Induced expression of p52(PAI-1) in normal rat kidney cells by the microfilament-disrupting agent cytochalasin D

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Abstract
In established normal rat kidney (NRK) cells, synthesis of the 52 kDa type-1 inhibitor of plasminogen activator [p52(PAI-1)] is stimulated by the cell shape—modulating fungal metabolite cytochalasin D (CD). Induction paralleled the time course of morphologic change and reflected relatively specific increases in sapo-nin-resistant p52(PAI-1) protein accumulation (approximating ten- to thirty-fold over control) and mRNA abundance (seven- to nine-fold). Augmented p52(PAI-1) mRNA levels closely correlated with increases in 43 kDa p52(PAI-1) core protein biosynthesis. Sensitivity to tunicamycin indicated that N-linked post-translational modifications to this 43 kDa core species generated the full complement of 50 kDa (intermediate) and 52 kDa (mature) p52(PAI-1) glycosylated isoforms. CD-induced p52(PAI-1) expression occurred efficiently in quiescent NRK cells maintained under serum-free conditions as well as in fully serum-supplemented actively growing cultures. While 8-bromo-cAMP reduced both constitutive and transforming growth factor-beta—induced p52(PAI-1) synthesis by >50%, no such inhibition was evident in short-term (4 h) CD-stimulated cultures. Long-term (24 h) exposure of NRK/CD cells to 8-bromo-cAMP did result in an approximately 34% reduction in stimulated p52(PAI-1) expression, however, levels expressed by NRK/CD + cAMP populations remained markedly elevated relative to control values. These data suggest the existence of a cell shape—dependent aspect of p52(PAI-1) expression control distinct from both the constitutive and growth factor—mediated pathways of gene regulation.