Metabolic Heterogeneity in Molecular Subsets of Diffuse Large B-cell Lymphoma

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Metabolic Heterogeneity in Molecular Subsets of Diffuse Large B-cell Lymphoma

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Title: Metabolic Heterogeneity in Molecular Subsets of Diffuse Large B-cell Lymphoma
Author: Stanley, Illana Allake
Citation: Stanley, Illana Allake. 2014. Metabolic Heterogeneity in Molecular Subsets of Diffuse Large B-cell Lymphoma. Doctoral dissertation, Harvard University.
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Abstract: Cells adapt their metabolism to satisfy changing bioenergetic and biosynthetic needs. Investigation of metabolic reprogramming in cancer has provided insight into the metabolic control of proliferation and survival. While the predominant focus of this field has been aerobic glycolysis (the Warburg effect), increasing evidence points to a complex landscape of tumor metabolic circuitries beyond aerobic glycolysis, including varied degrees of mitochondrial contribution to tumor metabolism.
To investigate alternative metabolic programs compatible with tumor growth, we turned to Diffuse Large B-cell Lymphoma (DLBCL), a highly heterogeneous disease encompassing discrete clusters or subtypes defined by tumor-intrinsic genetic distinctions. In one classification scheme, a B-cell receptor (BCR)/proliferation cluster identified BCR-dependent DLBCLs with elevated expression of BCR signaling components. A second subset, OxPhos-DLBCL, displayed increased expression of mitochondrial oxidative phosphorylation genes, and was insensitive to BCR inhibition. However, the functional attributes of OxPhos-DLBCLs and the nature of their BCR-independent survival were unknown.
Upon integrative analyses of DLBCL subtypes, we uncovered quantitative proteome- and metabolome-level signatures associated with differences in nutrient and energy metabolism. Specifically, BCR-DLBCLs have greater glycolytic flux typical of the Warburg phenotype. Unlike BCR-DLBCLs, OxPhos-DLBCLs channel the majority of glucose-derived pyruvate into mitochondria, display elevated mitochondrial electron transport chain (ETC) activity, ATP production, and fatty acid oxidation (FAO). Importantly, these metabolic distinctions are associated with subtype-selective survival mechanisms. Moreover, acute inhibition of BCR signaling in BCR-DLBCLs increased their FAO capacity, thus revealing a reciprocal relationship between BCR and FAO.
Further dissection of mitochondrial function in OxPhos-DLBCLs indicates that increased mitochondrial metabolism is integrated with at least two homeostatic mechanisms that help maintain ETC activity and FAO capacity. In particular, OxPhos-DLBCLs harbor robust protein-level enrichment of mitochondrial translation factors required for the synthesis of mitochondrial-DNA-encoded ETC subunits. Inhibition of the mitochondrial translation pathway is selectively toxic to OxPhos-DLBCLs. A second mitochondrial homeostatic pathway, mitochondrial network dynamics, also proved relevant to OxPhos-DLBCLs. Compared to BCR-DLBCLs, OxPhos-DLBCLs display a fragmented mitochondrial network that supports their FAO capacity. Overall, these findings demonstrate previously unappreciated metabolic heterogeneity in molecular subsets of DLBCL and uncover BCR-independent survival mechanisms linked to mitochondrial FAO, protein translation, and network architecture.
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