Communication between prespore and prestalk cells coordinates terminal differentiation in Dictyostelium discoideum. The signals include a 34 amino acid peptide, SDF-2, that has a sequence related to that of the neuropeptide DBI (Diazepam Binding Inhibitor). The neurotransmitter GABA is also used as a signal in Dictyostelium by acting through a G-protein coupled receptor similar to the GABAB receptor of mammals. The SDF-2 receptor, DhkA, on the other hand, is a """"""""two-component"""""""" histidine kinase completely unrelated to the DBI receptors, GABAA and """"""""peripheral type"""""""" BZ receptors. It seems that intercellular signals have been conserved over long periods of evolution while the receptors have changed in some cases. We will further elucidate the detailed mechanisms of intercellular signaling in this genetically tractable system since the results appear to have bearing on signaling in the mammalian central nervous system and may shed light on mechanisms underlying neuropsychiatric disorders. There is a complicated interchange of information between prespore and prestalk cells as they prepare to encapsulate and vacuolize, respectively. SDF-2 is generated by proteolytic processing of a protein, AcbA, released from prespore cells. Processing occurs on the surface of prestalk cells after priming by low levels of SDF-2 or by GABA. Prespore cells respond to priming by rapid release of AcbA from vesicles. AcbA is an acyl-CoA binding protein as is the precursor of DBI. Using site-directed mutagenesis we will determine whether this activity is essential for accumulation of AcbA in endosomes and subsequent release. We will determine whether exocytosis in response to either low levels of SDF-2 or GABA is dependent on signaling through the cAMP dependent protein kinase PKA. Extracellular AcbA is proteolytically cleaved by the membrane embedded prestalk specific protease TagC, which is only exposed following priming by either low levels of SDF-2 or GABA. We will determine whether this process is also dependent on PKA activity. Our results suggest that the precursor of the mammalian neuropeptide DBI, ACBP, may be synthesized in one cell type, stored in vesicles, and processed to the active peptides by another cell type. Such interactions could modulate the levels of this natural ligand that binds at the target of the widely used drug diazepam (Valium). Our observations that GABA appears to induces rapid exocytosis not only accounts for its priming activity in Dictyostelium but provides a test system for better understanding of the basic processes controlling exocytosis. Together these studies will add to the foundation for improvements in the diagnosis and treatment of neurological diseases. ? ? ?

Agency
National Institute of Health (NIH)
Institute
National Institute of General Medical Sciences (NIGMS)
Type
Research Project (R01)
Project #
1R01GM078175-01
Application #
7130324
Study Section
Development - 2 Study Section (DEV2)
Program Officer
Anderson, Richard A
Project Start
2006-06-26
Project End
2010-05-31
Budget Start
2006-06-26
Budget End
2007-05-31
Support Year
1
Fiscal Year
2006
Total Cost
$262,316
Indirect Cost
Name
University of California San Diego
Department
Biology
Type
Schools of Arts and Sciences
DUNS #
804355790
City
La Jolla
State
CA
Country
United States
Zip Code
92093
Anjard, Christophe; Su, Yongxuan; Loomis, William F (2011) The polyketide MPBD initiates the SDF-1 signaling cascade that coordinates terminal differentiation in Dictyostelium. Eukaryot Cell 10:956-63
Loomis, William F; Behrens, M Margarita; Williams, Megan E et al. (2010) Pregnenolone sulfate and cortisol induce secretion of acyl-CoA-binding protein and its conversion into endozepines from astrocytes. J Biol Chem 285:21359-65
Cabral, Matthew; Anjard, Christophe; Malhotra, Vivek et al. (2010) Unconventional secretion of AcbA in Dictyostelium discoideum through a vesicular intermediate. Eukaryot Cell 9:1009-17
Manjithaya, Ravi; Anjard, Christophe; Loomis, William F et al. (2010) Unconventional secretion of Pichia pastoris Acb1 is dependent on GRASP protein, peroxisomal functions, and autophagosome formation. J Cell Biol 188:537-46
Duran, Juan M; Anjard, Christophe; Stefan, Chris et al. (2010) Unconventional secretion of Acb1 is mediated by autophagosomes. J Cell Biol 188:527-36
Anjard, Christophe; Su, Yongxuan; Loomis, William F (2009) Steroids initiate a signaling cascade that triggers rapid sporulation in Dictyostelium. Development 136:803-12
Sasaki, Kazunori; Chae, Soo-Cheon; Loomis, William F et al. (2008) An immediate-early gene, srsA: its involvement in the starvation response that initiates differentiation of Dictyostelium cells. Differentiation 76:1093-103
Anjard, Christophe; Loomis, William F (2008) Cytokinins induce sporulation in Dictyostelium. Development 135:819-27
Kinseth, Matthew A; Anjard, Christophe; Fuller, Danny et al. (2007) The Golgi-associated protein GRASP is required for unconventional protein secretion during development. Cell 130:524-34
Anjard, Christophe; Loomis, William F (2006) GABA induces terminal differentiation of Dictyostelium through a GABAB receptor. Development 133:2253-61

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