OASIS is a transcriptional activator of CREB/ATF family with a transmembrane domain

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Abstract

Murine OASIS is a putative CREB/ATF family transcription factor that is induced in gliosis, but its molecular role has not been determined. We have isolated the human OASIS gene and investigated the potential of OASIS protein as a transcriptional activator. We found that OASIS can activate transcription through box-B elements but not through the somatostatin CRE. OASIS contains a putative C-terminal hydrophobic transmembrane domain, a typical structural feature for the transcription factors activated by regulated intramembrane proteolysis. Truncation of the OASIS transmembrane domain resulted in a significant increase in transcriptional activity and altered its subcellular localization from the endoplasmic reticulum to the nucleus. Western blot analysis of transfected cells identified OASIS polypeptides of 82 and 66 kDa. These results suggest that the transmembrane domain plays an important role in the regulation of transcriptional activation by OASIS.

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Materials and methods

Plasmids. pME18S, an SR α-driven expression plasmid (GenBank accession number AB009864), the luciferase reporter plasmid pbox-B-Luc, and pEF/Gal4-VP16 have been described previously [10].

pME-OASIS was constructed by inserting an EcoRI–NotI fragment from IMAGE clone #2621090 and an NotI–SalI fragment from IMAGE clone #2556940 between the EcoRI and XhoI sites of pME18S. Expression plasmids were generated using pME18SFLAG, which was constructed by inserting a DNA sequence encoding the FLAG epitope

Results

Through an EST homology search using the murine OASIS sequence (GenBank accession number AB017614), we obtained overlapping EST clones containing the human counterpart of OASIS. Nucleotide sequence analysis identified an open reading frame (ORF) encoding a full-length protein of 519 amino acids (Fig. 1A; GenBank accession number AB063321). The predicted amino acid sequence is 84.8% identical to that of murine OASIS. We also obtained a splice variant encoding 431 amino acids; this variant lacked

Discussion

OASIS expression patterns in gliosis correlate with those of GFAP [3], which is generally recognized as a marker of gliosis. Expression levels of various extracellular matrix components, cytokines, and growth factors also correlate with the increase in GFAP [19], [20], [21], [22]. We found that OASIS functioned as a transcriptional activator through binding to the box-B element (Fig. 4A) and showed higher activation levels through the box-B element relative to the other CRE-like elements (Fig. 5

Acknowledgements

This work was supported by Grants-in-Aid for Scientific Research on Priority Areas from the Ministry of Education, Science, Sports, and Culture of Japan, and by Special Coordination Funds for Promoting Science and Technology from the Science and Technology Agency of Japan. We thank K. Nakagawa, H. Hata, and K. Kataoka for helpful suggestions on experimental procedures.

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