Poster Presenter

Bradeion Project: Monitoring and Targeting of Cancer Characterization of Tissue - and Cell Type-Specific Expression of a Novel Human Septin Family Gene Bradeion
Tanaka M., Kijima H., Matsuda, H., Komori, K., Hori S, Yamamoto M. Tanaka T.
Japan

Expression changes in subsets of genes occur in the course of altering cell fates, i.e., ageing, cell death, and carcinogenesis.These changes simultaneously provide the good candidate as a biomarker for monitoring cancer. We have identified a novel human septin family gene Bradeion from adult brain cDNA library by a monoclonal antibody CE5 (1). Northern blot and in situ hybridization analysis showed that Bradeion has two distinct transcripts, approximately 2.2 and 1.7 kb length (α and β, respectively) mainly in brain and slightly in heart, and no expression in any fetal organs. Haplotype analysis placed the gene located at 17q23. The gene contains GTPase motifs highly conserved in the septin family genes that are essential for cytokinesis and cell separation. The transcript of β, form lacks a hydrophobic region, which suggests that this form arises from a single Bradeion gene through unique RNA splicing. Interestingly, this brain-specific gene Bradeion is also expressed in two human cancers, colorectal cancer and malignant melanoma. Ectopic expression of normal Bradeion alpha and beta, transcripts were confirmed both in patients' tumor samples and in in vitro cultured human cancer cell lines. Thus the Bradeion provides valuable tools as a tumor-specific and selective marker.

In addition, impaired expression of a human septin family gene Bradeion inhibits the growth and tumorigenesis of colorectal cancer in vitro and in vivo. In order to analyze the implications of tumor-specific gene expression, ribozymes and its derivatives were specifically designed and transfected into various colorectal adenocarcinoma cell lines for Bradeion-inactivation. We constructed ribozyme-expression plasmids controlled by a human tRNAVal promoter, and both hammerhead ribozyme and its allosteric derivaticve maxizyme were used for two different forms of Bradeion mRNAs. The sequence-specific cleavage of Bradeion mRNAs resulted in the significant growth inhibition and G2 arrest in human cancer cell lines, detected by flow cytometry analysis. In addition, in vivo mice studies demonstrated marked tumor growth suppression by the Bradeion-specific ribozymes. Thus the tumor-specific and selective marker Bradeion also provides valuable tools as a target for colorectal cancer.