Fully processed lysyl oxidase catalyst translocates from the extracellularspace into nuclei of aortic smooth-muscle cells

Lysyl oxidase (LO), a secreted protein, was recently identified within the nuclei of vascular smooth-muscle cells (SMC) and 3T3 fibroblasts. A possibl e pathway by which LO can enter cell nuclei was explored in the present stu dy. SMC were incubated with purified 32-kDa bovine aorta LO that had been f luorescently labeled with rhodamine (TRITC-LO). TRITC-LO entered the cytoso l and then rapidly concentrated within the nuclei of preconfluent cultures of these cells, whereas carbonic anhydrase, a protein of similar molecular weight and similarly labeled, did not enter the cells under these condition s. LO that had been reductively methylated at lysine residues with [C-14] H CHO was also taken up into the cytosolic and nuclear compartments. Intracel lular uptake and intracellular distribution were not altered by inhibiting CO activity with beta -aminopropionitrile. An excess of native LO but not o f carbonic anhydrase competitively inhibited the uptake of the isotopically labeled enzyme. Thus, once secreted and proteolytically processed, mature LO can enter the cells and concentrate within nuclei in a manner that appea rs to be specific and independent of its catalytic activity. (C) 2000 Wiley -Liss, Inc.