Identification of early growth response gene-1 (Egr-1) as a phorbol myristate acetate-induced gene in lung cancer cells by differential mRNA display.

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.