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 res ponse gene alpha (EGR alpha) was first isolated as a 291-base pair 3'- cDNA clone, which was highly expressed in the androgen-independent pro state carcinoma cell lines PC3 and DU145, as compared with the androge n-responsive prostate carcinoma cell line LNCaP. Full length cloning o f the EGR alpha coding region revealed that EGR alpha was a new member of an important subfamily of nuclear zinc finger transcription factor s (others members e.g. Sp1, EGR-2, and Wilms' tumor gene). Moreover, i t was observed that EGR alpha, 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 alpha mRNA expression. Androgens were observed to induce a down-regulation of EGR alpha mRNA expression (70% in 72 h), while epidermal growth factor induced a rapid transien t 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). Func tional analysis demonstrated that EGR alpha could bind to, and stimula te transcription from, a basic transcription element (BTE) consensus s equence on DNA (BTE is a transcription-modulating sequence in the prom oter region of some cytochrome P450 family members). Furthermore, in s tage-synchronized prostate cells, EGR alpha mRNA was highly expressed in the early G1 phase of the cell cycle, similar to c-fos mRNA express ion. These results indicated that the zinc finger transcription factor EGR alpha seems to play a role in cell cycle regulation.