title: RB1 gene in Merkel cell carcinoma: hypermethylation in all tumors and concurrent heterozygous deletions in the polyomavirus-negative subgroup.
abstract: Sequestration of the tumor suppressor retinoblastoma protein (RB) by the Merkel cell polyomavirus (MCV) is a crucial step in the pathogenesis of Merkel cell carcinoma (MCC). RB expression is frequently lost, particularly in MCV-negative MCC tumors, through yet unknown mechanisms. We compared the genomic copy number changes of 13 MCV-positive and 13 -negative MCC tumors by array comparative genomic hybridization. The analysis revealed increased genomic instability, amplification of 1p34.3-1p34.2, and losses of 11p in the absence of MCV infection. Deletions of the RB1 locus were also detected at high rates in MCV-negative tumors. None of the tumors with heterozygous RB1 losses expressed RB in immunohistochemistry. RB1 promoter hypermethylation was studied with a methylation-specific multiplex ligation-dependent probe amplification technique. The RB1 promoter was methylated in all tumor specimens at CpG islands located close to the ATG start codon, albeit at low levels. The pattern of hypermethylation was similar in all MCC samples, despite RB expression, survival or MCV status. In conclusion, the frequent heterozygous losses of the RB1 locus could partly explain the decreased RB expression in MCV-negative MCC tumors, although the effects of RB1 mutations, coinciding promoter hypermethylation and, for example, miRNA regulation, cannot be excluded.
authors.affiliation: Department of Pathology, Helsinki University and HUSLAB, Helsinki, Finland; Department of Plastic Surgery, Helsinki University Hospital, Helsinki, Finland.
authors.forename: Helka
authors.initials: H
authors.lastname: Sahi
authors.forename: Suvi
authors.initials: S
authors.lastname: Savola
authors.forename: Harri
authors.initials: H
authors.lastname: Sihto
authors.forename: Virve
authors.initials: V
authors.lastname: Koljonen
authors.forename: Tom
authors.initials: T
authors.lastname: Bohling
authors.forename: Sakari
authors.initials: S
authors.lastname: Knuutila
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D015266:Carcinoma, Merkel Cell / Q000235:genetics* / Q000473:pathology / Q000821:virology; D055028:Comparative Genomic Hybridization; D056915:DNA Copy Number Variations; D019175:DNA Methylation; D005260:Female; D017353:Gene Deletion; D015972:Gene Expression Regulation, Neoplastic; D056426:Genetic Loci; D006801:Humans; D008297:Male; D008875:Middle Aged; D011120:Polyomavirus / Q000302:isolation & purification; D011401:Promoter Regions, Genetic; D016160:Retinoblastoma Protein / Q000235:genetics* / Q000378:metabolism; D025521:Tumor Suppressor Proteins / Q000235:genetics* / Q000378:metabolism
chemical_list: D016160:Retinoblastoma Protein; D025521:Tumor Suppressor Proteins
keywords: Merkel cell carcinoma; Merkel cell polyomavirus; array comparative genomic hybridization; hypermethylation; retinoblastoma gene; retinoblastoma protein