Cloning, sequencing and expression analysis of a novel gene BR-1 that is expressed in normal human brain tissue but not in glioma tumor samples.

Using the technique of differential hybridization of a human fetal brain library, we identified a novel gene, brain 1 (BR-1). This gene is expressed in normal brain but has low or no expression in human gliomas. We have cloned and sequenced the full-length cDNA corresponding to this gene. A data base search for the nucleotide sequence homology was performed for BR-1. The BR-1 sequence showed strong homology to a human genomic clone from chromosome 2. Moderate sequence homology was observed between BR-1 and an expressed sequence tag (EST) from a human placenta library. Three different regions of BR-1 also showed homology to a mouse EST that is similar to EL-10 gene. Sequence analysis indicated that the protein sequence for BR-1 has one tyrosine kinase phosphorylation site and two N-myristoylation sites. Northern blot analysis indicated that the BR-1 gene is expressed in heart, placenta, lung, liver, skeletal muscle, kidney and pancreas. A low level of expression of BR-1 is observed in the cerebellum, cerebral cortex, spinal cord, occipital lobe and putamen. The BR-1 gene is also expressed in fetal brain, liver and kidney. Low expression of BR-1 gene was observed in a number of non-brain tumor cell lines. RT-PCR analysis indicated that the BR-1 gene was expressed in non-neoplastic (epilepsy specimens) but not in six oligodendrogliomas and three oligoastrocytoma tumor samples analyzed. BR-1 was not expressed in either seven low grade gliomas or eight grade IV glioblastoma tumor tissue samples analyzed. Three glioblastoma cell lines did show low expression of the BR-1 gene. On the basis of its expression properties, we conclude that BR-1 is a potential novel tumor suppressor gene.