The 52 kDa transformation-sensitive protein p52 was previously identified as a major substrate-associated component of normal rat kidney (NRK) fibroblasts [Higgins & Ryan (1989) Biochem. J. 257, 173-182]. p52 selectively localized to cellular fractions enriched in substrate focal-contact sites and associated ventral undersurface elements. Rapid attachment/spreading of NRK cells on to prepared p52 matrices and inhibition of fibroblast spreading by antibodies to p52 indicated that this protein participates in shape determination or cell-to-substrate adhesion. NRK cells transformed with Kirsten murine sarcoma virus (KiMSV), with a temperature-sensitive mutant (ts-371 KiMSV) and maintained at the permissive temperature, or with the cloned EJrasval.12 oncogene, exhibited down-regulated accumulation of p52 in the ventral undersurface region. Immunochemical, lectin-affinity and electrophoretic analyses indicated that p52 shares considerable sequence similarity with plasminogen-activator inhibitor type-1, which is consistent with its subcellular localization and likely morphoregulatory activity. The marked down-regulation of p52 expression seen in four different ras-mediated transformation systems, its induction prior to butyrate-induced morphological reorganization in KiMSV-transformed cells, and the morphological consequences of exogenously added p52 or p52 antibodies on NRK fibroblasts suggest that this protein probably functions in cell-shape regulation. Abrogation of p52 matrix accumulation typically seen in ras transformants may contribute, therefore, to the aberrant cytoarchitecture characteristic of malignant fibroblasts.
- © 1991 The Biochemical Society, London