A novel homeobox gene overexpressed in thyroid carcinoma

Serial analysis of gene expression (SAGE) was applied to compare expression profiles of normal thyroid tissue and papillary thyroid carcinoma (PTC). A SAGE tag corresponding to the partial cDNA for the small protein 31 (SMAP31) is upregulated approximately 13-fold in papillary thyroid cancer (PTC) and was selected for further research. BLAST-searching the human genome database reveals that the SMAP31 gene is located on chromosome 4q11-12 and contains 6 exons. Alternative splicing results in seven transcripts encoding 2 possible open reading frames (ORF) of 73 and 95 amino acids. Database searching in GenBank's dbEST shows that SMAP31 transcripts are expressed mainly in brain, heart, gingiva, and lung tissue. Thyroid tissue contains three transcripts caused by alternatively splicing in the 5' untranslated region (UTR), which all encode an identical ORF of 73 amino acids. Homology search shows that this protein contains a homeobox domain. Thyroid and/or thyroid carcinoma-specific expression of SMAP31 is studied using Northern blot and reverse transcriptase-polymerase chain reaction (RT-PCR) on a multiple tissue panel. RT-PCR experiments on a cDNA panel containing samples from different normal and tumor tissues shows expression of SMAP31 mRNA in brain, placenta, lung, heart, thyroid and thyroid carcinoma. SMAP31 expression is elevated in 4 of 6 PTC tumor samples compared to 4 normal thyroid controls.