Carcinogenesis Advance Access published online on June 16, 2009
Carcinogenesis, doi:10.1093/carcin/bgp149
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Differential repetitive DNA methylation in Multiple Myeloma molecular subgroups
1 Center of Molecular and Genetic Epidemiology, EPOCA, Epidemiology Research Center, University of Milan & IRCCS Maggiore Hospital, Mangiagalli and Regina Elena Foundation, Milan, Italy
2 Leukemia Study Center, Department of Medical Sciences, University of Milan & Hematology 1-CTMO, IRCCS Maggiore Hospital, Mangiagalli and Regina Elena Foundation, Milan, Italy
* Correspondence to: Professor Antonino Neri, Department of Medical Sciences, University of Milan, Via F. Sforza 35, 20122 Milano, Italy. Phone: +39.02.55033328; Fax: +39.02.50320403, +39.02.55034571. 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 elements-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-PCR 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%5mC), LINE-1 (70.0%5mC) and SAT- (77.9%5mC) methylation levels compared with controls (25.2%5mC, 79.5 %5mC and 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 nonhyperdiploid vs 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 methyltranferases (DNMTs) mRNA 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.
Key Words: fluorescence in situ hybridization • multiple myeloma • repetitive elements methylation • epigenetics • Pyrosequencing
Received April 2, 2009; revised June 3, 2009; accepted June 11, 2009.