Global methylation patterns in Primary Plasma Cell leukemia

Primary plasma cell leukemia (pPCL) is a rare and aggressive variant of multiple myeloma (MM), which is associated with a very poor prognosis. Specific molecular patterns distinguish pPCL in comparison to MM and in relation to main genomic alterations. In the present study, a whole-genome methylation profiling analysis by high-density array revealed a global gene hypomethylation profile in pPCL. Lower methylation levels were particularly observed in the promoter and 5’ untranslated regions (5’UTR), whereas higher levels were evidenced in gene body or 3’ untranslated regions (3’UTR). CpG islands (CGI) resulted largely hypomethylated, whereas higher methylation levels were observed in CGI distal regions. Peculiar differential methylation patterns were identified in association to major chromosomal aberrations and DIS3 mutational status and involved genes playing roles in cell migration, bone metabolism, transcription regulation or DNA damage response. Finally, decreasing methylation levels were evidenced for few genes in association to MM disease progression, from healthy condition to MM and pPCL. Our data may provide new insights into the molecular characterization of pPCL patients, thus being potentially useful in the prognostic stratification or identification of novel molecular targets. Bisulphite converted DNA from the 14 samples were hybridised to the Illumina Infinium HumanMethylation450 BeadChip array (Illumina Inc., San Diego, CA, USA)