Purpose: Lamins support the nuclear envelope and provide anchorage sites for chromatin, but they are also involved in DNA synthesis, transcription, and apoptosis. Although the lack of expression of A-type lamins in lymphoma and leukemia has been reported, the mechanism was unknown. We investigated the possible role of CpG island hypermethylation in lamin A/C silencing and its prognostic relevance.
Patients and methods: The promoter CpG island methylation status of the lamin A/C gene, encoding the A-type lamins, was analyzed by bisulfite genomic sequencing and methylation-specific polymerase chain reaction in human cancer cell lines (n = 74; from 17 tumor types), and primary leukemias (n = 60) and lymphomas (n = 80). Lamin A/C expression was determined by reverse-transcription polymerase chain reaction, Western blot, immunohistochemistry, and immunofluorescence.
Results: seven (50%) of 14 leukemia- and five (42%) of 13 lymphoma cell lines. The presence of hypermethylation was associated with the loss of gene expression while a demethylating agent restored expression. In primary malignancies, lamin A/C hypermethylation was present in 18% (nine of 50) of acute lymphoblastic leukemias and 34% (14 of 41) of nodal diffuse large B-cell lymphomas. The presence of lamin A/C hypermethylation in nodal diffuse large B-cell lymphomas correlated strongly with a decrease in failure-free survival (Kaplan-Meier, P = .0001) and overall survival (Kaplan-Meier, P = .0005).
Conclusion: Epigenetic silencing of the lamin A/C gene by CpG island promoter hypermethylation is responsible for the loss of expression of A-type lamins in leukemias and lymphomas. The finding that lamin A/C hypermethylation is associated with poor outcome in diffuse large B-cell lymphomas suggests important clinical implications.