Up-regulated expression of a novel gene in activated human peripheral blood mononuclear cells that is a truncated paralog of the human system L-amino acid transporter 1.

INTRODUCTION AND AIMS:The human system L-amino acid transporter1 (hLAT1) is one of the CD98 light chains and its gene has been mapped to chromosome 16q24. Our preliminary findings have indicated that in HeLa S3 cells there are transcripts whose nucleotide sequences are very similar but not identical to that of the amino acid transporter. This study intends to examine whether these novel transcripts have biological significance through elucidating their genetic aspects and expression profiles in human cells. METHODS:The expression levels of the transcripts were quantified by real-time PCR analysis. Chromosomal mapping of the gene was performed by fluorescence in situ hybridization (FISH). RESULTS:Three types of transcripts were identified and their nucleotide sequences were aligned with the chromosome 16p12 clone with high identity. They encoded 180- or 190-amino acid proteins, showing 92-94% of amino acid identity to the amino-terminal region of the hLAT1 (507 amino acids). However, their 3' non-coding sequences did not show homology to the nucleotide sequence of the amino acid transporter. Their genes were mapped to chromosome 16p11.2-p13.1 as low-copy repeats (LCRs). The transcription of one of these genes in peripheral blood mononuclear cells was significantly up-regulated when the cells were stimulated with concanavalin A. CONCLUSION:We have characterized the three truncated paralogs of the hLAT1 gene. It is suggested that the expression of one of these paralogs may play an important role in the activation of peripheral blood mononuclear cells.

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