Early induction of ribonucleotide reductase gene expression by transforming growth factor beta 1 in malignant H-ras transformed cell lines.

Previous investigations have indicated that the suppression of proliferation by transforming growth factor (TGF) beta-1 is often lost upon cellular transformation, and that proliferation of some tumors is stimulated by TGF-beta. The present study provides the first observation of a link between TGF-beta-1 regulation of this process and alterations in the expression of ribonucleotide reductase, a highly controlled rate-limiting step in DNA synthesis. A series of radiation and T24-H-ras-transformed mouse 10T1/2 cell lines exhibiting increasing malignant potential was evaluated for TGF-beta-1 induced alterations in ribonucleotide reductase M1 and M2 gene expression. Early increases in M1 and/or M2 message and protein levels were observed only in malignant cell lines. The TGF-beta-1 induced changes in M1 and/or M2 gene expression occurred prior to any detectable changes in the rates of DNA synthesis, supporting the novel concept that ribonucleotide reductase gene expression can be elevated by TGF-beta-1 without altering the proportion of cells in S phase. T24-H-ras-transformed 10T1/2 cells were transfected with a plasmid containing the coding region of TGF-beta-1 under the control of a zinc-sensitive metallothionein promoter. When these cells were cultured in the presence of zinc, a large induction of TGF-beta-1 message was observed within 1 h. Both M1 and M2 genes were also induced, with increased mRNA levels appearing 2 h after zinc treatment, or 1 h after TGF-beta-1 message levels were clearly elevated. In total, the data suggests a mechanism of autocrine stimulation of malignant cells by TGF-beta-1, in which early alterations in the regulation of ribonucleotide reductase may play an important role.