CONFOCAL FLUORESCENCE MICROSCOPY OF UROKINASE PLASMINOGEN-ACTIVATOR RECEPTOR AND CATHEPSIN-D IN HUMAN MDA-MB-231 BREAST-CANCER CELLS MIGRATING IN RECONSTITUTED BASEMENT-MEMBRANE

Using confocal fluorescence microscopy with a monoclonal antibody, we have localized the receptor for urokinase plasminogen activator (uPAR) in MDA-MB-231 human breast cancer cells migrating into a reconstitute d basement membrane. Patchy and polarized uPAR immunoreactivity was fo und at the cell membrane, and strong staining was found both in the ru ffled border or leading edge of the cells and at pseudopodia penetrati ng into the membrane. Intracellular uPAR staining was localized in the paranuclear region and in rounded granule-like structures; some of th ese were identified as lysosomes by double staining for uPAR and the l ysosomal enzyme cathepsin D. Urokinase plasminogen activator (uPA) act ivity has previously been shown to play a role in migration of cells i nto basement membranes, and it has been proposed that uPAR also is inv olved in this process. uPA is known to be internalized and degraded af ter complex formation with the inhibitor PAI-1. Lysosomal uPAR immunor eactivity may result from concomitant internalization of the receptor.