Characterization of an early growth response gene, which encodes a zinc finger transcription factor, potentially involved in cell cycle regulation

Using differential display polymerase chain reaction, early growth response gene α (EGR α) was first isolated as a 291-base pair 3'-cDNA clone, which was highly expressed in the androgen-independent prostate carcinoma cell lines PC3 and DU145, as compared with the androgen-responsive prostate carcinoma cell line LNCaP. Full length cloning of the EGR α coding region revealed that EGR α was a new member of an important subfamily of nuclear zinc finger transcription factors (others members e.g. Sp1, EGR-2, and Wilms' tumor gene). Moreover, it was observed that EGR α, as with most Sp1 subfamily members, was conserved between mammalian species ranging from human to rabbit. Two hormones important for prostate development and differentiation were found to be potent regulators of EGR α mRNA expression. Androgens were observed to induce a down-regulation of EGR α mRNA expression (70% in 72 h), while epidermal growth factor induced a rapid transient up-regulation (6-fold in 100 min). The up-regulation was controlled at the transcriptional level and effectively blocked by staurosporine (which suggests the involvement of the protein kinase C pathway). Functional analysis demonstrated that EGR α could bind to, and stimulate transcription from, a basic transcription element (BTE) consensus sequence on DNA (BTE is a transcription-modulating sequence in the promoter region of some cytochrome P450 family members). Furthermore, in stage-synchronized prostate cells, EGR α mRNA was highly expressed in the early G1 phase of the cell cycle, similar to c-fos mRNA expression. These results indicated that the zinc finger transcription factor EGR α seems to play a role in cell cycle regulation.