SLC5A8 , a sodium transporter, is a tumor suppressor gene silenced by methylation in human colon aberrant crypt foci and cancers

doi:10.1073/pnas.1430846100

SLC5A8, a sodium transporter, is a tumor suppressor gene silenced by methylation in human colon aberrant crypt foci and cancers

^*Cancer Center and Department of Medicine, and Ireland Cancer Center, Department of Medicine, and Research Institute, University Hospitals of Cleveland and Case Western Reserve University, Cleveland, OH 44106; ^†Departments of Molecular Biology and Microbiology, and ^§Physiology and Biophysics, and ^¶Department of Pathology and Cancer Center, Case Western Reserve University, Cleveland, OH 44106; ^‡Division of Human Cancer Genetics, Ohio State University, Columbus, OH 43210; ^∥Howard Hughes Medical Institute, Cleveland, OH 44106; ^**Lerner Research Institute, Cleveland Clinic Foundation, Cleveland, OH 44195; ^††Department of Leukemia, University of Texas M. D. Anderson Cancer Center, Houston, TX 77030; and ^‡‡Department of Pathology and Ireland Cancer Center, University Hospitals of Cleveland and Case Western Reserve University, Cleveland, OH 44106

Edited by Peter K. Vogt, The Scripps Research Institute, La Jolla, CA (received for review February 12, 2003)

Abstract

We identify a gene, SLC5A8, and show it is a candidate tumor suppressor gene whose silencing by aberrant methylation is a common and early event in human colon neoplasia. Aberrant DNA methylation has been implicated as a component of an epigenetic mechanism that silences genes in human cancers. Using restriction landmark genome scanning, we performed a global search to identify genes that would be aberrantly methylated at high frequency in human colon cancer. From among 1,231 genomic NotI sites assayed, site 3D41 was identified as methylated in 11 of 12 colon cancers profiled. Site 3D41 mapped to exon 1 of SLC5A8, a transcript that we assembled. In normal colon mucosa we found that SLC5A8 exon 1 is unmethylated and SLC5A8 transcript is expressed. In contrast, SLC5A8 exon 1 proved to be aberrantly methylated in 59% of primary colon cancers and 52% of colon cancer cell lines. SLC5A8 exon 1 methylated cells were uniformly silenced for SLC5A8 expression, but reactivated expression on treatment with a demethylating drug, 5-azacytidine. Transfection of SLC5A8 suppressed colony growth in each of three SLC5A8-deficient cell lines, but showed no suppressive effect in any of three SLC5A8-proficient cell lines. SLC5A8 exon 1 methylation is an early event, detectable in colon adenomas, and in even earlier microscopic colonic aberrant crypt foci. Structural homology and functional testing demonstrated that SLC5A8 is a member of the family of sodium solute symporters, which are now added as a class of candidate colon cancer suppressor genes.

colon cancer

Footnotes

↵ §§ To whom correspondence should be addressed. E-mail: sxm10{at}po.cwru.edu.
This paper was submitted directly (Track II) to the PNAS office.
Abbreviations: ACF, aberrant crypt foci; MS, methylation-specific; RLGS, restriction landmark genome scanning.
Data deposition: The sequences reported in this paper have been deposited in the GenBank database [accession nos. AF536216 (human SLC5A8 mRNA) and AF536217 (gene sequence)].