Growth state-regulated expression of p52(PAI-1) in normal rat kidney cells

In normal rat kidney (NRK) cells, synthesis of the 52-kDa substrate-associated type 1 inhibitor of plasminogen activator [p52(PAI-1)] is linked to alterations in cell shape and substrate adhesion. Subconfluent NRK cells accumulated significantly more ventral undersurface-associated p52(PAI-1) compared to newly confluent or 1-to 2-day postconfluent cultures, suggesting that p52(PAI-1) expression was also growth state-modulated. Since cytoarchitectural constraints function in cell growth control, changes in p52(PAI-1) synthesis were assessed with respect to defined morphologic events that accompany growth activation of cultured NRK cells. Stimulation of low population density, quiescent NRK cells with 20% serum-containing medium resulted in a rapid increase in matrix p52(PAI-1) protein content (6- and 26-fold after 1 and 5 hr, respectively). Growth activation in response to serum reflected activations in p52(PAI-1) cytoplasmic mRNA abundance, which peaked at 2 hr (125-fold increase) and subsequently declined (100-fold increase) at 5 hr poststimulation. Morphologic analysis indicated that quiescent NRK cells were devoid of transcytoplasmic actin filaments and focal contact-associated vinculin. A marked increase in the fraction of cells that elaborated transcytoplasmic microfilaments and vinculin-containing focal adhesions was evident within 5 min of serum addition. Such cytoarchitectural restructuring preceded p52(PAI-1) induction. Morphologic reorganization and p52(PAI-1) induction occurred prior to progression of cells through the S-phase, indicating they are early events associated with serum stimulation in the NRK cell system. The relevance of p52(PAI-1) induction during this growth state transition is not clear but may influence the established cytoarchitectural changes observed prior to p52(PAI-1) induction by regulating pericellular proteolysis and, thereby, cell-to-substrate adhesion.