A growth-responsive gene (16C8) in normal mouse fibroblasts homologous to a human collagenase inhibitor with erythroid-potentiating activity: evidence for inducible and constitutive transcripts

We present the DNA sequence of an essentially full-length cDNA clone of 16C8, a growth factor-inducible gene isolated from a mouse embryo fibroblast cDNA library. The 0.9-kb mRNA encodes an Mr 22,500 protein that has substantial homology to a human protein with the reported abilities to potentiate erythroid differentiation and to inhibit collagenases and other tissue metalloproteinases. The N-terminus of the predicted protein has a hydrophobic nature characteristic of secreted proteins, and two potential sites for N-linked glycosylation are present. The cytoplasmic concentration of 16C8 mRNA is maximal in mid G1 at about 6 h after serum stimulation of quiescent fibroblasts. Northern blot analysis showed a progressive reduction in the size of the induced 16C8 transcripts with increasing time after serum stimulation. This was shown to be due to the reduction in length of the poly(A) tails. S1 analysis of the 5' portion of the mRNA revealed the presence of three different species of transcript, only one of which was inducible.