Medical College of Wisconsin, 8701 Watertown Plank Rd., Milwaukee, WI 53226, USA.
Am J Physiol Endocrinol Metab. 2012 Jun 1;302(11):E1390-8. doi: 10.1152/ajpendo.00519.2011. Epub 2012 Mar 20.
Exposure of insulin-producing cells to elevated levels of the free fatty acid (FFA) palmitate results in the loss of β-cell function and induction of apoptosis. The induction of endoplasmic reticulum (ER) stress is one mechanism proposed to be responsible for the loss of β-cell viability in response to palmitate treatment; however, the pathways responsible for the induction of ER stress by palmitate have yet to be determined. Protein palmitoylation is a major posttranslational modification that regulates protein localization, stability, and activity. Defects in, or dysregulation of, protein palmitoylation could be one mechanism by which palmitate may induce ER stress in β-cells. The purpose of this study was to evaluate the hypothesis that palmitate-induced ER stress and β-cell toxicity are mediated by excess or aberrant protein palmitoylation. In a concentration-dependent fashion, palmitate treatment of RINm5F cells results in a loss of viability. Similar to palmitate, stearate also induces a concentration-related loss of RINm5F cell viability, while the monounsaturated fatty acids, such as palmoleate and oleate, are not toxic to RINm5F cells. 2-Bromopalmitate (2BrP), a classical inhibitor of protein palmitoylation that has been extensively used as an inhibitor of G protein-coupled receptor signaling, attenuates palmitate-induced RINm5F cell death in a concentration-dependent manner. The protective effects of 2BrP are associated with the inhibition of [(3)H]palmitate incorporation into RINm5F cell protein. Furthermore, 2BrP does not inhibit, but appears to enhance, the oxidation of palmitate. The induction of ER stress in response to palmitate treatment and the activation of caspase activity are attenuated by 2BrP. Consistent with protective effects on insulinoma cells, 2BrP also attenuates the inhibitory actions of prolonged palmitate treatment on insulin secretion by isolated rat islets. These studies support a role for aberrant protein palmitoylation as a mechanism by which palmitate enhances ER stress activation and causes the loss of insulinoma cell viability.
胰岛素生成细胞暴露于高水平的游离脂肪酸（FFA）棕榈酸会导致β细胞功能丧失和细胞凋亡。内质网（ER）应激的诱导被认为是导致棕榈酸处理后β细胞活力丧失的一种机制；然而，棕榈酸诱导 ER 应激的途径尚未确定。蛋白质棕榈酰化是一种主要的翻译后修饰，可调节蛋白质的定位、稳定性和活性。蛋白质棕榈酰化的缺陷或失调可能是棕榈酸诱导β细胞 ER 应激的一种机制。本研究的目的是评估棕榈酸诱导的 ER 应激和β细胞毒性是否通过过度或异常的蛋白质棕榈酰化来介导的假说。在浓度依赖性方式中，棕榈酸处理 RINm5F 细胞会导致细胞活力丧失。与棕榈酸类似，硬脂酸也会诱导 RINm5F 细胞活力呈浓度相关的丧失，而单不饱和脂肪酸，如棕榈油酸和油酸，对 RINm5F 细胞没有毒性。2-溴棕榈酸（2BrP）是一种经典的蛋白质棕榈酰化抑制剂，已被广泛用作 G 蛋白偶联受体信号转导的抑制剂，以浓度依赖性方式减弱棕榈酸诱导的 RINm5F 细胞死亡。2BrP 的保护作用与抑制[（3）H]棕榈酸掺入 RINm5F 细胞蛋白有关。此外，2BrP 不会抑制，而是似乎增强，棕榈酸的氧化。2BrP 减弱了棕榈酸处理引起的 ER 应激的诱导和半胱氨酸天冬氨酸蛋白酶活性的激活。与对胰岛素瘤细胞的保护作用一致，2BrP 还减弱了长期棕榈酸处理对分离的大鼠胰岛胰岛素分泌的抑制作用。这些研究支持异常蛋白质棕榈酰化作为棕榈酸增强 ER 应激激活并导致胰岛素瘤细胞活力丧失的机制的作用。
