Investigating the Expression of D-type Cyclins in Diffuse Large B-cell Lymphoma (DLBCL)

Diffuse Large B-cell Lymphoma (DLBCL) is a highly aggressive and highly heterogenous cancer which varies dramatically in response to treatment. Attempts to classify DLBCL have identified two distinct subgroups, an Activated B-cell like (ABC-DLBCL) and a Germinal centre B-cell line (GBC-DLBCL), based on gene expression profiling. Amongst the genes used to distinguish these two subgroups is Cyclin D2. Best known for their role in the regulating cell cycle, the three D-type cyclins, Cyclin D1, D2 and D3 share a high sequence homology (50-60%) and are often considered redundant. A CRISPR study performed by Phelan et al in 2018 suggested that ABC-DLBCL were dependent on the expression of Cyclin D2, despite co-expressing Cyclin D3, whilst GCB-DLBCL were dependent on Cyclin D3. How or why ABC-DLBCL are dependent on Cyclin D2 expression is unclear. This project therefore aimed to investigate the signalling pathways that are involved in regulating Cyclin D2 expression in ABC-DLBCL. During this study, we identify the existence of a previously undescribed Cyclin D2 Negative subgroup of ABC-DLBCL. RNA-seq analysis indicates that this subgroup has significantly lower IL10-STAT3 signalling than its Cyclin D2 positive counterpart. These findings were confirmed using publicly available Sc-RNA seq data, with further analysis of patient bulk RNA-seq suggesting the levels of Cyclin D2 and Cyclin D3 could be used as an effective prognostic marker for progression free survival in DLBCL. Preliminary studies investigating the subcellular localisation of D-type Cyclins found that Cyclin D3 appears to form distinct foci, the function of which are currently unknown. As part of this study, preliminary steps have been taken to developed a proteomics pipeline that could be used to compare to the binding partners of Cyclin D2 and Cyclin D3 in DLBCL in an attempt to elucidate how these distinct functions are performed. Taken together, these data generated as part of this study highlights the heterogeneity exhibited within the ABC-DLBCL subgroup, and indicate that a greater understanding of Cyclin D expression profiles, and associated pathways, could prove invaluable for treatment.