Differential gene expression in TPA responsive and non-responsive mouse fibroblasts.

Abstract

Our laboratory has previously isolated a 12-O-tetradecanoylphorbol-13-acetate (TPA)-nonresponsive variant line (VT-1) from mouse 3T3-L1 cells. Here the expression of type I collagen pro-α2 (pro-α2(I)) mRNA and production of type I collagen in these two cell lines is examined. In quiescent cells, the pro-α2(I) steady state mRNA levels were 4 times greater in 3T3-L1 cells than in VT-1 cells. TPA addition caused the steady-state levels of pro-α2(I) mRNA to be 6 times greater in 3T3-L1 cells than in VT-1 cells. The pro-α2(I) protein levels in the extracellular matrix or culture media of 3T3-L1 cells were substantially elevated by TPA treatment but no significant increase was detected in VT-1 cells. The correlation of collagen expression with a TPA-mediated mitogenic response suggests a new role for collagen as an early component of mitogenic signal transduction. Expression of protooncogenes and other mitogenically related genes were also examined in 3T3-L1 and VT-1 cells. c-fos, c-myc, c-jun and ornithine decarboxylase were expressed in both cell lines. These findings suggest that expression of these genes may be necessary but not sufficient for a TPA induced mitogenic response. Two of the TPA Inducible Early (TIE) genes selected had no homology with any other known sequence. Here, mRNA expression levels of these novel genes (TIE-10B and TIE-44) are examined in 3T3-L1 and VT-1 cells and in several mouse tissues. Within 30 minutes of TPA treatment, TIE gene mRNA is increased in 3T3-L1 cells; whereas, with the exception of TIE-10B, low levels or delayed mRNA expression is seen in VT-1 cells. The two genes are expressed in most mouse tissues tested. mRNA levels of both TIE genes also increased in response to serum supplemented medium. Typical mRNA expression patterns for protooncogenes c-fos, c-myc, c-jun are seen when cells are treated with TPA or serum-supplemented media. The differential mRNA expression of the TIE genes relative to other growth potentiating genes and in response to mitogens other than TPA is indicative of the complexity and wide range of genes involved in several possible pathways leading to the cells' mitogenic response. (Abstract shortened with permission of author.)