secreted rHLOXL2s, and the exogenous N‐glycosylated rHLOXL2s localize in the nucleus and induce epithelial‐to‐mesenchymal transition. Evidence supports that HLOXL2 goes beyond its traditional role of initiating collagen and elastin cross‐linking extracellularly, its intracellular accumulation leads to a dramatic increase of metastasis/invasion in breast cancer cells.