title: DNA methylation and expression of LINE-1 and HERV-K provirus sequences in urothelial and renal cell carcinomas.
abstract: Since DNA methylation is considered an important mechanism for silencing of retroelements in the mammalian genome, hypomethylation in human tumours may lead to their reactivation. The methylation status of LINE-1 retroposons was determined in 73 samples of urinary bladder cancers, 34 specimens of renal cell carcinoma and in the corresponding normal tissues by Southern blot analysis. LINE-1 sequences were strongly methylated in normal tissues and were significantly hypomethylated in 69 (95%) urothelial carcinomas, but in none of the renal carcinomas. Hypomethylation in bladder cancers was independent of stage and tended to increase with grade. The methylation status of HERV-K proviral DNA in normal and transformed urothelial cells paralleled that of LINE-1 sequences (r2 = 0.87). It was shown by ligation-mediated polymerase chain reaction that hypomethylation also extended to the LINE-1 promoter sequence located at the 5'-ends of full-length elements which is repressed by methylation in somatic tissues. Accordingly, full-length LINE-1 transcripts were detected by Northern blot analysis in two urothelial carcinoma cell lines. In contrast, transcripts from HERV-K proviruses were restricted to teratocarcinoma cell lines. Our data indicate that genome-wide DNA hypomethylation is an early change in urothelial carcinoma, but is absent from renal cell carcinoma. The coordinate changes of LINE-1 and HERV-K DNA methylation suggest that hypomethylation in urothelial cancer affects a variety of different retroelements to similar extents. We speculate that decreased methylation of LINE-1 retroelements, in particular, may contribute to genomic instability in specific human tumours such as urothelial carcinoma by rendering these normally repressed sequences competent for transcription and recombination.
authors.affiliation: Urologische Klinik, Heinrich-Heine-Universität, Düsseldorf, Germany.
authors.forename: A R
authors.initials: AR
authors.lastname: Florl
authors.forename: R
authors.initials: R
authors.lastname: Löwer
authors.forename: B J
authors.initials: BJ
authors.lastname: Schmitz-Dräger
authors.forename: W A
authors.initials: WA
authors.lastname: Schulz
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002292:Carcinoma, Renal Cell / Q000235:genetics* / Q000821:virology; D019175:DNA Methylation; D004279:DNA, Viral / Q000378:metabolism*; D020077:Endogenous Retroviruses / Q000235:genetics*; D005260:Female; D006801:Humans; D007680:Kidney Neoplasms / Q000235:genetics* / Q000821:virology; D008297:Male; D008875:Middle Aged; D016133:Polymerase Chain Reaction; D011533:Proviruses / Q000235:genetics*; D018626:Retroelements; D014407:Tumor Cells, Cultured; D001749:Urinary Bladder Neoplasms / Q000235:genetics* / Q000821:virology
chemical_list: D004279:DNA, Viral; D018626:Retroelements