Mitogen regulated induction of FRA-1 proto-oncogene is controlled by the transcription factors binding to both serum and TPA response elements

Abstract

FRA-1, a member of the FOS family of transcription factors, is overexpressed in a variety of human tumors, and contributes to tumor progression. In addition to mitogens, various toxicants and carcinogens persistently induce FRA-1 expression in vitro and in vivo. Although the mitogen induced expression of c-FOS is relatively well understood, it is poorly defined in the case of FRA-1. Our recent analysis of the FRA-1 promoter has shown a critical role for a TRE located at À318 in mediating the TPA-induced expression. The À379 to À283 bp promoter segment containing a critical TRE (À318), however, is insufficient for the induction of FRA-1 promoter. Here, we show that a 40-bp (À276/À237) segment, comprising a TCF binding site and the CArG box (collectively known as serum response element, SRE), and an ATF site, is also necessary for the FRA-1 induction by TPA and EGF. Interestingly, the À283 to þ 32 bp FRA-1 promoter fragment containing an SRE and an ATF site alone was also insufficient to confer TPA sensitivity to a reporter gene. However, in association with the À318 TRE, the SRE and ATF sites imparted a strong TPA-inducibility to the reporter. Similarly, EGF also required these motifs for the full induction of this gene. Using ChIP assays we show that, in contrast to c-Jun, SRF, Elk1, ATF1 and CREB proteins bind to SRE and ATF sites of the FRA-1 promoter, constitutively. RNAi-mediated knockdown of endogenous SRF, ELK1 and c-JUN protein expression significantly reduced TPA-stimulated FRA-1 promoter activity. Thus, a bipartite enhancer formed by an upstream TRE and the downstream SRE and ATF sites and the cognate factors is necessary and sufficient for the regulation of FRA-1 in response to mitogens.

FRA-1 Proto-Oncogene Induces Lung Epithelial Cell Invasion and Anchorage-Independent Growth In vitro, but Is Insufficient to Promote Tumor Growth In vivo

“…We have recently shown that FRA-1 up-regulates the expression of genes involved in airway squamous metaplasia (8). The expression of FRA-1 is persistently induced in bronchial epithelial cells by lung carcinogens such as tobacco smoke (9), tumor-promoting phorbol esters, and mitogens (10,11). Consistent with these observations, overexpression of FRA-1 has been noted in squamous cell carcinomas of the head and neck (12), esophagus, and stomach (13).…”

“…The results of assays measuring three-dimensional Matrigel migration and invasion and soft agar growth revealed that FRA-1 overexpression greatly enhances both the growth and invasive potential of lung epithelial cells. We have previously shown that various agents that promote tumor cell growth and invasion persistently activate FRA-1 expression in pulmonary (type II and bronchial) epithelial cells (9)(10)(11)20). Thus, the present findings are important in that the activation of this transcription factor by mitogens and carcinogens plays key roles in promoting cell growth, malignant transformation, and invasive potential of pulmonary epithelial cells.…”

“…To mimic the persistent expression of FRA-1 and to define its role in lung cancer cell growth, motility and invasion, we stably transfected the human adenocarcinoma cell line A549 with a FRA1-expression vector (16). We have previously shown that the endogenous FRA-1 expression is low in A549 cells but is strongly induced by mitogens, oxidants, cytokines, and carcinogens (9)(10)(11)20). Stable cell clones overexpressing FRA-1 (referred to as A549-F1 cells) or a control empty vector (termed A549-C) were isolated following selection with G418, pooled, and used for subsequent gene expression and functional studies.…”

The Activator Protein-1 Transcription Factor in Respiratory Epithelium Carcinogenesis

“…Nevertheless, recent data point to a positive effect of Fra-1, and partly Fra-2, on tumor invasion and progression in many tumor types (110,111). Moreover, a model was proposed in which both Fra-1 and c-Fos act as adaptors for other transcription factors, or as transcriptional repressors rather than transcriptional activators (112).…”

“…114). Yet, most data concerning the function of Fra-1 in respiratory epithelium carcinogenesis are based on experimental results, and the role of these transcription factors in clinical tumors is still obscure (110). In most of the tumor tissues analyzed thus far, Fra-1 expression has been found far below the protein amounts detected in undifferentiated cell lines, and the electrophoretic mobility of the Fra-1 protein indicates that it is not highly phosphorylated, which might lead to its stabilization and in vitro activation (40).…”