SPATIAL ORGANIZATION OF LAMIN A/C IN HODGKIN’S LYMPHOMA AND MULTIPLE MYELOMA

Genomic Instability is a complex phenomenon observed both at the DNA and the chromosome level. It is responsible for the generation of mutations and chromosomal rearrangements, which can potentially lead to tumor development. A common genomic instability feature found in some malignant tumors is the shortening of the telomeres, the end of the chromosomes. Shortening of telomeres leads to the formation of anaphase bridges, subsequent breakage and initiation new breakage-bridge-fusion (BFB) cycles. Classical Hodgkin’s lymphoma (cHL) and Multiple Myeloma (MM) are two blood tumor both characterized by genomic instability. cHL is a B-Cell lymphoma comprised of mononuclear Hodgkin cells (H) and bi- to multi-nucleated Reed-Sternberg (RS) cells, both characterized by numerical (nCIN) and structural chromosomal instability (sCIN). Transition from H to RS cells is correlated with aberrant number of mitotic spindles, aberrant 3D telomere organization, increase in the number of telomere aggregates and telomere loss. Advanced shortening of telomeres leads disruption of 3D interaction of the telomere with TRF2, a member of the shelterin proteins responsible for the protection of the chromosome ends from the DNA damage repair system. MM, an incurable plasma cell disorder, is also characterized by CIN, microsatellite instability (MSI), and telomere attrition. Lamin A/C, a nuclear envelope protein and component of the nuclear matrix, is important for the assembly of the mitotic spindles and for the maintenance of the 3D telomeres architecture by binding the shelterin protein TRF2. Due to lamin A/C involvement in the maintenance of genomic stability, our goal was to investigate lamin A/C 3D spatial organization in cHL and MM, and understand whether the localized uncapping of TRF2 from telomeres leads to their detachment from the nuclear matrix component lamin A/C causing genomic instability. Western blot analysis and qRT-PCR analysis revealed that H and RS are characterized by an overall overexpression of lamin A/C when compared to the B-lymphocytes control. Three dimensional (3D) fluorescent microscopy in cHL and MM cells revealed that the regular homogeneous lamin A/C pattern identified in normal activated B-lymphocytes, was replaced by an aberrant lamin A/C 3D spatial distribution characterized by the presence of internal lamin A/C structures. Different lamin A/C patterns where observed where the internal lamin A/C sub-divided the nucleus in to two or multiple compartments, suggesting a possible involvement of lamin A/C in the multi-nucleation process. To investigate lamin A/C involvement in the multinucleation process and transition from H to RS, the downregulation of lamin A/C with siRNA was performed. Downregulation of lamin A/C affected the transition from H to RS cells, as the number of RS cells found after lamin silencing was decreased. Telomere 3D structure and nuclear organization were also affected by the deregulation of lamin A/C. H and RS cells were also characterized by unbinding of telomere-TRF2-lamin A/C when compared to the healthy control. Lack of co-localization of telomere-TRF2-lamin A/C confirms lamin A/C involvement in genomic instability, and suggests that localized absence of TRF2 could be causal to the genome remodeling in cHL.