Altered distribution of Galphah/type 2 transglutaminase following catecholamine deprivation is associated with depression of adrenoreceptor signal transduction in cultured ventricular zone germinal cells
Abstract
Type 2 transglutaminase (Tg), which catalyzes the covalent cross-linking of cytoplasmic proteins during apoptosis, also functions as the alpha subunit of a heterodimeric G-protein (Gh) which can activate phospholipase C-delta1 during the signal transduction pathway linked to alpha1-adrenoreceptors. Continued stimulation of rat forebrain ventricular zone (VZ) germinal cells with the alpha1-agonist phenylephrine during development in vitro suppresses apoptosis and promotes DNA synthesis [Pabbathi et al., Brain Res., 760, 1997, 22-33]. Immunocytochemistry with a monoclonal antibody to Galphah/Tg reveals that alpha1-agonist deprivation during culture of VZ cells in the presence of a protein synthesis inhibitor results after 20 h in a loss of peripheral distribution of the protein and an increase in the reaction product of Tg in the cytoplasm of cells undergoing apoptosis. Using photoaffinity labelling, we observed reduced GTP binding to Galphah/Tg in phenylephrine-deprived cultures. Formation of inositol triphosphate (IP3) and intracellular Ca2+ transients occurred in the presence of phenylephrine. In cultures grown in phenylephrine-deprived conditions in the presence of protein synthesis inhibitor, both the IP3 response and the am...Continue Reading
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