J. Biol. Chem., Vol. 265, Issue 16, 9015-9021, Jun, 1990
Regulation of alpha 1 (I)-collagen gene expression in response to cell adhesion in Swiss 3T3 fibroblasts
J Dhawan and SR Farmer
Department of Biochemistry, Boston University School of Medicine, Massachusetts 02118.
Nonadhesive conditions cause Swiss 3T3 fibroblasts to enter a quiescent
state that is reversed upon reattachment to a surface. Previously, we
demonstrated that adhesion in serum-free conditions is sufficient to
activate suspension-arrested cells out of Go, with the induction of the
growth-associated genes, c-fos, c-myc, and actin. In this study, we have
employed this system to identify programs of gene expression that respond
primarily to the adhesive state of the cell, rather than the growth state.
We show that cells in different adhesive states can be distinguished by
their patterns of protein synthesis. Analysis of one adhesion-responsive
protein led to its identification as pro-alpha 1 (I)-collagen. Pro-alpha 1
(I)-collagen synthesis and mRNA levels are decreased up to 6-fold in
suspension-arrested fibroblasts, but are enhanced up to 5-fold as cells
approach confluence. This suggests that the reduced expression in
suspension-arrested cells is not simply a result of quiescence. In
addition, reattachment of suspended cells in serum-free conditions caused a
7-fold induction of collagen mRNA levels and a greater than 20-fold rise in
the rate of procollagen synthesis. The expression of c-myc was induced
during adhesion in serum-free medium as well as by serum addition to
suspension-arrested cells. However, alpha 1 (I)-collagen gene expression
was unaffected by serum in the absence of adhesion. These results indicate
that collagen gene expression is directly responsive to cell adhesion,
independent of the growth state.