Cancer-associated alternative usage of multiple promoters of human GalCer sulfotransferase gene

Abstract

The galactosylceramide sulfotransferase (cerebroside sulfotransferase, CST) (EC 2.8.2.11) gene is highly expressed in human renal cancer cells. To elucidate the regulatory mechanism of its gene expression, we have determined the genomic organization of the human CST gene. The gene comprises at least four exons and spans about 20 kb. The coding region is located in exons 3 and 4. To determine the transcription initiation sites, 5'-rapid amplification of cDNA ends analysis was performed using mRNA obtained from four human renal cancer cell lines, SMKT-R1-R4, and normal human renal proximal tubular cells. We found four transcription initiation sites and alternative usage of six exons corresponding to the 5'-untranslated region in cancer cells. On the other hand, the only transcript beginning at exon 1a was observed in normal cells. Using reverse transcriptase-PCR analysis, we confirmed that all of the exons 1a-d, especially exons 1c and 1d, are used as a transcription initiation site in cancer cells, whereas only exons 1a and 1b, mostly 1a, are utilized in normal cells. Analyzing the protein production from the mRNA variants with different 5'-UTRs, we found that all the transcripts examined produced the identical proteins. These observations suggest that the aberrant usage of transcription initiation sites flanked with promoters/enhancers is involved in the cancer-associated expression of the CST gene. Furthermore, this gene was assigned to human chromosome 22q12 by means of fluorescence in situ hybridization.