AbstractProtein kinase D (PKD) enzymes are a family of serine/threonine kinases that belong to the calcium/calmodulin-dependent kinase superfamily. Recently, a role for PKD enzymes has been established in the adaptive immune system where murine PKD2 was shown to be essential for normal peripheral CD4+ and CD8+ cytotoxic T lymphocyte function in vivo. PKD enzymes are known to be involved in adaptive immunity but it is not known if this is true for PKD in cells of the myeloid lineage, including dendritic cells (DCs) and macrophages or in myeloid malignancies such as chronic myeloid leukaemia (CML). Moreover, the literature on the role of PKD is complicated by the use of dual and non-specific pharmacological inhibitors.
Accordingly, one objective of this thesis was to characterise new generation small molecule inhibitors of PKD to verify their specificity. A second aim was to define PKD isoform expression and their role in the development and effector functions of myeloid cells. Thirdly, the requirement for PKD2 in the homeostasis of T lymphocytes within the small intestine was explored. The final objective was to determine if the development of regulatory T cells (Tregs) and if their effector functions in vivo from PKD2KI/KI mice were normal.
Three novel inhibitors of PKD were shown to be specific and target PKD catalytic activity effectively in a CML cell line, although someoff-target effects were observed. In vitro experiments revealed that PKD2 is the dominant isoform expressed in both primary DCs and macrophages but is not required for the development ofthese subsets in vivo. Analysis of DC effector function implicated a role for PKD in the negative regulation of TLR4 stimulation. In vivo studies of Tregs lacking PKD2 catalytic activity revealed normal Treg development within thethymus. However, analysis of the periphery including the spleen and mesenteric lymph nodes revealed significantly increased Treg populations. Finally, investigation of an in vivo colitis model suggested that PKD2 is required for normal Treg effector function in the suppression of colitis. Collectively, the data in this thesis reveal novel roles for PKD enzymes in both the innate and adaptive mammalian immune systems.
|Date of Award||2015|
|Sponsors||Medical Research Council|
|Supervisor||Sharon Matthews (Supervisor) & Charles Herrington (Supervisor)|