Cell Growth & Differentiation, Vol 5, Issue 2 117-124, Copyright © 1994 by American Association of Cancer Research
Analysis of transforming growth factor beta 1 messenger RNA degradation by the transcript-selective, 12-O-tetradecanoylphorbol-13-acetate-regulated ribonuclease system from U937 promonocytes
RE Wager, L Scotto and RK Assoian
Department of Biochemistry and Molecular Biophysics, College of Physicians and Surgeons, Columbia University, New York, New York 10032.
Transforming growth factor (TGF) beta 1 mRNA is selectively stabilized
during 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced differentiation
of U937 promonocytes. In previous studies (R. Wager and R. Assoian, Mol.
Cell. Biol., 10: 5983-5990, 1990), we showed that this phenotype results
from the action of a RNase system that (a) recognizes the transcript
selectively and (b) is inhibited upon exposure of cells to TPA. The studies
reported here were designed to localize domains of TGF-beta 1 mRNA required
for recognition by this TPA-regulated, transcript-selective RNase system.
By examining the degradation of several truncated TGF-beta 1 in vitro
transcripts with U937 cell extracts, we show that the coding domain is
sufficient to allow selective degradation of the mRNA and that this process
is enhanced by either the 5' or 3' untranslated regions. The 5' and 3'
untranslated regions of TGF-beta 1 mRNA are also required for TPA-mediated
inhibition of the transcript-selective RNase system. In contrast, an
analysis of the half-lives of the 2.1- and 1.8-kilobase TGF-beta 1 mRNAs
showed that the first 270 bases, unique to the larger TGF-beta 1 mRNA,
minimally affect degradation of the transcript. Finally, a survey of
several transcripts showed that gamma-actin mRNA levels are also controlled
by the TPA-regulated RNase system. The regulated decay of TGF-beta 1 mRNA
may reflect the behavior of a class of transcripts subject to similar
posttranscriptional controls on overall gene expression.