Arrestins function in cAR1 GPCR-mediated signaling and cAR1 internalization in the development of Dictyostelium discoideum.
Bottom Line: Although the G protein-coupled cAMP receptor cAR1 and ERK2 are both implicated in regulating the oscillation, the signaling circuit remains unknown.Cells lacking arrestins (adcB(-)C(-)) display cAMP oscillations during the aggregation stage that are twice as frequent as for wild- type cells.In addition, ligand-induced cAR1 internalization is compromised in adcB(-)C(-) cells, suggesting that arrestins are involved in elimination of high-affinity cAR1 receptors from cell surface after the aggregation stage of multicellular development.
Affiliation: Shanghai Institute of Immunology, Shanghai Jiao Tong University School of Medicine, Shanghai 200025, China.Show MeSH
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Mentions: A previous study showed that ERK2 activity oscillates in phase with extracellular cAMP waves during specific stages of development of D. discoideum (Maeda et al., 2004). To test whether arrestins play a role in cAR1-controlled oscillations of cAMP signaling, we assessed the frequency of cAMP oscillations in wild-type, adcB−C−, and adcB−C− cells expressing AdcC-YFP. Cells were plated on Petri dishes containing starvation buffer to initiate development, and the aggregation stage was recorded for cAMP wave analysis. cAMP oscillations (waves) can be measured by proxy by recording optical density oscillations of cells imaged by dark-field microscopy (Siegert and Weijer, 1989; see Figure 5A). Changes in grayscale values from subregions in frame-subtracted images were measured using ImageJ. We found that wild-type cells produced waves with ∼6-min period as expected (Figure 5, A and B) and displayed a robust dark-field wave pattern with broad spirals arms propagating from signaling centers (Figure 5A shows a still from the image sequence). In contrast, adcB−C− cells produced cAMP waves with a faster, ∼3-min period (Figure 5, A and B). The shorter distance between propagating wavefronts from multiple signaling centers can be observed in the still shown in Figure 5A. Of importance, this disrupted wave pattern was rescued by expressing AdcC-YFP in the adcB−C− cells (Figure 5, A and B). Furthermore, adcB− and adcC− cells did not display cAMP waves of higher frequencies (Supplemental Figure S9), suggesting that AdcB and AdcC can compensate for the loss of either one, and only in cells lacking both AdcC and AdcB is a defect in the formation of cAMP waves obvious. Our data indicate that AdcB and AdcC are involved in cAR1-mediated oscillations of cAMP signaling during the aggregation stage of D. discoideum development.
Affiliation: Shanghai Institute of Immunology, Shanghai Jiao Tong University School of Medicine, Shanghai 200025, China.