Cell adhesion regulates pro-alpha 1(I) collagen mRNA stability and transcription in mouse fibroblasts

Abstract

Adhesive interactions are important modulators of cellular phenotype. Previously, we demonstrated that quiescent, suspension-arrested cells are not equivalent to density-arrested cells in their patterns of gene expression (Dhawan, J., and Farmer, S.R. (1990) J. Biol. Chem. 265, 9015-9021). In particular, pro-alpha 1(I) collagen expression depended strongly on the extent of cell adhesion. In this paper, we demonstrate that the adhesion-induced rise in collagen gene expression is due to regulation at multiple levels. Steady state levels of pro-alpha 1(I) collagen mRNA increased up to 10-fold by 6 h after replating suspended cells, and this rise is blocked by inhibition of protein synthesis. Transcription of the pro-alpha 1(I) collagen gene was measured by run-on assay as well as by activation of a rat alpha 1(I) promoter-chloramphenicol acetyltransferase reporter gene construct. Both assays reveal a 5-fold depression of pro-alpha 1(I) collagen gene transcription in suspended cells. Reattachment of suspended cells resulted in the activation of alpha 1(I) gene transcription by 2-h postreplating, reaching a 3-5-fold level of induction by 18 h. The pro-alpha 1(I) collagen mRNA was substantially more labile in suspended cells than in adherent cells (t1/2 values of approximately 2 h in nonadherent cells and greater than 8 h in exponentially growing or density-arrested cells). Furthermore, reattachment of suspended cells for 18 h resulted in a stabilization of collagen mRNA. We conclude that cell adhesion regulates pro-alpha 1(I) collagen gene expression selectively and at transcriptional and posttranscriptional sites.