Cell Growth & Differentiation, Vol 4, Issue 12 985-991, Copyright © 1993 by American Association of Cancer Research
Characterization of a third transforming growth factor beta 1 transcript in rat tracheal epithelial cells
LE Ostrowski, TE Gray, SH Randell and P Nettesheim
Laboratory of Pulmonary Pathobiology, National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina 27709.
It has been previously reported (R. W. Steigerwalt et al., Mol. Carcinog.,
5:32-40, 1992) that primary cultures of rat tracheal epithelial (RTE) cells
and immortalized RTE cell lines produce three mRNA transcripts [2.5, 1.9,
1.4 kilobases (kb)] which hybridize to a murine transforming growth factor
beta 1 (TGF-beta 1) complementary DNA probe. In this report, we show that
the 1.9- and 1.4-kb transcripts are not detectable by Northern analysis of
resting adult trachea but are induced in regenerating tracheal grafts and
tumors formed from transformed RTE cells. Northern analysis of the TGF-beta
1 transcripts with subclones of the murine complementary DNA demonstrate
that the 1.4-kb transcript lacks much of the 5' untranslated region (UTR).
RNase protection analysis was used to map the transcriptional start site of
the 1.4-kb transcript to within 30-40 base pairs of the first ATG codon. No
differences in the coding or 3' UTR were detected between the 1.4-kb and
the 2.5-kb transcripts. Although RTE cells produce a 1.9-kb TGF-beta 1
mRNA, we were unable to detect a previously reported unique 3' UTR, which
we found to be almost identical to a rat mitochondrial ATPase sequence.
Because the 1.4-kb transcript is missing most of the long GC-rich 5' UTR,
it may be translated at a different rate than the 2.5- and 1.9-kb
transcripts, or it may code for an intracellular form of TGF-beta 1. The
1.4-kb transcript has been observed under several conditions of injury or
stress and, therefore, may be an important component of the TGF-beta 1
response to these conditions.