title: Differential repetitive DNA methylation in multiple myeloma molecular subgroups.
abstract: Multiple myeloma (MM) is characterized by a wide spectrum of genetic changes. Global hypomethylation of repetitive genomic sequences such as long interspersed nuclear element 1 (LINE-1), Alu and satellite alpha (SAT-alpha) sequences has been associated with chromosomal instability in cancer. Methylation status of repetitive elements in MM has never been investigated. In the present study, we used a quantitative bisulfite-polymerase chain reaction pyrosequencing method to evaluate the methylation patterns of LINE-1, Alu and SAT-alpha in 23 human myeloma cell lines (HMCLs) and purified bone marrow plasma cells from 53 newly diagnosed MM patients representative of different molecular subtypes, 7 plasma cell leukemias (PCLs) and 11 healthy controls. MMs showed a decrease of Alu [median: 21.1 %5-methylated cytosine (%5mC)], LINE-1 (70.0%5mC) and SAT-alpha (77.9%5mC) methylation levels compared with controls (25.2, 79.5and 89.5%5mC, respectively). Methylation levels were lower in PCLs and HMCLs compared with MMs (16.7 and 14.8%5mC for Alu, 45.5 and 42.4%5mC for LINE-1 and 33.3 and 43.3%5mC for SAT-alpha, respectively). Notably, LINE-1 and SAT-alpha methylation was significantly lower in the non-hyperdiploid versus hyperdiploid MMs (P = 0.01 and 0.02, respectively), whereas Alu and SAT-alpha methylation was significantly lower in MMs with t(4;14) (P = 0.02 and 0.004, respectively). Finally, we correlated methylation patterns with DNA methyltransferases (DNMTs) messenger RNA levels showing in particular a progressive and significant increase of DNMT1 expression from controls to MMs, PCLs and HMCLs (P < 0.001). Our results indicate that global hypomethylation of repetitive elements is significantly associated with tumor progression in MM and may contribute toward a more extensive stratification of the disease.
authors.affiliation: Center of Molecular and Genetic Epidemiology, EPOCA, Epidemiology Research Center, Università degli Studi di Milano and Fondazione IRCCS Ospedale Maggiore Policlinico, Mangiagalli e Regina Elena, 20122 Milan, Italy.
authors.forename: Valentina
authors.initials: V
authors.lastname: Bollati
authors.forename: Sonia
authors.initials: S
authors.lastname: Fabris
authors.forename: Valeria
authors.initials: V
authors.lastname: Pegoraro
authors.forename: Domenica
authors.initials: D
authors.lastname: Ronchetti
authors.forename: Laura
authors.initials: L
authors.lastname: Mosca
authors.forename: Giorgio Lambertenghi
authors.initials: GL
authors.lastname: Deliliers
authors.forename: Valeria
authors.initials: V
authors.lastname: Motta
authors.forename: Pier Alberto
authors.initials: PA
authors.lastname: Bertazzi
authors.forename: Andrea
authors.initials: A
authors.lastname: Baccarelli
authors.forename: Antonino
authors.initials: A
authors.lastname: Neri
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D020087:Alu Elements / Q000235:genetics; D002869:Chromosome Aberrations; D018899:CpG Islands; D000076123:DNA (Cytosine-5-)-Methyltransferase 1; D004248:DNA (Cytosine-5-)-Methyltransferases / Q000235:genetics*; D019175:DNA Methylation; D004273:DNA, Neoplasm / Q000235:genetics*; D004276:DNA, Satellite / Q000235:genetics; D005260:Female; D006801:Humans; D007952:Leukemia, Plasma Cell / Q000235:genetics* / Q000473:pathology; D020084:Long Interspersed Nucleotide Elements / Q000235:genetics; D008297:Male; D008875:Middle Aged; D009101:Multiple Myeloma / Q000145:classification / Q000235:genetics* / Q000473:pathology; D012091:Repetitive Sequences, Nucleic Acid / Q000235:genetics*; D014407:Tumor Cells, Cultured
chemical_list: D004273:DNA, Neoplasm; D004276:DNA, Satellite; D000076123:DNA (Cytosine-5-)-Methyltransferase 1; D004248:DNA (Cytosine-5-)-Methyltransferases; C000619380:DNMT1 protein, human