Protein kinase D (PKD) isoforms are PKC effectors in hormonally-controlled, DAG-regulated signaling cascades. Little is known about PKD regulation, substrates and functions in normal differentiated cells. C.elegans PKDs named DKF-2A and DKF-2B will be studied by mutagenesis, biochemical and in vivo analysis to determine how properties of 4 structural domains control plasma membrane recruitment, activation and intracellular routing of PKDs. Experiments will rigorously evaluate the idea that both C1a and C1b domains contribute equally to DAG-mediated translocation and activation of DKF-2A/2B in vivo and determine if two P- serines in the activation loop (A-loop) differentially regulate catalytic activity. DKF-2A and 2B are encoded by one gene, but the 2 kinases may be differentially regulated and govern distinct functions in vivo. DKF-2 deficient (null) C. elegans, as well as animals expressing DKF-2A or 2B transgenes in null and wild type (WT) backgrounds will be characterized to discover physiological functions of D kinases. Studies on WT, mutant and transgenic (TG) animals, using fluorescence microscopy and IgGs that bind crucial phosphorylation sites in the A-loop, will elucidate relationships among DKF-2A/2B activation, translocation and stability in individual cells in vivo. Microarray analysis will determine if DKF-2A and 2B regulate expression of groups of mRNAs encoding functionally related proteins. Cells expressing DKF-2 isoforms will be identified by using gene promoters that drive targeted expression of GFP-tagged DKF-2 proteins. Preliminary results indicate that DKF-2 isoforms link DAG signals to two critical physiological processes: DKF-2A controls expression of proteins that protect intestinal cells against pathogenic bacteria;neuronal DKF-2B mediates chemotaxis. This knowledge will be exploited to develop assays, based on measurements of DKF-2 regulated mRNAs and proteins, chemotaxis, and resistance to bacterial infection, that quantify (and allow visualization) of DKF-2A or 2B activity in vivo. The assays enable 3 lines of incisive investigation. (1) Mechanistic and regulatory properties of C1a, C1b, PH and A-Loop domains, determined heretofore by in vitro biochemical analysis, will be quantitatively analyzed in an in vivo context by expressing relevant DKF-2 mutant proteins in the """"""""reporter strains"""""""" of C.elegans. (2) In vivo activation assays will be combined with genetics to determine which heterotrimeric G proteins, PLCs and PKCs constitute upstream signaling pathways that control DKF-2A and 2B activity in intestinal cells and neurons. (3) The possibility that DKF-2 isoforms phosphorylate and control activities of a transcriptional regulator, HDA-4 (a histone deacetylase) and a member of a p38 MAP kinase cascade, NSY-1, will be rigorously assessed by in vivo analysis. Planned experiments will reveal signaling molecules, mechanisms and pathways that couple external stimuli to PKD-controlled physiological processes in normal differentiated cells. Studies on the C. elegans model will reveal how PKDs link DAG second messenger to regulation of chemotaxis and innate immunity. The results and will guide examination of these currently unexplored areas in mammalian systems.
Acquisition of new knowledge regarding protein kinase D (PKD, DKF) regulation and physiological functions will advance understanding of how tissues counter environmental immune and inflammatory stresses. PKDs regulate a genetic program that promotes cardiac hypertrophy (a precursor of contractile dysfunction and heart failure), which identifies PKDs and PKD substrates as high priority therapeutic targets for cardiovascular diseases. In addition, our preliminary studies on a model system reveal that PKDs link hormonal signals to control of innate immune responses that protect intestine and other epithelia against invading bacterial pathogens.
