p52 induction by cytochalasin D in rat kidney fibroblasts: Homologies between p52 and plasminogen activator inhibitor type-1

Normal rat kidney (NRK) fibroblasts respond to the cell shape-modulating chemical agent cytochalasin D (CD) with augmented synthesis of the 52-kDa substrate-associated protein p52. p52 is a complex glycoprotein, existing as 12 different isoforms, which include a 43-kDa “core” protein (p43), four 50-kDa species (p50-0,1,2,3), and at least seven distinct pl variants of the mature 52-kDa protein. A threshold of 2–4 μM CD was found to be necessary to augment p52 deposition into both the secreted protein- and saponin-resistant cytomatrix (SAP) fractions of NRK cells. This concentration of CD was also necessary to initiate significant cell rounding. Augmented p52 production in CD-treated NRK (NRK/CD) cells provided a means to assess the identity of this protein. p52 was found to be identical to rat plasminogen activator inhibitor type-1 (rPAI-1) and to PAI-1-like proteins of other species by comparative immunoprecipitation, 2-D electrophoretic profile, V8 protease digest mapping, and subcellular fractionation criteria. Quantitation of rPAI-1 cytoplasmic mRNA abundance, using the rPAI-1 cDNA probe pSS1-3, revealed an induction of rPAI-1 mRNA in NRK/CD cells which paralleled the increased protein production. CD-augmented p52(rPAI-1) synthesis and SAP deposition was blocked by actinomycin D, implicating a need for RNA synthesis during the period of CD exposure to effect induction. Augmentation of p52 expression in NRK/CD fibroblasts, thus, appears to involve both cell shape-associated metabolic processes and concomitant RNA synthesis.