Abstract
As glucose is known to induce insulin secretion in pancreatic Beta cells, this study investigated the role of a phospholipase D (PLD)-related signaling pathway in insulin secretion caused by high glucose in the pancreatic Beta-cell line MIN6N8. It was found that the PLD activity and PLD1 expression were both increased by high glucose (33.3 mM) treatment. The dominant negative PLD1 inhibited glucose-induced Beta2 expression, and glucose-induced insulin secretion was blocked by treatment with 1-butanol or PLD1-siRNA. These results suggest that high glucose increased insulin secretion through a PLD1-related pathway. High glucose induced the binding of Arf6 to PLD1. Pretreatment with brefeldin A (BFA), an Arf inhibitor, decreased the PLD activity as well as the insulin secretion. Furthermore, BFA blocked the glucose-induced mTOR and p70S6K activation, while mTOR inhibition with rapamycin attenuated the glucose induced Beta2 expression and insulin secretion. Thus, when taken together, PLD1 would appear to be an important regulator of glucose-induced insulin secretion through an Arf6/PLD1/mTOR/p70S6K/ Beta2 pathway in MIN6N8 cells.
Highlights
Glucose is the most potent nutrient in insulin secretion in pancreatic β-cells (Ashcroft, 1980; Goren, 2005)
PLD1 overexpression potentiated Beta2 expression increased by high glucose, whereas knockdown of PLD1 using DN-PLD1 transfection completely eliminated Beta2 expression (Figure 2B), strongly suggesting that PLD1 was involved in the Beta2 expression induced by glucose in the MIN6N8 cells
The depletion of PLD1 by PLD1siRNA significantly decreased insulin secretion in glucose-stimulated MIN6N8 cells (Figure 2D). When taken together, these results indicated that PLD1 acted as an important mediator for Beta2 expression and insulin secretion in the MIN6N8 cells stimulated by glucose
Summary
Glucose is the most potent nutrient in insulin secretion in pancreatic β-cells (Ashcroft, 1980; Goren, 2005). There is growing evidence that PLD1 is essential for the regulated secretion of insulin from pancreatic β-cells (Metz and Dunlop, 1990) and modulates vesicular trafficking and exocytosis (Shen et al, 2001). Many factors have already been implicated in the regulation of PLD and insulin secretion in response to glucose such as GTPases proteins. Arfs are small G-proteins of the Ras superfamily and have been shown to have some effect on vesicle transport, endocytosis, actin rearrangement and insulin secretion (Jalink et al, 1994; Donaldson, 2003). The mechanisms of glucose-induced PLD activation mediating insulin secretion in pancreatic-β cells are not yet well defined
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