DIFFERENTIAL GROWTH STATE-DEPENDENT REGULATION OF PLASMINOGEN-ACTIVATOR INHIBITOR TYPE-1 EXPRESSION IN SENESCENT IMR-90 HUMAN-DIPLOID FIBROBLASTS

The type-1 inhibitor of plasminogen activator (PAI-1) regulates perice llular proteolytic activity functioning, thereby to control matrix int egrity, cell growth, and morphology. Subconfluent late-passage IMR-90 human fibroblasts and normal rat kidney (NRK) cells, both at the stage of replicative senescence accumulated 15- to 30-fold more undersurfac e PAI-1 protein compared to early-passage, actively-proliferating, cul tures. Senescence-associated elevations in PAI-1 expression by IMR-90 cells reflected corresponding Ii-fold increases in the 3.0- and 2.2-kb PAI-1 mRNA species. The 2.2-kb transcript exhibited a greater age-dep endent increase (7.2-fold) compared to the 3.0-kb mRNA (3.7-fold). Sin ce PAI-1 expression is coupled to growth activation in serum-deprived cultures (Ryan and Higgins, 1993, J. Cell. Physiol., 155:376-384), it was important to determine if PAI-1 gene regulation was altered as a f unction of cellular aging. In contrast to early-passage cultures, sene scent IMR-90 fibroblasts did not down-regulate either PAI-1 protein ex pression or steady-state levels of PAI-1 mRNA transcripts upon serum-d eprivation. Late-passage human fibroblasts at their proliferative end- stage, thus, appear to regulate PAI-1 mRNA levels through different me chanisms than do young, actively-proliferating, cells. PAI-1 overexpre ssion during in vitro cellular aging, therefore, may contribute to the acquisition of specific senescence-associated phenotypic traits (e.g. , enlarged cell morphology; increased adhesivity) by altering the peri cellular proteolytic balance influencing, in turn, the formation or st ability of cell-to-substrate attachment complexes. (C) 1995 Wiley-Liss , Inc.