Abstract
Actin dynamics in pancreatic β-cells is involved in insulin secretion. However, the molecular mechanisms of the regulation of actin dynamics by intracellular signals in pancreatic β-cells and its role in phasic insulin secretion are largely unknown. In this study, we elucidate the regulation of actin dynamics by neuronal Wiskott-Aldrich syndrome protein (N-WASP) and cofilin in pancreatic β-cells and demonstrate its role in glucose-induced insulin secretion (GIIS). N-WASP, which promotes actin polymerization through activation of the actin nucleation factor Arp2/3 complex, was found to be activated by glucose stimulation in insulin-secreting clonal pancreatic β-cells (MIN6-K8 β-cells). Introduction of a dominant-negative mutant of N-WASP, which lacks G-actin and Arp2/3 complex-binding region VCA, into MIN6-K8 β-cells or knockdown of N-WASP suppressed GIIS, especially the second phase. We also found that cofilin, which severs F-actin in its dephosphorylated (active) form, is converted to the phosphorylated (inactive) form by glucose stimulation in MIN6-K8 β-cells, thereby promoting F-actin remodeling. In addition, the dominant-negative mutant of cofilin, which inhibits activation of endogenous cofilin, or knockdown of cofilin reduced the second phase of GIIS. However, the first phase of GIIS occurs in the G-actin predominant state, in which cofilin activity predominates over N-WASP activity. Thus, actin dynamics regulated by the balance of N-WASP and cofilin activities determines the biphasic response of GIIS.
Highlights
Actin dynamics is involved in insulin secretion, but the mechanism is unknown
In chromaffin cells and their derived PC12 cells, actin forms a complex and dynamic network of filaments beneath the plasma membrane, and rapid remodeling of the actin network is required for exocytosis of catecholamine [52]
We investigated the mechanism of glucose regulation of actin dynamics regulated by neuronal Wiskott-Aldrich syndrome protein (N-WASP) and cofilin, which are the major regulators of actin dynamics, and its role in the biphasic response of glucose-induced insulin secretion (GIIS)
Summary
Results: The G-actin predominant or F-actin remodeling state in pancreatic -cells, which is regulated by the balance of N-WASP and cofilin activities, determines the biphasic glucose-induced insulin secretion (GIIS). The molecular mechanisms of the regulation of actin dynamics by intracellular signals in pancreatic -cells and its role in phasic insulin secretion are largely unknown. We elucidate the regulation of actin dynamics by neuronal Wiskott-Aldrich syndrome protein (N-WASP) and cofilin in pancreatic -cells and demonstrate its role in glucose-induced insulin secretion (GIIS). We show that cofilin, which severs F-actin in its dephosphorylated form (active form), is converted to the phosphorylated form (inactive form) upon glucose stimulation, thereby promoting the F-actin remodeling necessary for the second phase of GIIS. Actin dynamics is regulated by the balance of N-WASP and cofilin activities, and it is critical in determining the biphasic response of GIIS
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