SLC5A8, a sodium transporter, is a tumor suppressor gene silenced by methylation in human colon aberrant crypt foci and cancers.
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.
Li
Hui
H
Ireland Cancer Center, Department of Medicine, and Research Institute, University Hospitals of Cleveland and Case Western Reserve University, Cleveland, OH 44106, USA.
Myeroff
Lois
L
Smiraglia
Dominic
D
Romero
Michael F
MF
Pretlow
Theresa P
TP
Kasturi
Lakshmi
L
Lutterbaugh
James
J
Rerko
Ronald M
RM
Casey
Graham
G
Issa
Jean-Pierre
JP
Willis
Joseph
J
Willson
James K V
JK
Plass
Christoph
C
Markowitz
Sanford D
SD
D000230:Adenocarcinoma / Q000235:genetics*; D000236:Adenoma / Q000235:genetics*; D001374:Azacitidine / Q000494:pharmacology; D001483:Base Sequence; D027682:Cation Transport Proteins / Q000235:genetics / Q000502:physiology; D003110:Colonic Neoplasms / Q000235:genetics*; D019175:DNA Methylation / Q000187:drug effects; D004273:DNA, Neoplasm / Q000235:genetics; D005091:Exons / Q000235:genetics; D020868:Gene Silencing / Q000187:drug effects; D016147:Genes, Tumor Suppressor; D006801:Humans; D007413:Intestinal Mucosa / Q000378:metabolism* / Q000473:pathology; D017136:Ion Transport; D008969:Molecular Sequence Data; D027501:Monocarboxylic Acid Transporters; D011993:Recombinant Fusion Proteins / Q000502:physiology; D012964:Sodium / Q000378:metabolism; D014162:Transfection; D014407:Tumor Cells, Cultured / Q000737:chemistry / Q000187:drug effects; D014410:Tumor Stem Cell Assay
D027682:Cation Transport Proteins; D004273:DNA, Neoplasm; D027501:Monocarboxylic Acid Transporters; D011993:Recombinant Fusion Proteins; C476760:SLC5A8 protein, human; D012964:Sodium; D001374:Azacitidine