Endocrine Unit (E.P., E.G., D.T., A.S., G.M.), Department of Clinical Sciences and Community Health, Neurosurgery Unit (M.L.), Fondazione Istituto di Ricovero e Cura a Carattere Scientifico Ca' Granda Ospedale Maggiore Policlinico, 20122, Milano, Italy; Laboratory of Cellular and Molecular Endocrinology (E.V., V.C.), Humanitas Research Center, Neurosurgery Unit (G.B.L.), and Endocrine Unit (A.G.L.), IRCCS Clinical and Research Institute Humanitas, Rozzano, University of Milan, 20089 Milan, Italy.
Endocrinology. 2014 Aug;155(8):2932-41. doi: 10.1210/en.2014-1063. Epub 2014 May 14.
Somatostatin receptor type 2 (SST2) is the main pharmacological target of medical therapy for GH-secreting pituitary tumors, but molecular mechanisms regulating its expression and signaling are largely unknown. The aim of this study was to investigate the role of cytoskeleton protein filamin A (FLNA) in SST2 expression and signaling in somatotroph tumor cells. We found a highly variable expression of FLNA in human GH-secreting tumors, without a correlation with SST2 levels. FLNA silencing in human tumoral cells did not affect SST2 expression and localization but abolished the SST2-induced reduction of cyclin D1 (-37% ± 15% in control cells, P < .05 vs basal) and caspase-3/7 activation (+63% ± 31% in control cells, P < .05 vs basal). Overexpression of a FLNA dominant-negative mutant that specifically prevents SST2-FLNA binding reduced SST2 expression after prolonged agonist exposure (-55% ± 5%, P < .01 vs untreated cells) in GH3 cells. Moreover, SST2-induced apoptotic effect (77% ± 54% increase of caspase activity, P < .05 vs basal) and SST2-mediated ERK1/2 inhibition (48% ± 17% reduction of ERK1/2 phosphorylation, P < .01 vs basal) were abrogated in cells overexpressing another FLNA mutant that prevents FLNA interaction with partner proteins but not with SST2, suggesting a scaffold function of FLNA in somatotrophs. In conclusion, these data demonstrate that FLNA is involved in SST2 stabilization and signaling in tumoral somatotrophs, playing both a structural and functional role.
生长抑素受体 2 (SST2) 是生长激素分泌性垂体肿瘤医学治疗的主要药理靶点，但调节其表达和信号的分子机制在很大程度上尚不清楚。本研究旨在探讨细胞骨架蛋白细丝蛋白 A (FLNA) 在生长激素分泌性肿瘤细胞中 SST2 表达和信号转导中的作用。我们发现 FLNA 在人类 GH 分泌性肿瘤中的表达存在高度可变性，与 SST2 水平无相关性。在人类肿瘤细胞中沉默 FLNA 并不影响 SST2 的表达和定位，但会消除 SST2 诱导的 cyclin D1 减少 (-37% ± 15%，在对照细胞中，P <.05 与基础相比) 和 caspase-3/7 激活 (+63% ± 31%，在对照细胞中，P <.05 与基础相比)。过表达一种 FLNA 显性负突变体，该突变体能特异性阻止 SST2-FLNA 结合，可在 GH3 细胞中延长激动剂暴露后降低 SST2 的表达 (-55% ± 5%，P <.01 与未处理细胞相比)。此外，SST2 诱导的凋亡作用 (caspase 活性增加 77% ± 54%，P <.05 与基础相比) 和 SST2 介导的 ERK1/2 抑制 (ERK1/2 磷酸化减少 48% ± 17%，P <.01 与基础相比) 在过表达另一种 FLNA 突变体的细胞中被阻断，该突变体阻止 FLNA 与伴侣蛋白相互作用，但不与 SST2 相互作用，提示 FLNA 在生长激素细胞中具有支架功能。总之，这些数据表明 FLNA 参与了肿瘤生长激素细胞中 SST2 的稳定和信号转导，发挥了结构和功能作用。
