Institute for Diabetes and Cancer, Helmholtz Zentrum München, Neuherberg, Germany.
Department of Endocrinology, Centre Hospitalier Universitaire de Liège, Liège Université, Liège, Belgium.
Int J Cancer. 2020 Dec 15;147(12):3523-3538. doi: 10.1002/ijc.33268. Epub 2020 Sep 10.
Pituitary adenomas (PAs) are intracranial tumors associated with significant morbidity due to hormonal dysregulation, mass effects and have a heavy treatment burden. Growth hormone (GH)-secreting PAs (somatotropinomas) cause acromegaly-gigantism. Genetic forms of somatotropinomas due to germline AIP mutations (AIPmut+) have an early onset and are aggressive and resistant to treatment with somatostatin analogs (SSAs), including octreotide. The molecular underpinnings of these clinical features remain unclear. We investigated the role of miRNA dysregulation in AIPmut+ vs AIPmut- PA samples by array analysis. miR-34a and miR-145 were highly expressed in AIPmut+ vs AIPmut- somatotropinomas. Ectopic expression of AIPmut (p.R271W) in Aip mouse embryonic fibroblasts (MEFs) upregulated miR-34a and miR-145, establishing a causal link between AIPmut and miRNA expression. In PA cells (GH3), miR-34a overexpression promoted proliferation, clonogenicity, migration and suppressed apoptosis, whereas miR-145 moderately affected proliferation and apoptosis. Moreover, high miR-34a expression increased intracellular cAMP, a critical mitogenic factor in PAs. Crucially, high miR-34a expression significantly blunted octreotide-mediated GH inhibition and antiproliferative effects. miR-34a directly targets Gnai2 encoding Gαi2, a G protein subunit inhibiting cAMP production. Accordingly, Gαi2 levels were significantly lower in AIPmut+ vs AIPmut- PA. Taken together, somatotropinomas with AIP mutations overexpress miR-34a, which in turn downregulates Gαi2 expression, increases cAMP concentration and ultimately promotes cell growth. Upregulation of miR-34a also impairs the hormonal and antiproliferative response of PA cells to octreotide. Thus, miR-34a is a novel downstream target of mutant AIP that promotes a cellular phenotype mirroring the aggressive clinical features of AIPmut+ acromegaly.
垂体腺瘤（PA）是与激素失调、肿块效应相关的颅内肿瘤，具有较高的发病率和沉重的治疗负担。生长激素（GH）分泌型 PA（促生长激素瘤）引起肢端肥大症-巨人症。由于种系 AIP 突变（AIPmut+）引起的 GH 分泌型腺瘤的遗传形式具有发病早、侵袭性强和对生长抑素类似物（SSA）包括奥曲肽治疗耐药的特点。这些临床特征的分子基础仍不清楚。我们通过阵列分析研究了 miRNA 失调在 AIPmut+与 AIPmut- PA 样本中的作用。miR-34a 和 miR-145 在 AIPmut+与 AIPmut- 促生长激素瘤中表达较高。AIPmut（p.R271W）在 Aip 小鼠胚胎成纤维细胞（MEFs）中的异位表达上调了 miR-34a 和 miR-145，确立了 AIPmut 与 miRNA 表达之间的因果关系。在 PA 细胞（GH3）中，miR-34a 的过表达促进增殖、集落形成、迁移并抑制凋亡，而 miR-145 则适度影响增殖和凋亡。此外，高 miR-34a 表达增加了细胞内 cAMP，这是 PA 中的关键有丝分裂因子。至关重要的是，高 miR-34a 表达显著减弱了奥曲肽介导的 GH 抑制和抗增殖作用。miR-34a 直接靶向编码 Gαi2 的 Gnai2 基因，Gαi2 是一种抑制 cAMP 产生的 G 蛋白亚基。因此，AIPmut+与 AIPmut- PA 相比，Gαi2 水平显著降低。综上所述，携带 AIP 突变的促生长激素瘤过度表达 miR-34a，进而下调 Gαi2 表达，增加 cAMP 浓度，最终促进细胞生长。miR-34a 的上调还损害了 PA 细胞对奥曲肽的激素和抗增殖反应。因此，miR-34a 是突变型 AIP 的一个新的下游靶标，促进了一种与 AIPmut+ 肢端肥大症侵袭性临床特征相吻合的细胞表型。
