Ramos-Alvarez Irene, Jensen Robert T
Digestive Diseases Branch, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892-1804, USA.
Am J Physiol Gastrointest Liver Physiol. 2025 May 15. doi: 10.1152/ajpgi.00308.2024.
Serine/threonine phosphatases, PP1 and PP2A, play important roles in mediating cellular signaling in different tissues to different stimuli, including glycogen metabolism, protein synthesis/growth and secretion. However, the roles of PP1/PP2A in pancreatic acinar cell secretion/growth are both unclear and controversial. To address this issue, in the present study, we examined the ability of GI hormones/growth factors (GFs) to activate PP1 and PP2A and the signaling cascades involved in rat pancreatic acini and the pancreatic acinar tumor cell line, AR42J cells. PP1 and PP2A were both detected in pancreatic acini and AR42J cells. In acini, PP1 and PP2A were activated by pancreatic secretagogues-stimulating phospholipase C (bombesin,CCK-8,carbachol) and endothelin; and by pancreatic GFs (insulin, hepatocyte growth factor,epidermal growth factor,basic fibroblast growth factor,platelet-derived growth factor and insulin-like growth factor 1). Full CCK-8 activation of PP1/PP2A required activation of both high- and low-affinity CCK1-receptor states. Using specific PP1 and PP2 assays, in both acini and AR42J cells, experimental conditions were established where calyculin A, a known nonselective PP1/PP2A inhibitor, inhibited activation of both; whereas okadaic acid and fostriecin inhibited only PP2A activation; and tautomycetin only PP1 activation. Under these conditions CCK-stimulated enzyme secretion and stimulation of p44/42, a key mediator of growth, required PP2A activation, without activation of PP1. Using specific siRNA for PP1/PP2A in AR42J cells similar results were found. These results establish that only PP2A activation is essential for CCK-mediated stimulation of growth and enzyme secretion in pancreatic acinar cells and pancreatic acinar AR42J tumor cells.
丝氨酸/苏氨酸磷酸酶PP1和PP2A在介导不同组织对不同刺激的细胞信号传导中发挥重要作用，这些刺激包括糖原代谢、蛋白质合成/生长和分泌。然而，PP1/PP2A在胰腺腺泡细胞分泌/生长中的作用尚不清楚且存在争议。为了解决这个问题，在本研究中，我们检测了胃肠激素/生长因子（GFs）激活PP1和PP2A的能力以及大鼠胰腺腺泡和胰腺腺泡肿瘤细胞系AR42J细胞中涉及的信号级联反应。在胰腺腺泡和AR42J细胞中均检测到了PP1和PP2A。在腺泡中，PP1和PP2A可被刺激磷脂酶C的胰腺促分泌素（蛙皮素、CCK-8、卡巴胆碱）和内皮素激活；也可被胰腺生长因子（胰岛素、肝细胞生长因子、表皮生长因子、碱性成纤维细胞生长因子、血小板衍生生长因子和胰岛素样生长因子1）激活。PP1/PP2A的完全CCK-8激活需要高亲和力和低亲和力CCK1受体状态的同时激活。使用特异性的PP1和PP2检测方法，在腺泡和AR42J细胞中均建立了实验条件，在这些条件下，已知的非选择性PP1/PP2A抑制剂花萼海绵诱癌素A可抑制两者的激活；而冈田酸和福司曲星仅抑制PP2A的激活；束丝放线菌素仅抑制PP1的激活。在这些条件下，CCK刺激的酶分泌以及对生长的关键介质p44/42的刺激需要PP2A的激活，而无需PP1的激活。在AR42J细胞中使用针对PP1/PP2A的特异性小干扰RNA也得到了类似的结果。这些结果表明，只有PP2A的激活对于CCK介导的胰腺腺泡细胞和胰腺腺泡AR42J肿瘤细胞的生长和酶分泌刺激至关重要。
