Erratum: Cyclic Adenosine Monophosphate-Mediated Enhancement of Vascular Endothelial Growth Factor Released by Differentiated Human Monocytic Cells: The Role of Protein Kinase A

Objective: Our investigation was designed to examine the signaling pathway involved in the enhancement of vascular endothelial growth factor (VEGF) release by β-adrenoceptor agonists. Materials and Methods: Human U937 cells differentiated into macrophages were primed with lipopolysaccharide (LPS) in the absence or presence of β-adrenoceptor agonists and antagonists. The VEGF released and the intracellular cyclic adenosine monophosphate (cAMP) generated were assayed by ELISA. Where necessary, differences between mean values were tested for significance using Student's t test. Results: Isoprenaline, procaterol and salbutamol concentration-dependently enhanced the release of VEGF induced by LPS in U937 cells. R*,R*-(±)-4-[2-[(2-(3-chlorophenyl)-2-hydroxyethyl)amino]propyl]phenoxyacetic acid (BRL 37344), a selective β3-adrenoceptor agonist, did not enhance VEGF release. Using isoprenaline as an agonist, propranolol, ICI 118551 and atenolol produced a parallel rightward shift of the concentration-response curve with no reduction in the maximum response. The -logKB values were 8.12 ± 0.17, 8.03 ± 0.05 and 7.23 ± 0.05 for propranolol, ICI 118551 and atenolol, respectively, indicating the possible involvement of both β1- and β2-adrenoceptor subtypes. Isoprenaline and prostaglandin E2 concentration-dependently increased cAMP generation in U937 cells. Isoprenaline, db-cAMP and 6-Bnz-cAMP, a protein kinase A (PKA) activator, all enhanced VEGF release induced by LPS, and this effect was abolished by KT 5720 and Rp-cAMPS, which are both selective PKA inhibitors, suggesting that PKA is the downstream effector of cAMP activity. 8-CPT-cAMP, a selective activator of the Epac system, had no effect on VEGF release induced by LPS, indicating that the Epac pathway played no role in the release process. Conclusion: In this study, we established that β1- and β2- but not β3-adrenoceptors mediated cAMP-dependent enhancement of VEGF release induced by LPS in differentiated U937 cells, and that PKA was the downstream effector of cAMP activity.

研究目的：本研究旨在探究β肾上腺素受体激动剂促进血管内皮生长因子（vascular endothelial growth factor, VEGF）释放所涉及的信号通路。
材料与方法：将诱导分化为巨噬细胞的人U937细胞，在添加或不添加β肾上腺素受体激动剂与拮抗剂的条件下，用脂多糖（lipopolysaccharide, LPS）进行预处理。采用酶联免疫吸附测定（enzyme-linked immunosorbent assay, ELISA）法检测上清中释放的VEGF以及细胞内生成的环磷酸腺苷（cyclic adenosine monophosphate, cAMP）。必要时，采用Student t检验对各组均值间的差异进行显著性分析。
结果：异丙肾上腺素、丙卡特罗与沙丁胺醇可浓度依赖性地增强U937细胞中LPS诱导的VEGF释放。R*,R*-(±)-4-[2-[(2-(3-氯苯基)-2-羟乙基)氨基]丙基]苯氧乙酸（BRL 37344）作为选择性β3肾上腺素受体激动剂，未对LPS诱导的VEGF释放产生促进作用。以异丙肾上腺素作为激动剂时，普萘洛尔、ICI 118551与阿替洛尔可使浓度-反应曲线平行右移，且最大反应幅度无明显降低。普萘洛尔、ICI 118551与阿替洛尔的-logKB值分别为8.12±0.17、8.03±0.05与7.23±0.05，提示β1与β2肾上腺素受体亚型均可能参与该调控过程。异丙肾上腺素与前列腺素E2可浓度依赖性地提升U937细胞内cAMP的生成水平。异丙肾上腺素、双丁酰环磷酸腺苷（db-cAMP）以及蛋白激酶A（protein kinase A, PKA）激活剂6-Bnz-cAMP均可增强LPS诱导的VEGF释放，且该效应可被两种选择性PKA抑制剂KT 5720与Rp-cAMPS所阻断，表明PKA是cAMP信号活性的下游效应分子。8-CPT-cAMP作为Epac系统的选择性激活剂，对LPS诱导的VEGF释放无显著影响，提示Epac通路未参与该VEGF释放过程。
结论：本研究证实，在分化的U937细胞中，β1和β2而非β3肾上腺素受体介导了cAMP依赖性的LPS诱导VEGF释放增强效应，且PKA是cAMP信号活性的下游效应因子。