Am. J. Respir. Cell Mol. Biol., Vol 17, No. 5, 11 1997, 617-624.
Identification of early growth response gene-1 (Egr-1) as a phorbol myristate acetate-induced gene in lung cancer cells by differential mRNA display
L You and SB Jakowlew
National Cancer Institute, Medicine Branch, Rockville, Maryland 20850, USA.
Cellular regulatory genes including transcription factors may play an
important role in the induction, maintenance, and progression of lung
cancer. These regulatory genes are inducible by various mitogenic stimuli
including phorbol myristate acetate (PMA). The differential mRNA display
method was used to identify potential early response genes regulated by PMA
in non-small cell lung cancer (NSCLC) cell lines. Using this technique,
several cDNA fragments were found to be potentially differentially
regulated by PMA in the squamous NSCLC cell line NCI-H157. One of these
cDNA fragments of approximately 100 bp was determined to be differentially
induced by at least 30-fold by PMA by northern blot analysis and to
hybridize to a single 3.4 kb mRNA species. This cDNA fragment was cloned,
sequenced, and identified to be identical to a portion of the
3'-untranslated region of the human early growth response gene-1 (Egr-1).
Using Egr-1 cDNA as a probe, it was demonstrated that PMA induces Egr-1
mRNA expression in at least three other NSCLC cells as well. In addition,
PMA caused a transient increase in expression of the Egr-1 transcript
reaching a maximum level by 1 h before decreasing in NCI-H157 and three
other types of NSCLC cells. Treatment of these NSCLC cells with TGF-beta1
showed a transient increase in Egr-1 mRNA similar to PMA which also reached
a maximum level after 1 h. Normal human bronchial epithelial (NHBE) cells
also showed a rapid, transient increase in expression of Egr-1 mRNA after
treatment with PMA. In contrast, treatment of NHBE cells with TGF-beta1
showed that expression of Egr-1 mRNA increased by 1 h but reached a maximum
level only after 6 h. These results indicate that both PMA and TGF-beta1
can induce Egr- mRNA expression in NSCLC cells and NHBE cells; however,
while PMA induces Egr-1 mRNA similarly in both cell types, TGF-beta1
induces Egr-1 mRNA expression more rapidly and more transiently in NSCLC
cells than in NHBE cells. Our results suggest that Egr-1 may play different
roles in response to mitogens in normal and malignant lung cells.
