| dc.description.abstract | Lamin B1 is a fundamental component of the nuclear meshwork, which regulates diverse cellular processes, including the stabilisation of the nucleus, chromatin organization, and gene regulation. More recent studies revealed that Lamin B1 is involved in the regulation of DNA damage repair and mutagenesis. In B cells, Lamin B1 epigenetically controls somatic hypermutagenesis in the immunoglobulin variable gene (IgV). Furthermore, decreased Lamin B1 is associated with a genomic instability signature and inferior survival of chronic lymphocytic leukaemia (CLL) patients. Despite the recent findings, the role of Lamin B1 in normal germinal centre (GC) B cells and malignant counterparts remains poorly understood. The principal analysis of the whole exome sequencing data revealed a transient Lamin B1 knockdown in lymphoma cells induces de novo mutational clustering outside of the IgV region. Doxycycline-inducible shRNA mediated Lamin B1 knockdown in vitro lymphoma models demonstrated that the removal of Lamin B1 from the nuclear periphery leads to the spontaneous double-strand breaks (DSBs) and elevated localisation of 53BP1, a mediator of the non-homologous end joining (NHEJ) pathway. Lamin B1 depletion was accompanied by increased cell proliferation and altered transcriptional landscape in BL2 cells. To complement the in vitro findings, a GC B cell-specific Lamin B1 knockout (Lamin B1fl/flCγ1cre/+) mouse model revealed that Lamin B1 depleted GC B cells undergo increased DNA damage without the impairment of humoral immune response. Interestingly, an increase of GC B cells and plasmablasts cells was observed in Lamin B1fl/flCγ1cre/+ mice 21 days after immunisation. The sBLISS (in situ labelling and sequencing) identified DSBs hotspots were enriched around transcriptional start sites of highly expressed genes in Lamin B1 depleted B cells and colocalised with genes mutated in lymphoma. A high proportion of DSB locations in mouse GC B cells contained a DNA sequence motif associated with activation-induced deaminase (AID) mutational signature, suggesting the open chromatin is susceptible to AID-mediated DSBs. Contrary to the findings from the functional studies, high Lamin B1 expression correlates with γH2AX in tissues from diffuse large B cell lymphoma (DLBCL) patients. Clinicopathological analysis of Lamin B1 demonstrated that decreased Lamin B1 expression associates with the advanced diagnostic stages and inferior progression-free survival, particularly in DLBCL patients. this study provides further evidence of Lamin B1’s involvment in the maintenance of genomic stability in B cells and has potential clinical applications in B cell-derived lymphomas. | en_US |
