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Regulation of Transforming Growth Factor Messenger RNA Expression in a Chemically Transformed Rat Hepatic Epithelial Cell Line by Phorbol Ester and Hormones¹

Lineberger Cancer Research Center, Cell Biology Program [V. W. R., D. C. L., J. W. G., H. S. E.], Department of Microbiology and Immunology [D. C. L.], Pathology [J. W. G.], Medicine [H. S. E.], and Pharmacology, [H. S. E.], The University of North Carolina, Chapel Hill, North Carolina 27599

Transforming growth factor (TGF-) is produced by many transformed cells, but little is known about the regulation of its expression. We examined TGF- mRNA levels in a set of cloned neoplastic cell lines derived by chemical transformation of a normal rat liver epithelial cell. The untransformed parental cell line, WB-344, did not express a detectable level of TGF- mRNA, whereas GP6ac, a transformed line capable of autonomous growth in soft agar, expressed TGF-. When GP6ac cells were treated with agents thought to regulate protein kinase C activity, e.g., the tumor promoter, 12-O-tetradecanoylphorbol-13-acetate (TPA), TGF- mRNA levels increased by 8- to 11-fold. The induction of TGF- mRNA was detectable at 2 h, was maximal at 8–12 h, and declined by 24 h. Angiotensin, bradykinin, epinephrine, and epidermal growth factor also increased TGF- mRNA by 2- to 5-fold. In contrast, parental WB cells neither expressed TGF- mRNA, nor responded to TPA. TPA also increased epidermal growth factor receptor mRNA in GP6ac cells but the effect was less prolonged; maximal levels were seen at 4 h after TPA exposure and returned to control levels by 12 h.

TPA increased TGF- mRNA in GP6ac cells, in part, by increasing transcription of the TGF- gene as measured by run-on transcription rates in isolated nuclei. In addition, the induction of TGF- by TPA was blocked by concurrent incubation with agents that inhibit protein synthesis. However, if TPA was present for at least 2 h, subsequent addition of cycloheximide enhanced the effect of TPA. This indicates that the induction of TGF- in GP6ac cells is comprised of at least two phases demarcated by the requirement for protein synthesis. The time course of induction and the sensitivity to inhibition of protein synthesis distinguish the effect of TPA on TGF- mRNA from that of other genes regulated by TPA, e.g., c-myc and c-fos. These data also suggest that chemical transformation of rat liver epithelial cells leads to expression of TGF- mRNA, and that once expressed, TGF- mRNA can be modulated in a protein kinase C-dependent manner.

¹ This work was supported by NIH Grants CA-43793 (D. C. L.), CA-29323 (J. W. G.), and DK-30002 (H. S. E.).

² Supported by NIH postdoctoral training Grant CA-09156-11. To whom requests for reprints should be addressed, at Lineberger Cancer Research Center, CB 7295, University of North Carolina, Chapel Hill, NC 27599.

Received 10/28/88. Revised 3/27/89. Accepted 3/31/89.

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