AUF1‐like protein binds specifically to DAS cis‐acting element that regulates mouse α‐fetoprotein gene expression

Abstract

Alpha-fetoprotein (AFP) is one of the major serum proteins in the early life of mammals. We have previously identified a novel cis-acting element designated as DAS at the 5'-flanking region of the AFP gene and demonstrated that the DAS sequence can be specifically recognized by nuclear protein DAP-II in AFP-producing hepatoma cells and retinoic acid (RA)-induced AFP-producing F9 cells. In this study, we used DNA affinity chromatography to purify the DAP-II proteins from the nuclear extracts (NE) of RA-treated F9 cells. The purified DAP-II complex mainly contained five proteins, with molecular weights of 45, 42, 32, 30, and 20 kDa, respectively. The identification of these proteins was determined by MALDI-TOF mass spectrometric analysis and a database search. These proteins were found to belong to the AUF1 RNA-binding protein family. Protein (30 kDa), one of five proteins in an isolated DAP-II complex, was matched with amino acid sequence highly similar to muAUF1-3. The expression of this protein is inducible by RA, and the pattern of the protein expression is the same as DAP-II proteins in F9 cells after treatment with RA during differentiation. Our results suggest that the 30-kDa protein is a novel isoform of AUF1 family and is the main component of the DAP-II complex that binds to the DAS sequence.

Similar Regulation of Human Inducible Nitric-oxide Synthase Expression by Different Isoforms of the RNA-binding Protein AUF1

“…3). In addition to its role in mRNA decay AUF1 may also participate in transcriptional processes (28,29,40,45). Therefore, we tested if AUF1 reduces iNOS expression by transcriptional repression.…”

“…Activity-Besides its post-transcriptional effects, AUF1 has been described to regulate the promoter activity of genes like ␣-fetoprotein or enkephalin by binding to AT-rich DNA sequences (28,29,40). Therefore, we investigated if the AUF1 isoforms mediate their effect on iNOS expression by modulation of human iNOS promoter activity.…”

“…Furthermore, some evidence exists that the individual AUF1 isoforms exert different effects in the regulation of mRNA stability depending on their expressional level (25)(26)(27). In addition to these post-transcriptional effects, also AUF1-dependent transcriptional regulation mechanisms have been published (28,29).…”

Modulation of neoplastic gene regulatory pathways by the RNA-binding factor AUF1

“…For example, p40 AUF1 can bind and activate transcription from the complement receptor 2 gene promoter (38), and in complex with nucleolin forms the B cell-specific transcription factor LR1 (39). Furthermore, multiple AUF1 isoforms have been shown to regulate transcription of the enkephalin gene in developing brain (40), and the α-fetoprotein gene (41), which encodes an onco-developmental protein that can be re-activated during liver regeneration or cancer (42). …”