Changes in actin network during calcium-induced exocytosis in permeabilized GH3 cells: calcium directly regulates F-actin disassembly

Abstract

Using digitonin-permeabilized GH3 cells, we investigated both the release of prolactin (PRL) and changes in the cytoskeleton. We determined that permeabilized GH3 cells released PRL in a dose-dependent manner upon addition of micromolar Ca 2+ . Phalloidin, a filamentous actin (F-actin) stabilizing agent, inhibited both Ca 2+ -dependent and -independent PRL release, whereas cytochalasin B, a destabilizing agent, had almost no effect on the release. Observation with a confocal laser scanning microscope revealed that F-actin existed mainly in the cortical region in the quiescent state. Increased cytosolic Ca 2+ induced a change in F-actin distribution: F-actin in the cortical region decreased, whereas F-actin inside the cells increased. This change in F-actin distribution was not observed when phalloidin was added. Addition of cytochalasin B induced patchy F-actin spots, but the pattern of the changes of F-actin distribution did not change. The time course of change in F-actin distribution showed that the F-actin network in the cortical region was reduced within 1 min, and Ca 2+ -dependent release of PRL continued for up to 20 min. These results suggest that the F-actin network near the membrane acts as a barrier to exocytosis and that Ca 2+ directly controls the cytoskeletal changes.

Depolymerisation and rearrangement of actin filaments during exocytosis in rat peritoneal mast cells: involvement of ryanodine-sensitive calcium stores

“…The amperometric results obtained with latrunculin A appear to be similar to those obtained with agents, such as ryanodine and caffeine that mobilise Ca 2+ from intracellular stores [5,14,17,36]. Thus, further experiments were carried out to study a possible relationship between Ca 2+ release from intracellular stores and the depolymerising effect of latrunculin in the absence of external Ca 2+ .…”

“…In fact, increases in the intracellular Ca 2+ concentration may induce F-actin depolymerisation [18,36]. It was also reported that increases in [Ca 2+ ]i mediated by high-affinity receptors for the Fc region of IgE (FcɛRI) in mast cells can be modulated by F-actin depolymerisation, which may thus affect Ca 2+ signalling [24,25].…”

Insulin-Increased Prolactin Gene Expression Requires Actin Treadmilling: Potential Role for P21 Activated Kinase

“…N-WASP is likely to be involved in the movement of secretory granules in GH4 cells because it was shown that prolactin secretion was dependent on the rearrangement of cortical actin (36 -38). This process would require remodeling of the cortical actin, which was both inhibitory to and required for secretion (37,38). The change from a stationary to a dynamic cytoskeleton could activate a kinase that then translocates to the nucleus to phosphorylate Elk1.…”

AQP4 knockout impairs proliferation, migration and neuronal differentiation of adult neural stem cells

“…Based on our results and evidence from other reports, we propose the following potential mechanism whereby AQP4 regulates the migration of ANSCs. At the initial stage of cell migration, AQP4 might facilitate Ca 2+ influx (Faux and Parnavelas, 2007), which directly regulates actin depolymerization (Disanza et al, 2005;Yoneda et al, 2000). Ion influx increases cytoplasmic osmolality followed by water influx via AQP4 at the front end of the migrating cell .…”