PLASMINOGEN-ACTIVATOR INHIBITOR TYPE-2 (PAI-2) IN HUMAN KERATINOCYTESREGULATES PERICELLULAR UROKINASE-TYPE PLASMINOGEN-ACTIVATOR

Plasminogen activation is observed in the human epidermis during reepi thelialization of epidermal defects and under certain pathological con ditions, The activation reaction depends on keratinocyte-associated pl asminogen activators (PAs), which convert the ubiquitous proenzyme pla sminogen into the active trypsin-like serine proteinase plasmin, The P As are controlled by PA inhibitors (PAIs), of which two major types ar e known: PAI-1 and PAI-2. ln vitro and in vivo keratinocytes express b oth PAIs. In the current study, we have addressed the possible functio n of PAI-S in regulating extracellular PA activity in cultured normal human epidermal keratinocytes (NHEK), the human keratinocyte cell line (Ha-CaT), and a Ha-ras transfected HaCaT variant (HaRas), PAI-2 was d etected intracellularly in all three cell types. Whereas only the NHEK and the HaCaT cells secreted detectable levels of PAI-2 into the cult ure medium, all three cell types released urokinase-type PA (uPA) into the supernatants, When comparing HaCaT and HaRas cells, we found that the cell lines secreted comparable levels of uPA antigen, whereas the levels of uPA activity were low in the presence of PAI-2, indicating that PAI-2 serves to regulate uPA activity. This assumption was suppor ted by the findings that PAI-S formed complexes with secreted uPA and that uPA/PAI-2 complexes were present at the surface of the PAI-2-secr eting HaCaT cells but not at the surface of PAI-2 nonsecreting HaRas c ells. Finally, PAI-2 was found to counteract the uPA-dependent and pla smin-mediated detachment of cultured HaCaT cells. Taken together, our findings indicate that secreted PAI-2 serves to regulate the activity of extracellular uPA in keratinocytes. (C) 1996 Academic Press, Inc.