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 pericellular proteolytic activity functioning, thereby to control matrix integrity, 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 undersurface PAI-1 protein compared to early-passage, actively-proliferating, cultures. Senescence-associated elevations in PAI-1 expression by IMR-90 cells reflected corresponding 11-fold increases in the 3.0- and 2.2-kb PAI-1 mRNA species. The 2.2-kb transcript exhibited a greater age-dependent increase (7.2-fold) compared to the 3.0-kb mRNA (3.7-fold). Since 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 function of cellular aging. In contrast to early-passage cultures, senescent IMR-90 fibroblasts did not down-regulate either PAI-1 protein expression or steady-state levels of PAI-1 mRNA transcripts upon serum-deprivation. Late-passage human fibroblasts at their proliferative end-stage, thus, appear to regulate PAI-1 mRNA levels through different mechanisms than do young, actively-proliferating, cells. PAI-1 overexpression 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 pericellular proteolytic balance influencing, in turn, the formation or stability of cell-to-substrate attachment complexes.
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X C
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Department of Microbiology, Immunology, and Molecular Genetics, Albany Medical College, New York 12208, USA.
Higgins
P J
PJ
D000818:Animals; D002455:Cell Division / Q000502:physiology*; D048429:Cell Size / Q000502:physiology; D016922:Cellular Senescence / Q000502:physiology; D015180:Electrophoresis, Gel, Two-Dimensional; D005347:Fibroblasts / Q000166:cytology / Q000201:enzymology; D006801:Humans; D007668:Kidney / Q000166:cytology; D017395:Plasminogen Activator Inhibitor 1 / Q000235:genetics / Q000378:metabolism*; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats
D017395:Plasminogen Activator Inhibitor 1; D012333:RNA, Messenger