Both positively and negatively acting intracellular pathways coordinate chemotactic movement. For numerous eukaryotic cell-types, chemoattractant gradients are perceived by seven-transmembrane receptors (7-TMRs) coupled to heterotrimeric G proteins to activate downstream signaling networks. 7-TMRs can activate a variety of signaling networks in addition to chemoattractant pathways, and in these systems, receptor phosphorylation is required to turn off downstream signaling. Dictyostelium discoideum, uses the 7-TMR CAR1 to sense secreted cAMP to coordinate movement into aggregates in response to starvation. Essential to aggregate formation is the process where cells desensitize (adapt) to cAMP stimulation. In addition, cells must destroy the secreted cAMP ligand via an extracellular phosphodiesterase to regain sensitivity. CAR1 activates multiple networks including the cAMP-synthesizing enzyme adenylyl cyclase A (ACA) and it initiates its own phosphorylation. We now show that ACA activity persists in cells expressing a non-phosphorylatable CAR1 mutant in the presence of continuous signal, demonstrating that receptor phosphorylation is required, at least, for adaptation of the ACA pathway. We have now mathematically modeled these events and successfully predict oscillatory signaling parameters and developmental response. AKT and PKBR1 are related AGC kinases that play pivotal roles in Dictyostelium chemotaxis during growth and development. AKT has a PH domain and is transiently recruited to the membrane by interaction with PIP3, whereas PKBR1 is myristoylated and is persistently at the membrane. The disparate locations of AKT and PKBR1 indicate the potential for different activation mechanisms and function. Nonetheless, AKT and PKBR1 both require phosphorylation within their kinase (PDK1) domains and within their HM motifs. Chemoattractant stimulation of AKT and PKBR1 was studied during growth, by folate, and during development, by cAMP. Under both situations, AKT activation requires PI3K, while activation of PKBR1 is PIP3-independent. TORC2 is another key module for chemotaxis and regulation for AKT and PKBR1. Phosphorylation of PKBR1 at both the PDK1 and HM sites is completely eliminated in Dictyostelium that lack TORC2 components Pia, RIP3, or lst8, but, following folate stimulation, AKT phosphorylations persist at both sites. We also show that PDK1 phosphorylation of AKT and PKBR1 requires HM phosphorylation, but, in contrast to what has been previously assumed, phosphorylation by TORC2 is insufficient to activate either AKT or PKBR1. We also investigated the proteins transiently phosphorylated by AKT and PKBR1 following chemoattractant stimulation. Interestingly, the phosphorylation profiles of substrates were different in akt- or pkbr1- null strains, depending upon stimulation with either folate or cAMP. We suggest that AKT and PKBR1 preferentially phosphorylate optimal substrates. We have investigated the pathways of activation of AKT and PKBR1 by different chemoattractants, and discovered that these two related kinases are distinctively regulated by upstream factors and function differently through phosphorylating specific substrates. Collectively, these data provide functional proof for differences in the regulation of AKT and PKBR1 and context for complexity of PDK1 and TORC2 regulation of multiple AGC protein kinases in other systems. Presenilin (PS) is the catalytic moiety of the g-secretase complex. PS/g-secretase components are well-conserved among metazoa, but their presence/function in more distant species is not resolved. Since inappropriate g-secretase processing of amyloid precursor protein (APP) in humans is associated with familial Alzheimer's disease, understanding essential elements within each PS/g-secretase component is critical to functional studies. Diverged proteins have been identified in primitive plants but experiments have failed to demonstrate g-secretase activity. We have identified highly diverged orthologs for each PS/g-secretase component in the ancient eukaryote Dictyostelium that lacks APP, Notch, and other characterized PS/ -secretase substrates. We show that WT Dictyostelium is capable of amyloidogenic processing of ectopically expressed human APP to generate Ab40 and Ab42 peptides;strains deficient in g-secretase cannot produce Ab peptides but accumulate processed intermediates of APP that co-migrate with the a- and b-CTF intermediates of APP that are found in mammalian cells. We further demonstrate that Dictyostelium require PS/g-secretase components for phagocytosis and cell-fate specification in a cell-autonomous manner;regulation of phagocytosis by PS-signaling had been suggested, but not proven, for mammalian and Drosophila cells. Our results indicate that PS-signaling is an ancient process that arose prior to metazoan radiation, perhaps independently of Notch. The PAT family of proteins has been identified in eukaryotic species as diverse as vertebrates, insects, and amebazoa. These proteins share a highly conserved sequence organization and avidity for the surfaces of intracellular, neutral lipid storage droplets. The current nomenclature of the various members lacks consistency and precision, deriving more from historic context than from recognition of evolutionary relationship and shared function. In consultation with the Mouse Genomic Nomenclature Committee, the HUGO Genomic Nomenclature Committee, and conferees at the 2007 FASEB Conference on Lipid Droplets: Metabolic Consequences of the Storage of Neutral Lipids, we have established a unifying nomenclature for the gene and protein family members. Each member will incorporate the root term PERILIPIN (PLIN), the founding gene of the PAT family, with the different genes/proteins numbered sequentially.
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