Sbiera Silviu, Tryfonidou Marianna A, Weigand Isabel, Grinwis Guy C M, Broeckx Bart, Herterich Sabine, Allolio Bruno, Deutschbein Timo, Fassnacht Martin, Meij Björn P
Department of Internal Medicine I, Division of Endocrinology and Diabetes, University Hospital Würzburg, University of Würzburg, Würzburg, Germany.
Department of Clinical Sciences of Companion Animals, Faculty of Veterinary Medicine, Utrecht University, Utrecht, The Netherlands.
PLoS One. 2016 Dec 22;11(12):e0169009. doi: 10.1371/journal.pone.0169009. eCollection 2016.
Cushing's disease (CD), also known as pituitary-dependent hyperadrenocorticism, is caused by adrenocorticotropic hormone (ACTH)-secreting pituitary tumours. Affected humans and dogs have similar clinical manifestations, however, the incidence of the canine disease is thousand-fold higher. This makes the dog an obvious model for studying the pathogenesis of pituitary-dependent hyperadrenocorticism. Despite certain similarities identified at the molecular level, the question still remains whether the two species have a shared oncogenetic background. Recently, hotspot recurrent mutations in the gene encoding for ubiquitin specific protease 8 (USP8) have been identified as the main driver behind the formation of ACTH-secreting pituitary adenomas in humans. In this study, we aimed to verify whether USP8 mutations also play a role in the development of such tumours in dogs.
Presence of USP8 mutations was analysed by Sanger and PCR-cloning sequencing in 38 canine ACTH-secreting adenomas. Furthermore, the role of USP8 and EGFR protein expression was assessed by immunohistochemistry in a subset of 25 adenomas.
None of the analysed canine ACTH-secreting adenomas presented mutations in the USP8 gene. In a subset of these adenomas, however, we observed an increased nuclear expression of USP8, a phenotype characteristic for the USP8 mutated human tumours, that correlated with smaller tumour size but elevated ACTH production in those tumours.
Canine ACTH-secreting pituitary adenomas lack mutations in the USP8 gene suggesting a different genetic background of pituitary tumourigenesis in dogs. However, elevated nuclear USP8 protein expression in a subset of tumours was associated with a similar phenotype as in their human counterparts, indicating a possible end-point convergence of the different genetic backgrounds in the two species. In order to establish the dog as a useful animal model for the study of CD, further comprehensive studies are needed.
库欣病（CD），也称为垂体依赖性肾上腺皮质功能亢进，由分泌促肾上腺皮质激素（ACTH）的垂体肿瘤引起。患病的人类和犬类有相似的临床表现，然而，犬类疾病的发病率要高上千倍。这使得犬类成为研究垂体依赖性肾上腺皮质功能亢进发病机制的理想模型。尽管在分子水平上发现了某些相似之处，但这两个物种是否具有共同的肿瘤发生背景仍是个问题。最近，泛素特异性蛋白酶8（USP8）编码基因中的热点复发突变已被确定为人类分泌ACTH的垂体腺瘤形成的主要驱动因素。在本研究中，我们旨在验证USP8突变是否也在犬类此类肿瘤的发生中起作用。
通过桑格测序和PCR克隆测序分析了38例犬分泌ACTH的腺瘤中USP8突变的存在情况。此外，通过免疫组织化学评估了25例腺瘤亚组中USP8和表皮生长因子受体（EGFR）蛋白表达的作用。
在所分析的犬分泌ACTH的腺瘤中，没有一个呈现USP8基因突变。然而，在这些腺瘤的一个亚组中，我们观察到USP8的核表达增加，这是USP8突变的人类肿瘤的特征性表型，与较小的肿瘤大小相关，但这些肿瘤中ACTH的产生增加。
犬分泌ACTH的垂体腺瘤缺乏USP8基因突变，提示犬垂体肿瘤发生的遗传背景不同。然而，一部分肿瘤中USP8蛋白核表达升高与人类肿瘤具有相似的表型，表明这两个物种不同遗传背景可能存在终点趋同。为了将犬类确立为研究库欣病的有用动物模型，还需要进一步的综合研究。
