Carcinogenesis Advance Access originally published online on June 16, 2009
Carcinogenesis 2009 30(8):1330-1335; doi:10.1093/carcin/bgp149
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Differential repetitive DNA methylation in multiple myeloma molecular subgroups
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
1 Leukemia Study Center, Department of Medical Sciences, Università degli Studi di Milano and Hematology 1-CTMO, Fondazione IRCCS Ospedale Maggiore Policlinico, Mangiagalli e Regina Elena, 20122 Milan, Italy
* To whom correspondence should be addressed. Department of Medical Sciences, University of Milan, Via F. Sforza 35, 20122 Milano, Italy. Tel: +39 02 55033328; Fax: +39 02 50320403; Email: antonino.neri{at}unimi.it
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-
) 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- 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- (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-, respectively). Notably, LINE-1 and SAT- methylation was significantly lower in the non-hyperdiploid versus hyperdiploid MMs (P = 0.01 and 0.02, respectively), whereas Alu and SAT- 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.
Abbreviations: DNMT, DNA methyltransferase; HMCL, human myeloma cell line; LINE-1, long interspersed nuclear element 1; PC, plasma cell; PCL, plasma cell leukemia; 5mC, 5 methylcytosine; MM, multiple myeloma; PCR, polymerase chain reaction; SAT-, satellite alpha
Received April 2, 2009; revised June 3, 2009; accepted June 11, 2009.